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. 2010 Jun;18(3):257-66.
doi: 10.1037/a0019814.

Methylphenidate as a reinforcer for rats: contingent delivery and intake escalation

Julie A Marusich  1 , Joshua S Beckmann, Cassandra D Gipson, Michael T Bardo
Affiliations

Methylphenidate as a reinforcer for rats: contingent delivery and intake escalation

Julie A Marusich et al. Exp Clin Psychopharmacol. 2010 Jun.

Abstract

Methylphenidate (MPH) is one of the most widely prescribed drugs for treating attention-deficit hyperactivity disorder. Previous research suggested that MPH is a reinforcer for rats, but not all of the manipulations to show that lever pressing is controlled by the contingency to obtain MPH have been examined. In Experiment 1, responding for MPH on a progressive ratio (PR) schedule was assessed. Rats self-administered varying doses of MPH (0.056-1.0 mg/kg/infusion) on a PR schedule of reinforcement, and self-administered more MPH than saline, with maximal responding occurring at a unit dose of 0.56 mg/kg/infusion. Experiment 2 examined if there were differences in responding between contingent and noncontingent MPH (0.56 mg/kg/infusion) on a fixed ratio schedule of reinforcement. Results showed that rats responded for contingent MPH, and that responding was not maintained when MPH was delivered noncontingently. Experiment 3 examined self-administration of MPH (0.1 or 0.3 mg/kg/infusion) during long access (6 hr) compared to short access sessions (1 hr). Results showed that rats given long access to MPH showed an escalation of intake across sessions, with this escalation being more pronounced at the lower unit dose (0.1 mg/kg/infusion); in contrast, rats given short access to MPH did not show an increase in MPH self-administration across sessions at either MPH dose tested. Taken together, these results indicate that MPH is an effective intravenous reinforcer for rats and that, similar to other stimulants such as cocaine, amphetamine and methamphetamine, MPH is subject to abuse as reflected by dysregulated intake across repeated long access sessions.

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Figures

Figure 1
Figure 1
Number of active and inactive lever presses for the group mean plotted as a function of FR session during acquisition of MPH self-administration for Experiment 1. During the first five sessions, data are plotted from the FR 1 session only, and not from the autoshaping session.
Figure 2
Figure 2
Number of infusions earned and breakpoints plotted as a function of MPH dose (log scale) for the group mean for Experiment 1. “S” stands for saline vehicle.
Figure 3
Figure 3
Number of lever presses (active and inactive) and infusions earned plotted as a function of session for the group mean during contingent and non-contingent MPH administration for Experiment 2.
Figure 4
Figure 4
a. Number of MPH infusions earned plotted as a function of session for the 0.1 MPH ShA and LgA group means for Experiment 3. Fit lines display the best fit straight line. b. Number of MPH infusions earned plotted as a function of session for the 0.3 MPH ShA and LgA group means for Experiment 3. Fit lines display the best fit straight line.
Figure 4
Figure 4
a. Number of MPH infusions earned plotted as a function of session for the 0.1 MPH ShA and LgA group means for Experiment 3. Fit lines display the best fit straight line. b. Number of MPH infusions earned plotted as a function of session for the 0.3 MPH ShA and LgA group means for Experiment 3. Fit lines display the best fit straight line.
Figure 5
Figure 5
a. Number of MPH infusions earned plotted for each 5-min bin within the first 60 min during sessions 1 and 21 for the 0.1 MPH LgA Group. b. Number of MPH infusions earned plotted for each 5-min bin within the first 60 min during sessions 1 and 21 for the 0.1 MPH ShA Group. c. Number of MPH infusions earned plotted for each 5-min bin within the first 60 min during sessions 1 and 21 for the 0.3 MPH LgA Group. d. Number of MPH infusions earned plotted for each 5-min bin within the first 60 min during sessions 1 and 21 for the 0.3 MPH ShA Group.
Figure 5
Figure 5
a. Number of MPH infusions earned plotted for each 5-min bin within the first 60 min during sessions 1 and 21 for the 0.1 MPH LgA Group. b. Number of MPH infusions earned plotted for each 5-min bin within the first 60 min during sessions 1 and 21 for the 0.1 MPH ShA Group. c. Number of MPH infusions earned plotted for each 5-min bin within the first 60 min during sessions 1 and 21 for the 0.3 MPH LgA Group. d. Number of MPH infusions earned plotted for each 5-min bin within the first 60 min during sessions 1 and 21 for the 0.3 MPH ShA Group.
Figure 5
Figure 5
a. Number of MPH infusions earned plotted for each 5-min bin within the first 60 min during sessions 1 and 21 for the 0.1 MPH LgA Group. b. Number of MPH infusions earned plotted for each 5-min bin within the first 60 min during sessions 1 and 21 for the 0.1 MPH ShA Group. c. Number of MPH infusions earned plotted for each 5-min bin within the first 60 min during sessions 1 and 21 for the 0.3 MPH LgA Group. d. Number of MPH infusions earned plotted for each 5-min bin within the first 60 min during sessions 1 and 21 for the 0.3 MPH ShA Group.
Figure 5
Figure 5
a. Number of MPH infusions earned plotted for each 5-min bin within the first 60 min during sessions 1 and 21 for the 0.1 MPH LgA Group. b. Number of MPH infusions earned plotted for each 5-min bin within the first 60 min during sessions 1 and 21 for the 0.1 MPH ShA Group. c. Number of MPH infusions earned plotted for each 5-min bin within the first 60 min during sessions 1 and 21 for the 0.3 MPH LgA Group. d. Number of MPH infusions earned plotted for each 5-min bin within the first 60 min during sessions 1 and 21 for the 0.3 MPH ShA Group.
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