Abstract
Bicifadine (1-p-tolyl-3-azabicyclo[3.1.0]hexane) inhibits monoamine neurotransmitter uptake by recombinant human transporters in vitro with a relative potency of norepinephrine > serotonin > dopamine (≈1:2:17). This in vitro profile is supported by microdialysis studies in freely moving rats, where bicifadine (20 mg/kg i.p.) increased extrasynaptic norepinephrine and serotonin levels in the prefrontal cortex, norepinephrine levels in the locus coeruleus, and dopamine levels in the striatum. Orally administered bicifadine is an effective antinociceptive in several models of acute, persistent, and chronic pain. Bicifadine potently suppressed pain responses in both the Randall-Selitto and kaolin models of acute inflammatory pain and in the phenyl-p-quinone-induced and colonic distension models of persistent visceral pain. Unlike many transport inhibitors, bicifadine was potent and completely efficacious in both phases of the formalin test in both rats and mice. Bicifadine also normalized the nociceptive threshold in the complete Freund's adjuvant model of persistent inflammatory pain and suppressed mechanical and thermal hyperalgesia and mechanical allodynia in the spinal nerve ligation model of chronic neuropathic pain. Mechanical hyperalgesia was also reduced by bicifadine in the streptozotocin model of neuropathic pain. Administration of the D2 receptor antagonist (-)-sulpiride reduced the effects of bicifadine in the mechanical hyperalgesia assessment in rats with spinal nerve ligations. These results indicate that bicifadine is a functional triple reuptake inhibitor with antinociceptive and antiallodynic activity in acute, persistent, and chronic pain models, with activation of dopaminergic pathways contributing to its antihyperalgesic actions.
Footnotes
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Article, publication date, and citation information can be found at http://jpet.aspetjournals.org.
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doi:10.1124/jpet.106.116483.
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ABBREVIATIONS: NE, norepinephrine; ANOVA, analysis of variance; AUC, area under the curve; CFA, complete Freund's adjuvant; CI, confidence interval; Cmax, maximal plasma concentration; [125I]RTI-55, 3β-(4-iodophenyl)tropan-2β-carboxylic acid methyl ester; COX, cyclooxygenase; DA, dopamine; DAT, dopamine transporter; U-50,488, 3,4-dichloro-N-methyl-N-[2-(1-pyrrolidinyl)cyclohexyl]benzeneacetamide; DOPAC, 3,4-dihydroxyphenylacetic acid; ED50, dose yielding a 50% of maximal response; 5-HT, serotonin; GABA, γ-aminobutyric acid; h, human; 5-HIAA, 5-hydroxyindoleacetic acid; HPLC, high pressure liquid chromatography; HVA, homovanillic acid; LC, locus coeruleus; LD50, dose lethal to 50% of subjects; %MPE, percentage of maximum possible effect; NET, norepinephrine transporter, NMDA, N-methyl-d-aspartate; NSAID, nonsteroidal anti-inflammatory; pfCTX, prefrontal cortex; PPQ, phenylparaquinone; SERT, serotonin transporter; SNL, spinal nerve ligation; STZ, streptozotocin, Str, striatum; TCA, tricyclic antidepressant; Veh, vehicle; RX 821002, 2-(2,3-dihydro-2-methoxy-1,4-benzodioxin-2-yl)-4,5-dihydro-1H-imidazole hydrochloride; SKF-10047, [2S-(2α,6α,11R*]-1,2,3,4,5,6-hexahydro-6,11-dimethyl-3-(2-propenyl)-2,6-methano-3-benzazocin-8-ol hydrochloride; MK 912, (2S-trans)-1,3,4,5′,6,6′,7,12b-octahydro-1′,3′,-dimethyl-spiro[2H-benzofuro[2,3-a]quinolizine-2,4′(1′H)-pyrimidin]-2′-(3′H)-one hydrochloride hydrate; MK-801, (+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine maleate.
- Received October 31, 2006.
- Accepted February 21, 2007.
- The American Society for Pharmacology and Experimental Therapeutics
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