| Part ?:Novel-graded traumatic brain injury model in rats induced by closed head impactsObjective: Traumatic brain injury(TBI)can cause various damage to human body,the pathophysiology of mild to severe brain injury are different.Several models of head injury in rodents include fluid percussion impact(FPI),controlled cortical impact systems(CCI)and weight-drop models to simulate and study the etiology and pathological mechanism of TBI.Although these models can mimic some of the pathological features of human TBI,none of the better animal models can be used to reproduce closed head injury(CHI)in humans.The purpose of this study was to change the way of injury and designed to develop a novel graded CHI rat model to simulate brain injury after head impact injury in human environment with pneumatic shock acceleration device which is induced by closed head impacts(CHI)with reproducible brain damage and neurological dysfunction.Methods: A total of 75 male Sprague-Dawley(SD)rats(200 ± 20)g were divided into five groups according to the driving air pressure: Sham Group(n = 15,Sham control);Injury groups:0.50 MPa Group,0.60 MPa Group,0.70 MPa Group and 0.80 MPa Group(n = 15/ Group).The impact force and speed were 785.3 ± 14.12 Newton(N)and 5.71 m/s in Group I,837.72 ± 10.41 N and 6.06 m/s in Group II,857.65 ± 11.11 N and 6.25 m/s in Group III,and 955.6 ± 16.35 N and 6.67 m/s in Group IV,respectively.A custom-made air-driven injury apparatus was used to induce closed head impacts.The kinematic parameters during the procedure were recorded by a force sensor and a high speed camera.Mortality rate,duration of unconsciousness(latency period of righting reflex),modified neurological severity score(mNSS)and whole brain water content(BWC)were examined.Pathological changes were evaluated by hematoxylin-eosin(HE)stain and immunohistochemical stain of amyloid precursor protein(APP).Results: With increasing pressure in the cylinder,the mechanical output also increased,leading to the degree of injury in rats increased.The periods of loss of righting reflex in 0.5,0.6,0.7 and 0.8 MPa Groups were significantly higher than that in Sham Group(P < 0.05).Quantitatively,The mNSS score,BWC and MRI scan data of 0.8 MPa Group remained higher 24 h post-injury was significantly higher than that of the 0.6 MPa and 0.7 MPa groups,but the 0.6 MPa and 0.7 MPa groups were markedly higher than that of the 0.5 MPa group(P < 0.05).Brain damage was indicated by increased APP expression in CHI rats.The increased expression of APP in cerebral cortex,corpus callosum and brainstem in CHI rats was also founded by our detected,which clearly indicated that diffuse axonal injury(DAI)occurred in brain tissue after simulated CHI.So,with the increase of air pressure,the acceleration is greater and the damage is aggravating.Therefore,injuries can be graded according to 0.5 / 0.6-0.7 / 0.8 MPa.Conclusion: The newly developed CHI rat model was a highly controlled and reproducible graded TBI model.The degree of injury caused by CHI is positively correlated with the change of impact velocity caused by the change of pressure.The degree of damage to nerve function can be controlled by adjusting air-pressure.The model provided a useful tool to investigate the underlying mechanism and therape utic effects of TBI with various injury severity.Part ?:Effects of transporting to different altitudes on mild-to-moderate closed head injury after acute high-altitude exposure in ratsBackground: Due to the special geographical environment in the plateau area,the injury and pathophysiological changes after mild-to-moderate closed head injury(mmCHI)following hypobaric and hypoxic at high altitude is not well understood to date.Inappropriate transport after injury could endanger the patients life.This study aims to explore the pathophysiological changes in mmCHI at different altitudes after acute high altitude exposure,and put forward a strategy of transport.So as to improve the success rate of treatment,improve the prognosis,and improve the quality of life.Methods: Healthy male Sprague-Dawley(SD)rats were selected to weigh the base weight in the first place(n = 108).Then,for simulate acute high altitude exposure(6,000 m above sea level),the rats were placed in a decompression chamber and continuous hypobaric hypoxia for 24 hours(h).A rat model of mmCHI was established with pneumatic impact device and the vital signs of injured rats was recorded.Then the rats grouped in different altitudes(6,000 m,4,500 m,3,000 m).The modified neurological severity score(mNSS),body weight(BW),brain water content(BWC)and ratio of brain water content to body weight at 6 h,12 h and 24 h after mmCHI were recorded respectively at corresponding altitudes.Results: After mmCHI,the reduction of mNSS at 6 h was the lowest than at 12 h and 24 h,P < 0.05.The body weight reduced significantly in each group.Among the injury groups,D-3,000 m group decreased least after injury,which was significantly different from those in ND group and D-4,500 m group,P < 0.05.There was no significant difference of BWC in the groups,but the ratio of BWC / BW is the highest was in group of maintained at 6,000 m(ND),and the lowest in groups which descended from 6,000 m to 4,500 m(D-4,500 m).Quantitative analysis showed that the degree of corpus callosum edema and ventricular dilatation of rats in D-4,500 m group were significantly lower than those in other high altitude groups,P < 0.05.Conclusion: The changes of the high altitudes condition following mild to moderate closed head injury at different altitudes within 24 hours were different.We should pay more attention within the first 24 h of mmCHI after acute high-altitude exposure.The patients of mmCHI after acute high altitude exposure can cause sever cerebral edema and body weight loss,which should be managed for appropriate ventilation and airway maintenance and transported at the earliest possible time.Furthermore,avoiding large-span descent altitudewas beneficial to reduce neurological impairment.Dynamic MRI results may have important implications in understanding altitude mmCHI and are translatable to clinical practice.Part ?: GFAP and inflammatory factors changes of transporting to different altitudes on mild-to-moderate closed head injury after acute high-altitude exposure in ratsBackground: The mechanism of immune stress response and secondary brain injury after acute high-altitude exposure mmCHI has not been clarified.Acute hypobaric,hypoxic(AHH)head injury can cause obvious inflammation,which is one of the mechanisms of secondary brain injury.To explore the possible mechanism of the effects in brain injury under the same conditions of traumatic at different hypobaric and hypoxic.On the basis of previous experiments,this study further examined the expression of glial fibrillary acidic protein(GFAP)positive cells and inflammatory factors(TNF-a),interleukin-1?(IL-1?)in brain tissues under different hypobaric and hypoxic conditions after injury.The relationship between inflammation and brain injury in AHH rats at different high altitudes and the regulation of NF-kappa B signaling pathway in inflammatory response were studied.Additionally,the effect of early transport after head injury on the change of injury and the underlying mechanism of secondary brain injury were further discussed in this study.Methods: Eighteen healthy SD rats were hypobaric and hypoxic treated at simulate altitude of 6,000 m for 24 hours.The model of mild-to-moderate closed head impact injury was established by pneumatic impact device.The injury rats were randomly divided into three groups according to altitude [ 6,000 m(ND),4,500 m(D-4,500 m),3,000 m(D-3,000 m),(n = 6 / group)].ND group as a positive control Group.Then,the rats were placed in the decompression chamber where they were allowed free access to chow and water.Rats were sacrificed 24 h after the injury under deep anesthesia for further processing.The brain tissue was taken out and subjected to glial fibrillary acidic protein(GFAP)immunofluorescence staining,and we performed western blot to analyze the tumor necrosisfactor-?(TNF-?),interleukins-1?(IL-1?)and nuclear transcription factor-?B(NF-?B).Results: The GFAP-positive astrocytes and inflammatory factors in the brain tissue of rats in each group increased significantly at 24 h after acute hypobaric and hypoxic brain injury.Quantitatively,D-4,500 m and D-3,000 m administration significantly reduced IL-1? and TNF-? levels compared with ND treatment(IL-1?/GAPDH: 0.69 ± 0.07 or 0.78 ± 0.08 vs.1.00 ± 0.09,P < 0.05;TNF-?/GAPDH: 0.72 ± 0.06 or 0.84 ± 0.08 vs.1.00 ± 0.10,P < 0.05).Additionally,IL-1? and TNF-? levels were lower in the group D-4,500 m than in the group D-3,000 m,P < 0.05.Next,we determined nuclear factor-kappaB(NF-?B)activation at 24 h after mmCHI to elucidate the mechanisms responsible for the effects of transporting to different altitudes.D-4,500 m and D-3,000 m administration significantly reduced phospho-p65 and p65 levels compared with ND treatment(phospho-p65/GAPDH: 0.62 ± 0.06 or 0.76 ± 0.07 vs.1.00 ± 0.09,P < 0.05;p65/GAPDH: 0.48 ± 0.05 or 0.78 ± 0.08 vs.1.00 ± 0.10,P < 0.05).Additionally,phospho-p65 and p65 levels were lower in the group D-4,500 m than in the group D-3,000 m,P < 0.05.Conclusion: GFAP can be used as one of the markers to diagnose the severity of mmCHI and to guide the clinical in the post-traumatic transport at high-altitude.The activation of NF-?B after hypobaric and hypoxic brain injury is involved in the regulation of inflammatory factors IL-1? and TNF-?,which was related to the secondary brain injury.Inhibition or activation of NF-?B is related to hypobaric and hypoxic state.Regulation of hypobaric and hypoxic state have a great benefit to reduce the secondary brain injury after high altitude head injury. |
PDF Full Text Request