A ROLE FOR 5HT3 RECEPTORS IN VISUAL PROCESSING IN THE MAMMALIAN RETINA

We investigated the role of 5HT3 receptors in the mammalian retina usi ng electrophysiological techniques to monitor ganglion cell activity. Activation of 5HT3 receptors with the selective agonist 1-phenylbiguan ide (PBG) increased the ON responses of ON-center ganglion cells, whil e decreasing the OFF responses of OFF-center cells. The application of a selective 5HT3 antagonist had a reciprocal effect, namely it reduce d the center response in ON-center cells and concomitantly increased t he center responses in OFF-center cells. Since putative serotoninergic amacrine cells in the retina are connected specifically to the rod bi polar cell, these agents most likely affect the rod bipolar terminal. These data, together with previous studies, suggest that both 5HT2 and 5HT3 receptors mediate an excitatory influence which serves to facili tate the output from rod bipolar cells, the former via a phosphatidyl inositol second-messenger system, and the latter via a direct ion chan nel.