AMPA glutamate receptors and their flip and flop mRNAs in human hippocampus.

AMPA-preferring glutamate receptor genes gluR1-4 undergo alternative splicing into flip and flop mRNA isoforms. In the rodent hippocampus, gluR1 and gluR2 isoforms are differentially expressed. We have studied their distribution in human hippocampus. As in the rat, flop isoforms predominate over flip in dentate gyrus, whereas gluR1 flip is prominent only in CA3. In contrast to the rat, flop mRNAs are clearly present in CA3. At a cellular level, pyramidal neurones express moderate amounts of each isoform. In several hippocampal fields, scattered non-pyramidal cells--putatively interneurones and glia--show abundant expression. The findings are supported by immunocytochemical detection of gluR1 and gluR2/3. As the four encoded isoforms have distinct properties, their differential expression within the hippocampus, and between species, should be taken into account when considering the roles of AMPA receptors in normal and abnormal brain states.