Abstract
A number of mammals undergo hibernation during their lifespan. The euthermal condition that occurs prior to hibernation is characterized by inhibition of cellular proliferation, reduction of stress reactivity, a decrease in metabolism, and changes in the immune system (seasonal thymus involution). Analysis of data of young red voles (Clethrionomys glareolus), common shrews (Sorex araneus), and fat dormice (Glis glis) while entering into the euthermal condition shows characteristic biphasic growth with a delay that can vary in its periods. A biological mechanism for reversible growth arrest effectively “stops the clock” of these animals. It is suspected that this mechanism is triggered by an increase in somatostatin synthesis with inhibition of growth hormone, thyroid-stimulating hormone, and melatonin, and with a loss of circadian function in the suprachiasmatic nuclei of the hypothalamus.
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