title: Ethanol exposure differentially alters pro-enkephalin mRNA expression in regions of the mesocorticolimbic system.
abstract: BACKGROUND
  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.
  
  
  OBJECTIVE
  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.
  
  
  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 mu) were obtained and pro-enk mRNA expression was studied by in situ hybridization and densitometry.
  
  
  RESULTS
  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%).
  
  
  CONCLUSIONS
  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.
authors.affiliation: Departamento de Neuroquímica, Subdirección de Investigaciones Clínicas, Instituto Nacional de Psiquiatría Ramón de la Fuente, Calzada México Xochimilco 101, Col. San Lorenzo Huipulco, 14370, México DF, México. ubach@imp.edu.mx
authors.forename: Milagros
authors.initials: M
authors.lastname: Méndez
authors.forename: Marcela
authors.initials: M
authors.lastname: Morales-Mulia
mesh_terms: D000428:Alcohol Drinking / Q000378:metabolism; D000818:Animals; D002492:Central Nervous System Depressants / Q000494:pharmacology*; D004745:Enkephalins / Q000235:genetics / Q000378:metabolism*; D000431:Ethanol / Q000494:pharmacology*; D017403:In Situ Hybridization; D007700:Kinetics; D008032:Limbic System / Q000187:drug effects* / Q000378:metabolism*; D008297:Male; D009714:Nucleus Accumbens / Q000187:drug effects / Q000378:metabolism; D017397:Prefrontal Cortex / Q000187:drug effects / Q000378:metabolism; D011498:Protein Precursors / Q000235:genetics / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D013997:Time Factors; D017557:Ventral Tegmental Area / Q000187:drug effects / Q000378:metabolism
chemical_list: D002492:Central Nervous System Depressants; D004745:Enkephalins; D011498:Protein Precursors; D012333:RNA, Messenger; C029992:proenkephalin; D000431:Ethanol