Suprachiasmatic Nuclear Lesions Eliminate Circadian Rhythms of Drinking and Activity, but Not of Body Temperature, in Male Rats

Male Long-Evans rats were maintained in lightproof cabinets while drinking, ac tivity, and telemetered body temperature (Tb) data were collected. After suprachiasmatic nuclear (SCN) lesions, the rats were exposed to a 12:12 light-dark cycle, a 6-hr delay in the lighting cycle, and constant dark. Lesions that abolished the drinking and activity rhythms did not eliminate the Tb rhythm. However, the amplitude, phase, and free-running period of the Tb rhythm were altered. Lesions that only partially damaged the SCN had similar, though lesser, effects. In some cases, Tb rhythms remained normal, activity rhythms were only temporarily disrupted, and drinking rhythms were eliminated in the same animals. These results support the conclusion that Tb can remain rhythmic after lesions that permanently or temporarily disrupt other circadian rhythms. Of the three rhythms, it appears that drinking rhythms are most easily and Tb rhythms least easily disrupted by SCN lesions.