The postnatal environment can counteract prenatal effects on cognitive ability, cell proliferation, and synaptic protein expression.

Many environmental factors during the pre- or postnatal period can affect an individual's cognitive function and neural development throughout life. Little is known, however, about the combined effects of the pre- and postnatal environments on cognitive function of adult offspring and structural alterations in the adult brain. In this study, we confirmed that pre- or postnatal stress impaired learning and memory performance of rats. Conversely, pre- or postnatal enriched housing improved behavioral performance. These experience-dependent behavioral alterations were consistent with changes in 5-bromo-2'-deoxyuridine-labeled cell number in the granule cell layer of the hippocampus and in the expression level of synaptic markers such as neuronal cell adhesion molecule and synaptophysin, and expression of a neurotrophic factor, brain-derived neurotrophic factor. Postnatal stress appeared to have no influence on cell proliferation, however. We did find that postnatal environment could attenuate prenatal effects partly via a longitudinal cross-housing study, in which pups born to mothers housed under enriched conditions were reared under stressful conditions and vice versa. These results suggest that postnatal environmental manipulations can counteract the cognitive alterations in early adulthood and the structural changes in the young adult brain induced by prenatal experience.