N-methyl-D-aspartate glutamate receptors (NRs) and glutamate circuit development have been implicated in neurological diseases with initiating events in perinatal periods when glutamate networks are developing. Two prevalent dysfunctions of this type, autism spectrum disorders and schizophrenia, are good examples. For both autism and schizophrenia, genetic linkage analyses have identified molecules involved in normal NR function. Our goal is to understand NR function in early circuit formation and provide information that would help mitigate or eliminate such devastating diseases. Recently, NRs containing NR2B subunits were shown to produce long-term synaptic depression (LTD) at Schaffer collateral-CAl synapses, and activation of NRs containing NR2A subunits produced long-term synaptic potentiation (LTP) at the same contacts. These studies did not reveal the differences between the two subunits responsible for their abilities to produce dichotomous outcomes. We hypothesize that the NR2A and NR2B subunit tails are responsible for the subunit-specific effect of the NR on synaptic plasticity. The tails contain phosphorylation and interaction domains and also have a differential ability to anchor the NR to PSD-95 and SAP102, the predominant membrane-associated guanylate kinases (MAGUK) that bind the NR and its signaling complex to post- synaptic densities in fore-and mid-brain regions. To test this hypothesis, we made two chimeric subunits. The coding regions of the external and transmembrane domains ( heads) of the NR2A and NR2B subunits were separated from the cytoplasmic tail regions, and the head sequences for each subunit were recombined with the tail sequences of the other, thereby producing two chimeric proteins. We propose to examine HEK293 cells co-transfected with each of these constructs and NR1. NR function will be examined with Ca++ imaging and with whole-cell patch-clamping to examine the currents and dynamic properties of the NRs containing each hybrid subunit. These responses will be compared with those from HEK cells expressing wild-type subunits. We will also test the chimeras after transfection into NR2AKO hippocampal neurons. Finally, using lentiviral transfection of each chimeric and each wild-type protein into NR2AKO mice and patch-clamping infected neurons in hippocampal slices, we will determine if the NR2 subunit tails dictate LTP versus LTD. ? ?
