CENTRAL AND PERIPHERAL MYELIN IN THE RAT COCHLEAR AND VESTIBULAR NERVES

In the bipolar neurons of vertebrate cochlear and vestibular nerves, t he myelin envelops without interruption the axon, the perikaryon and t he dendrite. The perikaryal myelin is thin and partially loose, wherea s axon and dendrite are enveloped by compacted myelin. The expression of protein 0 and myelin basic protein, constituents of peripheral and central myelin respectively, has been investigated in the rat by an im munohistochemical study at the light microscopic level. Our data indic ate that both in the cochlear and vestibular nerves the myelin of the perikaryon and dendrite is composed by specific peripheral myelin prot eins. The axon segment between the perikaryon and the transitional zon e expresses peripheral myelin proteins in the cochlear nerve, while bo th types of myelin proteins are present in the vestibular nerve. Betwe en the transitional zone and the brainstem the myelin of the axon is e xclusively of the central type. The peripheral-central myelin transiti onal zone is in close proximity to the axonal pole in the vestibular g anglion cells, while in the cochlear nerve it is near the spiral foram ina, at variable distance from the axonal pole of ganglion cells. (C) 1996 Elsevier Science ireland Ltd.