AJP - Regulatory, Integrative and Comparative Physiology, Vol 271, Issue 5 1388-R1395, Copyright © 1996 by American Physiological Society
Manipulation of potential perinatal zeitgebers for the juvenile circadian temperature rhythm in rats
B. Nuesslein-Hildesheim and I. Schmidt
Max-Planck-Institut, W. G. Kerckhoff-Institut, Bad Nauheim, Germany.
We investigated the importance of pre- and postnatal maternal rhythmicity
for the development and synchronization of the juvenile circadian core
temperature (Tc) rhythm in rats by evaluating the Tc of artificially reared
pups in six litters derived from mothers maintained in continuous bright
light (LL) and impregnated after drinking behavior stopped showing
circadian periodicity. Pups removed from their aperiodic mothers on
postnatal day 9 and artificially reared for 3 days showed a free-running Tc
rhythm whose amplitude (3.1 +/- 0.1 degrees C, n = 47) 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 acrophases 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 synchronization among littermates
was not significant. Additional experiments with cross-fostered pups showed
that synchronization is not caused by the time of birth. We conclude that
synchronization among littermates can develop even when maternal
rhythmicity has been suppressed even before conception, possibly because
the Tc decrease of several littermates happening to have similar phases at
birth acts as zeitgeber.
