title: Presynaptic nicotinic acetylcholine receptors in the myenteric plexus of guinea pig intestine.
abstract: Presynaptic nicotinic acetylcholine receptors (nAChRs) were studied in myenteric plexus preparations from guinea pig ileum using intracellular electrophysiological methods. Microapplication of nicotine (1 mM) caused a biphasic depolarization in all AH neurons (n = 30) and in 36 of 49 S neurons. Cytisine (1 mM) caused fast depolarizations in S neurons and no response in AH neurons. Mecamylamine (10 microM) blocked all responses caused by nicotine and cytisine. TTX (0.3 microM) blocked slow excitatory synaptic potentials in S and AH neurons but had no effect on fast depolarizations caused by nicotine. Nicotine-induced slow depolarizations were reduced by TTX in two of twelve AH neurons (79% inhibition) and four of nine S neurons (90+/-12% inhibition). Slow nicotine-induced depolarizations in the remaining neurons were TTX resistant. TTX-resistant slow depolarizations were inhibited after neurokinin receptor 3 desensitization caused by senktide (0.1 microM); senktide desensitization inhibited the slow nicotine-induced depolarization by 81+/-5% and 63+/-15% in AH and S neurons, respectively. A low-calcium and high-magnesium solution blocked nicotine-induced slow depolarizations in AH neurons. In conclusion, presynaptic nAChRs mediate the release of substance P and/or neurokinin A to cause slow depolarizations of myenteric neurons.
authors.affiliation: Department of Pharmacology and Toxicology and Neuroscience Program, Michigan State University, East Lansing, Michigan 48824-1317, USA.
authors.forename: D A
authors.initials: DA
authors.lastname: Schneider
authors.forename: J J
authors.initials: JJ
authors.lastname: Galligan
mesh_terms: D000470:Alkaloids / Q000494:pharmacology; D000818:Animals; D001392:Azocines; D002118:Calcium / Q000494:pharmacology; D004558:Electric Stimulation; D019706:Excitatory Postsynaptic Potentials / Q000187:drug effects / Q000502:physiology; D006168:Guinea Pigs; D007422:Intestines / Q000294:innervation*; D008274:Magnesium / Q000494:pharmacology; D008297:Male; D008845:Microinjections; D009197:Myenteric Plexus / Q000737:chemistry* / Q000502:physiology*; D009538:Nicotine / Q000494:pharmacology; D018722:Nicotinic Agonists / Q000494:pharmacology; D010446:Peptide Fragments / Q000494:pharmacology; D017729:Presynaptic Terminals / Q000737:chemistry* / Q000502:physiology; D011807:Quinolizines; D018042:Receptors, Neurokinin-3 / Q000032:analysis; D011978:Receptors, Nicotinic / Q000032:analysis*; D013373:Substance P / Q000031:analogs & derivatives / Q000494:pharmacology; D013779:Tetrodotoxin / Q000494:pharmacology; D000093843:Quinolizidine Alkaloids
chemical_list: D000470:Alkaloids; D001392:Azocines; D002118:Calcium; D008274:Magnesium; D009538:Nicotine; D018722:Nicotinic Agonists; D010446:Peptide Fragments; D011807:Quinolizines; D018042:Receptors, Neurokinin-3; D011978:Receptors, Nicotinic; D013373:Substance P; D013779:Tetrodotoxin; C054724:senktide; C004712:cytisine; D000093843:Quinolizidine Alkaloids