A MECHANISM OF ACTION UNDERLYING THE ANTIDEPRESSANT EFFECT OF LIGHT

In patients with winter seasonal affective disorder (SAD), delayed and reduced responses to corticotropin-releasing factor (CRF) have been o bserved. Bright light treatment has been shown to normalize these resp onses. In depressed patients, there is increased CRF activity in the e vening during the normally quiescent period between 19.30 and 22.00 ho urs. In patients with winter SAD, the level of subjective sleepiness i s increased in the evening between 20.00 and 21.00 hours. In the latte r group of patients, the CRF activity may be increased in the evening and associated with the increased level of subjective sleepiness. This increased activation is suggested to be normalized by bright light tr eatment, acting primarily on neurons of the paraventricular nucleus of the hypothalamus.