Nonphotic phase-shifting and the motivation to run: cold exposure reexamined.
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 degrees 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.
Mistlberger
R E
RE
Department of Psychology, Simon Fraser University, Burnaby, BC Canada.
Marchant
E G
EG
Sinclair
S V
SV
D000465:Algorithms; D000818:Animals; D002940:Circadian Rhythm / Q000502:physiology*; D003080:Cold Temperature; D006224:Cricetinae; D004326:Drinking; D004435:Eating; D004777:Environment; D008647:Mesocricetus; D009042:Motivation; D009043:Motor Activity / Q000502:physiology*