The Effect of Barbiturate on Retinal Functions. III. Effects on the Isolated Receptor Responses and the Inner Nuclear Layer Components in the Low‐intensity Electroretinogram of the Sheep Eye

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Abstract
The present study is the third in a series of investigations on the effects of barbiturate on retinal functions. The changes in the isolated receptor responses and inner nuclear layer components of the low‐intensity electroretinogram (ERG) of the intact sheep eye were studied after i.v. administration of an ultra‐short‐acting barbiturate, thiopental. The low‐intensity ERG, i.e. the electroretinographic responses below the b‐wave threshold, have recently been shown to consist of a slow corneanegative receptor potential and two d.c. responses of opposite polarity presumably generated in the inner nuclear layer. The administration of small doses of thiopental (5 mg/kg) had no effect on the receptor response, whereas larger doses (10 mg/kg) increased its amplitude. The most striking effect of thiopental was an enhancement of the positive d.c. response, which could be observed already at barbiturate doses of 5 mg/kg. The results are consistent with the assumption that barbiturates primarily influence the cells of the inner nuclear layer and secondly the receptors. It is suggested that the functional mechanism behind the barbiturate effect on the inner nuclear layer (as expressed in the increase of the positive d.c. component) constitutes an intraretinally mediated disinhibition of the “on‐type”‘ bipolar cells i.e. the presumed generators of the positive d.c. component.