title: Nicotinic acetylcholine receptors containing the α4 subunit modulate alcohol reward.
abstract: BACKGROUND
  Nicotine and alcohol are the two most co-abused drugs in the world, suggesting a common mechanism of action might underlie their rewarding properties. Although nicotine elicits reward by activating ventral tegmental area dopaminergic (DAergic) neurons via high-affinity neuronal nicotinic acetylcholine receptors (nAChRs), the mechanism by which alcohol activates these neurons is unclear.
  
  
  METHODS
  Because most high-affinity nAChRs expressed in ventral tegmental area DAergic neurons contain the α4 subunit, we measured ethanol-induced activation of DAergic neurons in midbrain slices from two complementary mouse models, an α4 knock-out (KO) mouse line and a knock-in line (Leu9'Ala) expressing α4 subunit-containing nAChRs hypersensitive to agonist compared with wild-type (WT). Activation of DAergic neurons by ethanol was analyzed with both biophysical and immunohistochemical approaches in midbrain slices. The ability of alcohol to condition a place preference in each mouse model was also measured.
  
  
  RESULTS
  At intoxicating concentrations, ethanol activation of DAergic neurons was significantly reduced in α4 KO mice compared with WT. Conversely, in Leu9'Ala mice, DAergic neurons were activated by low ethanol concentrations that did not increase activity of WT neurons. In addition, alcohol potentiated the response to ACh in DAergic neurons, an effect reduced in α4 KO mice. Rewarding alcohol doses failed to condition a place preference in α4 KO mice, paralleling alcohol effects on DAergic neuron activity, whereas a sub-rewarding alcohol dose was sufficient to condition a place preference in Leu9'Ala mice.
  
  
  CONCLUSIONS
  Together, these data indicate that nAChRs containing the α4 subunit modulate alcohol reward.
authors.affiliation: Brudnick Neuropsychiatric Research Institute, Department of Psychiatry, University of Massachusetts Medical School, Worcester, MA 01604, USA.
authors.forename: Liwang
authors.initials: L
authors.lastname: Liu
authors.forename: Linzy M
authors.initials: LM
authors.lastname: Hendrickson
authors.forename: Melissa J
authors.initials: MJ
authors.lastname: Guildford
authors.forename: Rubing
authors.initials: R
authors.lastname: Zhao-Shea
authors.forename: Paul D
authors.initials: PD
authors.lastname: Gardner
authors.forename: Andrew R
authors.initials: AR
authors.lastname: Tapper
mesh_terms: D000109:Acetylcholine / Q000494:pharmacology; D000200:Action Potentials / Q000187:drug effects / Q000502:physiology; D000818:Animals; D003213:Conditioning, Psychological / Q000187:drug effects / Q000502:physiology; D059290:Dopaminergic Neurons / Q000187:drug effects / Q000502:physiology; D004305:Dose-Response Relationship, Drug; D004357:Drug Synergism; D000431:Ethanol / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D055879:Gene Knock-In Techniques; D051379:Mice; D018345:Mice, Knockout; D011978:Receptors, Nicotinic / Q000235:genetics / Q000502:physiology*; D012201:Reward; D017557:Ventral Tegmental Area / Q000187:drug effects / Q000502:physiology
chemical_list: D000109:Acetylcholine; D000431:Ethanol; D011978:Receptors, Nicotinic