Localization of the 5‐hydroxytryptamine 4 receptor in equine enteric neurons and extrinsic sensory fibers
Background Serotonin plays a pivotal role in regulating gut motility, visceral sensitivity, and fluid secretion via specific receptors. Among these receptors, 5‐HT4 exerts a prominent control on gut motor function. Although the prokinetic effect exerted by 5‐HT4 agonists is well known, the cellular...
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| Published in: | Neurogastroenterology and motility Vol. 29; no. 7 |
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| Main Authors: | , , , , , , , , , |
| Format: | Journal Article |
| Language: | English |
| Published: |
England
Wiley Subscription Services, Inc
01-07-2017
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| Subjects: | |
| Online Access: | Get full text |
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| Summary: | Background
Serotonin plays a pivotal role in regulating gut motility, visceral sensitivity, and fluid secretion via specific receptors. Among these receptors, 5‐HT4 exerts a prominent control on gut motor function. Although the prokinetic effect exerted by 5‐HT4 agonists is well known, the cellular sites of 5‐HT4 expression remain poorly understood in large mammals, e.g., horses. In this study, we evaluated the distribution of 5‐HT4 in the horse intestine and in foals with enteric aganglionosis, reminiscent of human Hirschsprung's disease.
Methods
The intestine and spinal ganglia were obtained from three healthy horses and two foals with hereditary ileocolonic aganglionosis. Tissues were processed for immunohistochemistry using a specific antibody to 5‐HT4 and a variety of neuronal markers. Myenteric and submucosal plexus 5‐HT4‐immunoreactive (IR) neurons were quantified as relative percentage (mean±SD) to the total number of neurons counted. Furthermore, the density of 5‐HT4‐IR nerve fibers was evaluated in the mucosa and tunica muscularis.
Key Results
The 5‐HT4 immunoreactivity was localized to large percentages of myenteric neurons ranging from 28±9% (descending colon) to 63±19% (ileum), and submucosal neurons ranging from 54±6% (ileum) to 68±14% (duodenum). The 5‐HT4‐immunoreactivity was co‐expressed by some substance P‐IR (SP‐IR) spinal ganglion neurons and extrinsic sensory fibers of aganglionic foals.
Conclusions & Inferences
The presence of 5‐HT4 in many enteric and extrinsic sensory neurons and nerve fibers provides solid morphological evidence of the cellular sites of 5‐HT4 expression in horses. The evidence of SP‐IR sensory neurons positive for 5‐HT4 suggests its role in visceral sensitivity.
The 5‐hydroxytryptamine 4 receptor (5‐HT4) exerts a prominent control on gastrointestinal functions. Morphological data describing its localization in the enteric nervous system of large mammals, including horses, are lacking. In healthy horses, 5‐HT4 was identified in some spinal ganglia neurons and large percentages of enteric neurons; in aganglionic foals, 5‐HT4 was localized in visceral extrinsic sensory fibers. Our results demonstrate that 5‐HT4 is widely expressed by different subsets of enteric neurons and by extrinsic visceral sensory fibers. |
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| Bibliography: | Funding information This work was partly supported by the Italian Ministry of Public Health (Ricerca Finalizzata RER2009 ‐Ita‐MNGIE), the Italian Ministry of University and Research (PRIN/COFIN 2009MFSXNZ_002), the Telethon grant GGP15171 to RDG, and “Fondazione del Monte di Bologna e Ravenna,” Bologna, Italy to RDG and PC. ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23 |
| ISSN: | 1350-1925 1365-2982 |
| DOI: | 10.1111/nmo.13045 |