Abstract
Objectives: Reduction of hippocampal volumes has been consistently reported in patient with major depressive disorder (MDD). Meanwhile, alteration of serotonin transporter (SERT), which terminates the serotonin action, has been implicated in the pathophysiology of MDD. However, the study of the relationship between SERT and hippocampus was still limited. The aim of this study was to examine their relationship in MDD.
Methods: Twenty-seven patient with first-episode drug-naïve MDD and 27 age- gender-matched healthy controls (HCs) were recruited. All participants examined with 1.5T high-resolution magnetic resonance imaging. Two different methods were used for image analysis, included manual and FreeSurfer (v5.3.0). Manual method was applied to analyze the longitudinal axis of hippocampal volumes. FreeSurfer was used to analyze the volumes of hippocampal subfields. 123I-ADAM with single-photon emission computed tomography was applied for SERT imaging. Regions of interest included the midbrain, thalamus, caudate and putamen.
Results: The left total hippocampal volume was significantly reduced in MDD compared with HCs. In sub-analysis, the reduced volume was largely contributed to the body and tail part. The SERT was not significantly different between groups. There was no significant difference in subfields of hippocampal volume between groups. Pearson's correlation showed that right total hippocampal volume was significantly correlated with SERT in the midbrain and caudate, but not putamen and thalamus in HCs. For subfields analysis, SERT in midbrain was well correlated with both sides of fimbria. Additionally, SERT in the caudate and thalamus was correlated with CA1, CA4/DG, subiculum and presubiculum, respectively. Importantly, all of these correlations could not be found in MDD.
Conclusions: This study firstly demonstrated the relationship of the SERT and hippocampal volumes in HCs and MDD, respectively. The association of SERT and hippocampal volumes, which was seen in HCs but disappeared in MDD indicates the important role of functional and structural relationship in pathophysiology of MDD.