title: Fentanyl increases dopamine release in rat nucleus accumbens: involvement of mesolimbic mu- and delta-2-opioid receptors.
abstract: The effects of the mu-receptor agonist fentanyl on extracellular levels of dopamine in rat nucleus accumbens were studied in awake animals by in vivo brain microdialysis. Fentanyl dose-dependently increased the levels of dopamine when given intravenously (microg/kg) or via a microdialysis probe placed into the ventral tegmental area or the nucleus accumbens (nmol). The effect of fentanyl given into the nucleus accumbens was blocked by systemic administration of the non-selective opioid receptor antagonist naloxone and by accumbens administration of D-Phe-Cys-Tyr-D-Trp-Om-Thr-Phe-Thr-NH2 (nmol), a mu-opioid receptor antagonist, and naltrindole (nmol), a non-selective delta-opioid receptor antagonist, in a dose-dependent manner. The delta2-opioid receptor antagonist, naltriben (nmol), also blocked the effects of fentanyl, whereas the delta1-opioid receptor antagonist, (E)-7-benzylidenenaltrexone (nmol), was ineffective. When marginally effective doses of D-Phe-Cys-Tyr-D-Trp-Orn-Thr-Phe-Thr-NH2 and naltriben were given simultaneously, the effect of fentanyl was nearly fully blocked; the pretreatment itself had no effect. Administration of the mu-opioid receptor agonist [D-Ala2, N-Me-Phe4,Gly5-ol]-enkephalin (nmol), the delta1-opioid receptor agonist [D-Pen2,5]-enkephalin (nmol) or the delta2-opioid receptor agonist [D-Ala2,Glu4]-deltorphin (nmol) into the nucleus accumbens enhanced the amount of accumbal dopamine. This study provides evidence that not only activation of delta1- and delta2-opioid receptors, but also activation of mu-opioid receptors in the nucleus accumbens increases the release of accumbal dopamine in freely moving rats. We suggest that the effect of intra-accumbens administration of fentanyl upon accumbal release of dopamine is either due to the simultaneous activation of mu-opioid receptors and delta2-opioid receptors or due to activation of mu-opioid receptors that interact with delta2-opioid receptors in a complex manner.
authors.affiliation: Department of Dental Anaesthesiology, Nihon University School of Dentistry, Tokyo, Japan.
authors.forename: Y
authors.initials: Y
authors.lastname: Yoshida
authors.forename: S
authors.initials: S
authors.lastname: Koide
authors.forename: N
authors.initials: N
authors.lastname: Hirose
authors.forename: K
authors.initials: K
authors.lastname: Takada
authors.forename: K
authors.initials: K
authors.lastname: Tomiyama
authors.forename: N
authors.initials: N
authors.lastname: Koshikawa
authors.forename: A R
authors.initials: AR
authors.lastname: Cools
mesh_terms: D000701:Analgesics, Opioid / Q000494:pharmacology*; D000818:Animals; D004305:Dose-Response Relationship, Drug; D005283:Fentanyl / Q000494:pharmacology*; D007275:Injections, Intravenous; D008032:Limbic System / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D017551:Microdialysis; D009292:Narcotic Antagonists / Q000494:pharmacology; D009714:Nucleus Accumbens / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D017465:Receptors, Opioid, delta / Q000819:agonists / Q000037:antagonists & inhibitors / Q000187:drug effects*; D017450:Receptors, Opioid, mu / Q000819:agonists / Q000037:antagonists & inhibitors / Q000187:drug effects*; D013997:Time Factors
chemical_list: D000701:Analgesics, Opioid; D009292:Narcotic Antagonists; D017465:Receptors, Opioid, delta; D017450:Receptors, Opioid, mu; D005283:Fentanyl