Expression of the raf protooncogene in glial cells of the adult rat cerebral cortex, brain stem and spinal cord.

The raf protooncogenes encode cytoplasmic serine/threonine-specific protein kinases which can be activated from different growth factor receptors by phosphorylation. Our previous immunohistochemical studies proved that raf kinases are present in neurons of the mammalian central nervous system. The present study describes the immunohistochemical localization of raf kinases in glia-like cells of the rat cerebral cortex, spinal cord and brain stem. Small glia-like cells measuring 8-12 microns were observed in the neocortex, the entorhinal and prepiriform allocortical areas and the subcortical white matter. In the hippocampus, the immunoreactive cells were most numerous in the fimbria, the alveus and the molecular layer of the dentate fascia. Ultrastructural studies following preembedding immunohistochemistry revealed that in the cerebral cortex only astrocytes contained raf-protein-like immunoreactivity. Our immunofluorescence studies showed, that the white matter of the spinal cord, the pyramids of the medulla and the basis of the pons contained small glia-like cells, too. No electron microscopic investigations were performed, but the location (white matter tracts) and size (6-12 microns) of these cells suggested their glial nature. On the basis of data from other cell systems we expect that raf kinases participate in growth factor- and cytokine-regulated glial functions of the mammalian central nervous system.