Effects of some amino acids (GABA, glycine, taurine) and of their antagonists (picrotoxin, strychnine) on spatial and temporal features of frog retinal ganglion cell responses.

When intravitreally injected in the frog, GABA reduced the receptive field area of transient retinal ganglion cells, and it decreased the response duration and the number of spikes both at ON and at OFF. Conversely, its antagonist picrotoxin provoked an increase in the duration of both ON and OFF discharges as well as a marked increase in the number of spikes. Furthermore, picrotoxin provoked a marked increase in the size of the receptive field of both sustained and ON-OFF cells by abolishing the inhibition exerted by the surround upon the centre of the field. Glycine and taurine did not affect the size of the receptive field of these ganglion cells. They had no effect on the responses of sustained ganglion cells, while they totally suppressed OFF discharges of transient ganglion cells, without modifying their ON discharges. Conversely, their antagonist strychnine totally suppressed the ON dishcarges while the OFF discharges were still recorded, though with a reduced number of spikes and an increased latency, An histoautoradiographic study, carried out in parallel, showed that GABA is taken up by both horizontal cells and amacrine cells, while glycine and taurine are taken up by the amacrine cells only.