The Vestibular Complex in a Prosimian Primate (Galago senegalensis): Morphology and Spinovestibular Connections (Part 1 of 2)

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Abstract
The morphology of and distribution of spinal afferents to the vestibular complex of a prosimian primate (lesser bushbaby, G. senegalensis) were studied using cytoarchitectural, myeloarchitectural and selective silver impregnation methods. The vestibular complex of Galago consists of superior [vestibular] (SVN), lateral-(LVN), medial-(MVN) and spinal-(SpVN) [vestibular] 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, l, x, y and z and a hitherto undescribed subgroup located in dorsomedial portions of the rostral 2/3 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 MNV 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.