| Dysbaric injury, including Decompression sickness (DCS) and Barotrauma, is referred to the injury induced by unsafe hyperbaric exposure. The central nerve damage resulted from unsafe hyperbaric exposure is to conduced dysfunction of central nerve system which always become the fatal cause in chief. Unsafe hyperbaric exposure is known to affect the cerebral haemorheology of animal, impair the capillary blood vessel and brain tissue around, and aggregate the activated and proliferous microglia. Microglias, which are known to represent an intrinsic immune system of the CNS, are able to be activated in almost all brain pathologies. They are also the main source of neurotoxic factors such as tumor necrosis factor-alpha (TNF-α). A special kind of matrix metalloproteinase (MMPs), TNF-α converting enzyme (TACE, also called ADAM-17). which could distinctively hydrolyze membrane-type TNF-α (mTNF-α). participate in the releasing procedure of solute TNF-α (sTNF-α). The latter is one of the important substances to inducing neuron apoptosis. Now the main measures used to treat dysbaric injury are including Hyperbaric Oxygenation (HBO) and recompression therapy. But there is obvious insufficiency in dealing with special dysbaric injury (such as that induced by unsafe fast decompressing from deep depth) and those sufferers always unlucky to the remedy in time. The present researches were to profoundly study the underlaid mechanism of microglia participating in central nerve injury induced by fast decompressing and the effects of HBO in order to find new way to decrease neuron lose and attain new knowledge helpful to improve thetreatment of dysbaric injury in CNS induced by unsafe fast decompression.Methods:In this study, semi-quantification of activated microglia was carried out 6h, 24h, 48h, and 72h after the rat model of dysbaric central nerve injury induced by unsafe fast decompressing (FD) from l.OMPa. HBO treatment was inducted in 6h after injury, distribution of TNF-a and TACE in central nerve tissue were detected with the immunohistochemical (IHC) method; neuron apoptosis was manifested by TdT-mediated dUTP nick end labeling (TUNEL) reaction; concentration of TNF-a in tissue and bioactivity of sTNF-a in cerebrospinal fluid (CSF) were determined separately with sandwich enzyme-linked immunosorbent assay (ELISA) kit and L929 cell cytotoxicity bioassay. In the primary culture of neonate Sprague-Dawley rats' cortex, purity of microglia was assayed by flow cytometry with FITC linked Isolectin-B4 (IB4). CSF obtained from in vivo experiment was used as conditional media. The density changes of mTNF-a and TACE on the membrane of microglia were determined with flow cytometry assay; the bioactivity of sTNF-a was detected with bioassay; and Real-time PCR method was used to quantitate the gene expression of TNF-a and TACE.Main results:1. There were diffused tissue structure breakage and necrosis focus, as well as classical infracted focus of cerebral artery embolism. The apoptosis index and TNF- a concentration of spinal cord were high than that of brain (P<0.05 or P<0.01).2. Activated microglia (IB4 immunopositive) appeared in rats' CNS 6h after FD treatment. Its amount get to the peak in 24h (P<0.01), and declined later. Activated microglias were distributed mainly to spinal cord gray matter, pallium and hippocampus. Their morphology was ramified,cycloid, elliptic and amoeboid.3. The apoptosis indexes of CNS At 24h post injury were significantly higher than that at 6h (P<0.01), then get to the peak at 48h (P<0.01), then declined at 72h (P<0.01). The apoptosis cells were observed in the gray matter of spinal cord, pallium, and hippocampus, especially around the infracted focus and the periphery of gray matter of spinal cord. From the morphology, the apoptosis cells were supposed to be neuron. The distribution of neuron apoptosis was same as that of activated microglia. But the time course of appearance and peak were laggard than that of activated microglia. And its change was positive correlated to that of activated microglia (r=0.645, P<0.01).4. The concentration of TNF-a was detected in brain and spinal cord of FD 6h group, increased at 24h (P<0.05), peak at 48h (P<0.01). the change trend of TNF-a bioactivity in CSF of FD group was similar to that of TNF-a concentrations in tissues. The IHC results showed that, TNF-a and TACE immunopositive cell had the same morphology of IB4 immunopositive cells, and same distribution, content of TNF-a in tissues were correlated with IB4 positive cells (r=0.453, P<0.05) and apoptosis index(r=0.822, P<0.05).5. HBO treatment significantly decreased IB4 positive cells in 24h, 48h, and 72h (P<0.01, P<0.05); brought lower the apoptosis index in 48h and 72h (P<0.01, P<0.05); lessened the immunoreaction of TNF-a and TACE in CNS tissue(P<0.01, P<0.05); reduced the concentration of TNF-a in tissue and cytotoxicity in CSF(P<0.01, P<0.05).6. The cytotoxicity of TNF-a in supernatant of microglia co-cultured with conditional media of CSF obtained from FD-treated rats (FD-CM) was significantly increased (P<0.01), while added TACE blocker (GM6001) declined it remarkably (P<0.01 vs control, P<0.01 vs FD-CM). The cytotoxicity of TNF-a in supernatant of microglia co-cultured with HBO-CM was increased too (P<0.05 vs control)., but lower than that of FD-CM, while added GM6001 declined more (P<0.05 vs single HBO-CM,...
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