Light-dark rhythms in hamster eating, drinking and locomotor behaviors☆

Findings are consistent with the differential effects of constant light on rhythmic reproductive phenomena in the two species and suggest Hamster drinking and wheel-running behaviors are particularly appropriate endpoints for the analysis of neural and endocrine bases of circadian rhythmicity.

Abstract

Adult hamsters were exposed to alternating 12-hr periods of light (L) and darkness; 99% of daily wheel running activity occurred in the 12-hr dark (D) period. Water intake and food consumption also occurred more commonly in the dark but the extent to which these behaviors were displayed nocturnally, 85% and 58%, respectively, was significantly less than for wheel running. Activity cycles modulate drinking rhythms; nocturnal water intake was substantially reduced in hamsters with access to wheels while drinking during the light period was unaffected. Nocturnal drinking rhythms of hamsters phase-shifted very slowly after the L-D cycle was inverted; females required more than 40 days, whereas males re-established their normal nocturnal drinking rhythms in approximately 25 days. This sex difference disappeared after males and females were gonadectomized. Wheel running behavior of hamsters phase-shifted by 12 hr within 6–9 days of inversion of the L-D cycle. The great disparity in the rate of phase-shifting of hamster activity and drinking rhythms suggests different central pacemakers for these behaviors or different sensitivities to changes in the light-dark cycle in their respective phase-shifting and coupling mechanisms. Eating and drinking rhythms of blind hamsters were described and compared to those of blind rats. Constant illumination (L-L) decreased water intake of male and female hamsters; loss of entrainment to the previous L-D cycle occurred more slowly than for rats maintained in L-L. These findings are consistent with the differential effects of constant light on rhythmic reproductive phenomena in the two species. Hamster drinking and wheel-running behaviors are particularly appropriate endpoints for the analysis of neural and endocrine bases of circadian rhythmicity.