Evaluation of the spontaneously hypertensive rat as a model of attention deficit hyperactivity disorder: acquisition and performance of the DRL-60s test

The spontaneously hypertensive rat (SHR) has been proposed as an animal model of attention deficit hyperactivity disorder (ADHD). It is hyperactive in a variety of behavioural paradigms and has a sustained attention deficit. This study investigated whether the SHR would exhibit impaired acquisition and performance of a differential low rate (DRL) schedule of reinforcement because of increased impulsivity, compared with the Wistar-Kyoto (WKY) rat, its normotensive progenitor. In addition, the performance of both strains was compared with Sprague-Dawley (CD) rats. SHR rats were not impaired in the acquisition of this test compared with WKY or CD rats. Indeed, WKY rats took significantly longer to acquire this task than either SHR or CD rats. The WKY rats performed poorly compared with the other strains in those parts of training that required high response rates (e.g. FR-1), but better where low rates of responding were required (e.g. DRL-30s and DRL-60s). The rank order of efficiency when performance was measured under DRL-60s was WRY > SHR > CD. However, the pattern of responding at DRL-60s suggested poor schedule control for the WKY rats. Therefore, the performance of SHR in the DRL test does not appear to represent a valid model of ADHD. Further, our findings with the WKY rat suggest that this strain is a poor behavioural control for the SHR. (C) 2000 Elsevier Science B.V. All rights reserved.