Evidence for an increase in functional platelet 5-HT2A receptors in depressed patients using the new ligand [I]-DOI

Abnormalities in the serotonergic system have been implicated in the pathophysiology of depressive disorders. Human platelets possess serotonin-2A (5-HT(2A)) receptors, and previous research using LSD or ketanserin as ligands have indicated that their number is increased in depressed patients. Compared to other ligands previously used in platelet studies, DOI is highly selective for the 5-HT(2A) receptor and binds to its high-affinity state, therefore labeling only the receptors that are biologically coupled to the G-protein. We determined the density (Bmax) and the affinity (Kd) of 5-HT(2A) receptors labeled by (125)I]-DOI in platelets from 21 untreated patients with major depression and 21 healthy volunteers. The density of the 5-HT(2A) binding sites was found to be increased in platelets from female depressed patients as compared to controls. No changes were observed in the Kd. We did not find any relationship between the binding parameters and either the severity of the depressive episode or the suicidal tendencies of the patients. Our results show that the number of coupled platelet 5-HT(2A) receptors is increased in depressed patients, indicating that platelet 5-HT(2A) receptor function is enhanced in depression.