AJP - Regulatory, Integrative and Comparative Physiology, Vol 252, Issue 2 256-R261, Copyright © 1987 by American Physiological Society
Phase setting of circadian locomotor rhythm of infant rats
K. Honma, S. Honma, T. Shirakawa and T. Hiroshige
Postnatal phase setting of pup circadian rhythm by nursing mother was
examined in rats by mother-pup exchange experiments. To know the effect of
phase reversal of the nursing mother, pups were exchanged after birth so
that a mother rat raised pups, half of which were born to her and the other
half which came from a reversed mother, and activity onset and offset of
pup locomotor rhythm were measured at weaning. Effects of litter size were
also examined. Direct entrainment to light-dark cycles was excluded by
blinding pups. In the unexchanged group, a strong positive correlation was
detected between the phase of the circadian rhythm at weaning and the
free-running period measured after weaning. The area covered by the 99%
confidence interval of the regression line was used for the phase reference
zone, and the circadian rhythm of an exchanged pup whose phase at weaning
was located outside the reference zone was regarded as having been
influenced by the nursing mother. The complete phase reversal occurred in
two out of seven exchanged pups when litter size was relatively large (n =
5-7) and in 9 out of 11 when litter size was small (n = 2). It is concluded
that the nursing mother rat is capable of phase setting the circadian
locomotor rhythm of blinded pups. This maternal effect seems to be related
to litter size.
