Maternal deprivation in neonatal rats alters the expression of circadian system under light-dark cycles and restricted daily feeding in adulthood

Effects of maternal deprivation (MD) with different conditions were examined on the circadian rhythms in plasma corticosterone and locomotor activity in adult rats under ad libitum and restricted daily feeding (RF), in which rats had free access to food for 2 h for 3 weeks. Three different types of MD were performed from postnatal day 1 (P1) to day 6 (P6); MD for 12 h/day (MD12), for 3 h/day in the morning (MD3am) and in the afternoon (MD3pm). Under ad libitum feeding, corticosterone levels at 08:00 h and 24:00 h were significantly increased in MD12 rats. A similar increase was detected in MD3am rats, but not in MD3pm rats. Under the RF, corticosterone levels at 08:00 h, 24:00 h, and 04:00 h were significantly increased in MD12 rats. Similar elevations were detected in MD3am rats, but not in MD3pm rats. Furthermore, prefeeding locomotor activities under the RF increased significantly in MD12 rats. A similar increase was observed in MD3am rats, but not in MD3pm rats. Keeping ambient temperature and humidity at 37 °C and 70-80% during MD attenuated the effects of MD on the corticosterone rhythmicities under RF as well as ad lib feeding. It is concluded that MD in the early postnatal period influences the expressions of circadian rhythms in plasma corticosterone and locomotor activity in adult rats. Not only the length but also the time of day of MD seems to be critical for these effects. Ambient temperature and/or humidity are suggested to be one of the factors by which MD exerts its effect.