To investigate the relationship between the severities of symptom dimensions in obsessive-compulsive disorder (OCD) and white matter alterations.

We applied tract-based spatial statistics for diffusion tensor imaging (DTI) acquired by 3T magnetic resonance imaging. First, we compared fractional anisotropy (FA) between 20 OCD patients and 30 healthy controls (HC). Then, applying whole brain analysis, we searched the brain regions showing correlations between the severities of symptom dimensions assessed by Obsessive-Compulsive Inventory-Revised and FA in all participants. Finally, we calculated the correlations between the six symptom dimensions and multiple DTI measures [FA, axial diffusivity (AD), radial diffusivity (RD), mean diffusivity (MD)] in a region-of-interest (ROI) analysis and explored the differences between OCD patients and HC.

There were no between-group differences in FA or brain region correlations between the severities of symptom dimensions and FA in any of the participants. ROI analysis revealed negative correlations between checking severity and left inferior frontal gyrus white matter and left middle temporal gyrus white matter and a positive correlation between ordering severity and right precuneus in FA in OCD compared with HC. We also found negative correlations between ordering severity and right precuneus in RD, between obsessing severities and right supramarginal gyrus in AD and MD, and between hoarding severity and right insular gyrus in AD.

Our study supported the hypothesis that the severities of respective symptom dimensions are associated with different patterns of white matter alterations.

Glutamatergic neurotransmission via the N-methyl-d-aspartate (NMDA) receptor is integral to the pathophysiology of depression. This study was performed to examine whether amino acids related to NMDA receptor neurotransmission are altered in the serum of patients with depression.

We measured the serum levels of d-serine, l-serine, glycine, glutamate and glutamine in patients with depression (n=70), and age-matched healthy subjects (n=78).

Serum levels of d-serine and l-serine in patients with depression were significantly higher than those of healthy controls (p<0.001). In contrast, serum levels of glycine, glutamate and glutamine did not differ between the two groups. Interestingly, the ratio of l-serine to glycine in patients was significantly higher than that of healthy controls (p<0.001).

This study suggests that serine enantiomers may be peripheral biomarkers for depression, and that abnormality in the d-serine-l-serine-glycine cycle plays a role in the pathophysiology of depression.