Circadian rhythms in drinking behavior and locomotor activity of rats are eliminated by hypothalamic lesions

Bilateral electrolytic lesions in the suprachiasmatic nuclei permanently eliminated nocturnal and circadian rhythms in drinking behavior and locomotor activity of albino rats. The generation of 24-hr behavioral rhythms and the entrainment of these rhythms to the light-dark cycle of environmental illumination may be coordinated by neurons in the suprachiasmatic region of the rat brain. Destruction of the medial preoptic area had no effect on 24-hr drinking rhythms.