ENKEPHALIN-IMMUNOREACTIVE FASTIGIAL NEURONS IN THE RAT CEREBELLUM PROJECT TO UPPER CERVICAL CORD SEGMENTS

By using enkephalin immunohistochemistry combined with retrograde fluo rescent labelling, a great majority of neurons in the rat cerebellum s ending their axons to the spinal cord were shown to contain enkephalin immunoreactivity. These neurons were numerous and clustered in the fa stigial nucleus but far less abundant in other cerebellar nuclei. Enke phalin-immunoreactive fibers present in the ventral horn and the centr al cervical nucleus of upper cervical cord segments almost completely disappeared contralaterally following kainic acid-induced cell loss in the fastigial nucleus. The results indicate that fastigial and some o ther cerebellar nucleus neurons provide enkephalin-containing projecti ons toward these spinal sites.