Elsevier

Neuroscience

Volume 164, Issue 3, 15 December 2009, Pages 1377-1386
Neuroscience

Systems Neuroscience
Research Paper
Thermoregulation in the cold changes depending on the time of day and feeding condition: physiological and anatomical analyses of involved circadian mechanisms

https://doi.org/10.1016/j.neuroscience.2009.08.040Get rights and content

Abstract

The circadian rhythm of body temperature (Tb) is a well-known phenomenon. However, it is unknown how the circadian system including the suprachiasmatic nucleus (SCN) and clock genes affects thermoregulation. Food deprivation in mice induces a greater reduction of Tb particularly in the light phase. We examined the role of Clock, one of key clock genes and the SCN during induced hypothermia. At 20 °C with fasting, mice increased their metabolic heat production in the dark phase and maintained Tb, whereas in the light phase, heat production was less, resulting in hypothermia. Under these conditions, neuronal activity in the SCN, assessed by cFos expression, increased only in the light phase. However, such differences in thermoregulatory and neural responses between the phases in Clock mutant mice were less marked. The neural network between the SCN and paraventricular nucleus appeared to be important in hypothermia. These findings suggest that the circadian system per se is influenced by both the feeding condition and environmental temperature and that it modulates thermoregulation.

Section snippets

Animals

Male Clock mutant and wild-type mice (ICR back ground, 2–4 months old, 30–50 g body weight) were used in the present study. They were individually housed in a plastic cage (45×25×20 cm3) with water and food available ad libitum. Ambient temperature (Ta) was maintained at 27±0.5 °C, and the lighting cycle set at 12 h light (300 lx at the eye level, lights on at 07:00 am) And 12 h complete darkness. In this experiment, lights were always used as entraining agent for circadian rhythm (Zeitgeber,

Circadian changes in Tb, metabolism, and activity during ad-lib feeding and fasting

Figure 1 shows typical examples of the changes in Tb, VO2, and spontaneous activity during ad-lib feeding and fasting in wild-type and Clock mutant mice. With ad-lib feeding, each parameter for wild-type mice showed a clear circadian rhythm. Although there were small fluctuations in each parameter in Clock mutant mice, the light-linked rhythm appeared to be maintained. As previously reported, the 24 h rhythm in Clock mutant mice was abolished in constant darkness (data not shown). Fasting for 2

Discussion

We found different physiological responses in wild-type mice to the cold condition between ad-lib feeding and fasting, and between the dark and light phases. The neural responses in the hypothalamus, as shown by cFos expression, were also different. However, these differences in physiological and neural responses were absent or greatly decreased in Clock mutant mice. The SCN appears to be important in the changes in thermoregulatory responses.

Our earlier preliminary observations showed a

Acknowledgments

The present study was supported partly by KAKENHI No. 17390062 and 20790195 from the Japan Society for the Promotion of Science and Project Research of the Advanced Research Center for Human Sciences and Academic Frontier Center, Waseda University.

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