Involvement of the opioid system in the effects induced by nicotine on anxiety-like behaviour in mice.
BACKGROUND
Recent studies have revealed the participation of the endogenous opioid system in several behavioural responses induced by nicotine including antinociception, rewarding properties, and physical drug dependence.


OBJECTIVE
The present study was designed to examine the possible involvement of the various opioid receptors in the anxiolytic- and anxiogenic-like responses induced by nicotine in mice.


METHODS
The acute administration of low (0.05) or high (0.8 mg/kg) doses of nicotine subcutaneously produced opposite effects in the elevated plus maze, i.e. anxiolytic- and anxiogenic-like responses, respectively. Animals were only exposed once to nicotine. The effects of the pretreatment with the mu-opioid receptor antagonist, beta-funaltrexamine (5 mg/kg), the delta-opioid antagonist, naltrindole (2.5 mg/kg) and the kappa-opioid antagonist, nor-binaltorphimine (2.5 mg/kg) intraperitoneally were evaluated on the anxiolytic- and anxiogenic-like responses induced by nicotine.


RESULTS
beta-funaltrexamine, but not nor-binaltorphimine or naltrindole, abolished nicotine-induced anxiolytic-like effects, suggesting an involvement of mu-opioid receptors in this behavioural response. On the other hand, naltrindole, but not nor-binaltorphimine or beta-funaltrexamine, increased the anxiogenic-like responses of nicotine, suggesting an involvement of delta-receptors in this behavioural effect.


CONCLUSIONS
These results demonstrate that the endogenous opioid system is involved in the effects induced by nicotine on anxiety-like behaviour and provide new findings to further clarify the interaction between these two neurochemical systems.
Balerio
Graciela N
GN
Laboratori de Neurofarmacologia, Facultat de Ciències de la Salut i de la Vida, Universitat Pompeu Fabra, Barcelona, Spain.
Aso
Ester
E
Maldonado
Rafael
R
D000704:Analysis of Variance; D000818:Animals; D001008:Anxiety Disorders / Q000139:chemically induced / Q000503:physiopathology* / Q000517:prevention & control; D001522:Behavior, Animal / Q000187:drug effects / Q000502:physiology*; D004305:Dose-Response Relationship, Drug; D004336:Drug Antagonism; D004357:Drug Synergism; D007274:Injections, Intraperitoneal; D007279:Injections, Subcutaneous; D008297:Male; D018782:Maze Learning / Q000187:drug effects / Q000502:physiology; D008464:Mecamylamine / Q000494:pharmacology; D051379:Mice; D009271:Naltrexone / Q000031:analogs & derivatives / Q000494:pharmacology; D009292:Narcotic Antagonists / Q000494:pharmacology; D009538:Nicotine / Q000008:administration & dosage / Q000494:pharmacology*; D018722:Nicotinic Agonists / Q000008:administration & dosage / Q000494:pharmacology; D018733:Nicotinic Antagonists / Q000494:pharmacology; D011957:Receptors, Opioid / Q000502:physiology*
D009292:Narcotic Antagonists; D018722:Nicotinic Agonists; D018733:Nicotinic Antagonists; D011957:Receptors, Opioid; C051844:norbinaltorphimine; D009271:Naltrexone; D008464:Mecamylamine; D009538:Nicotine; C024524:beta-funaltrexamine; C055382:naltrindole