Abstract
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Objectives The aim of the present study was to investigate both serotonin (SERT) and dopamine transporter (DAT) availabilities in patients with major depressive disorder, first in a drug-naïve baseline condition, and again upon a six weeks’ treatment with the selective serotonin reuptake inhibitor (SSRI) escitalopram.
Methods 27 patients (10m, 42±16y) with the diagnosis of major depression were recruited and underwent neuropsychiatric testing for assessment of Hamilton Depression (HAM-D) and Beck Depression Inventory (BDI) scores at baseline and after six weeks of medication. At baseline and under treatment pairs of [123I]β-CIT SPECT recordings were acquired 4h and 20-24h p.i. in order to assess SERT and DAT availabilities. Parametric maps with specific to non-specific ratios (~ BPND) were calculated for each voxel using cerebellum as reference region. VOI-based BPND were calculated in striatum and midbrain/pons.
Results Mean baseline striatal (DAT) BPND was 6.44 ± 0.84 and mean midbrain (SERT) BPND was 0.94 ± 0.14. Baseline DAT binding in striatum declined with age, with the highest correlations in posterior putamen (r = -0.65; p < 0.01). Baseline SERT availabilities declined with age in midbrain (r = -0.55; p < 0.01) and thalamus (r = -0.5; p < 0.01). Under treatment, SERT BPND decreased by 36% (p < 0.0001), representing the occupancy by escitalopram. In this condition, striatal DAT availability increased by 14% (p < 0.001). Age was negatively correlated with DAT increase (p < 0.05) and was positively correlated with SERT occupancy.
Conclusions This is the first [123I]β-CIT SPECT study in patients with major depressive disorder before and under SSRI treatment. DAT and SERT availabilities decreased age-dependently comparable to studies in healthy volunteers. The SSRI-induced increase in DAT was less pronounced in elderly patients, even though occupancy of SERT by escitalopram was higher. These findings might have implications on dosage and side effect profile of SSRI in older patients