Fragile X syndrome is one of the most common forms of mental retardation, yet little is known about the physiological mechanisms causing the disease. In this study, we probed the ionotropic glutamate receptor content in synapses of hippocampal CA1 pyramidal neurons in a mouse model for fragile X (Fmr1 KO2). We found that Fmr1 KO2 mice display a significantly lower AMPA to NMDA ratio than wild-type mice at 2 weeks of postnatal development but not at 6-7 weeks of age. This ratio difference at 2 weeks postnatally is caused by down-regulation of the AMPA and up-regulation of the NMDA receptor components. In correlation with these changes, the induction of NMDA receptor-dependent long-term potentiation following a low-frequency pairing protocol is increased in Fmr1 KO2 mice at this developmental stage but not later in maturation. We propose that ionotropic glutamate receptors, as well as potentiation, are altered at a critical time point for hippocampal network development, causing long-term changes. Associated learning and memory deficits would contribute to the fragile X mental retardation phenotype.

alpha amino 3 hydroxy 5 methyl 4 isoxazolepropionic acid, animal cell, animal tissue, article, brain development, controlled study, developmental stage, disease association, down regulation, fragile X syndrome, hippocampus, ionotropic receptor, learning disorder, long term depression, long term potentiation, memory disorder, mental deficiency, mouse, n methyl dextro aspartic acid, n methyl dextro aspartic acid receptor, nerve cell membrane potential, nerve cell plasticity, nonhuman, pathophysiology, phenotype, postnatal development, priority journal, pyramidal nerve cell, receptor upregulation, wild type,
Journal of Physiology
Erasmus MC: University Medical Center Rotterdam

Pilpel, Y, Kolleker, A, Berberich, S, Ginger, M, Frick, A, Mientjes, E.J, … Seeburg, P.H. (2009). Synaptic ionotropic glutamate receptors and plasticity are developmentally altered in the CA1 field of Fmr1 knockout mice. Journal of Physiology, 587(4), 787–804. doi:10.1113/jphysiol.2008.160929