PROTEIN-KINASE-C IN CENTRAL VESTIBULAR, CEREBELLAR, AND PRECEREBELLARPATHWAYS OF THE RAT

The protein kinase C family of enzymes is composed of at least ten dif ferent isoforms that display a variety of distinct biochemical specifi cities. Many of these isoforms are highly expressed in brain, and some show regional specificity in their distribution, suggesting that they may serve specific functions. By using immunocytochemistry to localiz e the beta I, beta II, gamma, or delta isoforms of protein kinase C in the central vestibular system of the adult rat, we found the vestibul ar ganglion and its peripheral and central processes of the eighth ner ve to be heavily labeled with protein kinase C beta I immunoreactivity . Labeled axons and terminals were also found in all four vestibular n uclei. Some neurons of the vestibular ganglion were weakly stained wit h the antibody to protein kinase C beta II, as were scattered axons in the eighth nerve, and scattered axons and terminals were found in all four vestibular nuclei among weakly labeled neurons. A few axons in t he vestibular portion of the eighth nerve were labeled with protein ki nase C gamma immunoreactivity, and neurons of the spinal, lateral, and superior vestibular nuclei were heavily decorated with synapses, pres umably derived from Purkinje neurons, which were also strongly immunor eactive. Neurons of the medial vestibular nucleus were not as heavily innervated. With the antibody to protein kinase C delta, we found scat tered, weakly immunoreactive neurons in the vestibular portion of the eighth nerve. Myelinated fiber bundles of the spinal vestibular nucleu s contained moderate numbers of labeled axons, and the other vestibula r nuclei were well innervated by protein kinase C delta axons and term inals. Most of these probably derive from Purkinje cells, which were l abeled in longitudinal bands interspersed with bands of labeled basket cells. These data suggest that particular protein kinase C isoforms p lay specific roles in vestibular and cerebellar function. (C) 1997 Wil ey-Liss, Inc.