| People are often exposed to high G environment in aerospace activities. Sometimesthe G values they are subjected to may be even more than 10G. Can otolith organs not be damaged and work properly in this environment? The answer to this question is critical to solve the problems such as vertigo, spatial disorientation, space adaptation syndrome(SAS) etc.In this work, guinea pigs' vestibular disorders, the ultrastructure of the macula, the apoptosis cells, the expression of HSP70 mRNA, cytokeratin and actin in macula of the utricle, and the ChAT activities in VNC(vestibular necleon complex)were observed after they were exposed to +10Gy for 5mia A countermeasure of 8 days pre-habituation in 2G force-field was also tested. The results are as follows:1. Abnormalities of behavior, vestibule-spinal reflex (VSR) and vestibule-ocularreflex (VOR) were found in 22/28 of the guinea pigs after exposed to +10Gy for 5min(+10Gy group), which included head tremble, head deviation, spontaneous nystagmus, eye deviation, body roll and looping. All the symptoms disappeared within 30 rain. Among them, head tremble was of the highest incidence. In the group which was exposed to 2G environment for 8 days before being exposed to 10Gy(habituation group), only 14/28 showed vestibular disorders, which was statistically significant lower compared with that of +10Gy group.2. In +10Gy group, 0.5h later after lOGy exposure, two kinds of otoconia ultrastructure changes were observed: ヾisappearance of the otoconia and appearance of its precursor 棗global substance; ヾegeneration and fusion of the otoconia, including the disappearance of its classical prism-like structure and fusing into a larger one. 24h later, the incrassation of the utricle macula was prominent, and large dumb-bell shaped immature otoconia were observed in a high-power view. In habituation group, emergence of flaws and porous of otoconia were observed 0. 5h and 24h later respectively after lOGy exposure. Conglutination and sloping of the hair cell cilia were observed in both +10Gy group and habituation group. By using transmission electron microscope(TEM), plasmolysis and cell nucleus condensation were observed prominent in +10Gy group, while in habituation group, only a few cells showed cell nucleus condensation. By using HE staining method, both groups showed the cell swelling and vacuolation. The differences in ultrastructure changes between right and left utricles were non-significant.3. By using a TUNEL(terminal-deoxynucleotidyl transferase mediated d~LTP nick end labeling) method, The apoptosis hair cells were detected in both T10Gy and habituation groups, but absent in control group.4. The expression of HSP70 (by in situ hybridization methods) in habituation group is the strongest, +10Gy group was the second, and the control group was the weakest.5. No significant differences of expression of cytokeratin in macula were foundamong +10Gy, habituation and control groups by inmunohistochemistry technique. Negative reaction of actin was observed among above three groups.6.The ChAT(choHne acetytransferase) activities in VNC in brain stem were investigated by immunohistochemistry technique. The relative gamma of staining showed that the content of ChAT in VNC of the +lOGy group and habituated group were significant higher than that in control group, but no significant differences were found between the +10Gy and habituation groups.7. The precursor of otoconia global substance can be generated from both supporting cells and type I hair cells.According to the results, the following points may contribute to the mechanism of high G induced vestibular disorders: ?the otoconia displacement and/or its metabolic disorder, which was caused by high G induced damage of conjunction between the otoconia layer and gelatin layer;@under high G environment, the inefficiency of cardiopulmonary system, reduction in blood oxygen saturation, and metabolic disorder of energy in related tissues were another reason causing behavior abnormalities;?the hi...
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