Maternal separation decreases adult hippocampal cell proliferation and impairs cognitive performance but has little effect on stress sensitivity and anxiety in adult Wistar rats

Stressful events during childhood are thought to increase the risk for the development of adult psychopathology. A widely used animal model for early life stress is maternal separation (MS), which is thought to affect development and cause alterations in neuroendocrine stress reactivity and emotionality lasting into adulthood. However, results obtained with this paradigm are inconsistent. Here we investigated whether this variation may be related to the type of stressor or the tests used to assess adult stress sensitivity and behavioral performance. Rat pups were exposed to a 3 h daily MS protocol during postnatal weeks 1–2. In adulthood, animals were subjected to a wide variety of stressors and tests to obtain a better view on the effects of MS on adult hypothalamic–pituitary–adrenal (HPA) axis regulation, anxiety-like behavior, social interaction and cognition. Also, the influence of MS on adult hippocampal neurogenesis was studied because it might underlie changes in neuroendocrine regulation and behavioral performance. The results show that, independent of the nature of the stressor, MS did not affect the neuroendocrine response. MS did not influence anxiety-like behavior, explorative behavior and social interaction, but did affect cognitive function in an object recognition task. The amount of new born cells in the hippocampal dentate gyrus was significantly decreased in MS animals; yet, cell differentiation and survival were not altered. In conclusion, while interfering with the mother–infant relationship early in life did affect some aspects of adult neuroplasticity and cognitive function, it did not lead to permanent changes in stress sensitivity and emotionality.