Long-term effects of the periadolescent environment on exploratory activity and aggressive behaviour in mice: social versus physical enrichment.
Physiology & Behavior. 2004-05-01; 81(3): 443-453
DOI: 10.1016/j.physbeh.2004.02.022
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Pietropaolo S(1), Branchi I, Cirulli F, Chiarotti F, Aloe L, Alleva E.
Author information:
(1)Section of Behavioural Neurosciences, Department of Cell Biology and
Neurosciences, Istituto Superiore di Sanità, Viale Regina Elena 299, 00161 Rome,
Italy.
The aims of the present study were (i) to investigate the effects of
environmental enrichment during periadolescence on different behavioural and
neurochemical responses in male CD-1 mice at adulthood and (ii) to describe the
relative role of the physical and social components of the enrichment in
producing these effects. Thirty 5-day-old mice were randomly assigned to one of
the following housing conditions lasting five consecutive days: (i) individually
housed in a standard cage, (ii) housed in pairs in a standard cage, (iii)
individually housed in a physically enriched cage, and (iv) housed in pairs in a
physically enriched cage. At adulthood, 80 days after the enrichment exposure,
the explorative behaviour in an open field, as well as the behaviour in
agonistic encounters, was evaluated in association with the analysis of selected
central (hypothalamic levels of nerve growth factor (NGF) and brain-derived
growth factor(BDNF)) and peripheral (plasma corticosterone levels) biochemical
parameters. The results show that the long-term effects of the physical and the
social enrichment are different and not additive. In particular, while social
enrichment by itself exerted very limited effects, physical enrichment decreased
the exploratory activity and altered social behaviour. Mice housed in pairs in
an enriched cage showed low activity levels in the open field, and they tended
to become more frequently dominant, although showing a more affiliative and less
aggressive social interaction strategy. Furthermore, they presented low levels
of hypothalamic NGF and high levels of brain-derived growth factor, suggesting
an important effect of the combination of social and physical enrichment on
neurobehavioral markers of brain plasticity and on animal ability to cope with
social challenges.