Maternal deprivation in neonatal rats of different conditions affects growth rate, circadian clock, and stress responsiveness differentially.

Effects of periodic maternal deprivation (MD) were examined in rat pups on growth rate, circadian phase and period at weaning, and stress responsiveness in adulthood. MD was performed from postnatal day 1 to day 6 or day 7, with or without keeping ambient temperature at 37 degrees C and humidity at 70-80% during deprivation. Times of day and length of MD were also changed. Body weights were significantly reduced at weaning in MD12 (MD for 12 h) and MD6am (MD for 6 h in the morning) pups, whereas they were not changed in MD6pm (MD in the afternoon) and all MD3 groups. At 8 weeks old, body weight was still significantly lower in MD12 than the control, but not different from the control in other groups. Circadian phases of free-running locomotor rhythm at weaning were almost reversed in MD12, MD6am and MD6pm as compared with those in the control. Intermediate phase-shifts were observed in MD3Eam (3 h MD in the first quarter of the light phase; early am) and MD3Lam (late am; the second quarter), whereas no phase-shift was detected in MD3Epm (early pm; the third quarter) and MD3Lpm (late pm; the fourth quarter). Elevation of plasma corticosterone level after novelty exposure at 8 weeks old was more robustly in MD12 and MD3Lam than in the control, but the hormone response in MD3Lpm was not different from the control. Keeping ambient temperature at 37 degrees C during MD did not rescue the MD-induced body weight loss, but attenuated the phase-shifts of the circadian clock, and completely cancelled the stress-induced hormone response in MD12 rats. These findings indicate that MD in rat pups differentially affects growth rate, circadian clock, and stress responsiveness in adulthood, depending on time of day, length of MD and ambient temperature during MD.