[I-123]-beta-CIT SPECT imaging shows reduced brain serotonin transporter availability in drug-free depressed patients with seasonal affective disorder

Background: Numerous findings indicate alterations in brain serotonin syste ms in seasonal affective disorder (SAD). [I-123]-2-beta-carbomethoxy-3-beta -(4-iodophenyl)-tropane ([I-123]-beta-CIT) labels serotonin transporters (5 -HTTs) in the midbrain. We performed a [I-123]-beta-CIT single photon emiss ion computer tomography (SPECT) study under the hypothesis of lower [I-123] -beta-CIT binding reflecting reduced central 5-HTT availability in depresse d SAD patients. Methods: Depressed SAD patients and healthy control subjects were investiga ted using [I-123]-beta-CIT SPECT 4 hours and again 24 hours after tracer in jection. Subjects had either never used psychotropic medication or had been drug-free for at least 6 months prior to the investigation. Specific-to-no ndisplaceable partition coefficient (V-3") was calculated for the thalamus- hypothalamus and the midbrain-pons; the cerebellum sewed as a reference reg ion. Results: Patients showed a reduction in V-3" in thalamus-hypothalamus (2.41 +/- 0.3 vs. 2.84 +/- 0.4; p = .026) 24 hours post tracer injection (p.i). No difference between patients and control subjects was found in midbrain-p ens (1.31 +/- 0.2 vs. 1.42 +/- 0.2; p = .39). No differences were detected in the SPECT acquisitions 4 hours p.i. Conclusions: Depressed SAD patients showed lower specific-to-nondisplaceabl e [I-123]-beta-CIT binding in the region of interest (ROI) thalamus-hypotha lamus. The small size of the midbrain-pens ROI may have contributed to the failure to show a difference in this ROI as well. Similar to reduced midbra in 5-HTT availability in nonseasonal depression, depression in SAD seems to be associated with reduced 5-HTT availability to the thalamus-hypothalamus . (C) 2000 Society of Biological Psychiatry.