Neuronal expression of Raf protooncogene in the brain stem of adult guinea pig

Abstract

The Raf protooncogenes encode for cytoplasmic serine/threonine-specific protein kinases which can be activated via growth factor receptors by phosphorylation. Immunohistochemical and Western blotting studies have proven the existence of Raf protein kinases in neurons of the cerebral cortex of rats and guinea pigs. The aim of the present study was to map the immunohistochemical distribution of Raf kinase-like staining in the brain stem of guinea pig. Polyclonal antibodies were used that were raised against a recombinant viral protein in combination with the avidin-biotin-peroxidase system for detection of immunoreactivity. Specificity of the antibodies was tested in Western blotting experiments. Cytoplasmic immunostaining was observed in motor nuclei of hypoglossal, accessory, vagus, facial, trigeminal, abducent, oculomotor and trochlear nerves, and in the nucleus ambiguus, nucleus retroambigualis, lateral vestibular nucleus, mesencephalic nucleus of the trigeminal nerve, the red nucleus, raphe nuclei and reticular formation. Scattered neurons were stained in other sensory nuclei, such as solitary tract nuclei, medial, dorsal and ventral vestibular nuclei and cochlear nuclei. The spinal trigeminal nucleus and the main sensory nucleus of the trigeminal nerve contained few medium-sized immunoreactive cells. In general, staining was mainly somatodendritic; the axonal plexus was not positive. It is concluded, that the widespread neuronal appearance of cytoplasmic Raf kinase suggests an important role in transmission of trophic and growth factor signals in these neurons.