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 t ransporter binding in depressed patients is due to previous antidepres sant drug exposure. In addition, the binding of both [H-3]imipramine a nd the more specific ligand [H-3]paroxetine to the platelet 5-HT trans porter was compared in drug-free depressed patients and age- and sex-m atched normal comparison subjects. Method: In the first experiment blo od samples were obtained from 12 depressed patients who had never rece ived antidepressant drugs and 12 normal comparison subjects, and plate let 5-HT transporter binding was measured by using [H-3]imipramine. In the second experiment blood samples were obtained from 28 drug-free d epressed patients and 28 age- and sex-matched comparison subjects, and platelet 5-HT transporter binding was assessed by using both [H-3]imi pramine and [H-3]paroxetine. Results: In the first experiment the neve r-medicated depressed patients exhibited fewer platelet [H-3]imipramin e binding sites than did the comparison subjects. In the second experi ment the drug-free depressed patients had fewer platelet binding sites for both [H-3]imipramine and [H-3]paroxetine than did the comparison subjects. Conclusions: The low number of platelet [H-3]imipramine bind ing sites does not appear to be due to prior antidepressant drug expos ure. The B-max of platelet binding sites for both [H-3]imipramine and [H-3]paroxetine, ligands used to measure 5-HT transporter binding, is abnormally low in depressed patients.