Projection of dorsal column nuclei and spinal cord to brainstem and thalamus in the tree shrew, Tupaia glis

Abstract

The aim of this study was to compare the projections of the dorsal column nuclei and spinal pathways to the brainstem and thalamus in Tupaia glis. Animals with unilateral lesions in the dorsal column nuclei or with lateral hemisections were perfused after 5 to 14 days survival time and sections were treated with Nauta or Fink/Heimer silver impregnation methods. The findings indicate that efferent fibers of dorsal column nuclei terminate not only in the thalamus but also in the dorsal accessory nucleus of the inferior olive and bilaterally in the external nucleus of the inferior colliculus. Some fibers terminate in periaqueductal gray and a few in pontine nuclei. In the diencephalon, efferents of the dorsal column nuclei were found to terminate in the posterior group (PO), ventroposterior nucleus (VP) and zona incerta. Spinal efferents were traced to the medial and dorsal accessory nuclei of the inferior olive, medullary and mesencephalic reticular formation, facial and vestibular nuclei, cuneiform nucleus, locus caeruleus, parabrachial nuclei and periaqueductal gray, and also to the external nucleus of the inferior colliculus. Evidence was found of more limited additional spinal projections to PO intralaminar nuclei and VP. The results of this study indicate that the dorsal column system, generally considered to be a phylogenetically new direct pathway to the thalamus, contains other components comparable to some of the spinal efferent connections with the brainstem. Moreover, even in this intermediate form, whose exact taxonomic position is unsettled, the dorsal column‐medial lemniscus system to the thalamus appears to be of greater volume than the anterolateral spinothalamic connection.