Effects Of Maternal Separation On Neurogenesis And Synaptic Plasticity Of Dentate Gyrus In Offspring Mice

The mammalian brain has two important specific areas in which neurogenesis exists persistently throughout life: the subventricular zone(SVZ)of the lateral ventricles and the subgranular zone(SGZ)of the dentate gyrus(DG)in the hippocampus.Among them,the neurogenesis in the SGZ plays a vital role in the development of hippocampus and the acquisition of high-order function.Any deficits which occur during the neurogenesis of SGZ may affect the normal formation of brain,resulting in a series of developmental neural disorders.At present,accumulating evidence suggested the close connection between depression and the damage of hippocampal structure and function,especially DG.The presence of mothers plays an important role in the early development of newborn rodents.Keeping close contact with mothers,newborn rodents can be provided with various essential resources,such as nutrition,somatosensory,temperature and so on,which are crucial for shaping behavioral,emotional and physiological responses in adulthood.However,repeated maternal separation(MS)at early postnatal developmental stage disrupts the motheroffspring contact,which could increase the risk of psychological disturbances such as depression,autism,psychoses and anxiety in adulthood.As common models for adverse early life experiences and depression,MS imitates the human depression and adverse early life experiences better by employing psychological and social stress,which was accompanied by the destruction or change of social relations.At present,a variety of literatures documented the adverse effects of MS on development and function of brain.Therefore,the investigation of the effect mechanism of MS on brain development arouses wide attention nowadays.In the present study,we established the two models,MS for 15 min(MS15)and 3 h(MS180),to investigate the effect of MS on the neurogenesis and synaptic plasticity of DG in the mouse hippocampus.The anxiety-like and depression-like states were examined by the western blot and a series of behavioral tests,such as open field test(OFT),elevated plus maze(EPM),forced swimming test(FST),tail suspension test(TST)and Morris water maze(MWM).To investigate the effect of MS on the postnatal neurogenesis and synaptic plasticity of DG in the hippocampus,the postnatal in vivo electroporation and Imaris three-dimensional reconstruction,combining with Brd U labeling,western blot,immunofluorescence staining and confocal laser microscope,were used.The main results are as follows:1.MS180 induced the anxiety-like and depression-like behaviors and enhanced the learning and memory of offspring in adulthood.During the establishment of MS model,the body weight gain of offspring in MS180 group significantly slowed within the first week after birth.Mice of MS180 group spent less time in inner area of OFT and open arms of EPM,suggesting the decline of curiosity and exploratory response in face of unfamiliar environment and increase of anxiety-like behavior.Immobility time increases of MS180 group in FST and TST also implied depression-like state.Then,we examined the expression of TPH2 in different regions of brain by western blot to indirectly reflect the content of 5-HT,showing higher expression of TPH2 in hippocampus and midbrain of MS180 group.In MWM,lower escape time during late training and more time spent in the target quadrant of test in MS180 group suggest the enhancement of spatial learning and memory caused by MS.2.MS180 impaired the postnatal neurogenesis of DG of offspring.The results suggest that MS180 inhibited the proliferation of neural progenitor cells and impaired the survival of newly-generated cells,further resulting in the decrease of newborn granule cells(GCs).And the fate decision of newborn cells was also altered by MS180.As a result of MS180,newborn cells tended to differentiate into neurons and astrocytes,while the differentiation into microglia was inhibited.3.MS180 altered the synaptic plasticity of DG of offspring.Sholl analysis showed that MS180 increased the total length and terminal tips but not the complexity(the number of intersections between the dendrites and concentric circles)of dendrite.The expression of synapse-associated protein in the hippocampus were examined by western blot,suggesting the slight increase in synaptophysin and significant decrease in PSD95 and spinophilin.Moreover,to explore effects of MS180 on the synaptic plasticity,the postnatal in vivo electroporation and Imaris three-dimensional reconstruction were used in this study,showing that MS180 significantly increased the spine density,especially the thin spine,and the puncta of synaptophysin,spinophilin and PSD95 in the molecular layer,especially the outer molecular layer,in MS180 group.In conclusion,our investigation suggests that the possible mechanism of depression induced by prolonged MS is associated with impaired postnatal neurogenesis of DG and the increased density of spine,especially thin spine,is due to the increase in the total length and terminal tips of dendrites,thereby enhancing the learning and memory.All above results of adverse effects induced by MS provide the reference for future studies on MS relevant research and clinical prevention and treatment.