title: 5-HT3 receptor involvement in descending reflex relaxation in the rabbit isolated distal colon.
abstract: In whole segments of rabbit distal colon with mucosa removed, descending reflex relaxations of the circular muscle (descending inhibition) elicited by inflating (0.1-1 ml) an intraluminal balloon, were partially antagonized by 100 microM hexamethonium and the 5-HT3 receptor antagonist, ondansetron (3 microM), and abolished by 1 microM tetrodotoxin. The inhibitory effects of hexamethonium and ondansetron were additive. Conversely, hexamethonium (100 microM) and ondansetron (3 microM) failed to reduce electrically induced non-adrenergic non-cholinergic (NANC) relaxations of colonic circular muscle. It is concluded that interneuronally released acetylcholine and 5-hydroxytryptamine (5-HT) activate descending inhibitory pathways supplying the circular coat, via nicotinic and 5-HT3 receptors, respectively. This evidence suggests a functional involvement of 5-hydroxytryptaminergic transmission in the descending inhibition of rabbit colon.
authors.affiliation: Department of Internal Medicine and Therapeutics, University of Pavia, Italy.
authors.forename: E
authors.initials: E
authors.lastname: Messori
authors.forename: S M
authors.initials: SM
authors.lastname: Candura
authors.forename: T
authors.initials: T
authors.lastname: Coccini
authors.forename: B
authors.initials: B
authors.lastname: Balestra
authors.forename: M
authors.initials: M
authors.lastname: Tonini
mesh_terms: D000818:Animals; D003106:Colon / Q000294:innervation / Q000502:physiology*; D005260:Female; D018738:Hexamethonium / Q000494:pharmacology; D066298:In Vitro Techniques; D008297:Male; D011817:Rabbits; D011985:Receptors, Serotonin / Q000502:physiology*; D012018:Reflex; D012702:Serotonin Antagonists / Q000494:pharmacology; D014664:Vasodilation
chemical_list: D011985:Receptors, Serotonin; D012702:Serotonin Antagonists; D018738:Hexamethonium