AMPA and kainate receptors in turtle retina: an immunocytochemical study

1. Glutamate is one of the main neurotransmitters in the retina. Its effects are mediated by a large number of ionotropic and metabotropic receptors.2. The distribution of ionotropic AMPA receptor subunits GluR1-4, kainate receptor subunits GluR5-7 and KA2, as well as delta receptors 1-2 was studied in turtle retina. Indirect immunofluorescence was used to localize the different receptor subunits viewed using light microscopy.3. Results show that all subunits, with exception of GluR1 and GluR5, are widely distributed in the turtle retina.4. They are mainly located in the both plexiform layers of the retina where punctate staining, a sign for synaptic localization, is observed.5. The vast majority of the subunits possess specific pattern of staining that allow to suppose that they are involved in different retinal circuits.6. It can be assumed that the GluR2/3 and GluR6/7 subunits are expressed on the dendrites of a subpopulation of bipolar cells that are immunopositive for alpha-isoform of protein kinase C (PKCalpha). The GluR2/3 and GluR6/7 subunits are most probably used by the same PKCalpha immunopositive bipolar cells in their synaptic contacts with the third-order retinal neurons, the amacrine and ganglion cells.