Effects of maternal separation on baseline sleep and cold stress-induced sleep rebound in adult Wistar rats.
OBJECTIVE
To evaluate the influence of early life environments on basal and cold stress-induced sleep patterns in rats.


METHODS
The design was a 3 (Groups [control, early handling, maternal separation]) x 2 (Situations [basal, poststress]) x 11 (Time-blocks) factorial design. From postnatal days 2 to 14, whole litters were either submitted to early handling (15 minutes per day away from the mother) or maternal separation (180 minutes per day away from the mother). At 75 to 90 days of age, sleep was recorded for 22 hours (beginning at 9:00 AM) before and after 1 hour of cold stress (4 degrees C).


METHODS
Wistar male rats (n = 7-10 animals per group).


RESULTS
Sleep was analyzed in blocks of 2 hours, in 30-second epochs, separately in the daytime and nighttime sleep recordings. Maternally separated rats exhibited more paradoxical sleep at baseline, compared to both control and early-handled rats. In the first 2 hours following the end of cold stress, all groups showed a decrease in paradoxical sleep, whereas slow-wave sleep was reduced only in the control group. The highest corticosterone plasma concentration was observed immediately after stress. Sleep rebound after stress was equally manifested in all groups in the dark part of the light-dark cycle.


CONCLUSIONS
Maternal separation during early infancy resulted in permanent changes of the sleep architecture reflected by augmented time spent in paradoxical sleep. Although these findings were not expected in light of the literature, they emphasize the importance of the early familiar environment on future behavior of rats.
Tiba
Paula Ayako
PA
Department of Psychobiology, Universidade Federal de São Paulo, Brazil.
Tufik
Sergio
S
Suchecki
Deborah
D
D000818:Animals; D001522:Behavior, Animal / Q000502:physiology*; D003080:Cold Temperature; D003345:Corticosterone / Q000097:blood; D004567:Electrodes, Implanted; D006185:Habituation, Psychophysiologic; D009035:Mothers; D051381:Rats; D017208:Rats, Wistar; D012890:Sleep / Q000502:physiology*; D013312:Stress, Physiological / Q000523:psychology*; D014851:Wakefulness
D003345:Corticosterone