Dual component in receptive field centre of bipolar cells in carp retina

Receptive field centre profiles of depolarizing (ON-) and hyperpolarizing (OFF-) bipolar cells in dark adapted carp retina were determined by using a narrow slit of light. The spatial decline of the photoresponse was found to consist of double exponential function with small and large length constants, about 100 microns and 1 mm, respectively. These were only observed in dark adapted retinae where antagonistic surround responses were not observed. These findings suggest dual sites of electrical coupling, one among dendrites and the other among axon terminals. The gap junctional conductance of the axon terminals was estimated to be 100 times larger than that of the dendrites.