Pathways and polarities of synaptic interactions in the inner retina of the mudpuppy: I. Synaptic blocking studies.

Intracellular recording techniques were applied to the perfused retina-eyecup of the mudpuppy (Necturus maculosus). The use of input resistance measurements and the application of cobalt as a synaptic blocking agent provided evidence about the mode of synaptic operation for depolarizing and hyperpolarizing bipolar cell input to cells of the inner retina. In addition, cobalt produced a more rapid block of hyperpolarizing bipolars compared to depolarizing bipolars; in some postbipolar neurons, a temporary simplification of neuronal response waveform was observed and such cells resembled the depolarizing bipolar. These experiments suggest that bipolar cell input is excitatory and that response characteristics of third-order neurons is partially dependent on the relative input from the two types of bipolar cells.