Maternal care counteracts behavioral effects of prenatal environmental stress in female rats.

There is extensive evidence in rats that prenatal environmental stress (PES) exposure and early postnatal altered maternal care, as a consequence of stress during gestation, can detrimentally affect the brain and behavioral development of the offspring. In order to separate the effect of PES on the fetuses from that on the behavior of the mother, in the present study, we used a cross-fostering procedure in which PES-fetuses were raised by non-stressed mothers and non PES-fetuses were raised by stressed mothers. In Experiment 1, non-stressed mothers showed significantly more maternal behavior than stressed mothers. In Experiment 2, when the female offspring from Experiment 1 reached maturity, they were tested for: (1) induced maternal behavior (MB), (2) plasma levels of corticosterone (Cpd B), progesterone (P), and estradiol (E(2)), (3) number of accessory olfactory bulb (AOB) mitral cells, and (4) c-fos expression measured in AOB and medial preoptic area (MPOA) neurons. We replicated our previous findings that the PES group reared by their own stressed mothers, when adult, attacked the young, expressed disorganized MB and showed altered Cpd B, P and E(2) levels, plus a male-like neuro-morphological pattern in the AOB, by comparison with the non-PES group, reared by their own non-stressed mothers. By contrast, when adult, the PES group reared by non-stressed mothers showed hormonal and morphological neuronal alterations, but they displayed appropriate (full) MB. The non-PES group raised by stressed mothers also showed altered hormone levels, but showed full MB and no morphological neuronal changes. Significant differences in the AOB and MPOA c-fos activity, related to whether or not MB was expressed, were found in the non-PES groups, but not in the PES group reared by non-stressed mothers. To our knowledge, this is the first study to document that adequate maternal care, early in development, can shape the subsequent expression of induced MB, overcoming neuro-morphological and hormonal alterations that are produced by prenatal environmental stress. We conclude that maternal care during early postnatal development can counteract detrimental effects of prenatal environmental stress, exerting long-lasting effects that modulate the behavioral phenotype of the offspring.