Several studies have demonstrated that the early postweaning phase (3-7 weeks of age) is a crucial ontogenic period for rodent neurobehavioral development. During this phase, both brain and behavior are highly sensitive to environmental variations (i.e., changes in the standard housing conditions). In the present study, male and female C57BL/6 mice were housed at weaning in cages provided with a Plexiglas lid, and thus, they were deprived of the opportunity to perform climbing activity on the cage grid--a major component of mouse behavior in standard laboratory environments. At early adulthood (7-10 weeks old), mice underwent an extensive battery of behavioral tests. The present study demonstrates for the first time the psychological, sex-specific relevance of home-cage grid-climbing activity in mice, showing that its prevention alters fear-conditioned responses in mice of both sexes and induces psychotic-like and anxious behaviors in females only. The data further highlight the importance of the early postweaning phase for the study of environmentally induced neurobehavioral plasticity and the design of animal models of psychiatric disorders on the basis of environmental manipulation in early postweaning life.
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