The inferior olive of a prosimian primate Galago senegalensis. I. Conformation and spino-olivary projections.

Abstract

Spino-olivary projections to inferior olive (IO) in a prosimian primate, Galago senegalensis, were studied by using a modification of the Fink and Heimer ('67) technique. Prior to examining the arrangement of spinal axons within IO, its conformation was determined from a series of cresyl violet acetate sections. Galago IO is composed of typical medial accessory (MAO), dorsal accessory (DAO), and principal (PO) olivary nuclei. The MAO is divisible into subgroups a, b, c, d, a ventrolateral outgrowth (VLO), and a dorso-medial cell column (DMCC). Cytoarchitectural and experimental data indicate that DAO is subdivided into lateral (DAOl) and medial (DAOm) parts. The PO of Galago consists of dorsal and ventral lamellae connected by a lateral bend. Following hemisections of the spinal cord at cervical, thoracic, and lumbar cord levels, degeneration is present in essentially identical subgroups of Galago IO. The preponderance of degeneration is found throughout the rostrocaudal extent of ipsilateral DAOl. Moderate amounts of axonal debris are located in caudal parts of subgroup a of ipsilateral MAO, and only a few degenerated fibers extend into adjacent subgroup b after cervical lesions. A distinct contralateral component is evident only following a C1 hemisection. The moderate numbers of degenerated axons found in contralateral DAOm arise exclusively from cervical levels C1 to C3. Spino-olivary fibers terminating in MAO appear to ascend in the ventral funiculus while the majority of those to DAOl course through the lateral funiculus.