Further studies on platelet serotonin transporter binding in depression

OBJECTIVE: There is an impressive literature implicating abnormalities in serotonergic neural systems in depression. Many investigators, but not all, have reported low numbers of platelet and brain serotonin (5-HT) transporter sites in drug-free depressed patients. In the present study the authors sought to determine whether the low platelet 5-HT transporter binding in depressed patients is due to previous antidepressant drug exposure. In addition, the binding of both 3Himipramine and the more specific ligand 3Hparoxetine to the platelet 5-HT transporter was compared in drug-free depressed patients and age- and sex-matched normal comparison subjects. METHOD: In the first experiment blood samples were obtained from 12 depressed patients who had never received antidepressant drugs and 12 normal comparison subjects, and platelet 5-HT transporter binding was measured by using 3Himipramine. In the second experiment blood samples were obtained from 28 drug-free depressed patients and 28 age- and sex-matched comparison subjects, and platelet 5-HT transporter binding was assessed by using both 3Himipramine and 3Hparoxetine. RESULTS: In the first experiment the never-medicated depressed patients exhibited fewer platelet 3Himipramine binding sites than did the comparison subjects. In the second experiment the drug-free depressed patients had fewer platelet binding sites for both 3Himipramine and 3Hparoxetine than did the comparison subjects. CONCLUSIONS: The low number of platelet 3Himipramine binding sites does not appear to be due to prior antidepressant drug exposure. The Bmax of platelet binding sites for both 3Himipramine and 3Hparoxetine, ligands used to measure 5-HT transporter binding, is abnormally low in depressed patients.