Differential effects of hypoxia on sleep of warm- and cold-acclimated rats

We studied the effect of different levels of hypoxia (10, 12 or 13, 15, and 18% O2) on the sleep-waking pattern (SWP) and the maximum-minimum core temperature of warm-acclimated (WA) and cold-acclimated (CA) rats at their neutral temperature, 29 degrees C. Whereas the SWP of WA rats showed a trend toward increasing disruption as the degree of hypoxia increased, CA rats exhibited no such trend. The effect was chiefly on the frequency of state changes and less on epoch durations. The SWP of WA rats was more vulnerable to hypoxia than that of CA rats. Maximum and minimum body temperatures of WA and CA rats were not significantly affected by O2 lack down to 10% inspired O2. We conclude that in the rat 1) hypoxia primarily affects the neural mechanism that governs the frequency of changes in sleep-waking states; 2) the extent of alterations in SWP's depends on the ambient temperature to which the rats are acclimated; and 3) hypoxia does not significantly affect deep body temperature at the animal's neutral temperature.