The interplay of genetic makeup and environmental influences is known to be complex, with important and sometimes irreversible consequences for the development of molecular and behavioral phenotypes. Separating mother rat and pup for long periods of time (3 hours per day during the first 2 weeks of life) has been shown to heighten the response of the hypothalamus-pituitary-adrenal axis to stressful stimuli; in addition, expression of corticotropin-releasing factor increases, and the dampening effect of glucocorticoids is reduced. These pups also display a reluctance to explore novel environments. Francis et al. have examined the extent to which subsequent rearing of these maternally separated pups in enriched circumstances (a larger cage with playground and toys) can compensate for their early life experiences. They find that the behavioral responses to stress and novelty can be reversed, but that the molecular setpoints remain unchanged. -- GJC
J. Neurosci. 22, 7840 (2002).
