Adolescent Methylphenidate Exposure Alters Nicotine Self-Administration and the Accumbal Firing Response to Nicotine
This study was designed to analyze the effects of adolescent exposure to methylphenidate (MPH; trade name: Ritalin) on nicotine self-administration, the motivation to obtain nicotine, and accumbal neuronal firing rate in female adolescent rats. MPH is the most commonly prescribed medication for Attention Deficit-Hyperactivity Disorder (ADHD) which is diagnosed in 3-5% of adolescents in the United States. However, this disorder is often misdiagnosed, and MPH is often prescribed to individuals not diagnosed with ADHD. Adolescent female Sprague-dawley rats were ip administered 1 mg/kg MPH or saline using a “school day” regimen of five days on, two days off, beginning on postnatal day (P)28 and this regimen was maintained throughout testing. A 1 mg/kg dose of MPH has been shown to result in brain plasma levels equivalent to clinical dosing in humans. Indwelling catheters were implanted in the jugular vein at P35, and one week later on P42, animals began nicotine self-administration. MPH (1 mg/kg) was administered each day approximately 6 h before each self-administration session began, which allows for nearly full plasma clearance of MPH (half-life = 1 h) before self-administration commenced. Rats were reduced to 85% of their free-feeding body weight and sipper tubes were made available to the rats in this paradigm, and responses to licking the tube produced an infusion of nicotine solution (15μg/kg) over a range of fixed ratio (FR) reinforcement schedules followed by a progressive ratio (PR) schedule, a measure of motivation. The schedule of reinforcement during 60 min sessions was increased from an FR5 to FR15 over approximately a three-week period. Results revealed that MPH pre-exposed rats self-administered significantly higher amounts of nicotine as compared to animals treated with saline throughout the FR5 and FR10 schedules. Further, MPH enhanced the motivation to self-administer nicotine on the PR schedule compared to controls, demonstrating an enhanced motivation to obtain nicotine produced by MPH. Finally, animals that had been pre-exposed to MPH and self-administered nicotine demonstrated a lower rate of basal accumbal firing as compared to controls, but a burst firing in response to nicotine that was higher than rats pre-exposed to saline. In conclusion, MPH altered the behavioral and neural response to nicotine in the nucleus accumbens.
De Preter, C. C.; Hernandez, Liza J.; Kirby, Seth L.; Campbell, R. B.; Beaumont, E.; Bradley, C. A.; Palmatier, Matthew I.; and Brown, Russell W.. 2016. Adolescent Methylphenidate Exposure Alters Nicotine Self-Administration and the Accumbal Firing Response to Nicotine. Poster presentation. Society for Neuroscience Conference, Washington, DC. http://www.abstractsonline.com/pp8/#!/4071/presentation/9410