title: Effects of ethanol on midbrain neurons: role of opioid receptors.
abstract: BACKGROUND
  Although ethanol addiction is believed to be mediated by the mesolimbic dopamine system, originating from the ventral tegmental area (VTA), how acute ethanol increases the activity of VTA dopaminergic (DA) neurons remains unclear.
  
  
  METHODS
  Patch-clamp recordings of spontaneous firings of DA and GABAergic neurons in the VTA in acute midbrain slices from rats.
  
  
  RESULTS
  Ethanol (20-80 mM) excites DA neurons, and more potently depresses firing of local GABAergic neurons. The ethanol-induced excitation of DA neurons is considerably attenuated by DAMGO (Tyr-d-Ala-Gly-N-Me-Phe-Gly-ol enkephalin), a mu-opioid agonist that suppresses firing of GABAergic neurons, or by naloxone, a general opioid antagonist. The ongoing opioid-induced facilitation of DA cell firing (revealed by naloxone) is enhanced by ethanol, probably by an increase in opioid release or action.
  
  
  CONCLUSIONS
  Ethanol excites VTA DA neurons at least partly by increasing ongoing opioid-mediated suppression of local GABAergic inhibition. This indirect mechanism may contribute significantly to the positively reinforcing properties of ethanol.
authors.affiliation: Department of Anesthesiology, New Jersey Medical School, Newark, NJ 07103-2714, USA.
authors.forename: Cheng
authors.initials: C
authors.lastname: Xiao
authors.forename: Jingli
authors.initials: J
authors.lastname: Zhang
authors.forename: Kresimir
authors.initials: K
authors.lastname: Krnjević
authors.forename: Jiang Hong
authors.initials: JH
authors.lastname: Ye
mesh_terms: D000437:Alcoholism / Q000503:physiopathology; D000818:Animals; D001921:Brain / Q000187:drug effects* / Q000502:physiology; D004298:Dopamine / Q000502:physiology; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)- / Q000187:drug effects / Q000502:physiology; D000431:Ethanol / Q000494:pharmacology*; D018756:GABA Antagonists / Q000494:pharmacology; D006801:Humans; D009474:Neurons / Q000187:drug effects / Q000502:physiology; D018408:Patch-Clamp Techniques; D051381:Rats; D017207:Rats, Sprague-Dawley; D011957:Receptors, Opioid / Q000187:drug effects* / Q000502:physiology; D009435:Synaptic Transmission / Q000187:drug effects* / Q000502:physiology; D017557:Ventral Tegmental Area / Q000187:drug effects / Q000502:physiology; D005680:gamma-Aminobutyric Acid / Q000187:drug effects / Q000502:physiology
chemical_list: D018756:GABA Antagonists; D011957:Receptors, Opioid; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; D000431:Ethanol; D005680:gamma-Aminobutyric Acid; D004298:Dopamine