Response properties of long-range axon-bearing amacrine cells in the dark-adapted rabbit retina.

Axon-bearing amacrine cells in mammalian retinae are encountered relatively infrequently during electrophysiological investigations, and thus very little is known about their physiological properties. Patch-clamp electrodes were used to record light responses from two axon-bearing amacrine cells in flat-mounted, dark-adapted rabbit retina. The recorded cells were stained, and the morphology visualized. Both cells were capable of generating action potentials. In one case, a linear relationship between mean depolarization and action-potential frequency was demonstrated. The cells had a proximal dendritic arbor and a morphologically distinct, much larger axon terminal system. The receptive field of the center response was coextensive with the dendritic arbor, and thus also much smaller than the axon terminal system. The center response was suppressed by activation of an inhibitory surround. Both cells responded to center illumination with an inward current which became more transient as the size of the illuminating spot was increased. It is suggested that axon-bearing amacrine cells receive input over a receptive field defined by the dendritic arbor, and distribute their output over a much more extensive axon terminal system, most probably via action potentials.