Impact Of Simulated Microgravity On Neurogenesis Of Subventricular Zone In Adult Rats

Being identical to actual spaceflight, simulated microgravity via tail-suspended model could induce a major fluid shift to the upper regions of the body and change the functional status of brain circulation, vestibular receptor and proprioceptor associated with gesture maintaining and gravity bearing. The plasticity of cerebral would be changed because of changing functional status in these subunits. Astronauts during spceflight had been reported abnormal functional status of sensory cognition, visual perception and motor coordination. Adaptive changes induced by weightlessness included cephalad fluid shift, space motion sickness, functional disorder of circulation , nerves disequilibrium and decreasing immune function.In decades, adult mammalian brain is indeed capable of neurogenesis and that the process is primarily confined to the subventricular zone (SVZ) of the forebrain the subgranular zone (SGZ) of the hippocampus. Of these regions, the SVZ is the largest neurogenic niche in the adult mammalian brain . Within this niche resides a subpopulation of astrocytes with stem cell-like features of self-renewal and multipotentiality and also contains affluent blood vassels. This niche was sensitive to many pathological and physiological conditions in organism (cerebral ischemia, hemorrhage, tumor and dietary restriction, etc) which had important significance to the functional plasticity of brain.Since the functional changes of brain induced by microgravity or simulated microgravity had been paid great attention, the need for further research in this field is clearly indicated.In the present study, we sought to determine whether simulated microgravity could influence the process of neurogenesis and the vascular microenvironment in SVZ.Experiment 1:Adult SD rats had been randomly divided into 6 groups: tail-suspended for 2 weeks(TS2W), 4 weeks(TS4W), 8 weeks(TS8W) and control groups for each TS groups. The changes of neurogenesis were investigated utilizing the immunohistochemical and light microscope methods.Experiment 2:The number of microglia in SVZ was counted in each groups and the cells morphological changes were observed under light microscope after staining by immunohistochemical method.Experiment 3:Double-labeled cells for BrdU/RECA-1 by immunofluorescent technology were counted in rats'SVZ, OB and cortex after 4 weeks tail-suspended. Morphological changes of vascular induced by simulated microgravity were also observed.Results were showed as following:(1) Compared to each control group, all experimental groups showed decreased number of proliferated cells in SVZ and neuroblast cells in granular layer of OB. Also, the neuroblast cells in OB showed more migrating states, which indicated lower maturity in TS groups. This phenomenon was manifested most obviously after 4 weeks suspension.(2) The number of microglia around SVZ increased in all TS groups and most of cells showed activated state compared to CON. In group of TS4W, the number of activated microglia was higher than that in TS2W and TS8W and most of activated microglia showed large ameboid morphology. TS8W showed the least number of microglia and activated state.(3) After 4 weeks suspension, the number of double-labeled cells for BrdU/RECA-1 decreased, which indicated less proliferated EC around SVZ. But in OB, increased number of double-labeled cells was observed and some vascular morphological changes were noticed, for example, in some vessels, the gap between ECs widened and the whole blood vessel seemed to be stiff. We also found the exist of proliferating EC in cortex of TS groups but none in CON.