The effect of dorsal raphe nucleus (DRN) lesions on the locomotor activityrhythm in mice

The study employed electrical lesions of dorsal raphe nucleus (DRN) to dete rmine the functional significance of those nuclei in the regulation of whee l-running activity rhythm in mice in light/dark (LD 12:12), constant light (LL), and constant dark (DD) conditions. The wheel-running records showed t hat raphe nucleus lesions resulted in few days' decrease in common activity and amplitude in LD. The activity phase was not compact but in fragmentary form, especially in DD condition. In some animals an earlier onset of acti vity after DRN lesion in LD was observed. In LL extension of the rhythm per iod occurred. Destruction of DRN only slightly modulates the wheel-running circadian rhythm in mice.