GLYCINE AND GABA RECEPTORS IN THE MAMMALIAN RETINA

Molecular cloning has introduced an unexpected diversity of neurotrans mitter receptors. In this study we review the types, the localization and possible synaptic function of the inhibitory neurotransmitter rece ptors in the mammalian retina. Glycine receptors (GlyRs) and their loc alization in the mammalian retina were analyzed immunocytochemically. Specific antibodies against the al subunit of the GlyR (mAb2b) and aga inst all subunits of the GlyR (mAb4a) were used. Both antibodies produ ced a punctate immunofluorescence, which was shown by electron microsc opy to represent clustering of GlyRs at synaptic sites. Synapses expre ssing the alpha 1 subunit of the GlyR were found on ganglion tell dend rites and on bipolar cell axons. GlyRs were also investigated in the o scillator mutant mouse. The complete loss of the al subunit was compen sated for by an apparent upregulation of the other subunits of the Gly R. GABA(A) receptors (GABA(A)Rs) and their retinal distribution were s tudied with specific antibodies that recognize the alpha 1, alpha 2, a lpha 3, beta 1, beta 2, beta 3, gamma 2 and delta subunits. Most antib odies produced a punctate immunofluorescence in the inner plexiform la yer (IPL) which was shown by electron microscopy to represent synaptic clustering of GABA(A)Rs. The density of puncta varied across the IPL and different subunits were found in characteristic strata. This strat ification pattern was analyzed with respect to the ramification of cho linergic amacrine cells. Using intracellular injection with Lucifer ye llow followed by immunofluorescence, we found that GABA(A)Rs composed of different subunits were expressed by the same ganglion cell, howeve r, they were clustered at different synaptic sites. The distribution o f GABA(C) receptors was studied in the mouse and in the rabbit retina using an antiserum that recognizes the p1, p2 and p3 subunits. GABA(C) receptors were found to be clustered at postsynaptic sites. Most, if not all of the synapses were found on rod and cone bipolar axon termin als. In conclusion we find a great diversity of glycine and GABA recep tors in the mammalian retina: which might match the plethora of morpho logical types of amacrine cells. This may also point to subtle differe nces in synaptic function still to be elucidated. (C) 1998 Elsevier Sc ience Ltd. All rights reserved.