In Vivo Characterization of a Novel Phenylisothiocyanate Tropane Analog at Monoamine Transporters in Rat Brain

• Published in: The Journal of pharmacology and experimental therapeutics 2008-08, Vol.326 (2), p.587-595
• Main Authors: Murthy, Vishakantha, Martin, Thomas J, Kim, Susy, Davies, Huw M L, Childers, Steven R
• Format: Article
• Language: English
• Subjects: Animals; Behavior, Animal - drug effects; Cocaine - pharmacology; Corpus Striatum - drug effects; Corpus Striatum - metabolism; Dopamine Plasma Membrane Transport Proteins - metabolism; Dose-Response Relationship, Drug; Isothiocyanates - chemistry; Isothiocyanates - pharmacology; Male; Molecular Structure; Motor Activity - drug effects; Nortropanes - chemistry; Nortropanes - pharmacology; Protein Binding; Rats; Rats, Inbred F344; Serotonin Plasma Membrane Transport Proteins - metabolism; Tropanes - chemistry; Tropanes - pharmacology
• ISSN: 0022-3565; 1521-0103
• DOI: 10.1124/jpet.108.138842

Previous studies have shown that the phenylisothiocyanate tropane analog 2-β-propanoyl-3-β-(2-naphthyl)-8-[4-isothiocyanato)benzyl]nortropane (HD-205) binds covalently to dopamine and serotonin transporters (DAT and SERT, respectively) in rat brain membranes ( Biochem Pharmacol 74: 336–344, 2007). The present study evaluated the irreversible effects of HD-205 in vivo in rats after intracranial injection. Rats were implanted with unilateral cannulae in rat striatum, and HD-205 (0.001–3 nmol) was administered by intrastriatal injection. In vitro autoradiography of DAT binding with [ 125 I]2-carbomethoxy-3-(4-iodophenyl)tropane (RTI-55) on brain sections obtained 24 h after injection showed a highly localized blockade of binding in striatum, with maximal blockade of binding by 1 to 3 nmol HD-205. Similar blockade of SERT binding (using [ 3 H]-citalopram) was observed in the same area. No blockade of DAT or SERT binding was observed after intrastriatal injections of the reversible analog 2-β-propanoyl-3-β-(2-naphthyl)-8-benzyl nortropane (HD-206), and HD-205 treatment had no effect on D 2 - and μ-opioid-stimulated guanosine 5′- O -(3-[ 35 S]thio)-triphosphate binding in sections from the same animals. In a time course study, rats administered with 1 nmol HD-205 showed recovery of 50% DAT binding after 3 to 4 days postinjection, and full recovery after 6 weeks. Rats implanted with bilateral cannulae were tested for cocaine-induced locomotor activity. Two days after intrastriatal injection of 1 nmol of HD-205, systemic (20 mg/kg i.p.) cocaine-induced locomotor activity was not affected; however, locomotor activity induced by intrastriatal administration of cocaine (6 nmol) was eliminated. This strategy of site-specific chemical blockade of transporters could serve as a valuable tool to evaluate the neuroanatomical basis of DAT-mediated cocaine effects.