Nicotine and ethanol activate protein kinase A synergistically via G(i) betagamma subunits in nucleus accumbens/ventral tegmental cocultures: the role of dopamine D(1)/D(2) and adenosine A(2A) receptors

J Pharmacol Exp Ther. 2007 Jul;322(1):23-9. doi: 10.1124/jpet.107.120675. Epub 2007 Apr 27.


Tobacco and alcohol are the most commonly used drugs of abuse and show the most serious comorbidity. The mesolimbic dopamine system contributes significantly to nicotine and ethanol reinforcement, but the underlying cellular signaling mechanisms are poorly understood. Nicotinic acetylcholine (nACh) receptors are highly expressed on ventral tegmental area (VTA) dopamine neurons, with relatively low expression in nucleus accumbens (NAcb) neurons. Because dopamine receptors D(1) and D(2) are highly expressed on NAcb neurons, nicotine could influence NAcb neurons indirectly by activating VTA neurons to release dopamine in the NAcb. To investigate this possibility in vitro, we established primary cultures containing neurons from VTA or NAcb separately or in cocultures. Nicotine increased cAMP response element-mediated gene expression only in cocultures; this increase was blocked by nACh or dopamine D(1) or D(2) receptor antagonists. Furthermore, subthreshold concentrations of nicotine with ethanol increased gene expression in cocultures, and this increase was blocked by nACh, D(2) or adenosine A(2A) receptor antagonists, Gbetagamma or protein kinase A (PKA) inhibitors, and adenosine deaminase. These results suggest that nicotine activated VTA neurons, causing the release of dopamine, which in turn stimulated both D(1) and D(2) receptors on NAcb neurons. In addition, subthreshold concentrations of nicotine and ethanol in combination also activated NAcb neurons through synergy between D(2) and A(2A) receptors. These data provide a novel cellular mechanism, involving Gbetagamma subunits, A(2A) receptors, and PKA, whereby combined use of tobacco and alcohol could enhance the reinforcing effect in humans as well as facilitate long-term neuroadaptations, increasing the risk for developing coaddiction.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Animals
  • Cells, Cultured
  • Coculture Techniques
  • Cyclic AMP-Dependent Protein Kinases / physiology*
  • Enzyme Activation
  • Ethanol / pharmacology*
  • GTP-Binding Protein alpha Subunits, Gi-Go / physiology*
  • Gene Expression / drug effects
  • Nicotine / pharmacology*
  • Nucleus Accumbens / drug effects*
  • Nucleus Accumbens / enzymology
  • Protein Subunits
  • Rats
  • Rats, Sprague-Dawley
  • Receptor, Adenosine A2A / physiology*
  • Receptors, Dopamine D1 / physiology*
  • Receptors, Dopamine D2 / physiology*
  • Response Elements / physiology
  • Ventral Tegmental Area / drug effects*
  • Ventral Tegmental Area / enzymology


  • Protein Subunits
  • Receptor, Adenosine A2A
  • Receptors, Dopamine D1
  • Receptors, Dopamine D2
  • Ethanol
  • Nicotine
  • Cyclic AMP-Dependent Protein Kinases
  • GTP-Binding Protein alpha Subunits, Gi-Go