Bisphenol-A differently affects estrogen receptors-alpha in estrous-cycling and lactating female rats

The PCOS-NAFLD Multidisease Phenotype Occurred in Medaka Fish Four Generations after the Removal of Bisphenol A Exposure

As a heterogeneous reproductive disorder, polycystic ovary syndrome (PCOS) can be caused by genetic, diet, and environmental factors. Bisphenol A (BPA) can induce PCOS and nonalcoholic fatty liver disease (NAFLD) due to direct exposure; however, whether these phenotypes persist in future unexposed generations is not currently understood. In a previous study, we observed that transgenerational NAFLD persisted in female medaka for five generations (F4) after exposure to an environmentally relevant concentration (10 μg/L) of BPA. Here, we demonstrate PCOS in the same F4 generation female medaka that developed NAFLD. The ovaries contained immature follicles, restricted follicular progression, and degenerated follicles, which are characteristics of PCOS. Untargeted metabolomic analysis revealed 17 biomarkers in the ovary of BPA lineage fish, whereas transcriptomic analysis revealed 292 genes abnormally expressed, which were similar to human patients with PCOS. Metabolomic-transcriptomic joint pathway analysis revealed activation of the cancerous pathway, arginine-proline metabolism, insulin signaling, AMPK, and HOTAIR regulatory pathways, as well as upstream regulators esr1 and tgf signaling in the ovary. The present results suggest that ancestral BPA exposure can lead to PCOS phenotypes in the subsequent unexposed generations and warrant further investigations into potential health risks in future generations caused by initial exposure to EDCs.

Impact of a bisphenol A, F, and S mixture and maternal care on the brain transcriptome of rat dams and pups

Products containing BPA structural analog replacements have increased in response to growing public concern over adverse effects of BPA. Although humans are regularly exposed to a mixture of bisphenols, few studies have examined effects of prenatal exposure to BPA alternatives or bisphenol mixtures. In the present study, we investigate the effect of exposure to an environmentally-relevant, low-dose (150 ug/kg body weight per day) mixture of BPA, BPS, and BPF during gestation on the brain transcriptome in Long-Evans pups and dams using Tag RNA-sequencing. We also examined the association between dam licking and grooming, which also has enduring effects on pup neural development, and the transcriptomes. Associations between licking and grooming and the transcriptome were region-specific, with the hypothalamus having the greatest number of differentially expressed genes associated with licking and grooming in both dams and pups. Prenatal bisphenol exposure also had region-specific effects on gene expression and pup gene expression was affected more robustly than dam gene expression. In dams, the prelimbic cortex had the greatest number of differentially expressed genes associated with prenatal bisphenol exposure. Prenatal bisphenol exposure changed the expression of over 2000 genes in pups, with the majority being from the pup amygdala. We used Gene Set Enrichment Analysis (GSEA) to asses enrichment of gene ontology biological processes for each region. Top GSEA terms were diverse and varied by brain region and included processes known to have strong associations with steroid hormone regulation, cilium-related terms, metabolic/biosynthetic process terms, and immune terms. Finally, hypothesis-driven analysis of genes related to estrogen response, parental behavior, and epigenetic regulation of gene expression revealed region-specific expression associated with licking and grooming and bisphenol exposure that were distinct in dams and pups. These data highlight the effects of bisphenols on multiple physiological process that are highly dependent on timing of exposure (prenatal vs. adulthood) and brain region, and reiterate the contributions of multiple environmental and experiential factors in shaping the brain.

Estrogens and phytoestrogens in body functions

Estrogens are the hormones of reproduction in women as well as of many other important functions in the male and female body. They undergo significant changes in the different phases of life, e.g. during puberty, pregnancy or at menopause/andropause. Phytoestrogens are natural non-steroidal phenolic plant compounds that can mimic the activity of estrogens and their beneficial effects in women and in men. This narrative review summarizes the literature on the physiological role of estrogens and the several potential health benefits of phytoestrogens, with particular attention given to the possible role of phytoestrogens in aging.

Hormone receptor expression in aging mammary tissue and carcinoma from a rodent model after xenoestrogen disruption

AIMS

Hormone receptors are the main markers applied for prognosis of breast cancer subtypes. Among modulators, exogenous chemical agents known as endocrine disruptors interact with certain receptors, triggering molecular pathways or increasing their expression. Bisphenol A (BPA), a xenoestrogen, interacts with several hormone receptors. Thus, our aim was to characterize the hormone receptor status in the mammary gland (MG) of aged female Mongolian gerbils exposed to BPA in pregnancy and lactation.

METHODS

We evaluated the expression of receptors for estrogens (ERα and ERβ), progesterone (PR), prolactin (PRL-R), HER2/ErbB2, and androgen (AR) in normal and hyperplastic mammary tissue and in carcinomas developed after BPA exposure.

KEY FINDINGS

BPA-exposed MG presented increased ERα, whereas ERβ, PR, and PRL-R showed lower expression. AR and HER2/ErbB2 showed similar expression in normal and hyperplastic tissue from control, vehicle, and BPA groups. Both receptors were found in cytoplasm and nucleus in BPA-induced carcinoma. We demonstrate the presence of EZH2 expression, an epigenetic and epithelial-mesenchymal transition (EMT) marker, with a high H-score in BPA-exposed MG, which was associated with poor prognosis of cancer. Co-localization of ERα and EZH2 was present in normal and carcinoma features, corroborating the installation of ERα-positive mammary cancer associated with the EMT process. Enhanced EZH2 in BPA-exposed mammary tissue could decrease ERβ expression and promote tumorigenesis progress through HER2/ErbB2.

SIGNIFICANCE

The present study proposes the Mongolian gerbil as an experimental model for mammary carcinogenesis studies, based on BPA disruption that triggers a phenotype of increased ERα/HER2 positivity and depletion of ERβ/PR expression.

Depressive behavior induced by nonylphenol and its effect on the expression of ER-α and ER-β in nerve cells of rats

OBJECTIVE

To investigate the effects of nonylphenol (NP) exposure on the depressive behavior in rats, and the effects of the expressions of estrogen receptor-α (ER-α) and estrogen receptor-β (ER-β) in nerve cells in vivo and vitro.

METHODS

Forty male SD rats were randomly divided into 4 groups: blank control group (0 mg/kg), low dose group (0.4 mg/kg), middle dose group (4 mg/kg) and high dose group (40 mg/kg), which were exposed to NP for 180 days. The exposure dose of NP in HT22 was 20μM, which was divided into4 groups: blank control group, NP group, ICI182780 group and ICI182780+NP group.

RESULTS

In vivo, in the open field experiment, the number of entries in the central area and duration of attention in central square decreased gradually in the NP high dose group compared with the control (F = 3.561, p = .029). In forced swimming experiment, with the increase of NP dose, the immobility time increased, and the increasing degree of middle dose group and high dose group was higher than that of the low dose group (F = 3.047, p = .048). The concentrations of serum dopamine (DA) in the middle dose and high dose groups decreased greatly compared with the control (F = 3.967, p = .023). NP exposure at the doses of 4 mg/kg and 40 mg/kg induced an increase in the level of serum corticosterone compared to the control (F = 11.536, p<.001). Compared with the control group, the expression of ER-β decreased gradually with an increase of NP dose in the NP treatment groups (F = 4.513, p = .014). In vitro, the activity of HT22 cells decreased with an increase of NP dose (F = 316.6, p<.001). When the dose of NP was 200 μM, the growth inhibition rate of HT22 cells was (0.54±0.11)%. The expression levels of ER-α and ER-β in ICI182780+NP group was lower than those in the control and ICI182780 groups, but higher than those in the NP group (F = 1.592, p=.266; F = 10.166, p=.004).

CONCLUSION

Long-term exposure to NP could induce the alterations in depressive behavior, and the levels of neurotransmitters as well as the expression of ER in the hippocampus of rats. Moreover, NP could reduce the activity of HT22 cells and decrease the expression levels of ER-α and ER-β in vitro.

The parental brain and behavior: A target for endocrine disruption

During pregnancy, the sequential release of progesterone, 17β-estradiol, prolactin, oxytocin and placental lactogens reorganize the female brain. Brain structures such as the medial preoptic area, the bed nucleus of the stria terminalis and the motivation network including the ventral tegmental area and the nucleus accumbens are reorganized by this specific hormonal schedule such that the future mother will be ready to provide appropriate care for her offspring right at parturition. Any disruption to this hormone pattern, notably by exposures to endocrine disrupting chemicals (EDC), is therefore likely to affect the maternal brain and result in maladaptive maternal behavior. Development effects of EDCs have been the focus of intense study, but relatively little is known about how the maternal brain and behavior are affected by EDCs. We encourage further research to better understand how the physiological hormone sequence prepares the mother's brain and how EDC exposure could disturb this reorganization.

Bisphenol A increases hydrogen peroxide generation by thyrocytes both in vivo and in vitro

Bisphenol A (BPA) is the most common monomer in polycarbonate plastics and an endocrine disruptor. Though some effects of BPA on thyroid hormone (TH) synthesis and action have been described, the impact of this compound on thyroid H2O2 generation remains elusive. H2O2 is a reactive oxygen species (ROS) which could have deleterious effect on thyrocytes if in excess. Therefore, herein we aimed at evaluating the effect of BPA exposition both in vivo and in vitro on H2O2 generation in thyrocytes, besides other essential steps for TH synthesis. Female Wistar rats were treated with vehicle (control) or BPA 40 mg/Kg BW for 15 days, by gavage. We then evaluated thyroid iodide uptake, mediated by sodium-iodide symporter (NIS), thyroperoxidase (TPO) and dual oxidase (DOUX) activities (H2O2 generation). Hydrogen peroxide generation was increased, while iodide uptake and TPO activity were reduced by BPA exposition. We have also incubated the rat thyroid cell line PCCL3 with 10-9 M BPA and evaluated Nis and Duox mRNA levels, besides H2O2 generation. Similar to that found in vivo, BPA treatment also led to increased H2O2 generation in PCCL3. Nis mRNA levels were reduced and Duox2 mRNA levels were increased in BPA-exposed cells. To evaluate the importance of oxidative stress on BPA-induced Nis reduction, PCCL3 was treated with BPA in association to n-acetylcysteine, an antioxidant, which reversed the effect of BPA on Nis. Our data suggest that BPA increases ROS production in thyrocytes, what could lead to oxidative damage thus possibly predisposing to thyroid disease.

Hypothalamic gene expression changes in F1 California mice (Peromyscus californicus) parents developmentally exposed to bisphenol A or ethinyl estradiol

Bisphenol A (BPA) is a pervasive industrial chemical used in many common household items. To examine how early exposure to BPA and ethinyl estradiol (EE, estrogen in birth control pill) might affect biparental care, effects of these chemicals in male and female California mice (Peromyscus californicus), who are monogamous and biparental, were examined. California mice exposed during pre- and peri-natal life to BPA at an environmentally relevant concentration or EE show later disrupted biparental behaviors. The hypothalamus is an important brain region for regulating parental behaviors. Thus, it was hypothesized compromised biparental care might be partially due to hypothalamic gene alterations. To address this question, brains from F1 parenting female and male California mice from controls, BPA- and EE-exposed groups were collected at postnatal day (PND) 2, and RNA was isolated from hypothalamic micropunches. Gene expression was examined in this brain region for genes affected by BPA exposure and attributed to governing parental care in rodents and humans. BPA-exposed California mice showed increased hypothalamic expression of Kiss1, Esr1 and Esr2 relative to AIN control and EE-exposed parents in the case of Esr2. Notably, current studies represent the first report to show that early exposure to BPA can induce longstanding effects on hypothalamic gene expression in parenting male and female rodents. Absence of such hypothalamic gene expression changes in EE-exposed parents indicates early BPA exposure may induce later transcriptomic effects through estrogen receptor-independent pathways. BPA-driven changes in hypothalamic function of California mice might contribute to decreased biparental investment, which could result in F2 multigenerational effects.

Sex hormone levels and expression of their receptors in lactating and lactating pregnant rats

Parturient rats show a postpartum estrus, a period of sexual receptivity that occurs from 6 to 15 h after the birth of a litter, which allows the mother to gestate a second litter while simultaneously nursing the first one (lactating and pregnant). The present study investigated hormone levels and the expression pattern of estrogen receptor α, and β, progesterone receptor isoforms and SRC1 in the hypothalamus and the preoptic area of lactating as well as in lactating-pregnant rats. In the latter, estradiol levels were 3-fold higher than those observed in lactating rats on day 14, meanwhile progesterone levels did not change in any condition. There were higher levels of prolactin in both lactating and lactating-pregnant rats on day 7 and decreased on the following days. In the hypothalamus of the lactating rat, the content of ERα increased during lactation meanwhile that of ERβ decreased 50% on day 10. The content of both estrogen receptor subtypes in the hypothalamus increased 3-fold on day 21 in lactating-pregnant rats. In the preoptic area, the content of ERα was higher in lactating-pregnant rats on days 14 and 21 while the content of progesterone receptor isoforms was lower as compared with those found in lactating animals on days 7 and 10. The content of SRC1 increased 2-fold in the preoptic area only in lactating rats at day 14 and 21. These findings suggest that lactating- pregnant animals should exhibit differential neuroendocrine and molecular characteristics as compared to lactating animals.

Bisphenol S Alters the Lactating Mammary Gland and Nursing Behaviors in Mice Exposed During Pregnancy and Lactation

High doses of estrogenic pharmaceuticals were once prescribed to women to halt lactation. Yet, the effects of low-level xenoestrogens on lactation remain poorly studied. We investigated the effects of bisphenol S (BPS), an estrogen receptor (ER) agonist, on the lactating mammary gland; the arcuate nucleus, a region of the hypothalamus important for neuroendocrine control of lactational behaviors; and nursing behavior in CD-1 mice. Female mice were exposed to vehicle, 2 or 200 µg BPS/kg/d from pregnancy day 9 until lactational day (LD) 20, and tissues were collected on LD21. Tissues were also collected from a second group at LD2. BPS exposure significantly reduced the fraction of the mammary gland comprised of lobules, the milk-producing units, on LD21, but not LD2. BPS also altered expression of Esr1 and ERα in the mammary gland at LD21, consistent with early involution. In the arcuate nucleus, no changes were observed in expression of signal transducer and activator of transcription 5, a marker of prolactin signaling, or ERα, suggesting that BPS may act directly on the mammary gland. However, observations of nursing behavior collected during the lactational period revealed stage-specific effects on both pup and maternal nursing behaviors; BPS-treated dams spent significantly more time nursing later in the lactational period, and BPS-treated pups were less likely to initiate nursing. Pup growth and development were also stunted. These data indicate that low doses of BPS can alter lactational behaviors and the maternal mammary gland. Together, they support the hypothesis that pregnancy and lactation are sensitive to low-dose xenoestrogen exposures.

The “Low Dose” Hypothesis: Validity and Implications for Human Risk

In the late 1990s, a “low dose” hypothesis was proposed based on studies that purported to show that hormonally active environmental agents were causing a variety of effects, mainly reproductive and developmental, at “low doses.” The supporters of this hypothesis claim that traditional “high-dose” toxicity studies are not adequate to assess adverse effects from these hormonally active agents in that they do not detect effects that are occurring at “low doses.” In addition, it is claimed that these “low dose” effects are occurring at levels comparable to those to which humans are being exposed. These claims have been controversial and expert panels evaluated the evidence behind them in the early 2000s. Although these panels generally concluded that such “low dose” effects were not conclusively established, proponents of the “low dose” hypothesis assert that a large number of more recent studies now provide clear support for their hypothesis. This review carefully examines both recent and older studies that have been cited to support the “low dose” hypothesis, including their relevance for the human population. These include in vivo and in vitro laboratory studies as well as a very limited number of epidemiological investigations. Based on the evidence, it is concluded that these “low dose” effects have yet to be established, that the studies purported to support these cannot be validly extrapolated to humans, and the doses at which the studies have been performed are significantly higher than the levels to which humans are exposed.

Bisphenol S (BPS) Alters Maternal Behavior and Brain in Mice Exposed During Pregnancy/Lactation and Their Daughters

Estrogenic endocrine disrupting chemicals have been shown to disrupt maternal behavior in rodents. We investigated the effects of an emerging xenoestrogen, bisphenol S (BPS), on maternal behavior and brain in CD-1 mice exposed during pregnancy and lactation (F0 generation) and in female offspring exposed during gestation and perinatal development (F1 generation). We observed different effects in F0 and F1 dams for a number of components of maternal behavior, including time on the nest, time spent on nest building, latency to retrieve pups, and latency to retrieve the entire litter. We also characterized expression of estrogen receptor α in the medial preoptic area (MPOA) and quantified tyrosine hydroxylase immunoreactive cells in the ventral tegmental area, 2 brain regions critical for maternal care. BPS-treated females in the F0 generation had a statistically significant increase in estrogen receptor α expression in the caudal subregion of the central MPOA in a dose-dependent manner. In contrast, there were no statistically significant effects of BPS on the MPOA in F1 dams or the ventral tegmental area in either generation. This work demonstrates that BPS affects maternal behavior and brain with outcomes depending on generation, dose, and postpartum period. Many studies examining effects of endocrine disrupting chemicals view the mother as a means by which offspring can be exposed during critical periods of development. Here, we demonstrate that pregnancy and lactation are vulnerable periods for the mother. We also show that developmental BPS exposure alters maternal behavior later in adulthood. Both findings have potential public health implications.

Beyond a means of exposure: a new view of the mother in toxicology research

Toxicological studies generally view pregnant animals as a conduit through which gestational exposure of offspring to chemicals can be achieved, allowing for the study of developmental toxicity.

Neurological Effects of Bisphenol A and its Analogues

The endocrine disrupting chemical bisphenol A (BPA) is widely used in the production of polycarbonate plastics and epoxy resins. The use of BPA-containing products in daily life makes exposure ubiquitous, and the potential human health risks of this chemical are a major public health concern. Although numerous in vitro and in vivo studies have been published on the effects of BPA on biological systems, there is controversy as to whether ordinary levels of exposure can have adverse effects in humans. However, the increasing incidence of developmental disorders is of concern, and accumulating evidence indicates that BPA has detrimental effects on neurological development. Other bisphenol analogues, used as substitutes for BPA, are also suspected of having a broad range of biological actions. The objective of this review is to summarize our current understanding of the neurobiological effects of BPA and its analogues, and to discuss preventive strategies from a public health perspective.

Exposure to bisphenol A exacerbates migraine-like behaviors in a multibehavior model of rat migraine

Migraine is a common and debilitating neurological disorder suffered worldwide. Women experience this condition 3 times more frequently than men, with estrogen strongly implicated to play a role. Bisphenol A (BPA), a highly prevalent xenoestrogen, is known to have estrogenic activity and may have an effect in migraine onset, intensity, and duration through estrogen receptor signaling. It was hypothesized that BPA exposure exacerbates migraine symptoms through estrogen signaling and downstream activation of nociception related pathways. Utilizing a multibehavior model of migraine in ovariectomized female rats, changes in locomotion, light and sound sensitivity, grooming, and acoustic startle were examined. Furthermore, changes in the expression of genes related to estrogen (ERα, GPR30), and nociception (extracellular signal regulated kinase, ERK, sodium gated channel, Nav1.8, and fatty acid amide hydrolase, FAAH) were studied following behavioral experiments. The following results were obtained: BPA treatment significantly exacerbated migraine-like behaviors in rats. Rats exposed to BPA demonstrated decreased locomotion, exacerbated light and sound aversion, altered grooming habits, and enhanced startle reflexes. Furthermore, BPA exposure increased mRNA expression of estrogen receptors, total ERK mRNA and ERK activation, as well as Nav1.8, and FAAH mRNA, indicative of altered estrogen signaling and altered nociception. These results show that BPA, an environmentally pervasive xenoestrogen, exacerbates migraine-like behavior in a rat model and alters expression of estrogen and nociception-related genes.

Prolonged exposure to a low-dose of bisphenol A increases spontaneous motor activity in adult male rats

We investigated the effects of bisphenol A (BPA), an environmental endocrine-disrupting chemical, on spontaneous motor activity in adult male rats. The rats were implanted intraperitoneally with mini-osmotic pumps containing either BPA (50 μg/kg body weight per day) in sesame oil (BPA-treated group) or sesame oil only (vehicle-treated group). Spontaneous motor activity during a 24-h period was measured over 5 days from day 9 to day 13 after implantation using an animal movement analysis system. Spontaneous motor activity during the last 2 h of the dark phase and during the first 1-h of the light phase was increased in the BPA-treated group. Total spontaneous motor activity during the 12-h light phase, but not the 12-h dark phase, was higher in the BPA-treated group than in the vehicle-treated group. These findings suggest that BPA may induce hyperactivity in adult male rats during the 12-h light phase, especially during the 2 h immediately preceding sleep-onset and 1 h immediately following sleep-onset.

Sex-specific effects of bisphenol-A on memory and synaptic structural modification in hippocampus of adult mice

Humans are routinely exposed to low levels of bisphenol A (BPA), a synthetic xenoestrogen widely used in the production of polycarbonate plastics. The effects of long-term exposure to BPA on memory and modification of synaptic structure in hippocampus of adult mice were investigated in the present study. The adult mice were exposed to BPA (0.4, 4, and 40 mg/kg/day) or arachis oil for 12 weeks. In open field test, BPA at 0.4, 4, or 40 mg/kg/day increased the frequency of rearing and time in the central area of the males, while BPA at 0.4 mg/kg/day reduced the frequency of rearing in the females. Exposure to BPA (0.4 or 40 mg/kg/day) extended the average escape pathlength to the hidden platform in Morris water maze task and shortened the step-down latency 24 h after footshock of the males, but no changes were found in the females for these measures. Meanwhile, BPA induced a reduced numeric synaptic density and a negative effect on the structural parameters of synaptic interface, including an enlarged synaptic cleft and the reduced length of active zone and PSD thickness, in the hippocampus of the male mice. Western blot analyses further indicated that BPA down-regulated expressions of synaptic proteins (synapsin I and PSD-95) and synaptic NMDA receptor subunit NR1 and AMPA receptor subunit GluR1 in the hippocampus of the males. These results suggest that long-term exposure to low levels of BPA in adulthood sex-specifically impaired spatial and passive avoidance memory of mice. These effects may be associated with the higher susceptibility of the hippocampal synaptic plasticity processes, such as remodeling of spinal synapses and the expressions of synaptic proteins (e.g. synapsin I and PSD-95) and NMDA and AMPA receptors, to BPA in the adult male mice.

The epigenetic lorax: gene-environment interactions in human health

Over the last decade, we have witnessed an explosion of information on genetic factors underlying common human diseases and disorders. This 'human genomics' information revolution has occurred as a backdrop to a rapid increase in the rates of many human disorders and diseases. For example, obesity, Type 2 diabetes, asthma, autism spectrum disorder and attention deficit hyperactivity disorder have increased at rates that cannot be due to changes in the genetic structure of the population, and are difficult to ascribe to changes in diagnostic criteria or ascertainment. A likely cause of the increased incidence of these disorders is increased exposure to environmental factors that modify gene function. Many environmental factors that have epidemiological association with common human disorders are likely to exert their effects through epigenetic alterations. This general mechanism of gene-environment interaction poses special challenges for individuals, educators, scientists and public policy makers in defining, monitoring and mitigating exposures.

Endocrine disrupters: a review of some sources, effects, and mechanisms of actions on behaviour and neuroendocrine systems

Some environmental contaminants interact with hormones and may exert adverse consequences as a result of their actions as endocrine disrupting chemicals (EDCs). Exposure in people is typically a result of contamination of the food chain, inhalation of contaminated house dust or occupational exposure. EDCs include pesticides and herbicides (such as dichlorodiphenyl trichloroethane or its metabolites), methoxychlor, biocides, heat stabilisers and chemical catalysts (such as tributyltin), plastic contaminants (e.g. bisphenol A), pharmaceuticals (i.e. diethylstilbestrol; 17α-ethinylestradiol) or dietary components (such as phytoestrogens). The goal of this review is to address the sources, effects and actions of EDCs, with an emphasis on topics discussed at the International Congress on Steroids and the Nervous System. EDCs may alter reproductively-relevant or nonreproductive, sexually-dimorphic behaviours. In addition, EDCs may have significant effects on neurodevelopmental processes, influencing the morphology of sexually-dimorphic cerebral circuits. Exposure to EDCs is more dangerous if it occurs during specific 'critical periods' of life, such as intrauterine, perinatal, juvenile or puberty periods, when organisms are more sensitive to hormonal disruption, compared to other periods. However, exposure to EDCs in adulthood can also alter physiology. Several EDCs are xenoestrogens, which can alter serum lipid concentrations or metabolism enzymes that are necessary for converting cholesterol to steroid hormones. This can ultimately alter the production of oestradiol and/or other steroids. Finally, many EDCs may have actions via (or independent of) classic actions at cognate steroid receptors. EDCs may have effects through numerous other substrates, such as the aryl hydrocarbon receptor, the peroxisome proliferator-activated receptor and the retinoid X receptor, signal transduction pathways, calcium influx and/or neurotransmitter receptors. Thus, EDCs, from varied sources, may have organisational effects during development and/or activational effects in adulthood that influence sexually-dimorphic, reproductively-relevant processes or other functions, by mimicking, antagonising or altering steroidal actions.

Pubertal exposure to bisphenol A disrupts behavior in adult C57BL/6J mice

Bisphenol A (BPA) is a widespread endocrine disrupting chemical that influences adult physiology and behavior after perinatal exposure. However, it is not clear if pubertal exposure to BPA exerts hormone dependent effects on behaviors. Using C57BL/6J mice, we sought to determine how pubertal exposure to BPA affects locomotion, exploration, anxiety and sociability in adulthood. Compared to controls, pubertal exposure to BPA or E(2) (17β-estradiol) significantly altered female exploratory and anxiety behavior. Moreover, BPA and E(2)-treated female mice displayed increased levels of affiliation to female stimulus mice and decreased levels of affiliation to male stimulus mice; while our control males showed affiliation preference to female stimulus. These results indicate that pubertal exposure to BPA or E(2) may masculinize female social and emotional behavior.

Perinatal exposure of rats to Bisphenol A affects fertility of male offspring--an overview

Endocrine disruptors (ED) induce both functional and behavioral reproductive abnormalities. Bisphenol A (BPA) is a known ED that leaches from polycarbonate plastics, as such human exposure is common. Maternal BPA exposure has been shown to have negative effects on the fertility of male offspring. Pregnant rats exposed perinatally to environmentally relevant doses of BPA gave birth to offspring with significantly impaired spermatogenesis and fertility. Perinatal exposure had deleterious effects on the male germ line which manifested as impairments in the fertility of F(1) male offspring and subsequent F(2) and F(3) generations. This overview is an attempt to summarize the currently available data in the literature with regards to perinatal BPA exposure and male fertility.

Mother counts: how effects of environmental contaminants on maternal care could affect the offspring and future generations

Various compounds of anthropogenic origin represent environmental contaminants (EC) that penetrate the food chain and are frequently detected in human milk and maternal blood at the time of delivery. These ECs can affect the development of the fetus and can be transferred to the newborn during lactation. Many studies have used animal models to study the impact of ECs on the development of the nervous system and have reported effects of early exposure on neural and neuroendocrine systems and on behavior, when the exposed animals are tested as adults. Some of these effects persist across generations and may involve epigenetic mechanisms. The majority of these studies in developmental toxicology treat the pregnant or lactating animal with ECs in order to deliver the contaminants to the developing offspring. Almost universally, the mother is viewed as a passive conduit for the ECs, and maternal behavior is rarely assessed. Here we review the literature on the effects of ECs on maternal care and find mounting evidence that important components of the care given to the offspring are affected by maternal exposure to different ECs. Some of these changes in maternal behavior appear to be secondary to changes in the behavior and/or stimulus properties of the exposed offspring, but others are likely to be direct effects of the ECs on the maternal nervous and endocrine systems. Considering the extent to which the quality of maternal care affects the development of the offspring, it becomes imperative to determine the contributions that changes in maternal behavior make to the deficits traditionally ascribed solely to direct effects of ECs on the developing organism. Given the complexity and importance of mother-infant interactions, future research on developmental toxicology must consider the effects of ECs not only on the offspring, but also on the mother and on the interactions and social bond between mother and infant.

Perinatal exposure to bisphenol-A impairs learning-memory by concomitant down-regulation of N-methyl-D-aspartate receptors of hippocampus in male offspring mice

Bisphenol-A (BPA) has been shown to influence development of the brain and behaviors. The purpose of the present report was to investigate the effects of perinatal exposure to BPA on learning/memory and its mechanism of action, especially focusing on N-methyl-d-aspartate receptor (NMDAR). Perinatal maternal exposure to BPA at 0.5, 5, and 50mg/kg/d significantly extended the escape length to find the hidden platform in Morris water maze, and BPA at 0.5 or 5mg/kg/d markedly decreased the percentage of time spent in the quadrant where the platform had been during training both in postnatal day (PND) 21 and PND 56 mice. The results of passive avoidance test showed that the error frequency to step down from a platform after received footshock was significantly increased, and the latency of the step-down response onto the grid floor 24h after received footshock was obviously reduced by exposure to BPA at 5 and 50mg/kg/d (P<0.01) in the PND 21 offspring or at 50mg/kg/d in the PND 56 offspring (P<0.01). Furthermore, perinatal exposure to BPA significantly inhibited the expressions of NMDAR subunits NR1, NR2A, and 2B in the hippocampus during the development stage, especially in PND 56 mice. The expressions of estrogen receptor beta (ERbeta) in both PND 21 and PND 56 mice were markedly down-regulated by BPA at 0.5, 5, and 50mg/kg/d. These results indicate that perinatal exposure to BPA affects normal behavioral development in both spatial memory and avoidance memory, and also permanently influences the behavior of offspring in adulthood. The inhibition of expressions of NMDAR subunits and ERbeta in hippocampus during postnatal development stage may be involved.

Perinatal exposure to bisphenol-A changes N-methyl-D-aspartate receptor expression in the hippocampus of male rat offspring

Bisphenol-A (BPA) is one of the most common environmental endocrine disrupters with mixed estrogen agonist/antagonist properties. The toxicity of BPA has been extensively evaluated in a variety of tests in rodents, including developmental and reproductive toxicity, and carcinogenicity. The objective of the present study is to evaluate whether or not perinatal maternal exposure to BPA at 0.05, 0.5, 5, 50, and 200 mg/kg/d affects N-methyl-D-aspartate (NMDA) receptor (NMDAR) subunits NR1, NR2A, 2B, estrogen receptor beta (ERbeta), and aromatase cytochrome P450 (P450arom) protein expressions of hippocampus in male rat offspring during postnatal development. Western-blotting analyses showed that perinatal exposure to BPA significantly affected the expression of NMDAR subunits. At the lower doses of 0.05 to 50 mg/kg/d, BPA concentration dependently inhibited the expression of NMDAR subunits. However, at the higher dose (200 mg/kg/d), the effects of BPA on these subunits were different, with a stronger inhibition of NR1 expression and a slighter inhibition of NR2A, 2B expression when compared with those at the lower dosage of BPA. In addition, perinatal exposure to BPA inhibited the expression of ERbeta protein, but increased P450arom protein expression in a concentration-dependent manner, especially during the early postnatal period (the first 1-3 postnatal weeks). No significant influence of BPA on P450arom was observed at postnatal week 8. These data suggest that environmental BPA exposure may affect the development of the brain, enhancing the local biosynthesis of estrogen in the brain, inhibiting ERbeta and NMDAR expressions.

Effects of developmental exposure to bisphenol A on brain and behavior in mice

Bisphenol A (BPA) is a widespread estrogenic chemical used in the production of polycarbonate, and epoxy resins lining food and beverage cans and in dental sealants. During fetal life the intrauterine environment is critical for the normal development, and even small changes in the levels of hormones, such as estradiol or estrogen-mimicking chemicals, can lead to changes in brain function and consequently in behavior. We review here a series of ethological studies on the effects of maternal oral exposure during the last part of gestation (prenatal exposure) or from gestation day 11 to postnatal day 7 (perinatal exposure) to a low, environmentally relevant dose of BPA (10 microg/kg bw/day) on behavioral responses of CD-1 mouse offspring. We examined both male and female offspring and found that maternal exposure to BPA affected: (1) behavioral responses to novelty before puberty and, as adults; (2) exploration and activity in a free-exploratory open field; (3) exploration in the elevated plus maze and (4) sensitivity to amphetamine-induced reward in the conditioned place preference test. A consistent effect of the maternal exposure to BPA is that in all these different experimental settings, while a significant sex difference was observed in the control group, exposure to BPA decreased or eliminated the sex difference in behavior. In addition, exposure of female mice to BPA in both adulthood or during fetal life altered subsequent maternal behavior. These findings, together with those from other laboratories, are evidence of long-term consequences of maternal exposure to low-dose BPA at the level of neurobehavioral development.

Impact of acute bisphenol-A exposure upon intrauterine implantation of fertilized ova and urinary levels of progesterone and 17beta-estradiol

Bisphenol-A (BPA), a monomer used in production of polycarbonate plastics and epoxy resins, has established estrogenic properties. We assessed the impact of acute and repeated subcutaneous BPA administration upon intrauterine implantation of fertilized ova and urinary levels of 17beta-estradiol and progesterone in inseminated female mice. In Experiment 1, females received varied doses of BPA on days 1-4 of gestation. Daily doses of 6.75 and 10.125mg/animal significantly reduced the number of implantation sites. Urinary progesterone was significantly reduced by the higher dose, but no other dose had an effect on progesterone levels and no dose altered estradiol levels. In Experiment 2, inseminated females received a single dose of BPA on days 0, 1, or 2 of gestation. A single dose of 10.125mg reduced the number of implantation sites when given on day 0 or day 1, and 6.75mg on day 1 also produced fewer implantation sites, but there was no such effect of any dose when administered on day 2. These data show a lower threshold for BPA-induced pregnancy disruption than previously reported, also indicating effects of just one exposure. They confirm that this disruption is due to the actions of BPA upon implantation sites, and show that higher doses can influence systemic progesterone levels.

Derivation of a bisphenol A oral reference dose (RfD) and drinking-water equivalent concentration

Human exposure to bisphenol A (BPA) is due to that found in the diet, and BPA and its metabolites were detected at parts per billion (or less) concentrations in human urine, milk, saliva, serum, plasma, ovarian follicular fluid, and amniotic fluid. Adverse health effects in mice and rats may be induced after parenteral injection or after massive oral doses. Controlled ingestion trials in healthy adult volunteers with 5 mg d16-BPA were unable to detect parent BPA in plasma despite exquisitely sensitive (limit of detection = 6 nM) methods, but by 96 h 100% of the administered dose was recovered in urine as the glucuronide. The extensive BPA glucuronidation following ingestion is not seen after parenteral injection; only the parent BPA binds plasma proteins and estrogen receptors (ER). The hypothesis that BPA dose-response may be described by a J- or U-shape curve was not supported by toxicogenomic data collected in fetal rat testes and epididymes (after repeated parenteral exposure at 2-400,000 microg/kg-d), where a clear monotonic dose-response both in the numbers of genes and magnitude of individual gene expression was evident. There is no clear indication from available data that the BPA doses normally consumed by humans pose an increased risk for immunologic or neurologic disease. There is no evidence that BPA poses a genotoxic or carcinogenic risk and clinical evaluations of 205 men and women with high-performance liquid chromatography (HPLC)-verified serum or urinary BPA conjugates showed (1) no objective signs, (2) no changes in reproductive hormones or clinical chemistry parameters, and (3) no alterations in the number of children or sons:daughters ratio. Results of benchmark dose (BMD10 and BMDL10) calculations and no-observed-adverse-effect level (NOAEL) inspections of all available and reproducible rodent studies with oral BPA found BMD and NOAEL values all greater than the 5 mg/kg-d NOAELs from mouse and rat multigeneration reproduction toxicity studies. While allometric and physiologically based pharmacokinetic (PBPK) models were constructed for interspecies scaling of BPA and its interaction with ER, multigeneration feeding studies with BPA at doses spanning 5 orders of magnitude failed to identify signs of developmental toxicity or adverse changes in reproductive tract tissues; the 5-mg/kg-d NOAELs identified for systemic toxicity in rats and mice were less than the oral NOAELs for reproductive toxicity. Thus, it is the generalized systemic toxicity of ingested BPA rather than reproductive, immunologic, neurobehavioral, or genotoxic hazard that represents the point of departure. Using U.S. Environmental Protection Agency (EPA) uncertainty factor guidance and application of a threefold database uncertainty factor (to account for the fact that the carcinogenic potential of transplacental BPA exposure has yet to be fully defined and comprehensive neurobehavioral and immunotoxicologic evaluations of BPA by relevant routes and at relevant doses have yet to be completed) to the administered dose NOAEL results in an oral RfD of 0.016 mg/kg-d. Assuming the 70-kg adult consumes 2 L of water each day and adopting the default 20% U.S. EPA drinking water relative source contribution yields a 100 microg/L BPA total allowable concentration (TAC).

Effects of xenoestrogens on the differentiation of behaviorally-relevant neural circuits

It has become increasingly clear that environmental chemicals have the capability of impacting endocrine function. Moreover, these endocrine disrupting chemicals (EDCs) have long term consequences on adult reproductive function, especially if exposure occurs during embryonic development thereby affecting sexual differentiation. Of the EDCs, most of the research has been conducted on the effects of estrogen active compounds. Although androgen active compounds are also present in the environment, much less information is available about their action. However, in the case of xenoestrogens, there is mounting evidence for long-term consequences of early exposure at a range of doses. In this review, we present data relative to two widely used animal models: the mouse and the Japanese quail. These two species long have been used to understand neural, neuroendocrine, and behavioral components of reproduction and are therefore optimal models to understand how these components are altered by precocious exposure to EDCs. In particular we discuss effects of bisphenol A and methoxychlor on the dopaminergic and noradrenergic systems in rodents and the impact of these alterations. In addition, the effects of embryonic exposure to diethylstilbestrol, genistein or ethylene,1,1-dichloro-2,2-bis(p-chlorophenyl) is reviewed relative to behavioral impairment and associated alterations in the sexually dimorphic parvocellular vasotocin system in quail. We point out how sexually dimorphic behaviors are particularly useful to verify adverse developmental consequences produced by chemicals with endocrine disrupting properties, by examining either reproductive or non-reproductive behaviors.

Developmental exposure to low-dose estrogenic endocrine disruptors alters sex differences in exploration and emotional responses in mice

Estrogenic endocrine disruptors (EEDs) are naturally occurring or man-made compounds present in the environment that are able to bind to estrogen receptors and interfere with normal cellular development in target organs and tissues. There is mounting evidence that EEDs can interfere with the processes of sexual differentiation of brain and behavior in different animal models. We investigated the effects of maternal exposure to EEDs, at concentrations within the range of human exposure and not patently teratogenic, on behavioral responses of male and female house mice (Mus musculus domesticus) before and after puberty. Pregnant dams were trained to spontaneously drink daily doses of corn oil with or without the estrogenic plastic derivative, bisphenol A (BPA 10 microg/kg), or the estrogenic insecticide methoxychlor (MXC 20 microg/kg) from gestation day 11 to postpartum day 8. Their male and female offspring were examined at different ages to examine several components of explorative and emotional behaviors in 3 experimental paradigms: a novelty test before puberty and, as adults, a free-exploratory open-field test and the elevated plus maze test. The main results are sex differences in control mice on a number of behavioral responses at both ages and in all experimental paradigms, while perinatal exposure to BPA or MXC decreased or eliminated such sex differences. The present findings are evidence of long-term consequences of developmental exposure to BPA and MXC on neurobehavioral development and suggest a differential effect of low-dose exposure to these estrogenic chemicals in males and females.

In vivo effects of bisphenol A in laboratory rodent studies

Concern is mounting regarding the human health and environmental effects of bisphenol A (BPA), a high-production-volume chemical used in synthesis of plastics. We have reviewed the growing literature on effects of low doses of BPA, below 50 mg/(kg day), in laboratory exposures with mammalian model organisms. Many, but not all, effects of BPA are similar to effects seen in response to the model estrogens diethylstilbestrol and ethinylestradiol. For most effects, the potency of BPA is approximately 10-1000-fold less than that of diethylstilbestrol or ethinylestradiol. Based on our review of the literature, a consensus was reached regarding our level of confidence that particular outcomes occur in response to low dose BPA exposure. We are confident that adult exposure to BPA affects the male reproductive tract, and that long lasting, organizational effects in response to developmental exposure to BPA occur in the brain, the male reproductive system, and metabolic processes. We consider it likely, but requiring further confirmation, that adult exposure to BPA affects the brain, the female reproductive system, and the immune system, and that developmental effects occur in the female reproductive system.

Changes in estrogen receptors alpha and beta expression in the brain of mice exposed prenatally to bisphenol A

The expression of ERs alpha and beta and serotonergic neurons were evaluated in the brains of mice prenatally exposed to Bisphenol A, a known endocrine disrupting chemical (EDc). Bisphenol A was administered orally at a dose of 2ng/g body weight on gestinational days 11-17 to pregnant ICR mice. Newborn male offspring (Bis-A mice) were evaluated for the immunoreactivity of ERs alpha and beta, serotonin, and serotonin transporter positive cells in the dorsal raphe nucleus (DRN). The serum testosterone level was also evaluated. In the Bis-A mice, the expression of ERs alpha and beta at 5 and 13 weeks was increased compared with the controls (P<0.04), but this difference disappeared by the 9th week. The serotonin, serotonin transporter, and testosterone level differences between two groups did not reach significance. Exposure to bisphenol A may have changed the expression of ERs in the brain, but did not directly affect serotonin neurons in the DRN.

Estrogenic chemicals at puberty change ERα in the hypothalamus of male and female rats

The effects of two environmental endocrine disruptors, the synthetic pharmaceutical estrogen 17-ethinylestradiol (EE) and bisphenol-A (BPA), were analysed in male and female rats in a very sensitive developmental period, puberty. Immunohistochemistry was used to evaluate changes in the number of cells expressing estrogen receptors (ER-alpha) in the arcuate nucleus (ARC), ventromedial nucleus (VMH) and medial preoptic area (MPA) of the hypothalamus. Animals were treated during early puberty, from PND 23 to PND 30, with EE and BPA given orally every day. They were then sacrificed and perfused on PND 37 or PND 90, and blood and brains were collected for hormonal determination (testosterone and estradiol) and immunohistochemistry (estrogen receptors, ER). At PND 37, ER-labelled neurons were higher in males than in females in the ARC and MPA. EE and BPA increased ER-labelled neurons in the ARC and MPA. At PND 90, females showed higher ER-labelled neurons in the VMH. EE and BPA increased ER-labelled neurons in the MPA in females. EE increased testosterone in males at PND 37 and estradiol in females at PND 90. These results indicate the ability of estrogenic chemicals to change the reproductive neural circuits during puberty in male and female rats.

Bisphenol A induces transforming growth factor-β3 mRNA in the preoptic area: A cDNA expression array and Northern blot study

To gain better understanding of the effects of bisphenol A (BPA) in the adult brain, a cDNA expression array was used to screen possible candidates for BPA-inducible genes in the medial preoptic area (MPOA). Adult ovariectomized rats were given a subcutaneous injection of 10 mg BPA or sesame oil alone as a control. Twenty-four hours after the injection, the MPOAs were dissected and total RNAs were extracted. When expression levels of cDNAs derived from pooled samples were compared to controls, the expression levels of some genes in BPA-injected rats appeared to be different from those in sesame oil-injected rats. Among the candidate genes, we focused on an increase in the expression of transforming growth factor (TGF)-beta3 mRNA. To quantify the change in TGF-beta3 mRNA by BPA, we examined the effects of 10 mg BPA (n=6), 1 microg 17beta-estradiol (n=6), or oil injection (n=6) on the expression of TGF-beta3 mRNA in the MPOA of ovariectomized rats by Northern blot. The TGF-beta3 mRNA level in the MPOA of BPA-injected rats was significantly increased compared to the level in oil-injected rats (p<0.05). Injection of 1 microg 17beta-estradiol did not have any significant effect. The results suggest that, in the adult female rat, BPA acts on the MPOA by altering the expression of the TGF-beta3 gene in a manner distinct from that of estrogen.

Large effects from small exposures. II. The importance of positive controls in low-dose research on bisphenol A

Over six-billion pounds per year of the monomer bisphenol A (BPA) are used to manufacture polycarbonate plastic products, resins lining cans, dental sealants, and polyvinyl chloride plastic products. There are 109 published studies as of July 2005 that report significant effects of low doses of BPA in experimental animals, with many adverse effects occurring at blood levels in animals within and below average blood levels in humans; 40 studies report effects below the current reference dose of 50 microg/kg/day that is still assumed to be safe by the US-FDA and US-EPA in complete disregard of the published findings. The extensive list of significant findings from government-funded studies is compared to the 11 published studies that were funded by the chemical industry, 100% of which conclude that BPA causes no significant effects. We discuss the importance of appropriate controls in toxicological research and that positive controls are required to determine whether conclusions from experiments that report no significant effects are valid or false.

Neurobiological Effects of Bisphenol A May Be Mediated by Somatostatin Subtype 3 Receptors in Some Regions of the Developing Rat Brain

Considerable attention has been focused on environmental disruptors such as the xenoestrogen bisphenol A, which influences reproductive, developmental, and cognitive activities through its interaction with specific neuromediating systems in an estrogen-like fashion. In the present study, the effects of this xenoestrogen proved to be preferentially directed toward hypothalamic and extrahypothalamic somatostatin receptor subtype 3, which displayed a higher binding affinity of its specific nonpeptide agonist L-796-778 than that of L-779-976 (subtype 2). One type of action, with respect to animals treated with vehicle alone, consisted of a very strong (p < 0.001) decrease of somatostatin receptor subtype 3 mRNA levels in layer V of the frontoparietal cortex of adult rats (Sprague-Dawley) after transplacental and lactational exposure to bisphenol A (400 microg/kg/day). Similarly, such treatment in 7-day-old rats was responsible for a very strong reduction of the subtype 3 mRNA levels in the hypothalamic periventricular nuclei and a strong (p < 0.01) increase of the subtype 3 mRNA levels in the ventromedial nuclei. Moreover, even greater upregulated and downregulated activities were reported when subtype 3 mRNA levels were determined in the presence of receptor agonists specific for distinct alpha GABA(A) receptor subunits (alpha(1,5)). The predominant effects of bisphenol A on somatostatin receptor subtype 3 mRNA levels occurring in an alpha GABA(A) subunit-dependent manner tend to suggest the early modulatory importance of this environmental disruptor on cross-talking mechanisms that are implicated in the plasticity of neural circuits, with consequential influence on neuroendocrine/sociosexual behaviors.

An extensive new literature concerning low-dose effects of bisphenol A shows the need for a new risk assessment

Bisphenol A (BPA) is the monomer used to manufacture polycarbonate plastic, the resin lining of cans, and other products, with global capacity in excess of 6.4 billion lb/year. Because the ester bonds in these BPA-based polymers are subject to hydrolysis, leaching of BPA has led to widespread human exposure. A recent report prepared by the Harvard Center for Risk Analysis and funded by the American Plastics Council concluded that evidence for low-dose effects of BPA is weak on the basis of a review of only 19 studies; the report was issued after a delay of 2.5 years. A current comprehensive review of the literature reveals that the opposite is true. As of December 2004, there were 115 published in vivo studies concerning low-dose effects of BPA, and 94 of these report significant effects. In 31 publications with vertebrate and invertebrate animals, significant effects occurred below the predicted "safe" or reference dose of 50 microg/kg/day BPA. An estrogenic mode of action of BPA is confirmed by in vitro experiments, which describe disruption of cell function at 10(-12) M or 0.23 ppt. Nonetheless, chemical manufacturers continue to discount these published findings because no industry-funded studies have reported significant effects of low doses of BPA, although > 90% of government-funded studies have reported significant effects. Some industry-funded studies have ignored the results of positive controls, and many studies reporting no significant effects used a strain of rat that is inappropriate for the study of estrogenic responses. We propose that a new risk assessment for BPA is needed based on a) the extensive new literature reporting adverse effects in animals at doses below the current reference dose; b) the high rate of leaching of BPA from food and beverage containers, leading to widespread human exposure; c) reports that the median BPA level in human blood and tissues, including in human fetal blood, is higher than the level that causes adverse effects in mice; and d) recent epidemiologic evidence that BPA is related to disease in women.

17beta-estradiol attenuates alpha, beta-meATP-induced currents in rat dorsal root ganglion neurons

The effects of 17beta-estradiol on the alpha,beta-me ATP-induced currents were studied on dorsal root ganglion (DRG) neurons using whole-cell recording technique. Three types of currents (transient, sustained or biphasic) were evoked by alpha,beta-me ATP in acutely dissociated DRG neurons. When neurons were pre-incubated with 17beta-estradiol (10-1000 nM) for 4 min, an inhibition of the transient current and the transient component of the biphasic current was observed. In contrast, 17beta-estradiol did not have any significant effect on the sustained current evoked by alpha,beta-meATP. The inhibitory effects were concentration-dependent, reversible and could be blocked by the estradiol receptor inhibitor, ICI 182,780 (1 microM). However, bovine serum albumin-conjugated 17beta-estradiol (17beta-estradiol-BSA, 10 nM) failed to mimic the effects of 17beta-estradiol. 17alpha-estradiol, the inactive isoform, did not have significant effects on alphabeta-meATP-induced currents, either. Sustained currents induced by ATP (100 microM) in nodose ganglion (NG), superior cervical ganglion (SCG) and otic ganglion (OTG) neurons were not affected by 17beta-estradiol. These results suggest that the female gonadal hormone, 17beta-estradiol, might participate in control of pain by modulating P2X3 receptor-mediated events in sensory neurons.

Bisphenol-A exposure during pregnancy and lactation affects maternal behavior in rats

In mammals, endogenous estrogens are crucial for sexual differentiation during the perinatal period, and the modulation in adulthood of many neuroendocrine and behavioral functions involved in reproduction. In rats, the estrogenic environment during pregnancy and lactation affects directly maternal behavior. This experiment was aimed to test whether the exposure to the estrogenic compound bisphenol-A (BPA; 0.040 mg/kg/die, orally) of adult female rats, from mating to weaning of the pups, could alter maternal behavior. An appropriate methodology was applied to reveal differences in the behavior of dams directed to male and female pups, testing the dams on postnatal days 3-4 and 8-9. Results show different maternal behavioral patterns towards male and female pups of control mothers, with more ano-genital licking to males than to females. Exposure of mothers to BPA modified their behavior, reducing specific components of maternal behavior, both active and passive, irrespective of the sex of pups and the period of observation. This experiment shows that maternal behavior is affected by a prolonged exposure to a low dose of BPA during pregnancy and lactation, thus suggesting an effect on neural circuits in adulthood.

Chronic exposure to low doses bisphenol A interferes with pair-bonding and exploration in female Mongolian gerbils

Estrogenic endocrine disruptors, synthetic or naturally occurring substances found in the environment, can interfere with the vertebrate endocrine system and, mimicking estrogens, interact with the neuroendocrine substrates of behavior. Since species vary in their sensitivity to steroids, it is of great interest to widen the range of species included in the researches on neurobehavioral effects of estrogenic endocrine disruptors. We examined socio-sexual and exploratory behavior of Mongolian gerbil females (Meriones unguiculatus), a monogamous rodent, in response to chronic exposure to the estrogenic endocrine disruptor bisphenol A. Paired females were daily administered with one of the following treatments: bisphenol A (2 or 20 microg/kg body weight/day); 17alpha-ethynil estradiol (0.04 microg/kg body weight/day 17alphaE); oil (vehicle). Females were treated for 3 weeks after pairing. Starting on day of pairing, social interactions within pairs were daily recorded. Three weeks after pairing, females were individually tested in a free exploratory paradigm. Bisphenol A and 17alphaE affected male-female social interactions by increasing social investigation. Bisphenol A reduced several exploratory parameters, indicating a decreased exploratory propensity of females. These results highlight the sensitivity of adult female gerbils to bisphenol A during the hormonally sensitive period of pair formation, also considering that the bisphenol A doses tested are well below the suggested human tolerable daily intake.

D-amphetamine-related reinforcing effects are reduced in mice exposed prenatally to estrogenic endocrine disruptors

Estrogenic endocrine disruptors are hormonally active compounds that can bind to estradiol receptors. Central dopamine pathways have been reported to be affected by early developmental exposure to estrogenic endocrine disruptors. In the present study, pregnant female CD-1 mice were allowed to drink spontaneously either oil or environmentally relevant low doses of two estrogenic compounds, methoxychlor (20 microg/kg) or bisphenol-A (10 microg/kg) during gestation days 11-18. Their adult offspring were assessed for conditioned place preference produced by D-amphetamine (0, 1 or 2 mg/kg). Interestingly, prenatal treatment effects were sex-dependent and no changes in conditioned place preference emerged for the male offspring. Conversely, a clear-cut profile of D-amphetamine-induced conditioned place preference was only shown by oil-exposed females, whereas exposure to bisphenol-A or methoxychlor resulted in little or no place conditioning. Locomotor effects of acute d-amphetamine were not affected by prenatal exposure to bisphenol-A or methoxychlor. As a whole, prenatal exposure to estrogenic endocrine disruptors affected some steps in the organization of the brain dopaminergic systems in the female offspring, thus leading to long-term alterations in neurobehavioral function. These data confirm that exposure to weak environmental estrogens in the period of brain sexual differentiation can influence adult behavior.