The vestibular complex in a prosimian primate (Galago senegalensis): morphology and spinovestibular connections.

The morphology of, and distribution of spinal afferents to, the vestibular complex of a prosimian primate (lesser bushbaby, Galago senegalensis) were studied using cytoarchitectural, myeloarchitectural and selective silver impregnation methods. The vestibular complex of Galago consists of superior (SVN), lateral (LVN), medial (MVN) and spinal (SpVN) nuclei, each nucleus having cell populations of characteristic size, shape and distribution within its borders. There is morphological and experimental evidence for the existence of subgroups f, 1, x, y and z and a hitherto undescribed subgroup located in dorsomedial portions of the rostral two-thirds of the MVN. Following partial or complete hemisections at cord levels C1-L6 brain stem sections were impregnated according to the method of Fink and Heimer. Preterminal debris is concentrated mainly in subgroups x and z, relatively sparse in adjacent SpVN and moderate to sparse in LVN and MVN following hemisections at upper and mid-cervical levels. Axonal debris is noticeably absent from the MVN after lesions below the C8 spinal level; this indicates that the MVN receives spinal input from cervical levels only. Following lesions at C8 and progressively lower spinal levels, degeneration was found primarily in subgroups x and z and in LVN and SpVN although in lesser amounts; as lesions were placed at progressively lower levels there was a proportionate decrease in the amount of axonal debris found in these respective nuclei. No degeneration was found in SVN following lesions at any spinal level.