Dissection of the neuron network in the catfish inner retina. II. Interactions between ganglion cells

1. To characterize signal interactions between ganglion cells, extrinsic current, either sinusoidally or white-noise modulated, was injected into a ganglion cell and the resulting extracellular spike discharges were recorded from a neighboring ganglion cell. 2. Current injected into an ON-ganglion (GA) cell modulated the spike discharges of a neighboring ON-ganglion cell (GA). Similarly, a current injected into an OFF-ganglion (GB) cell modulated the spike discharges of a neighboring OFF-ganglion (GB) cell. The signal transmission between ganglion cells of the same response polarity was fast and sign-noninverting. The transfer function was lowpass with a cutoff frequency of 30 Hz. The efficacy of the transmission was comparable to that from bipolar or amacrine to ganglion cells of the same polarity. 3. Current injected into an ON-ganglion (GA) cell modulated the spike discharges of a neighboring OFF-ganglion (GB) cell; the signal transmission was slow and sign-noninverting. Correspondingly, current injected into an OFF-ganglion (GB) cell modulated the spike discharges of a neighboring ON-ganglion (GA) cell; transmission was slow and sign-inverting. 4. A brief electrical stimulation of the optic nerve activated a single antidromic ganglion cell spike at threshold. With suprathreshold stimulation, multiple spikes appeared, which probably were activated orthodromically. Changes in membrane potential of ganglion and amacrine cells induced by optic nerve stimulation usually lasted 50-80 ms, with an initial depolarization followed by hyperpolarization. We interpret such long-lasting responses to be mediated by reciprocal circuits that include amacrine, bipolar, and ganglion cells. 5. Together with the observations made by Sakai and Naka, we conclude that virtually almost all amacrine, bipolar, and ganglion cells are functionally interconnected; direct and fast connections are established among ON-cells and similarly among OFF-cells, and complex, indirect connections are established between ON- and OFF-cells.