Maternal Programming of Sexual Behavior and Hypothalamic-Pituitary-Gonadal Function in the Female Rat

Variations in parental care predict the age of puberty, sexual activity in adolescence and the age at first pregnancy in humans. These findings parallel descriptions of maternal effects on phenotypic variation in reproductive function in other species. Despite the prevalence of such reports, little is known about potential biological mechanisms and this especially true for effects on female reproductive development. We examined the hypothesis that parental care might alter hypothalamic-pituitary-ovarian function and thus reproductive function in the female offspring of rat mothers that vary pup licking/grooming (LG) over the first week postpartum. As adults, the female offspring of Low LG mothers showed 1) increased sexual receptivity; 2) increased plasma levels of luteinizing hormone (LH) and progesterone at proestrus; 3) an increased positive-feedback effect of estradiol on both plasma LH levels and gonadotropin releasing-hormone (GnRH) expression in the medial preoptic region; and 4) increased estrogen receptor α (ERα) expression in the anterioventral paraventricular nucleus, a system that regulates GnRH. The results of a cross-fostering study provide evidence for a direct effect of postnatal maternal care as well as a possible prenatal influence. Indeed, we found evidence for increased fetal testosterone levels at embryonic day 20 in the female fetuses of High compared to Low LG mothers. Finally, the female offspring of Low LG mothers showed accelerated puberty compared to those of High LG mothers. These data suggest maternal effects in the rat on the development of neuroendocrine systems that regulate female sexual behaviour. Together with studies revealing a maternal effect on the maternal behavior of the female offspring, these findings suggest that maternal care can program alternative reproductive phenotypes in the rat through regionally-specific effects on ERα expression

Effect of maternal care on maternal responsiveness and astrocyte plasticity in the medial amygdala and medial preoptic nucleus in the rat

Estrogen acts on maternal circuitry to establish maternal behaviour in otherwise non-maternal rats. The precise mechanisms by which estrogen primes maternal circuitry are unknown; however, the medial preoptic area (MPOA) stimulates maternal behaviour whilst the medial amygdala (MeA) inhibits it. This thesis aimed to address the link between estrogen sensitivity, astroglia and maternal behaviour. Maternal care influences maternal behaviour of female offspring. One mechanism underlying this influence is differential estrogen sensitivity within the MPOA. Estrogen receptor alpha (ERalpha) expression was examined in offspring of High and Low licking/grooming (LG) dams within the MPOA. Enhanced expression ERalpha was limited to the medial preoptic nucleus in offspring of High LG dams and the anteroventral periventricular nucleus in Low LG dams. Adult nulliparous offspring of High and Low LG dams were assessed for maternal responsiveness using the pup sensitization paradigm. Offspring of Highs showed maternal behaviour significantly earlier than offspring of Lows. Brains of pup-exposed and pup-naive High and Low offspring were analyzed for astroglial markers glial fibrillary acidic protein (GFAP) and glutamine synthetase. Pup-naive animals showed more GFAP positive cells within the posteroventral MeA, with no differences within the MPOA and no effect of maternal care. Glutamine synthetase, a glial-derived enzyme necessary for glutamate production, showed greater expression within the MeA of High LG pup-naive animals; with no maternal care differences observed in pup-experienced animals. Thus, long-lasting changes within maternal circuitry established in early life are reflected in regionally specific enhanced estrogen sensitivity and latency to display maternal behaviour, but the effects are less clear with respect to astroglia

Effect of ovariectomy and steroid treatment in the sexual behavior of the female.

<p>Mean±SEM lordosis rating or inter-intromission interval in the adult female offspring of Low or High LG mothers tested with a stud male in the pacing chamber arena (n = 7–10/group) either intact (at proestrus) or following ovariectomy with E2B+progesterone replacement. For the lordosis rating data, groups lying underneath the line differ significantly (<i>p</i> <0.05) from the High LG/intact group such that the maternal effect is apparent among intact animals, but not ovariectomized animals with a common level of steroid replacement. For the inter-intromission interval data, the maternal effect is apparent (* <i>p</i> <0.05) among both intact and ovariectomy/steroid-primed conditions.</p