Involvement of the pineal gland in diurnal cocaine reward in mice.

Contribution of circadian mechanisms to the psychostimulant-induced behaviors has been suggested. The pineal gland is important component of circadian mechanisms. Using pinealectomized mice and sham-operated controls, we tested the contribution of pineal gland to the rewarding effects of cocaine in conditioned place preference test. Experiments were performed both during the day and at night. Controls with intact pineal glands demonstrated significant decrease in cocaine-induced conditioned place preference at night compared to daytime, whereas pinealectomized mice did not show any diurnal differences. Circadian mechanisms regulated by the pineal gland thus appear critically involved in cocaine-induced reward.