Alteration of Red Nucleus Microstructure in Depressive Bipolar II Disorder and Unipolar Depression: A Diffusion Kurtosis and Perfusion Imaging Study

Introduction The red nucleus is an important node of the prefrontal-thalamic-cerebellar circuit, which is related to both cognitive and affective functions. However, the structural and functional changes of the red nucleus in depressive bipolar II disorder (BD-II) or unipolar depression (UD) have rarely been studied. Methods Thirty-five patients with depressive BD-II, 29 patients with UD, and 40 healthy controls underwent diffusion kurtosis imaging (DKI) and three-dimensional arterial spin labeling (3D ASL). Region-of-interest analysis was performed to measure the mean kurtosis (MK), axial kurtosis (Ka), radial kurtosis (Kr), fractional anisotropy (FA), mean diffusivity (MD), axial diffusivity (Da), radial diffusivity (Dr), and cerebral blood flow (CBF) in the red nucleus. Multivariate analysis of variance (MANOVA) with Bonferroni pairwise comparison tests was performed to compare the DKI parameters and CBF values of the ROIs among patients with depressive BD-II, patients with UD, and HCs, in the left and right red nucleus respectively; Pearson correlation coefficients were then used to assess whether the clinical variables for the patients correlated with their measured DKI or 3D ASL parameters. Results Compared with controls, patients with UD exhibited significantly decreased MK and Kr in the left red nucleus; patients with depressive BD-II exhibited significantly decreased MK in the right red nucleus. No significant changes were found in the remaining DKI/3D ASL parameters, and no significant correlations were revealed between the DKI/3D ASL parameters and clinical variables in patients with either depressive BD-II or UD. Conclusion The present study suggests that microstructural impairment exists in the red nucleus in patients with depressive BD-II and patients with UD, which may provide new insights into the underlying neurobiological mechanisms of the two disorders.