Differences in open-field behavior and in learning tasks between two rat strains differing in their reactivity to stressors.

The study characterizes differences between inbred Wistar-Kyoto (WKYs) and Brown-Norway (BNs) rats in open-field behavior, and in discriminative learning and acquisition of an avoidance learning task. Hyper-reactivity of WKYs to novelty was demonstrated in an open-field test. Discriminative learning and retention thereof was slower in WKYs, but as efficient as in BNs. Acquisition of avoidance learning was also slower in WKYs, but their maximal avoidance score was much higher (∼85%) than in BNs. Also, recall of avoidance learning was slower for WKYs. We conclude: (1) hyper-reactivity of WKYs to novelty is expressed by their exceptional immobility and excess defecation in the open-field and is paralleled by their known hyper-reactivity to stressful stimuli, and (2) no strain differences exist in the ability to learn a discriminative task, but both acquisition and recall of an avoidance task are slower in WKYs. This may imply that the degree of reactivity to stressful environmental stimuli may play an important role in the acquisition of learning.