Expression and significance of three types of Fos-immunoreactive cells after gamma knife irradiation of the forebrain in the rat

The expression and significance of three types of Fos-like immunoreactive ( Li) cells were investigated after gamma knife irradiation of the forebrain in the rat. Three months after the irradiation, the brain sections were imm unostained with an antiserum against Fos protein. It was shown that the Fos -like immunoreactivity (LI) appeared in some of the neurons, glial cells an d endothelial cells in the target area, the white matter surrounding the la teral ventricle, the cerebral cortex and the hippocampus. Three characteris tic types of Fos-Li cells were identified in these regions. (1). Only the n uclei of the cells were Fos-ir, (2). Only the cytoplasm was immunostained, and (3). Both the nuclei and the cytoplasm showed Fos-LI. It is suggested t hat type 1 are the normal responsive cells, type 2 are seriously injured ce lls, so that the Fos translocation mechanism is damaged, and type 3 represe nts the intermediate form. (C) 1999 Elsevier Science Ireland Ltd. All right s reserved.