Effects of pre- and postnatal stimulation on developmental, emotional, and cognitive aspects in rodents: a review

Interactions between the organism and its environment, during pregnancy as well as during the postnatal period, can lead to important neurobehavioral changes. We briefly review the literature, and successively present the main results from our laboratory concerning the behavioral effects of prenatal stress, differential rearing conditions, and postnatal handling. We show that submitting primiparous DA/HAN rats to an acute emotional stress (exposure to a cat) at gestational day10, 14, or 19 leads to greatly increased mortality of pups and to decreased body weight of surviving animals. The effects of such a stressor on emotional reactivity are less obvious. Cognitive processes are impaired depending on the learning task. Enriched environments restore abnormal behaviors (emotional reactivity, motor skills, motor and spatial learning) due to brain trauma or genetic deficiencies. In any case, environmental enrichment does prevent or slow down aging effects. The effects of postnatal handling noted when using classical tests of emotional reactivity also are clear when defensive reaction paradigms are used. Furthermore, pregnant females that are early handled are less anxious than nonhandled females. We hypothesize that, when subjected to a stressor, the offspring of early-handled females would be protected from the deleterious effects of this stress compared to pups of nonhandled females.