Platelet [3H]paroxetine and [3H]lysergic acid diethylamide binding in seasonal affective disorder and the effect of bright light therapy

Background: Seasonal affective disorder (SAD) has been regarded as a melatonin disorder bur the pathophysiological mechanisms of SAD are to a large extent unclarified. Serotonergic mechanisms have also been studied, bur they have shown inconsistent results. Methods: We have compared [H-3]paroxetine and [H-3]lysergic acid diethylamide (LSD) binding in platelets from 23 SAD patients and 23 controls. Then SAD patients had 4 weeks of light therapy. On the last treatment day new blood samples were drawn. Symptoms before and after light treatment were measured by SIGH-SAD. Results: B-max for paroxetine binding before light treatment was higher in SAD patients compared to controls and also higher in responders than in nonresponders. B-max decreased significantly during light treatment. We also found a negative correlation between the two B-max values before bur not after light treatment. There was a negative correlation between B-max for paroxetine binding before treatment and clinical status after treatment. Patients with reduced B-max for LSD binding after treatment had a better clinical treatment response. Conclusions: The present study indicates that serotonin receptor parameters might be suitable in the prediction of clinical response to light treatment. (C) 1999 Society of Biological Psychiatry.