acta histochem. 102, 203±217 (2000) Ó Urban&FischerVerlag Neuronal expression of Raf protooncogene in the brain stem of adult guinea pig Andra ÂsMiha Âly 1 andVale ÂriaEndre Âsz 2 1 Departments of Anatomy and 2 Microbiology, Albert Szent-Gyo Èrgyi Health Science Center, Faculty of Medicine, University of Szeged, Szeged, Hungary Received3October1999andinrevisedform10January2000;accepted15January2000 Summary The Raf protooncogenes encode for cytoplasmic serine/threonine-specific pro- tein kinases which can be activated via growth factor receptors by phosphory- lation. Immunohistochemical and Western blotting studies have proven the ex- istence 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 immunohistochem- ical 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 blot- ting 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 nu- cleus, 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 im- munoreactive cells. In general, staining was mainly somatodendritic; the axo- nal plexus was not positive. It is concluded, that the widespread neuronal ap- pearance of cytoplasmic Raf kinase suggests an important role in transmission of trophic and growth factor signals in these neurons. Correspondence to: Prof. Dr. A. Miha Âly, Department of Anatomy, Faculty of Medicine, University of Szeged,P.O.Box427,H-6701Szeged,Hungary,tel:+36-62-545-665,fax:+36-62-420-584, e-mail:mihaly@anat-fm.szote.u-szeged.hu http://www.urbanfischer.de/journals/actahist 0065±1281/00/102/2±203$12.00/0