ARE THERE IONOTROPIC GLUTAMATE RECEPTORS ON THE ROD BIPOLAR CELL OF THE MOUSE RETINA

There is some evidence that the mammalian rod bipolar cell expresses i onotropic glutamate receptors. This is surprising in light of the stro ng evidence that the glutamate released by the rod photoreceptor acts upon a metabotropic glutamate receptor-mGluR6-present in the dendrites of the rod bipolar cell. To reexamine the issue of which glutamate re ceptor subunits may be present on the rod bipolar cell, an immunohisto chemical study of acutely dissociated retinal cells was undertaken. Tw o monoclonal antibodies provided some evidence that GluR2 and/or GluR4 , as well as NMDAR1 subunit, are present on the rod bipolar cell. A mo noclonal antibody directed against the N-terminus of GluR2 labeled the rod bipolar cells, but two antisera directed against the C-terminus o f the same subunit did not. One possible explanation for this discrepa ncy could be that the rare splice variant GluR2-long, which is endowed with a different C-terminus, could be expressed by the rod bipolar ce ll. To explore this possibility, RT-PCR was used to amplify the transc ripts encoding GluR2 in the neural retina. This revealed that GluR2-lo ng transcripts, with the flop exon, are present.