Diurnal rhythm in the electroretinogram of the Royal College of Surgeons (RCS) pigmented rat.

RCS pigmented rats, born and raised in cyclic light for 22-23 days and then placed in darkness for up to 24 hr, showed a diurnal rhythm in the rod electroretinogram (ERG) that was comparable with that seen in normal pigmented rats. a-Wave and b-wave sensitivities were 21- and 34% lower, respectively, 1.5 hr after expected light onset compared with those at other times of day. In contrast to findings in normal rats, however, these sensitivity decreases in the RCS rats were not associated with an increase in the frequency of large phagosomes in the pigment epithelium; phagosome frequency was subnormal and relatively constant over the day. These findings suggest that depressed ERG sensitivities 1.5 hr after expected light onset in both normal and RCS pigmented rats reflect altered rod photoreceptor function associated with the process of outer-segment disc shedding and not with engulfment of shed discs into phagosomes by the pigment epithelium.