title: Nicotine-induced antinociception, rewarding effects, and physical dependence are decreased in mice lacking the preproenkephalin gene.
abstract: It has been shown previously that the endogenous opioid system may be involved in the behavioral effects of nicotine. In the present study, the participation of endogenous enkephalins on nicotine responses has been investigated by using preproenkephalin knock-out mice. Acute nicotine-induced hypolocomotion remained unaffected in these mice. In contrast, antinociception elicited in the tail-immersion and hot-plate tests by acute nicotine administration was reduced in mutant animals. The rewarding properties of nicotine were then investigated using the place-conditioning paradigm. Nicotine induced a conditioned place preference in wild-type animals, but this effect was absent in knock-out mice. Accordingly, in vivo microdialysis studies revealed that the enhancement in dopamine extracellular levels in the nucleus accumbens induced by nicotine was also reduced in preproenkephalin-deficient mice. Finally, the somatic expression of the nicotine withdrawal syndrome precipitated in nicotine-dependent mice by mecamylamine was significantly attenuated in mutant animals. In summary, the present results indicate that endogenous opioid peptides derived from preproenkephalin are involved in the antinociceptive and rewarding properties of nicotine and participate in the expression of physical nicotine dependence.
authors.affiliation: Laboratori de Neurofarmacologia, Facultat de Ciències de la Salut i de la Vida, Universitat Pompeu Fabra, Barcelona, Spain.
authors.forename: Fernando
authors.initials: F
authors.lastname: Berrendero
authors.forename: Victoria
authors.initials: V
authors.lastname: Mendizábal
authors.forename: Patricia
authors.initials: P
authors.lastname: Robledo
authors.forename: Lola
authors.initials: L
authors.lastname: Galeote
authors.forename: Andras
authors.initials: A
authors.lastname: Bilkei-Gorzo
authors.forename: Andreas
authors.initials: A
authors.lastname: Zimmer
authors.forename: Rafael
authors.initials: R
authors.lastname: Maldonado
mesh_terms: D000700:Analgesics / Q000494:pharmacology / Q000633:toxicity; D000818:Animals; D003214:Conditioning, Classical; D004298:Dopamine / Q000032:analysis; D004745:Enkephalins / Q000172:deficiency / Q000235:genetics / Q000502:physiology*; D005260:Female; D006358:Hot Temperature; D008297:Male; D008464:Mecamylamine / Q000633:toxicity; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D017551:Microdialysis; D009043:Motor Activity / Q000187:drug effects / Q000502:physiology; D009538:Nicotine / Q000494:pharmacology* / Q000633:toxicity; D009714:Nucleus Accumbens / Q000737:chemistry / Q000187:drug effects* / Q000503:physiopathology; D018847:Opioid Peptides / Q000096:biosynthesis / Q000172:deficiency / Q000502:physiology*; D010147:Pain Measurement; D017288:Pain Threshold / Q000187:drug effects* / Q000502:physiology; D011498:Protein Precursors / Q000172:deficiency / Q000235:genetics / Q000502:physiology*; D012201:Reward; D013037:Spatial Behavior / Q000187:drug effects / Q000502:physiology; D013375:Substance Withdrawal Syndrome / Q000209:etiology / Q000235:genetics / Q000503:physiopathology; D014029:Tobacco Use Disorder / Q000235:genetics / Q000503:physiopathology*
chemical_list: D000700:Analgesics; D004745:Enkephalins; D018847:Opioid Peptides; D011498:Protein Precursors; D008464:Mecamylamine; D009538:Nicotine; C033660:preproenkephalin; D004298:Dopamine