The spontaneously hypertensive rat (SHR) as an animal model of childhood hyperactivity (ADHD): changed reactivity to reinforcers and to psychomotor stimulants

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Childhood hyperactivity (attention-deficit hyperactivity disorder, ADHD) is a behavior disorder affecting 2–6% of grade-school children. The main symptoms are attention problems and hyperkinesis. The disorder is commonly treated with psychomotor stimulants, usually methylphenidate hydrochloride (ritalin) or d-amphetamine. Neither the cause of the disorder nor the basis of the effectiveness of the drug treatment is well understood. Differences in reinforcement processes have been implicated as part of the underlying problem. The main purpose of the present research was to investigate reinforcement processes and motor characteristics with and without stimulant medication in SHR, as an animal model of ADHD, and WKY controls, its normoactive progenitor strain. SHR behavior turned out to be more sensitive to immediate reinforcement and proportionately less sensitive to delayed reinforcement when compared to the behavior of WKY, as demonstrated by systematic changes in rates of responding throughout fixed-interval schedules of reinforcement of bar-presses by water. The psychomotor stimulants weakened the control by immediate reinforcers and strengthened the control by delayed reinforcers, with the effect of the drugs being more pronounced in WKY than in SHR. The results are consistent with clinical observations that ADHD children are less willing than others to accept “delayed gratification” and that methylphenidate increases the control of delayed reward over their behavior.

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    • Spontaneously hypertensive (SHR) rats choose more impulsively than Wistar-Kyoto (WKY) rats on a delay discounting task

      2019, Behavioural Brain Research
      Citation Excerpt :

      Investigating the impulsive choices of the SHR is important because the SHR strain of rats is used as an animal model of Attention Deficit Hyperactivity Disorder (ADHD), capturing the notion that ADHD is a developmental disorder [29], and this idea is consistent with theoretical approaches predicting ADHD [30]. Derived from the WKY and originally selected for its hypertensive phenotype (high systolic blood pressure) [31], the SHR shows behavioral symptoms of ADHD such as poor sustained attention [32], learning insufficiencies [33], resistance to extinction [34], memory deficits [35], hyperactivity [36,37], hypersensitivity to delayed consequences [38], and impulsivity [8,39]. The WKY, then, may serve as a useful control to the SHR [44,29,30], and these two animal models can be used to examine aspects of impulsivity characterizing ADHD [45–48].

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    1

    Current address: The National Cerebral Palsy Hospital, Oslo, Norway.

    2

    Current address: The National Hospital for Epilepsy, Sandvika, Norway.

    3

    These studies were supported by the Norwegian Research Council for Science and the Humanities Grant 326.91/039 (T.S.) and by NSF Grant BNS-9020357 (M.A.M.).

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