Standard housed rats are more sensitive to rewards than enriched housed rats as reflected by their anticipatory behaviour

The present study was designed to investigate the effects of potentially stressful standard housing conditions for laboratory rats on the sensitivity to rewards as reflected by their anticipatory behaviour for sucrose. This anticipatory response is evoked in a conditioning paradigm in which a sucrose reward is repeatedly announced by a stimulus. The underlying neurocircuitry of this anticipatory response in expectation of a reward involves mesolimbic dopaminergic systems of which it is known that they can be sensitised by stressors. The results show that the anticipatory response for the sucrose reward is stronger in the standard housed animals which indicates that these animals are more sensitive to the reward than the enriched animals. From this, it is concluded that standard housed rats are stressed which is likely to be caused by deprivation of the ability to satisfy behavioural needs in these impoverished housing conditions. (C) 2002 Elsevier Science B.V. All rights reserved.