Circadian rhythm of drinking and running-wheel activity in rats with 6-hydroxydopamine lesions of the ventral tegmental area

Circadian rhythms in drinking and running-wheel (locomotor) activity of rats with 6-hydroxydopamine (6-OHDA, 4 mug/2 mul per rat)-induced lesions in the ventral tegmental area (VTA) were examined under a light-dark (LD) cycle and constant dim light (5 lux). Under the LD cycle, the length of the locomotor activity period was decreased during the dark, and increased during the light period in the lesioned rats. Under the constant dim light conditions, the free-running circadian period (tau) of drinking and activity rhythm was longer in lesioned rats than in sham-operated controls. The elongation of the circadian period was accompanied by decrements in activity. These observations suggest that the mesolimbic dopaminergic system modulates rhythms in circadian drinking and locomotor activity. (C) 2001 Elsevier Science B.V. All rights reserved.