Siberian hamsters free run or become arrhythmic after a phase delay
of the photocycle.
Ruby, Norman F., Atul Saran, Tom Kang, Paul Franken, and H. Craig
Heller.
Dept. of Biological Sciences, Stanford University, Stanford, CA
94305
APStracts 3:0147R, 1996.
Body temperature (Tb) and locomotor activity were recorded
telemetrically from male Siberian hamsters (Phodopus sungorus
sungorus) that were 3 or 12 months of age and maintained in a light
-dark (LD) cycle of 16 h light/day for 2-4 months. After 3 weeks of Tb
recording, the LD cycle was phase delayed by extending the light
phase by 5 h for one day; animals remained on a 16:8 LD cycle for the
remainder of the experiment. Tb and activity rhythms of all animals
were stably entrained to the LD cycle prior to the phase shift. After
the phase shift, >/=80% of the animals in each age group failed to
reentrain and expressed free running Tb rhythms with stable periods
that ranged from 24.33-26.33 h; one hamster in each age group
reentrained within several days. Tb became arrhythmic in 10% of all
animals immediately after, and in 28% of free running animals several
weeks after, the phase shift. Changes in tau and phase of activity
rhythms closely parallelled Tb rhythms in individual hamsters. Daily
mean Tb was unchanged but Tb rhythm amplitude decreased by 25-50% in
individual animals after the phase shift. We believe this to be the
first report of neurologically intact animals failing to reentrain to
a phase shift of the LD cycle. These phenomena are not readily
explained by current knowledge of circadian systems and suggest that
the entrainment process in Siberian hamsters differs markedly from
other rodent species.
Received 26 October 1995; accepted in final form 9 April 1996.
APS Manuscript Number R667-5.
Article publication pending Am. J. Physiol. (Regulatory Integrative
Comp. Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 23 April 96