Fastigiofugal projection to the brainstem nuclei in the cat: an anterograde PHA-L tracing study.

Fastigial projections to brainstem nuclei were studied using an anterograde neural tracer, Phaseolus vulgaris leucoagglutinin (PHA-L). Microinjections of PHA-L were made into the rostral pole, and middle and caudal parts of the left fastigial nucleus in cat. In addition to fastigioreticular and fastigiovestibular projections, fastigiofugal projections to cranial motor nuclei (IV, VI and VII) and those nuclei involved in autonomic control were identified. At the medullary level, a topographic arrangement of fastigioreticular projection was observed. Rostral and caudal parts of the fastigial nucleus projected to the ventral and dorsal parts of the medial reticular formation, respectively. Fastigiofugal fibers which originated from the rostral part of the fastigial nucleus innervated heavily the nucleus reticularis gigantocellularis (NRGc), nucleus reticularis magnocellularis (NRMc) and the ventral paramedian reticular nucleus (PRN). Those fibers from the middle part innervated heavily the ventrolateral vestibular nucleus (VLV), NRGc, NRMc, ventral and dorsal PRN and parasolitary tract nucleus. From the caudal part of the fastigial nucleus, projections to the cranial motor nuclei (IV, VI and VII), VLV and inferior vestibular nucleus were observed.