Prepositus hypoglossi neurons projecting to the posterior vermis of the rat cerebellum

Distribution of efferent neurons projecting to the posterior vermal lobules of the rat cerebellum was studied in the prepositus hypoglossi nucleus (PRH) and the nucleus of Roller (R) by retrograde labeling with wheat germ agglutinin-horseradish peroxidase (WGA-HRP). After a single injection of the tracer into each lobule of the anterior (lobule V) and posterior vermis (Lobules VI-IX), medium-sized to small neurons in the caudal half of the PRH and in the R were labeled. An abundance of labeled neurons were found after WGA-HRP infection into either lobule IX or VII, but were less numerous following injection into lobule VIII. Retrograde double labeling with fluorescent dyes showed that a considerable number of neurons in the caudal part of the PRH and in the R sent divergent axons to vermal lobule IX and the parafloccular lobe of the cerebellar hemisphere. Following retrograde neuronal labeling combined with immunohistochemistry, about 70% of the corticotropin releasing factor (CFR)-like immunopositive neurons which clustered in the caudal half of the PRH were found to project their axons to the posterior vermis.