Expression and localization of ionotropic glutamate receptor subunits in the goldfish retina - an in situ hybridization and immunocytochemical study

The expression and distribution of AMPA, kainate and NMDA glutamate recepto r subunits was studied in the goldfish retina. For the immunocytochemical l ocalization of the AMPA receptor antisera against GluR2, GluR2/3 and GluR4 were used, and for in situ hybridization rat specific probes for GluR1 and GluR2 and goldfish specific probes for GluR3 and GluR4 were used. The local ization of the low affinity kainate receptor and NMDA receptor was studied using antisera against GluR5-7 and NR1. All AMPA receptor subtypes were dem onstrated to be present in the goldfish retina both by immunocytochemistry and in situ hybridization. In situ hybridization revealed expression of all AMPA receptors subunit at the inner border of the INL. Only GluR3 was also strongly expressed in the outer border of the INL. Some of the ganglion ce lls displayed a strong signal for GluR1, GluR3 and GluR4. GluR1-immunoreact ivity was present in subsets of bipolar, amacrine, and ganglion cells. GluR 2 and GluR2/3-immunoreactivity was mainly localized in the outer plexiform layer. GluR2 and GluR2/3-immunoreactivity are associated with the photorece ptor synaptic terminals. GluR4-immunoreactivity is present on Muller cells in the inner retina and on dendrites of bipolar cells in the OPL, whereas G luR5-7-immunoreactivity was prominently present on horizontal cell axon ter minals. Finally, NR1-immunoreactivity was confined to amacrine cells, the i nner plexiform layer and ganglion cells. This study shows that there is a s trong heterogeneity of glutamate receptor subunit expression in the various layers of the retina. Of the AMPA receptor subunits GluR3 seems to be expr essed the most widely in all layers with strong glutamatergic synaptic inte ractions whereas all the other subunits seem to have a more restricted expr essed pattern.