PATTERNS OF PROJECTIONS FROM THE PONTINE-NUCLEI AND THE NUCLEUS-RETICULARIS TEGMENTI PONTIS TO THE POSTERIOR VERMIS IN THE RHESUS-MONKEY - A STUDY USING RETROGRADE TRACERS

In an attempt to estimate the relative importance of the various affer ent systems impinging on the oculomotor regions of the posterior cereb ellar vermis of rhesus monkeys in quantitative terms, we made small in jections of the retrograde tracers fast blue, fluorogold, and cholera toxin into different parts of a region of the posterior vermis, spanni ng lobuli VI through VIII. We found that the vast majority of cells re trogradely labeled by injections of lobulus VII and its vicinity lay i n the pontine nuclei (PN), the nucleus reticularis tegmenti pontis (NR TP), and subnuclei a and b of the medial accessory olive. The remainin g retrogradely labeled cells were distributed among a number of other brainstem nuclei or regions including the paramedian pontine reticular formation (PPRF). A quantitative analysis showed that the projection from the NRTP to the posterior vermis was focused on lobulus VII. Whil e the projection from the PN as a whole demonstrated a preference for the more caudal parts of the posterior vermis, a closer look at the di fferent regions of the PN revealed that cells located in the dorsal pa rts of the PN showed the same preference for lobulus VII as cells in t he NRTP. The dorsal PN are a major, gateway for cortical input to the cerebellum, related to visual processing and visually guided eye movem ents. Conversely, the NRTP, likewise involved in visually guided eye m ovements, is much more dependent on subcortical afferents. The observe d convergence of input derived from the dorsal PN and the NRTP in ocul omotor lobulus VII therefore suggests that a major function of this pa rt of the vermis might be the integration of cortical and subcortical signals important for visually guided eye movements. (C) 1993 Wiley-Li ss, Inc.