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Identification of cells that express 5‐ hydroxytryptamine 1A receptors in the nervous systems of the bowel and pancreas
Author(s) -
Kirchgessner A.L.,
Liu M.T.,
Raymond J.R.,
Gershon M.D.
Publication year - 1996
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/(sici)1096-9861(19960115)364:3<439::aid-cne5>3.0.co;2-5
Subject(s) - biology , immunocytochemistry , calbindin , myenteric plexus , receptor , enteric nervous system , vasoactive intestinal peptide , in situ hybridization , pathology , pancreas , medicine , submucous plexus , 5 ht receptor , serotonin , endocrinology , neuropeptide , immunohistochemistry , messenger rna , immunology , biochemistry , gene
Although serotonin (5‐HT) 1A receptors are known to be present on neural elements in both the bowel and the pancreas, the precise location of these receptors has not previously been determined. Earlier investigations have suggested that 5‐HT 1A receptors are synthesized in enteric, but not pancreatic ganglia, and that they mediate pre‐ and postjunctional inhibition. Wholemount in situ hybridization was used to identify cells that contain mRNA encoding 5‐HT 1A receptors, and immunocytochemistry was employed to locate receptor protein. mRNA encoding 5‐HT 1A receptors was found in the majority of neurons in both submucosal and myenteric plexuses. 5‐HT 1A immunoreactivity, however, was abundant only on the surfaces of a limited subset of nerve cell bodies and processes. 5‐HT‐immunoreactive axons were found in close proximity to sites of 5‐HT 1A immunoreactivity. Myenteric, but not submucosal calbindin‐immunoreactive neurons (with Dogiel type II morphology) were surrounded by rings of 5‐HT 1A immunoreactivity. The cytoplasm of the cell bodies and dendrites of a small subset of Dogiel type I neurons was also intensely 5‐HT 1A immunoreactive. Most of the Dogiel type I 5‐HT 1A ‐immunoreactive myenteric neurons, and some of the type II neurons that were ringed by 5‐HT 1A immunoreactivity became doubly labeled following injections of the retrograde tracer, FluoroGold (FG), into the submucosal plexus. 5‐HT 1A immunoreactive neurons in distant submucosal ganglia also became labeled by retrograde transport of FG. None of the 5‐HT 1A ‐immunoreactive cells were labeled by the intraluminal administration of the β‐subunit of cholera toxin, a marker for vasoactive intestinal peptide‐containing secretomotor neurons. These observations suggest that some of the myenteric 5‐HT 1A ‐immunoreactive neurons project to submucosal ganglia and that the submucosal 5‐HT 1A ‐immunoreactive cells are interneurons. In addition to neurons, a subset of 5‐HT‐containing enterochromaffin cells expressed 5‐HT 1A immunoreactivity, which was co‐localized with 5‐HT in secretory granules. In the pancreas, 5‐HT 1A immunoreactivity was observed in ganglia, acinar nerves, and glucagon‐immunoreactive islet cells. Serotonergic enteropancreatic axons have been found to terminate in close proximity to each of these structures, which may thus be the targets of this innervation. The abundance of 5‐HT 1A receptor immunoreactivity on nerves of the gut and pancreas suggests that drugs designed to interact with these receptors may have unanticipated visceral actions. © 1996 Wiley‐Liss, Inc.