Background: Seasonal variations in onset of mood disorders and in serotonergic function are reported, but their relationship is unclear.
Methods: Circannual variation in platelet 5-HT(2A) binding was measured in 68 healthy subjects and 121 patients with a major depressive episode. In 73 patients the current episode began during Spring or Fall.
Results: Significant, but different, circannual variations were found in patients compared with controls. Controls had two peaks of B(max), one in Spring and another in Fall. Fall and Winter K(D) was 41% lower compared with Spring and Summer K(D). Patients had a peak of B(max) in early Spring and a lesser one in late Fall. B(max) during Spring and Fall was 12% higher compared with Winter and Summer. K(D) was higher during October through February compared with the rest of the year. B(max) in patients was higher compared with controls in March. The opposite difference was observed in September-December. These differences from controls were mostly due to patients with an onset of the current major depressive episode during Spring or Fall.
Conclusions: Patients with a major depressive episode differed from controls in circannual variation of platelet 5-HT(2A) binding. This may reflect a vulnerability to seasonal effects in patients with mood disorders.