Synaptic organization and ionic basis of on and off channels in mudpuppy retina. II. Chloride-dependent ganglion cell mechanisms.

Extracellular ganglion cell recordings in the perfused mudpuppy eyecup show that a chloride-free (c-f) perfusate abolishes the center and surround excitation of on-center cells, the surround excitation of off-center cells, and the on discharge of on-off cells. These changes in ganglion cell receptive field organization are anticipated in view of the effects of a c-f environment on the neurons which are presynaptic to the ganglion cells. However, chloride-dependent inhibitory postsynaptic (IPS) responses have been observed in on-off ganglion cells. These inhibitory postsynaptic potentials (IPSP's) are preceeded by (ESPS's) exitatory postsynaptic potentials and are apparently mediated by amacrine cells. The light-activated hyperpolarization of off cells is not the result of a chloride-dependent IPSP and probably results from disfacilitation.