Circadian rhythms of self-selected lighting in golden hamsters: relation to gonadal condition.
Golden hamster (20 males, 8 females) were maintained in isolation boxes for 4-7 weeks. The animals had access to wheels and selected their own lighting by pressing one bar to turn light-on and another bar to turn the light-off. All hamsters maintained circadian rhythms of wheel-running activity. Seventeen of 28 hamsters selected lighting with a circadian periodicty. For 9 hamsters, there was a significant positive correlation between wheel-running activity and self-selected darkness, while this correlation was significantly negative for 10 hamsters. Four hamsters had regressed testes at the end of the experiment. These 4 had significant positive correlations between activity and self-selected darkness, while none of the  hamsters with significant negative correlations between activity and self-selected darkness had regressed testes. Light in phase with activity seems to be more important to the prevention of testicular regression than is the total daily amount of light.
D000818:Animals; D002940:Circadian Rhythm; D006224:Cricetinae / Q000502:physiology*; D003624:Darkness; D005260:Female; D008027:Light; D008297:Male; D008647:Mesocricetus / Q000502:physiology*; D009043:Motor Activity; D009929:Organ Size; D013737:Testis / Q000033:anatomy & histology / Q000502:physiology*