| Objective: Diffuse axonal injury (DAI) is also called diffuse alba injury, with the feature of wide-spread degeneration in the white matter of brain evoked by either the shear or tensile forces generated by the injury. DAI can occur itself or concomitantly with other head injury. It is considerded to be the most common cause of coma without haematoma, nervous functional impairment or vegetative state after traumatic brain injury. It is reported that 80% of craniocerebral injury induced by traffic accident and 50% severe craniocerebral injury,even one third of fatality provoked by head injury all related to DAI. Therefore, DAI usually results in high handicap rate and high mortality rate. Moreover, there is no effective examination can be used as a marker to diagnosis DAI in the clinical practice. In addition, DAI can lead to kinds of complications, such as dysnoesia, epilepsia, sensory disability, adrenergic nerve system disturbance, et al. The identification of DAI has been a tough problem in postmortem examinations of forensic medicine.Some researches indicated that the functional disturbance induced by DAI was evoked by the shear or tensile forces generated by the primary injury, but also caused by the "seconndary attack",or neuron seconndary injury,happened in the following time after the injury. In our previous study, we have found that quantity of microglia were activated after DAI. But the factors participated in the activation of microglia, even its feature have not be identified. It is essential to take further research to explore the effect of inflammatory factor mediated by microglia in the seconndary injury.Our present study will detect some inflammatory factors from an injury model according to Marmarou A et al. reported in 1994, such as IL-1β,TNF-αand IFN-γ,also the distribution of activated microglia will observed, to explore the effect of inflammatory on neurons and axons in central nervous system (CNS), furthermore, in order to provide experimental evidence and diagnosis of DAI for the practice of forensic medcine, also the treatment of DAI in clinical medicine.Methods: Sprague-Dawley rats (weight: 260±21g) were randomly divided into eleven groups: normal control group(N), sham group(S), injured group including different phase after injury: 30min, 1h, 3h, 6h, 12h, 24h, 48h, 72h, and 7days. DAI model in Sprague-Dawley rats was induced by an injury model established by Marmarou A et al.Normal control group rats gave no disposal; Sham group rats were subjected to the same conditions including placing the animals under the impactor but without batting. After general anaesthesia by Chloral Hydrate, rats were transcardially perfused with paraform, brain was carefully removed and paraffin imbedded, the morphological changes of neural and axonal injury were observed under microscopy by HE staining, thionine staining, silver impregnation technique,and then detect the expression of IL-1β,TNF-αand IFN-γby immuno- histochemical staining .The data were presented as Mean±SD and analyzed with ANOVA and LSD by SPSS statistical program. A level of P<0.05 was considered to be significant.Results: 1 Estabished animal model of DAI: the damage of brainstem was most severe by HE staining observation. And then by sect serial sections of brainstem, pink shrunken neurons were further studied by Gless'silver staining, found that varicose axons, waving axons and retraction balls were obvious. In addition, the extent was related to the degree of damage.2 The result of immunostaining forβ-APP: There was low expression ofβ-APP in normal and sham control group. Varicose axons, waving axons and retraction balls were detected byβ-APP at 30min~6h postinjury in corpus callosum and brain stem. The number and diameter of positive axons increased and achieved peak at 48h and 72h postinjury, microglia were gathered around the varicose axons.3 There was low expression of IL-1β, TNF-α,IFN-γin normal and sham control group, but the positive neuron and microglia increased at 30min postinjury, and got the peak at 6h postinjury. After that, the expression of IL-1βdecreased, and reached the lowest level at 24h postinjury, but re-increased again at 48h postinjury at following time, even get a high level at 72h postinjury. And then, the positive neuron and microglia decreased to a low level at 7d postinjury, but still significant different from normal and sham control group.Conclusions:DAI model in Sprague-Dawley rats was successfully established with high reproducibility, which could be used for the further study of DAI. With the extension of injury time, We had observed the expression of IL-1β, TNF-α, IFN-γin brain stem neurons and microglia. Conclusively, inflammatory induced by microglia plays an important role in the seconndary injury after DAI.
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