Seasonal variation of availability of serotonin transporter binding sites in healthy female subjects as measured by [123I]-2β-carbomethoxy-3β- (4-iodophenyl)tropane and single photon emission computed tomography

%Background: Previous studies have indicated annual variations in central and peripheral serotonergic activity. In the present study we studied five women in summer and six women in winter and evaluated possible differences in availability of brain serotonin transporters between summer and winter. Methods: We employed the single photon emission computed tomography ligand [123I]-2β-carbomethoxy-3β-(4-iodophenyl)tropane ([123I]β-CIT) to visualize binding to the serotonin transporter site in the human thalamus/hypothalamus midbrain area in vivo. Brain imaging studies were performed in one group between May and August and in the other between November and December. Results: We found significant differences in displaceable [123I]β-CIT binding in the region corresponding to thalamus/hypothalamus between the summer group and the winter group (1.9 ± 0.3 vs. 1.4 ± 0.2, respectively; p< .01). Conclusions: The results of the present study suggest reduced brain serotonin transporter availability in winter. This finding further substantiates evidence of seasonal variations in brain serotonergic function.