Desynchronisation of circadian activity rhythms in golden hamsters (Mesocricetus auratus) housed in deep bedding

摘要

In the wild, golden hamsters live in deep burrow systems, and hidings like shelters or burrows should also be available to animals in captivity. The aim of the present paper was to investigate putative effects on the circadian activity rhythm of golden hamsters with bedding material as enrichment. Three different bedding depths (10cm, 40cm, 80cm) were investigated in 45 males (15 per group) kept singly. Their wheel-running activity was recorded continuosly. The light-dark cycle was 12:12h with 30-min dusk and dawn periods. Activity onsets coincided well with lights-off in low bedding depth, but in the groups with 40 and 80cm the activity rhythms did free run with a significant increase in tau with bedding depth. All hamsters in medium and deep bedding built and lived in self-constructed burrows. It is possible the difference in light intensity between light (50-85 lux) and dark conditions (0.5-2 lux) might have been too low. As a consequence the LD zeitgeber was not strong enough to entrain the activity rhythms, though the light was bright enough to stop running at least in some animals (masking). Hamsters of the low bedding group were continuously exposed to the light-dark cycle and thus were able to synchronise their activity rhythm. We conclude that bedding depth can influence the circadian rhythm of golden hamsters which has to be taken into account when performing chronobiological studies.