Aquaporin-4 (AQP4) is the most popular water channel protein expressed in brain tissue and plays a very important role in regulating the water balance in and outside of brain parenchyma. To investigate the expression of aquaporin-4 in the rat brain tissue after dexamethasone therapy of meningitis induced by Streptococcus pneumonia, total 40 of 3-week old Sprague-Dawley rats were divided into infection group (n=30) and normal control group (n=10). The meningitis groups were infected with 1×10(7) cfu/ml of Streptococcus pneumoniae and then randomized into no treatment (untreated group, n=10), treatment with ceftriaxone (CTRX group, n=10) and treatment with dexamethasone combined ceftriaxone (CTRX+DEXA group, n=10). The normal control group was established by using saline. The rats were euthanized when they reached terminal illness or five days after infection, followed by detection of AQP4 through using immunohistochemistry and Western blot methods. Data has showed that expression of AQP4 in model group remained higher than the control and treatment group (P<0.05). AQP4 expression in CTRX+DEXA group was lower than that in CTRX group (P<0.05). There was no statistical difference between CTRX+DEXA group and the control group (P>0.05). These data suggested that Dexamethasone could down-regulate the expression of AQP4 in the brain tissue of rats with meningitis and provides evidence for the mechanism of protective effect of Dexamethasone on central neurosystem.

Objective To investigate the expressions of aquaporin 4 (AQP4) in the bacterial meningitis in rats and to explore the molecular mechanism for brain edema caused by bacterial meningitis.Methods Totally 40 of 3-week-old-Sprague-Dawley healthy rats,body weight 60-80 g,male or female,were divided into a normal control group(n =10),and infection groups:24 hours after injection(n =10),48 hours after injection(n =10),and 5 days after injection(n =10).The expressions of AQP4 in the brain were detected by immunohistochemistry and Western blot methods respectively after 24 hours,48 hours,5 days of inoculation.Results Mortality rate:no rats in the control group and the infection group after 24 hours were dead.Two rats in the infection group after 48 hours and 4 rats in the infection group after 5 days were dead because of serious sickness,with the mortality rates 20％ and 40％,respectively.AQP4 expression was slightly positive under light microscope,and the positive cells mainly surrounded glial cells and blood vessels,while neurons were not dyed.Immunohistochemical staining showed that AQP4 expression in the model group increased with the severity of edema;compared with the control group,the AQP4 expression in the brain tissues increased in different periods after rats were infected,and the differences between groups were statistically significant (F--91.84,P ＜ 0.01).Western blot analysis showed that after the brain received streptococcus pneumoniae injection,expression of AQP4 began to increase in 24 hours after streptococcal injection,and reached to the peak in 48 hours,but decreased in 5 days,but the expression still remained higher than that of the normal control group.Each group had statistically significant difference(F =14.23,P ＜ 0.01).Conclusions Expression of AQP4 in the models with bacterial meningitis may increase initially and decrease later.It suggests that AQP4 plays a protective role during the development of infectious brain edema.