Abstract
Stressful events in an early postnatal period have critical implications for the individual's life and can increase later risk for psychiatric disorders. The aim of this study was to investigate the influence of early-life stress on the social behavior of adult male and female mice. C57Bl/6 mice were exposed to maternal separation (MS, 3 h once a day) or handling (HD, 15 min once a day) on postnatal day 2 through 14. Adult male and female mice were tested for social behavior in the social interaction test and for individual behavior in the plus-maze and open-field tests. Female mice exposed to maternal separation had increased social behavior and increased anxiety. MS male mice had no changes in social behavior but had significantly disrupted individual behavior, including locomotor and exploratory activity. Handling had positive effects on social behavior in males and females and decreased anxiety in males. Our results support the hypothesis that brief separation of pups from their mothers (handling), which can be considered as moderate stress, may result in future positive changes in behavior. Maternal separation has deleterious effects on individual behavior and significant sex-specific effects on social behavior.
Highlights
There is a wealth of data demonstrating that exposure to stressful events early in life can increase the risk for psychiatric disorders, including mood and anxiety disorders [1,2,3,4]
Postnatal stress has an effect on body weight in males (H (2, 27) = 6.8, p = 0 03); in HD males, the body weight is reduced in comparison with the control (p = 0 017), and Maternal separation (MS) males have a tendency to reduce the body weight (p = 0 0841)
Males were less anxious than females (more time spent in open arms (H (1, 52) = 6.6, p = 0 01) and center (H (1, 52) = 19.9, p < 0 001)) and have higher locomotor activity than females (more total number of entries (H (1, N = 52) = 15.9, p = 0 0001); more passages (H (1, N = 52) = 6.2, p = 0 0126))
Summary
There is a wealth of data demonstrating that exposure to stressful events early in life can increase the risk for psychiatric disorders, including mood and anxiety disorders [1,2,3,4]. Separation of pups from their dams and nest for 3 or more hours once a day during the first two postnatal weeks produces increased anxiety-like behavior and exaggerated hypothalamicpituitary-adrenal (HPA)-axis responses to stress in adulthood as well as behavioral and cognitive disturbances [20,21,22,23,24]. These effects have well been studied in rats, while behavioral changes in MS mice remain inconsistent [18, 25]
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