Study On The Improvement Of Insulin-like Growth Factor 1 On Spatial Memory Abnormalities In Female Maternal-separation Rats

Objective: Early life stress(ELS)refers to the long-term abuse and emotional neglect that individuals experience during their critical periods of growth and development,which can impair memory ability and increase the risk of developing mental illnesses in adulthood.Maternal separation(MS)is a typical rodent model used to simulate ELS,where the most common method of modeling involves separating rat pups from their mothers for three hours per day during the first 14 days after birth.Studies have shown that MS can alter synaptic function and impair spatial memory in rats.The soluble N-ethylmaleimidesensitive factor attachment protein receptor(SNARE)complex is central to synaptic vesicle signaling,mainly composed of synaptic vesicle proteins(V-SNARE or VAMP),synaptosome-associated protein(SNAP25)and synaptic fusion protein(Syntaxin),whose abnormalities often lead to nervous system dysfunction,especially in learning and memory ability.Insulin-like growth factor-1(IGF-1)supports neuronal growth and differentiation,improves synaptic function,and regulates synaptic plasticity,which offers the possibility of treating ELS-induced psychiatric disorders.There are few reports on spatial memory abnormalities in MS rats and how to improve them.Our laboratory found that MS female rats are more prone to spatial memory abnormalities than males.Therefore,this study first investigated the gender differences in the ability of adult MS rats to synthesize SNARE complexes based on the degree of spatial memory abnormalities between MS females and males.Secondly,based on these experimental results,the study focused on investigating the effect of IGF-1 injection on improving spatial memory in adult MS female rats Methods: 1.The MS model was used to simulate chronic ELS,the rats were separated from their mothers for 3 hours at a fixed time fromPND2 to PND14.2.The rats were randomly selected from the experimental and control groups for intracerebroventricular IGF-1 injection on PND63.3.The open field(OF)test and elevated plus maze(EPM)test were used to observe the spontaneous exploration behavior of rats in open places on PND65,and the Morris water maze(MWM)was used to evaluate the spatial memory ability of rats on PND66 to PND69.4.Western blot and co-immunoprecipitation were applied to detect the protein levels of IGF-1 receptor(IGF-1R)and SNARE complex-related proteins(VAMP2,SNAP25,Syntaxin1 a,Syntaxin6,Synaptotagmin1,and Munc18-1)in the hippocampus and medial prefrontal cortex(mPFC).5.Dendritic complexity and density of dendritic spine changes in the hippocampal CA1 region and mPFC were observed by Golgi staining experiments.6.The number and ultrastructure of synapses in the hippocampal CA1 region were studied by using transmission electron microscopy.Results: 1.Compared to MS male rats,the protein levels of the SNARE complex of MS female rats changed more pronouncedly.The levels of VAMP2,SNAP25,Syntaxin6,and IGF-1R proteins in the hippocampus of MS female rats decreased significantly,and the level of Munc18-1 proteins increased significantly.The MS male rats showed a decrease in VAMP2 and Syntaxin1 a protein levels in the hippocampus,while no significant alterations were observed in other related proteins.In mPFC,the results were similar to those of the hippocampus,The levels of VAMP2,Syntaxin1 a,Syntaxin6,and IGF-1R proteins in the mPFC of MS female rat decreased significantly,and the level of Munc18-1protein in the mPFC of MS female rat increased significantly.The levels of SNAP25 and Munc18-1 proteins in the mPFC of MS male rats increased significantly,the level of IGF-1R protein decreased,and there were no significant changes in other related proteins.This indicates a decrease in the ability to synthesize SNARE complexes and IGF-1R protein levels in the hippocampal and mPFC of MS female rats.2.The behavioral test results showed that IGF-1 did not improve the anxiety-like behavior of MS female rats but improved the spatial memory ability of MS female rats.3.The Western blot showed that IGF-1 increased the levels of VAMP2,SNAP25,Syntaxin6,and IGF-1R,and decreased the level of Munc18-1 in the hippocampus of MS female rats.IGF-1 significantly increased VAMP2,Syntaxin1 a,Syntaxin6,Synaptotagmin1,and IGF-1R protein levels,and decreased Munc18-1 protein level in the mPFC of MS female rats,which indicates that the ability to synthesize SNARE complexes and IGF-1R protein levels in the hippocampus and mPFC were increased after IGF-1 in MS female rats.4.The co-immunoprecipitation results showed that VAMP2,SNAP25,and Syntaxin1 a were bound to each other by Western blot.IGF-1 increases the synthesis of SNARE complexes in MS rats.5.IGF-1 increases dendritic spine density and dendritic complexity in hippocampal and mPFC in MS female rats.6.The transmission electron microscopy results showed that IGF-1 could improve the abnormal changes in synaptic ultrastructure and increase the efficiency of synaptic transmission in the hippocampus of MS female rats.Conclusions: 1.MS female rats are more prone to abnormal behavior with impaired spatial memory,which may be related to the reduced ability to synthesize SNARE complexes.2.IGF-1 may improve spatial memory abnormalities in adult MS female rats by upregulating synaptic SNARE complexes synthesis.