MANIPULATION OF POTENTIAL PERINATAL ZEITGEBERS FOR THE JUVENILE CIRCADIAN TEMPERATURE RHYTHM IN RATS

We investigated the importance of pre- and postnatal maternal rhythmic ity for the development and synchronization of the juvenile circadian core temperature (T-c) rhythm in rats by evaluating the T-c of artific ially reared pups in six litters derived from mothers maintained in co ntinuous bright light (LL) and impregnated after drinking behavior sto pped showing circadian periodicity. Pups removed from their aperiodic mothers on postnatal day 9 and artificially reared for 3 days showed a free-running T-c rhythm whose amplitude (3.1 +/- 0.1 degrees C, n = 4 7) was only slightly smaller than that of control pups born to mothers maintained in a 12:12-h light-dark cycle. In four litters the acropha ses were not much less synchronized than in the four control litters ( mean vector lengths 0.79 +/- 0.05 vs. 0.94 +/- 0.04). In two litters s ynchronization among littermates was not significant. Additional exper iments with cross-fostered pups showed that synchronization is not cau sed by the time of birth. We conclude that synchronization among litte rmates can develop even when maternal rhythmicity has been suppressed even before conception, possibly because the T-c decrease of several l ittermates happening to have similar phases at birth acts as zeitgeber .