Electrical coupling between bipolar cells in carp retina.

Intracellular recordings were made simultaneously from pairs of neighboring bipolar cells by advancing two independent microelectrodes into retinas of carp (Cyprinus carpio). Bipolar cells were identified by their response properties and in several samples were verified by intracellular injection of Lucifer yellow. Current of either polarity injected into one member of the bipolar cell pair elicited a signconserving, sustained potential change in the other bipolar cell without any significant delay. This electrical coupling was reciprocal, and it was observed between cell types similar in function and in morphology. Our results strongly suggest that there is a spatial summation of signals at the level of bipolar cells, which makes central receptive field areas much larger than their dendritic fields.