Identifying the Alteration Patterns of Brain Functional Connectivity in Progressive Mild Cognitive Impairment Patients: A Longitudinal Whole-Brain Voxel-Wise Degree Analysis

Patients with mild cognitive impairment (MCI) are at high risk for developing Alzheimer’s disease (AD), while some of them may remain stable over decades. The underlying mechanism is still not fully understood. In this study, we aimed to explore the connectivity differences between progressive MCI (PMCI) and stable MCI (SMCI) individuals on a whole-brain scale and on a voxel-wise basis, and we also aimed to reveal the differential dynamic alternation patterns between these two disease subtypes. The resting-state functional magnetic resonance images of PMCI and SMCI patients at baseline and year-one were obtained from the Alzheimer’s Disease Neuroimaging Initiative dataset, and the progression was determined based on a three-year follow-up. A whole-brain voxel-wise degree map that was calculated based on graph-theory was constructed for each subject, and then the cross-sectional and longitudinal analyses on the degree maps were performed between PMCI and SMCI patients. In longitudinal analyses, compared with SMCI group, PMCI group showed decreased long-range degree in the left middle occipital/supramarginal gyrus, while the short-range degree was increased in the left supplementary motor area and middle frontal gyrus and decreased in the right middle temporal pole. A significant longitudinal alteration of decreased short-range degree in the right middle occipital was found in PMCI group. Taken together with previous evidence, our current findings may suggest that PMCI, compared with SMCI, might be a severe presentation of disease along the AD continuum, and the rapidly reduced degree in the right middle occipital gyrus may have indicative value for the disease progression. Moreover, the cross-sectional comparison results and corresponding receiver-operator characteristic-curves analyses may indicate that the baseline degree difference is not a good predictor of disease progression in MCI patients. Overall, these findings may provide objective evidence and an indicator to characterize the progression-related brain connectivity changes in MCI patients

In Vivo Structural and Functional Abnormalities of the Striatums Is Related to Decreased Astrocytic BDNF in Itpr2-/- Mice Exhibiting Depressive-Like Behavior

Background. Previous researches indicate that Itpr2-/- mice (inositol 1,4,5-trisphosphate receptor type 2 knockout mice) show depressive-like symptoms; however, little is known regarding the in vivo neurobiological effect of Itpr2 as well as the specific pattern of brain abnormalities in Itpr2-/- mice. Methods/Materials. First, behavioral tests, structural magnetic resonance imaging (MRI), and resting-state functional MRI were performed on Itpr2-/- mice and matched healthy controls. Voxel-based morphometry and seed-based voxel-wise functional connectivity (FC) were, respectively, calculated to assess the gray matter volume and the functional activities of the brain in vivo. Second, the sample of relevant changed brain regions was extracted to detect the expression of BDNF. Finally, to further validate the relationship between Itpr2 deficiency and the observed brain abnormalities, we performed Western blotting to detect the expression of pro-BDNF and mBDNF in Itpr2-/- C8-D1A (a type of astrocyte). Results. Compared with controls, Itpr2-/- mice showed depressive-like behaviors as well as significantly lower gray matter volume in striatums mainly, periaqueductal GM, and the right frontoparietal cortices as well as lower striatal-hippocampal and striatal-right parietal cortex (mainly for the primary and secondary somatosensory cortex) FC. Moreover, decreased expression of mBDNF was found in both sample tissues of the striatum in Itpr2-/- mice and Itpr2-/- C8-D1A. Conclusion. By combining biochemistry and MR analyses, this study provides evidences to support that the Itpr2-related neuropathological effect is possibly mediated by the striatal abnormality associated with dysfunctional astrocytes in Itpr2-/- mice in vivo, thus may help us better understand underlying mechanisms of Itpr2 deficiency as well as its relation to depressive-like behavior