Ionizing radiation as one of the strongest cytogenetic factors can induce significant injury to adult brain. In the present study, adult male Wistar rats were exposed to single whole-body gamma irradiation with the dose of 3 Gy. One, 5, 10, 25, 40 or 80 days after irradiation, proliferating cells were labelled using BrdU immunohistochemistry. BrdU-positive cells were counted individually in the three anatomical parts of the brain RMS: the vertical arm, elbow, and horizontal arm. The number of BrdU+ cells decreased rapidly during the 1st day after exposure in the whole extent of the RMS. In course of the following days, considerable increase was observed in the elbow and vertical arm of the RMS with the maximal values on the 5th and 10th days, respectively; until the 40th day after irradiation, the numbers of BrdU+ cells returned to the control level. Contrary to the two previous parts of the RMS, in the horizontal arm, no statistically significant increase was found and the decrease under control values occurred at the longest survival time. Our results suggest that the whole-body irradiation of rats with the sublethal dose of gamma irradiation can induce acute as well as long-lasting changes in the brain regions where proliferation activity is retained during adulthood.