Risk taking during exploration of a plus-maze is greater in adolescent than in juvenile or adult mice

We investigated age-related changes in exploratory drive and anxiety in a plus-maze paradigm. We observed the behaviour of outbred CD-1 mice, Mus musculus, of both sexes at three ages: juvenile (35 days), adolescent (48 days) and adult (61 days). Juvenile and adult mice strongly avoided the open arms of the apparatus, suggesting high levels of anxiety. In contrast, adolescents spent similar amounts of time in both open and closed arms. They also entered the open arms more quickly and more often than the other age groups. No age-related differences were found in the frequency of the stretched-attend posture, a behavioural pattern considered to indicate risk assessment. The data can be interpreted in terms of either an increased exploratory drive or reduced environment-related anxiety, or both, during the adolescent period. This is consistent with previous evidence of elevated levels of novelty seeking and reduced behavioural and physiological responses to stressful situations in mice and rats around this age. (C) 2002 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.