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Adolescent atomoxetine treatment in a rodent model of ADHD: effects on cocaine self-administration and dopamine transporters in frontostriatal regions.

ABSTRACT: Cocaine abuse and attention deficit/hyperactivity disorder (ADHD) are often comorbid. Preclinical research indicates that medial prefrontal (mPFC) and orbitofrontal (OFC) cortices are important neural substrates for both disorders. Using the spontaneously hypertensive rat (SHR) model of ADHD, we reported that adolescent treatment with the stimulant methylphenidate, a dopamine (DAT) and norepinephrine (NET) transporter inhibitor, enhanced cocaine self-administration during adulthood, and was associated with increased DAT function in mPFC. This study investigates the effects of atomoxetine ((R)-N-methyl-?-(2-methylphenoxy)-benzenepropanamine hydrochloride) treatment, a selective NET inhibitor, during adolescence on cocaine self-administration and on DAT function and cell-surface expression in mPFC and OFC during adulthood. SHR acquired cocaine self-administration faster than Wistar-Kyoto and Wistar. Across cocaine doses, SHR earned more cocaine infusions and had higher progressive-ratio breakpoints than Wistar-Kyoto and Wistar, demonstrating that the SHR phenotype models comorbid ADHD and cocaine abuse. Prior atomoxetine treatment did not augment cocaine self-administration in SHR, but acquisition was enhanced in Wistar-Kyoto. No strain differences were found for DAT kinetic parameters or cellular localization in the vehicle controls. Atomoxetine did not alter DAT kinetic parameters or localization in SHR mPFC. Rather, atomoxetine decreased V(max) and DAT cell surface expression in SHR OFC, indicating that inhibition of NET by atomoxetine treatment during adolescence indirectly reduced DAT function and trafficking to the cell surface in OFC, specifically in the ADHD model. Thus, atomoxetine, unlike methylphenidate, does not enhance vulnerability to cocaine abuse in SHR and may represent an important alternative for teens with ADHD when drug addiction is a concern.

SUBMITTER: Somkuwar SS

PROVIDER: S-EPMC3828528 | biostudies-literature | 2013 Dec

REPOSITORIES: biostudies-literature

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Adolescent atomoxetine treatment in a rodent model of ADHD: effects on cocaine self-administration and dopamine transporters in frontostriatal regions.

Somkuwar Sucharita S SS Jordan Chloe J CJ Kantak Kathleen M KM Dwoskin Linda P LP

Neuropsychopharmacology : official publication of the American College of Neuropsychopharmacology 20130703 13

Cocaine abuse and attention deficit/hyperactivity disorder (ADHD) are often comorbid. Preclinical research indicates that medial prefrontal (mPFC) and orbitofrontal (OFC) cortices are important neural substrates for both disorders. Using the spontaneously hypertensive rat (SHR) model of ADHD, we reported that adolescent treatment with the stimulant methylphenidate, a dopamine (DAT) and norepinephrine (NET) transporter inhibitor, enhanced cocaine self-administration during adulthood, and was asso ...[more]

PMID: 23822950

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Project description:BackgroundThe degree of ADHD-related difficulties - reflecting overall impairment, social functioning, and quality of life - may be perceived differently by adolescent patients, parents and physicians. The primary aim of this study was to investigate ADHD-related difficulties during atomoxetine treatment, as perceived by the three different raters. Secondary objectives focused on effectiveness and tolerability of atomoxetine treatment in a population of adolescent patients with ADHD.MethodsAdolescents with ADHD, aged 12-17 years, received open-label atomoxetine (0.5-1.2 mg/kg/day) up to 24 weeks. ADHD-related difficulties at various times of the day were rated using the Global Impression of Perceived Difficulties (GIPD) instrument. Inter-rater agreement was analyzed using Cohen's Kappa with 95% confidence intervals (95% CI). ADHD-Rating Scale (ADHD-RS) and Clinical Global Impression Severity (GGI-S) scores were assessed by the investigator; and spontaneous adverse events, vital signs and laboratory parameters were collected for tolerability assessments.Results159 patients received atomoxetine. Patients' baseline mean GIPD total ratings were significantly lower than parents' and physicians' scores (12.5 [95%CI 11.6;13.5] vs. 17.2 [16.2;18.2] and 18.8 [17.8;19.8]). For all raters, GIPD scores significantly improved over time. Changes were greatest within the first two weeks. Kappa coefficients varied between 0.186 [0.112;0.259] and 0.662 [0.529;0.795], with strongest agreements between parent and physician assessments, and significant improvements of patient/physician agreements over time (based on 95% CIs). ADHD-RS and CGI-S scores significantly improved over the course of the study (based on 95% CIs). Tolerability results were consistent with earlier reports.ConclusionADHD-related difficulties were perceived differently by the raters in this open-label trial, but consistently improved during atomoxetine treatment. The GIPD instrument appeared sensitive to treatment-related change. These primarily quantitative findings may guide future studies to more systematically investigate the clinical and practical relevance of the differences observed. Additionally, in order to further validate these results, placebo- and comparator-controlled trials are recommended as well as inclusion of healthy controls and other patient populations.Trial registrationClinical trial registryClinicalTrials.gov: NCT00191737.

Project description:The dopamine transporter (DAT), a member of the neurotransmitter:sodium symporter family, mediates the reuptake of dopamine at the synaptic cleft. DAT is the primary target for psychostimulants such as cocaine and amphetamine. We previously demonstrated that cocaine binding and dopamine transport alter the accessibility of Cys342 in the third intracellular loop (IL3). To study the conformational changes associated with the functional mechanism of the transporter, we made cysteine substitution mutants, one at a time, from Phe332 to Ser351 in IL3 of the background DAT construct, X7C, in which 7 endogenous cysteines were mutated. The accessibility of the 20 engineered cysteines to polar charged sulfhydryl reagents was studied in the absence and presence of cocaine or dopamine. Of the 11 positions that reacted with methanethiosulfonate ethyl ammonium, as evidenced by inhibition of ligand binding, 5 were protected against this inhibition by cocaine and dopamine (S333C, S334C, N336C, M342C and T349C), indicating that reagent accessibility is affected by conformational changes associated with inhibitor and substrate binding. In some of the cysteine mutants, transport activity is disrupted, but can be rescued by the presence of zinc, most likely because the distribution between inward- and outward-facing conformations is restored by zinc binding. The experimental data were interpreted in the context of molecular models of DAT in both the inward- and outward-facing conformations. Differences in the solvent accessible surface area for individual IL3 residues calculated for these states correlate well with the experimental accessibility data, and suggest that protection by ligand binding results from the stabilization of the outward-facing configuration. Changes in the residue interaction networks observed from the molecular dynamics simulations also revealed the critical roles of several positions during the conformational transitions. We conclude that the IL3 region of DAT undergoes significant conformational changes in transitions necessary for both cocaine binding and substrate transport.

Dataset Information

Adolescent atomoxetine treatment in a rodent model of ADHD: effects on cocaine self-administration and dopamine transporters in frontostriatal regions.

Publications

Adolescent atomoxetine treatment in a rodent model of ADHD: effects on cocaine self-administration and dopamine transporters in frontostriatal regions.

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