The Early Reaction Of Neuron And Glia In The Brain Of The Linear Accelerator_irradiated Rats--Immunohistochemical Study Of Fos And S-100 Protein

Radiotherapy to tumors is a sort of local treatment similar to operation, which focuses the radioactive rays on the target to the greatest extent so as to destruct it, whereas surrounding regions are not to be injured. Among all sorts of radiotherapy equipments, linear accelerator fundamentally takes use of electronics rays and X-rays to treat an illness. After several decades' improvement in technology and accumulated experience in clinical use, more and more intracranial tumors have been treated with this unit, but the detailed mechanisms are not understood about its neuroradiobiological effects, especially the early or acute damage and time-dependent changes of neural cells in the target and surrounding brain regions. The present studies aimed to find the responses of neurons and glias in the target and other brain areas of the linear accelerator-irradiated rats. In the first experiment, time-dependent neuronschanges in the brain after hemispheric irradiation at an single-fraction maximal dose of 20 Gy were observed by investigating the expression of an immediate early gene, Fos protein. The results shown: Compared with that of the un-radiated rats, the expression of Fos protein in the irradiated brain decreased distinctly 24 hours and 1 week after irradiation. However, the quantity of Fos immuno-positive cells increased gradually afterwards. At four weeks after radiation, expression of Fos protein recovered progressively in medulla oblongata and pons, in which Fos immuno-positive cells were more than those in control group. In contrast, expression level of Fos protein in mesencephalon, diencephalons or telencephalon was still less compared with that of the un-irradiated rats. The above results suggested that the neuronal activity may be inhibited in certain nuclei of the rat brain in early stages after hemisphere irradiation, and this inhibitory phenomenon was more obviously in higher neural centers. On the basis of these results, time-dependent glias changes in the brain were observed with the same model by investigating the expression of S-100 protein, a specific marker for glias, mainly for astrocytes. Our results shown: Compared with those of the unradiated rats, the number of S-100 protein immunoreactive positive glial cells in the brains of the irradiated rats increased gradually. More S-100-positive glial cells with multiple long processes and hypertrophic cell bodies were also observed in these areas. Our results indicated that: Since S-100 protein is a sensitive functional marker for astrocytes, the increased expression of S-100 protein suggest that astrocytes may be involved in the pathological processes of the ion-radiation injury of brain and neural-hormone reaction of the rat.