OTHER RHYTHMS...Infradian (page 2)

Hibernation is another type of circannual rhythm which is hardly understood. Hibernation is the dropping of an animal's body temperature on a seasonal basis carried out for the purpose of energy conservation. It is obvious that an animal that has some mechanism by which it can avoid winter weather and extreme food shortages would gain a survival feature [23]. The typical behavior of an animal that hibernates is to have a constant body temperature through it's euthermic season. When conditions are correct, possibly the photoperiod, the animal goes into hibernation and it's body temperature drops to within a few degrees above ambient temperature. How the animal knows when to begin hibernation and when to end is still not understood. An animal does not hibernate continually through the winter, but has, after a few days or weeks, a period of arousal when the animal's body temperature rises back to normal and the animal falls to sleep. It is a common misconception to think that an animal is sleeping during hibernation. In fact the animals do exhibit some of the characteristics of non-REM sleep, however after studying the EEG of a group of hibernators it was actually found that they were undergoing sleep deprivation and the arousal period appears to compensate for this. After a short time the animal slips back into a state of hibernation and this cyclic behavior continues until the final arousal time in the spring [33].

If an old fashioned clock with a pendulum is exposed to colder ambient temperatures than normal, the clock begins to run faster than real time. Why? The pendulum, being made of metal, shrinks slightly and would have a shorter period. Thus the clock would "tick-tock" faster. It would seem logical that homeotherms undergoing hibernation or poikilotherms would also have there clock pendulum or time affected by dramatic changes in temperature.

However this is not the case, the clock does compensate for the drop in temperature of the organism. Investigators know that the clock is definitely still running and shows a circadian rhythm in hibernators. "How" is still under investigation. They know that the SCN cells in the hypothalamus of mammals are temperature sensitive when placed in vitro. So it would appear the "gears" of the clock are sensitive, but how it compensates for this is not well understood. Thus, as hibernation relates to the clock and being a timed event, researchers know it is under control of the clock, however many of the specifics are still a mystery [34].

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