Effects of environmental enrichment on the behavioural consequences of early-life stress in rats

Background: Maternal separation (MS) is a major cause of chronic life stress and increased risk of psychiatric illness. Environmental enrichment (EE) enhances brain plasticity and neurogenesis. We investigated the consequences of maternal separation and early weaning and whether these could be prevented by environment enrichment. Methods: Wistar rat pups were divided into 3 groups; an MS group subjected to 3 h/day of maternal separation from postnatal day (PND) 4 till early weaning at PND 18; a maternal separation + environment enrichment (MSEE) group subjected to 3 h/day of maternal separation from PND 4 during which rats were transferred to an enriched cage, till early weaning at PND 18; and a control group. Rats were then subjected to a series of behavioural tests to assess exploratory behaviour, anxiety, memory, species-typical behaviour and depression. At PND 48, rats were sacrificed, and their brains excised for biochemical assessment. Results: Anxiety was increased in MS rats, evidenced by a marked reduction of time spent in the light side of the black-white alley. Anxiety was significantly decreased by EE. MS rats had suppression of their natural exploratory behaviour, with decreased number of squares crossed in the open field test (P = 0.031), and a complete absence of rearing behaviour. Early life EE of MS rats restored exploratory behaviour to or towards control values in the open field test. Spatial memory showed a marked improvement by EE. Conclusion: Early life EE during and after maternal separation in rats ameliorates multiple adverse psychological consequences. Keywords