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| Modeling the Characteristics of Attention Deficit/Hyperactivity Disorder in the Spontaneously Hypertensive Rat |
| Monday, May 28, 2007 |
| 10:30 AM–11:50 AM |
| Madeleine AB |
| Area: EAB; Domain: Basic Research |
| Chair: Andrew T. Fox (Central Michigan University) |
| Discussant: James S. MacDonall (Fordham University) |
| Abstract: This symposium will highlight current research regarding the Spontaneously Hypertensive Rat (SHR) as an animal model of Attention/Deficit Hyperactivity Disorder (ADHD). Because ADHD is defined by such behavioral characteristics as impulsivity, inattention, hyperactivity, and learning difficulties, it is reasonable to assert that an appropriate animal model also ought to display these features. Research presented here will use mathematical modeling to explore the validity of the SHR as an animal model of ADHD with regard to these characteristics. |
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| Preference for Smaller, More Immediate Reinforcers in the Spontaneously Hypertensive Rat. |
| ANDREW T. FOX (Central Michigan University), Dennis J. Hand (Central Michigan University), Mark P. Reilly (Central Michigan University) |
| Abstract: Previous research (Adriani et al., 2003) failed to demonstrate strain differences between SHRs and controls (Wistar-Kyoto; WKYs) in preference for smaller, more immediate reinforcers over larger, more delayed reinforcers. Additional research is needed to assess the reliability of these results. To this end, we employed an intertemporal choice procedure in which SHRs and WKYs chose between a single pellet delivered immediately and three pellets delivered after a delay that varied in duration across sessions (0 to 24 s). In Experiment 1, delays were presented in ascending and then descending order and remained in effect for only one session. In Experiment 2, the order of conditions was random, each delay was left in effect for multiple sessions, and returns to baseline preceded each condition. In Experiment 1, SHRs chose the single pellet more than WKYs at the larger delays during the ascending series and at all delays during the descending series. In Experiment 2, SHRs chose the single pellet more than WKYs at the two highest delays. Modeling with hyperbolic discounting functions supported the notion that SHRs are more impulsive than WKYs. Thus, using an intertemporal choice procedure, SHRs can be shown to be more impulsive than WKYs. |
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| More than Just Waiting: Impulsivity, Hyperactivity, Inattention, and Timing in the DRL Performance of SHR, WKY, and Long Evans Rats. |
| FEDERICO SANABRIA (Arizona State University) |
| Abstract: Inefficient collection of reinforcers in DRL (differential reinforcement of low rates) is the kind of impulsivity that characterizes attention deficit hyperactivity disorder (ADHD). On the basis of such DRL performance, the utility of Spontaneously Hypertensive Rats (SHR) as a model of ADHD has been disputed (Bull et al, 2000; van den Bergh et al, 2006). These data were replicated in the performance of SHR relative to two control strains in two DRL tasks (5 and 60 s). Performance was analyzed using a model that assumes the concurrent operation of four independent processes: impulse control, activity, attention, and timing. Fits of this model suggest that, relative to other strains, SHRs were impulsive, hyperactive in DRL 60 s, but neither inattentive nor poor timers. Results support SHR as a model of the predominantly hyperactive/impulsive subtype of ADHD and indicate that inefficiency in reinforcer collection may confound impulsivity with the operation of other processes. Consistency with prior SHR data, diagnostic relevance, and potential implications for the study of timing disorders in ADHD, are discussed. |
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| Response Acquisition with Delayed Reinforcement in the Spontaneously Hypertensive Rat. |
| DENNIS J. HAND (Central Michigan University), Andrew T. Fox (Central Michigan University), Mark P. Reilly (Central Michigan University) |
| Abstract: The present study was conducted to further evaluate the validity of the SHR model of ADHD by characterizing learning of a novel response under conditions of delayed reinforcement. Seven experimentally naïve SHRs and a control group of seven normotensive Wistar-Kyoto (WKY) rats were exposed to a contingency where one lever press initiated pellet delivery after a 15-s, resetting delay. Rats in both groups acquired lever pressing, and the pattern of acquisition was well-described with a three-parameter, sigmoidal equation. Response acquisition was retarded in the SHRs; they took longer to acquire the behavior, exhibited lower response rates and earned fewer reinforcers over the course of the experiment. When reinforcer delivery was made immediate in a subsequent condition, the SHR exhibited higher response rates than the WKY, suggesting that the lower rates of responding seen in the SHR were due to the reinforcer delay. The results replicate previous research on response acquisition with delayed reinforcement and provide further validation of the SHR strain as a model of ADHD. Like humans diagnosed with ADHD, the SHRs appear to be hypersensitive to delayed consequences, which in the present context, interfered with learning a novel behavior. |
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