Neuronal expression of Raf protooncogene in the brain stem of adult guineapig

The Raf protooncogenes encode for cytoplasmic serine/threonine-specific pro tein kinases which can be activated via growth factor receptors by phosphor ylation. Immunohistochemical and Western blotting studies have proven the e xistence of Raf protein kinases in neurons of the cerebral cortex of rats a nd guinea pigs. The aim of the present study was to map the immunohistochem ical distribution of Raf kinase-like staining in the brain stem of guinea p ig. Polyclonal antibodies were used that were raised against a recombinant viral protein in combination with the avidin-biotin-peroxidase system for d etection of immunoreactivity. Specificity of the antibodies was tested in W estern blotting experiments. Cytoplasmic immunostaining was observed in mot or nuclei of hypoglossal, accessory, vagus, facial, trigeminal, abducent, o culomotor and trochlear nerves, and in the nucleus ambiguus, nucleus retroa mbigualis, lateral vestibular nucleus, mesencephalic nucleus of the trigemi nal nerve, the red nucleus, raphe nuclei and reticular formation. Scattered neurons were stained in other sensory nuclei, such as solitary tract nucle i, medial, dorsal and ventral vestibular nuclei and cochlear nuclei. The sp inal trigeminal nucleus and the main sensory nucleus of the trigeminal nerv e contained few medium-sized immunoreactive cells. In general, staining was mainly somatodendritic; the axonal plexus was not positive. It is conclude d, that the widespread neuronal appearance of cytoplasmic Raf kinase sugges ts an important role in transmission of trophic and growth factor signals i n these neurons.