Study Of Magnetic Resonance Imaging And BDNF Expression In IP3R2 Deficient Mice Exhibiting Depressive Symptoms

Objective:Inositol 1,4,5-trisphosphate receptor type 2(IP3R2)is Ca2+ channel receptor specifically exist in the endoplasmic reticulum of astrocytes in the brain,it combined with IP3 specifically promote Ca2+ release from endoplasmic reticulum,and the rise of Ca2+ level in astrocytes is associated with many physiological functions,one of the most important function is exocytosis of astrocytes,such as secretion of ATP and BDNF.Previous studies have reported that IP3R2 knockout mice(Ip3r2-/-mice)perform depressive behaviours,which is associated with the decrease content of extracellular ATP secreted from astrocytes.The purpose of this study was to investigate the relationship between IP3R2 gene deletion and depressive behavior as well as structural and functional magnetic resonance imaging changes and alternation of BDNF expression.Materials and Methods:In this study,three-month old Ip3r2-/-C57BL/6 mice and wild-type C57BL/6 mice were selected as the experimental group and control group respectively.Behavioural tests were conducted on the mice in both groups to explore whether IP3R2 deficiency would induce depressive behaviours,these behavioural tests including sucrose consumption test,tail suspension test,forced swimming test and open field test.Then,magnetic resonance imaging was performed on the mice,and voxel-based morphometry(VBM)was used to analyze the gray matter volume changes in the whole brain of Ip3r2-/-mice.Then,based on the main results of gray matter volume changes,the changes in resting-state functional connections of Ip3r2-/mice were analyzed by the region of interest method.Then,lentivirus was transfected to knock down the expression of IP3R2 of astrocytes called C8-D1A,and western blot was used to detect the expression changes of IP3R2 and BDNF in astrocytes after knocking down IP3R2 by lentivirus.Meanwhile,western blot and frozen section immunofluorescence were used to detect the expression changes of BDNF in brain regions with major gray matter volume changesResults:The behavioral test results showed that,compared with the control group,the experimental group Ip3r2-/-mice showed a significant tendency to depression,which supported the behavioral changes of Ip3r2-/-mice reported in previous literatures.The results of VBM analysis showed that the volume of gray matter in bilateral striatum areas,periventricular gray matter and right frontotemporal cortex of Ip3r2-/-mice decreased,and no brain regions with increased volume of gray matter were found.The region of interest method using bilateral striatum as the seed points showed that the functional connection between bilateral striatum and bilateral hippocampal region as well as right parietal lobe of Ip3r2-/-.mice in the experimental group decreased,while no brain region with increased functional connection with bilateral striatum was found.Western blot method showed that IP3R2 expression and mBDNF expression level decreased obviously after knockdown of IP3R2 by lentivirus transfection in astrocytes,while the expression level of pro-BDNF decreased sightly.Besides,western blot method aslo showed that IP3R2 and mBDNF expression level of bilateral striatums decreased significantly in Ip3r2-/-C57BL/6 mice brain,whilie the expression level of pro-BDNF did not significantly change,immunofluorescence suggested that declined green fluorescence in the striatum regions of Ip3r2-/-mice which showed the decreased expression level of total BDNF content.Conclusion:The absence of IP3R2 led to significant depression behaviour in the mice.The volume of gray matter in the bilateral striatum region,periventricular gray matter,and right frontotemporal cortex decreased in Ip3r2-/-mice.The resting-state functional connections between the bilateral striatum and the bilateral hippocampus as well as right parietal lobe were decreased in Ip3r2-/-mice.The expression level of mBDNF in IP3R2 deficient astrocytes decreased significantly,while the expression level of pro-BDNF decreased significantly.The expression level of total BDNF in the bilateral striatum brain region of Ip3r2-/-mice decreased,in which the expression level of mBDNF decreased,while the expression level of pro-BDNF did not change significantly.