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. 2011 Dec;22(8):794-804.
doi: 10.1097/FBP.0b013e32834d623e.

Strain differences in self-administration of methylphenidate and sucrose pellets in a rat model of attention-deficit hyperactivity disorder

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

Strain differences in self-administration of methylphenidate and sucrose pellets in a rat model of attention-deficit hyperactivity disorder

Julie A Marusich et al. Behav Pharmacol. 2011 Dec.

Abstract

Despite its abuse potential, methylphenidate (MPH) is widely prescribed for treatment of attention-deficit hyperactivity disorder (ADHD). The purpose of the present study was to examine MPH self-administration in a rat model of ADHD. Experiment 1 examined the acquisition of MPH self-administration and assessed the MPH dose-effect curve in spontaneously hypertensive rats (SHR), an inbred rat model of ADHD, Wistar Kyotos (WKY), the progenitor strain for SHR, and Sprague-Dawley (SD), an outbred control strain. Experiment 2 replicated Experiment 1, but replaced MPH infusions with sucrose pellets. Initial acquisition of MPH self-administration was greater in SHR and SD than WKY. However, with extended training using an incrementing fixed ratio schedule SHR and WKY did not differ in responding for MPH using the training dose (0.3 mg/kg/infusion) or other unit doses, except that SHR showed greater responding than WKY at 0.1 mg/kg/infusion. SHR also showed greater acquisition and maintenance of sucrose-reinforced responding compared with both WKY and SD. Greater initial acquisition of MPH self-administration in SHR than WKY may not be due to a strain-specific difference in sensitivity to the reinforcing effect of MPH.

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Conflict of interest statement

The authors have no conflicts of interest.

Figures

Figure 1
Figure 1
Upper panel; Number of active lever presses for the group mean of each strain plotted as a function of session during acquisition of MPH self-administration for Experiment 1. Data are plotted from the FR 1 session that followed the autoshaping session. Lower panel; Number of active lever presses for the mean of each strain plotted as a function of FR requirement during MPH self-administration for Experiment 1.
Figure 1
Figure 1
Upper panel; Number of active lever presses for the group mean of each strain plotted as a function of session during acquisition of MPH self-administration for Experiment 1. Data are plotted from the FR 1 session that followed the autoshaping session. Lower panel; Number of active lever presses for the mean of each strain plotted as a function of FR requirement during MPH self-administration for Experiment 1.
Figure 2
Figure 2
Number of active lever presses for the mean of each strain plotted as a function of session during food restriction compared to during free feeding conditions.
Figure 3
Figure 3
Upper panel. Number of active lever presses plotted as a function of MPH dose (log scale) for the mean of each strain for Experiment 1. “S” stands for saline vehicle. * significant difference (p < .05) between SD and WKY. # significant difference (p < .05) between SHR and WKY. Lower panel: Amount of MPH intake plotted as a function of MPH dose (log scale) for the mean of each strain for Experiment 1. “S” stands for saline vehicle. * significant difference (p < .05) between SD and WKY.
Figure 3
Figure 3
Upper panel. Number of active lever presses plotted as a function of MPH dose (log scale) for the mean of each strain for Experiment 1. “S” stands for saline vehicle. * significant difference (p < .05) between SD and WKY. # significant difference (p < .05) between SHR and WKY. Lower panel: Amount of MPH intake plotted as a function of MPH dose (log scale) for the mean of each strain for Experiment 1. “S” stands for saline vehicle. * significant difference (p < .05) between SD and WKY.
Figure 4
Figure 4
Figure 4a. Number of active lever presses for the group mean of each strain plotted as a function of session during acquisition of sucrose-reinforced responding for Experiment 2. Data are plotted from the FR 1 session that followed the autoshaping session. Figure 4b. Number of active lever presses for the mean for each strain plotted as a function of FR requirement during sucrose-reinforced responding for Experiment 2.
Figure 4
Figure 4
Figure 4a. Number of active lever presses for the group mean of each strain plotted as a function of session during acquisition of sucrose-reinforced responding for Experiment 2. Data are plotted from the FR 1 session that followed the autoshaping session. Figure 4b. Number of active lever presses for the mean for each strain plotted as a function of FR requirement during sucrose-reinforced responding for Experiment 2.
Figure 5
Figure 5
Number of active lever presses for the mean of each strain plotted as a function of session during food restriction, free feeding, and extinction phases with sucrose-reinforced responding for Experiment 2.
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