Environmental enrichment in BALB/c mice: effects in classical tests of anxiety and exposure to a predatory odor.

Early stimulation by environmental enrichment generally leads to improved learning abilities in rodents. However, the effects of environmental enrichment on emotional reactivity remain more questionable and were mostly studied by using classical tests of anxiety based on confrontation with a novel environment. The main goal of our study was to use different tests of anxiety to compare BALB/c mice reared in either a standard condition (SC) or enriched condition (EC). Exposure to cat feces was used to assess anxiety according to an ethoexperimental approach and a comparison was made with the elevated plus maze and the open field as classical tests of anxiety. In accordance with previous works, our results show that EC mice were more active than SC mice in the elevated plus maze and the open field. Thus, possibly as a direct consequence of frequent changes in their breeding conditions, reactivity to a novel environment was reduced in EC mice. However, the cat odor test revealed no intergroup differences for behavior, although corticosterone levels were reduced in EC mice. These results indicate that classical (i.e. reaction to novel environments) and ethoexperimental-based tests (i.e. exposure to predator cues) measure different aspects of emotional reactivity. Further studies using ECs should be useful for the delineation of the neurobiological substrates of these different reactions.