J Neurophysiol (April 1, 2003). 10.1152/jn.01008.2002
Submitted on Submitted 6 November 2002; accepted in final form 3 December 2002

Temporal Modulation of Scotopic Visual Signals by A17 Amacrine Cells in Mammalian Retina In Vivo

Department of Biological Sciences, Allergan Pharmaceuticals, Irvine, California 92612

Dong, Cun-Jian and William A. Hare. Temporal Modulation of Scotopic Visual Signals by A17 Amacrine Cells in Mammalian Retina In Vivo. J. Neurophysiol. 89: 2159-2166, 2003. We examined function of the feedback pathway from A17 GABAergic amacrine cells to rod bipolar cells (A17 feedback), a critically located inhibitory circuit in the classic rod pathway of the mammalian retina whose role in processing of scotopic visual information is still poorly understood. We show evidence that this A17 feedback has a profound influence on the temporal properties of rod-driven postphotoreceptoral responses (assessed with the scotopic electroretinogram b-wave). Application of a GABA_c antagonist prolonged preferentially the decay of the scotopic b-wave. The degree of prolongation increased as the light intensity decreased. Application of selective GABA_a antagonists accelerated the kinetics of the scotopic b-wave. This effect was abolished when the GABA_c antagonist was coapplied. Selective ablation of A17 cells mimicked the action of the GABA_c antagonist. In A17 cell-ablated retinas, the GABA_c antagonist was no longer very effective to slow the decay of the scotopic b-wave. Thus the A17 feedback, activated by light stimulation and mediated mainly by the GABA_c receptors, makes the scotopic b-wave more transient by accelerating preferentially its decay. The strength of the feedback can be modulated by GABA_a receptor-mediated inhibition and by light intensity. Our results also suggest that in the mammalian retina the feedback may be a novel mechanism that contributes postphotoreceptorally to the termination of rod signals, especially those elicited by very dim light stimuli.