We tested the general assumption that enrichment of the housing environment is rewarding to laboratory rats, Rattus norvegicus. We used the behavioural response in anticipation of a forthcoming reward as a measure of the rewarding property of a simple enriched cage. For this, a Pavlovian conditioning schedule was applied to announce the oncoming transfer to an enriched cage. The response of rats in anticipation of this transfer was compared with that of rats that expected sexual contact, transfer to a standard cage or forced swimming. We also characterized the behavioural profile of the anticipatory response, because until now only general descriptions of this behaviour have been available. The strong increase in activity in anticipation of both an enriched cage and sexual contact and the similar response in terms of the behavioural elements analysed indicate that the appraisal of access to an enriched cage shares a common denominator with the perception of sexual contact. Because sexual contact is generally accepted to have highly rewarding properties to rats, we concluded that the enriched cage is highly rewarding as well. The anticipatory response for sexual contact or an enriched cage was clearly different from the anticipation for access to a standard cage or a forced swim session, indicating that the anticipatory response is related to the positive nature of the stimulus. In general, anticipation appears to be quantifiable by the level of activity measured by the total frequency of behavioural elements displayed. Some behavioural elements, such as exploration, locomotion, arousal and grooming, seem to be more specifically related to the nature of the forthcoming stimulus. (C) 2003 Published by Elsevier Ltd on behalf of The Association for the Study of Animal Behaviour.
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