ADAPTATION IN CATFISH RETINA

Absolute sensitivity (voltage/illuminance) and incremental sensitivity as the peak-to-peak amplitude of the 1st order (Wiener) kernels was defined. Incremental sensitivity of the horizontal cells is the local slopes of the Michaelis-Menten equation and that of more proximal neurons is the Fechner slope. In a log-log plot, the former has a slope of -2, whereas the latter a slope of -1, as predicted by Williams and Gale. During a moderate to strong steady illumination, absolute sensitivity decreases but incremental sensitivity increases. The reverse occurs during dark adaptation. The presence of a steady illumination did not prevent signal transmission from horizontal to ganglion cells. Adaptation in the catfish [Ictaturus punctatus] retina includes 2 components: a lateral shift of the voltage-intensity curve along the intensity axis, and changes in the time course of light-evoked response. The latter phenomenon is related to the presumed horizontal cell-to-receptor cell negative feedback.