The effects of maternal isolation and light and feeding cycles on the growth of rat pups.

Rat pups were implanted with intragastric catheters and reared in isolation from their dams and siblings from 3 to 18 days postnatally. They were kept in 12:12 LD or DL, constant light, or constant darkness and were fed with one of three feeding schedules: equal amounts of food delivered during the light and dark periods, 65.3% of the food delivered during the light period, or 65.3% of the food delivered during the dark period. At 18 days postnatally the body, spleen, and kidney weights of all isolated pups did not differ from those of their mother-reared littermates. The isolated pups had smaller cerebellums and forebrains and heavier livers than mother-reared pups. Heavier body and spleen weights and smaller livers were observed in pups with cyclic feeding. Heavier body and forebrain weights were associated with a predominantly diurnal feeding schedule--the schedule which most closely approximated the natural nursing rhythm. Isolated pups opened their eyes sooner than mother-reared littermates. These results suggest that interactions between feeding and light cycles may influence growth and development.