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

Abstract

A SLOW form of rod dark adaptation lasting tens of minutes has been observed in isolated retinae1–5, including those of the rat6,7, 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 reported8,9 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.