Dissociation of motor activity circadian rhythm in rats following
exposure to ld cycles of 4-hour period.
Vilaplana, J., T. Cambras, A. D[acute]iez-Noguera.
Unitat de Fisiologia, Facultat de Farm[grave]acia, Universitat de
Barcelona
APStracts 3:0287R, 1996.
For more than 30 days Wistar rats were subjected to six dark pulses
per day (T4 cycles; 3 hours light, 1 hour dark) in order to study the
possibility of dissociating their motor activity rhythm into distinct
circadian components. Rats of both sexes were used, half of which
were pinealectomized to examine the effect of the pineal gland on the
entrainment process. Results show that when rats were maintained
under T4, a 4-hour rhythm in their motor activity was present. Rats
showed anticipatory activity to dark phases, suggesting that the
motor activity components are actually entrained to the external
light/dark cycles. When rats were left under constant darkness
following T4, some motor activity components coming from the dark
phases free-ran for several days with different circadian periods.
This suggests that the motor activity pattern is generated by several
circadian oscillators. Moreover, the free-running components of motor
activity following T4 were more evident when T4 was applied after
exposure to constant light than after exposure to constant darkness.
These results support the hypothesis that the circadian system of the
rat is formed by several circadian oscillators, whose degree of
coupling depends on light conditions. In constant light, bright light
may inhibit internal coupling within the system, making it
subsequently more susceptible to the T4 cycles. No differences were
observed between pinealectomized and sham operated animals, while
females were more sensitive to T4 cycles than males.
Received 22 August 1994; accepted in final form 11 July 1996.
APS Manuscript Number R469-4.
Article publication pending Am. J. Physiol. (Regulatory Integrative
Comp. Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 4 August 1996