Changes in human in vivo serotonin and dopamine transporter availabilities during chronic antidepressant administration

Few studies have demonstrated in vivo alterations of human serotonin and dopamine transporters (SERTS and DATS) during antidepressant treatment. The current study measured these transporter availabilities with [I-123]beta-CIT single photon emission computed tomography (SPECT) during administration of selective serotonin reuptake inhibitors (SSRIs) or a non-SSRI, bupropion. A total of 17 healthy human subjects were randomly assigned to two different treatment protocols: (I) citalopram (40 mg/day) followed by augmentation with bupropion (100 mg/day) or (2) bupropion (100-200 mg/day) for 16 days. Citalopram significantly inhibited [I-123]beta-CIT binding to SERT in brainstem (51.4%) and diencephalon (39.4%) after 8 days of administration, which was similarly observed after 16 days. In contrast, citalopram significantly increased striatal DAT binding by 15-17% after 8 and 16 days of administration. Bupropion and its augmentation to citalopram did not have a sgnifcant effect on DAT or SERT. In 10 depressed patients who were treated with paroxetine (20 mg/day), a similar increase in DAT and inhibition of SERT were observed during 6 weeks treatment. The results demonstrated the inhibition of SERT by SSRI in human in vivo during the chronic treatment and, unexpectedly, an elevation of DAT. This apparent SSRI-induced modulation of the dopamine system may be associated with the side effects of these agents, including sexual dysfunction.