Interactions between the Serotoninergic System and the Ionotropic GABA Receptors in Frog and Turtle Retina: An Immunofluorescent Study

Abstract

The aim of the present study was to elucidate the putative interactions between the serotoninergic and the GABAergic systems in the lower vertebrate retinas. Experiments were performed on 12-14 µm frozen frog and turtle retinal sections, processed with more than 10 different antibodies directed against serotonin, GABA and their membrane receptors by means of the indirect immunocytochemical method. The results showed that some of the GABAergic retinal neurons possess the serotonin receptors 5-HT2A and 5-HT3A on their cell membrane, and vice versa: certain serotoninergic neurons possess the ionotropic GABA A and GABA C receptors. A simple neuronal chart is proposed to explain how the activation of serotonin receptors on a subgroup of GABAergic amacrine cells can decrease the GABA C receptor mediated inhibition on the retinal bipolar cells, the main generators of ERG. As the retina is a natural biological model of CNS, the relationships between both neurotransmitter systems described here may elucidate their participation in certain brain functions and to explain the possible mechanisms of action of some antidepressant drugs.