title: Deltorphin II enhances extracellular levels of dopamine in the nucleus accumbens via opioid receptor-independent mechanisms.
abstract: The effects of the delta2-opioid receptor agonist, deltorphin II, on extracellular levels of dopamine in the rat nucleus accumbens were investigated in awake animals by in vivo brain microdialysis. In agreement with previous studies, perfusion of deltorphin II (50.0 nmol) into the nucleus accumbens significantly increased the extracellular amount of accumbal dopamine. The effect of deltorphin II (50.0 nmol) was not altered by the selective delta2-opioid receptor antagonist, naltriben (1.5 nmol), which alone did not significantly affect the basal levels of dopamine. Selective antagonists of neither the mu-opioid receptors, D-Phe-Cys-Tyr-D-Trp-Orn-Thr-Phe-Thr-NH2 (0.15 nmol), nor the delta1-opioid receptors, (E)-7-benzylidenenaltrexone tartrate (0.15 nmol), failed to significantly alter the effects of deltorphin II. The nonselective opioid receptor antagonist, naloxone (0.75 and 1.5 nmol), which alone did not significantly affect the basal levels of dopamine, also failed to affect the effects of deltorphin II. Moreover, under the condition that the sodium channel blocker, tetrodotoxin (0.1 nmol), was perfused continuously into the nucleus accumbens, the deltorphin II-induced increase in extracellular levels of dopamine was reduced by 72%. These results suggest that deltorphin II enhances extracellular dopamine in the nucleus accumbens via opioid receptor-independent, tetrodotoxin-sensitive mechanisms.
authors.affiliation: Department of Pharmacology, Nihon University School of Dentistry, 1-8-13 Kanda-Surugadai, Chiyoda, Tokyo, 101-8310, Japan.
authors.forename: Kaoru
authors.initials: K
authors.lastname: Murakawa
authors.forename: Noriya
authors.initials: N
authors.lastname: Hirose
authors.forename: Koji
authors.initials: K
authors.lastname: Takada
authors.forename: Tsutomu
authors.initials: T
authors.lastname: Suzuki
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Nagase
authors.forename: Alexander R
authors.initials: AR
authors.lastname: Cools
authors.forename: Noriaki
authors.initials: N
authors.lastname: Koshikawa
mesh_terms: D000704:Analysis of Variance; D000779:Anesthetics, Local / Q000494:pharmacology; D000818:Animals; D001597:Benzylidene Compounds / Q000494:pharmacology; D004298:Dopamine / Q000378:metabolism*; D005110:Extracellular Space / Q000378:metabolism; D008297:Male; D017551:Microdialysis; D009270:Naloxone / Q000494:pharmacology; D009271:Naltrexone / Q000031:analogs & derivatives* / Q000494:pharmacology; D009292:Narcotic Antagonists / Q000494:pharmacology; D009714:Nucleus Accumbens / Q000033:anatomy & histology / Q000187:drug effects* / Q000378:metabolism; D009842:Oligopeptides / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D011957:Receptors, Opioid / Q000502:physiology*; D013004:Somatostatin / Q000031:analogs & derivatives* / Q000494:pharmacology; D013779:Tetrodotoxin / Q000494:pharmacology; D013997:Time Factors
chemical_list: D000779:Anesthetics, Local; D001597:Benzylidene Compounds; D009292:Narcotic Antagonists; D009842:Oligopeptides; D011957:Receptors, Opioid; C049352:phenylalanyl-cyclo(cysteinyltyrosyl-tryptophyl-ornithyl-threonyl-penicillamine)threoninamide; C068868:naltrindole benzofuran; C060209:deltorphin II, Ala(2)-; C077358:7-benzylidenenaltrexone; D009270:Naloxone; D013779:Tetrodotoxin; D013004:Somatostatin; D009271:Naltrexone; D004298:Dopamine