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Brainstem projections to the rat cuneate nucleus
Author(s) -
Weinberg Richard J.,
Rustioni Aldo
Publication year - 1989
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.902820111
Subject(s) - dorsal column nuclei , cuneate nucleus , brainstem , tegmentum , anatomy , neuroscience , nucleus , pretectal area , serotonergic cell groups , biology , vestibular nuclei , horseradish peroxidase , dorsal raphe nucleus , medulla oblongata , spinal trigeminal nucleus , medial vestibular nucleus , axoplasmic transport , raphe nuclei , central nervous system , midbrain , nociception , serotonergic , biochemistry , receptor , serotonin , enzyme
Neurons in the pontomedullary tegmentum have been proposed as a final common pathway subserving descending inhibition in the dorsal column nuclei. To investigate the anatomical substrate for these descending effects, brainstem projections to the cuneate nucleus of rats were studied with injections of lectin‐conjugated horseradish peroxidase. In rats with iontophoretic tracer injections in this nucleus, many labeled neurons were detected near the injection site, especially ventral and caudal to it. Intrinsic reciprocal projections were observed after injections in caudal, middle, or rostral levels of the cuneate nucleus. Neurons were labeled in the red nucleus, in agreement with previous anatomical studies, and also in the trigeminal, vestibular, and cochlear nuclei. An ipsilateral dorsomedial group of neurons was labeled in the upper cervical segments and scattered neurons were also labeled bilaterally near the central canal. Sparse retrograde labeling in the tegmetum was focused in the lateral paragigantocellular nucleus and caudal raphe. Consistent with the retrograde experiments, anterograde labeling after pressure injections of lectin‐conjugated horseradish peroxidase in the pontomedullary tegmentum was very sparse within the dorsal column nuclei; labeling was dense, however, in the region immediately ventral to these nuclei. These results confirm previous work indicating that the activity of cuneate neurons is modulated by brainstem sensory nuclei. However, it appears that direct projections to the cuneate nucleus from pontine and rostral medullary regions are sparser than previously suggested. The last link of a polysynaptic descending inhibitory pathway may include GABAergic neurons immediately adjacent to the dorsal column nuclei and/or intrinsic to these nuclei.