Axoplasmic Flow in Cerebellar Mossy and Climbing Fibers

Abstract

Tritiated leucine was injected unilaterally into pontine, inferior olivary, or reticular nuclei of cat brainstem to establish sources of cerebellar mossy and climbing terminals. Allowing 24 to 72 hours for label uptake and active transport by axoplasmic flow to cerebellar cortex, autoradiographs were prepared with the use of parasagittal sections from both sides. Larger volumes (1μI to 5μI) were injected initially to facilitate identification of labeled terminals. Thereafter, smaller volumes were used to obtain more discrete and reliable results. Several types of control eliminated alternative routes of transport. Both inferior olive and pontine nuclei were shown to be sources of contralaterally labeled mossy and climbing terminals, the former somewhat more numerous in pontine injections, the latter significantly so in olivary ones. Reticular sites prinicipally showed climbing terminals. Labeled terminals were also seen homolaterally to the injection, but much less frequently than contralaterally.