Fastigial nucleus projections to the brain stem in beagles: pathways for autonomic regulation.

Efferent connections from a portion of the cerebellar fastigial nucleus were investigated using autoradiography. Bipolar stimulating electrodes were placed in the fastigial nucleus of anesthetized beagles and the area that produced increases in blood pressure and heart rate was localized. A mixture of [3H]leucine and [3H]proline (4:1) was injected into the area and autoradiograms of transported material were prepared. Injections filled the rostral and various parts of the caudal fastigial nucleus. Labeled axons reached the brain stem via two routes, the ipsilateral juxtarestiform body and the contralateral uncinate fasciculus. Ventral portions of the lateral vestibular nucleus were labeled bilaterally, projections to the inferior vestibular and medial vestibular nuclei are contralateral. Nucleus tractus solitarius was heavily labeled on the side opposite the injection. The contralateral medial reticular formation contained many labeled terminals and axons. Label was found in the nucleus reticularis ventralis, lateral reticular nucleus, nucleus gigantocellularis, nucleus pontis caudalis and the paramedian reticular nucleus. No terminal labeling was found in nucleus parvocellularis or nucleus ambiguous. Stimulation of the rostral fastigial nucleus produces increases in blood pressure and heart rate by generalized sympathoexcitation. Many cell groups which facilitate the activity of preganglionic sympathetic neurons do not receive direct fastigial input. It is suggested that that sympathoexcitation resulting from stimulation of the fastigial nucleus occurs through multisynaptic connections in the brain stem.