Mechanisms of paradoxical sleep
(e) Effects of temperature on P.S. in the pontile animal
The poikilothermic pontile animal is subject to changes in the environmental
temperature, so that the effects of hypothermia on P.S. can be readily
studied. The fall in rectal temperature occurring when the animal is placed
in a cold environment causes P.S. to disappear almost entirely. If, however,
cooling is stopped and the rectal temperature remains stable, P.S. reappears
periodically. Its duration is then in inverse proportion to the rectal
temperature (Fig. 22). An increase in the duration
of P.S. during hypothermia goes hand in hand with an increase in the length
of the intervals between each episode of P.S., the proportion of the latter
always remaining in the region of 10%. We have observed periods of P.S.
lasting 25 min at a rectal temperature of 29°. At this temperature
the animals exhibit generalized clonism of the head and limbs, even when
they are returned to a warm environment. There is no real shivering, however.
During phases of P.S. clonism disappears almost completely. If the animal
is rewarmed so that the rectal temperature increases P.S. occurs more
frequently and in animals whose temperature rises from 30° to 37°
in 4 h the amount of sleep can increase to up to 35% of the total time.
In contrast, we have never observed P.S. at temperatures above 40.5¡.
(This was the maximum temperature attempted, as hyperthermia has serious
effects in pontile animals.)