, Volume 189, Issue 1, pp 117–124

Ethanol exposure differentially alters pro-enkephalin mRNA expression in regions of the mesocorticolimbic system

Original Investigation



Opioid peptides have been suggested to play a major role in ethanol reinforcement mechanisms and alcohol drinking behaviour. However, in non-selected strains of rodents, it is not known whether opioid biosynthesis is a critical event in these processes.


The aim of this work was to study the effects of a high dose of ethanol (2.5 g/kg body weight) on pro-enkephalin (pro-enk) mRNA expression in brain regions of the mesocorticolimbic system for up to 24 h after drug administration.

Materials and methods

Male Wistar rats were administered with ethanol (2.5 g/kg body weight) or distilled water and were killed 30 min, 1, 2, 4, 8 or 24 h after treatment. Coronal brain sections (20 μ) were obtained and pro-enk mRNA expression was studied by in situ hybridization and densitometry.


Acute ethanol administration induced a transient decrease and increase in pro-enk mRNA expression in the ventral tegmental area (33.2%) and prefrontal cortex (26.5%) 2 and 4 h after treatment, respectively. In contrast, ethanol induced prolonged increases in pro-enk mRNA expression in the core and shell regions of the nucleus accumbens, with different kinetics. Maximal effects were observed 2 h after ethanol exposure (core, 70.0%; shell, 60.0%).


Our results indicate that enkephalin expression in regions of the rat mesocorticolimbic system is differentially altered by acute ethanol treatment and suggest that enkephalins may play a key role in ethanol reinforcement mechanisms.


Alcohol Ethanol Opioid peptides Enkephalins Pro-enkephalin mRNA Mesocorticolimbic system 


  1. Acquas E, Meloni M, Di Chiara G (1993) Blockade of δ-opioid receptors in the nucleus accumbens prevents ethanol-induced stimulation of dopamine release. Eur J Pharmacol 230:239–241PubMedCrossRefGoogle Scholar
  2. Benjamin D, Grant ER, Pohorecky LA (1993) Naltrexone reverses ethanol-induced dopamine release in the nucleus accumbens in awake, freely moving rats. Brain Res 621:137–140PubMedCrossRefGoogle Scholar
  3. Cowen MS, Lawrence AJ (2001) Alterations in central preproenkephalin mRNA expression after chronic free-choice ethanol consumption by Fawn-Hooded rats. Alcohol Clin Exp Res 25:1126–1133PubMedCrossRefGoogle Scholar
  4. Cowen MS, Rezvani A, Jarrott B, Lawrence AJ (1998) Distribution of opioid peptide gene expression in the limbic system of Fawn-Hooded (alcohol-preferring) and Wistar-Kyoto (alcohol-non-preferring) rats. Brain Res 796:323–326PubMedCrossRefGoogle Scholar
  5. de Gortari P, Méndez M, Rodríguez-Keller I, Pérez-Martínez L, Joseph-Bravo P (2000) Acute ethanol administration induces changes in TRH and proenkephalin expression in hypothalamic and limbic regions of rat brain. Neurochem Int 37:483–496PubMedCrossRefGoogle Scholar
  6. de Waele J-P, Papachristou DN, Gianoulakis C (1992) The alcohol-preferring C57BL/6 mice present an enhanced sensitivity of the hypothalamic β-endorphin system to ethanol than the alcohol-avoiding DBA/2 mice. J Pharmacol Exp Ther 261:788–794PubMedGoogle Scholar
  7. Di Chiara G, Imperato A (1985) Ethanol preferentially stimulates dopamine release in the nucleus accumbens of freely moving rats. Eur J Pharmacol 115:131–132PubMedCrossRefGoogle Scholar
  8. Di Chiara G, Acquas E, Tanda G (1996) Ethanol as a neurochemical surrogate of conventional reinforcers: the dopamine–opioid link. Alcohol 13:13–17PubMedCrossRefGoogle Scholar
  9. Froehlich JC (1995) Genetic factors in alcohol self-administration. J Clin Psychiatry 56(Suppl 7):15–23PubMedGoogle Scholar
  10. Froehlich JC, Zweifel M, Harts J, Lumeng L, Li T-K (1991) Importance of delta opioid receptors in maintaining high alcohol drinking. Psychopharmacology 103:467–472PubMedCrossRefGoogle Scholar
  11. Gessa GL, Muntoni F, Collu M, Vargiu L, Mereu G (1985) Low doses of ethanol activate dopaminergic neurons in the ventral tegmental area. Brain Res 348:201–203PubMedCrossRefGoogle Scholar
  12. Gianoulakis C, de Waele JP, Kiianmaa K (1992) Differences in the brain and pituitary beta-endorphin system between the alcohol-preferring AA and alcohol-avoiding ANA rats. Alcohol Clin Exp Res 16:453–459PubMedCrossRefGoogle Scholar
  13. Harlan RE, Shivers BD, Romano GJ, Howells RD, Pfaff DW (1987) Localization of preproenkephalin mRNA in the rat brain and spinal cord by in situ hybridization. J Comp Neurol 258:159–184PubMedCrossRefGoogle Scholar
  14. Howells RD, Kilpatrick DL, Bhatt R, Monahan JJ, Poonian M, Undenfriend S (1984) Molecular cloning and sequence determination of rat preproenkephalin cDNA: sensitive probe for studying transcriptional changes in rat tissues. Proc Natl Acad Sci USA 81:7651–7655PubMedCrossRefGoogle Scholar
  15. Hyytiä P, Kiianmaa K (2001) Suppression of ethanol responding by centrally administered CTOP and naltrindole in AA and Wistar rats. Alcohol Clin Exp Res 25:25–33PubMedCrossRefGoogle Scholar
  16. Joyce EM, Iversen SD (1979) The effect of morphine applied locally to mesencephalic dopamine cell bodies on spontaneous motor activity in the rat. Neurosci Lett 14:207–212PubMedCrossRefGoogle Scholar
  17. Kalivas PW, Widerläv E, Stanley D, Breese G, Prange AJ Jr (1983) Enkephalin action on the mesolimbic system: a dopamine-dependent and a dopamine-independent increase in locomotor activity. J Pharmacol Exp Ther 227:229–237PubMedGoogle Scholar
  18. Koob GF, Sanna PP, Bloom FE (1998) Neuroscience of addiction. Neuron 21:467–476PubMedCrossRefGoogle Scholar
  19. Krishnan-Sarin S, Jing SL, Kurtz DL, Zweifel M, Portoghese PS, Li T-K, Froehlich JC (1995) The delta opioid receptor antagonist naltrindole attenuates both alcohol and saccharin intake in rats selectively bred for alcohol preference. Psychopharmacology 120:177–185PubMedCrossRefGoogle Scholar
  20. Li X-W, Li T-K, Froehlich JC (1998) Enhanced sensitivity of the nucleus accumbens proenkephalin system to alcohol in rats selectively bred for alcohol preference. Brain Res 794:35–47PubMedCrossRefGoogle Scholar
  21. Marinelli PW, Kiianmaa K, Gianoulakis C (2000) Opioid propeptide mRNA content and receptor density in the brains of AA and ANA rats. Life Sci 66:1915–1927PubMedCrossRefGoogle Scholar
  22. Marinelli PW, Quirion R, Gianoulakis C (2003) A microdialysis profile of β-endorphin and catecholamines in the rat nucleus accumbens following alcohol administration. Psychopharmacology 169:60–67PubMedCrossRefGoogle Scholar
  23. Marinelli PW, Bai L, Quirion R, Gianoulakis C (2005) A microdialysis profile of Met-enkephalin release in the rat nucleus accumbens following alcohol administration. Alcohol Clin Exp Res 29:1821–1828PubMedCrossRefGoogle Scholar
  24. Mathieu-Kia A-M, Besson M-J (1998) Repeated administration of cocaine, nicotine and ethanol: effects on preprodynorphin, preprotachykinin A and preproenkephalin mRNA expression in the dorsal and the ventral striatum of the rat. Mol Brain Res 54:141–151PubMedCrossRefGoogle Scholar
  25. Méndez M, Leriche M, Calva JC (2001) Acute ethanol administration differentially modulates μ opioid receptors in the rat meso-accumbens and mesocortical pathways. Mol Brain Res 94:148–156PubMedCrossRefGoogle Scholar
  26. Méndez M, Morales-Mulia M, Leriche M (2004) [3H]DPDPE binding to δ opioid receptors in the rat mesocorticolimbic and nigrostriatal pathways is transiently increased by acute ethanol administration. Brain Res 1028:180–190PubMedCrossRefGoogle Scholar
  27. Ng GYK, O’Dowd BF, George SR (1996) Genotypic differences in mesolimbic enkephalin gene expression in DBA/2J and C57BL/6J inbred mice. Eur J Pharmacol 311:45–52PubMedCrossRefGoogle Scholar
  28. Nylander I, Hyytiä P, Forsander O, Terenius L (1994) Differences between alcohol-preferring (AA) and alcohol-avoiding (ANA) rats in the prodynorphin and proenkephalin systems. Alcohol Clin Exp Res 18:1272–1279PubMedCrossRefGoogle Scholar
  29. Paxinos G, Watson C (1998) The rat brain in stereotaxic coordinates, 4th edn. Academic, San DiegoGoogle Scholar
  30. Ploj K, Roman E, Kask A, Hyytiä P, Schiöth HB, Wikberg JES, Nylander I (2002) Effects of melanocortin receptor ligands on ethanol intake and opioid peptide levels in alcohol-preferring AA rats. Brain Res Bull 59:97–104PubMedGoogle Scholar
  31. Reid LD, Hunter GA (1984) Morphine and naloxone modulate intake of ethanol. Alcohol 1:33–37PubMedCrossRefGoogle Scholar
  32. Schulz R, Wüster M, Duka T, Herz A (1980) Acute and chronic ethanol treatment changes endorphin levels in brain and pituitary. Psychopharmacology 68:221–227PubMedCrossRefGoogle Scholar
  33. Seizinger BR, Bovermann K, Maysinger D, Holt V, Herz A (1983) Differential effects of acute and chronic ethanol treatment on particular opioid systems in discrete regions of rat brain and pituitary. Pharmacol Biochem Behav 18:361–369PubMedCrossRefGoogle Scholar
  34. Ulm RR, Volpicelli JR, Volpicelli LA (1995) Opiates and alcohol self-administration in animals. J Clin Psychiatry 56(Suppl 7):5–14PubMedGoogle Scholar
  35. Valles S, Pitarch J, Renau-Piqueras J, Guerri C (1997) Ethanol exposure affects glial fibrillary acidic protein gene expression and transcription during rat brain development. J Neurochem 69:2484–2493PubMedCrossRefGoogle Scholar
  36. Volpicelli JR, Ulm RR, Hopson N (1991) Alcohol drinking in rats during and following morphine injections. Alcohol 8:289–292PubMedCrossRefGoogle Scholar
  37. Wild KD, Reid LD (1990) Modulation of ethanol intake by morphine: evidence for a central site of action. Life Sci 47:PL49–PL54PubMedCrossRefGoogle Scholar
  38. Wise RA, Bozarth MA (1982) Action of drugs of abuse on brain reward systems: an update with specific attention to opiates. Pharmacol Biochem Behav 17:239–243PubMedCrossRefGoogle Scholar
  39. Yim HJ, Robinson DL, White ML, Jaworski JN, Randall PK, Lancaster FE, Gonzales RA (2000) Dissociation between the time course of ethanol and extracellular dopamine concentrations in the nucleus accumbens after a single intraperitoneal injection. Alcohol Clin Exp Res 24:781–788PubMedCrossRefGoogle Scholar
  40. Yoshikawa K, Williams C, Sabol SL (1984) Rat brain preproenkephalin mRNA. cDNA cloning, primary structure, and distribution in the central nervous system. J Biol Chem 259:14301–14308PubMedGoogle Scholar

Copyright information

© Springer-Verlag 2006

Authors and Affiliations

  1. 1.Departamento de Neuroquímica, Subdirección de Investigaciones ClínicasInstituto Nacional de Psiquiatría Ramón de la FuenteMéxico DFMéxico

Personalised recommendations