Early changes of aquaporin-4 in the cortex of rats following whole brain irradiation

Objective: To investigate the early changes of aquaporin-4 (AQP4) expression in the cortex of rats following whole brain irradiation and its role in the early phase irradiation-induced brain injury. Methods: 100 male Sprague-Dawley rats were randomly divided into sham-irradiation group, and irradiation group. One day, 1 week and 1 month after whole brain irradiation of these rats with a single-dose of 2, 10 and 30 Gy by 4 MeV electron beam. Tissue microarray of radiation-induced brain injury, in rats was constructed and AQP4 expression in the cortex was examined by immunohisto-chemical method. Results: Compared with the sham-irradiation group, AQP4 expression in the cortex of rats in the 2 Gy group showed no obvious change. However, AQP4 expression in 10 Gy and 30 Gy groups decreased quickly in D1 post-radiation and reached the lowest point one week post-radiation. Then, it increased slowly and the level of AQP4 expression in M1 was obviously higher than those of the sham-irradiation group (P<0.05). AQP4 expression lowered in a manner of dose-dependent after whole brain irradiation and reached the lowest point at 30 Gy. Conclusions: Aquaporin-4 expression in the rat cortex changed at in a time-and-dose-dependent manner after whole brain irradiation. After irradiation, the lowered AQP4 expression is a protective response to blood-brain barrier, as it could reduce cerebral edema. (authors)