Scotopic and photopic dark adaptation of the b wave in isolated rat retina

Abstract

A SLOW form of rod dark adaptation lasting tens of minutes has been observed in isolated retinae^1–5, including those of the rat^6,7, following exposures to intense lights which bleach significant proportions of the rod pigment. Yet in the isolated rat retina in similar circumstances it has been reported^8,9 that the cells which produce the b wave of the electroretinogram adapt within minutes. Since this adaptation is finished before any of the slow thermal reactions of rhodopsin bleaching reach completion, a ‘neural’ basis for the phenomenon has been suggested. Experiments¹⁰ have, however, confirmed earlier work¹¹ showing that there is more than one pigment in the rat. This provides an alternative explanation for the fast adaptation of the rat b wave. We have been able to demonstrate that during the fast adaptation the dominant input to the cells producing the b wave comes from the non-rhodopsin pigment system. We have also found conditions in which the b wave shows the slower form of adaptation. Then, the dominant input to the b-wave cells is from a rhodopsin-based mechanism.