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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