Temporal organisation of hibernation in wild-type and tau mutant Syrian hamsters

The temporal pattern of hibernation was studied in three genotypes of Syria n hamsters with different circadian periodicity to assess a potential circa dian control of alternating torpor and euthermy. We recorded the pattern of hibernation by measuring activity in continuous dim light and constant env ironmental temperature (6 +/- 1 degreesC). In spite of differences in the e ndogenous circadian period of three genotypes (tau +/+: congruent to 24 h, tau + /-: congruent to 22 h, and tau -/-: congruent to 20 h) torpor bout du ration was statistically indistinguishable (tau +/+: 86.9 +/- 5.3 h; tau +/ -: 94.2 +/- 3.3 h; tact -/-: 88.8 +/- 6.2 h). The time between two consecut ive arousals from torpor showed unimodal distributions not significantly di fferent between genotypes. The first entry into torpor occurred within the active phase of the circadian cycle in all genotypes whereas the first arou sal from torpor appeared to be timed randomly with respect to the prior cir cadian cycle. The amplitude of the activity rhythm was lower after hibernat ion compared with the amplitude before hibernation. The results suggest tha t in the Syrian hamster the circadian system does not control periodicity o f torpor and arousal onsets in prolonged hibernation at 6 degreesC.