Organization of on-off cells in the retina of the turtle.

1. The organization of central and peripheral responses for one type of spike-producing cell in the retina of the turtle (Pseudemys scripta elegans) has been studied. These cells produced a short burst of spikes following the onset and offset of a small spot of illumination (i.e. ON-OFF cells). The effect of increasing the area of illumination was to include a peripheral inhibition. Intracellular ON and OFF responses were, however, affected differently.2. ON-OFF cells marked intracellularly with Procion Yellow M4R had somata in the inner nuclear and ganglion cell layers.3. Peripheral inhibition could be evoked without a change in the membrane potential of horizontal cells.4. Passing 5 nA hyperpolarizing or depolarizing current through a micropipette within a horizontal cell elicited in ON-OFF cells a transient excitation following the onset and offset of current.5. It is concluded that inhibition from the periphery of an ON-OFF cell receptive field is not mediated by luminosity horizontal cells but more probably by peripheral bipolar cells.