Circadian organization of locomotor activity in the Turkish hamster (Mesocricetus brandti)

The circadian organization of locomotor activity was examined in Turkish hamsters while exposed to a light-dark (LD) cycle, constant illumination (LL), and following blinding and gonadectomy. Under LD 16:8 the activity rhythm of all hamsters became well entrained with activity beginning approximately 30 min after dark onset. In contrast, when activity rhythms free-ran as the result of exposure to LL or blinding, a variety of spontaneous perturbations in the period and/or phase of the activity rhythm were observed.