Intracellular recordings were carried out in the perfused retina-eyecup preparation of the mudpuppy. Taurine and glycine were added to the bathing medium to study their effects on different retinal neurons. In a few cases, γ-aminobutyric acid was exogenously applied to compare GABA vs taurine/glycine action. Receptors and horizontal cells were relatively insensitive to taurine/glycine, while amacrines and ganglion cells were comparatively more sensitive to these agents. Bipolar cells proved to be differentially effected by inhibitory amino acids: hyperpolarizing (OFF) bipolars were depressed by taurine/glycine and proved less sensitive to GABA; depolarizing (ON) bipolars were suppressed by GABA and were comparatively less sensitive to glycine/taurine. Taurine and glycine had identical actions on neurons and both were about equally effective at the same concentration. Strychnine blocked the action of taurine and glycine. The patterns of glycine/taurine sensitivity and their effects on second order neurons eliminate taurine as a photoreceptor transmitter; one or both of these agents may be utilized by a subclass of amacrine cells which interact with hyperpolarizing bipolars, other amacrine cells and ganglion cells. It appears that taurine or glycine or both may be selectively involved in OFF channel activity, while GABA may subserve an equivalent role for the ON channel.
- intracellular recording
- on- and off-path-ways