Effects of hypothalamic lesions on the body temperature rhythm of the golden hamster.

The effects of electrolytic and neurotoxic lesions of the suprachiasmatic nucleus (SCN) and preoptic area (POA) of the anterior hypothalamus were studied by temperature telemetry in the golden hamster (Mesocricetus auratus) examined under two ambient temperature conditions: 24 degrees C and 6 degrees C. Although attempted lesions with microinjections of ibotenic acid proved unsuccessful, electrolytic lesions of the SCN eliminated the circadian rhythm of body temperature (CRT), indicating an active role of this nucleus in the establishment of the CRT. Electrolytic lesions of the POA, but not of the SCN, resulted in an increased amplitude of the CRT at both 24 degrees C and 6 degrees C, with the lower ambient temperature enhancing this amplitude change to a greater extent. These results suggest that the POA and the SCN are independently responsible for the homeostatic and circadian regulation of body temperature, respectively. The increased amplitude of the CRT after POA lesions raises the possibility that the thermoregulatory system may oppose rather than defend the circadian control of body temperature in normal animals, which is consistent with several recent behavioral findings.