Dorsal Column Nuclei in a Prosimian Primate <i>(Galago senegalensis)</i>

Abstract

The morphology and brachial cord primary afferent projections of the cuneate and lateral cuneate nuclei have been studied in the lesser bushbaby. The cuneate nucleus was divided into three regions. From caudal to rostral these were the large cell, cell column and rostral regions. Primary afferents from C₂, C₄, C₆, C₇, C₈, T₁ and T₃ terminated within distinct partially overlapping terminal zones in the ipsilateral large cell and cell column regions of the cuneate nucleus (CN) and the lateral cuneate nucleus (LCN). Segmentotopic was the greatest in the rostal region of the CN due to a more diffuse projection pattern. In the LCN, the transverse terminal fields appeared as curved mediolaterally oriented laminae. In each case, ascending fibers of passage from C₄, C₆ and C₇ in the cuneate fasciculus were organized so that two distinct fiber laminae were present. The separation of fibers and the formation of the two ascending laminae was completed either within two segments rostral to their respective level of entry (for C₆ and C₇ lesions) or in the caudal medulla (for C₄ lesion). For each of these segments, the laminae consisted of a small dorsomedial one and a larger lateral one. The organization of primary afferents from one segment into two ascending fiber laminae in the cuneate fasciculus was reflected in a differential termination pattern within both the CN and LCN. The results of this study were discussed relative to earlier anatomical and physiological studies on the DCN in other animals.

The Vestibular Complex in a Prosimian Primate <i>(Galago senegalensis): </i>Morphology and Spinovestibular Connections (Part 2 of 2)

“…Afferent input to the vestibular com plex of Galago was briefly mentioned by Albright and Haines [3] in their study of primary afferents to the cuneate nuclei. These authors found very sparse amounts of preterminal degeneration in ipsilateral subgroups x and z and in the immediately adjacent SpVN following dorsal rhizoto mies at cervical and high thoracic levels.…”

“…The paucity of debris be tween caudal aspects of subgroups z and the rostral terminus of the gracile nucleus indicates that few fibers enter subgroup z by way of the dorsal column route. How ever, the sparse amounts of degeneration reported in subgroups x and z of Galago following dorsal rhizotomies at upper thoracic and cervical levels [3] suggest that a very minor'spinal contribution to these subgroups may course through the dorsal column system. Differing opinions on dorsal column input to x and z [4,11,14] may be partially a result of difficulty in distinguishing the fine fibers projecting to the vestibular complex from the more coarse fibers pro jecting to the dorsal column nuclei [39].…”

“…The results of the present study on Galago appear to substantiate this sugges tion. For example, in Galago, with its un ique upright locomotor style [44], the pri mary route of spinal input to the vestibu lar complex is via the restiform body route with only very sparse numbers of fibers coursing through the dorsal column sys tem [3]. However, those vertebrate forms which have greater input to the vestibular complex via the dorsal column route (li zards, opossum, cat) not only occupy a lower taxonomic position than Galago (a primate) but also have more basic quadru pedal styles of locomotion.…”