title: Ethanol blocks the reversal of prolonged dopamine inhibition of dopaminergic neurons of the ventral tegmental area.
abstract: BACKGROUND
  Dopaminergic (DAergic) neurons of the ventral tegmental area (VTA) are important for the rewarding and reinforcing properties of alcohol and other drugs of abuse. Regulation of the firing of DAergic VTA neurons is controlled by a number of factors, including autoregulation of firing by D2 dopamine (DA) receptors. The inhibitory effects of DA on these neurons exhibit concentration- and time-dependent desensitization, which we have termed dopamine inhibition reversal (DIR), as it requires concurrent stimulation of D1/D5 and D2 receptors.
  
  
  METHODS
  Extracellular recording of DAergic VTA neurons in brain slices was used to test the effects of ethanol (EtOH) (10 to 80 mM) on DIR.
  
  
  RESULTS
  DIR was reduced by concentrations of EtOH as low as 10 mM and was blocked by higher EtOH concentrations. In addition, as we have shown that reversal of inhibition by the selective D2 agonist quinpirole can be observed in the presence of an activator of protein kinase C (PKC), we tested whether EtOH could antagonize the reversal of quinpirole inhibition in the presence of phorbol 12-myristate 13-acetate (PMA). EtOH (80 mM) blocked the reversal of quinpirole seen in the presence of PMA, suggesting that the antagonism of DIR by EtOH is owing to an action at a stage in the mechanism at or distal to PKC. Once achieved, DIR is not antagonized by EtOH.
  
  
  CONCLUSIONS
  The blockade by relatively low concentrations of EtOH of DIR may play an important role in the spectrum of action of EtOH on DAergic neurons of the VTA and may be important in the acute and chronic actions of EtOH on the excitability of these brain reward/reinforcement neurons.
authors.affiliation: Department of Physiology and Biophysics, University of Illinois at Chicago, IL 60612, USA.
authors.forename: Sudarat
authors.initials: S
authors.lastname: Nimitvilai
authors.forename: Devinder S
authors.initials: DS
authors.lastname: Arora
authors.forename: Maureen A
authors.initials: MA
authors.lastname: McElvain
authors.forename: Mark S
authors.initials: MS
authors.lastname: Brodie
mesh_terms: D000818:Animals; D004298:Dopamine / Q000502:physiology*; D018492:Dopamine Antagonists / Q000494:pharmacology; D059290:Dopaminergic Neurons / Q000187:drug effects* / Q000502:physiology; D004305:Dose-Response Relationship, Drug; D000431:Ethanol / Q000494:pharmacology*; D009433:Neural Inhibition / Q000187:drug effects* / Q000502:physiology; D009924:Organ Culture Techniques; D051381:Rats; D011916:Rats, Inbred F344; D017557:Ventral Tegmental Area / Q000187:drug effects* / Q000502:physiology
chemical_list: D018492:Dopamine Antagonists; D000431:Ethanol; D004298:Dopamine