Set shifting in a rodent model of attention-deficit/hyperactivity disorder

Two experiments compared spontaneously hypertensive rats (SHRs; a rodent model of attention-deficit/hyperactivity disorder) and Wistar rats (a normoactive control strain), on the acquisition of a set-shifting strategy. In Experiment 1, SHRs and Wistar rats were equivalent in trials to criterion to learn a brightness or a texture discrimination but SHRs were faster than Wistar rats in shifting to the opposite discrimination when there was 1 or 2 days between the initial discrimination and the shift. In Experiment 2, SHRs and Wistar rats were equivalent in shifting when the shift between discriminations occurred immediately after a criterion had been met in the first discrimination. The results are discussed in terms of a failure of SHRs to store or retrieve an initial discrimination and/or latent inhibition over a delay, leading to faster acquisition of a set-shift. This failure in storage or retrieval may be the result of a hypoactive dopamine system in the prefrontal cortex and nucleus accumbens shell as well as abnormalities in entorhinal cortex in SHRs.