| Infrasound is a mechanical vibrational wave whose frequency is between 0.0001 to 20Hz.It's widespread around us.It has strong penetration ability and hardly attenuates when it spreads through the air. The primary mechanism of action of infrasound on human being is biology resonance.Many experiments have proved that infrasound could make series of biology effects on the humen and animals,especially on central nervous system.We have found that infrasound have influenced on the spacial learning and memory ability of rats,which may due to the nerve injury of the rats'hippocampus.The rat's brain shown an adaption to infrasound.After the infrasound was ended, the injury of brains could gradually recovered.So we can conclude that the brain could be repaired by itself after infrasound exposure.Neural stem cell is a kind of multipotential cell in central nervous system which can self-renewal and differentiate mature brain cell(including neurons,glial cells and oligodendroglial cells).There are two germinal regions in mature mammalian central nervous system: Subventricular zone(SVZ)and Subgranular zone(SGZ).It has been shown that various insults including cerebral ischemia stimulate the endogenous neural stern cells proliferation,migration and differentiation.So we conclude that the brain injuries result from infrasound exposure could enhance the proliferation and migration of neural stem cells in rats'hippocampus which might participate in the repairment of neural injuries.Nestin,a new member of of intermediate filament protein ,is a kind of important cytoskeletal protein in progenitor cell of central nervous system. It mainly expressed in neural stem cells and neural precursor cells during the embryo stage .The space-time sequence of nestin expression corresponds to the process of progenitor terminal differentiation. Cerebral njuries due to ischemia, physical,chemical and other factors can induce its re-expression. Now nestin has been considered as the most important and most commonly used indexes for identifying neural stem cells.Nestin can be used as a quick-responding and sensitive marker to central neural system injuries. It may be involved in the repair of neural cells.The neural cell adhesion molecule (NCAM) has long been implicated to be related to cell-cell and cell-substrate interactions. It is a cell surface glycoprotein of the immunoglobulin superfamily. Polysialic acid chains (PSA) can be attached to NCAM to modulate the interaction of cell-cell. The expression of PSA is generally thought to attenuate adhesive forces among cells to promote development of nerves.High amounts of PSA-NCAM were found in the developing and injuried brain,which indicated that (PSA) -NCAM took part in the development and regeneration of nerves.Many paradigms have shown that PSA-NCAM played an important part in the migration of neural stem cell and the expression of PSA-NCAM reflected the migration of neural stem cells directly.We used the infrasonic barochamber and detection system made by the fourth military medical university at the assistance of Chinese acaidemy of sciences acoustic institute and the 41st research institute of aerospace industry company.The frequency was 16Hz and the pressure were 90dB,130dB.Rats were under the exposure of infrasound,2h/d for1,7,14,21days.Theri brains were removed and by the aid of immunohistochemistrial staining(ABC) we detected the expression of Nestin and polysialic acid-neural cell adhesion molecule (PSA-NCAM) in rats'hippocampus to discuss the effect on the proliferation and migration of NSCs after infrasound exposure.The results were:(1) One hundred and sixty-eight SD rats were randomized into 16Hz, 130dB infrasound exposure groups,16Hz, 90dB infrasound exposure groups and control groups.â‘ Rats of the infrasound exposure groups were exposed to 16Hz 90dB/130dB infrasound barochamber system, 2h/d for1,7,14,21days. Their brains were removed and anti-Nestin immunohistochemistry was used to observe the expression of Nestin in rats'hippocampus.We find the expression of Nestin in rats'hippocampus increased after exposure for once and increased with the exposure times. It reached its peak at 14 days, decreased at 21 days but remained higher level. The reaction of 90dB group was weaker than that of 130dB group.â‘¡After infrasound exposure was ended, the rats'brains of 130dB group were removed and immunohistochemical method was used to detect the expression of Nestin in rats'hippocampus on that very day, the 7th day and the 14th day ,the 21th day and the 28th day after the treatment. We found that the expression of nestin in rat hippocampus continued increasing and reached its peak on the 7th day ,then it began to decrease and reached the least on the 28th day.(2) Ninety-six SD rats were randomized into 16Hz, 130dB infrasound exposure group(n=72) and control group(n=24). Rats of the infrasound exposure groups were exposed to 16Hz,130dB infrasound barochamber system, 2h/d for1,7,14 and 21days. Their brains were removed and immunohistochemical method was used to detect the expression of PSA-NCAM in rats'hippocampus on that very day, the 7th day and the 14th day after the treatment.We find the expression of PSA-NCAM in rats'hippocampus increased after exposure for one day, reached its peak at 14 days, decreased at 21 days but remained higher level. After infrasound exposure was ended, the expression of PSA-NCAM in rat hippocampus began to decrease, and reached to the least on the 14th day but still higher than the normal level.So we conclude that the exposure of 16Hz,90dB/130dB infrasound could enhance the expression of Nestin and PSA-NCAM in rats'hippocampus which might participate in the repairment of neural injuries.The expression of Nestin and PSA-NCAM are in positive correlation to the degree of the brain injuries result from infrasound exposure.With the reinforcement of the infrasonic pressure and increacement of the exposure times,the expression of Nestin and PSA-NCAM increase gradually. It reach its peak at 14 days.The proliferous neural stern cells can migrate to the injured region to differentiate new nerve cell. At this time there are more proliferous neural stern cells than ever,we think there are more neural stern cells will differentiate new nerve cells to repair the injured nerves.The expression of Nestin and PSA-NCAM decrease after exposure to infrasound 21 tims,which perhaps due to the improvement of injured nerves. This may be one of reasons for rats'adaption to infrasound.After the infrasonic sound was ended,the expression of Nestin and PSA-NCAM can recover gradually.The reason may be the 16Hz infrasound exposure could enhance the proliferation and migration of neural stem cells in rats'hippocampus,which might participate in the repairment of neural injuries. The experiment expatiate the mechanism of repairment after infrasonic injury,it provide a new thought for infranic prevention and protection.
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