Seasonal variations in the binding of [3H]paroxetine to the platelet serotonin transporter sites in African-American cocaine-dependent patients and healthy volunteers.

Although seasonal fluctuations in several indices of serotonin function have been described, little is known about seasonality and serotonergic activity in substance abusers. We investigated whether there were seasonal differences in platelet serotonin transporter sites among cocaine dependent patients and controls. Platelet [(3)H]paroxetine binding, a measure of serotonin transporter sites, was assayed in 141 African-American cocaine-dependent subjects and in 60 race matched healthy volunteers who served as the control group. B(max) (density of serotonin transporter) and K(d) (affinity constant) values of [(3)H]paroxetine binding were compared during spring, summer, fall and winter. Consistent with our previous findings B(max) values were significantly lower in cocaine patients (639 +/- 234) than in controls (906 +/- 225) (t = 7.12, p < 0.001). Moreover, B(max) values showed a significant seasonal variation in controls with the highest values in summer and spring compared with fall and winter (F = 4.47, p < 0.01). However, there were no significant seasonal differences in B(max) values in cocaine patients. K(d) values did not show any seasonal changes in either group. There were no effects of age or gender on seasonal variations in B(max). The study demonstrates a seasonal effect on platelet serotonin uptake in healthy African-American volunteers. The lack of seasonal differences in transporter availability in cocaine patients indicates that the normal seasonal rhythm of serotonergic activity may be disturbed in cocaine abusers. Biological studies that employ platelet serotonin transporter sites as a marker of serotonin function should consider seasonal variations in these markers as a potential source of variance.