Studies on putative neurotransmitters in the distal retina

Histochemical and cytochemical studies of the retinas of the teleosts Carassius carassius and Eugerres plumieri revealed that acetylcholinesterase, besides its main localization in the inner retinal layers, can be also found in the outer plexiform and inner nuclear layers, and between the apposed processes of horizontal cells of a given layer. Similar studies of catecholamine (CA) containing cells in Cyprinus carpio and Eugerres plumieri have identified cells with bodies located in the inner plexiform and nuclear layers, where amacrine cells are found, and which send processes to both plexiform layers. As a part of our search for the possible role of cholinergic and catecholaminergic systems in the lateral spread of horizontal cell activity, the effects of CA's and acetylcholine (ACh) were studied in the perfused retina of Eugerres plumieri . Dopamine (0.2 mM) and other CA's slightly depolarize horizontal cells while markedly increasing their response to local illumination and decreasing their response to the surround. ACh(10mM) plus BW anticholinesterase (1 mM) produced similar effects on most of the cells studied. Hexamethonium (cholinegic antagonist), interferes with the ACh but not with the catecholamine effects. The effects of both types of agents are suppressed by the ?-adrenergic blocking phentolamine (0.5 mM).