Maternal behavior, novelty confrontation, and subcortical c-Fos expression during lactation period are shaped by gestational environment.

The environmental context during gestation may modulate the postpartum variations in maternal behaviors observed within different animal species. Most of our experimental knowledge on this phenomenon and its physiological effects have been gained by confronting the pregnant mother with stressful situations, with the consensual results indicating a reduced maternal behavior and a hyper reactivity of stress-related neural paths. Here, in contrast, by exposing nulliparous rats strictly during pregnancy to a standard laboratory environment (STD) or a highly stimulating sensory and social environment (EE), we investigated the hypothesis that subjects frequently exposed to social stimuli and novel situations during pregnancy will show postpartum changes in subcortical brain areas' activity related to the processing of social stimuli and novelty, such that there will be modifications in maternal behavior. We found that EE mothers doubled the levels of licking and grooming, and active hovering over pups during the first postpartum week than STD dams, without a difference in the time of contact with the pups. Associated with these behaviors, EE dams showed increased c-Fos immunoreaction in hypothalamic nuclei and distinct responses in amygdalar nuclei, than STD dams. In the maternal defensive test, EE dams tripled the levels of aggressive behaviors of the STD rats. Additionally, in two different tests, EE mothers showed lower levels of postpartum anxiety-like behaviors when confronted with novel situations. Our results demonstrate that the activity of brain areas related to social behavior is adaptable by environmental circumstances experienced during gestation, presumably to prepare the progeny for these particular conditions.

Enriched environment restricted to gestation accelerates the development of sensory and motor circuits in the rat pup.

The effects of stimulating environments on the neural plasticity of the adult brain have been well explored; however, how an enriched environment (EE) affects the mother-fetus interaction is poorly understood. We hypothesized that an enriched environment restricted to pregnancy will succeed in accelerating the development of sensory and motor circuits in the offspring. Pregnant Wistar rats were maintained either under a standard condition - two animals per standard cage- or an enriched environment - eight subjects in larger cages with different physical configurations-. After birth, litters from both groups (n=16 per group) were cross-fostered with mothers that were simultaneously maintained under standard environment during pregnancy. Sensory and motor development were studied in the pups of both groups with a battery of reflex and physical tests. Auditory and gait reflexes appeared two days earlier in the offspring of EE rats as compared to control subjects (p<0.05). In addition, EE pups displayed a better performance in righting reflex, inclined board and geotaxis tests (p<0.05). Differences were found even three weeks after birth. We conclude that EE limited to the phase of pregnancy stimulates the development of pups inutero so that they are born with a higher grade of development.