Regeneration of the cerebellofugal projection after transection of the superior cerebellar peduncle in kittens: morphological and electrophysiological studies.

In contrast to the current concept of abortive regeneration of mammalian central axons, occurrence of marked, functionally active regeneration of the cerebellofugal projection was proved in kittens after complete transection of the decussation of the brachium conjunctivum (BCX). By means of the anterograde axonal transport of horseradish peroxidase that was injected into the cerebellar lateral and interpositus nuclei, the origin, course, and destination of the regenerated fibers were identified unambiguously and the time-course of axonal regeneration was clarified. Functional connectivity of the regenerated cerebellothalamic projection was tested electrophysiologically. In eight out 82 animals, marked regeneration of the cerebellofugal projection occurred; in the majority of the rest of the animals, trace amounts of regenerated fibers were observed. In the former but not in the latter animals, marked cerebellocerebral responses, as in intact animals, were evoked in the frontal motor and parietal association cortices. Most of the regenerated axons took a course similar to that of the normal projection and terminated in the normal projection areas, whereas a small proportion of fibers showed an aberrant course and termination. The cut ends of axons began to swell as early as 15 minutes after transection, and the regenerated axons produced dense terminals in the thalamus by 19 days.