Seasonal and daily rhythms of body temperature in the European hamster (Cricetus cricetus) under semi-natural conditions

Abstract

Body temperature of five European hamsters exposed to semi-natural environmental conditions at 47 degrees N in Southern Germany was recorded over a 1.5-year period using intraperitoneal temperature-sensitive radio transmitters. The animals showed pronounced seasonal changes in body weight and reproductive status. Euthermic body temperature changed significantly throughout the year reaching its maximum of 37.9 +/- 0.2 degrees C in April and its minimum of 36.1 +/- 0.4 degrees C in December. Between November and March the hamsters showed regular bouts of hibernation and a few bouts of shallow torpor. During hibernation body temperature correlated with ambient temperature. Monthly means of body temperature during hibernation were highest in November (7.9 +/- 0.8 degrees C) and March (8.2 +/- 0.5 degrees C) and lowest in January (4.4 +/- 0.7 degrees C). Using periodogram analysis methods, a clear diurnal rhythm of euthermic body temperature could be detected between March and August, whereas no such rhythm could be found during fall and winter. During hibernation bouts, no circadian rhythmicity was evident for body temperature apart from body temperature following ambient temperature with a time lag of 3-5 h. On average, hibernation bouts lasted 104.2 +/- 23.8 h with body temperature falling to 6.0 +/- 1.7 degrees C. When entering hibernation the animals cooled at a rate of -0.8 +/- 0.2 degrees C.h-1; when arousing from hibernation they warmed at a rate of 9.9 +/- 2.4 degrees C.h-1. Warming rates were significantly lower in November and December than in January and February, and correlated with ambient temperature (r = -0.46, P < 0.01) and hibernating body temperature (r = -0.47, P < 0.01). Entry into hibernation occurred mostly in the middle of the night (mean time of day 0148 hours +/- 3.4 h), while spontaneous arousals were widely scattered across day and night. For all animals regression analysis revealed free-running circadian rhythms for the timing of arousal. These results suggest that entry into hibernation is either induced by environmental effects or by a circadian clock with a period of 24 h, whereas arousal from hibernation is controlled by an endogenous rhythm with a period different from 24 h.

The circadian clock stops ticking during deep hibernation in the European hamster

“…For our investigations, we used the European hamster (Cricetus cricetus L.), a well defined hibernator (14,21,23,24). Hamsters raised outdoors were transferred in September to a climatic room kept at 6 Ϯ 2°C under short photoperiodic regimen, and individual Tbs were recorded by a telemetric system.…”

“…The European hamster enters hibernation preferentially in the middle of the night (14,21). We took advantage of this characteristic to design our experiment, as illustrated in Fig.…”

“…We describe here the arrest of the master circadian clock over several days. The issue has been debated for many years (3,5,9), with various data either denying (10,11,(13)(14)(15)(16)(17) or supporting (12,(18)(19)(20)22) the existence of a functional pacemaker during deep torpor. Importantly, these contradictions may stem from species differences as well as from the variety of markers used to assess the functional state of the clock.…”

“…After they were fixed, acetylated, and dehydrated, 20-m-thick coronal brain sections were hybridized overnight at 54°C with 35 S-UTP-labeled riboprobes. The sections were then treated with RNase A (10 g/ml), washed (saline sodium citrate 0.1ϫ, 60°C), dehydrated, and exposed to a Kodak BioMax MR Film (Sigma-Aldrich, Lyon, France) for 3-5 days along with 14 C radioactive standards to allow standardization of densitometric measurements across films. X-ray films were scanned on an Epson 4990 transmittance scanner (Levallois-Perret, France), and background was subtracted.…”

“…However, it has long been debated whether the circadian system remains functional during deep hibernation (3,5,9). Although several studies have addressed this question (10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22), uncertainty prevails because clock outputs rather than the core clockwork machinery were examined. In mammals, the master circadian clock is located in the suprachiasmatic nucleus of the hypothalamus (SCN) (6)(7)(8).…”