N-Methyl-D-Aspartic acid (NMDA) receptors contribute to synapse formation, learning and memory and the pathogenesis of neurological disorders. Recent developments in molecular cloning of NMDA receptors have revealed a substantial heterogeneity of molecular forms of these receptors. It is proposed that the heterogeneity of molecular forms of NMDA receptors at excitatory synapses and their posttranslational modifications, underlie the effectiveness of the NMDA component of EM mediated synaptic transmission and in turn synaptic plasticity. Specific physiological manipulations that result in differential subunit expression and posttranslational modifications leading to alteration of NMDA receptor-mediated synaptic function will be studied. The functional diversity of synaptic and extrasynaptic NMDA in distinct neuronal populations in brain slices and primary culture will be investigated with electrophysiological, anatomical and pharmacological techniques. The result of this study will reveal how the relative contribution of the NMDA subunit NR1 and NR2B determines the kinetics of NMDA-mediated synaptic currents in developing rat neocortical and cerebellar neurons. The main hypothesis is that the relative proportion of NR1/NR2A heteromers are the crucial component that controls the efficacy of synaptic NMDA receptors. Recombinant receptors will be used to compare and contrast functional differences related to those observed in neurons and to understand mechanisms underlying the kinetic differences observed between different molecular forms of NMDA receptors. Preliminary results with recombinant receptors suggest that subunit composition is not the only kinetic determinant of synaptic NMDA receptors. Therefore, the role for posttranslational modifications in producing distinct kinetics of synaptic NMDA currents in cortical neurons will be determined. Lastly, experimental strategies will be used to regulate expression of distinct NMDA receptor subtypes in neocortical and cerebellar neurons resulting in the understanding of how neuronal activity, protein kinases and neurotrophins control the expression of NMDA receptor subtypes. Data obtained from these specific aims will permit the understanding of the molecular determinant responsible for synaptic plasticity in CNS.
