Olivary afferents from the brain stem reticular formation.

The projections from the brain stem reticular formation to the inferior olive have been studied in cats in which microinjections of horseradish peroxidase have been made into the inferior olive from a ventral approach. Retrogradely labelled cells were observed within the reticular formation proper of the medulla, pons and mesencephalon (within the nucleus reticularis parvicellularis, reticularis ventralis, reticularis gigantocellularis, reticularis lateralis, reticularis pontis caudalis, reticularis pontis oralis, cuneiformis and subcuneiformis). Labelled cells were also found within the lateral reticular nucleus (the nucleus of the lateral funiculus), the paramedian reticular and the perihypoglossal nuclei. The connections are bilateral (the projection from the lateral reticular nucleus is only contralateral). The observations demonstrate a more widespread origin for the reticulo-olivary fibres than has previously been shown and indicate that the medullary reticular formation is the area with the highest number of cells projecting to the olivary complex.