A novel model for neuroendocrine toxicology: neurobehavioral effects of BPA exposure in a prosocial species, the prairie vole (Microtus ochrogaster)

Evaluating endocrine disrupting chemicals: A perspective on the novel assessments in CLARITY-BPA

BACKGROUND

The Consortium Linking Academic and Regulatory Insights on Bisphenol A Toxicity (CLARITY-BPA) was a collaborative research effort to better link academic research with governmental guideline studies. This review explores the secondary goal of CLARITY-BPA: to identify endpoints or technologies from CLARITY-BPA and prior/concurrent literature from these laboratories that may enhance the capacity of rodent toxicity studies to detect endocrine disrupting chemicals (EDCs).

METHODS

A systematic literature search was conducted with search terms for BPA and the CLARITY-BPA participants. Relevant studies employed a laboratory rodent model and reported results on 1 of the 10 organs/organ systems evaluated in CLARITY-BPA (brain and behavior, cardiac, immune, mammary gland, ovary, penile function, prostate gland and urethra, testis and epididymis, thyroid hormone and metabolism, and uterus). Study design and findings were summarized, and a risk-of-bias assessment was conducted.

RESULTS

Several endpoints and methods were identified as potentially helpful to detect effects of EDCs. For example, molecular and quantitative morphological approaches were sensitive in detecting alterations in early postnatal development of the brain, ovary, and mammary glands. Hormone challenge studies mimicking human aging reported increased susceptibility of the prostate to disease following developmental BPA exposure. Statistical analyses for nonmonotonic dose responses, and computational approaches assessing multiple treatment-related outcomes concurrently in linked hormone-sensitive organ systems, reported effects at low BPA doses.

CONCLUSIONS

This review provided an opportunity to evaluate the unique insights provided by nontraditional assessments in CLARITY-BPA to identify technologies and endpoints to enhance detection of EDCs in future studies.

Early-Life Exposure to a Mixture of Phenols and Phthalates in Relation to Child Social Behavior: Applying an Evidence-Based Prioritization to a Cohort with Improved Exposure Assessment

BACKGROUND

Previous studies aiming at relating exposure to phenols and phthalates with child social behavior characterized exposure using one or a few spot urine samples, resulting in substantial exposure misclassification. Moreover, early infancy exposure was rarely studied.

OBJECTIVES

We aimed to examine the associations of phthalates and phenols with child social behavior in a cohort with improved exposure assessment and to a priori identify the chemicals supported by a higher weight of evidence.

METHODS

Among 406 mother-child pairs from the French Assessment of Air Pollution exposure during Pregnancy and Effect on Health (SEPAGES) cohort, 25 phenols/phthalate metabolites were measured in within-subject pools of repeated urine samples collected at the second and third pregnancy trimesters (∼ 21 samples/trimester) and at 2 months and 1-year of age (∼ 7 samples/period). Social behavior was parent-reported at 3 years of age of the child using the Social Responsiveness Scale (SRS). A structured literature review of the animal and human evidence was performed to prioritize the measured phthalates/phenols based on their likelihood to affect social behavior. Both adjusted linear regression and Bayesian Weighted Quantile Sum (BWQS) regression models were fitted. False discovery rate (FDR) correction was applied only to nonprioritized chemicals.

RESULTS

Prioritized compounds included bisphenol A, bisphenol S, triclosan (TCS), diethyl-hexyl phthalate (Σ DEHP ), mono-ethyl phthalate (MEP), mono-n -butyl phthalate (MnBP), and mono-benzyl phthalate (MBzP). With the exception of bisphenols, which showed a mixed pattern of positive and negative associations in pregnant mothers and neonates, few prenatal associations were observed. Most associations were observed with prioritized chemicals measured in 1-y-old infants: Each doubling in urinary TCS (β = 0.78 ; 95% CI: 0.00, 1.55) and MEP (β = 0.92 ; 95% CI: - 0.11 , 1.96) concentrations were associated with worse total SRS scores, whereas MnBP and Σ DEHP were associated with worse Social Awareness (β = 0.25 ; 95% CI: 0.01, 0.50) and Social Communication (β = 0.43 ; 95% CI: - 0.02 , 0.89) scores, respectively. BWQS also suggested worse total SRS [Beta  1 = 1.38 ; 95% credible interval (CrI): - 0.18 , 2.97], Social Awareness (Beta  1 = 0.37 ; 95% CrI: 0.06, 0.70), and Social Communication (Beta  1 = 0.91 ; 95% CrI: 0.31, 1.53) scores per quartile increase in the mixture of prioritized compounds assessed in 1-y-old infants. The few associations observed with nonprioritized chemicals did not remain after FDR correction, with the exception of benzophenone-3 exposure in 1-y-old infants, which was suggestively associated with worse Social Communication scores (corrected p = 0.07 ).

DISCUSSION

The literature search allowed us to adapt our statistical analysis according to the weight of evidence and create a corpus of experimental and epidemiological knowledge to better interpret our findings. Early infancy appears to be a sensitive exposure window that should be further investigated. https://doi.org/10.1289/EHP11798.

Dysfunction of the medial prefrontal cortex contributes to BPA-induced depression- and anxiety-like behavior in mice

Bisphenol A (BPA), a well-known environmental endocrine disruptor, has been implicated in anxiety-like behavior. But the neural mechanism remains elusive. Herein, we found that mice exposed to 0.5 mg/kg/day BPA chronically from postnatal days (PND) 21 to PND 80 exhibited depression- and anxiety-like behavior. Further study showed that medial prefrontal cortex (mPFC), was associated with BPA-induced depression- and anxiety-like behavior, as evidenced by decreased c-fos expression in mPFC of BPA-exposed mice. Both the morphology and function of glutamatergic neurons (also called pyramidal neurons) in mPFC of mice were impaired following BPA exposure, characterized by reduced primary branches, weakened calcium signal, and decreased mEPSC frequency. Importantly, optogenetic activation of the pyramidal neurons in mPFC greatly reversed BPA-induced depression- and anxiety-like behavior in mice. Furthermore, we reported that microglial activation in mPFC of mice may also have a role in BPA-induced depression- and anxiety-like behavior. Taken together, the results indicated that mPFC is the brain region that is greatly damaged by BPA exposure and is associated with BPA-induced depression- and anxiety-like behavior. The study thus provides new insights into BPA-induced neurotoxicity and behavioral changes.

Re-evaluation of the risks to public health related to the presence of bisphenol A (BPA) in foodstuffs

In 2015, EFSA established a temporary tolerable daily intake (t-TDI) for BPA of 4 μg/kg body weight (bw) per day. In 2016, the European Commission mandated EFSA to re-evaluate the risks to public health from the presence of BPA in foodstuffs and to establish a tolerable daily intake (TDI). For this re-evaluation, a pre-established protocol was used that had undergone public consultation. The CEP Panel concluded that it is Unlikely to Very Unlikely that BPA presents a genotoxic hazard through a direct mechanism. Taking into consideration the evidence from animal data and support from human observational studies, the immune system was identified as most sensitive to BPA exposure. An effect on Th17 cells in mice was identified as the critical effect; these cells are pivotal in cellular immune mechanisms and involved in the development of inflammatory conditions, including autoimmunity and lung inflammation. A reference point (RP) of 8.2 ng/kg bw per day, expressed as human equivalent dose, was identified for the critical effect. Uncertainty analysis assessed a probability of 57-73% that the lowest estimated Benchmark Dose (BMD) for other health effects was below the RP based on Th17 cells. In view of this, the CEP Panel judged that an additional uncertainty factor (UF) of 2 was needed for establishing the TDI. Applying an overall UF of 50 to the RP, a TDI of 0.2 ng BPA/kg bw per day was established. Comparison of this TDI with the dietary exposure estimates from the 2015 EFSA opinion showed that both the mean and the 95th percentile dietary exposures in all age groups exceeded the TDI by two to three orders of magnitude. Even considering the uncertainty in the exposure assessment, the exceedance being so large, the CEP Panel concluded that there is a health concern from dietary BPA exposure.

Endocrine disrupting chemicals: effects on pituitary, thyroid and adrenal glands

BACKGROUND

In recent years, scientific research has increasingly focused on Endocrine Disrupting Chemicals (EDCs) and demonstrated their relevant role in the functional impairment of endocrine glands. This induced regulatory authorities to ban some of these compounds and to carefully investigate others in order to prevent EDCs-related conditions. As a result, we witnessed a growing awareness and interest on this topic.

AIMS

This paper aims to summarize current evidence regarding the detrimental effects of EDCs on pivotal endocrine glands like pituitary, thyroid and adrenal ones. Particularly, we directed our attention on the known and the hypothesized mechanisms of endocrine dysfunction brought by EDCs. We also gave a glimpse on recent findings from pioneering studies that could in the future shed a light on the pathophysiology of well-known, but poorly understood, endocrine diseases like hormone-producing adenomas.

CONCLUSIONS

Although intriguing, studies on endocrine dysfunctions brought by EDCs are challenging, in particular when investigating long-term effects of EDCs on humans. However, undoubtedly, it represents a new intriguing field of science research.

Effects of developmental exposure to FireMaster® 550 (FM 550) on microglia density, reactivity and morphology in a prosocial animal model

Microglia are known to shape brain sex differences critical for social and reproductive behaviors. Chemical exposures can disrupt brain sexual differentiation but there is limited data regarding how they may impact microglia distribution and function. We focused on the prevalent flame retardant mixture Firemaster 550 (FM 550) which is used in foam-based furniture and infant products including strollers and nursing pillows because it disrupts sexually dimorphic behaviors. We hypothesized early life FM 550 exposure would disrupt microglial distribution and reactivity in brain regions known to be highly sexually dimorphic or associated with social disorders in humans. We used prairie voles (Microtus ochrogaster) because they display spontaneous prosocial behaviors not seen in rats or mice and are thus a powerful model for studying chemical exposure-related impacts on social behaviors and their underlying neural systems. We have previously demonstrated that perinatal FM 550 exposure sex-specifically impacts socioemotional behaviors in prairie voles. We first established that, unlike in rats, the postnatal colonization of the prairie vole brain is not sexually dimorphic. Vole dams were then exposed to FM 550 (0, 500, 1000, 2000 µg/day) via subcutaneous injections through gestation, and pups were directly exposed beginning the day after birth until weaning. Adult offspring's brains were assessed for number and type (ramified, intermediate, ameboid) of microglia in the medial prefrontal cortex (mPFC), cerebellum (lobules VI-VII) and amygdala. Effects were sex- and dose-specific in the regions of interests. Overall, FM 550 exposure resulted in reduced numbers of microglia in most regions examined, with the 1000 µg FM 550 exposed males particularly affected. To further quantify differences in microglia morphology in the 1000 µg FM 550 group, Sholl and skeleton analysis were carried out on individual microglia. Microglia from control females had a more ramified phenotype compared to control males while 1000 µg FM 550-exposed males had decreased branching and ramification compared to same-sex controls. Future studies will examine the impact on the exposure to FM 550 on microglia during development given the critical role of these cells in shaping neural circuits.

Individual and Combined Effects of Paternal Deprivation and Developmental Exposure to Firemaster 550 on Socio-Emotional Behavior in Prairie Voles

The prevalence of neurodevelopmental disorders (NDDs) is rapidly rising, suggesting a confluence of environmental factors that are likely contributing, including developmental exposure to environmental contaminants. Unfortunately, chemical exposures and social stressors frequently occur simultaneously in many communities, yet very few studies have sought to establish the combined effects on neurodevelopment or behavior. Social deficits are common to many NDDs, and we and others have shown that exposure to the chemical flame retardant mixture, Firemaster 550 (FM 550), or paternal deprivation impairs social behavior and neural function. Here, we used a spontaneously prosocial animal model, the prairie vole (Microtus ochrogaster), to explore the effects of perinatal chemical (FM 550) exposure alone or in combination with an early life stressor (paternal absence) on prosocial behavior. Dams were exposed to vehicle (sesame oil) or 1000 µg FM 550 orally via food treats from conception through weaning and the paternal absence groups were generated by removing the sires the day after birth. Adult offspring of both sexes were then subjected to open-field, sociability, and a partner preference test. Paternal deprivation (PD)-related effects included increased anxiety, decreased sociability, and impaired pair-bonding in both sexes. FM 550 effects include heightened anxiety and partner preference in females but reduced partner preference in males. The combination of FM 550 exposure and PD did not exacerbate any behaviors in either sex except for distance traveled by females in the partner preference test and, to a lesser extent, time spent with, and the number of visits to the non-social stimulus by males in the sociability test. FM 550 ameliorated the impacts of parental deprivation on partner preference behaviors in both sexes. This study is significant because it provides evidence that chemical and social stressors can have unique behavioral effects that differ by sex but may not produce worse outcomes in combination.

Prenatal Exposure to an EDC Mixture, NeuroMix: Effects on Brain, Behavior, and Stress Responsiveness in Rats

Humans and wildlife are exposed to endocrine-disrupting chemicals (EDCs) throughout their lives. Environmental EDCs are implicated in a range of diseases/disorders with developmental origins, including neurodevelopment and behavior. EDCs are most often studied one by one; here, we assessed outcomes induced by a mixture designed to represent the real-world situation of multiple simultaneous exposures. The choice of EDCs, which we refer to as “NeuroMix,” was informed by evidence for neurobiological effects in single-compound studies and included bisphenols, phthalates, vinclozolin, and perfluorinated, polybrominated, and polychlorinated compounds. Pregnant Sprague Dawley rats were fed the NeuroMix or vehicle, and then offspring of both sexes were assessed for effects on postnatal development and behaviors and gene expression in the brain in adulthood. In order to determine whether early-life EDCs predisposed to subsequent vulnerability to postnatal life challenges, a subset of rats were also given a stress challenge in adolescence. Prenatal NeuroMix exposure decreased body weight and delayed puberty in males but not females. In adulthood, NeuroMix caused changes in anxiety-like, social, and mate preference behaviors only in females. Effects of stress were predominantly observed in males. Several interactions of NeuroMix and stress were found, especially for the mate preference behavior and gene expression in the brain. These findings provide novel insights into how two realistic environmental challenges lead to developmental and neurobehavioral deficits, both alone and in combination, in a sex-specific manner.

Effects of endocrine-disrupting chemicals on hypothalamic oxytocin and vasopressin systems

Exposures to endocrine disrupting chemicals (EDCs) perturb hormonal systems. EDCs are particularly problematic when exposure happens in the fetus and infant due to the high sensitivity of developing organisms to hormone actions. Previous work has shown that prenatal polychlorinated biphenyl (PCB) exposure disrupts hypothalamic development, reproductive physiology, mate preference behavior, and social behaviors in a sexually dimorphic manner. Based on evidence that EDCs perturb social behaviors in rodents, we examined effects of PCBs on the neuropeptides oxytocin (OXT) and vasopressin (AVP) that are involved in regulating these behaviors. Rats were exposed prenatally (gestational days 16 and 18) to the weakly estrogenic PCB mixture Aroclor 1221 (0.5 or 1 mg/kg), to estradiol benzoate (EB, a positive control), or to the vehicle (3% dimethyl sulfoxide). In adult (~P90) brains, we counted immunolabeled oxytocin and vasopressin cell numbers in the paraventricular nucleus (PVN) and supraoptic nucleus (SON) of the hypothalamus. EDCs did not change absolute numbers of oxytocin or vasopressin cells in either region, although there were some modest shifts in the rostral-caudal distribution. Second, expression of genes for these nonapeptides (Oxt, Avp), their receptors (Oxtr, Avpr1a), and the estrogen receptor beta (Esr2), was determined by qPCR. In the PVN, there were dose-dependent effects of PCBs in males (Oxt, Oxtr), and effects of EB in females (Avp, Esr2). In the SON, Oxt, and Esr2 were affected by treatments in males. These changes to protein and gene expression caused by prenatal treatments suggest that transcriptional and posttranscriptional mechanisms play roles in mediating how EDCs reprogram hypothalamic development.

Pubertal exposure to bisphenol-A affects social recognition and arginine vasopressin in the brain of male mice

Social recognition is an ability of animals to identify and distinguish conspecifics, which is essential for nearly all social species to establish social relationships. Social recognition provides the basis for a variety of social behaviors. Because of modulated by gonadal hormones, it is possible that social cognition is affected by environmental endocrine disruptors (EEDs). In the present study, after being pubertal exposed to bisphenol A (BPA, 0.04, 0.4, and 4 mg/kg) for 18 days, adult male mice did not show significant dishabituation to a novel female stimulus in habituation-dishabituation task. The capacity for discriminating the odors between familiar and novel female urine or between male and female urine was suppressed in BPA-exposed male. In addition, BPA (0.4, 4 mg/kg) decreased the number of immunoreaction of AVP (AVP-ir) neurons in both the bed nucleus of the stria terminalis (BNST) and the medial amygdala (MeA), and BPA (0.04, 0.4, 4 mg/kg) reduced the level of V1αR in the lateral septum (LS) of adult male. Further, BPA decreased the levels of testosterone (T) in the brain and androgens receptor (AR) in the LS, the amygdala, and BNST, as well the levels of estrogen receptor α and β (ERα/β) in the amygdala and BNST. These results indicate that pubertal exposure to BPA affected the actions of both androgens and estrogens in the brain and inhibited AVP system of social circuits, and these alterations may be associated with impaired social recognition of adult male mice.

Early developmental exposure to bisphenol A and bisphenol S disrupts socio-cognitive function, isotocin equilibrium, and excitation-inhibition balance in developing zebrafish

Dysregulation of the oxytocinergic system and excitation/inhibition (E/I) balance in synaptic transmission and neural circuits are common hallmarks of various neurodevelopmental disorders. Several experimental and epidemiological studies have shown that perinatal exposure to endocrine-disrupting chemicals bisphenol A (BPA) and bisphenol S (BPS) may contribute to a range of childhood neurodevelopmental disorders. However, the effects of BPA and BPS on social-cognitive development and the associated mechanisms remain largely unknown. In this study, we explored the impacts of early developmental exposure (2hpf-5dpf) to environmentally relevant concentrations of BPA, and its analog BPS (0.001, 0.01, and 0.1 μM), on anxiety, social behaviors, and memory performance in 21 dpf zebrafish larvae. Our results revealed that early-life exposure to low concentrations of BPA and BPS elevated anxiety-like behavior, while fish exposed to higher concentrations of these chemicals displayed social deficits and impaired object recognition memory. Additionally, we found that co-exposure with an aromatase inhibitor antagonized BPA- and BPS-induced effects on anxiety levels and social behaviors, while the co-exposure to an estrogen receptor antagonist restored recognition memory in zebrafish larvae. These results indicate that BPA and BPS may affect social-cognitive function through distinct mechanisms. On the other hand, exposure to low BPA/BPS concentrations increased both the mRNA and protein levels of isotocin (zebrafish oxytocin) in the zebrafish brain, whereas a reduction in its mRNA level was observed at higher concentrations. Further, alterations in the transcript abundance of chloride transporters, and molecular markers of gamma-aminobutyric acid (GABA) and glutamatergic systems, were observed in the zebrafish brain, suggesting possible E/I imbalance following BPA or BPS exposure. Collectively, the results of this study demonstrate that early-life exposure to low concentrations of the environmental contaminants BPA and BPS can interfere with the isotocinergic signaling pathway and disrupts the establishment of E/I balance in the developing brain, subsequently leading to the onset of a suite of behavioral deficits and neurodevelopmental disorders.

REPRODUCTIVE TOXICOLOGY: Endocrine disruption and reproductive disorders: impacts on sexually dimorphic neuroendocrine pathways

We are all living with hundreds of anthropogenic chemicals in our bodies every day, a situation that threatens the reproductive health of present and future generations. This review focuses on endocrine-disrupting compounds (EDCs), both naturally occurring and man-made, and summarizes how they interfere with the neuroendocrine system to adversely impact pregnancy outcomes, semen quality, age at puberty, and other aspects of human reproductive health. While obvious malformations of the genitals and other reproductive organs are a clear sign of adverse reproductive health outcomes and injury to brain sexual differentiation, the hypothalamic-pituitary-gonadal (HPG) axis can be much more difficult to discern, particularly in humans. It is well-established that, over the course of development, gonadal hormones shape the vertebrate brain such that sex-specific reproductive physiology and behaviors emerge. Decades of work in neuroendocrinology have elucidated many of the discrete and often very short developmental windows across pre- and postnatal development in which this occurs. This has allowed toxicologists to probe how EDC exposures in these critical windows can permanently alter the structure and function of the HPG axis. This review includes a discussion of key EDC principles including how latency between exposure and the emergence of consequential health effects can be long, along with a summary of the most common and less well-understood EDC modes of action. Extensive examples of how EDCs are impacting human reproductive health, and evidence that they have the potential for multi-generational physiological and behavioral effects are also provided.

Transcriptomic, proteomic, and metabolomic analyses identify candidate pathways linking maternal cadmium exposure to altered neurodevelopment and behavior

Cadmium (Cd) is a ubiquitous toxic heavy metal of major public concern. Despite inefficient placental transfer, maternal Cd exposure impairs fetal growth and development. Increasing evidence from animal models and humans suggests maternal Cd exposure negatively impacts neurodevelopment; however, the underlying molecular mechanisms are unclear. To address this, we utilized multiple -omics approaches in a mouse model of maternal Cd exposure to identify pathways altered in the developing brain. Offspring maternally exposed to Cd presented with enlarged brains proportional to body weights at birth and altered behavior at adulthood. RNA-seq in newborn brains identified exposure-associated increases in Hox gene and myelin marker expression and suggested perturbed retinoic acid (RA) signaling. Proteomic analysis showed altered levels of proteins involved in cellular energy pathways, hypoxic response, and RA signaling. Consistent with transcriptomic and proteomic analyses, we identified increased levels of retinoids in maternally-exposed newborn brains. Metabolomic analyses identified metabolites with significantly altered abundance, supportive of changes to cellular energy pathways and hypoxia. Finally, maternal Cd exposure reduced mitochondrial DNA levels in newborn brains. The identification of multiple pathways perturbed in the developing brain provides a basis for future studies determining the mechanistic links between maternal Cd exposure and altered neurodevelopment and behavior.

Sex-specific Disruption of the Prairie Vole Hypothalamus by Developmental Exposure to a Flame Retardant Mixture

Prevalence of neurodevelopmental disorders (NDDs) with social deficits is conspicuously rising, particularly in boys. Flame retardants (FRs) have long been associated with increased risk, and prior work by us and others in multiple species has shown that developmental exposure to the common FR mixture Firemaster 550 (FM 550) sex-specifically alters socioemotional behaviors including anxiety and pair bond formation. In rats, FRs have also been shown to impair aspects of osmoregulation. Because vasopressin (AVP) plays a role in both socioemotional behavior and osmotic balance we hypothesized that AVP and its related nonapeptide oxytocin (OT) would be vulnerable to developmental FM 550 exposure. We used the prairie vole (Microtus ochrogaste) to test this because it is spontaneously prosocial. Using siblings of prairie voles used in a prior study that assessed behavioral deficits resulting from developmental FM 550 exposure across 3 doses, here we tested the hypothesis that FM 550 sex-specifically alters AVP and OT neuronal populations in critical nuclei, such as the paraventricular nucleus (PVN), that coordinate those behaviors, as well as related dopaminergic (determined by tyrosine hydroxylase (TH) immunolabeling) populations. Exposed females had fewer AVP neurons in the anterior PVN and more A13 TH neurons in the zona incerta than controls. By contrast, in FM 550 males, A13 TH neuron numbers in the zona incerta were decreased but only in 1 dose group. These results expand on previous work showing evidence of endocrine disruption of OT/AVP pathways, including to subpopulations of PVN AVP neurons that coordinate osmoregulatory functions in the periphery.

Endocrine disrupting chemicals (EDCs) and the neuroendocrine system: Beyond estrogen, androgen, and thyroid

Hundreds of anthropogenic chemicals occupy our bodies, a situation that threatens the health of present and future generations. This chapter focuses on endocrine disrupting compounds (EDCs), both naturally occurring and man-made, that affect the neuroendocrine system to adversely impact health, with an emphasis on reproductive and metabolic pathways. The neuroendocrine system is highly sexually dimorphic and essential for maintaining homeostasis and appropriately responding to the environment. Comprising both neural and endocrine components, the neuroendocrine system is hormone sensitive throughout life and touches every organ system in the body. The integrative nature of the neuroendocrine system means that EDCs can have multi-system effects. Additionally, because gonadal hormones are essential for the sex-specific organization of numerous neuroendocrine pathways, endocrine disruption of this programming can lead to permanent deficits. Included in this review is a brief history of the neuroendocrine disruption field and a thorough discussion of the most common and less well understood neuroendocrine disruption modes of action. Also provided are extensive examples of how EDCs are likely contributing to neuroendocrine disorders such as obesity, and evidence that they have the potential for multi-generational effects.

Familiarity and Mate Preference Assessment with the Partner Preference Test

In contrast to traditional laboratory animals, prairie voles form socially monogamous partnerships in the wild and exhibit lasting social preferences for familiar individuals-both mates and same-sex peers-in the laboratory. Decades of research into the mechanisms supporting pair bonding behavior have made prairie voles an important model organism for the study of social relationships. The partner preference test is a laboratory test of familiarity preference that takes place over an extended interval (typically 3 hr), during which test subjects can directly interact with conspecifics and often engage in resting side-by-side contact (i.e., huddling). The use of this test has enabled study of the neural pathways and mechanisms involved in promoting or impairing relationship formation. The tendency to form partner preferences is also used as a behavioral indicator of the effects of early life experiences and environmental exposures. While this test was developed to assess the extent of social preference for mates in prairie voles, it has been adapted for use in other social contexts and in multiple other species. This article provides instructions for conducting the classic partner preference test, as well as variations including same-sex "peer" partner preference tests. The effects of several protocol variations are examined, including duration of cohousing, separation interval, use of tethers versus barriers, linear versus branched apparatus configuration, and duration of the test. The roles of social variables including sex of the focal individual, sex of conspecifics, reproductive state, and use of the test in other species are then considered. Finally, sample data are provided along with discussion of scoring and statistical analysis of partner preference tests. © 2021 Wiley Periodicals LLC. Basic Protocol: Partner preference test Support Protocol: Behavioral scoring.

A Neuroscientist's Guide to the Vole

Prairie voles have emerged as an important rodent model for understanding the neuroscience of social behavior. Prairie voles are well known for their capacity for pair bonding and alloparental care. These behavioral phenomena overlap with human social behavior but are not commonly observed in traditional rodent models. In this article, we highlight the many benefits of using prairie voles in neuroscience research. We begin by describing the advantages of using diverse and non-traditional study models. We then focus on social behaviors, including pair bonding, alloparental care, and peer interactions, that have brought voles to the forefront of social neuroscience. We describe many additional features of prairie vole biology and behavior that provide researchers with opportunities to address an array of research questions. We also survey neuroethological methods that have been used with prairie voles, from classic to modern techniques. Finally, we conclude with a discussion of other vole species, particularly meadow voles, and their own unique advantages for neuroscience studies. This article provides a foundation for researchers who are new to working with voles, as well as for experienced neuroscientists who want to expand their research scope. © 2021 Wiley Periodicals LLC.

EDCs Reorganize Brain-Behavior Phenotypic Relationships in Rats

All species, including humans, are exposed to endocrine-disrupting chemicals (EDCs). Previous experiments have shown behavioral deficits caused by EDCs that have implications for social competence and sexual selection. The neuromolecular mechanisms for these behavioral changes induced by EDCs have not been thoroughly explored. Here, we tested the hypothesis that EDCs administered to rats during a critical period of embryonic brain development would lead to the disruption of normal social preference behavior, and that this involves a network of underlying gene pathways in brain regions that regulate these behaviors. Rats were exposed prenatally to human-relevant concentrations of EDCs (polychlorinated biphenyls [PCBs], vinclozolin [VIN]), or vehicle. In adulthood, a sociosexual preference test was administered. We profiled gene expression of in preoptic area, medial amygdala, and ventromedial nucleus. Prenatal PCBs impaired sociosexual preference in both sexes, and VIN disrupted this behavior in males. Each brain region had unique sets of genes altered in a sex- and EDC-specific manner. The effects of EDCs on individual traits were typically small, but robust; EDC exposure changed the relationships between gene expression and behavior, a pattern we refer to as dis-integration and reconstitution. These findings underscore the effects that developmental exposure to EDCs can have on adult social behavior, highlight sex-specific and individual variation in responses, and provide a foundation for further work on the disruption of genes and behavior after prenatal exposure to EDCs.

Endocrine-Disrupting Chemicals: Introduction to the Theme

BACKGROUND

Endocrine-disrupting chemicals (EDCs) are natural or synthetic compounds deriving from different human activities and are widely spread into the environment, contributing to indoor and outdoor pollution. EDCs may be conveyed by food and water consumption and skin, airways, placental, and breastfeeding. Upon entering the circulation, they can interfere with endocrine system homeostasis by several mechanisms.

AIM

In this narrative review, the authors overviewed the leading mechanisms by which EDCs interact and disrupt the endocrine system, leading to possible human health concerns.

RESULTS

The leading mechanisms of EDCs-related toxicity have been illustrated in in vitro studies and animal models and may be summarized as follows: receptor agonism and antagonism; modulation of hormone receptor expression; interference with signal transduction in hormone-responsive cells; epigenetic modifications in hormone-producing or hormone-responsive cells; interference with hormone synthesis; interference with hormone transport across cell membranes; interference with hormone metabolism or clearance; interference with the destiny of hormone-producing or hormone-responsive cells.

DISCUSSION

Despite these well-defined mechanisms, some limitations do not allow for conclusive assumptions. Indeed, epidemiological and ecological studies are currently lacking and usually refer to a specific cluster of patients (occupational exposure). Methodological aspects could further complicate the issue since these studies could require a long time to provide useful information. The lack of a real unexposed group in environmental conditions, possible interference of EDCs mixture on biological results, and unpredictable dose-response curves for some EDCs should also be considered significant limitations.

CONCLUSION

Given these limitations, specific observational and long-term studies are needed to identify at-risk populations for adequate treatment of exposed patients and effective prevention plans against excessive exposure to EDCs.

Oxytocin, Dopamine, and Opioid Interactions Underlying Pair Bonding: Highlighting a Potential Role for Microglia

Pair bonds represent some of the strongest attachments we form as humans. These relationships positively modulate health and well-being. Conversely, the loss of a spouse is an emotionally painful event that leads to numerous deleterious physiological effects, including increased risk for cardiac dysfunction and mental illness. Much of our understanding of the neuroendocrine basis of pair bonding has come from studies of monogamous prairie voles (Microtus ochrogaster), laboratory-amenable rodents that, unlike laboratory mice and rats, form lifelong pair bonds. Specifically, research using prairie voles has delineated a role for multiple neuromodulatory and neuroendocrine systems in the formation and maintenance of pair bonds, including the oxytocinergic, dopaminergic, and opioidergic systems. However, while these studies have contributed to our understanding of selective attachment, few studies have examined how interactions among these 3 systems may be essential for expression of complex social behaviors, such as pair bonding. Therefore, in this review, we focus on how the social neuropeptide, oxytocin, interacts with classical reward system modulators, including dopamine and endogenous opioids, during bond formation and maintenance. We argue that an understanding of these interactions has important clinical implications and is required to understand the evolution and encoding of complex social behaviors more generally. Finally, we provide a brief consideration of future directions, including a discussion of the possible roles that glia, specifically microglia, may have in modulating social behavior by acting as a functional regulator of these 3 neuromodulatory systems.

Data integration, analysis, and interpretation of eight academic CLARITY-BPA studies

"Consortium Linking Academic and Regulatory Insights on BPA Toxicity" (CLARITY-BPA) was a comprehensive "industry-standard" Good Laboratory Practice (GLP)-compliant 2-year chronic exposure study of bisphenol A (BPA) toxicity that was supplemented by hypothesis-driven independent investigator-initiated studies. The investigator-initiated studies were focused on integrating disease-associated, molecular, and physiological endpoints previously found by academic scientists into an industry standard guideline-compliant toxicity study. Thus, the goal of this collaboration was to provide a more comprehensive dataset upon which to base safety standards and to determine whether industry-standard tests are as sensitive and predictive as molecular and disease-associated endpoints. The goal of this report is to integrate the findings from the investigator-initiated studies into a comprehensive overview of the observed impacts of BPA across the multiple organs and systems analyzed. For each organ system, we provide the rationale for the study, an overview of methodology, and summarize major findings. We then compare the results of the CLARITY-BPA studies across organ systems with the results of previous peer-reviewed studies from independent labs. Finally, we discuss potential influences that contributed to differences between studies. Developmental exposure to BPA can lead to adverse effects in multiple organs systems, including the brain, prostate gland, urinary tract, ovary, mammary gland, and heart. As published previously, many effects were at the lowest dose tested, 2.5μg/kg /day, and many of the responses were non-monotonic. Because the low dose of BPA affected endpoints in the same animals across organs evaluated in different labs, we conclude that these are biologically - and toxicologically - relevant.

Sex-biased impact of endocrine disrupting chemicals on behavioral development and vulnerability to disease: Of mice and children

Sex is a fundamental biological characteristic that influences many aspects of an organism's phenotype, including neurobiological functions and behavior as a result of species-specific evolutionary pressures. Sex differences have strong implications for vulnerability to disease and susceptibility to environmental perturbations. Endocrine disrupting chemicals (EDCs) have the potential to interfere with sex hormones functioning and influence development in a sex specific manner. Here we present an updated descriptive review of findings from animal models and human studies regarding the current evidence for altered sex-differences in behavioral development in response to early exposure to EDCs, with a focus on bisphenol A and phthalates. Overall, we show that animal and human studies have a good degree of consistency and that there is strong evidence demonstrating that EDCs exposure during critical periods of development affect sex differences in emotional and cognitive behaviors. Results are more heterogeneous when social, sexual and parental behaviors are considered. In order to pinpoint sex differences in environmentally-driven disease vulnerabilities, researchers need to consider sex-biased developmental effects of EDCs.

Consensus on the key characteristics of endocrine-disrupting chemicals as a basis for hazard identification

Endocrine-disrupting chemicals (EDCs) are exogenous chemicals that interfere with hormone action, thereby increasing the risk of adverse health outcomes, including cancer, reproductive impairment, cognitive deficits and obesity. A complex literature of mechanistic studies provides evidence on the hazards of EDC exposure, yet there is no widely accepted systematic method to integrate these data to help identify EDC hazards. Inspired by work to improve hazard identification of carcinogens using key characteristics (KCs), we have developed ten KCs of EDCs based on our knowledge of hormone actions and EDC effects. In this Expert Consensus Statement, we describe the logic by which these KCs are identified and the assays that could be used to assess several of these KCs. We reflect on how these ten KCs can be used to identify, organize and utilize mechanistic data when evaluating chemicals as EDCs, and we use diethylstilbestrol, bisphenol A and perchlorate as examples to illustrate this approach.

Achieving CLARITY on bisphenol A, brain and behaviour

There is perhaps no endocrine disrupting chemical more controversial than bisphenol A (BPA). Comprising a high-volume production chemical used in a variety of applications, BPA has been linked to a litany of adverse health-related outcomes, including effects on brain sexual differentiation and behaviour. Risk assessors preferentially rely on classical guideline-compliant toxicity studies over studies published by academic scientists, and have generally downplayed concerns about the potential risks that BPA poses to human health. It has been argued, however, that, because traditional toxicity studies rarely contain neural endpoints, and only a paucity of endocrine-sensitive endpoints, they are incapable of fully evaluating harm. To address current controversies on the safety of BPA, the United States National Institute of Environmental Health Sciences, the National Toxicology Program (NTP), and the US Food and Drug Administration established the Consortium Linking Academic and Regulatory Insights on BPA Toxicity (CLARITY-BPA). CLARITY-BPA performed a classical regulatory-style toxicology study (Core study) in conjunction with multiple behavioural, molecular and cellular studies conducted by academic laboratories (grantee studies) using a collaboratively devised experimental framework and the same animals and tissues. This review summarises the results from the grantee studies that focused on brain and behaviour. Evidence of altered neuroendocrine development, including age- and sex-specific expression of oestrogen receptor (ER)α and ERβ, and the abrogation of brain and behavioural sexual dimorphisms, supports the conclusion that developmental BPA exposure, even at doses below what regulatory agencies regard as "safe" for humans, contribute to brain and behavioural change. The consistency and the reproducibility of the effects across CLARITY-BPA and prior studies using the same animal strain and almost identical experimental conditions are compelling. Combined analysis of all of the data from the CLARITY-BPA project is underway at the NTP and a final report expected in late 2019.

Sex-specific effects of perinatal FireMaster® 550 (FM 550) exposure on socioemotional behavior in prairie voles

The rapidly rising incidence of neurodevelopmental disorders with social deficits is raising concern that developmental exposure to environmental contaminants may be contributory. Firemaster 550 (FM 550) is one of the most prevalent flame-retardant (FR) mixtures used in foam-based furniture and baby products and contains both brominated and organophosphate components. We and others have published evidence of developmental neurotoxicity and sex specific effects of FM 550 on anxiety-like and exploratory behaviors. Using a prosocial animal model, we investigated the impact of perinatal FM 550 exposure on a range of socioemotional behaviors including anxiety, attachment, and memory. Virtually unknown to toxicologists, but widely used in the behavioral neurosciences, the prairie vole (Microtus ochrogaster) is a uniquely valuable model organism for examining environmental factors on sociality because this species is spontaneously prosocial, biparental, and displays attachment behaviors including pair bonding. Dams were exposed to 0, 500, 1000, or 2000 μg of FM 550 via subcutaneous (sc) injections throughout gestation, and pups were directly exposed beginning the day after birth until weaning. Adult offspring of both sexes were then subjected to multiple tasks including open field, novel object recognition, and partner preference. Effects were dose responsive and sex-specific, with females more greatly affected. Exposure-related outcomes in females included elevated anxiety, decreased social interaction, decreased exploratory motivation, and aversion to novelty. Exposed males also had social deficits, with males in all three dose groups failing to show a partner preference. Our studies demonstrate the utility of the prairie vole for investigating the impact of chemical exposures on social behavior and support the hypothesis that developmental FR exposure impacts the social brain. Future studies will probe the possible mechanisms by which these effects arise.

Phosphorus-Containing Flame Retardants from Biobased Chemicals and Their Application in Polyesters and Epoxy Resins

Phosphorus-containing flame retardants synthesized from renewable resources have had a lot of impact in recent years. This article outlines the synthesis, characterization and evaluation of these compounds in polyesters and epoxy resins. The different approaches used in producing biobased flame retardant polyesters and epoxy resins are reported. While for the polyesters biomass derived compounds usually are phosphorylated and melt blended with the polymer, biobased flame retardants for epoxy resins are directly incorporated into the polymer structure by a using a phosphorylated biobased monomer or curing agent. Evaluating the efficiency of the flame retardant composites is done by discussing results obtained from UL94 vertical burning, limiting oxygen index (LOI) and cone calorimetry tests. The review ends with an outlook on future development trends of biobased flame retardant systems for polyesters and epoxy resins.

Perinatal bisphenol A (BPA) exposure alters brain oxytocin receptor (OTR) expression in a sex- and region- specific manner: A CLARITY-BPA consortium follow-up study

Bisphenol A (BPA) is a well-characterized endocrine disrupting chemical (EDC) used in plastics, epoxy resins and other products. Neurodevelopmental effects of BPA exposure are a major concern with multiple rodent and human studies showing that early life BPA exposure may impact the developing brain and sexually dimorphic behaviors. The CLARITY-BPA (Consortium Linking Academic and Regulatory Insights on BPA Toxicity) program was established to assess multiple endpoints, including neural, across a wide dose range. Studies from our lab as part of (and prior to) CLARITY-BPA have shown that BPA disrupts estrogen receptor expression in the developing brain, and some evidence of oxytocin (OT) and oxytocin receptor (OTR) disruption in the hypothalamus and amygdala. While BPA disruption of steroid hormone function is well documented, less is known about its capacity to alter nonapeptide signals. In this CLARITY-BPA follow up study, we used remaining juvenile rat tissues to test the hypothesis that developmental BPA exposure affects OTR expression across the brain. Perinatal BPA exposure (2.5, 25, or 2500 μg/kg body weight (bw)/day) spanned gestation and lactation with dams gavaged from gestational day 6 until birth and then the offspring gavaged directly through weaning. Ethinyl estradiol (0.5 μg/kg bw/day) was used as a reference estrogen. Animals of both sexes were sacrificed as juveniles and OTR expression assessed by receptor binding. Our results demonstrate prenatal exposure to BPA can eliminate sex differences in OTR expression in three hypothalamic regions, and that male OTR expression may be more susceptible. Our data also identify a sub-region of the BNST with sexually dimorphic OTR expression not previously reported in juvenile rats that is also susceptible to BPA.

Transgenerational Bisphenol A Causes Deficits in Social Recognition and Alters Postsynaptic Density Genes in Mice

Bisphenol A (BPA) is a ubiquitous endocrine-disrupting chemical. Developmental exposure produces changes in behavior and gene expression in the brain. Here, we examined social recognition behaviors in mice from the third familial generation (F3) after exposure to gestational BPA. Second-generation mice were bred in one of four mating combinations to reveal whether characteristics in F3 were acquired via maternal or paternal exposures. After repeated habituation to the same mouse, offspring of dams from the BPA lineage failed to display increased investigation of a novel mouse. Genes involved in excitatory postsynaptic densities (PSDs) were examined in F3 brains using quantitative PCR. Differential expression of genes important for function and stability of PSDs were assessed at three developmental ages. Several related PSD genes-SH3 and multiple ankyrin repeat domains 1 (Shank1), Homer scaffolding protein 1c (Homer1c), DLG associated protein 1 (Gkap), and discs large MAGUK scaffold protein 4 (PSD95)-were differentially expressed in control- vs BPA-lineage brains. Using a second strain of F3 inbred mice exposed to BPA, we noted the same differences in Shank1 and PSD95 expression in C57BL/6J mice. In sum, transgenerational BPA exposure disrupted social interactions in mice and dysregulated normal expression of PSD genes during neural development. The fact that the same genetic effects were found in two different mouse strains and in several brain regions increased potential for translation. The genetic and functional relationship between PSD and abnormal neurobehavioral disorders is well established, and our data suggest that BPA may contribute in a transgenerational manner to neurodevelopmental diseases.

Effects of methamphetamine on alloparental behavior in male and female prairie voles

Psychostimulant abuse is associated with a variety of impairments in social functioning, including an increased frequency of depression and aggression and deficits in social cognition. Psychostimulants reduce social investigation in rats and mice; however, it is less clear how other forms of social behavior (e.g., prosocial behavior) are affected. Females are also generally more sensitive to the effects of psychostimulants on locomotion and stereotyped behavior, which suggests that females might also display greater disruption of prosocial behavior. In order to test the hypothesis that psychostimulants reduce prosocial behavior and that females are more vulnerable, we treated adult male and female prairie voles with methamphetamine for three days (0, 0.2 or 2.0mg/kg, i.p.) and examined effects on locomotion and alloparental behavior. The lower methamphetamine dose increased activity in the open field in males and reduced locomotion in females. Methamphetamine-treated males took longer to enter the pup chamber, but both sexes displayed reduced pup contact following treatment with the lower methamphetamine dose. The methamphetamine-induced reduction in prosocial behavior was not associated with changes in pup-directed aggression in males or females. In order to investigate potential mechanisms underlying these changes in behavior, we measured adrenal weights as a proxy for activation of the hypothalamic-pituitary-adrenal (HPA) axis. The higher methamphetamine dose increased adrenal weights. Collectively, these data demonstrate that methamphetamine administration reduces alloparental behavior in both sexes and that females are more sensitive to some of the effects of this drug (e.g., locomotion/stereotyped behavior and possibly stimulation of the HPA axis).

Endocrine-disrupting chemicals: Effects on neuroendocrine systems and the neurobiology of social behavior

A contribution to SBN/ICN special issue. Endocrine-disrupting chemicals (EDCs) are pervasive in the environment. They are found in plastics and plasticizers (bisphenol A (BPA) and phthalates), in industrial chemicals such as polychlorinated biphenyls (PCBs), and include some pesticides and fungicides such as vinclozolin. These chemicals act on hormone receptors and their downstream signaling pathways, and can interfere with hormone synthesis, metabolism, and actions. Because the developing brain is particularly sensitive to endogenous hormones, disruptions by EDCs can change neural circuits that form during periods of brain organization. Here, we review the evidence that EDCs affect developing hypothalamic neuroendocrine systems, and change behavioral outcomes in juvenile, adolescent, and adult life in exposed individuals, and even in their descendants. Our focus is on social, communicative and sociosexual behaviors, as how an individual behaves with a same- or opposite-sex conspecific determines that individual's ability to exist in a community, be selected as a mate, and reproduce successfully.

Environmental Mechanisms of Neurodevelopmental Toxicity

PURPOSE OF REVIEW

With the incidence of neurodevelopmental disorders on the rise, it is imperative to identify and understand the mechanisms by which environmental contaminants can impact the developing brain and heighten risk. Here, we report on recent findings regarding novel mechanisms of developmental neurotoxicity and highlight chemicals of concern, beyond traditionally defined neurotoxicants.

RECENT FINDINGS

The perinatal window represents a critical and extremely vulnerable period of time during which chemical insult can alter the morphological and functional trajectory of the developing brain. Numerous chemical classes have been associated with alterations in neurodevelopment including metals, solvents, pesticides, and, more recently, endocrine-disrupting compounds. Although mechanisms of neurotoxicity have traditionally been identified as pathways leading to neuronal cell death, neuropathology, or severe neural injury, recent research highlights alternative mechanisms that result in more subtle but consequential changes in the brain and behavior. These emerging areas of interest include neuroendocrine and immune disruption, as well as indirect toxicity via actions on other organs such as the gut and placenta. Understanding of the myriad ways in which the developing brain is vulnerable to chemical exposures has grown tremendously over the past decade. Further progress and implementation in risk assessment is critical to reducing risk of neurodevelopmental disorders.

Social and neuromolecular phenotypes are programmed by prenatal exposures to endocrine-disrupting chemicals

Exposures to endocrine-disrupting chemicals (EDCs) affect the development of hormone-sensitive neural circuits, the proper organization of which are necessary for the manifestation of appropriate adult social and sexual behaviors. We examined whether prenatal exposure to polychlorinated biphenyls (PCBs), a family of ubiquitous industrial contaminants detectable in virtually all humans and wildlife, caused changes in sexually-dimorphic social interactions and communications, and profiled the underlying neuromolecular phenotype. Rats were treated with a PCB commercial mixture, Aroclor 1221 (A1221), estradiol benzoate (EB) as a positive control for estrogenic effects of A1221, or the vehicle (4% DMSO), on embryonic day (E) 16 and 18. In adult F1 offspring, we first conducted tests of ultrasonic vocalization (USV) calls in a sociosexual context as a measure of motivated communications. Numbers of certain USV call types were significantly increased by prenatal treatment with A1221 in males, and decreased by EB in females. In a test of sociosexual preference for a hormone-vs. a non-hormone-primed opposite sex conspecific, male (but not female) nose-touching with opposite-sex rats was significantly diminished by EDCs. Gene expression profiling was conducted in two brain regions that are part of the social decision-making network in the brain: the medial preoptic nucleus (MPN) and the ventromedial nucleus (VMN). In both regions, many more genes were affected by A1221 or EB in females than males. In female MPN, A1221 changed expression of steroid hormone receptor and neuropeptide genes (e.g., Ar, Esr1, Esr2, and Kiss1). In male MPN, only Per2 was affected by A1221. The VMN had a number of genes affected by EB compared to vehicle (females: Kiss1, Kiss1r, Pgr; males: Crh) but not A1221. These differences between EB and A1221 indicate that the mechanism of action of A1221 goes beyond estrogenic pathways. These data show sex-specific effects of prenatal PCBs on adult behaviors and the neuromolecular phenotype.

Endocrine Disrupting Chemicals: An Occult Mediator of Metabolic Disease

Endocrine disrupting chemicals (EDCs), a heterogeneous group of exogenous chemicals that can interfere with any aspect of endogenous hormones, represent an emerging global threat for human metabolism. There is now considerable evidence that the observed upsurge of metabolic disease cannot be fully attributed to increased caloric intake, physical inactivity, sleep deficit, and ageing. Among environmental factors implicated in the global deterioration of metabolic health, EDCs have drawn the biggest attention of scientific community, and not unjustifiably. EDCs unleash a coordinated attack toward multiple components of human metabolism, including crucial, metabolically-active organs such as hypothalamus, adipose tissue, pancreatic beta cells, skeletal muscle, and liver. Specifically, EDCs' impact during critical developmental windows can promote the disruption of individual or multiple systems involved in metabolism, via inducing epigenetic changes that can permanently alter the epigenome in the germline, enabling changes to be transmitted to the subsequent generations. The clear effect of this multifaceted attack is the manifestation of metabolic disease, clinically expressed as obesity, metabolic syndrome, diabetes mellitus, and non-alcoholic fatty liver disease. Although limitations of EDCs research do exist, there is no doubt that EDCs constitute a crucial parameter of the global deterioration of metabolic health we currently encounter.

Novel unconditioned prosocial behavior in prairie voles (Microtus ochrogaster) as a model for empathy

OBJECTIVE

In this study, empathy is quantified using a novel social test. Empathy and prosocial behavior are linked to the expression of oxytocin in humans and rodent models. Specifically, prosocial behavior in prairie voles (Microtus ochrogaster) has been linked to the expression of oxytocin in the paraventricular nucleus of the hypothalamus. The animal's behavior was considered empathic if it spends significantly more time attempting to remove a loos fitting restraint (tether) from the stimulus animal than time in contact with a, simultaneously presented, non-social object similar to the tether. The behavioral data was cross-referenced with the number of neurons expressing oxytocin and arginine vasopressin, as well as the density of dopaminergic neurons (identified by the expression of tyrosine hydroxylase), in the paraventricular nucleus of the hypothalamus. These proteins influence empathic behavior in humans, non-human primates, rats, mice, and prairie voles.

RESULTS

The consistency between neuroanatomical mechanisms linked to empathy, and the durations of time spent engaging in empathic contact, support the prediction that the empathic contact in this test is a distinct prosocial behavior, lacking prior behavioral training or the naturally occurring ethological relevance of other prosocial behaviors, and is a measure of empathy.

CLARITY-BPA academic laboratory studies identify consistent low-dose Bisphenol A effects on multiple organ systems

Bisphenol A (BPA) is a high-production chemical used in a variety of applications worldwide. While BPA has been documented as an endocrine-disrupting chemical (EDC) having adverse health-related outcomes in multiple studies, risk assessment for BPA has lagged due to reliance on guideline toxicology studies over academic ones with end-points considered more sensitive and appropriate. To address current controversies on BPA safety, the United States National Institute of Environmental Health Sciences (NIEHS), the National Toxicology Program (NTP) and the Food and Drug Administration (FDA) established the Consortium Linking Academic and Regulatory Insights on BPA Toxicity (CLARITY-BPA) using the NCTR Sprague-Dawley rats. The goal of CLARITY-BPA is to perform a traditional regulatory toxicology study (Core study) in conjunction with multiple behavioural, molecular and cellular studies by academic laboratories focused on previously identified BPA-sensitive organ systems (Academic studies). Combined analysis of the data from both study types will be undertaken by the NTP with the aim of resolving uncertainties on BPA toxicity. To date, the Core study has been completed and a draft report released. Most of the academic studies have also been finalized and published in peer-reviewed journals. In light of this important milestone, the PPTOX-VI meeting held in the Faroe Islands, 27-30 May 2018 devoted a plenary session to CLARITY-BPA with presentations by multiple investigators with the purpose of highlighting key outcome. This MiniReview synthesizes the results of three academic studies presented at this plenary session, evaluates recently published findings by other CLARITY-BPA academic studies to provide an early combined overview of this emerging data and places this in the context of the Core study findings. This co-ordinated effort revealed a plethora of significant BPA effects across multiple organ systems and BPA doses with non-monotonic responses across the dose range utilized. Remarkably consistent across most studies, including the Core study, are low-dose effects (2.5, 25 and 250 μg BPA/kg body-weight). Collectively, the findings highlighted herein corroborate a significant body of evidence that documents adverse effects of BPA at doses relevant to human exposures and emphasizes the need for updated risk assessment analysis.

Animal models of endocrine disruption

Endocrine disrupting chemicals (EDCs) are compounds that alter the structure and function of the endocrine system and may be contributing to disorders of the reproductive, metabolic, neuroendocrine and other complex systems. Typically, these outcomes cannot be modeled in cell-based or other simple systems necessitating the use of animal testing. Appropriate animal model selection is required to effectively recapitulate the human experience, including relevant dosing and windows of exposure, and ensure translational utility and reproducibility. While classical toxicology heavily relies on inbred rats and mice, and focuses on apical endpoints such as tumor formation or birth defects, EDC researchers have used a greater diversity of species to effectively model more subtle but significant outcomes such as changes in pubertal timing, mammary gland development, and social behaviors. Advances in genomics, neuroimaging and other tools are making a wider range of animal models more widely available to EDC researchers.

Effects of maternal or paternal bisphenol A exposure on offspring behavior

Bisphenol A (BPA) is an endocrine disrupting chemical used in the production of polycarbonate plastics and resins. Exposure to BPA during gestation has been proposed as a risk factor for the development of neurobehavioral disorders, such as autism spectrum disorder. To address the behavioral impact of developmental exposure to BPA, we tested offspring of mice exposed to a daily low dose of BPA during pregnancy. We also asked if preconception exposure of the sire affected behaviors in offspring. Sires that consumed BPA for 50days prior to mating weighed less than controls, but no effects on any reproductive measures were noted. Juvenile offspring exposed to BPA maternally, but not paternally, spent less time in the open arms of the elevated plus maze than controls, indicating increased anxiety-like behavior. However, neither parental exposure group differed significantly from controls in the social recognition task. We also assessed the behaviors of maternally exposed offspring in two novel tasks: ultrasonic vocalizations (USVs) in pups and operant reversal learning in adults. Maternal BPA exposure increased the duration and median frequency of USVs emitted by pups during maternal separation. In the reversal learning task, females responded more accurately and earned more rewards than males. Additionally, control females received more rewards than BPA females during the acquisition phase of the task. These are among the first studies conducted to ask if BPA exposure via the sire affects offspring behavior and the first study to report effects of gestational BPA exposure on pup USVs and adult operant responding.

Mate choice, sexual selection, and endocrine-disrupting chemicals

Humans have disproportionately affected the habitat and survival of species through environmental contamination. Important among these anthropogenic influences is the proliferation of organic chemicals, some of which perturb hormone systems, the latter referred to as endocrine-disrupting chemicals (EDCs). EDCs are widespread in the environment and affect all levels of reproduction, including development of reproductive organs, hormone release and regulation through the life cycle, the development of secondary sexual characteristics, and the maturation and maintenance of adult physiology and behavior. However, what is not well-known is how the confluence of EDC actions on the manifestation of morphological and behavioral sexual traits influences mate choice, a process that requires the reciprocal evaluation of and/or acceptance of a sexual partner. Moreover, the outcomes of EDC-induced perturbations are likely to influence sexual selection; yet this has rarely been directly tested. Here, we provide background on the development and manifestation of sexual traits, reproductive competence, and the neurobiology of sexual behavior, and evidence for their perturbation by EDCs. Selection acts on individuals, with the consequences manifest in populations, and we discuss the implications for EDC contamination of these processes, and the future of species.

Neurodevelopmental and neurological effects of chemicals associated with unconventional oil and natural gas operations and their potential effects on infants and children

Heavy metals (arsenic and manganese), particulate matter (PM), benzene, toluene, ethylbenzene, xylenes (BTEX), polycyclic aromatic hydrocarbons (PAHs) and endocrine disrupting chemicals (EDCs) have been linked to significant neurodevelopmental health problems in infants, children and young adults. These substances are widely used in, or become byproducts of unconventional oil and natural gas (UOG) development and operations. Every stage of the UOG lifecycle, from well construction to extraction, operations, transportation and distribution can lead to air and water contamination. Residents near UOG operations can suffer from increased exposure to elevated concentrations of air and water pollutants. Here we focus on five air and water pollutants that have been associated with potentially permanent learning and neuropsychological deficits, neurodevelopmental disorders and neurological birth defects. Given the profound sensitivity of the developing brain and central nervous system, it is reasonable to conclude that young children who experience frequent exposure to these pollutants are at particularly high risk for chronic neurological diseases. More research is needed to understand the extent of these concerns in the context of UOG, but since UOG development has expanded rapidly in recent years, the need for public health prevention techniques, well-designed studies and stronger state and national regulatory standards is becoming increasingly apparent.

Transgenerational Effects of Bisphenol A on Gene Expression and DNA Methylation of Imprinted Genes in Brain

Bisphenol A (BPA) is a ubiquitous man-made endocrine disrupting compound (EDC). Developmental exposure to BPA changes behavioral and reproductive phenotypes, and these effects can last for generations. We exposed embryos to BPA, producing two lineages: controls and BPA exposed. In the third filial generation (F3), brain tissues containing the preoptic area, the bed nucleus of the stria terminalis, and the anterior hypothalamus were collected. RNA sequencing (RNA-seq) and subsequent data analyses revealed 50 differentially regulated genes in the brains of F3 juveniles from BPA vs control lineages. BPA exposure can lead to loss of imprinting, and one of the two imprinted genes in our data set, maternally expressed gene 3 (Meg3), has been associated with EDCs and neurobehavioral phenotypes. We used quantitative polymerase chain reaction to examine the two imprinted genes in our data set, Meg3 and microRNA-containing gene Mirg (residing in the same loci). Confirming the RNA-seq, Meg3 messenger RNA was higher in F3 brains from the BPA lineage than in control brains. This was true in brains from mice produced with two different BPA paradigms. Next, we used pyrosequencing to probe differentially methylated regions of Meg3. We found transgenerational effects of BPA on imprinted genes in brain. Given these results, and data on Meg3 methylation in humans, we suggest this gene may be a biomarker indicative of early life environmental perturbation.

Prenatal bisphenol A (BPA) exposure alters the transcriptome of the neonate rat amygdala in a sex-specific manner: a CLARITY-BPA consortium study

Bisphenol A (BPA) is a widely recognized endocrine disruptor prevalent in many household items. Because experimental and epidemiological data suggest links between prenatal BPA exposure and altered affective behaviors in children, even at levels below the current US FDA No Observed Adverse Effect Level (NOAEL) of 5mg/kg body weight (bw)/day, there is concern that early life exposure may alter neurodevelopment. The current study was conducted as part of the CLARITY-BPA (Consortium Linking Academic and Regulatory Insights on BPA Toxicity) program and examined the full amygdalar transcriptome on postnatal day (PND) 1, with the hypothesis that prenatal BPA exposure would alter the expression of genes and pathways fundamental to sex-specific affective behaviors. NCTR Sprague-Dawley dams were gavaged from gestational day 6 until parturition with BPA (2.5, 25, 250, 2500, or 25000μg/kg bw/day), a reference estrogen (0.05 or 0.5μg ethinyl estradiol (EE₂)/kg bw/day), or vehicle. PND 1 amygdalae were microdissected and gene expression was assessed with qRT-PCR (all exposure groups) and RNAseq (vehicle, 25 and 250μg BPA, and 0.5μg EE₂ groups only). Our results demonstrate that that prenatal BPA exposure can disrupt the transcriptome of the neonate amygdala, at doses below the FDA NOAEL, in a sex-specific manner and indicate that the female amygdala may be more sensitive to BPA exposure during fetal development. We also provide additional evidence that developmental BPA exposure can interfere with estrogen, oxytocin, and vasopressin signaling pathways in the developing brain and alter signaling pathways critical for synaptic organization and transmission.

Effects of perinatal bisphenol A exposure on the volume of sexually-dimorphic nuclei of juvenile rats: A CLARITY-BPA consortium study

Bisphenol A (BPA) is a high volume endocrine disrupting chemical found in a wide variety of products including plastics and epoxy resins. Human exposure is nearly ubiquitous, and higher in children than adults. Because BPA has been reported to interfere with sex steroid hormone signaling, there is concern that developmental exposure, even at levels below the current FDA No Observed Adverse Effect Level (NOAEL) of 5mg/kg body weight (bw)/day, can disrupt brain sexual differentiation. The current studies were conducted as part of the CLARITY-BPA (Consortium Linking Academic and Regulatory Insights on BPA Toxicity) program and tested the hypothesis that perinatal BPA exposure would induce morphological changes in hormone sensitive, sexually dimorphic brain regions. Sprague-Dawley rats were randomly assigned to 5 groups: BPA (2.5, 25, or 2500μg/kgbw/day), a reference estrogen (0.5μg ethinylestradiol (EE₂)/kgbw/day), or vehicle. Exposure occurred by gavage to the dam from gestational day 6 until parturition, and then to the offspring from birth through weaning. Unbiased stereology was used to quantify the volume of the sexually dimorphic nucleus (SDN), the anteroventral periventricular nucleus (AVPV), the posterodorsal portion of the medial amygdala (MePD), and the locus coeruleus (LC) at postnatal day 28. No appreciable effects of BPA were observed on the volume of the SDN or LC. However, AVPV volume was enlarged in both sexes, even at levels below the FDA NOAEL. Collectively, these data suggest the developing brain is vulnerable to endocrine disruption by BPA at exposure levels below previous estimates by regulatory agencies.

Elucidating environmental dimensions of neurological disorders and disease: Understanding new tools from federal chemical testing programs

BACKGROUND

Federal agencies are making significant investments to advance predictive approaches to evaluate chemical hazards and risks. Environmental Defense Fund (EDF) believes that engagement with the broader scientific community is critical to building and maintaining a strong biological foundation for these approaches.

OBJECTIVES

On June 18-19, 2015, EDF organized a meeting to 1) foster a conversation between federal scientists advancing predictive approaches and environmental health researchers investigating environmental exposures and neurological outcomes, and 2) explore opportunities and challenges for the use of federal chemical high-throughput in vitro screening (HTS) data in hypothesis-driven research toward, ultimately, improved data for public health decision-making.

DISCUSSION

The meeting achieved its objectives. Government scientists showcased their chemical testing programs and vision for how emerging data may be used to meet agency missions. Environmental health researchers shared their experiences using federal HTS data, offered recommendations for strengthening federal HTS platforms, and expressed great interest in continued engagement with evolving federal chemical testing initiatives.

CONCLUSIONS

The meeting provided an invaluable exchange between two scientific communities with a shared interest in protecting public health from harmful environmental exposures, but who have not sufficiently engaged with each other. Discussions identified opportunities and work ahead for the use of HTS data in hypothesis-driven research. Though the meeting focused on neurological outcomes, the purpose, objectives and experience of the meeting are broadly applicable. EDF strongly encourages more discourse and collaboration between federal and non-government scientists working to understand environmental influences on health outcomes.

Endocrine-disrupting chemicals and the regulation of energy balance

Energy balance involves the adjustment of food intake, energy expenditure and body fat reserves through homeostatic pathways. These pathways include a multitude of biochemical reactions, as well as hormonal cues. Dysfunction of this homeostatic control system results in common metabolism-related pathologies, which include obesity and type 2 diabetes mellitus. Metabolism-disrupting chemicals (MDCs) are a particular class of endocrine-disrupting chemicals that affect energy homeostasis. MDCs affect multiple endocrine mechanisms and thus different cell types that are implicated in metabolic control. MDCs affect gene expression and the biosynthesis of key enzymes, hormones and adipokines that are essential for controlling energy homeostasis. This multifaceted spectrum of actions precludes compensatory responses and favours metabolic disorders. Herein, we review the main mechanisms used by MDCs to alter energy balance. This work should help to identify new MDCs, as well as novel targets of their action.

Early postnatal genistein administration permanently affects nitrergic and vasopressinergic systems in a sex-specific way

Genistein (GEN) is a natural xenoestrogen (isoflavonoid) that may interfere with the development of estrogen-sensitive neural circuits. Due to the large and increasing use of soy-based formulas for babies (characterized by a high content of GEN), there are some concerns that this could result in an impairment of some estrogen-sensitive neural circuits and behaviors. In a previous study, we demonstrated that its oral administration to female mice during late pregnancy and early lactation induced a significant decrease of nitric oxide synthase-positive cells in the amygdala of their male offspring. In the present study, we have used a different experimental protocol mimicking, in mice, the direct precocious exposure to GEN. Mice pups of both sexes were fed either with oil, estradiol or GEN from birth to postnatal day 8. Nitric oxide synthase and vasopressin neural systems were analyzed in adult mice. Interestingly, we observed that GEN effect was time specific (when compared to our previous study), sex specific, and not always comparable to the effects of estradiol. This last observation suggests that GEN may act through different intracellular pathways. Present results indicate that the effect of natural xenoestrogens on the development of the brain may be highly variable: a plethora of neuronal circuits may be affected depending on sex, time of exposure, intracellular pathway involved, and target cells. This raises concern on the possible long-term effects of the use of soy-based formulas for babies, which may be currently underestimated.

Multi- and Transgenerational Consequences of Bisphenol A on Sexually Dimorphic Cell Populations in Mouse Brain

Bisphenol A (BPA) is an endocrine-disrupting compound used to manufacture plastics; it is present in linings of food cans, bottles, thermal receipts, and many other everyday items and is detectable in human urine and blood. Exposure to BPA during development can disrupt sexual differentiation of some brain regions. Moreover, BPA can have transgenerational effects on gene expression and behaviors. Here, we used a diet and breeding regimen that produces transgenerational effects on behaviors. C57BL/6J mice consumed control or BPA-containing diets during pregnancy. We examined vasopressin (AVP) and estrogen receptor α (ERα) immunoreactivity (ir) in sexually dimorphic brain regions from first-generation (F1) offspring and transgenerational effects of BPA in third-generation offspring. In all but one brain region examined, the expected sex differences were noted in both generations of control mice. In F1 mice, a diet by sex interaction was present for AVP-ir in the lateral septum and posterodorsal medial amygdala. In both regions, BPA exposure reduced immunoreactivity in male brains. An interaction between diet and sex for ERα-ir in the ventromedial hypothalamus was caused by reduced immunoreactivity in BPA-exposed females. Of interest, BPA had transgenerational effects on ERα-ir in the anteroventral periventricular nucleus and bed nucleus of the stria terminalis. Our data show that BPA produces immunoreactive differences in ERα-ir generations after exposure to BPA. We speculate that actions of BPA in utero on ERα-ir in brain have long-term consequences for reproduction and social behavior.

Endocrine Disruption of Vasopressin Systems and Related Behaviors

Endocrine disrupting chemicals (EDCs) are chemicals that interfere with the organizational or activational effects of hormones. Although the vast majority of the EDC literature focuses on steroid hormone signaling related impacts, growing evidence from a myriad of species reveals that the nonapeptide hormones vasopressin (AVP) and oxytocin (OT) may also be EDC targets. EDCs shown to alter pathways and behaviors coordinated by AVP and/or OT include the plastics component bisphenol A (BPA), the soy phytoestrogen genistein (GEN), and various flame retardants. Many effects are sex specific and likely involve action at nuclear estrogen receptors. Effects include the elimination or reversal of well-characterized sexually dimorphic aspects of the AVP system, including innervation of the lateral septum and other brain regions critical for social and other non-reproductive behaviors. Disruption of magnocellular AVP function has also been reported in rats, suggesting possible effects on hemodynamics and cardiovascular function.