http://repub.eur.nl/res/aut/7532/ List of Publications en http://repub.eur.nl/static-eur/img/logo.png http://repub.eur.nl http://repub.eur.nl/res/pub/29848/ 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. http://repub.eur.nl/res/pub/10738/ 2007-12-05T00:00:00Z The level of electrotonic coupling in the inferior olive is higher than in any other brain region. Connexin36 is the main protein that forms the olivary gap junctions. Yet, the functional role of electrotonic coupling in the cerebellar motor control remains to be determined. In this thesis mice that lack coupling among their olivary neurons were subjected to classical eyeblink conditioning. Cx36 deficient mice showed impaired learning-dependent timing in that they were not able to fix the timing of their conditioned responses at the moment when the unconditioned stimulus is about to occur. The timing of spike activities generated in the olive of coupling- deficient mice was abnormal in that their latencies in response to the unconditioned stimulus were inconsistent and that their overall synchrony was reduced. Whole cell recordings of olivary neurons in vivo showed that these different spiking activities over time result in part from altered interaction! s with their subthreshold oscillations. These results, combined with analysis of olivary activities in a computer simulation of the cerebellar system, suggest that electrotonic coupling among olivary neurons is necessary for proper synchronous oscillations in the inferior olive, which in turn determine the pace of the olivary responses necessary for learning-dependent timing in cerebellar motor control. http://repub.eur.nl/res/pub/36838/ 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. http://repub.eur.nl/res/pub/35148/ 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. http://repub.eur.nl/res/pub/36483/ 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. http://repub.eur.nl/res/pub/8440/ 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.