Dopamine and circadian rhythms in seasonal affective disorder.

In seasonal affective disorder, there is evidence of both increased and decreased dopaminergic transmission in the central nervous system. Bright light treatment appears to normalize these abnormalities among the patients. Dopamine is suggested to have a direct effect on heat loss via the vascular system, in addition to its capability of resetting the circadian system by changes in both heat production and heat loss. Therefore, impaired dopamine availability may result in a decreased heat loss response to an endogenous thermal challenge as well as abnormalities in the generation of circadian rhythms in some patients with seasonal affective disorder.