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The origin of spinocerebellar pathways. II. The nucleus centrobasalis of the cervical enlargement and the nucleus dorsalis of the thoracolumbar spinal cord
Author(s) -
Petras J. M.,
Cummings J. F.
Publication year - 1977
Publication title -
journal of comparative neurology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.855
H-Index - 209
eISSN - 1096-9861
pISSN - 0021-9967
DOI - 10.1002/cne.901730405
Subject(s) - spinal cord , rhizotomy , anatomy , biology , nucleus , cerebellum , forelimb , red nucleus , cordotomy , lumbar spinal cord , neuroscience
The origin of spinocerebellar projections from the caudal cervical, the thoracic, and the cranial lumbar regions of the spinal cord was studied in neonatal dogs. The present cytoarchitectonic and experimental studies of the cervical intumescence of the spinal cord led to the description of a cell group prominent in the dorsal horn, the nucleus centrobasalis. This nucleus, comprised of neurons of varying size and shape, extended over the length of the cervical intumescence. The largest neurons of the n. centrobasah exhibited retrograde reaction following cerebellar injury or they accumulated horseradish peroxidase (HRP) after injection of the enzyme into the cerebellum. Unilateral cerebellar ablation or cordotomy evoked retrograde changes in the ipsilateral nucleus. The cerebellar‐projecting neurons were large, multipolar and chromatophilic. They occured singly, in small clusters, or in columns. The columnar arrangement was common at caudal levels of the cervical intumescence where these large cells were most abundant. The results of earlier experiments with cats and rhesus monkeys have demonstrated massive fiber degeneration in the n. centrobasah following dorsal rhizotomy (Petras, '65, '66; Petras and Cummings, '72). The presence of spinal afferents in this nucleus suggests that its largest neurons may serve as a link for the passage of forelimb afferent information to the cerebellum by way of an uncrossed brachiospinocerebellar projection. The present anatomical data suggest too that these large neurons are the cells of origin for the rostral spinocerebellar tract (Oscarsson and Uddenberg, '64; Oscarsson, '65). The cellular composition of the nucleus dorsalis was studied also, and the results compared with Loewy's ('70) findings in the cat. Three types of neurons were present in the n. dorsalis . These have been classified as giant, medium, and small‐sized neurons. The giant and medium‐sized neurons responded to cerebellectomy, and accumulated enzyme following HRP injections into the cerebellum. The retrograde responses, generally, were most pronounced in cranial thoracic segments and diminished progressively in more caudal segments. Unilateral cerebellar ablations, cerebellar pedunculotomy, and cordotomy almost exclusively affected ipsilateral neurons. The present study provides the first demonstration of discrete retrograde changes in the giant cells of Clarke's column following cerebellectomy. The contribution of the medium‐sized neurons of the n. dorsalis to spinocerebellar projections is established for the first time.