Zeeuw, C.I. de

The cerebellar nuclei take center stage (Article)

2011-12-01T00:00:00Z

STD-dependent and independent encoding of input irregularity as spike rate in a computational model of a cerebellar nucleus neuron (Article)

2011-12-01T00:00:00Z

Neurons in the cerebellar nuclei (CN) receive inhibitory inputs from Purkinje cells in the cerebellar cortex and provide the major output from the cerebellum, but their computational function is not well understood. It has recently been shown that the spike activity of Purkinje cells is more regular than previously assumed and that this regularity can affect motor behaviour. We use a conductance-based model of a CN neuron to study the effect of the regularity of Purkinje cell spiking on CN neuron activity. We find that increasing the irregularity of Purkinje cell activity accelerates the CN neuron spike rate and that the mechanism of this recoding of input irregularity as output spike rate depends on the number of Purkinje cells converging onto a CN neuron. For high convergence ratios, the irregularity induced spike rate acceleration depends on short-term depression (STD) at the Purkinje cell synapses. At low convergence ratios, or for synchronised Purkinje cell input, the firing rate increase is independent of STD. The transformation of input irregularity into output spike rate occurs in response to artificial input spike trains as well as to spike trains recorded from Purkinje cells in tottering mice, which show highly irregular spiking patterns. Our results suggest that STD may contribute to the accelerated CN spike rate in tottering mice and they raise the possibility that the deficits in motor control in these mutants partly result as a pathological consequence of this natural form of plasticity.

Anatomical pathways involved in generating and sensing rhythmic whisker movements (Article)

2011-12-01T00:00:00Z

The rodent whisker system is widely used as a model system for investigating sensorimotor integration, neural mechanisms of complex cognitive tasks, neural development, and robotics. The whisker pathways to the barrel cortex have received considerable attention. However, many subcortical structures are paramount to the whisker system. They contribute to important processes, like filtering out salient features, integration with other senses, and adaptation of the whisker system to the general behavioral state of the animal. We present here an overview of the brain regions and their connections involved in the whisker system. We do not only describe the anatomy and functional roles of the cerebral cortex, but also those of subcortical structures like the striatum, superior colliculus, cerebellum, pontomedullary reticular formation, zona incerta, and anterior pretectal nucleus as well as those of level setting systems like the cholinergic, histaminergic, serotonergic, and noradrenergic pathways. We conclude by discussing how these brain regions may affect each other and how they together may control the precise timing of whisker movements and coordinate whisker perception.

Anomalous diffusion imposed by dendritic spines (Commentary on Santamaria et al.) (Article)

2011-08-01T00:00:00Z

fMRI Activities in the Emotional Cerebellum: A Preference for Negative Stimuli and Goal-Directed Behavior (Article)

2011-07-15T00:00:00Z

Several studies indicate that the cerebellum might play a role in experiencing and/or controlling emphatic emotions, but it remains to be determined whether there is a distinction between positive and negative emotions, and, if so, which specific parts of the cerebellum are involved in these types of emotions. Here, we visualized activations of the cerebellum and extracerebellar regions using high-field fMRI, while we asked participants to observe and imitate images with pictures of human faces expressing different emotional states or with moving geometric shapes as control. The state of the emotions could be positive (happiness and surprise), negative (anger and disgust), or neutral. The positive emotional faces only evoked mild activations of crus 2 in the cerebellum, whereas the negative emotional faces evoked prominent activations in lobules VI and VIIa in its hemispheres and lobules VIII and IX in the vermis. The cerebellar activations associated with negative emotions occurred concomitantly with activations of mirror neuron domains such as the insula and amygdala. These data suggest that the potential role of the cerebellum in control of emotions may be particularly relevant for goal-directed behavior that is required for observing and reacting to another person's (negative) expressions.

Spatiotemporal firing patterns in the cerebellum (Article)

2011-06-01T00:00:00Z

Neurons are generally considered to communicate information by increasing or decreasing their firing rate. However, in principle, they could in addition convey messages by using specific spatiotemporal patterns of spiking activities and silent intervals. Here, we review expanding lines of evidence that such spatiotemporal coding occurs in the cerebellum, and that the olivocerebellar system is optimally designed to generate and employ precise patterns of complex spikes and simple spikes during the acquisition and consolidation of motor skills. These spatiotemporal patterns may complement rate coding, thus enabling precise control of motor and cognitive processing at a high spatiotemporal resolution by fine-tuning sensorimotor integration and coordination.

Motor deficits in neurofibromatosis type 1 mice: The role of the cerebellum (Article)

2011-06-01T00:00:00Z

Neurofibromatosis type 1 (NF1) is an autosomal dominantly inherited disease, characterized by various neurocutaneous symptoms, cognitive impairments and problems in fine and gross motor performance. Although cognitive deficits in NF1 have been attributed to increased release of the inhibitory neurotransmitter γ-amino butyric acid (GABA) in the hippocampus, the origin of the motor deficits is unknown. Cerebellar Purkinje cells, the sole output neurons of the cerebellar cortex, are GABAergic neurons and express neurofibromin at high levels, suggesting an important role for the cerebellum in the observed motor deficits in NF1. To test this, we determined the cerebellar contribution to motor problems in Nf1+/-mice, a validated mouse model for NF1. Using the Rotarod, a non-specific motor performance test, we confirmed that, like NF1 patients, Nf1+/-mice have motor deficits. Next, to evaluate the role of the cerebellum in these deficits, mice were subjected to cerebellum-specific motor performance and learning tests. Nf1+/-mice showed no impairment on the Erasmus ladder, as step time and number of missteps were not different. Furthermore, when compensatory eye movements were tested, no performance deficits were found in the optokinetic reflex and vestibulo-ocular reflex in the dark (VOR) or in the light (VVOR). Finally, Nf1+/-mice successfully completed short- and long-term VOR adaptation paradigms, tests that both depend on cerebellar function. Thus, despite the confirmed presence of motor performance problems in Nf1+/-mice, we found no indication of a cerebellar component. These results, combined with recent clinical data, suggest that cerebellar function is not overtly affected in NF1 patients. © 2011 The Authors. Genes, Brain and Behavior

Reevaluating the Role of LTD in Cerebellar Motor Learning (Article)

2011-04-14T00:00:00Z

Long-term depression at parallel fiber-Purkinje cell synapses (PF-PC LTD) has been proposed to be required for cerebellar motor learning. To date, tests of this hypothesis have sought to interfere with receptors (mGluR1) and enzymes (PKC, PKG, or αCamKII) necessary for induction of PF-PC LTD and thereby determine if cerebellar motor learning is impaired. Here, we tested three mutant mice that target the expression of PF-PC LTD by blocking internalization of AMPA receptors. Using three different cerebellar coordination tasks (adaptation of the vestibulo-ocular reflex, eyeblink conditioning, and locomotion learning on the Erasmus Ladder), we show that there is no motor learning impairment in these mutant mice that lack PF-PC LTD. These findings demonstrate that PF-PC LTD is not essential for cerebellar motor learning.

NR2A subunit of the N-methyl d-aspartate receptors are required for potentiation at the mossy fiber to granule cell synapse and vestibulo-cerebellar motor learning (Article)

2011-03-10T00:00:00Z

Traditionally studies aimed at elucidating the molecular mechanisms underlying cerebellar motor learning have been focused on plasticity at the parallel fiber to Purkinje cell synapse. In recent years, however, the concept is emerging that formation and storage of memories are both distributed over multiple types of synapses at different sites. Here, we examined the potential role of potentiation at the mossy fiber to granule cell synapse, which occurs upstream to plasticity in Purkinje cells. We show that null-mutants of N-methyl d-aspartate-NR2A receptors (NMDA-NR2A-/- mice) have impaired induction of postsynaptic long-term potentiation (LTP) at the mossy fiber terminals and a reduced ability to raise the granule cell synaptic excitation, while the basic excitatory output of the mossy fibers is unaffected. In addition, we demonstrate that these NR2A-/- mutants as well as mutants in which the C terminal in the NR2A subunit is selectively truncated (NR2AδC/δC mice) have deficits in phase reversal adaptation of their vestibulo-ocular reflex (VOR), while their basic eye movement performance is similar to that of wild type littermates. These results indicate that NMDA-NR2A mediated potentiation at the mossy fiber to granule cell synapse is not required for basic motor performance, and they raise the possibility that it may contribute to some forms of vestibulo-cerebellar memory formation.

Corrigendum to " Cerebellar molecular layer interneurons - computational properties and roles in learning" [Trends in Neurosciences 33(11), 2010, 524-532] (Article)

2011-03-01T00:00:00Z

Motor learning in children with neurofibromatosis type I (Article)

2011-03-01T00:00:00Z

The aim of this study was to quantify the frequently observed problems in motor control in Neurofibromatosis type 1 (NF1) using three tasks on motor performance and motor learning. A group of 70 children with NF1 was compared to age-matched controls. As expected, NF1 children showed substantial problems in visuo-motor integration (Beery VMI). Prism-induced hand movement adaptation seemed to be mildly affected. However, no significant impairments in the accuracy of simple eye or hand movements were observed. Also, saccadic eye movement adaptation, a cerebellum dependent task, appeared normal. These results suggest that the motor problems of children with NF1 in daily life are unlikely to originate solely from impairments in motor learning. Our findings, therefore, do not support a general dysfunction of the cerebellum in children with NF1.

Cerebellar molecular layer interneurons - computational properties and roles in learning (Article)

2010-11-01T00:00:00Z

In recent years there has been an increased interest in the function of inhibitory interneurons. In the cerebellum this interest has been paired with successes in obtaining recordings from these neurons in vivo and genetic manipulations to probe their function during behavioral tasks such as motor learning. This review focuses on a synthesis of recent findings on the computational properties that these neurons confer to the cerebellar circuitry and on their recently discovered capacity for plasticity and learning in vivo. Since the circuitry of the cerebellar cortex is relatively well-defined, the specificity with which the potential roles of these interneurons can be described will help to guide new avenues of research on the functions of interneurons in general.

Long-term changes in cerebellar activation during functional recovery from transient peripheral motor paralysis (Article)

2010-11-01T00:00:00Z

Localized altered cerebellar cortical activity can be associated with short-term changes in motor learning that take place in the course of hours, but it is unknown whether it can be correlated to long-term recovery from transient peripheral motor diseases, and if so, whether it occurs concomitantly in related brain regions. Here we show in a longitudinal fMRI study of patients with unilateral Bell's palsy that increases in ipsilateral cerebellar activity follow the recovery course of facial motor functions over at least one and a half years. These findings hold true for changes in brain activity related to both oral and peri-orbital activation, even though these processes are differentially mediated by unilateral and bilateral brain connectivities, respectively. Activation of non-facial musculature, which was studied for control, does not show any change in cerebellar activity over time. The localized changes in cerebellar activities following activation of facial functions occur concomitantly with increases in activity of the facial region in the contralateral primary motor cortex suggesting that the cerebellum acts together with the cerebral cortex in long-term adaptation to transient pathological sensorimotor processing.

Intrinsic plasticity complements long-term potentiation in parallel fiber input gain control in cerebellar Purkinje cells (Article)

2010-10-13T00:00:00Z

Synaptic gain control and information storage in neural networks are mediated by alterations in synaptic transmission, such as in long-term potentiation (LTP). Here,weshowusingboth in vitroandin vivo recordingsfromthe rat cerebellum that tetanization protocols for the induction of LTP at parallel fiber (PF)-to-Purkinje cell synapsescanalsoevokeincreases in intrinsic excitability. Thisformof intrinsic plasticity shares with LTP a requirement for the activation of protein phosphatases 1, 2A, and 2B for induction. Purkinje cell intrinsic plasticity resembles CA1 hippocampal pyramidal cell intrinsic plasticity in that it requires activity of protein kinase A(PKA) and casein kinase 2 (CK2) and is mediated by a downregulation of SK-type calcium-sensitive K conductances. In addition, Purkinje cell intrinsic plasticity similarly results in enhanced spine calcium signaling. However, there are fundamental differences: first, while in the hippocampus increases in excitability result in a higher probability for LTP induction, intrinsic plasticity in Purkinje cells lowers the probability for subsequent LTP induction. Second, intrinsic plasticity raises the spontaneous spike frequency of Purkinje cells. The latter effect does not impair tonic spike firing in the target neurons of inhibitory Purkinje cell projections in the deep cerebellar nuclei, but lowers the Purkinje cell signal-to-noise ratio, thus reducing the PF readout. These observations suggest that intrinsic plasticity accompanies LTP of active PF synapses, while it reduces at weaker, nonpotentiated synapses the probability for subsequent potentiation and lowers the impact on the Purkinje cell output. Copyright

Role of the cerebellar cortex in conditioned goal-directed behavior (Article)

2010-10-06T00:00:00Z

Learning a new goal-directed behavioral task often requires the improvement of at least two processes, including an enhanced stimulus-response association and an optimization of the execution of the motor response. The cerebellum has recently been shown to play a role in acquiring goal-directed behavior, but it is unclear to what extent it contributes to a change in the stimulus-response association and/or the optimization of the execution of the motor response.Wetherefore designed the stimulus-dependent water Y-maze conditioning task, which allows discrimination between both processes, and we subsequently subjected Purkinje cell-specific mutant mice to this new task. The mouse mutants L7-PKCi, which suffer from impaired PKC-dependent processes such as parallel fiber to Purkinje cell long-term depression (PF-PC LTD), were able to acquire the stimulus-response association, but exhibited a reduced optimization of their motor performance. These data show that PF-PC LTD is not required for learning a stimulus-response association, but they do suggest that a PKC-dependent process in cerebellar Purkinje cells is required for optimization of motor responses. Copyright

Encoding of whisker input by cerebellar Purkinje cells (Article)

2010-10-01T00:00:00Z

The cerebellar cortex is crucial for sensorimotor integration. Sensorimotor inputs converge on cerebellar Purkinje cells via two afferent pathways: the climbing fibre pathway triggering complex spikes, and the mossy fibre-parallel fibre pathway, modulating the simple spike activities of Purkinje cells. We used, for the first time, the mouse whisker system as a model system to study the encoding of somatosensory input by Purkinje cells. We show that most Purkinje cells in ipsilateral crus 1 and crus 2 of awake mice respond to whisker stimulation with complex spike and/or simple spike responses. Single-whisker stimulation in anaesthetised mice revealed that the receptive fields of complex spike and simple spike responses were strikingly different. Complex spike responses, which proved to be sensitive to the amplitude, speed and direction of whisker movement, were evoked by only one or a few whiskers. Simple spike responses, which were not affected by the direction of movement, could be evoked by many individual whiskers. The receptive fields of Purkinje cells were largely intermingled, and we suggest that this facilitates the rapid integration of sensory inputs from different sources. Furthermore, we describe that individual Purkinje cells, at least under anaesthesia, may be bound in two functional ensembles based on the receptive fields and the synchrony of the complex spike and simple spike responses. The 'complex spike ensembles' were oriented in the sagittal plane, following the anatomical organization of the climbing fibres, while the 'simple spike ensembles' were oriented in the transversal plane, as are the beams of parallel fibres. © 2010 The Authors. Journal compilation

Visuomotor Cerebellum in Human and Nonhuman Primates (Article)

2010-09-09T00:00:00Z

In this paper, we will review the anatomical components of the visuomotor cerebellum in human and, where possible, in non-human primates and discuss their function in relation to those of extracerebellar visuomotor regions with which they are connected. The floccular lobe, the dorsal paraflocculus, the oculomotor vermis, the uvula-nodulus, and the ansiform lobule are more or less independent components of the visuomotor cerebellum that are involved in different corticocerebellar and/or brain stem olivocerebellar loops. The floccular lobe and the oculomotor vermis share different mossy fiber inputs from the brain stem; the dorsal paraflocculus and the ansiform lobule receive corticopontine mossy fibers from postrolandic visual areas and the frontal eye fields, respectively. Of the visuomotor functions of the cerebellum, the vestibulo-ocular reflex is controlled by the floccular lobe; saccadic eye movements are controlled by the oculomotor vermis and ansiform lobule, while control of smooth pursuit involves all these cerebellar visuomotor regions. Functional imaging studies in humans further emphasize cerebellar involvement in visual reflexive eye movements and are discussed.

Purkinje cell-specific knockout of the protein phosphatase PP2B impairs potentiation and cerebellar motor learning (Article)

2010-08-01T00:00:00Z

Cerebellar motor learning is required to obtain procedural skills. Studies have provided supportive evidence for a potential role of kinase-mediated long-term depression (LTD) at the parallel fiber to Purkinje cell synapse in cerebellar learning. Recently, phosphatases have been implicated in the induction of potentiation of Purkinje cell activities in vitro, but it remains to be shown whether and how phosphatase-mediated potentiation contributes to motor learning. Here, we investigated its possible role by creating and testing a Purkinje cell-specific knockout of calcium/calmodulin-activated protein-phosphatase-2B (L7-PP2B). The selective deletion of PP2B indeed abolished postsynaptic long-term potentiation in Purkinje cells and their ability to increase their excitability, whereas LTD was unaffected. The mutants showed impaired "gain-decrease" and "gain-increase" adaptation of their vestibulo-ocular reflex (VOR) as well as impaired acquisition of classical delay conditioning of their eyeblink response. Thus, our data indicate that PP2B may indeed mediate potentiation in Purkinje cells and contribute prominently to cerebellar motor learning.

Differential olivo-cerebellar cortical control of rebound activity in the cerebellar nuclei (Article)

2010-05-04T00:00:00Z

The output of the cerebellar cortex is controlled by two main inputs, (i.e., the climbing fiber and mossy fiber-parallel fiber pathway) and activations of these inputs elicit characteristic effects in its Purkinje cells: that is, the so-called complex spikes and simple spikes. Target neurons of the Purkinje cells in the cerebellar nuclei show rebound firing, which has been implicated in the processing and storage of motor coordination signals. Yet, it is not known to what extent these rebound phenomena depend on different modes of Purkinje cell activation. Using extracellular as well as patch-clamp recordings, we show here in both anesthetized and awake rodents that simple and complex spike-like train stimuli to the cerebellar cortex, as well as direct activation of the inferior olive, all result in rebound increases of the firing frequencies of cerebellar nuclei neurons for up to 250 ms, whereas single-pulse stimuli to the cerebellar cortex predominantly elicit well-timed spiking activity without changing the firing frequency of cerebellar nuclei neurons. We conclude that the rebound phenomenon offers a rich and powerful mechanism for cerebellar nuclei neurons, which should allow them to differentially process the climbingfiber andmossyfiber inputs in a physiologically operating cerebellum.

Autofluorescent flavoprotein imaging of spinal nociceptive activity (Article)

2010-03-17T00:00:00Z

Pain arises from activation of peripheral nociceptors, and strong noxious stimuli may cause an increase in spinal excitability called central sensitization, which is likely involved in many pathological pain states. So far, it has not been achieved to simultaneously visualize in vivo both the temporal and spatial aspects of spinal activity, including central sensitization. Using autofluorescent flavoprotein imaging (AFI), an optical technique suitable for mapping activity in nervous tissue, we demonstrate a close temporal and spatial correlation of electrically evoked nociceptive input with the spinal AFI signal, representing spinal neuronal activity. The AFI signal increases linearly with stimulation intensity. Furthermore, we found that the AFI signal was much larger in intensity and size when the same electrical stimulation was applied after the induction of central sensitization by a subcutaneous capsaicin injection. Finally, innocuous palpation of the hindpaw did not evoke an AFI response in naive animals, but after capsaicin injection a strong response was obtained. This is the first report demonstrating simultaneously the temporal and spatial propagation of spinal nociceptive activity in vivo. Copyright

High cortical spreading depression susceptibility and migraine-associated symptoms in Cav2.1 S218L mice (Article)

2010-03-11T00:00:00Z

Objective: The CACNA1A gene encodes the pore-forming subunit of neuronal Cav2.1 Ca2+channels. In patients, the S218L CACNA1A mutation causes a dramatic hemiplegic migraine syndrome that is associated with ataxia, seizures, and severe, sometimes fatal, brain edema often triggered by only a mild head trauma. Methods: We introduced the S218L mutation into the mouse Cacna1a gene and studied the mechanisms for the S218L syndrome by analyzing the phenotypic, molecular, and electrophysiological consequences. Results: Cacna1aS218Lmice faithfully mimic the associated clinical features of the human S218L syndrome. S218L neurons exhibit a gene dosage-dependent negative shift in voltage dependence of Cav2.1 channel activation, resulting in enhanced neurotransmitter release at the neuromuscular junction. Cacna1aS218Lmice also display an exquisite sensitivity to cortical spreading depression (CSD), with a vastly reduced triggering threshold, an increased propagation velocity, and frequently multiple CSD events after a single stimulus. In contrast, mice bearing the R192Q CACNA1A mutation, which in humans causes a milder form of hemiplegic migraine, typically exhibit only a single CSD event after one triggering stimulus. Interpretation: The particularly low CSD threshold and the strong tendency to respond with multiple CSD events make the S218L cortex highly vulnerable to weak stimuli and may provide a mechanistic basis for the dramatic phenotype seen in S218L mice and patients. Thus, the S218L mouse model may prove a valuable tool to further elucidate mechanisms underlying migraine, seizures, ataxia, and trauma-triggered cerebral edema.

Genetic dissection of the function of hindbrain axonal commissures (Article)

2010-03-01T00:00:00Z

In Bilateria, many axons cross the midline of the central nervous system, forming well-defined commissures. Whereas in mammals the functions of commissures in the forebrain and in the visual system are well established, functions at other axial levels are less clearly understood. Here, we have dissected the function of several hindbrain commissures using genetic methods. By taking advantage of multiple Cre transgenic lines, we have induced site-specific deletions of the Robo3 receptor. These lines developed with the disruption of specific commissures in the sensory, motor, and sensorimotor systems, resulting in severe and permanent functional deficits. We show that mice with severely reduced commissures in rhombomeres 5 and 3 have abnormal lateral eye movements and auditory brainstem responses, respectively, whereas mice with a primarily uncrossed climbing fiber/Purkinje cell projection are strongly ataxic. Surprisingly, although rerouted axons remain ipsilateral, they still project to their appropriate neuronal targets. Moreover, some Cre;Robo3 lines represent potential models that can be used to study human syndromes, including horizontal gaze palsy with progressive scoliosis (HGPPS). To our knowledge, this study is one of the first to link defects in commissural axon guidance with specific cellular and behavioral phenotypes.

Cerebellar and extracerebellar involvement in mouse eyeblink conditioning: the ACDC model (Article)

2010-01-01T00:00:00Z

Over the past decade the advent of mouse transgenics has generated new perspectives on the study of cerebellar molecular mechanisms that are essential for eyeblink conditioning. However, it also appears that results from eyeblink conditioning experiments done in mice differ in some aspects from results previously obtained in other mammals. In this review article we will, based on studies using (cell-specific) mouse mutants and region-specific lesions, re-examine the general eyeblink behavior in mice and the neuro-anatomical circuits that might contribute to the different peaks in the conditioned eyeblink trace. We conclude that the learning process in mice has at least two stages: An early stage, which includes short-latency responses that are at least partly controlled by extracerebellar structures such as the amygdala, and a later stage, which is represented by well-timed conditioned responses that are mainly controlled by the pontocerebellar and olivocerebellar systems. We refer to this overall concept as the Amygdala-Cerebellum-Dynamic-Conditioning Model (ACDC model).

Perceptual learning, motor learning, and automaticity (Article)

2010-01-01T00:00:00Z

Anticipatory grip force control using a cerebellar model (Article)

2009-09-01T00:00:00Z

Grip force modulation has a rich history of research, but the results remain to be integrated as a neurocomputational model and applied in a robotic system. Adaptive grip force control as exhibited by humans would enable robots to handle objects with sufficient yet minimal force, thus minimizing the risk of crushing objects or inadvertently dropping them. We investigated the feasibility of grip force control by means of a biological neural approach to ascertain the possibilities for future application in robotics. As the cerebellum appears crucial for adequate grip force control, we tested a computational model of the olivo-cerebellar system. This model takes into account that the processing of sensory signals introduces a 100 ms delay, and because of this delay, the system needs to learn anticipatory rather than feedback control. For training, we considered three scenarios for feedback information: (1) grip force error estimation, (2) sensory input on deformation of the fingertips, and (3) as a control, noise. The system was trained on a data set consisting of force and acceleration recordings from human test subjects. Our results show that the cerebellar model is capable of learning and performing anticipatory grip force control closely resembling that of human test subjects despite the delay. The system performs best if the delayed feedback signal carries an error estimation, but it can also perform well when sensory data are used instead. Thus, these tests indicate that a cerebellar neural network can indeed serve well in anticipatory grip force control not only in a biological but also in an artificial system.

Timing in the cerebellum: oscillations and resonance in the granular layer (Article)

2009-09-01T00:00:00Z

The brain generates many rhythmic activities, and the olivo-cerebellar system is not an exception. In recent years, the cerebellum has revealed activities ranging from low frequency to very high-frequency oscillations. These rhythms depend on the brain functional state and are typical of certain circuit sections or specific neurons. Interestingly, the granular layer, which gates sensorimotor and cognitive signals to the cerebellar cortex, can also sustain low frequency (7-25 Hz) and perhaps higher-frequency oscillations. In this review we have considered (i) how these oscillations are generated in the granular layer network depending on intrinsic electroresponsiveness and circuit connections, (ii) how these oscillations are correlated with those in other cerebellar circuit sections, and (iii) how the oscillating cerebellum communicates with extracerebellar structures. It is suggested that the granular layer can generate oscillations that integrate well with those generated in the inferior olive, in deep-cerebellar nuclei and in Purkinje cells. These rhythms, in turn, might play a role in cognition and memory consolidation by interacting with the mechanisms of long-term synaptic plasticity.

Synaptic inhibition of Purkinje cells mediates consolidation of vestibulo-cerebellar motor learning (Article)

2009-08-01T00:00:00Z

Although feedforward inhibition onto Purkinje cells was first documented 40 years ago, we understand little of how inhibitory interneurons contribute to cerebellar function in behaving animals. Using a mouse line (PC-Δγ2) in which GABA A receptor-mediated synaptic inhibition is selectively removed from Purkinje cells, we examined how feedforward inhibition from molecular layer interneurons regulates adaptation of the vestibulo-ocular reflex. Although impairment of baseline motor performance was relatively mild, the ability to adapt the phase of the vestibulo-ocular reflex and to consolidate gain adaptations was strongly compromised. Purkinje cells showed abnormal patterns of simple spikes, both during and in the absence of evoked compensatory eye movements. On the basis of modeling our experimental data, we propose that feedforward inhibition, by controlling the fine-scale patterns of Purkinje cell activity, enables the induction of plasticity in neurons of the cerebellar and vestibular nuclei.

betaCaMKII controls the direction of plasticity at parallel fiber–Purkinje cell synapses (Article)

2009-07-01T00:00:00Z

Abstract We found that betaCaMKII, the predominant CaMKII isoform of the cerebellum, is important for controlling the direction of plasticity at the parallel fiber-Purkinje cell synapse; a protocol that induced synaptic depression in wild-type mice resulted in synaptic potentiation in Camk2b knockout mice and vice versa. These findings provide us with unique experimental insight into the mechanisms that transduce graded calcium signals into either synaptic depression or potentiation.

βCaMKII controls the direction of plasticity at parallel fiber–Purkinje cell synapses (Article)

2009-06-07T00:00:00Z

We found that betaCaMKII, the predominant CaMKII isoform of the cerebellum, is important for controlling the direction of plasticity at the parallel fiber-Purkinje cell synapse; a protocol that induced synaptic depression in wild-type mice resulted in synaptic potentiation in Camk2b knockout mice and vice versa. These findings provide us with unique experimental insight into the mechanisms that transduce graded calcium signals into either synaptic depression or potentiation.

Timing and plasticity in the cerebellum: focus on the granular layer (Article)

2009-01-01T00:00:00Z

Two of the most striking properties of the cerebellum are its control in timing of motor operations and its ability to adapt behavior to new sensorimotor associations. Here, we propose a 'time-window matching' hypothesis for granular layer processing. Our hypothesis states that mossy fiber inputs to the granular layer are transformed into well-timed spike bursts by intrinsic granule cell processing, that feedforward Golgi cell inhibition sets a limit to the duration of such bursts and that these activities are spread over particular fields in the granular layer so as to generate ongoing time-windows for proper control of interacting motor domains. The role of synaptic plasticity would be that of fine-tuning pre-wired circuits favoring activation of specific granule cell groups in relation to particular time windows. This concept has wide implications for processing in the olivo-cerebellar system as a whole.

Alcohol impairs long-term depression at the cerebellar parallel fiber-Purkinje cell synapse (Article)

2008-12-01T00:00:00Z

Acute alcohol consumption causes deficits in motor coordination and gait, suggesting an involvement of cerebellar circuits, which play a role in the fine adjustment of movements and in motor learning. It has previously been shown that ethanol modulates inhibitory transmission in the cerebellum and affects synaptic transmission and plasticity at excitatory climbing fiber (CF) to Purkinje cell synapses. However, it has not been examined thus far how acute ethanol application affects long-term depression (LTD) and long-term potentiation (LTP) at excitatory parallel fiber (PF) to Purkinje cell synapses, which are assumed to mediate forms of cerebellar motor learning. To examine ethanol effects on PF synaptic transmission and plasticity, we performed whole cell patch-clamp recordings from Purkinje cells in rat cerebellar slices. We found that ethanol (50 mM) selectively blocked PF-LTD induction, whereas it did not change the amplitude of excitatory postsynaptic currents at PF synapses. In contrast, ethanol application reduced voltage-gated calcium currents and type 1 metabotropic glutamate receptor (mGluR1)-dependent responses in Purkinje cells, both of which are involved in PF-LTD induction. The selectivity of these effects is emphasized by the observation that ethanol did not impair PF-LTP and that PF-LTP could readily be induced in the presence of the group I mGluR antagonist AIDA or the mGluR1a antagonist LY367385. Taken together, these findings identify calcium currents and mGluR1-dependent signaling pathways as potential ethanol targets and suggest that an ethanol-induced blockade of PF-LTD could contribute to the motor coordination deficits resulting from alcohol consumption. Copyright

Purkinje cell input to cerebellar nuclei in tottering: Ultrastructure and physiology (Article)

2008-12-01T00:00:00Z

Homozygous tottering mice are spontaneous ataxic mutants, which carry a mutation in the gene encoding the ion pore of the P/Q-type voltage-gated calcium channels. P/Q-type calcium channels are prominently expressed in Purkinje cell terminals, but it is unknown to what extent these inhibitory terminals in tottering mice are affected at the morphological and electrophysiological level. Here, we investigated the distribution and ultrastructure of their Purkinje cell terminals in the cerebellar nuclei as well as the activities of their target neurons. The densities of Purkinje cell terminals and their synapses were not significantly affected in the mutants. However, the Purkinje cell terminals were enlarged and had an increased number of vacuoles, whorled bodies, and mitochondria. These differences started to occur between 3 and 5 weeks of age and persisted throughout adulthood. Stimulation of Purkinje cells in adult tottering mice resulted in inhibition at normal latencies, but the activities of their postsynaptic neurons in the cerebellar nuclei were abnormal in that the frequency and irregularity of their spiking patterns were enhanced. Thus, although the number of their terminals and their synaptic contacts appear quantitatively intact, Purkinje cells in tottering mice show several signs of axonal damage that may contribute to altered postsynaptic activities in the cerebellar nuclei.

Endocochlear potential depends on Cl- channels: Mechanism underlying deafness in Bartter syndrome IV (Article)

2008-11-05T00:00:00Z

Human Bartter syndrome IV is an autosomal recessive disorder characterized by congenital deafness and severe renal salt and fluid loss. It is caused by mutations in BSND, which encodes barttin, a β-subunit of ClC-Ka and ClC-Kb chloride channels. Inner-ear-specific disruption of Bsnd in mice now reveals that the positive potential, but not the high potassium concentration, of the scala media depends on the presence of these channels in the epithelium of the stria vascularis. The reduced driving force for K+-entry through mechanosensitive channels into sensory hair cells entails a profound congenital hearing loss and subtle vestibular symptoms. Although retaining all cell types and intact tight junctions, the thickness of the stria is reduced early on. Cochlear outer hair cells degenerate over several months. A collapse of endolymphatic space was seen when mice had additionally renal salt and fluid loss due to partial barttin deletion in the kidney. Bsnd-/-mice thus demonstrate a novel function of Cl-channels in generating the endocochlear potential and reveal the mechanism leading to deafness in human Bartter syndrome IV.

Savings and extinction of conditioned eyeblink responses in fragile X syndrome (Article)

2008-10-01T00:00:00Z

The fragile X syndrome (FRAXA) is the most widespread heritable form of mental retardation caused by the lack of expression of the fragile X mental retardation protein (FMRP). This lack has been related to deficits in cerebellum-mediated acquisition of conditioned eyelid responses in individuals with FRAXA. In the present behavioral study, long-term effects of deficiency of FMRP were investigated by examining the acquisition, savings and extinction of delay eyeblink conditioning in male individuals with FRAXA. In the acquisition experiment, subjects with FRAXA displayed a significantly poor performance compared with controls. In the savings experiment performed at least 6 months later, subjects with FRAXA and controls showed similar levels of savings of conditioned responses. Subsequently, extinction was faster in subjects with FRAXA than in controls. These findings confirm that absence of the FMRP affects cerebellar motor learning. The normal performance in the savings experiment and aberrant performance in the acquisition and extinction experiments of individuals with FRAXA suggest that different mechanisms underlie acquisition, savings and extinction of cerebellar motor learning.

Effect of simvastatin on cognitive functioning in children with neurofibromatosis type 1: A randomized controlled trial (Article)

2008-07-16T00:00:00Z

Context: Neurofibromatosis type 1 (NF1) is among the most common genetic disorders that cause learning disabilities. Recently, it was shown that statin-mediated inhibition of 3-hydroxy-3-methylglutaryl coenzyme A reductase restores the cognitive deficits in an NF1 mouse model. Objective: To determine the effect of simvastatin on neuropsychological, neurophysiological, and neuroradiological outcome measures in children with NF1. Design, Setting, and Participants: Sixty-two of 114 eligible children (54%) with NF1 participated in a randomized, double-blind, placebo-controlled trial conducted between January 20, 2006, and February 8, 2007, at an NF1 referral center at a Dutch university hospital. Intervention: Simvastatin or placebo treatment once daily for 12 weeks. Main Outcome Measures: Primary outcomes were scores on a Rey complex figure test (delayed recall), cancellation test (speed), prism adaptation, and the mean brain apparent diffusion coefficient based on magnetic resonance imaging. Secondary outcome measures were scores on the cancellation test (standard deviation), Stroop color word test, block design, object assembly, Rey complex figure test (copy), Beery developmental test of visual-motor integration, and judgment of line orientation. Scores were corrected for baseline performance, age, and sex. Results: No significant differences were observed between the simvastatin and placebo groups on any primary outcome measure: Rey complex figure test (β=0.10; 95% confidence interval [CI], -0.36 to 0.56); cancellation test (β=-0.19; 95% CI, -0.67 to 0.29); prism adaptation (odds ratio=2.0; 95% CI, 0.55 to 7.37); and mean brain apparent diffusion coefficient (β=0.06; 95% CI, -0.07 to 0.20). In the secondary outcome measures, we found a significant improvement in the simvastatin group in object assembly scores (β=0.54; 95% CI, 0.08 to 1.01), which was specifically observed in children with poor baseline performance (β=0.80; 95% CI, 0.29 to 1.30). Other secondary outcome measures revealed no significant effect of simvastatin treatment. Conclusion: In this 12-week trial, simvastatin did not improve cognitive function in children with NF1. Trial Registration: isrctn.org Identifier: ISRCTN14965707

Changes of cerebral blood flow during the secondary expansion of a cortical contusion assessed by 14C-iodoantipyrine autoradiography in mice using a non-invasive protocol (Article)

2008-07-01T00:00:00Z

Although changes of cerebral blood flow (CBF) in and around traumatic contusions are well documented, the role of CBF for the delayed death of neuronal cells in the traumatic penumbra ultimately resulting in secondary contusion expansion remains unclear. The aim of the current study was therefore to investigate the relationship between changes of CBF and progressive peri-contusional cell death following traumatic brain injury (TBI). CBF and contusion size were measured in C57Bl6 mice under continuous on-line monitoring ofETpCO2before, and at 15 min and 24 h following controlled cortical impact by14C-iodoantipyrine autoradiography (IAP-AR; n = 5-6 per group) and by Nissl staining, respectively. Contused and ischemic (CBF < 10%) tissue volumes were calculated and compared over time. Cortical CBF in not injured mice varied between 69 and 93 mL/100mg/min depending on the anatomical location. Fifteen minutes after trauma, CBF decreased in the whole brain by ∼50% (39 ± 18 mL/100mg/min; p < 0.05), except in contused tissue where it fell by more than 90% (3 ± 2 mL/100mg/min; p < 0.001). Within 24 h after TBI, CBF recovered to normal values in all brain areas except the contusion where it remained reduced by more than 90% (p < 0.001). Contusion volume expanded from 24.9 to 35.5 mm3(p < 0.01) from 15 min to 24 h after trauma (+43%), whereas the area of severe ischemia (CBF < 10%) showed only a minimal (+13%) and not significant increase (22.3 to 25.1 mm3). The current data therefore suggest that the delayed secondary expansion of a cortical contusion following traumatic brain injury may not be caused by a reduction of CBF alone.

Rescue of behavioral phenotype and neuronal protrusion morphology in Fmr1 KO mice (Article)

2008-07-01T00:00:00Z

Lack of fragile X mental retardation protein (FMRP) causes Fragile X Syndrome, the most common form of inherited mental retardation. FMRP is an RNA-binding protein and is a component of messenger ribonucleoprotein complexes, associated with brain polyribosomes, including dendritic polysomes. FMRP is therefore thought to be involved in translational control of specific mRNAs at synaptic sites. In mice lacking FMRP, protein synthesis-dependent synaptic plasticity is altered and structural malformations of dendritic protrusions occur. One hypothesized cause of the disease mechanism is based on exaggerated group I mGluR receptor activation. In this study, we examined the effect of the mGluR5 antagonist MPEP on Fragile X related behavior in Fmr1 KO mice. Our results demonstrate a clear defect in prepulse inhibition of startle in Fmr1 KO mice, that could be rescued by MPEP. Moreover, we show for the first time a structural rescue of Fragile X related protrusion morphology with two independent mGluR5 antagonists.

Causes and Consequences of Oscillations in the Cerebellar Cortex (Article)

2008-06-12T00:00:00Z

Cerebellar high-frequency oscillations have been observed for many decades, but their underlying mechanisms have remained enigmatic. In this issue of Neuron, two papers indicate that specific intrinsic mechanisms in the cerebellar cortex contribute to the generation of these oscillations. Middleton et al. show that GABAAreceptor activation and nonchemical transmission are required for nicotine-dependent oscillations at 30-80 Hz and 80-160 Hz, respectively, while de Solages et al. provide evidence that recurrent inhibition by Purkinje cells is essential for oscillations around 200 Hz.

Adaptation of the cervico- and vestibulo-ocular reflex in whiplash injury patients (Article)

2008-06-01T00:00:00Z

The aim of this study was to investigate the underlying mechanisms of the increased gains of the cervico-ocular reflex (COR) and the lack of synergy between the COR and the vestibulo-ocular reflex (VOR) that have been previously observed in patients with whiplash-associated disorders (WAD). Eye movements during COR or VOR stimulation were recorded in four different experiments. The effect of restricted neck motion and the relationship between muscle activity and COR gain was examined in healthy controls. The adaptive ability of the COR and the VOR was tested in WAD patients and healthy controls. Reduced neck mobility yielded an increase in COR gain. No correlation between COR gain and muscle activity was observed. Adaptation of both the COR and VOR was observed in healthy controls, but not in WAD patients. The increased COR gain of WAD patients may stem from a reduced neck mobility. The lack of adaptation of the two stabilization reflexes may result in a lack of synergy between them. These abnormalities may underlie several of the symptoms frequently observed in WAD, such as vertigo and dizziness.

Role of Olivary Electrical Coupling in Cerebellar Motor Learning (Article)

2008-05-22T00:00:00Z

The level of electrotonic coupling in the inferior olive is extremely high, but its functional role in cerebellar motor control remains elusive. Here, we subjected mice that lack olivary coupling to paradigms that require learning-dependent timing. Cx36-deficient mice showed impaired timing of both locomotion and eye-blink responses that were conditioned to a tone. The latencies of their olivary spike activities in response to the unconditioned stimulus were significantly more variable than those in wild-types. Whole-cell recordings of olivary neurons in vivo showed that these differences in spike timing result at least in part from altered interactions with their subthreshold oscillations. These results, combined with analyses of olivary activities in computer simulations at both the cellular and systems level, suggest that electrotonic coupling among olivary neurons by gap junctions is essential for proper timing of their action potentials and thereby for learning-dependent timing in cerebellar motor control.

Tragedy of conducting a clinical trial; generic alert system needed (Article)

2008-05-01T00:00:00Z

Stopping a clinical trial without reaching the final objective is not the ideal outcome any researcher wants; sometimes ceasing is inevitable. Due to marginal inclusion of patients we were forced to cease our randomized clinical trial on the effectiveness of proprioceptive training on the development of chronic whiplash complaints a year after the start. Although incidence figures demonstrate that recruitment of the planned number of whiplash patients would be easily feasible, we were unable to enroll the amount of subjects. Several motives can be proposed that would have prevented this obliged halting from happening. Other studies also report impracticability of the planned number of whiplash injury patients.

Neuron-specific expression of mutant superoxide dismutase is sufficient to induce amyotrophic lateral sclerosis in transgenic mice (Article)

2008-02-27T00:00:00Z

Mutations in superoxide dismutase (SOD1) cause amyotrophic lateral sclerosis (ALS), an adult-onset progressive paralytic disease characterized by loss of motor neurons, and cause an ALS-like disease when expressed in mice. Recent data have suggested that motor neuron degeneration results from toxic actions of mutant SOD1 operating in both motor neurons and their neighboring glia, raising the question whether mutant SOD1 expression selectively in neurons is sufficient to induce disease. Here we show that neuronal expression of mutant SOD1 is sufficient to cause motor neuron degeneration and paralysis in transgenic mice with cytosolic dendritic ubiquitinated SOD1 aggregates as the dominant pathological feature. In addition, we show that crossing our neuron-specific mutant SOD1 mice with ubiquitously wild-type SOD1-expressing mice leads to dramatic wild-type SOD1 aggregation in oligodendroglia after the onset of neuronal degeneration. Together, our findings support a pathogenic scenario in which mutant SOD1 in neurons triggers neuronal degeneration, which in turn may facilitate aggregate formation in surrounding glial cells. Copyright

Altered olivocerebellar activity patterns in the connexin36 knockout mouse (Article)

2007-12-04T00:00:00Z

The inferior olive (IO) has among the highest densities of neuronal gap junctions in the nervous system. These gap junctions are proposed to be the underlying mechanism for generating synchronous Purkinje cell complex spike (CS) activity. Gap junctions between neurons are formed mostly by connexin36 proteins. Thus, the connexin36 knockout (Cx36KO) mouse provides an opportunity to test whether gap junction coupling between IO neurons is the basis of CS synchrony. Multiple electrode recordings of crus 2 CSs were obtained from wildtype (Wt) and Cx36KO mice. Wts showed statistically significant levels of CS synchrony, with the same spatial distribution as has been reported for other species: high CS synchrony levels occurred mostly among Purkinje cells within the same parasagittally-oriented cortical strip. In contrast, in Cx36KOs, synchrony was at chance levels and had no preferential spatial orientation, supporting the gap junction hypothesis. CS firing rates for Cx36KOs were significantly lower than for Wts, suggesting that electrical coupling is an important determinant of IO excitability. Rhythmic CS activity was present in both Wt and Cx36KOs, suggesting that individual IO cells can act as intrinsic oscillators. In addition, the climbing fiber reflex was absent in the Cx36KOs, validating its use as a tool for assessing electrical coupling of IO neurons. Zebrin II staining and anterograde tracing showed that cerebellar cortical organization and the topography of the olivocerebellar projection are normal in the Cx36KO. Thus, the differences in CS activity between Wts and Cx36KOs likely reflect the loss of electrical coupling of IO cells.

Estradiol improves cerebellar memory formation by activating estrogen receptor β (Article)

2007-10-03T00:00:00Z

Learning motor skills is critical for motor abilities such as driving a car or playing piano. The speed at which we learn those skills is subject to many factors. Yet, it is not known to what extent gonadal hormones can affect the achievement of accurate movements in time and space. Here we demonstrate via different lines of evidence that estradiol promotes plasticity in the cerebellar cortex underlying motor learning. First, we show that estradiol enhances induction of long-term potentiation at the parallel fiber to Purkinje cell synapse, whereas it does not affect long-term depression; second, we show that estradiol activation of estrogen receptor β receptors in Purkinje cells significantly improves gain-decrease adaptation of the vestibulo-ocular reflex, whereas it does not affect general eye movement performance; and third, we show that estradiol increases the density of parallel fiber to Purkinje cell synapses, whereas it does not affect the density of climbing fiber synapses. We conclude that estradiol can improve motor skills by potentiating cerebellar plasticity and synapse formation. These processes may be advantageous during periods of high estradiol levels of the estrous cycle or pregnancy. Copyright

In vivo mouse inferior olive neurons exhibit heterogeneous subthreshold oscillations and spiking patterns (Article)

2007-10-02T00:00:00Z

In vitro whole-cell recordings of the inferior olive have demonstrated that its neurons are electrotonically coupled and have a tendency to oscillate. However, it remains to be shown to what extent subthreshold oscillations do indeed occur in the inferior olive in vivo and whether its spatiotemporal firing pattern may be dynamically generated by including or excluding different types of oscillatory neurons. Here, we did whole-cell recordings of olivary neurons in vivo to investigate the relation between their subthreshold activities and their spiking behavior in an intact brain. The vast majority of neurons (85%) showed subthreshold oscillatory activities. The frequencies of these subthreshold oscillations were used to distinguish four main olivary subtypes by statistical means. Type I showed both sinusoidal subthreshold oscillations (SSTOs) and low-threshold Ca2+oscillations (LTOs) (16%); type II showed only sinusoidal subthreshold oscillations (13%); type III showed only low-threshold Ca2+oscillations (56%); and type IV did not reveal any subthreshold oscillations (15%). These subthreshold oscillation frequencies were strongly correlated with the frequencies of preferred spiking. The frequency characteristics of the subthreshold oscillations and spiking behavior of virtually all olivary neurons were stable throughout the recordings. However, the occurrence of spontaneous or evoked action potentials modified the subthreshold oscillation by resetting the phase of its peak toward 90° . Together, these findings indicate that the inferior olive in intact mammals offers a rich repertoire of different neurons with relatively stable frequency settings, which can be used to generate and reset temporal firing patterns in a dynamically coupled ensemble.

Comparing two diagnostic laboratory tests for Williams syndrome: Fluorescent in situ hybridization versus multiplex ligation-dependent probe amplification (Article)

2007-09-01T00:00:00Z

Most people with Williams syndrome (WS) have a heterozygous 1.55 Mb deletion on chromosome 7q11.23. For diagnostic purposes, fluorescence in situ hybridisation (FISH) with commercial FISH probes is commonly used to detect this deletion. We investigated whether multiplex ligation-dependent probe amplification (MLPA) is a reliable alternative for FISH. The MLPA kit (SALSA P029) contains probes for eight genes in the WS critical region: FKBP6, FZD9, TBL2, STX1A, ELN, LIMK1, RFC2, and CYLN2. The experimental FISH assay that was used consists of four probes covering the WS critical region. A total number of 63 patients was tested; in 53 patients, a deletion was detected both with FISH and MLPA(P029), in 10 patients both techniques failed to demonstrate a deletion. In only one patient, a deletion was detected which was not previously detected by two commercial FISH probes. This patient appeared to carry a small, atypical deletion. We conclude that MLPA is a reliable technique to detect WS. Compared with FISH, MLPA is less time consuming and has the possibility to detect also smaller, atypical deletions and duplications in the WS critical region.

Exceptional good cognitive and phenotypic profile in a male carrying a mosaic mutation in the FMR1 gene (Article)

2007-08-01T00:00:00Z

Fragile X (FRAX) syndrome is a commonly inherited form of mental retardation resulting from the lack of expression of the fragile X mental retardation protein (FMRP). It is caused by a stretch of CGG repeats within the fragile X gene, which can be unstable in length as it is transmitted from generation to generation. Once the repeat exceeds a threshold length, the FMR1 gene is methylated and no protein is produced resulting in the fragile X phenotype. The consequences of FMRP absence in the mechanisms underlying mental retardation are unknown. We have identified a male patient in a classical FRAX family without the characteristic FRAX phenotype. His intelligence quotient (IQ) is borderline normal despite the presence of a mosaic pattern of a pre-mutation (25%), full mutation (60%) and a deletion (15%) in the FMR1 gene. The cognitive performance was determined at the age of 28 by the Raven test and his IQ was 81. However, FMRP expression studies in both hair roots and lymphocytes, determined at the same time as the IQ test, were within the affected male range. The percentage of conditioned responses after delay eyeblink conditioning was much higher than the average percentage measured in FRAX studies. Moreover, this patient showed no correlation between FMRP expression and phenotype and no correlation between DNA diagnostics and phenotype.

Regular patterns in cerebellar Purkinje cell simple spike trains (Article)

2007-05-30T00:00:00Z

Background. Cerebellar Purkinje cells (PC) in vivo are commonly reported to generate irregular spike trains, documented by high coefficients of variation of interspike-intervals (ISI). In strong contrast, they fire very regularly in the in vitro slice preparation. We studied the nature of this difference in firing properties by focusing on short-term variability and its dependence on behavioral state. Methodology/Principal Findings. Using an analysis based on CV2values, we could isolate precise regular spiking patterns, lasting up to hundreds of milliseconds, in PC simple spike trains recorded in both anesthetized and awake rodents. Regular spike patterns, defined by low variability of successive ISIs, comprised over half of the spikes, showed a wide range of mean ISIs, and were affected by behavioral state and tactile stimulation. Interestingly, regular patterns often coincided in nearby Purkinje cells without precise synchronization of individual spikes. Regular patterns exclusively appeared during the up state of the PC membrane potential, while single ISIs occurred both during up and down states. Possible functional consequences of regular spike patterns were investigated by modeling the synaptic conductance in neurons of the deep cerebellar nuclei (DCN). Simulations showed that these regular patterns caused epochs of relatively constant synaptic conductance in DCN neurons. Conclusions/Significance. Our findings indicate that the apparent irregularity in cerebellar PC simple spike trains in vivo is most likely caused by mixing of different regular spike patterns, separated by single long intervals, over time. We propose that PCs may signal information, at least in part, in regular spike patterns to downstream DCN neurons.

Cerebellar LTD and Pattern Recognition by Purkinje Cells (Article)

2007-04-05T00:00:00Z

Many theories of cerebellar function assume that long-term depression (LTD) of parallel fiber (PF) synapses enables Purkinje cells to learn to recognize PF activity patterns. We have studied the LTD-based recognition of PF patterns in a biophysically realistic Purkinje-cell model. With simple-spike firing as observed in vivo, the presentation of a pattern resulted in a burst of spikes followed by a pause. Surprisingly, the best criterion to distinguish learned patterns was the duration of this pause. Moreover, our simulations predicted that learned patterns elicited shorter pauses, thus increasing Purkinje-cell output. We tested this prediction in Purkinje-cell recordings both in vitro and in vivo. In vitro, we found a shortening of pauses when decreasing the number of active PFs or after inducing LTD. In vivo, we observed longer pauses in LTD-deficient mice. Our results suggest a novel form of neural coding in the cerebellar cortex.

Contribution of CYLN2 and GTF2IRD1 to neurological and cognitive symptoms in Williams Syndrome (Article)

2007-04-01T00:00:00Z

Williams Syndrome (WS, [MIM 194050]) is a disorder caused by a hemizygous deletion of 25-30 genes on chromosome 7q11.23. Several of these genes including those encoding cytoplasmic linker protein-115 (CYLN2) and general transcription factors (GTF2I and GTF2IRD1) are expressed in the brain and may contribute to the distinct neurological and cognitive deficits in WS patients. Recent studies of patients with partial deletions indicate that hemizygosity of GTF2I probably contributes to mental retardation in WS. Here we investigate whether CYLN2 and GTF2IRD1 contribute to the motoric and cognitive deficits in WS. Behavioral assessment of a new patient in which STX1A and LIMK1, but not CYLN2 and GTF2IRD1, are deleted showed that his cognitive and motor coordination functions were significantly better than in typical WS patients. Comparative analyses of gene specific CYLN2 and GTF2IRD1 knockout mice showed that a reduced size of the corpus callosum as well as deficits in motor coordination and hippocampal memory formation may be attributed to a deletion of CYLN2, while increased ventricle volume can be attributed to both CYLN2 and GTF2IRD1. We conclude that the motor and cognitive deficits in Williams Syndrome are caused by a variety of genes and that heterozygous deletion of CYLN2 is one of the major causes responsible for such dysfunctions.

The neuropeptide corticotropin-releasing factor regulates excitatory transmission and plasticity at the climbing fibre-Purkinje cell synapse (Article)

2007-03-01T00:00:00Z

The climbing fibre (CF) input controls cerebellar Purkinje cell (PC) activity as well as synaptic plasticity at parallel fibre (PF)-PC synapses. Under high activity conditions, CFs release not only glutamate, but also the neuropeptide corticotropin-releasing factor (CRF). Brief periods of such high CF activity can lead to the induction of long-term depression (LTD) at CF-PC synapses. Thus, we have examined for the first time the role of CRF in regulating excitatory postsynaptic currents (EPSCs) and long-term plasticity at this synapse. Exogenous application of CRF alone transiently mimicked three aspects of CF-LTD, causing reductions in the CF-evoked excitatory postsynaptic current, complex spike second component and complex spike afterhyperpolarization. The complex spike first component is unaffected by CF-LTD induction and was similarly unaffected by CRF. Application of a CRF receptor antagonist reduced the expression amplitude and induction probability of CF-LTD monitored at the EPSC level. Collectively, these results suggest that under particular sensorimotor conditions, co-release of CRF from climbing fibres could down-regulate excitatory transmission and facilitate LTD induction at CF-PC synapses. Inhibition of either protein kinase C (PKC) or protein kinase A (PKA) attenuated the effects of CRF upon CF-EPSCs. We have previously shown that CF-LTD induction is PKC-dependent, and here demonstrate PKA-dependence as well. These results suggest that both the acute effects of CRF on CF-EPSCs as well as the facilitating effect of CRF on CF-LTD induction can be explained by a CRF-mediated recruitment of PKC and PKA.

Echinoderm microtubule-associated protein like protein 4, a member of the echinoderm microtubule-associated protein family, stabilizes microtubules (Article)

2007-02-23T00:00:00Z

Echinoderm microtubule-associated protein (EMAP) is the major microtubule binding protein in dividing sea urchin (Strongylocentrotus purpuratus) eggs. Echinoderm microtubule-associated protein like protein 4 (Eml4, restrictedly overexpressed proliferation-associated protein 120 kDa (Ropp120)) is one of the five mammalian EMAP homologues, the cellular function of which remains to be elucidated. In our first set of experiments we determined the spatio-temporal expression pattern of Eml4 in mouse brain. Our results demonstrate that Eml4 is a highly developmentally regulated gene with high expression levels in the developing nervous system of E11 embryos declining to low levels in adult. Spatially, Eml4 expression becomes restricted to the olfactory bulb, hippocampus and cerebellum. Transient transfection of a fusion construct of full-length mouse Eml4 with green fluorescent protein (GFP-Eml4) into Cos7 and HeLa cells resulted in colocalization of GFP-Eml4 with microtubules. This colocalization was observed both with microtubules of non-dividing cells and with the mitotic spindle of dividing cells. In addition, transient overexpression of GFP-Eml4 in Cos7 cells resulted in microtubules that were resistant to nocodazole treatment suggesting that Eml4 stabilizes microtubules. A consequence of microtubule stabilization is a net reduction in the amount of free tubulin. Microtubule stabilizing proteins therefore are expected to indirectly decrease the microtubule growth rate. Indeed, transient transfection of GFP-Eml4 resulted in a marked decrease in the microtubule growth rate, which is in line with our hypothesis that Eml4 functions as a microtubule stabilizing protein. In summary, our results suggest that Eml4 is a developmentally regulated protein that colocalizes with and stabilizes microtubules.

Formation of microtubule-based traps controls the sorting and concentration of vesicles to restricted sites of regenerating neurons after axotomy (Article)

2007-02-12T00:00:00Z

Transformation of a transected axonal tip into a growth cone (GC) is a critical step in the cascade leading to neuronal regeneration. Critical to the regrowth is the supply and concentration of vesicles at restricted sites along the cut axon. The mechanisms underlying these processes are largely unknown. Using online confocal imaging of transected, cultured Aplysia californica neurons, we report that axotomy leads to reorientation of the microtubule (MT) polarities and formation of two distinct MT-based vesicle traps at the cut axonal end. Approximately 100 μm proximal to the cut end, a selective trap for anterogradely transported vesicles is formed, which is the plus end trap. Distally, a minus end trap is formed that exclusively captures retrogradely transported vesicles. The concentration of anterogradely transported vesicles in the former trap optimizes the formation of a GC after axotomy.

Bicaudal D induces selective dynein-mediated microtubule minus end-directed transport. (Article)

2003-11-17T00:00:00Z

Bicaudal D is an evolutionarily conserved protein, which is involved in dynein-mediated motility both in Drosophila and in mammals. Here we report that the N-terminal portion of human Bicaudal D2 (BICD2) is capable of inducing microtubule minus end-directed movement independently of the molecular context. This characteristic offers a new tool to exploit the relocalization of different cellular components by using appropriate targeting motifs. Here, we use the BICD2 N-terminal domain as a chimera with mitochondria and peroxisome-anchoring sequences to demonstrate the rapid dynein-mediated transport of selected organelles. Surprisingly, unlike other cytoplasmic dynein-mediated processes, this transport shows very low sensitivity to overexpression of the dynactin subunit dynamitin. The dynein-recruiting activity of the BICD2 N-terminal domain is reduced within the full-length molecule, indicating that the C-terminal part of the protein might regulate the interaction between BICD2 and the motor complex. Our findings provide a novel model system for dissection of the molecular mechanism of dynein motility.

Compensatory increase of the cervico-ocular reflex with age in healthy humans. (Article)

2003-11-15T00:00:00Z

The cervico-ocular reflex (COR) is an ocular stabilization reflex that is elicited by rotation of the neck. It works in conjunction with the vestibulo-ocular reflex (VOR) and the optokinetic reflex (OKR) in order to prevent visual slip over the retina due to self-motion. The gains of the VOR and OKR are known to decrease with age. We have investigated whether the COR, a reflexive eye movement elicited by rotation of the neck, shows a compensatory increase and whether a synergy exists between the COR and the other ocular stabilization reflexes. In the present study 35 healthy subjects of varying age (20-86 years) were rotated in the dark in a trunk-to-head manner (the head fixed in spaced with the body passively rotated under it) at peak velocities between 2.1 and 12.6 deg s-1 as a COR stimulus. Another 15 were subjected to COR, VOR and OKR stimuli at frequencies between 0.04 and 0.1 Hz. Three subjects participated in both tests. The position of the eyes was recorded with an infrared recording technique. We found that the COR-gain increases with increasing age and that there is a significant covariation between the gains of the VOR and COR, meaning that when VOR increases, COR decreases and vice versa. A nearly constant phase lag between the COR and the VOR of about 25 deg existed at all stimulus frequencies.

Long-term depression of climbing fiber-evoked calcium transients in Purkinje cell dendrites. (Article)

2003-03-01T00:00:00Z

In recent years much has been learned about the molecular requirements for inducing long-term synaptic depression (LTD) in various brain regions. However, very little is known about the consequences of LTD induction for subsequent signaling events in postsynaptic neurons. We have addressed this issue by examining homosynaptic LTD at the cerebellar climbing fiber (CF)-Purkinje cell (PC) synapse. This synapse is built for reliable and massive excitation: Activation of a single axon produces an unusually large alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid receptor-mediated synaptic current, the depolarization of which drives a regenerative complex spike producing a large, widespread Ca(2+) transient in PC dendrites. Here we test whether CF LTD has an impact on dendritic, complex spike-evoked Ca(2+) signals by simultaneously performing long-term recordings of complex spikes and microfluorimetric Ca(2+) measurements in PC dendrites in rat cerebellar slices. Our data show that LTD of the CF excitatory postsynaptic current produces a reduction in both slow components of the complex spike waveform and complex spike-evoked dendritic Ca(2+) transients. This LTD of dendritic Ca(2+) signals may provide a neuroprotective mechanism and/or constitute "heterosynaptic metaplasticity" by reducing the probability for subsequent induction of those forms of use-dependent plasticity, which require CF-evoked Ca(2+) signals such as parallel fiber-PC LTD and interneuron-PC LTP.

Visualization of microtubule growth in cultured neurons via the use of EB3-GFP (end-binding protein 3-green fluorescent protein) (Article)

2003-01-01T00:00:00Z

Several microtubule binding proteins, including CLIP-170 (cytoplasmic linker protein-170), CLIP-115, and EB1 (end-binding protein 1), have been shown to associate specifically with the ends of growing microtubules in non-neuronal cells, thereby regulating microtubule dynamics and the binding of microtubules to protein complexes, organelles, and membranes. When fused to GFP (green fluorescent protein), these proteins, which collectively are called +TIPs (plus end tracking proteins), also serve as powerful markers for visualizing microtubule growth events. Here we demonstrate that endogenous +TIPs are present at distal ends of microtubules in fixed neurons. Using EB3-GFP as a marker of microtubule growth in live cells, we subsequently analyze microtubule dynamics in neurons. Our results indicate that microtubules grow slower in neurons than in glia and COS-1 cells. The average speed and length of EB3-GFP movements are comparable in cell bodies, dendrites, axons, and growth cones. In the proximal region of differentiated dendrites approximately 65% of EB3-GFP movements are directed toward the distal end, whereas 35% are directed toward the cell body. In more distal dendritic regions and in axons most EB3-GFP dots move toward the growth cone. This difference in directionality of EB3-GFP movements in dendrites and axons reflects the highly specific microtubule organization in neurons. Together, these results suggest that local microtubule polymerization contributes to the formation of the microtubule network in all neuronal compartments. We propose that similar mechanisms underlie the specific association of CLIPs and EB1-related proteins with the ends of growing microtubules in non-neuronal and neuronal cells.

Deformation of network connectivity in the inferior olive of connexin 36-deficient mice is compensated by morphological and electrophysiological changes at the single neuron level (Article)

2003-01-01T00:00:00Z

Compensatory mechanisms after genetic manipulations have been documented extensively for the nervous system. In many cases, these mechanisms involve genetic regulation at the transcription or expression level of existing isoforms. We report a novel mechanism by which single neurons compensate for changes in network connectivity by retuning their intrinsic electrical properties. We demonstrate this mechanism in the inferior olive, in which widespread electrical coupling is mediated by abundant gap junctions formed by connexin 36 (Cx36). It has been shown in various mammals that this electrical coupling supports the generation of subthreshold oscillations, but recent work revealed that rhythmic activity is sustained in knock-outs of Cx36. Thus, these results raise the question of whether the olivary oscillations in Cx36 knock-outs simply reflect the status of wild-type neurons without gap junctions or the outcome of compensatory mechanisms. Here, we demonstrate that the absence of Cx36 results in thicker dendrites with gap-junction-like structures with an abnormally wide interneuronal gap that prevents electrotonic coupling. The mutant olivary neurons show unusual voltage-dependent oscillations and an increased excitability that is attributable to a combined decrease in leak conductance and an increase in voltage-dependent calcium conductance. Using dynamic-clamp techniques, we demonstrated that these changes are sufficient to transform a wild-type neuron into a knock-out-like neuron. We conclude that the absence of Cx36 in the inferior olive is not compensated by the formation of other gap-junction channels but instead by changes in the cytological and electroresponsive properties of its neurons, such that the capability to produce rhythmic activity is maintained.

Bicaudal-D regulates COPI-independent Golgi-ER transport by recruiting the dynein-dynactin motor complex (Article)

2002-12-01T00:00:00Z

The small GTPase Rab6a is involved in the regulation of membrane traffic from the Golgi apparatus towards the endoplasmic reticulum (ER) in a coat complex coatomer protein I (COPI)-independent pathway. Here, we used a yeast two-hybrid approach to identify binding partners of Rab6a. In particular, we identified the dynein-dynactin-binding protein Bicaudal-D1 (BICD1), one of the two mammalian homologues of Drosophila Bicaudal-D. BICD1 and BICD2 colocalize with Rab6a on the trans-Golgi network (TGN) and on cytoplasmic vesicles, and associate with Golgi membranes in a Rab6-dependent manner. Overexpression of BICD1 enhances the recruitment of dynein-dynactin to Rab6a-containing vesicles. Conversely, overexpression of the carboxy-terminal domain of BICD, which can interact with Rab6a but not with cytoplasmic dynein, inhibits microtubule minus-end-directed movement of green fluorescent protein (GFP)-Rab6a vesicles and induces an accumulation of Rab6a and COPI-independent ER cargo in peripheral structures. These data suggest that coordinated action between Rab6a, BICD and the dynein-dynactin complex controls COPI-independent Golgi-ER transport.

Repeated mild injury causes cumulative damage to hippocampal cells (Article)

2002-01-01T00:00:00Z

An interesting hypothesis in the study of neurotrauma is that repeated traumatic brain injury may result in cumulative damage to cells of the brain. However, post-injury sequelae are difficult to address at the cellular level in vivo. Therefore, it is necessary to complement these studies with experiments conducted in vitro. In this report, the effects of single and repeated traumatic injury in vitro were investigated in cultured mouse hippocampal cells using a well characterized model of stretch-induced injury. Cell damage was assessed by the level of propidium iodide (PrI) uptake and retention of fluorescein diacetate (FDA). Uninjured control wells displayed minimal PrI uptake and high levels of FDA retention. Mild, moderate and severe levels of stretch caused increasing amounts of PrI uptake, respectively, when measured at 15 min and 24 h post-injury, indicating increased cellular damage with increasing amounts of stretch. For repeated injury studies, cultures received a second injury 1 h after the initial insult. Repeated mild injury caused a slight increase in PrI uptake compared with single injury at 15 min and 24 h post-injury, which was evident primarily in glial cells. However, the neurites of neurones in cultures that received repeated insults showed signs of damage that were not evident after a single mild injury. The release of neurone-specific enolase (NSE) and S-100beta protein, two common clinical markers of CNS damage, was also measured following the repeated injuries paradigm. When measured at 6 h post-injury, both NSE and S-100beta were found to be elevated after repeated mild injuries when compared with the single injury group. These results suggest that cells of the hippocampus may be susceptible to cumulative damage following repeated mild traumatic insults. Both glial cells and neurones appear to exhibit increased signs of damage after repetitive injury. To our knowledge, this study represents the first report on the effects of repeated mechanical insults on specific cells of the brain using an in vitro model system. The biochemical pathways of cellular degradation following repeated mild injuries may differ considerably from those that are activated by a single mild insult. Therefore, we hope to use this model in order to investigate secondary pathways of cellular damage after repeated mild traumatic injury, and as a rapid and economical means of screening possibilities for treatment strategies, including pharmaceutical intervention.

Monitoring kinetic and frequency-domain properties of eyelid responses in mice with magnetic distance measurement technique (Article)

2002-01-01T00:00:00Z

Classical eye-blink conditioning in mutant mice can be used to study the molecular mechanisms underlying associative learning. To measure the kinetic and frequency domain properties of conditioned (tone - periorbital shock procedure) and unconditioned eyelid responses in freely moving mice, we developed a method that allows adequate, absolute, and continuous determination of their eyelid movements in time and space while using an electrical shock as the unconditioned stimulus. The basic principle is to generate a local magnetic field that moves with the animal and that is picked up by either a field-sensitive chip or coil. With the use of this magnetic distance measurement technique (MDMT), but not with the use of electromyographic recordings, we were able to measure mean latency, peak amplitude, velocity, and acceleration of unconditioned eyelid responses, which equaled 7.9 +/- 0.2 ms, 1.2 +/- 0.02 mm, 28.5 +/- 1 mm/s, and 637 +/- 22 mm/s(2), respectively (means +/- SD). During conditioning, the mice reached an average of 78% of conditioned responses over four training sessions, while animals that were subjected to randomly paired conditioned and unconditioned stimuli showed no significant increases. The mean latency of the conditioned responses decreased from 222 +/- 40 ms in session 2 to 127 +/- 6 ms in session 4, while their mean peak latency increased from 321 +/- 45 to 416 +/- 67 ms. The mean peak amplitudes, peak velocities, and peak acceleration of these responses increased from 0.62 +/- 0.02 to 0.77 +/- 0.02 mm, from 3.9 +/- 0.3 to 7.7 +/- 0.5 mm/s, and from 81 +/- 7 to 139 +/- 10 mm/s(2), respectively. Power spectra of acceleration records illustrated that both the unconditioned and conditioned responses of mice had oscillatory properties with a dominant peak frequency close to 25 Hz that was not dependent on training session, interstimulus interval, or response size. These data show that MDMT can be used to measure the kinetics and frequency domain properties of conditioned eyelid responses in mice and that these properties follow the dynamic characteristics of other mammals.

Mammalian Golgi-associated Bicaudal-D2 functions in the dynein-dynactin pathway by interacting with these complexes. (Article)

2001-08-01T00:00:00Z

Genetic analysis in Drosophila suggests that Bicaudal-D functions in an essential microtubule-based transport pathway, together with cytoplasmic dynein and dynactin. However, the molecular mechanism underlying interactions of these proteins has remained elusive. We show here that a mammalian homologue of Bicaudal-D, BICD2, binds to the dynamitin subunit of dynactin. This interaction is confirmed by mass spectrometry, immunoprecipitation studies and in vitro binding assays. In interphase cells, BICD2 mainly localizes to the Golgi complex and has properties of a peripheral coat protein, yet it also co-localizes with dynactin at microtubule plus ends. Overexpression studies using green fluorescent protein-tagged forms of BICD2 verify its intracellular distribution and co-localization with dynactin, and indicate that the C-terminus of BICD2 is responsible for Golgi targeting. Overexpression of the N-terminal domain of BICD2 disrupts minus-end-directed organelle distribution and this portion of BICD2 co-precipitates with cytoplasmic dynein. Nocodazole treatment of cells results in an extensive BICD2-dynactin-dynein co-localization. Taken together, these data suggest that mammalian BICD2 plays a role in the dynein- dynactin interaction on the surface of membranous organelles, by associating with these complexes.

Clasps are CLIP-115 and -170 associating proteins involved in the regional regulation of microtubule dynamics in motile fibroblasts (Article)

2001-03-23T00:00:00Z

CLIP-170 and CLIP-115 are cytoplasmic linker proteins that associate specifically with the ends of growing microtubules and may act as anti-catastrophe factors. Here, we have isolated two CLIP-associated proteins (CLASPs), which are homologous to the Drosophila Orbit/Mast microtubule-associated protein. CLASPs bind CLIPs and microtubules, colocalize with the CLIPs at microtubule distal ends, and have microtubule-stabilizing effects in transfected cells. After serum induction, CLASPs relocalize to distal segments of microtubules at the leading edge of motile fibroblasts. We provide evidence that this asymmetric CLASP distribution is mediated by PI3-kinase and GSK-3 beta. Antibody injections suggest that CLASP2 is required for the orientation of stabilized microtubules toward the leading edge. We propose that CLASPs are involved in the local regulation of microtubule dynamics in response to positional cues.

Transcription factor GATA-3 alters pathway selection of olivocochlear neuron and affects morphogenesis of the ear. (Article)

2001-01-01T00:00:00Z

Patterning the vertebrate ear requires the coordinated expression of genes that are involved in morphogenesis, neurogenesis, and hair cell formation. The zinc finger gene GATA-3 is expressed both in the inner ear and in afferent and efferent auditory neurons. Specifically, GATA-3 is expressed in a population of neurons in rhombomere 4 that extend their axons across the floor plate of rhombomere 4 (r4) at embryonic day 10 (E10) and reach the sensory epithelia of the ear by E13.5. The distribution of their cell bodies corresponds to that of the cell bodies of the cochlear and vestibular efferent neurons as revealed by labeling with tracers. Both GATA-3 heterozygous and GATA-3 null mutant mice show unusual axonal projections, such as misrouted crossing fibers and fibers in the facial nerve, that are absent in wild-type littermates. This suggests that GATA-3 is involved in the pathfinding of efferent neuron axons that navigate to the ear. In the ear, GATA-3 is expressed inside the otocyst and the surrounding periotic mesenchyme. The latter expression is in areas of branching of the developing ear leading to the formation of semicircular canals. Ears of GATA-3 null mutants remain cystic, with a single extension of the endolymphatic duct and no formation of semicircular canals or saccular and utricular recesses. Thus, both the distribution of GATA-3 and the effects of null mutations on the ear suggest involvement of GATA-3 in morphogenesis of the ear. This study shows for the first time that a zinc finger factor is involved in axonal navigation of the inner ear efferent neurons and, simultaneously, in the morphogenesis of the inner ear.

GATA-3 is involved in the development of serotonergic neurons in the caudal raphe nuclei (Article)

1999-01-01T00:00:00Z

Abstract The GATA-3 transcription factor shows a specific and restricted expression pattern in the developing and adult mouse brain. In the present study we investigated the role of GATA-3 in the caudal raphe system, which is known to operate as a modulator of motor activity. We demonstrate that virtually all neurons in the caudal raphe nuclei that express GATA-3 also produce serotonin. Absence of GATA-3, as analyzed in chimeric -/- mice, affects the cytoarchitecture of serotonergic neurons in the caudal raphe nuclei. As a result the chimeras show a serious defect in their locomotor performance on a rotating rod. In sum, we conclude that GATA-3 plays a major role in the development of the serotonergic neurons of the caudal raphe nuclei, and that it is crucial for their role in locomotion.

The Murine CYLN2 Gene: genomic organization, chromosome localization and comparison to the human gene that is located within the 7q11.23 Williams Syndrome Critical Region. (Article)

1998-11-01T00:00:00Z

Cytoplasmic linker proteins (CLIPs) have been proposed to mediate the interaction between specific membranous organelles and microtubules. We have recently characterized a novel member of this family, called CLIP-115. This protein is most abundantly expressed in the brain and was found to associate both with microtubules and with an organelle called the dendritic lamellar body. CLIP-115 is highly homologous to CLIP-170, or restin, which is a protein involved in the binding of endosomes to microtubules. Using the rat cDNA as a probe we have isolated overlapping cosmids containing the complete murine and part of the humanCYLN2(cytoplasmic linker-2) genes, which encode CLIP-115. The murine gene spans 60 kb and consists of 17 exons, and its promoter is embedded in a CpG island. MurineCYLN2maps to the telomeric end of mouse chromosome 5. The humanCYLN2gene is localized to a syntenic region on chromosome 7q11.23, which is commonly deleted in Williams syndrome. It spans at least 140 kb at the 3′ end of the deletion. HumanCYLN2is very likely identical to the previously characterized, incompleteWSCR4andWSCR3transcription units

The centromeric/nucleolar chromatin protein ZFP-37 may function to specify neuronal nuclear domains (Article)

1998-01-01T00:00:00Z

Murine ZFP-37 is a member of the large family of C2H2 type zinc finger proteins. It is characterized by a truncated NH2-terminal Kruppel-associated box and is thought to play a role in transcriptional regulation. During development Zfp-37 mRNA is most abundant in the developing central nervous system, and in the adult mouse expression is restricted largely to testis and brain. Here we show that at the protein level ZFP-37 is detected readily in neurons of the adult central nervous system but hardly in testis. In brain ZFP-37 is associated with nucleoli and appears to contact heterochromatin. Mouse and human ZFP-37 have a basic histone H1-like linker domain, located between KRAB and zinc finger regions, which binds double-stranded DNA. Thus we suggest that ZFP-37 is a structural protein of the neuronal nucleus which plays a role in the maintenance of specialized chromatin domains.

CLIP-115, a novel brain-specific cytoplasmic linker protein, mediates the localization of dendritic lamellar bodies. (Article)

1997-12-01T00:00:00Z

Intracellular localization of organelles may depend in part on specific cytoplasmic linker proteins (CLIPs) that link membranous organelles to microtubules. Here, we characterize rat cDNAs encoding a novel, brain-specific CLIP of 115 kDa. This protein contains two N-terminal microtubule-binding domains and a long coiled-coil region; it binds to microtubules and is homologous to CLIP-170, a protein mediating the binding of endosomes to microtubules. CLIP-115 is enriched in the dendritic lamellar body (DLB), a recently discovered organelle predominantly present in bulbous dendritic appendages of neurons linked by dendrodendritic gap junctions. Local microtubule depolymerization leads to a temporary reduction of DLBs. These results suggest that CLIP-115 operates in the control of brain-specific organelle translocations.

Association between dendritic lamellar bodies and complex spike synchrony in the olivocerebellar system (Article)

1997-01-01T00:00:00Z

Dendritic lamellar bodies have been reported to be associated with dendrodendritic gap junctions. In the present study we investigated this association at both the morphological and electrophysiological level in the olivocerebellar system. Because cerebellar GABAergic terminals are apposed to olivary dendrites coupled by gap junctions, and because lesions of cerebellar nuclei influence the coupling between neurons in the inferior olive, we postulated that if lamellar bodies and gap junctions are related, then the densities of both structures will change together when the cerebellar input is removed. Lesions of the cerebellar nuclei in rats and rabbits resulted in a reduction of the density of lamellar bodies, the number of lamellae per lamellar body, and the density of gap junctions in the inferior olive, whereas the number of olivary neurons was not significantly reduced. The association between lamellar bodies and electrotonic coupling was evaluated electrophysiologically in alert rabbits by comparing the occurrence of complex spike synchrony in different Purkinje cell zones of the flocculus that receive their climbing fibers from olivary subnuclei with different densities of lamellar bodies. The complex spike synchrony of Purkinje cell pairs, that receive their climbing fibers from an olivary subnucleus with a high density of lamellar bodies, was significantly higher than that of Purkinje cells, that receive their climbing fibers from a subnucleus with a low density of lamellar bodies. To investigate whether the complex spike synchrony is related to a possible synchrony between simple spikes, we recorded simultaneously the complex spike and simple spike responses of Purkinje cell pairs during natural visual stimulation. Synchronous simple spike responses did occur, and this synchrony tended to increase as the synchrony between the complex spikes increased. This relation raises the possibility that synchronously activated climbing fibers evoke their effects in part via the simple spike response of Purkinje cells. The present results indicate that dendritic lamellar bodies and dendrodendritic gap junctions can be downregulated concomitantly, and that the density of lamellar bodies in different olivary subdivisions is correlated with the degree of synchrony of their climbing fiber activity. Therefore these data support the hypothesis that dendritic lamellar bodies can be associated with dendrodendritic gap junctions. Considering that the density of dedritic lamellar bodies in the inferior olive is higher than in any other area of the brain, this conclusion implies that electrotonic coupling is important for the function of the olivocerebellar system.

Topography of saccadic eye movements evoked by microstimulation in rabbit cerebellar vermis (Article)

1994-01-01T00:00:00Z

1. We investigated saccadic eye movements elicited by microstimulation in the vermis of the rabbit. Scleral search coils were implanted under the conjunctiva of both eyes and a recording chamber was placed over the cerebellar vermis. 2. Conjugate saccadic eye movements were evoked in lobules VIa, b and c and VII of the vermis by currents ranging from 4 to 60 microA. All movements were horizontal with no apparent vertical component. 3. The cortex on both sides of the vermal mid-line could be divided in two zones, dependent on the direction of elicited saccades. In the medial zone saccades were directed ipsilaterally, in the lateral zone contralaterally. 4. We conclude that the topography of saccadic eye movements in the rabbit cerebellar vermis is, unlike in monkey and cat, organized in parasagittal zones.