Rearing environmental enrichment in two inbred strains of mice: 1. Effectson emotional reactivity

The effects of an enriched rearing environment on two types of anxiety-like behavior (designated "trait" and "state" anxiety) and on spontaneous activ ity were investigated in two inbred strains of mice, BALB/c (C) and C57BL/6 (B6). Subjects were socially reared from birth to 56 days of age under enri ched or standard rearing conditions. The enriched environment consisted of an assembly of plastic boxes in which a various number of objects (running wheels, pieces of plastic, etc.) offered the possibility of multiple activi ties. The subjects were subsequently tested in three situations: a spontane ous activity recorder, an elevated plus-maze test (a model of state anxiety ), and a free exploration test (a model of trait anxiety). No group differe nces could be found in spontaneous activity. Environmental enrichment, howe ver, decreased the level of both types of anxiety-like behavior in the C st rain. In contrast, the level of trait anxiety of the B6 mite was not modifi ed. The results were discussed in relation to possible CNS modifications, e specially in the limbic system.