The applicant is using the superficial layers of the superior colliculus (sSC) in rodents to study the relationship between neural activity and the reduction of NMDA receptor (NR) current duration that occurs during development. The applicant has shown that synaptic NR current decay time decreases abruptly (24hrs) in the rat sSC in association with changes in both transcripts and protein for NR subunits NR1 and NR2A. This decrease occurs before eye opening and at the end of retinocollicular map refinement. We have also shown that GABAergic inhibition, which can modulate NR function heterosynaptically, begins later, after eye-opening and during cortico-collicular map refinement. However, chronic application of NMDA to the sSC beginning at P8 increases GABAergic inhibition abnormally early and disrupts the normal pattern of NR regulation. This proposal will test four hypotheses that emerge from this work: (1) that subsynaptic post-translational protein modification or subsynaptic regulation of NR subunit incorporation is responsible for the speed with which NR current decay time decreases, (2) that the increase in NR2A subunit level also contributes to this change, (3) that NR activation triggers the NR current decay tie decrease and/or NR subunit composition changes and (4) that increased GABAergic inhibition is a specific response to NR activation during a restricted developmental critical period. To assay transcript and protein changes in NMDA-treated rat sSC, the proposal will use RNase protection assays, competitive PCR, immunoblotting, immunocytochemistry, immunoprecipitation and cell fractionation procedures. Whole-cell patch clamping in slices and in a dissociated sSC culture, along with calcium imaging in culture, will be used to assay NR function. In addition, the sSC of wildtype and NR2A knockout mice will be examined to determine if this subunit contributes to rapid NR current changes and whether the GABA system of the knockout has up-regulated as a result of increases in activity that a re expected to result from this mutation. The applicant seeks a mechanistic understanding of the interaction of neurotransmission-related gene products and activity in the development of neural circuits. The findings should facilitate cures or treatments for disorders of childhood thought to have an environmental or epigenetic component. These range from mild speech and language deficits to devastating and prevalent neurological diseases such as epilepsy, cerebral palsy and autism.
