Bisphenol A (BPA) is a widespread estrogenic compound. We investigated the effects of maternal exposure to BPA at reference doses on sexual behavior and neuroendocrine functions of female offspring in C57BL/6J mice. The dams were orally exposed to vehicle alone or vehicle-containing BPA at doses equivalent to the no observed adverse effect level (5 mg/kg body weight per day) and tolerable daily intake (TDI, 0.05 mg/kg body weight per day) level from gestational day 15 until weaning. Developmental exposure to BPA increased the lordosis quotient in naive females exposed to BPA at the TDI dose only. BPA exposure had no effect on olfactory preference, ability to express masculine behaviors or number of calbindin-positive cells, a sexually dimorphic population of the preoptic area. BPA at both doses selectively increased kisspeptin cell number in the preoptic periventricular nucleus of the rostral periventricular area of the third ventricle in adult females. It did not affect the number of GNRH-positive cells or percentage of kisspeptin appositions on GNRH neurons in the preoptic area. These changes were associated with higher levels of estradiol (E2) at the TDI dose while levels of LH, estrus cyclicity, ovarian and uterine weights, and fertility remained unaffected. Delay in the time of vaginal opening was observed during the postnatal period at TDI dose, without any alteration in body growth. This shows that developmental exposure to BPA at reference doses did not masculinize and defeminize the neural circuitry underlying sexual behavior in female mice. The TDI dose specifically exacerbated responses normally induced by ovarian E2, through estrogen receptor α, during the postnatal/prepubertal period.
Lydie Naulé, Marie Picot, Mariangela Martini, Caroline Parmentier, Hélène Hardin-Pouzet, Matthieu Keller, Isabelle Franceschini and Sakina Mhaouty-Kodja
Caroline Alfaia, Vincent Robert, Kevin Poissenot, Yves Levern, Daniel Guillaume, Shel-Hwa Yeo, William H Colledge and Isabelle Franceschini
Kiss1 neurons of the arcuate (ARC) nucleus form an interconnected network of cells that communicate via neurokinin B (encoded by Tac2) and its receptor (encoded by Tacr3) and play key roles in the control of the reproductive axis through sex hormone-regulated synthesis and release of kisspeptin peptides (Kp, encoded by Kiss1). The aim of this study was to determine whether the Kiss1 cell population of the ARC already displays sexually dimorphic features at embryonic age E16.5 in mice. At this time of development, Kiss1-GFP- and Kp-immunoreactive cell bodies were restricted to the ARC and not found in the pre-optic area (POA). The Kiss1-GFP cell population was identical in size between sexes but had significantly lower Kiss1, Tac2, and Tacr3 mRNA levels and lower Kp-ir fiber density in the POA in male compared to female fetuses. Receptors for androgen (Ar) and estrogen (Esr1, Esr2, Gpr30) and the Cyp19a1 gene (encoding the estradiol-producing enzyme aromatase) transcripts were also detected in fetal ARC Kiss1-GFP cells with significant sex differences for Ar (higher in males) and Esr1 (higher in females). Functional studies on primary cultures of sorted fetal Kiss1-GFP cells revealed a significant negative effect of estradiol treatment on neurite outgrowth on the fourth day of culture in the female group specifically. We conclude that the ARC Kiss1 cell population is already sexually differentiated at E16.5 and that its morphogenetic development may be particularly vulnerable to estradiol exposure at this early developmental time.