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Nonphotic Phase-Shifting and the Motivation to Run: Cold Exposure Reexamined

Department of Psychology, Simon Fraser University, Burnaby, BC Canada, V5A 1S6

Elliott G. Marchant

Department of Psychology, Simon Fraser University, Burnaby, BC Canada, V5A 1S6

Sherrill V. Sinclair

Department of Psychology, Simon Fraser University, Burnaby, BC Canada, V5A 1S6

Circadian rhythms in rodents can be phase shifted by appropriately timed activity. This may be dependent on motivational context; running induced by a novel wheel is effective, whereas running induced by cold has been inferred to be ineffective. This issue was reexamined using a different cold exposure procedure. On the first day of constant dark, 6 h before usual dark onset, Syrian hamsters were exposed to cold (±4°C) in their home cages, or were confined to novel wheels for 3 h. Activity rhythms were significantly phase advanced by 92 ± 10 min following cold exposure and 86 ± 17 min following novel wheel running, compared to 13 ± 18 min in a control condition. Most hamsters exhibited eating, drinking, and modest levels of wheel running (1367 ± 292 counts/6 h) during and for 3 h after cold exposure. Phase shifts following cold were not affected by food and water deprivation but were significantly attenuated by locking the wheel for 6 h beginning at cold onset (24 ± 12 min). These data indicate that cold-induced running, even at modest levels, is an effective nonphotic Zeitgeber and do not provide support for a hypothesis that motivational contexts determine the phase-shifting value of physical activity.

Key Words: circadian rhythms • nonphotic entrainment • zeitgeber • wheel running • motivation • arousal • reward

Journal of Biological Rhythms, Vol. 11, No. 3, 208-215 (1996)
DOI: 10.1177/074873049601100303


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