Afferents of the caudal fastigial nucleus in a New World monkey (Cebus apella)

The afferents of the fastigial nucleus (FN) were studied in two capuchin monkeys (Cebus apella) one of which had received a unilateral injection of horseradish peroxidase in the caudal FN, and a second monkey which received a control injection that involved the lateral caudal FN but extended into the cerebellar white matter between the FN and posterior interposed nucleus (PIN). All of the sources of FN afferents were found to be labeled bilaterally. In addition to the restricted distribution of labeled Purkinje cells in lobules VI and VII of the posterior lobe vermis ("oculomotor vermis"), retrogradely labeled cells were present in the dorsolateral pontine nucleus (DLPN), dorsomedial pontine nucleus (DMPN), nucleus reticularis tegmenti pontis (NRTP), pontine raphe (PR), paramedian nucleus reticularis pontis caudalis (NRPC), nucleus prepositus hypoglossi (NPH), subnucleus b of the medial accessory olivary nucleus (sbMAO), and vestibular complex (VC). The second (control) injection appeared to confirm a proposed (Langer et al. 1985b) projection from the flocculus to the basal interstitial nucleus. The results are discussed in terms of the functional relationships of the FN to the frontal eye field and oculomotor-related brainstem structures involved in the production of saccadic and smooth pursuit eye movements.