Neonatal agonism of ERβ impairs male reproductive behavior and attractiveness

Perinatal exposure to FireMaster® 550 (FM550), brominated or organophosphate flame retardants produces sex and compound specific effects on adult Wistar rat socioemotional behavior

Firemaster 550 (FM550) is a flame retardant (FR) mixture that has become one of the most commonly used FRs in household items such as foam-based furniture and baby products. Because this mixture readily leaches from products, contamination of the environment and human tissues is widespread. Prior work by us and others has reported sex-specific behavioral deficits in rodents and zebrafish following early life exposure. In an effort to understand the mechanisms by which these behavioral effects occur, here we explored the effects of its constituents on behavioral outcomes previously shown to be altered by developmental FM550 exposure. The FM550 commercial mixture is composed of two brominated compounds (BFR) and two organophosphate compounds (OPFRs) at almost equivalent proportions. Both the BFR and the OPFR components are differentially metabolized and structurally distinct, but similar to known neurotoxicants. Here we examined adult Wistar rat offspring socioemotional behaviors following perinatal exposure (oral, to the dam) to vehicle, 2000 μg/day FM550, 1000 μg/day BFR or 1000 μg/day OPFR from gestation day 0 to weaning. Beginning on postnatal day 65 offspring from all groups were subjected to a series of behavioral tasks including open field, elevated plus maze, marble burying, social interaction tests, and running wheel. Effects were exposure-, sex- and task-specific, with BFR exposure resulting in the most consistent behavioral deficits. Overall, exposed females showed more deficits compared to males across all dose groups and tasks. These findings help elucidate how different classes of flame retardants, independently and as a mixture, contribute to sex-specific behavioral effects of exposure.

Estradiol Treatment during Perinatal Development Alters Adult Partner Preference, Mating Behavior and Estrogen Receptors α and β in the Female Mandarin Vole (Microtus mandarinus)

During development, many aspects of behavior, including partner preferences and sexual conduct, are "organized" by estradiol. This study aimed at analyze these processes in the mandarin vole (Microtus mandarinus), a novel experimental mammal with strong monogamous pair bonds. Female pups were treated daily with an oil vehicle (FC) or β-Estradiol (E2, FT) from prenatal day 14 to postnatal day 10. Male pups were treated daily with the oil vehicle only (MC). Partner preferences, sexual conduct and the expression of estrogen receptors α (ERα) and β (ERβ) were examined when animals were 3 months old. FT and MC groups showed female-directed partner preferences and masculinized behavior. ERα- immunoreactive neurons (ERα-IRs) in the bed nucleus of stria terminalis (BNST) and medial amygdaloid nucleus (MeA) was greater in FT females than MC males, and there was no significant difference in the number of ERα-IRs between FT and FC females. No difference was found for ERα-IRs in the preoptic area (mPOA) or ventromedial nucleus of the hypothalamus (VMH) of FT females or MC males, and they were significantly fewer than in FC females. ERβ-immunoreactive neurons (ERβ-IRs) in these four brain regions did not alter the ERβ/ERα ratio in different brain regions during perintal developments. However, the number of ERβ-IRs in FT females and MC males were greater than in FC females. We propose that estradiol treatment during perinatal development is responsible for adult partner preferences and mating behavior.

Postnatal genistein administration selectively abolishes sexual dimorphism in specific hypothalamic dopaminergic system in mice

As demonstrated in previous studies, early postnatal genistein (GEN) administration to mice pups of both sexes, at doses similar to that of infant soy-based formulas, may affect the development of some steroid-sensitive neuronal circuits (i.e. nitrergic and vasopressinergic systems), causing irreversible alterations in adults. Here, we investigated the hypothalamic and mesencephalic dopaminergic system (identified with tyrosine hydroxylase immunohistochemistry). GEN administration (50 mg/kg) to mice of both sexes during the first week of postnatal life specifically affected tyrosine hydroxylase immunohistochemistry in the hypothalamic subpopulation of neurons, abolishing their sexual dimorphism. On the contrary, we did not observe any effects in the mesencephalic groups. Due to the large involvement of dopamine in circuits controlling rodent sexual behavior and food intake, these results clearly indicate that the early postnatal administration of GEN may irreversibly alter the control of reproduction, of energetic metabolism, and other behaviors. These results suggest the need for a careful evaluation of the use of soy products in both human and animal newborns.

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.

Effects of neonatal treatment with two phytoestrogens on male rat sexual behavior and partner preference

The aim of this work was to compare the effect of neonatal treatment with the phytoestrogens coumestrol (COU) and genistein (GEN), administered in equimolecular doses, on the sexual behavior and partner preference of male rats. Four groups of male rats were injected daily from day 1 to 5 with 150 µg of GEN, an equivalent amount of COU, 1 µg of β-estradiol 3-benzoato (EB), or olive oil (VEH) (control). A fifth group remained intact. In the GEN group, intromission and ejaculation latencies decreased, whereas ejaculatory frequency increased. Contrasting results were observed in COU males. EB males could not ejaculate and their mount and intromission latencies increased significantly. To determine sexual-partner preferences, a multiple partner preference arena was used and two types of tests were performed, the first one without allowing contact test (CT) with the stimulus animals, followed by a CT. COU and GEN groups did not show preference for any stimulus animal, whereas the EB males preferred the expert male. When CT with the stimulus animals was allowed, GEN-males preferred the receptive female, unlike the COU and EB groups. It is concluded that neonatal treatment with COU and GEN induced opposite effects, the effects of COU being more estrogenic.

Interaction of bisphenol A (BPA) and soy phytoestrogens on sexually dimorphic sociosexual behaviors in male and female rats

Concerns have been raised regarding the potential for endocrine disrupting compounds (EDCs) to alter brain development and behavior. Developmental exposure to bisphenol A (BPA), a ubiquitous EDC, has been linked to altered sociosexual and mood-related behaviors in various animal models and children but effects are inconsistent across laboratories and animal models creating confusion about potential risk in humans. Exposure to endocrine active diets, such as soy, which is rich in phytoestrogens, may contribute to this variability. Here, we tested the individual and combined effects of low dose oral BPA and soy diet or the individual isoflavone genistein (GEN; administered as the aglycone genistin (GIN)) on rat sociosexual behaviors with the hypothesis that soy would obfuscate any BPA-related effects. Social and activity levels were unchanged by developmental exposure to BPA but soy diet had sex specific effects including suppressed novelty preference, and open field exploration in females. The data presented here reinforce that environmental factors, including anthropogenic chemical exposure and hormone active diets, can shape complex behaviors and even reverse expected sex differences.

CYP7B1 Enzyme Deletion Impairs Reproductive Behaviors in Male Mice

In addition to androgenic properties mediated via androgen receptors, dihydrotestosterone (DHT) also regulates estrogenic functions via an alternate pathway. These estrogenic functions of DHT are mediated by its metabolite 5α-androstane-3β, 17β-diol (3β-diol) binding to estrogen receptor β (ERβ). CYP7B1 enzyme converts 3β-diol to inactive 6α- or 7α-triols and plays an important role as a regulator of estrogenic functions mediated by 3β-diol. Using a mutant mouse carrying a null mutation for the CYP7B1 gene (CYP7B1KO), we examined the contribution of CYP7B1 on physiology and behavior. Male, gonadectomized (GDX) CYP7B1KO and their wild type (WT) littermates were assessed for their behavioral phenotype, anxiety-related behavioral measures, and hypothalamic pituitary adrenal axis reactivity. No significant effects of genotype were evident in anxiety-like behaviors in open field (OFA), light-dark (L/D) exploration, and elevated plus maze (EPM). T significantly reduced open arm time on the EPM while not affecting L/D exploratory and OFA behaviors in CYP7B1KO and WT littermates. T also attenuated the corticosterone response to EPM in both genotypes. In GDX animals, T was able to reinstate male-specific reproductive behaviors (latencies and number of mounts, intromission, and ejaculations) in the WT but not in the CYP7B1KO mice. The male reproductive behavior defect in CYP7B1KO seems to be due to their inability to distinguish olfactory cues from a behavioral estrus female. CYP7B1KO mice also showed a reduction in androgen receptor mRNA expression in the olfactory bulb. Our findings suggest a novel role for the CYP7B1 enzyme in the regulation of male reproductive behaviors.

Estrogen receptors alpha (ERα) and beta (ERβ): subtype-selective ligands and clinical potential

Estrogen receptors alpha (ERα) and beta (ERβ) are nuclear transcription factors that are involved in the regulation of many complex physiological processes in humans. Modulation of these receptors by prospective therapeutic agents is currently being considered for prevention and treatment of a wide variety of pathological conditions, such as, cancer, metabolic and cardiovascular diseases, neurodegeneration, inflammation, and osteoporosis. This review provides an overview and update of compounds that have been recently reported as modulators of ERs, with a particular focus on their potential clinical applications.

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

Impacts on brain and behavior have been reported in laboratory rodents after developmental exposure to bisphenol A (BPA), raising concerns about possible human effects. Epidemiological data suggest links between prenatal BPA exposure and altered affective behaviors in children, but potential mechanisms are unclear. Disruption of mesolimbic oxytocin (OT)/vasopressin (AVP) pathways have been proposed, but supporting evidence is minimal. To address these data gaps, we employed a novel animal model for neuroendocrine toxicology: the prairie vole (Microtus ochrogaster), which are more prosocial than lab rats or mice. Male and female prairie vole pups were orally exposed to 5-μg/kg body weight (bw)/d, 50-μg/kg bw/d, or 50-mg/kg bw/d BPA or vehicle over postnatal days 8-14. Subjects were tested as juveniles in open field and novel social tests and for partner preference as adults. Brains were then collected and assessed for immunoreactive (ir) tyrosine hydroxylase (TH) (a dopamine marker) neurons in the principal bed nucleus of the stria terminalis (pBNST) and TH-ir, OT-ir, and AVP-ir neurons in the paraventricular nucleus of the hypothalamus (PVN). Female open field activity indicated hyperactivity at the lowest dose and anxiety at the highest dose. Effects on social interactions were also observed, and partner preference formation was mildly inhibited at all dose levels. BPA masculinized principal bed nucleus of the stria terminalis TH-ir neuron numbers in females. Additionally, 50-mg/kg bw BPA-exposed females had more AVP-ir neurons in the anterior PVN and fewer OT-ir neurons in the posterior PVN. At the 2 lowest doses, BPA eliminated sex differences in PVN TH-ir neuron numbers and reversed this sex difference at the highest dose. Minimal behavioral effects were observed in BPA-exposed males. These data support the hypothesis that BPA alters affective behaviors, potentially via disruption of OT/AVP pathways.

Soy but not bisphenol A (BPA) induces hallmarks of polycystic ovary syndrome (PCOS) and related metabolic co-morbidities in rats

Polycystic ovarian syndrome (PCOS) is the most common female endocrine disorder with a prevalence as high as 8-15% depending on ethnicity and the diagnostic criteria employed. The basic pathophysiology and mode of inheritance remain unclear, but environmental factors such as diet, stress and chemical exposures are thought to be contributory. Developmental exposure to endocrine disrupting compounds (EDCs) have been hypothesized to exacerbate risk, in part because PCOS hallmarks and associated metabolic co-morbidities can be reliably induced in animal models by perinatal androgen exposure. Here we show that lifetime exposure to a soy diet, containing endocrine active phytoestrogens, but not developmental exposure (gestational day 6-lactational day 40) to the endocrine disrupting monomer bisphenol A (BPA), can induce key features of PCOS in the rat; results which support the hypothesis that hormonally active diets may contribute to risk when consumed throughout gestation and post-natal life.

Estrogen receptor β expression in the mouse forebrain: age and sex differences

Estrogen receptors regulate multiple brain functions, including stress, sexual, and memory-associated behaviors as well as controlling neuroendocrine and autonomic function. During development, estrogen signaling is involved in programming adult sex differences in physiology and behavior. Expression of estrogen receptor α changes across development in a region-specific fashion. By contrast, estrogen receptor β (ERβ) is expressed in many brain regions, yet few studies have explored sex and developmental differences in its expression, largely because of the absence of selective reagents for anatomical localization of the protein. This study utilized bacterial artificial chromosome transgenic mice expressing ERβ identified by enhanced green fluorescent protein (EGFP) to compare expression levels and distribution of ERβ in the male and female mouse forebrain on the day of birth (P0), on postnatal day 4 (P4), and on P21. By using qualitative analysis, we mapped the distribution of ERβ-EGFP and found developmental alterations in ERβ expression within the cortex, hippocampus, and hypothalamic regions including the arcuate, ventromedial, and paraventricular nuclei. We also report a sex difference in ERβ in the bed nucleus of the stria terminalis, with males showing greater expression at P4 and P21. Another sex difference was found in the anteroventral periventricular nucleus of P21, but not P0 or P4, mice, in which ERβ-EGFP-immunoreactive cells were densely clustered near the third ventricle in females but not males. These developmental changes and sex differences in ERβ indicate a mechanism through which estrogens might differentially affect brain functions or program adult physiology at select times during development.

Perinatal exposure to genistein affects the normal development of anxiety and aggressive behaviors and nitric oxide system in CD1 male mice

Genistein is a phytoestrogen, particularly abundant in soybeans, that is able to bind estrogen receptors exerting both estrogenic and antiestrogenic activities. Genistein is largely present in the human diet even during pregnancy. Embryos and fetuses are therefore, commonly exposed to genistein during the development and after birth. In the present study, we used a murine model as a test end-point to investigate the effects of early exposure to genistein on adult male behavior and related neural circuits. Daily exposure of dams to genistein (100 μg/g of body weight) during late pregnancy and early lactation, produced in male offspring, when adults, significant changes in anxiety and aggressive behaviors. Moreover, we found statistically significant variations in the number of neuronal nitric-oxide synthase positive cells in the amygdala. In conclusions, these data indicate that early exposure to phytoestrogens may induce life-long effects on the differentiation of brain structures and behaviors.

Perinatal exposure to genistein, a soy phytoestrogen, improves spatial learning and memory but impairs passive avoidance learning and memory in offspring

This study investigated the effects of perinatal genistein (GEN) exposure on the central nervous system of rat offspring. Pregnant dams orally received GEN (1 or 10 mg/kg/day) or vehicle (1 ml/kg/day) from gestation day 10 to postnatal day 14. In order to assess the effects of GEN on rat offspring, we used a battery of behavioral tests, including the open-field, elevated plus-maze, MAZE and step-through passive avoidance tests. MAZE test is an appetite-motivation test, and we used this mainly for assessing spatial learning and memory. In the MAZE test, GEN groups exhibited shorter latency from start to goal than the vehicle-treated group in both sexes. On the other hand, performances in the step-through passive avoidance test were non-monotonically inhibited by GEN in both sexes, and a significant difference was observed in low dose of the GEN-treated group compared to the vehicle-treated group in female rats. Furthermore, we found that perinatal exposure to GEN did not significantly alter locomotor activity or emotionality as assessed by the open-field and elevated-plus maze tests. These results suggest that perinatal exposure to GEN improved spatial learning and memory of rat offspring, but impaired their passive avoidance learning and memory.

Sex-specific Esr2 mRNA expression in the rat hypothalamus and amygdala is altered by neonatal bisphenol A exposure

Perinatal life is a critical window for sexually dimorphic brain organization, and profoundly influenced by steroid hormones. Exposure to endocrine-disrupting compounds may disrupt this process, resulting in compromised reproductive physiology and behavior. To test the hypothesis that neonatal bisphenol A (BPA) exposure can alter sex-specific postnatal Esr2 (Erβ) expression in brain regions fundamental to sociosexual behavior, we mapped Esr2 mRNA levels in the principal nucleus of the bed nucleus of the stria terminalis (BNSTp), paraventricular nucleus (PVN), anterior portion of the medial amygdaloid nucleus (MeA), super optic nucleus, suprachiasmatic nucleus, and lateral habenula across postnatal days (PNDs) 0-19. Next, rat pups of both sexes were subcutaneously injected with 10 μg estradiol benzoate (EB), 50 μg/kg BPA (LBPA), or 50 mg/kg BPA (HBPA) over the first 3 days of life and Esr2 levels were quantified in each region of interest (ROI) on PNDs 4 and 10. EB exposure decreased Esr2 signal in most female ROIs and in the male PVN. In the BNSTp, Esr2 expression decreased in LBPA males and HBPA females on PND 10, thereby reversing the sex difference in expression. In the PVN, Esr2 mRNA levels were elevated in LBPA females, also resulting in a reversal of sexually dimorphic expression. In the MeA, BPA decreased Esr2 expression on PND 4. Collectively, these data demonstrate that region- and sex-specific Esr2 expression is vulnerable to neonatal BPA exposure in regions of the developing brain critical to sociosexual behavior in rat.

Anxiogenic effects of developmental bisphenol A exposure are associated with gene expression changes in the juvenile rat amygdala and mitigated by soy

Early life exposure to Bisphenol A (BPA), a component of polycarbonate plastics and epoxy resins, alters sociosexual behavior in numerous species including humans. The present study focused on the ontogeny of these behavioral effects beginning in adolescence and assessed the underlying molecular changes in the amygdala. We also explored the mitigating potential of a soy-rich diet on these endpoints. Wistar rats were exposed to BPA via drinking water (1 mg/L) from gestation through puberty, and reared on a soy-based or soy-free diet. A group exposed to ethinyl estradiol (50 µg/L) and a soy-free diet was used as a positive estrogenic control. Animals were tested as juveniles or adults for anxiety-like and exploratory behavior. Assessment of serum BPA and genistein (GEN), a soy phytoestrogen, confirmed that internal dose was within a human-relevant range. BPA induced anxiogenic behavior in juveniles and loss of sexual dimorphisms in adult exploratory behavior, but only in the animals reared on the soy-free diet. Expression analysis revealed a suite of genes, including a subset known to mediate sociosexual behavior, associated with BPA-induced juvenile anxiety. Notably, expression of estrogen receptor beta (Esr2) and two melanocortin receptors (Mc3r, Mc4r) were downregulated. Collectively, these results show that behavioral impacts of BPA can manifest during adolescence, but wane in adulthood, and may be mitigated by diet. These data also reveal that, because ERβ and melanocortin receptors are crucial to their function, oxytocin/vasopressin signaling pathways, which have previously been linked to human affective disorders, may underlie these behavioral outcomes.

Reproductive consequences of developmental phytoestrogen exposure

Phytoestrogens, estrogenic compounds derived from plants, are ubiquitous in human and animal diets. These chemicals are generally much less potent than estradiol but act via similar mechanisms. The most common source of phytoestrogen exposure to humans is soybean-derived foods that are rich in the isoflavones genistein and daidzein. These isoflavones are also found at relatively high levels in soy-based infant formulas. Phytoestrogens have been promoted as healthy alternatives to synthetic estrogens and are found in many dietary supplements. The aim of this review is to examine the evidence that phytoestrogen exposure, particularly in the developmentally sensitive periods of life, has consequences for future reproductive health.