Thermoregulatory response to thermal challenge in seasonal affective disorder: a preliminary report

It has recently been proposed that alterations in central dopamine (DA) functional activity may, in part, account for certain behavioral changes observed in seasonal affective disorder (SAD) during the winter. To explore this possibility, a preliminary study of thermoregulatory heat loss to an endogenous heat challenge--a strongly DA-dependent process--was undertaken in groups of four SAD woman and four nonpsychiatric control women across three conditions (winter, after successful phototherapy, and summer). Homeostatic heat loss during recovery from heat challenge in SAD, but not in control, subjects was found to be a significant function of light condition and of clinical state. Thermoregulatory heat loss in SAD subjects was significantly blunted in winter during depression, was similar in efficiency to control subjects after a successful antidepressant response to phototherapy, and tended to be more efficient than controls in summer during a euthymic state. Results raise the possibility that a common effect of phototherapy and summer light conditions is a facilitation of central DA activity in SAD.