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 immunostained with an antiserum against Fos protein. It was shown that the Fos-like immunoreactivity (LI) appeared in some of the neurons, glial cells and endothelial cells in the target area, the white matter surrounding the lateral ventricle, the cerebral cortex and the hippocampus. Three characteristic types of Fos-Li cells were identified in these regions. (1). Only the nuclei 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 that type 1 are the normal responsive cells, type 2 are seriously injured cells, so that the Fos translocation mechanism is damaged, and type 3 represents the intermediate form.