DIVERSITY OF GLUTAMATE-RECEPTOR SUBUNIT MESSENGER-RNA EXPRESSION WITHIN LIVE HIPPOCAMPAL CA1 NEURONS

Glutamate-mediated neurotransmission occurs through the activation of multimeric postsynaptic receptors. One mechanism by which functional d iversity of glutamate responsiveness may occur is by a single cell exp ressing multiple receptors containing different subunits. In a direct test of this hypothesis, we examined the glutamate receptor subunit mR NA composition of several individual CA1 neurons in hippocampal slices . Experiments used amplified antisense RNA coupled with expression pro filing and polymerase chain reaction amplification to identify and det ermine the relative amounts of subunit mRNAs co-localized in single ce lls. The results demonstrate that each CA1 neuron contains varying amo unts of most glutamate receptor mRNAs. In addition to relative mRNA le vels, the single-cell approach also highlighted other possible sources of receptor diversity. This included the existence of novel, alternat ively spliced forms of the NS-methyl-D-aspartate receptor type 1 and g lutamate-kainate receptor type 2 subunits. Surprisingly, levels of NS- methyl-D-aspartate receptor type 1 mRNA were relatively low, compared with those of other glutamate receptor mRNAs. One postulated source of potential heterogeneity, RNA editing, was not a general cellular mech anism. There was no evidence that glutamate receptor type 5 mRNA was e dited in any of the cells that were examined. These data show that ind ividual CA1 neurons, in the intact synaptic network of hippocampal sli ces, generate glutamate receptor mRNA diversity in several ways, which together contribute to the diversity of functional receptors observed electrophysiologically.