Effective Of Different Doses Of Dexamthasone On AQP4 Expression After Fluid Percussion Injury In Rats

PartⅠThe relationship between the expression of AQP4 and nerve function scores after fluid percussion injuryObjective: To establish animal model of fluid percussion injury and explore the relationship between AQP4 and nerve function scores in ratsMethods:Adult male Sprague-Dawley rats (250–350g) were used in this study. The rats were randomly divided into three exerimental groups: NC group(n=4),sham group(n=4),TBI group(n=48).The TBI group was also randomly divided into three exerimental sub-groups according to the time points of sacrifice such as 1h, 6h, 12h, 24h, 3d and 7d after injury. We established the fluid percussion model following documents. Sham-operated rats were anesthetized and surgically prepared in the exact same manner, but did not receive FPI brain injury. NC group did not accepted any treatment.Under 10%cholralhydrate anesthesia, the group of NC and SO was killed by decapitation after injury,TBI group was disposeded with same way at 1h, 6h, 12h, 24h, 3d and 7d after injury.The histology was detected by HE staining, the expression of AQP4 was detected by immunohistochemical and western blot. The brain water content (BWC) was measured by Wet–Dry Method in each group.Results:1 After fluid percussion injury, the rats immediately appeared grasp hole forelimb flexion, and increased muscle tone, vertical hair, and there may be apnea duration of about (15±2)s. Followed by coma, reflecting weakened. Conscious spiritual malaise and reduced activities existed. 2 Neurological score: The Neurological score of TBI group increased from 1h, showed inflection point in the 12h after injury,and then began to reduce at 24^th h, lasted to 3^rd day, increased from 3^rd day, and nearly returned to normal level at 7^th day .3 Histological observation: cellular edema in lesions around the TPI can be seen at 6h after the injury. Brain edema at 12h after injury became much severe than before. At 24h after injury, edema further expanded the scope and depth from the damage to the white paper around the development of lesions, and edema reached peak. The edema can be observed at 3d after injury, but was lower than that at 24h and the proliferation of glial cells was highter than obvious; At 7d after injury, edema nearly disppeared and glial cell proliferation was still evident.4 The water content: the water content of TBI group increased from 6h(79.21±1.09%), reached its peak at 24^th h (82.19±0.97%), lasted to 3^rd day (81.74±1.69%), and then began to reduce, nearly to normal level at 7^th day (80.45±0.7%) .5 Immunohistochemical analysis: The expression of AQP4 increased in TBI model group from 6h (0.1738±0.076), reached its peak at 24^th h(0.1912±0.085), lasted to 3^rd day (0.1788±0.099), and then began to reduce, nearly to normal level at 7^th day .6 Western Blot: The expression of AQP4 increased from 6h (0.3896±0.098), reached its peak at 24^th h(0.7211±0.0784) ,lasted to 3^rd day (0.5617±0.0726), and then began to reduce,nearly to normal level at 7^th day .7 Relativity: Neurological score from 12h to 7d after injury has a negative correlationship with brain water content (r=-0.615,P<0.001), and a correlationship with AQP4 expression (r=-0.605,P<0.05).The water content has a positive correlationship with AQP4 expression.Conclusion:The neurological dysfunction has a corralationship with secondary brain edema in models of the fluid percussion injury, and brain edema mediated by AQP4 aggravates neurological dysfunction. PartⅡEffect of different doses dexamthasone on AQP4 of the brain edema from fluid percussion injury in ratsObjective: The different doses of dexamethasone were employed to treat rat models of fluid percussion brain injury. AQP4 protein and its mRNA were examined by immunohistochemistry, Western Blot and RT-PCR, to explore effect of different doses dexamthasone on AQP4 of the brain edema and to search the best dose for clinic use.Methods:Adult male Sprague-Dawley rats (250–350 g) were used in this study. The rats were randomly divided into six exerimental groups:D0 group(n=48), D1 group(n=48), D2 group(n=48), D4 group(n=48), sham group(n=4) and saline group(n=4).The former four groups were also randomly divided into six sub-groups according to the time points of sacrifice such as 1h, 6h, 12h, 24h, 3d and 7d after injury. Sham-operated rats were anesthetized and surgically prepared in the exact same manner, but did not receive FPI brain injury. NC group did not accepted any treatment.Animals from D1,D2,D4 groups received an intraperitoneal (IP) injection of dexamethasone with 2 times every day. The dose was 1mg/kg(D1), 2mg/kg(D2), 4mg/kg(D4). Immunohistochemical, Western Blot and RT-PCT was used to analysis of AQP4 protein and mRNA. The brain water content (BWC) was measured by Wet–Dry Method.Results:1 The neurological score: D0 group decreased compared with the sham group(P<0.05). The neurological score of D0 group decreased significantly compared with D1,D2,D4 group,the neurological score difference between D0 group and D1,D2,D4 group was statistically significant (P<0.05). 2 Histological observation: Compared with D0 group, the extent and scope of the brain edema in D1or D2 or D4 group was reduced, and the swelling of glial cells and the gap around neuron also reduced.3 The brain water content: There was no significantly difference in the 1^thh between B0 group and sham operated group (P>0.05). Compared with sham operated group, the water content of D0 group increased from 6h(79.36±1.09%), reached its peak at 24^th h(82.19±0.97%), lasted to 3^rd day(81.74±1.69%), and then began to reduce, nearly return to normal level at 7^th day (80.45±0.7%). Compared with D0 group at the corresponding time points, the difference of water content in D1,D2 and D4 group was statistically significant (P<0.05).4 Immunohistochemical, RT-PCR, Western blot: Compared with sham operated group, AQP4 and its mRNA expression increased in D0 group from 6^th h, reached its peak at 24^th h, lasted to 3^rd day, and then began to reduce at 7^th day, when AQP4 expression was still higher than that of saline group. Compared with D0 group at the corresponding time points, the difference of AQP4 and its mRNA in D1,D2 and D4 group was statistically significant (P<0.05).Conclusion:1 Dexamethasone can reduce brain edema from fluid percussion brain injury by inhibiting AQP4mRNA and protein.2 The effect of dexamethasone on brain edema and AQP4 does not depent on its dose, and so low dose of dexamethasone is recommended in early stage with short-term.