Fig. 9.

Effect of lesions of the VLPO or ventromedial preoptic nucleus on body temperature recorded over 24 hr at three weekly intervals. A, B, Severe bilateral lesions of the VLPO in four rats had no effect on the mean body temperature or its daily circadian rhythm (A) when compared with that of four control rats (B). Although the animals with VLPO lesions had a slightly greater circadian excursion of body temperature, this did not differ statistically from that of the saline-injected control animals. C, In contrast, in four animals with lesions of the ventromedial preoptic nucleus, the circadian rhythm of body temperature was unaffected, but the range was ∼2°C during the course of the day (approximately twice normal), and the peaks and troughs of body temperature both differed significantly from that of control animals (p < 0.05). Body temperature showed substantial instability in these animals, as evidenced by the significantly larger variance compared with that of the control or VLPO-lesioned animals (p < 0.05).