University of Kentucky
Methylphenidate as an Intravenous Reinforcer for Rats: Evidence from Progressive Ratio Schedule and Long Access Sessions
Institution
University of Kentucky
Faculty Advisor/ Mentor
Julie Marusich; Michael Bardo
Abstract
Despite the abuse potential of methylphenidate (MPH) found in humans, one of the most widely prescribed drugs for treatment of attention deficit hyperactivity disorder (ADHD), little research has been done using MPH as a reinforcer for rats. The purpose of these experiments was to provide additional data on whether or not MPH was an intravenous reinforcer for rats. Experiment 1 tested for self-administration of MPH on a progressive ratio, as well as examining a variety of doses of MPH. Results of this experiment showed that subjects earned significantly more MPH than saline, and also had higher breakpoints for all doses of MPH examined than for saline. In experiment 2, subjects were divided into long access groups (LgA), rats exposed to six hour daily MPH self-administration sessions, and short access groups (ShA), rats exposed to one hour daily MPH self-administration sessions. Subjects in LgA groups administered significantly more MPH over the course of the 21 sessions, whereas subjects in the ShA groups did not change in the amount of MPH intake. The combined results demonstrated that rats will selfadminister more MPH on a PR schedule of reinforcement than saline, rats given long access to MPH self-administration will escalate in the amount of MPH intake, and that rats can be trained to lever press for MPH without prior lever press training for food or another drug. These results indicated that MPH use is subject to dysregulated use and abuse, similar to that of other drugs of abuse.
Methylphenidate as an Intravenous Reinforcer for Rats: Evidence from Progressive Ratio Schedule and Long Access Sessions
Despite the abuse potential of methylphenidate (MPH) found in humans, one of the most widely prescribed drugs for treatment of attention deficit hyperactivity disorder (ADHD), little research has been done using MPH as a reinforcer for rats. The purpose of these experiments was to provide additional data on whether or not MPH was an intravenous reinforcer for rats. Experiment 1 tested for self-administration of MPH on a progressive ratio, as well as examining a variety of doses of MPH. Results of this experiment showed that subjects earned significantly more MPH than saline, and also had higher breakpoints for all doses of MPH examined than for saline. In experiment 2, subjects were divided into long access groups (LgA), rats exposed to six hour daily MPH self-administration sessions, and short access groups (ShA), rats exposed to one hour daily MPH self-administration sessions. Subjects in LgA groups administered significantly more MPH over the course of the 21 sessions, whereas subjects in the ShA groups did not change in the amount of MPH intake. The combined results demonstrated that rats will selfadminister more MPH on a PR schedule of reinforcement than saline, rats given long access to MPH self-administration will escalate in the amount of MPH intake, and that rats can be trained to lever press for MPH without prior lever press training for food or another drug. These results indicated that MPH use is subject to dysregulated use and abuse, similar to that of other drugs of abuse.