Nucleus suprachiasmaticus: the biological clock in the hamster?

Destruction of the suprachiasmatic nuclei in the golden hamster by bilateral radiofrequency lesions abolishes three well-documented circadian rhythms--locomotor activity, estrous cyclicity, and photoperiodic photosensitivity. Entrainment of these rhythms by light cycles fails in lesioned hamsters; females become persistently estrous; in both sexes locomotor activity becomes sporadic, confined primarily to the light instead of darkness, and is totally arrhythmic when lesioned animals are exposed to continuous darkness; the photoperiodic gonadal response (gonadal regression induced by short day lengths) is abolished; lesioned animals remain reproductively mature irrespective of photoperiodic treatment.