The release of acetylcholine and amino acids from the rabbit retina in vivo

Rabbits were anaesthetised with urethane and an eye-cup was prepared by removing the cornea, iris, lens and vitreous. The retina was loaded with |(3)H|choline by filling the eye-cup with medium containing labelled choline and eserine. The retina was washed and then 10 min samples of medium from the eye-cup were assayed for |(3)H|ACh, and in some experiments, endogenous amino acids. The ERG was routinely recorded. Exposure of the dark adapted retina to flashes of light (3Hz) produced a striking increase in the efflux of |(3)H|ACh. This light evoked release of |(3)H|ACh was reduced by the presence of GABA in the eye-cup, an effect which was abolished by picrotoxin. Both picrotoxin and bicuculline caused striking increases in the spontaneous resting release of |(3)H|ACh. Flashes of light (3Hz) did not alter the efflux of glutamate, glutamine, alanine, glycine or GABA from the dark adapted retina. However, the release of taurine was greatly increased and the release of aspartate was significantly reduced (by more than 50%), a result consistent with the suggestion that aspartate but not ACh or taurine may be a photoreceptor transmitter substance.