Journal of Neuroscience, Vol 9, 1668-1682, Copyright © 1989 by Society for Neuroscience
A circumscribed projection from the nucleus of the solitary tract to the nucleus ambiguus in the rat: anatomical evidence for somatostatin- 28-immunoreactive interneurons subserving reflex control of esophageal motility
ET Cunningham Jr and PE Sawchenko
Department of Neurosciences, University of California, San Diego, La Jolla 92093.
Axonal transport and immunohistochemical methods were used to investigate
the anatomical and biochemical organization of projections from the nucleus
of the solitary tract (NTS) to the rostral, esophageal, part of the nucleus
ambiguus (NA) in the rat. Discrete iontophoretic deposits of a retrogradely
transported tracer, fluorogold, placed in the rostral NA labeled a column
of cells within the NTS, termed the central part of the NTS (after Ross et
al., 1985), situated just medial to the solitary tract and extending from
about 300 to 1000 microns rostral to the obex. Iontophoretic deposits of
the anterogradely transported tracer, Phaseolus vulgaris-leucoagglutinin
(PHA-L), placed in the central part of the NTS gave rise to dense and
topographically restricted projections to the rostral NA. More caudal and
ventral aspects of the NA did not receive prominent inputs from the central
part of the NTS, and deposits that spared the central part of the NTS gave
rise to only sparse projections to the rostral NA. Antisera against
somatostatin-28 (SS-28) stained cell bodies within the central part of the
NTS. In addition, a double-labeling procedure, capable of colocalizing
anterogradely transported PHA-L and endogenous peptides to individual
fibers and/or terminals, demonstrated an appreciable number of
SS-28-immunoreactive terminals within the rostral NA that arose from the
NTS. Correspondingly, unilateral lesions that involved the central part of
the NTS resulted in a marked depletion of SS-28 immunoreactivity in the
ipsilateral rostral NA. These data provide evidence for a discrete, partly
somatostatinergic, projection from the central part of the NTS to the
rostral NA. Anatomical and physiological studies implicating the central
part of the NTS and the rostral NA in esophageal function suggest this
pathway to be involved in the reflex control of esophageal motility.
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