Abstract

Impulsivity and hyperactivity are two facets of attention deficit/hyperactivity disorder (ADHD). Impulsivity is expressed as reduced response inhibition capacity, an executive control mechanism that prevents premature execution of an intermittently reinforced behavior. During methylphenidate treatment, impulsivity and hyperactivity are decreased in adolescents with ADHD, but there is little information concerning levels of impulsivity and hyperactivity in adulthood after adolescent methylphenidate treatment is discontinued. The current study evaluated impulsivity, hyperactivity as well as cocaine sensitization during adulthood after adolescent methylphenidate treatment was discontinued in the Spontaneously Hypertensive Rat (SHR) model of ADHD. Treatments consisted of oral methylphenidate (1.5 mg/kg) or water vehicle provided Monday-Friday from postnatal days 28–55. During adulthood, impulsivity was measured in SHR and control strains (Wistar Kyoto and Wistar rats) using differential reinforcement of low rate (DRL) schedules. Locomotor activity and cocaine sensitization were measured using the open-field assay. Adult SHR exhibited decreased efficiency of reinforcement under the DRL30 schedule and greater levels of locomotor activity and cocaine sensitization compared to control strains. Compared to vehicle, methylphenidate treatment during adolescence reduced hyperactivity in adult SHR, maintained the lower efficiency of reinforcement, and increased burst responding under DRL30. Cocaine sensitization was not altered following adolescent methylphenidate in adult SHR. In conclusion, adolescent treatment with methylphenidate followed by discontinuation in adulthood had a positive benefit by reducing hyperactivity in adult SHR rats; however, increased burst responding under DRL compared to SHR given vehicle, i.e., elevated impulsivity, constituted an adverse consequence associated with increased risk for cocaine abuse liability.

Document Type

Article

Publication Date

2016

Notes/Citation Information

0091-3057/© 2015 Elsevier Inc. All rights reserved.

Digital Object Identifier (DOI)

http://dx.doi.org/10.1016/j.pbb.2015.12.002

Funding Information

This study was funded by grants R01 DA011716 and P50 DA05312 and a Kentucky Opportunity Fellowship. The content is solely the responsibility of the authors and does not represent the official views of the National Institute on Drug Abuse. Experiments adhered to the Institutional Animal Care and Use Committee guidelines for animal research. We thank Emily Denehy and Travis McCuddy for technical assistance with data collection and Dr. Richard Charnigo and Dr. Federico Sanabria for assisting with data analyses.

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