arousal in Syrian hamsters: the role of stress and activity. Am

Circadian rhythms in the Syrian hamster can be markedly phase shifted by 3 h of wheel running or arousal stimulation during their usual daily rest period (“subjective day”). Con-tinuous wheel running is predictive but not necessary for phase shifts of this “nonphotic ” type; hamsters aroused by gentle handling without running can also show maximal shifts. By contrast, physical restraint, a standard stress procedure and thus presumably arousing, is ineffective. To resolve this apparent paradox, phase-shifting effects of 3-h sessions of restraint or other stress procedures were as-sessed. In a preliminary study, phase shifts to arousal by gentle handling were significantly potentiated by the cortisol synthesis inhibitor metyrapone, suggesting that stress-re-lated cortisol release may inhibit phase shifts to arousal. Next, it was confirmed that restraint in the subjective da