Nonphotic enhancement of adjustment to new light-dark cycles: masking interpretation discounted.
The adjustment of hamsters to advanced light-dark (LD) cycles can be greatly accelerated by scheduling a single 3-hr bout of extra activity in a novel running wheel, starting about 7 hr before the time when the animals become active in the preceding LD cycle. The present experiments were designed to provide stronger evidence that this effect depends on a shift in the pacemaker rather than on masking. It was shown that when hamsters were put into continuous darkness (DD) 1 day after the exercise-accelerated phase shift, their free-running rhythms took off from a time nearer to the onset of darkness in the new LD cycle than in the preceding LD cycle. An incidental finding was that in DD the free-running period of the hamsters with the accelerated phase shifts was longer than that of the control animals. Further evidence that the 3-hr exercise pulse had produced a greater phase advance than that occurring in undisturbed control animals was obtained by giving a light pulse at the same clock time to all animals after they had been in DD for 8 days. The animals that had previously exercised for the additional 3-hr phase-advanced in response to the light pulse, while the undisturbed control animals phase-delayed.
Mrosovsky
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N
Department of Zoology, University of Toronto, Ontario, Canada.
D000222:Adaptation, Physiological / Q000502:physiology; D000818:Animals; D006224:Cricetinae / Q000502:physiology*; D003624:Darkness; D008027:Light; D008297:Male; D008647:Mesocricetus; D008954:Models, Biological; D009043:Motor Activity / Q000502:physiology; D010507:Periodicity; D013997:Time Factors