Aberrations of circadian body temperature rhythms in rats with medial preoptic lesions

Abstract

The normal amplitude of the circadian rhythm of telemetered body temperature (Tb) in male rats was 2.degree. C (from 36-38.degree. C). For several weeks after large medial preoptic lesions Tb cycled from as low as 29.degree. C to as high as 41.degree. C in a single day. With recovery, or in rats with smaller lesions, peak-to-trough Tb amplitudes decreased, ranging from 3-5.degree. C for many months, with normal or slightly raised troughs in the light part and grossly higher peaks in the dark part of a 12:12 light-dark cycle. Rats in whom some periventricular tissue was spared had normal amplitudes of Tb, but the whole curve was displaced 0.5-1.0.degree. C above control values. These effects persisted in constant darkness. In the weeks after medial preoptic lesions thermoregulatory responses are not activated until Tb is abnormally high or low. As recovery progresses, or if the lesions are smaller to begin with, there may be an imbalance between heat loss and heat production systems so that heat production mechanisms are either always dominant or overshoot when activated.