title: Neuropeptide Y inhibits cholinergic transmission in the isolated guinea pig colon: mediation through alpha-adrenergic receptors.
abstract: Neuropeptide Y, a member of the pancreatic polypeptide family, caused dose-dependent relaxation of guinea pig colon longitudinal muscle. This inhibitory effect was unaffected by hexamethonium but was abolished by atropine and tetrodotoxin, suggesting that neuropeptide Y is acting via postganglionic cholinergic neurons. Studies utilizing alpha-adrenergic and dopamine receptor antagonists revealed that neuropeptide Y-mediated relaxation was blocked only by the alpha 2 antagonist yohimbine. Neuropeptide Y also antagonized muscle response to electric field stimulation that was reversed by yohimbine. Additional studies with muscle slices incubated with [3H]norepinephrine or [3H]choline showed that neuropeptide Y stimulated norepinephrine release from sympathetic nerves, which, in turn, inhibited the release of acetylcholine via alpha 2 receptors located on postganglionic nerves. This pathway provides a mechanism for neuropeptide modulation of classical neurotransmitter function.
mesh_terms: D000109:Acetylcholine / Q000378:metabolism*; D000818:Animals; D003106:Colon / Q000187:drug effects / Q000294:innervation / Q000502:physiology*; D006168:Guinea Pigs; D006892:Hydroxydopamines / Q000494:pharmacology; D066298:In Vitro Techniques; D007700:Kinetics; D009130:Muscle, Smooth / Q000187:drug effects / Q000294:innervation / Q000502:physiology*; D009478:Neuropeptide Y / Q000494:pharmacology*; D009638:Norepinephrine / Q000378:metabolism*; D011188:Potassium / Q000494:pharmacology; D011942:Receptors, Adrenergic, alpha / Q000187:drug effects / Q000502:physiology*
chemical_list: D006892:Hydroxydopamines; D009478:Neuropeptide Y; D011942:Receptors, Adrenergic, alpha; D000109:Acetylcholine; D011188:Potassium; D009638:Norepinephrine