title: Enhanced Sensitivity of α3β4 Nicotinic Receptors in Enteric Neurons after Long-Term Morphine: Implication for Opioid-Induced Constipation.
abstract: Opioid-induced constipation is a major side effect that persists with long-term opioid use. Previous studies demonstrated that nicotine-induced contractions are enhanced after long-term morphine exposure in guinea pig ileum. In the present study, we examined whether the increased sensitivity to nicotine could be observed in single enteric neurons after long-term morphine exposure, determined the subunits in mouse enteric neurons, and examined the effect of nicotine in reversing opioid-induced constipation. Nicotine (0.03-1 mM) dose-dependently induced inward currents from a holding potential of -60 mV in isolated single enteric neurons from the mouse ileum. The amplitude of the currents, but not the potency to nicotine, was significantly increased in neurons receiving long-term (16-24 h) but not short-term (10 min) exposure to morphine. Quantitative mRNA analysis showed that nicotinic acetylcholine receptor (nAChR) subunit expression in the mouse ileum was α3 ≥ β2 > β4 > α5 > α4 > β3 > α6. Nicotine-induced currents were obtained in neurons from α7, β2, α5, and α6 knockout mice. The currents were, however, inhibited by mecamylamine (10 μM) and the α3β4 blocker α-conotoxin AuIB (3 μM), suggesting that nicotine-induced currents were mediated by the α3β4 subtype of nAChRs on enteric neurons. Conversely, NS3861, a partial agonist at α3β4 nAChR, enhanced fecal pellet expulsion in a dose-dependent manner in mice that received long-term, but not short-term, morphine treatment. Overall, our findings suggest that the efficacy of nAChR agonists on enteric neurons is enhanced after long-term morphine exposure, and activation of the α3β4 subtype of nAChR reverses chronic, but not acute, morphine-induced constipation.
authors.affiliation: Department of Pharmacology and Toxicology (A.R.G., M.K., F.K., M.I.D., W.L.D., H.I.A.), and Department of Physiology and Biophysics (J.R.G.), and VCU Program in Enteric Neuromuscular Sciences (J.R.G., H.I.A.), Medical College of Virginia Campus, Virginia Commonwealth University, Richmond, Virginia.
authors.forename: Aravind R
authors.initials: AR
authors.lastname: Gade
authors.affiliation: Department of Pharmacology and Toxicology (A.R.G., M.K., F.K., M.I.D., W.L.D., H.I.A.), and Department of Physiology and Biophysics (J.R.G.), and VCU Program in Enteric Neuromuscular Sciences (J.R.G., H.I.A.), Medical College of Virginia Campus, Virginia Commonwealth University, Richmond, Virginia.
authors.forename: Minho
authors.initials: M
authors.lastname: Kang
authors.affiliation: Department of Pharmacology and Toxicology (A.R.G., M.K., F.K., M.I.D., W.L.D., H.I.A.), and Department of Physiology and Biophysics (J.R.G.), and VCU Program in Enteric Neuromuscular Sciences (J.R.G., H.I.A.), Medical College of Virginia Campus, Virginia Commonwealth University, Richmond, Virginia.
authors.forename: Fayez
authors.initials: F
authors.lastname: Khan
authors.affiliation: Department of Pharmacology and Toxicology (A.R.G., M.K., F.K., M.I.D., W.L.D., H.I.A.), and Department of Physiology and Biophysics (J.R.G.), and VCU Program in Enteric Neuromuscular Sciences (J.R.G., H.I.A.), Medical College of Virginia Campus, Virginia Commonwealth University, Richmond, Virginia.
authors.forename: John R
authors.initials: JR
authors.lastname: Grider
authors.affiliation: Department of Pharmacology and Toxicology (A.R.G., M.K., F.K., M.I.D., W.L.D., H.I.A.), and Department of Physiology and Biophysics (J.R.G.), and VCU Program in Enteric Neuromuscular Sciences (J.R.G., H.I.A.), Medical College of Virginia Campus, Virginia Commonwealth University, Richmond, Virginia.
authors.forename: M Imad
authors.initials: MI
authors.lastname: Damaj
authors.affiliation: Department of Pharmacology and Toxicology (A.R.G., M.K., F.K., M.I.D., W.L.D., H.I.A.), and Department of Physiology and Biophysics (J.R.G.), and VCU Program in Enteric Neuromuscular Sciences (J.R.G., H.I.A.), Medical College of Virginia Campus, Virginia Commonwealth University, Richmond, Virginia.
authors.forename: William L
authors.initials: WL
authors.lastname: Dewey
authors.affiliation: Department of Pharmacology and Toxicology (A.R.G., M.K., F.K., M.I.D., W.L.D., H.I.A.), and Department of Physiology and Biophysics (J.R.G.), and VCU Program in Enteric Neuromuscular Sciences (J.R.G., H.I.A.), Medical College of Virginia Campus, Virginia Commonwealth University, Richmond, Virginia hamid.akbarali@vcuhealth.org.
authors.forename: Hamid I
authors.initials: HI
authors.lastname: Akbarali
mesh_terms: D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D003248:Constipation / Q000139:chemically induced* / Q000378:metabolism / Q000473:pathology / Q000503:physiopathology; D054333:Drug Partial Agonism; D004357:Drug Synergism; D055724:Electrophysiological Phenomena / Q000187:drug effects; D017615:Enteric Nervous System / Q000166:cytology* / Q000473:pathology; D005769:Gastrointestinal Motility / Q000187:drug effects; D005786:Gene Expression Regulation / Q000187:drug effects; D007421:Intestine, Small / Q000294:innervation; D008297:Male; D051379:Mice; D009020:Morphine / Q000009:adverse effects*; D009474:Neurons / Q000166:cytology* / Q000187:drug effects* / Q000378:metabolism / Q000473:pathology; D009538:Nicotine / Q000494:pharmacology; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D011978:Receptors, Nicotinic / Q000235:genetics / Q000378:metabolism*; D013997:Time Factors
chemical_list: D012333:RNA, Messenger; D011978:Receptors, Nicotinic; C403530:nicotinic receptor alpha3beta4; D009538:Nicotine; D009020:Morphine; D000255:Adenosine Triphosphate