Background: Numerous findings indicate alterations in brain serotonin systems in seasonal affective disorder (SAD). [(123)I]-2-beta-carbomethoxy-3-beta-(4-iodophenyl)-tropane ([(123)I]-beta-CIT) labels serotonin transporters (5-HTTs) in the midbrain. We performed a [(123)I]-beta-CIT single photon emission computer tomography (SPECT) study under the hypothesis of lower [(123)I]-beta-CIT binding reflecting reduced central 5-HTT availability in depressed SAD patients.
Methods: Depressed SAD patients and healthy control subjects were investigated using [(123)I]-beta-CIT SPECT 4 hours and again 24 hours after tracer injection. Subjects had either never used psychotropic medication or had been drug-free for at least 6 months prior to the investigation. Specific-to-nondisplaceable partition coefficient (V(3)") was calculated for the thalamus-hypothalamus and the midbrain-pons; the cerebellum served as a reference region.
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-pons (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-nondisplaceable [(123)I]-beta-CIT binding in the region of interest (ROI) thalamus-hypothalamus. The small size of the midbrain-pons ROI may have contributed to the failure to show a difference in this ROI as well. Similar to reduced midbrain 5-HTT availability in nonseasonal depression, depression in SAD seems to be associated with reduced 5-HTT availability to the thalamus-hypothalamus.