title: Maternal deprivation increases vulnerability to morphine dependence and disturbs the enkephalinergic system in adulthood.
abstract: Maternal deprivation can trigger long-lasting molecular and cellular modifications in brain functions and might facilitate the appearance of pathogenic behaviors. This study focuses on the vulnerability to develop morphine dependence in adult rats that were separated from their mother and littermates for 3 h per day for 14 d after birth and examines the adaptive changes in the enkephalinergic pathways. Place-preference conditioning was observed with 2 mg/kg morphine in deprived rats, whereas 5 mg/kg morphine was necessary to induce conditioning in nondeprived animals. A prolonged morphine conditioning was shown in deprived rats. A strong increase in oral morphine self-administration behavior and preference was observed in deprived rats. Only a very slight increase in preference for sucrose solution, a more ethological reinforcer known to interact with the opioid system, was shown in deprived rats. These results indicate that this postnatal environment change leads to a hypersensitivity to the reinforcing properties of morphine and to the development of morphine dependence. A significant decrease in preproenkephalin mRNA expression was observed in the nucleus accumbens and the caudate-putamen nucleus of deprived rats. The basal extracellular levels of the Met-enkephalin-like immunoreactivity in the nucleus accumbens were significantly lower in deprived rats when compared with nondeprived animals, whereas no change in mu-opioid receptor binding occurred. These results strongly support that maternal deprivation leads to a basal hypoactivity of the enkephalinergic system and hypersensitivity to morphine effects. Together, our results suggest that maternal deprivation in pups likely represents a risk factor for morphine dependence in adult rats.
authors.affiliation: Institut National de la Santé et de la Recherche Médicale, U513, Laboratoire de Neurobiologie et Psychiatrie, Université Paris XII, Faculté de Médecine, 94010 Créteil, France.
authors.forename: Vincent
authors.initials: V
authors.lastname: Vazquez
authors.forename: Jacqueline
authors.initials: J
authors.lastname: Penit-Soria
authors.forename: Claudette
authors.initials: C
authors.lastname: Durand
authors.forename: Marie Jo
authors.initials: MJ
authors.lastname: Besson
authors.forename: Bruno
authors.initials: B
authors.lastname: Giros
authors.forename: Valérie
authors.initials: V
authors.lastname: Daugé
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D000831:Animals, Newborn; D001345:Autoradiography / Q000379:methods; D001522:Behavior, Animal; D001921:Brain / Q000187:drug effects / Q000378:metabolism; D002755:Choice Behavior / Q000187:drug effects; D003213:Conditioning, Psychological / Q000187:drug effects; D003956:Dialysis / Q000379:methods; D004305:Dose-Response Relationship, Drug; D004327:Drinking Behavior / Q000187:drug effects; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)- / Q000493:pharmacokinetics; D004744:Enkephalin, Methionine / Q000378:metabolism; D004745:Enkephalins / Q000235:genetics / Q000378:metabolism*; D005260:Female; D017403:In Situ Hybridization / Q000379:methods; D008426:Maternal Deprivation; D009020:Morphine / Q000008:administration & dosage*; D009021:Morphine Dependence / Q000378:metabolism*; D009294:Narcotics / Q000008:administration & dosage*; D009714:Nucleus Accumbens / Q000187:drug effects / Q000378:metabolism; D011247:Pregnancy; D011498:Protein Precursors / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D011863:Radioimmunoassay / Q000379:methods; D051381:Rats; D020318:Rats, Long-Evans; D017450:Receptors, Opioid, mu / Q000378:metabolism; D012646:Self Administration; D013395:Sucrose / Q000378:metabolism; D013997:Time Factors; D014316:Tritium / Q000493:pharmacokinetics
chemical_list: D004745:Enkephalins; D009294:Narcotics; D011498:Protein Precursors; D012333:RNA, Messenger; D017450:Receptors, Opioid, mu; D014316:Tritium; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; D013395:Sucrose; D004744:Enkephalin, Methionine; D009020:Morphine; C033660:preproenkephalin