Effects of pre- and neonatal exposure to bisphenol A on murine brain development

Adolescent exposure to bisphenol-a antagonizes androgen regulation of social behavior in male mice

Social behavior is sexually dimorphic, which is regulated by gonadal hormones in the brain. Our recent study found that exposure to low doses of bisphenol-A (BPA) during adolescence, permanently alters social behavior in adult male mice, but the underlying mechanisms remain unclear. Using adolescent gonadectomy (GDX) male mice with testosterone propionate (TP, 0.5 mg/kg) supplement (TP-GDX), this study showed that BPA antagonized promoting effects of TP on social interaction, sexual behavior, and aggression in GDX mice. BPA eliminated the reversal effects of TP on GDX-induced decrease in the number of immunoreactive to arginine vasopressin (AVP-ir) neurons in the medial amygdala (MeA) and the levels of AVP receptor 1a (V1aR) in the MeA and the nucleus accumbens (NAc). In addition, BPA removed down-regulation in the levels of dopamine (DA) transporter (DAT) and DA receptor 1 (DR1) in the NAc of TP-GDX mice. BPA exposure reduced testosterone (T) levels in the brain and serum and the expression of androgen receptor (AR) protein in the amygdala and striatum of sham-operated and TP-GDX males. These results suggest that adolescent exposure to BPA inhibits regulation of androgen in AVP and DA systems of the brain regions associated with social behavior, and thus alters social behaviors of adult male mice.

The passive avoidance task ameliorate the toxic effects of bisphenol A on dopamine D1 receptor density in hippocampus, amygdala, and cerebellum of male rats

INTRODUCTION

Dopamine D1 receptor seems to play a role in mediating plasticity. Therefore, the present study aimed to investigate the effects of passive avoidance tasks postexposed to BPA on dopamine D1 receptor density in the hippocampus, amygdala, and cerebellum of male rats.

METHODS

Thirty-five male Sprague-Dawley rats weighing 220.300 g, in standard light-dark 12 h light/12 h dark were used in the present study; water and food were ad libitum. Animals were divided into six groups. Administration of BPA 5 and 50 mg/kg/day were gavaged for 15 days. Learning and memory assessment were done by a shuttle box after 15 days of BPA administration. The density of the dopamine D1 receptor was investigated using an immunohistochemistry (IH) procedure. For determining the color difference in IH sections, Image Analyzer software was used. The data were analyzed by one-way ANOVA followed by Tukey's as a post hoc test.

RESULTS

The data showed that BPA in both doses could significantly increase the density of dopamine D1 receptors in the hippocampus, amygdala, and cerebellum of male rats; learning in rats postexposed to BPA improves dopamine D1 receptor density significantly in three brain structures.

DISCUSSION

According to the results, passive avoidance learning and memory can improve the density of dopamine D1 receptors in the hippocampus, amygdala, and cerebellum of male rats.

The effects of prenatal bisphenol A exposure on brain volume of children and young mice

Bisphenol A (BPA) is a synthetic chemical used for the manufacturing of plastics, epoxy resin, and many personal care products. This ubiquitous endocrine disruptor is detectable in the urine of over 80% of North Americans. Although adverse neurodevelopmental outcomes have been observed in children with high gestational exposure to BPA, the effects of prenatal BPA on brain structure remain unclear. Here, using magnetic resonance imaging (MRI), we studied the associations of maternal BPA exposure with children's brain structure, as well as the impact of comparable BPA levels in a mouse model. Our human data showed that most maternal BPA exposure effects on brain volumes were small, with the largest effects observed in the opercular region of the inferior frontal gyrus (ρ = -0.2754), superior occipital gyrus (ρ = -0.2556), and postcentral gyrus (ρ = 0.2384). In mice, gestational exposure to an equivalent level of BPA (2.25 μg BPA/kg bw/day) induced structural alterations in brain regions including the superior olivary complex (SOC) and bed nucleus of stria terminalis (BNST) with larger effect sizes (1.07≤ Cohens d ≤ 1.53). Human (n = 87) and rodent (n = 8 each group) sample sizes, while small, are considered adequate to perform the primary endpoint analysis. Combined, these human and mouse data suggest that gestational exposure to low levels of BPA may have some impacts on the developing brain at the resolution of MRI.

Changes in the Population Size of Calbindin D-28k-Immunoreactive Enteric Neurons in the Porcine Caecum under the Influence of Bisphenol A: A Preliminary Study

Calbindin D-28k (CB) is a calcium-binding protein widely distributed in living organisms that may act as a calcium buffer and sensory protein. CB is present in the enteric nervous system (ENS) situated in the gastrointestinal tract, which controls the majority of activities of the stomach and intestine. The influence of various doses of bisphenol A (BPA)—a chemical compound widely used in plastics production—on the number and distribution of CB-positive enteric neuronal cells in the porcine caecum was investigated with an immunofluorescence technique. The obtained results showed that low dosages of BPA resulted in an increase in the number of CB-positive neuronal cells in the myenteric (MP) and inner submucous (ISP) plexuses, whereas it did not alter the number of such neuronal cells in the outer submucous plexus (OSP). High dosages of BPA caused the increase in the amount of CB-positive perikarya in all the above-mentioned kinds of the caecal neuronal plexuses. These observations strongly suggest that CB in the ENS participates in the processes connected with the toxic activity of BPA. Most likely, the changes noted in this experiment result from the adaptive and protective properties of CB.

Perinatal exposure to bisphenol A causes a disturbance of neurotransmitter metabolic pathways in female mouse offspring: A focus on the tryptophan and dopamine pathways

Perinatal exposure to bisphenol A (BPA) contributes to neurological disorders in offspring, but the underlying mechanisms are still poorly understood. The abnormal release of neuroactive metabolites in the tryptophan (TRP) and dopamine (DA) pathways is considered to be closely associated with some disorders. Thus, in this study, TRP and DA pathways in adult female mouse offspring were investigated when the pregnant mice were given either vehicle or BPA (2, 10, or 100 μg/kg/d) from day 6 of gestation until weaning. Then, the serum and brain samples of offspring were collected at 3, 6 and 9 months, and 12 neuroactive metabolites in the TRP and DA pathways were detected. The results showed that, in the TRP pathway, TRP levels decreased, whereas kynurenine (KYN) levels and TRP turnover increased in the brain. In the serum, TRP, KYN and 5-hydroxytryptamine (5-HT) levels decreased significantly. For the DA pathway, DA and DA metabolites, including 3,4-dihydroxyphenylacetic acid (DOPAC), 3-methoxytyramine (3-MT) and homovanillic acid (HVA), reduced significantly in the brain and serum. DA turnover decreased dramatically in the brain but enhanced in the serum. The disturbance of these two metabolic pathways might be one of the potential mechanisms of BPA-induced neuropsychiatric disorders.

Gestational Exposure to Common Endocrine Disrupting Chemicals and Their Impact on Neurodevelopment and Behavior

Endocrine disrupting chemicals are common in our environment and act on hormone systems and signaling pathways to alter physiological homeostasis. Gestational exposure can disrupt developmental programs, permanently altering tissues with impacts lasting into adulthood. The brain is a critical target for developmental endocrine disruption, resulting in altered neuroendocrine control of hormonal signaling, altered neurotransmitter control of nervous system function, and fundamental changes in behaviors such as learning, memory, and social interactions. Human cohort studies reveal correlations between maternal/fetal exposure to endocrine disruptors and incidence of neurodevelopmental disorders. Here, we summarize the major literature findings of endocrine disruption of neurodevelopment and concomitant changes in behavior by four major endocrine disruptor classes:bisphenol A, polychlorinated biphenyls, organophosphates, and polybrominated diphenyl ethers. We specifically review studies of gestational and/or lactational exposure to understand the effects of early life exposure to these compounds and summarize animal studies that help explain human correlative data.

Sex Differences in the Effects of Prenatal Bisphenol A Exposure on Genes Associated with Autism Spectrum Disorder in the Hippocampus

Autism spectrum disorder (ASD) is a neurodevelopmental disorder inexplicably biased towards males. Although prenatal exposure to bisphenol A (BPA) has recently been associated with the ASD risk, whether BPA dysregulates ASD-related genes in the developing brain remains unclear. In this study, transcriptome profiling by RNA-seq analysis of hippocampi isolated from neonatal pups prenatally exposed to BPA was conducted and revealed a list of differentially expressed genes (DEGs) associated with ASD. Among the DEGs, several ASD candidate genes, including Auts2 and Foxp2, were dysregulated and showed sex differences in response to BPA exposure. The interactome and pathway analyses of DEGs using Ingenuity Pathway Analysis software revealed significant associations between the DEGs in males and neurological functions/disorders associated with ASD. Moreover, the reanalysis of transcriptome profiling data from previously published BPA studies consistently showed that BPA-responsive genes were significantly associated with ASD-related genes. The findings from this study indicate that prenatal BPA exposure alters the expression of ASD-linked genes in the hippocampus and suggest that maternal BPA exposure may increase ASD susceptibility by dysregulating genes associated with neurological functions known to be negatively impacted in ASD, which deserves further investigations.

Opening the black box of endocrine disruption of brain development: Lessons from the characterization of Bisphenol A

Bisphenol A (BPA) is among the best-studied endocrine disrupting chemicals, known to act via multiple steroid hormone receptors to mediate a myriad of cellular effects. Pre-, peri-, and postnatal BPA exposure have been linked to a variety of altered behaviors in multiple model organisms, ranging from zebrafish to frogs to mammalian models. Given that BPA can cross the human placental barrier and has been found in the serum of human fetuses during gestation, BPA has been postulated to adversely affect ongoing neurodevelopment, ultimately leading to behavioral disorders later in life. Indeed, the brain has been identified as a key developmental target for BPA disruption. Despite these known associations between gestational BPA exposure and adverse developmental outcomes, as well as an extensive body of evidence existing in the literature, the mechanisms by which BPA induces its cellular- and tissue-specific effects on neurodevelopmental processes still remains poorly understood at a mechanistic level. In this review we will briefly summarize the effects of gestational BPA exposure on neural developmental mechanisms and resulting behaviors, and then present suggestions for how we might address gaps in our knowledge to develop a fuller understanding of endocrine neurodevelopmental disruption to better inform governmental policy against the use of BPA or other endocrine disruptors.

Bisphenol-A antagonizes the rapidly modulating effect of DHT on spinogenesis and long-term potentiation of hippocampal neurons

Bisphenol A (BPA), a common environmental endocrine disruptor, modulates estrogenic, antiestrogenic, and antiandrogenic effects throughout the lifespan. Recent studies found more obvious adverse effect of BPA on some neurobehavior in males than that in females. In this study, BPA at 10-100 nM rapidly increased the densities of the dendrite spine and synapse in cultured hippocampal neurons of rats in vitro within 1 h. Co-treatment of BPA (100 nM) with dihydrotestosterone (DHT, 10 nM) or with 17β-E₂ (10 nM) completely eliminated the promotion of DHT or 17β-E₂ in the densities of the dendritic spine and synapse. Pretreatment of estrogen receptors (ERs) antagonist ICI182,780 but not of androgen receptors (ARs) antagonist flutamide (Flu) for 30min completely blocked BPA-enhanced densities of the dendritic spine and synapse. Pretreatment of flutamide for 30min before BPA and DHT completely rescued BPA-enhanced densities of the dendritic spine and synapse. Furthermore, pretreatment of ERK1/2 inhibitor U0126 or p38 inhibitor SB203580 entirely eliminated BPA-induced increases in the densities of the dendritic spine and synapse. Meanwhile, BPA (100 nM) enhanced long-term potentiation (LTP) induction of dentate gyrus in hippocampal slices of younger male rats, which was not blocked by co-incubation of flutamide but was inhibited by pretreatment of an P38 inhibitor SB203580. Co-application of BPA with DHT inhibited DHT-suppressed LTP. These results are the first demonstrating the antagonism of BPA to the rapid modification of DHT in synaptic plasticity. However, BPA alone rapidly promotes spinogenesis and synaptic activity through ER instead of AR, and both ERKs and p38 signaling pathways are involved in these processes.

Prenatal and lactational bisphenol A exposure does not alter serotonergic neurons morphologically in the murine dorsal raphe nucleus

OBJECTIVE

There is concern that bisphenol A (BPA), an endocrine-disrupting chemical, affects brain development when exposed to a fetus and/or infant. We previously reported that increased serotonin (5-HT) and its metabolite (5-HIAA) in the dorsal raphe nucleus (DRN) in murine adult brains when they were prenatally exposed to low doses of BPA. This study investigates the morphological alteration of the dorsal raphe nucleus (DRN) in order to explain the disrupted serotonergic system after prenatal and lactational exposure to bisphenol A (BPA).

METHODS

The murine dams were orally administrated with 500μg/kg/day of BPA from embryonic day 0 to postnatal 3weeks. The DRN, the main region of serotonin production, was morphometrically analyzed at 14weeks, using immunohistochemistry and image analysis combined with 3-dimensional reconstruction.

RESULTS

No significant differences were revealed in the number of tryptophan hydroxylase 2-immunoreactive neurons in any of the DRN sub-regions or the morphometric parameters, including the whole volume, ventrodorsal, longitudinal, and wing lengths of the DRN among the BPA treatment and sex groups.

CONCLUSIONS

The murine DRN was not morphologically affected by prenatal and lactational exposure to low doses of BPA. Further studies are necessary regarding the function of serotonergic neurons and the activity of different kinds of related receptors in the brain.

Association of Bisphenol A exposure and Attention-Deficit/Hyperactivity Disorder in a national sample of U.S. children

BACKGROUND

Bisphenol A (BPA) has been linked to changes in the dopamine system and development of an Attention-Deficit/Hyperactivity Disorder (ADHD) phenotype in animal models, with differing effects in males compared to females. We examined the association between urinary BPA concentrations and ADHD in a national sample of U.S. children, and whether this association differs by child sex.

METHODS

We used data from the 2003-2004 National Health and Nutrition Examination Survey, a cross-sectional, nationally representative sample of the U.S.

POPULATION

Participants were 8-15 years of age (N=460). Using a diagnostic interview to ascertain the presence of ADHD in the past year, multivariable logistic regression examined the link between concurrent urinary BPA concentrations and ADHD status.

RESULTS

Of the 460 participants, 7.1% [95% CI: 4.4-11.3] met Diagnostic and Statistical Manual of Mental Disorders - Fourth Edition (DSM-IV) criteria for ADHD. Children who had BPA concentrations at or above the median of the sample had higher prevalence of meeting criteria for ADHD (11.2% [95% CI: 6.8-17.8]) than those with BPA concentrations below the median (2.9% [95% CI: 1.1-7.2]). Higher urinary BPA concentrations were associated with ADHD (adjusted odds ratio [aOR]: 5.68 [95% CI: 1.6-19.8] for BPA concentrations above vs. below the median). In sex-stratified analyses, these associations were stronger in boys (aOR=10.9 [95% CI: 1.4-86.0]) than in girls (aOR=2.8 [95% CI: 0.4-21.3]), although the BPA by sex interaction term was not significant (p=0.25).

CONCLUSION

We found evidence that higher urinary BPA concentrations were associated with ADHD in U.S. children; these associations were stronger in boys than in girls. Considering the widespread use of BPA and growing literature on neurobehavioral effects of BPA in children, further study is warranted to determine if reducing exposure to BPA may represent an important avenue for ADHD prevention.

Alterations of neurotransmitter norepinephrine and gamma-aminobutyric acid correlate with murine behavioral perturbations related to bisphenol A exposure

AIM

Humans are commonly exposed to endocrine-disrupting chemical bisphenol A (BPA), giving rise to concern over the psychobehavioral effects of BPA. The aim of this study was to investigate the effects of prenatal and lactational BPA exposure on neurotransmitters, including norepinephrine (NE), gamma-aminobutyric acid (GABA) and glutamate (Glu), and to assess the association with behavioral phenotypes.

METHODS

C57BL/6J mice were orally administered with BPA (500 μg/bwkg/day) or vehicle daily from embryonic day 0 to postnatal week 3 (P3W), through their dams. The IntelliCage behavioral experiments were conducted from P11W to P15W. At around P14-16W, NE, GABA and Glu levels in nine brain regions were measured by high performance liquid chromatography. Furthermore, the associations between the neurotransmitter levels and the behavioral indices were statistically analyzed.

RESULTS

In females exposed to BPA, the GABA and Glu levels in almost all regions, and the NE levels in the cortex, hypothalamus and thalamus were higher than those in the controls. In males exposed to BPA, the GABA levels in the amygdala and hippocampus showed lower values, while Glu levels were higher in some regions, compared with the controls. In regard to the associations, the number of "diurnal corner visits without drinking" was correlated with the NE levels in the cortex and thalamus in females. The "nocturnal corner visit duration without drinking" was correlated with the GABA level in the hippocampus in males.

CONCLUSION

These results suggest that prenatal and lactational exposure to low doses of BPA might modulate the NE, GABA and Glu systems, resulting in behavioral alterations.

Effects of uterine and lactational exposure to di-(2-ethylhexyl) phthalate on spatial memory and NMDA receptor of hippocampus in mice

Di-(2-ethylhexyl) phthalate (DEHP) is an environmental endocrine disrupter. Currently, little is known about neurodevelopmental toxicity of DEHP in wildlife and humans. The present study investigated the effects of DEHP, focusing on the changes in the behavior of offspring mice at the ages of 6 and 12w, respectively, following utero and lactational exposure to DEHP (10, 50, and 200mg/kg/d) from gestation day 7 through postnatal day 21. The results of open field tasks showed that DEHP increased the grooming of males at age 6w and females at age 12w but decreased the frequency of rearing of 6-w-old females and the number of grid crossings of 12-w-old females. In the Morris water maze task, 50 and 200mg/kg/d DEHP significantly prolonged the time of searching the hidden platform in water maze and reduced the time staying in the target quadrant during a probe trial of 6-w-old male mice, but not of 6-w-old females nor 12-w-old mice of both sexes, suggesting an impaired spatial learning and memory among younger males after perinatal exposure to DEHP. Western blot analyses further showed that DEHP at 50 and 200mg/kg/d decreased the levels of the N-methyl-d-aspartic acid (NMDA) receptor subunits NR1 and NR2B in the hippocampus of 6-w-old males. These results suggest that uterine and lactational exposure to low doses of DEHP sex-specifically impacted behaviors, including locomotion activity and spatial memory, via the concomitant inhibition of the NMDA receptor of the hippocampus in offspring mice.

Current concepts in neuroendocrine disruption

In the last few years, it has become clear that a wide variety of environmental contaminants have specific effects on neuroendocrine systems in fish, amphibians, birds and mammals. While it is beyond the scope of this review to provide a comprehensive examination of all of these neuroendocrine disruptors, we will focus on select representative examples. Organochlorine pesticides bioaccumulate in neuroendocrine areas of the brain that directly regulate GnRH neurons, thereby altering the expression of genes downstream of GnRH signaling. Organochlorine pesticides can also agonize or antagonize hormone receptors, adversely affecting crosstalk between neurotransmitter systems. The impacts of polychlorinated biphenyls are varied and in many cases subtle. This is particularly true for neuroedocrine and behavioral effects of exposure. These effects impact sexual differentiation of the hypothalamic-pituitary-gonadal axis, and other neuroendocrine systems regulating the thyroid, metabolic, and stress axes and their physiological responses. Weakly estrogenic and anti-androgenic pollutants such as bisphenol A, phthalates, phytochemicals, and the fungicide vinclozolin can lead to severe and widespread neuroendocrine disruptions in discrete brain regions, including the hippocampus, amygdala, and hypothalamus, resulting in behavioral changes in a wide range of species. Behavioral features that have been shown to be affected by one or more these chemicals include cognitive deficits, heightened anxiety or anxiety-like, sociosexual, locomotor, and appetitive behaviors. Neuroactive pharmaceuticals are now widely detected in aquatic environments and water supplies through the release of wastewater treatment plant effluents. The antidepressant fluoxetine is one such pharmaceutical neuroendocrine disruptor. Fluoxetine is a selective serotonin reuptake inhibitor that can affect multiple neuroendocrine pathways and behavioral circuits, including disruptive effects on reproduction and feeding in fish. There is growing evidence for the association between environmental contaminant exposures and diseases with strong neuroendocrine components, for example decreased fecundity, neurodegeneration, and cardiac disease. It is critical to consider the timing of exposures of neuroendocrine disruptors because embryonic stages of central nervous system development are exquisitely sensitive to adverse effects. There is also evidence for epigenetic and transgenerational neuroendocrine disrupting effects of some pollutants. We must now consider the impacts of neuroendocrine disruptors on reproduction, development, growth and behaviors, and the population consequences for evolutionary change in an increasingly contaminated world. This review examines the evidence to date that various so-called neuroendocrine disruptors can induce such effects often at environmentally-relevant concentrations.

Abbreviated assessment of bisphenol A toxicology literature

Bisphenol A (BPA), synthesized in 1891, is produced in quantities of >2 million metric tons annually for polycarbonate plastics, epoxy resins and food contact applications. BPA can be a weak estrogen mimic, and is ubiquitous in humans (in 93% US population; in 96% US pregnant women). European/US food/drug agencies conclude that current BPA levels present no risk to the general population (some include infants/children); basic endocrine disruption (ED) researchers state that entire populations are at risk from these levels. The US Food and Drug Administration banned BPA in baby bottles in 2012 'not based on safety concerns'; the US Environmental Protection Agency and its UK counterpart concurred. Basic ED researchers report reproductive/developmental effects from perinatal BPA exposure in mice at very low doses, e.g. 2 ng/g body weight (0.002 mg/kg body weight), with non-monotonic dose-response (NMDR) curves, using few animals per group and few groups; contract research organizations, in good laboratory practice- and guideline-compliant large studies in rats and mice, report no low-dose effects or NMDR curves. The argument rages!

Social behavior is perturbed in mice after exposure to bisphenol A: a novel assessment employing an IntelliCage

In order to investigate whether or not prenatal and lactational exposure to bisphenol A (BPA) affects social behavior in mice, pregnant mice were exposed to 500 μg/kg of BPA daily from embryonic day 0 (E0) until postnatal day 21 (P21). The behavior of offspring was monitored at 11-13 and 13-15 weeks of age using an automated behavior assessment system (IntelliCage). Groups of eight mice were tasked with a nose poke, which enabled the mice to open a door to drink bottled water at the corner of their cage. BPA-exposed females visited the corner without drinking behavior during the light cycle less frequently than control female mice did. BPA-exposed males stayed at the corner for longer periods of time and showed a significantly stronger bias in the visit with drinking. In addition, the BPA-exposed males showed a shorter time interval before they visited the corner after preceding animals had visited it, compared with the control males. These findings suggest that prenatal and lactational BPA exposure might affect murine motivational behavior in a social setting differently in males and females.

Early embryogenesis in zebrafish is affected by bisphenol A exposure

Exposure of a developing embryo or fetus to endocrine disrupting chemicals (EDCs) has been hypothesized to increase the propensity of an individual to develop a disease or dysfunction in his/her later life. Although it is important to understand the effects of EDCs on early development in animals, sufficient information about these effects is not available thus far. This is probably because of the technical difficulties in tracing the continuous developmental changes at different stages of mammalian embryos. The zebrafish, an excellent model currently used in developmental biology, provides new insights to the field of toxicological studies. We used the standard whole-mount in situ hybridization screening protocol to determine the early developmental defects in zebrafish embryos exposed to the ubiquitous pollutant, bisphenol A (BPA). Three stages (60–75% epiboly, 8–10 somite, and prim-5) were selected for in situ screening of different molecular markers, whereas BPA exposure altered early dorsoventral (DV) patterning, segmentation, and brain development in zebrafish embryos within 24 hours of exposure.

Effects of perinatal exposure to low dose of bisphenol A on anxiety like behavior and dopamine metabolites in brain

Bisphenol A (BPA), an endocrine-disrupting chemical, is widely present in the environment. It has been reported that perinatal exposure to low doses of BPA that are less than the tolerable daily intake level (50μg/kg/day) affects anxiety-like behavior and dopamine levels in the brain. Although the dopaminergic system in the brain is considered to be related to anxiety, no study has reported the effects of low-dose BPA exposure on the dopaminergic system in the brain and on anxiety-like behavior using the same methods of BPA exposure. To investigate the relationship between alterations in anxiety-like behavior and changes in the dopaminergic system in the brain induced by BPA, we examined the effects of BPA on anxiety-like behavior using an open field test in juvenile and adult mice and measured DA and DOPAC levels and the DOPAC/DA ratio in the dorsal hippocampus (HIP), amygdala (AMY), and medulla oblongata (MED) using high-performance liquid chromatography (HPLC) in adult mice. In males, BPA decreased the time spent in the center area of the open field in both juveniles and adults. In addition, BPA increased DA levels in the dorsal HIP and MED and decreased the DOPAC/DA ratio in the dorsal HIP, AMY, and MED in adults. The activity of monoamine oxidase (MAO)-B, the enzyme that metabolizes DA into DOPAC, was reduced in the MED. In females, those changes were not observed. These results suggest that an increase in anxiety-like behavior induced by perinatal exposure to BPA may be related to decreases in DA metabolites in the brain, and there are sex differences in those BPA effects.

Characteristics of Molecularly Imprinted Polymer Thin Layer for Bisphenol A and Response of the MIP-Modified Sensor

We examine the characteristics of molecularly imprinted polymer (MIP) layers for bisphenol A (BPA) to investigate the effect of their thickness on the performance of the BPA sensor. MIP thin layers for bisphenol A were polymerized on a sputtered gold electrode by UV light irradiation for 2 to 30 min. Their thickness, as determined by a QCM analyzer, was 3.6 ±  0.3 nm after 5 min of irradiation and increased as the irradiation time increased to 30 min. AFM images of the MIP-modified surface suggested that the gold electrode was covered with a smooth MIP layer. The anodic peaks of BPA and ascorbic acid caused by gold electrode and the MIP-modified electrode were compared, and the electrode with MIP polymerized for 5 min showed more selectivity to BPA than that polymerized for 2 min. The MIP thin layer thus has potential as a sensing element of a chemical sensor.

Bisphenol A, an endocrine-disrupting chemical, and brain development

Bisphenol A (BPA) is an endocrine-disrupting chemical, widely used in various industries and the field of dentistry. The consequent increase in BPA exposure among humans has led us to some concerns regarding the potential deleterious effects on reproduction and brain development. The emphasis of this review is on the effects of prenatal and lactational exposure to low doses of BPA on brain development in mice. We demonstrated that prenatal exposure to BPA affected fetal murine neocortical development by accelerating neuronal differentiation/migration during the early embryonic stage, which was associated with up- and down-regulation of the genes critical for brain development, including the basic helix-loop-helix transcription factors. In the adult mice brains, both abnormal neocortical architecture and abnormal corticothalamic projections persisted in the group exposed to the BPA. Functionally, BPA exposure disturbed murine behavior, accompanied with a disrupted neurotransmitter system, including monoamines, in the postnatal development period and in adult mice. We also demonstrated that epigenetic alterations in promoter-associated CpG islands might underlie some of the effects on brain development after exposure to BPA.

Prenatal and lactational exposure to low-doses of bisphenol A alters adult mice behavior

Bisphenol A (BPA) is an endocrine-disrupting chemical, widely used in dentistry and various industries. We previously reported that BPA affected murine neocortical development by accelerating neuronal differentiation/migration, resulting in abnormal neocortical architecture as well as aberrant thalamocortical connections in the brains of adult mice. The aim of this study was to investigate whether prenatal and lactational BPA exposure affected behavior in adult mice. Pregnant mice were injected subcutaneously with 20μg/kg of BPA daily from embryonic day 0 (E0) until postnatal day 21 (P21). Control animals received a vehicle alone. Behavioral tests (n=15-20) were conducted at postnatal 3weeks (P3W) and P10-15W. After an open-field test, an elevated plus maze and Morris water maze tests were performed. The total distance in the elevated plus maze test at P3W and in the open-field test at P10W was significantly decreased in the BPA-exposed group, compared with the control group. Significant sex differences were observed in the time spent in the central area in the open-field test at P3W and in the total distance in the elevated plus maze test at P11W. These results indicated that prenatal and lactational BPA exposure disturbed the murine behavior in the postnatal development period and the adult mice.

Epigenetic perspective on the developmental effects of bisphenol A

Bisphenol A (BPA) is an estrogenic environmental toxin widely used in the production of plastics and ubiquitous human exposure to this chemical has been proposed to be a potential risk to public health. Animal studies suggest that in utero and early postnatal exposure to this compound may produce a broad range of adverse effects, including impaired brain development, sexual differentiation, behavior, and immune function, which could extend to future generations. Molecular mechanisms that underlie the long-lasting effects of BPA continue to be elucidated, and likely involve disruption of epigenetic programming of gene expression during development. Several studies have provided evidence that maternal exposure to BPA results in postnatal changes in DNA methylation status and altered expression of specific genes in offspring. However, further studies are needed to extend these initial findings to other genes in different tissues, and to examine the correlations between BPA-induced epigenetic alterations, changes in gene expression, and various phenotypic outcomes. It will be also important to explore whether the epigenetic effects of BPA are related to its estrogenic activity, and to determine which downstream effector proteins could mediate changes in DNA methylation. In this review, we will highlight research indicating a consequence of prenatal BPA exposure for brain, behavior, and immune outcomes and discuss evidence for the role of epigenetic pathways in shaping these developmental effects. Based on this evidence, we will suggest future directions in the study of BPA-induced epigenetic effects and discuss the transgenerational implications of exposure to endocrine disrupting chemicals.

Bisphenol A: developmental toxicity from early prenatal exposure

Bisphenol A (BPA) exposure has been documented in pregnant women, but consequences for development are not yet widely studied in human populations. This review presents research on the consequences for offspring of BPA exposure during pregnancy. Extensive work in laboratory rodents has evaluated survival and growth of the conceptus, interference with embryonic programs of development, morphological sex differentiation, sex differentiation of the brain and behavior, immune responsiveness, and mechanism of action. Sensitive measures include RAR, aryl hydrocarbon receptor, and Hox A10 gene expression, anogenital distance, sex differentiation of affective and exploratory behavior, and immune hyperresponsiveness. Many BPA effects are reported at low doses (10-50 µg/kg d range) by the oral route of administration. At high doses (>500,000 µg/kg d) fetal viability is compromised. Much of the work has centered around the implications of the estrogenic actions of this agent. Some work related to thyroid mechanism of action has also been explored. BPA research has actively integrated current knowledge of developmental biology, concepts of endocrine disruption, and toxicological research to provide a basis for human health risk assessment.

The role of Bisphenol A in shaping the brain, epigenome and behavior

Bisphenol A (BPA) is a xenoestrogen that was first synthesized in 1891. Its estrogenic properties were discovered in 1930, and shortly after that chemists identified its usefulness in the production of epoxy resins. Since the 1950s BPA has been used as a synthetic monomer in the manufacturing of polycarbonate plastic, polystyrene resins, and dental sealants. Roughly 6.5 billion pounds of BPA are produced each year and it is the major estrogenic compound that leaches into nearby water and food supplies (vom Saal et al., 2007). BPA has been detected in 95% of human urine samples, which indicates that environmental exposure is widespread (Calafat et al., 2005). Moreover, BPA affects reproductive tissues and the brain. Thus many studies have focused on the effects of BPA during embryonic development. The most recent FDA update (Administration January 2010) points to "some concern about the potential effects of Bisphenol A on the brain, behavior, and prostate gland in fetuses, infants, and young children." In light of this concern, we present an updated review of BPA's action on the brain and behavior. We begin with a discussion of BPA's role as both an endocrine active compound and an agent that alters DNA methylation. Next, we review publications that have reported effects of BPA on brain and behavior. We end with our interpretation of these data and suggestions for future research directions.

Prenatal and Lactational Exposure to Bisphenol A in Mice Alters Expression of Genes Involved in Cortical Barrel Development without Morphological Changes

It has been reported that premature infants in neonatal intensive care units are exposed to a high rate of bisphenol A (BPA), an endocrine disrupting chemical. Our previous studies demonstrated that corticothalamic projection was disrupted by prenatal exposure to BPA, which persisted even in adult mice. We therefore analyzed whether prenatal and lactational exposure to low doses of BPA affected the formation of the cortical barrel, the barreloid of the thalamus, and the barrelette of the brainstem in terms of the histology and the expression of genes involved in the barrel development. Pregnant mice were injected subcutaneously with 20 µg/kg of BPA daily from embryonic day 0 (E0) to postnatal 3 weeks (P3W), while the control mice received a vehicle alone. The barrel, barreloid and barrelette of the adult mice were examined by cytochrome C oxidase (COX) staining. There were no significant differences in the total and septal areas and the patterning of the posterior medial barrel subfield (PMBSF), barreloid and barrelette, between the BPA-exposure and control groups in the adult mice. The developmental study at postnatal day 1 (PD1), PD4 and PD8 revealed that the cortical barrel vaguely appeared at PD4 and completely formed at PD8 in both groups. The expression pattern of some genes was spatiotemporally altered depending on the sex and the treatment. These results suggest that the trigeminal projection and the thalamic relay to the cortical barrel were spared after prenatal and lactational exposure to low doses of BPA, although prenatal exposure to BPA was previously shown to disrupt the corticothalamic projection.

Neurotoxicity of endocrine disruptors: possible involvement in brain development and neurodegeneration

Environmental chemicals that act as endocrine disruptors do not appear to pose a risk to human reproduction; however, their effects on the central nervous systems are less well understood. Animal studies suggested that maternal exposure to endocrine-disrupting chemicals (EDC) produced changes in rearing behavior, locomotion, anxiety, and learning/memory in offspring, as well as neuronal abnormalities. Some investigations suggested that EDC exert effects on central monoaminergic neurons, especially dopaminergic neurons. Our data demonstrated that EDC attenuate the development of dopaminergic neurons, which might be involved in developmental disorders. Perinatal exposure to EDC might affect neuronal plasticity in the hippocampus, thereby potentially modulating neuronal development, leading to impaired cognitive and memory functions. Endocrine disruptors also attenuate gender differences in brain development. For example, the locus ceruleus is larger in female rats than in males, but treatments with bisphenol-A (BPA) enlarge this region in males. Some reports indicated that EDC induce hypothyroidism, which might be evidenced as abnormal brain development. Endocrine disruptors might also affect mature neurons, resulting in neurodegenerative disorders such as Parkinson's disease. The current review focused on alterations in the brain induced by EDC, specifically on the possible involvement of EDC in brain development and neurodegeneration.

Epigenomic disruption: the effects of early developmental exposures

Through DNA methylation, histone modifications, and small regulatory RNAs the epigenome systematically controls gene expression during development, both in utero and throughout life. The epigenome is also a very reactive system; its labile nature allows it to sense and respond to environmental perturbations to ensure survival during fetal growth. This pliability can lead to aberrant epigenetic modifications that persist into later life and induce numerous disease states. Endocrine-disrupting compounds (EDCs) are ubiquitous chemicals that interfere with growth and development. Several EDCs also interfere with epigenetic programming. The investigation of the epigenotoxic effects of bisphenol A (BPA), an EDC used in the production of plastics and resins, has further raised concern over the impact of EDCs on the epigenome. Using the Agouti viable yellow (A(vy)) mouse model, dietary BPA exposure was shown to hypomethylate both the A(vy) and the Cabp(IAP) metastable epialleles. This hypomethylating effect was counteracted with dietary supplementation of methyl donors or genistein. These results are consistent with reports of BPA and other EDCs causing epigenetic effects. Epigenotoxicity could lead to numerous developmental, metabolic, and behavioral disorders in exposed populations. The heritable nature of epigenetic changes also increases the risk for transgenerational inheritance of phenotypes. Thus, epigenotoxicity must be considered when assessing these compounds for safety.

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 bisphenol-A and other endocrine disruptors compared with abnormalities of schizophrenia: an endocrine-disruption theory of schizophrenia

In recent years, numerous substances have been identified as so-called "endocrine disruptors" because exposure to them results in disruption of normal endocrine function with possible adverse health outcomes. The pathologic and behavioral abnormalities attributed to exposure to endocrine disruptors like bisphenol-A (BPA) have been studied in animals. Mental conditions ranging from cognitive impairment to autism have been linked to BPA exposure by more than one investigation. Concurrent with these developments in BPA research, schizophrenia research has continued to find evidence of possible endocrine or neuroendocrine involvement in the disease. Sufficient information now exists for a comparison of the neurotoxicological and behavioral pathology associated with exposure to BPA and other endocrine disruptors to the abnormalities observed in schizophrenia. This review summarizes these findings and proposes a theory of endocrine disruption, like that observed from BPA exposure, as a pathway of schizophrenia pathogenesis. The review shows similarities exist between the effects of exposure to BPA and other related chemicals with schizophrenia. These similarities can be observed in 11 broad categories of abnormality: physical development, brain anatomy, cellular anatomy, hormone function, neurotransmitters and receptors, proteins and factors, processes and substances, immunology, sexual development, social behaviors or physiological responses, and other behaviors. Some of these similarities are sexually dimorphic and support theories that sexual dimorphisms may be important to schizophrenia pathogenesis. Research recommendations for further elaboration of the theory are proposed.

Prenatal exposure to bisphenol A affects adult murine neocortical structure

Prenatal exposure to low-doses of bisphenol A (BPA) has been shown to affect murine neocortical development by accelerating neuronal differentiation/migration through disrupting thyroid hormone function. We therefore studied whether prenatal exposure to low-doses of BPA affected organization of adult neocortical structures. Pregnant mice were injected with 20 microg/kg of BPA daily from embryonic day 0.5 (E0.5) and bromodeoxyuridine (BrdU) was injected at E12.5, E14.5 and at E16.5, and the fetal brains were analyzed after birth. The BrdU-positive cells labeled at E14.5 were significantly increased in the Vth and VIth cortical layers of BPA-treated mice at postnatal 3 weeks (P3W), whereas they were confined to the IVth layer of control mice, though such differences disappeared at P12W. The thalamocortical projections demonstrated by DiI-labeling were abnormal at P3W and P12W in BPA-treated mice. These results indicate that BPA might affect not only neocortical development but also thalamocortical connections.