Platelet [³H]paroxetine binding, 5-HT-stimulated Ca²⁺ response, and 5-HT content in winter seasonal affective disorder

The present study was designed to evaluate cellular serotonergic functions in winter seasonal affective disorder (SAD) using serotonin (5-HT)-stimulated Ca²⁺ response as an integrated measure of 5-HT₂ receptor function in platelets, [³H]paroxetine binding to characterize the platelet 5-HT transporter and 5-HT content as an index of the platelet storage capacity for this neurotransmitter amine. Purified density-dependent subpopulations of platelets in untreated and light-treated SAD patients and matched controls were investigated in order to control for possible variations in platelet turnover. We found no differences between SAD patients and controls on any of the measures, nor between light therapy conditions in SAD patients, although we found a higher B_max of [³H]paroxetine binding and 5-HT content in heavy platelets compared to light platelets. Although the validity of platelets serotonergic measures as a model for brain serotonergic systems still remains to be elucidated, we found no evidence of platelet serotonergic abnormalities in our sample of SAD patients.