Physical exercise restores adult neurogenesis deficits induced by simulated microgravity

Memory deficits have been reported in astronauts during spaceflights and documented in models of simulated microgravity (SMG) in animals. However, the neuronal causes of these behavioral effects remain largely unknown. We explored whether adult neurogenesis, known to be a crucial plasticity mechanism supporting memory processes, is altered by SMG. Adult male Long-Evans rats were submitted to hindlimb unloading (HU) model. We studied the proliferation, survival and maturation of newborn cells in neurogenic niches: the subventricular zone (SVZ) and the dentate gyrus (DG) of the hippocampus, at different delays following the SMG exposure period. We observed that, while unaffected immediately after SMG exposure, newborn cell proliferation was decreased in the DG after 7 days of SMG exposure. Moreover, SMG also induced a decrease in short-term (7 days), but not long-term (21 days), survival of newborn cells in the SVZ and DG. Physical exercise, used as a countermeasure, was able to reverse the decrease in newborn cell survival observed in the SVZ and DG. In addition, depending on duration of SMG, transcriptomic analysis revealed modifications in gene expression involved in neurogenesis and others as mitochondrial functions. These findings highlight the sensitivity of adult neurogenesis to gravitational environmental factors during a transient period, suggesting that there is a period of adaptation of physiological systems to this new environment.