Systems NeuroscienceResearch PaperThermoregulation in the cold changes depending on the time of day and feeding condition: physiological and anatomical analyses of involved circadian mechanisms
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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