Altered serotonin and dopamine transporter availabilities in brain of depressed patients upon treatment with escitalopram: A [123I]β-CIT SPECT study

Altered SERT and DAT availabilities during treatment with escitalopram were investigated with [123I]2β-carbomethoxy-3β-(4-iodophenyl)tropane (β-CIT) SPECT in a series of patients fulfilling the criteria for unipolar major depressive disorder (MDD). 27 patients (10 m, 42±16 y) with diagnosis of MDD were recruited for the study. All patients underwent neuropsychiatric testing for assessment of Hamilton Depression (HAM-D) and Beck Depression Inventory (BDI) scores. At baseline, [123I]β-CIT SPECT recordings were acquired 4 h (SERT-weighted) and 20–24 h p.i (DAT-weighted). Follow-up scans and neuropsychiatric testing were performed after six weeks of stable escitalopram medication. Voxel-wise parametric maps of specific/ non-specific ratios-1 (~BPND) were calculated. At baseline, DAT-weighted BPND was 5.06±0.81 in striatum and SERT-weighted BPND was 0.94±0.18 in thalamus. There were significant negative correlations with age for DAT in striatum (R=−0.60; p<0.01) and SERT in thalamus (R=−0.45; p<0.05). Under SSRI treatment there was an apparent 42% occupancy of SERT in thalamus (p<0.0001), whereas DAT availability increased significantly by 20% in striatum (p<0.001); higher apparent SERT occupancy in thalamus was associated with lesser DAT increase in striatum (R=−0.62; p<0.005). The low apparent SERT occupancy may be confounded by alterations in SERT expression during treatment. Thus, [123I]β-CIT SPECT revealed age-dependent declines in DAT and SERT availabilities in un-medicated MDD patients, comparable to that seen previously in healthy controls. At follow-up, the SSRI-evoked increase in DAT was less pronounced in the older patients, even though apparent SERT occupancy and clinical improvement were not age-dependent. Present findings may have implications for escitalopram dosage and side effect profile in younger MDD patients.