Maternal separation and early social enrichment increase anxiety-related behaviours of adolescent rats in the elevated plus maze

Introduction: Adverse or favourable rearing conditions early in life affect emotional response during adolescence. To study the effect of early rearing on emotional response, animal models such as maternal separation (MS) and social enrichment (SE) by community nesting have been useful. However, the comparison of the effect of MS and SE on anxiety-related behaviours in adolescent rats is unknown. Objective: This study aimed to assess the effects of MS and SE on the emotional response of adolescent rats exposed to the elevated plus-maze test (EPM). Method: Pregnant Wistar rats were randomly distributed into three groups according to the rearing condition. In the MS group, pups were separated daily from their dams for 180 minutes, from postnatal day (P) 2 to 14. In the SE group, two females that gave birth synchronously were housed in a cage with a litter of eight pups. Females from control standard housing (SH) were individually housed and kept with their offspring until weaning (P23). On P32, anxiety-related measures were evaluated using an EPM. Results: MS and SE increase anxiety-related behaviours and locomotion in rats exposed to the EPM. SE had sex-dependent effects on anxiety-related measures, increasing vertical activity in females and horizontal activity in males. MS but not SE increased body weight gain in female rats. Conclusion: Adverse or favourable rearing conditions early in life may result in an increased anxiety phenotype in the EPM during adolescence. It is likely that the favourable effect of SE depends on the number of dams per communal nest.