PFOS induces behavioral alterations, including spontaneous hyperactivity that is corrected by dexamfetamine in zebrafish larvae

Comparative behavioral toxicology with two common larval fish models: Exploring relationships among modes of action and locomotor responses

Behavioral responses inform toxicology studies by rapidly and sensitively detecting molecular initiation events that propagate to physiological changes in individuals. These behavioral responses can be unique to chemical specific mechanisms and modes of action (MOA) and thus present diagnostic utility. In an initial effort to explore the use of larval fish behavioral response patterns in screening environmental contaminants for toxicity and to identify behavioral responses associated with common chemical specific MOAs, we employed the two most common fish models, the zebrafish and the fathead minnow, to define toxicant induced swimming activity alterations during interchanging photoperiods. Though the fathead minnow (Pimephales promelas) is a common model for aquatic toxicology research and regulatory toxicology practice, this model has received little attention in behavioral studies compared to the zebrafish, a common biomedical model. We specifically compared behavioral responses among 7 different chemicals (1-heptanol, phenol, R-(-)-carvone, citalopram, diazinon, pentylenetetrazole (PTZ), and xylazine) that were selected and classified based on anticipated MOA (nonpolar narcosis, polar narcosis, electrophile, specific mechanism) according to traditional approaches to examine whether these comparative responses differ among chemicals with various structure-based predicted toxicity. Following standardized experimental guidelines, zebrafish embryos and fathead minnow larvae were exposed for 96 h to each compound then were observed using digital behavioral analysis. Behavioral observations included photomotor responses, distance traveled, and stimulatory, refractory and cruising locomotor activity. Though fathead minnow larvae displayed greater behavioral sensitivity to 1-heptanol, phenol and citalopram, zebrafish were more sensitive to diazinon and R-(-)-carvone. Both fish models were equally sensitive to xylazine and PTZ. Further, the pharmaceuticals citalopram and xylazine significantly affected behavior at therapeutic hazard values, and each of the seven chemicals elicited unique behavioral response profiles. Larval fish behaviors appear useful as early tier diagnostics to identify mechanisms and pathways associated with diverse biological activities for chemicals lacking mechanistic data.

Methylmercury interferes with glucocorticoid receptor: Potential role in the mediation of developmental neurotoxicity

Methylmercury (MeHg) is a widespread environmental contaminant with established developmental neurotoxic effects. Computational models have identified glucocorticoid receptor (GR) signaling to be a key mediator behind the birth defects induced by Hg, but the mechanisms were not elucidated. Using molecular dynamics simulations, we found that MeHg can bind to the GR protein at Cys736 (located close to the ligand binding site) and distort the conformation of the ligand binging site. To assess the functional consequences of MeHg interaction with GR, we used a human cell line expressing a luciferase reporter system (HeLa AZ-GR). We found that 100 nM MeHg does not have any significant effect on GR activity alone, but the transactivation of gene expression by GR upon Dex (a synthetic GR agonist) administration was reduced in cells pre-treated with MeHg. Similar effects were found in transgenic zebrafish larvae expressing a GR reporter system (SR4G). Next we asked whether the effects of developmental exposure to MeHg are mediated by the effects on GR. Using a mutant zebrafish line carrying a loss-of-function mutation in the GR (gr^S357) we could show that the effects of developmental exposure to 2.5 nM MeHg are mitigated in absence of functional GR signaling. Taken together, our data indicate that inhibition of GR signaling may have a role in the developmental neurotoxic effects of MeHg.

Thyroid disrupting effects of halogenated and next generation chemicals on the swim bladder development of zebrafish

Endocrine disrupting chemicals (EDCs) can alter thyroid function and adversely affect growth and development. Halogenated compounds, such as perfluorinated chemicals commonly used in food packaging, and brominated flame retardants used in a broad range of products from clothing to electronics, can act as thyroid disruptors. Due to the adverse effects of these compounds, there is a need for the development of safer next generation chemicals. The objective of this study was to test the thyroid disruption potential of old use and next generation halogenated chemicals. Zebrafish embryos were exposed to three old use compounds, perfluorooctanoic acid (PFOA), tetrabromobisphenol A (TBBPA) and tris (1,3-dichloro-2-propyl) phosphate (TDCPP) and two next generation chemicals, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxdie (DOPO) and perfluorobutyric acid (PFBA). Sub-chronic (0-6days post fertilization (dpf)) and chronic (0-28dpf) exposures were conducted at 1% of the concentration known to kill 50% (LC₅₀) of the population. Changes in the surface area of the swim bladder as well as in expression levels of genes involved in the thyroid control of swim bladder inflation were measured. At 6dpf, zebrafish exposed to all halogenated chemicals, both old use and next generation, had smaller posterior swim bladder and increased expression in the gene encoding thyroid peroxidase, tpo and the genes encoding two swim bladder surfactant proteins, sp-a and sp-c. These results mirrored the effects of thyroid hormone-exposed positive controls. Fish exposed to a TPO inhibitor (methimazole, MMI) had a decrease in tpo expression levels at 28dpf. Effects on the anterior swim bladder at 28dpf, after exposure to MMI as well as both old and new halogenated chemicals, were the same, i.e., absence of SB in ∼50% of fish, which were also of smaller body size. Overall, our results suggest thyroid disruption by the halogenated compounds tested via the swim bladder surfactant system. However, with the exception of TBBPA and TDCPP, the concentrations tested (∼5-137ppm) are not likely to be found in the environment.

Exposure to Perfluorinated Alkyl Substances and Health Outcomes in Children: A Systematic Review of the Epidemiologic Literature

Perfluoroalkyl substances (PFAS), chemicals used to make products stain and stick resistant, have been linked to health effects in adults and adverse birth outcomes. A growing body of literature also addresses health effects in children exposed to PFAS. This review summarizes the epidemiologic evidence for relationships between prenatal and/or childhood exposure to PFAS and health outcomes in children as well as to provide a risk of bias analysis of the literature. A systematic review was performed by searching PubMed for studies on PFAS and child health outcomes. We identified 64 studies for inclusion and performed risk of bias analysis on those studies. We determined that risk of bias across studies was low to moderate. Six categories of health outcomes emerged. These were: immunity/infection/asthma, cardio-metabolic, neurodevelopmental/attention, thyroid, renal, and puberty onset. While there are a limited number of studies for any one particular health outcome, there is evidence for positive associations between PFAS and dyslipidemia, immunity (including vaccine response and asthma), renal function, and age at menarche. One finding of note is that while PFASs are mixtures of multiple compounds few studies examine them as such, therefore the role of these compounds as complex mixtures remains largely unknown.

An optimized method to assess ototoxic effects in the lateral line of zebrafish (Danio rerio) embryos

In order to clarify the suitability of the lateral line of zebrafish (Danio rerio) embryos as a model for the screening of ototoxic (neurotoxic) effects, existing neuromast assays were adapted, improved and validated with a series of chemicals known or unknown for their ototoxic potential (caffeine copper sulfate, dichlorvos, 2.4-dinitrotoluene, neomycin, 4-nonylphenol, perfluorooctanesulfonic acid). Present methods were improved by (1) the introduction of a 4-step scoring system, (2) the selection of neuromasts from both the anterior and posterior lateral line systems, (3) a combined DASPEI/DAPI staining applied after both a continuous and pulse exposure scenario, and (4) an additional screening for nuclear fragmentation. Acute toxicities of the model substances were determined by means of the fish embryo test as specified in OECD TG 236, and EC₁₀ concentrations were used as the highest test concentration in the neuromast assay. The enhanced neuromast assay identified known ototoxic substances such as neomycin and copper sulfate as ototoxic at sensitivities similar to those of established methods, with pulse exposure leading to stronger effects than continuous exposure. Except for caffeine, all substances tested (dichlorvos, 2.4-dinitrotoluene, 4-nonylphenol, perfluorooctanesulfonic acid) produced significant toxic effects in neuromasts at EC₁₀ concentrations. Depending on the test substances and their location along the lateral line, specific neuromasts differed in sensitivity. Generally, neuromasts proved more sensitive in the pulse exposure scenario. Whereas for neomycin and copper sulfate neuromasts located along the anterior lateral line were more sensitive, posterior lateral line neuromasts proved more sensitive for the other test substances. Nuclear fragmentation could not only be associated with all test substances, but, albeit at lower frequencies, also with negative controls, and could, therefore, not be assigned specifically to chemical damage. The study thus documented that for a comprehensive evaluation of lateral line damage both neuromasts from the anterior and the posterior lateral line have to be considered. Given the apparently rapid regeneration of hair cells, pulse exposure seems more appropriate for the identification of lateral line neurotoxicity than continuous exposure.

A Mixture of Persistent Organic Pollutants and Perfluorooctanesulfonic Acid Induces Similar Behavioural Responses, but Different Gene Expression Profiles in Zebrafish Larvae

Persistent organic pollutants (POPs) are widespread in the environment and some may be neurotoxic. As we are exposed to complex mixtures of POPs, we aimed to investigate how a POP mixture based on Scandinavian human blood data affects behaviour and neurodevelopment during early life in zebrafish. Embryos/larvae were exposed to a series of sub-lethal doses and behaviour was examined at 96 h post fertilization (hpf). In order to determine the sensitivity window to the POP mixture, exposure models of 6 to 48 and 48 to 96 hpf were used. The expression of genes related to neurological development was also assessed. Results indicate that the POP mixture increases the swimming speed of larval zebrafish following exposure between 48 to 96 hpf. This behavioural effect was associated with the perfluorinated compounds, and more specifically with perfluorooctanesulfonic acid (PFOS). The expression of genes related to the stress response, GABAergic, dopaminergic, histaminergic, serotoninergic, cholinergic systems and neuronal maintenance, were altered. However, there was little overlap in those genes that were significantly altered by the POP mixture and PFOS. Our findings show that the POP mixture and PFOS can have a similar effect on behaviour, yet alter the expression of genes relevant to neurological development differently.

Developmental toxicity of the common UV filter, benophenone-2, in zebrafish embryos

Benozophenone (BP) type UV filters are extensively used in the personal care products to provide protection against the harmful effects of UV radiation. BPs are one of the primary components in the UV filter family, in which benophenone-2 (BP2) is widely used as a UV filter reagent in the sunscreen. Humans used these personal care products directly on skin and the chemicals will be washed away to the water system. BP2 has been identified as one of the endocrine disruptor chemicals, which can inference the synthesis, metabolism, and action of endogenous hormones. Environmentally, it has been found to contaminate water worldwide. In this study, we aimed to unfold the possible developmental toxicology of this chemical. Zebrafish are used as the screening model to perform in situ hybridization staining to investigate the effects of BP2 on segmentation, brain regionalization, and facial formation at four developmental stages (10-12 somite, prim-5, 2 and 5 days post-fertilization). Results showed 40 μM (9.85 mg L^-1) or above BP2 exposure in zebrafish embryos for 5 days resulted in lipid accumulation in the yolk sac and facial malformation via affecting the lipid processing and the expression of cranial neural crest cells respectively. To conclude, the study alarmed its potential developmental toxicities at high dosage exposure.

Behavioral, morphometric, and gene expression effects in adult zebrafish (Danio rerio) embryonically exposed to PFOA, PFOS, and PFNA

Perfluoroalkylated substances (PFAS) are a class of persistent anthropogenic chemicals that have been detected worldwide. PFASs consist of fluorinated carbon chains of varying length, terminal groups, and have a number of industrial uses. A previous zebrafish study from our laboratory showed that acute (3-120h post fertilization, 0.02-2.0μM), waterborne embryonic exposure to these chemicals resulted in chemical specific alterations at 5days post fertilization (dpf), and some effects persisted up to 14 dpf. Using a gene battery consisting of 100 transcripts identified several genes that were up or down regulated. This current study looks at the long-term impacts of PFASs in adult zebrafish using the same exposure regimen. It was hypothesized that sub-lethal exposure of perfluorooctane sulfonate (PFOS), perfluorononanoic acid (PFNA), or perfluorooctane sulfonate (PFOA) in embryonic zebrafish (3-120 hpf) would result in permanent morphometric, gene expression, and behavioral changes in adult fish similar to those observed at 5 and 14 dpf. Zebrafish were exposed to PFOS, PFOA, and PFNA (Control 0μM, 2.0μM) for the first five days post fertilization. At six months post fertilization, no PFAS treatment resulted in a significant change in total body length or weight. In terms of behavior, PFNA males showed a reduction in total distance traveled and time of immobility, and an increase in thigmotaxis behavior, aggressive attacks, and preference for the bright section of the tank. PFOS treated males had a reduced aggression behavior, and PFOA females preferred the dark section of the tank. Gene expression of slco2b1, slco1d1, and tgfb1a were analyzed because these transcripts were previously found to be affected by PFAS exposure in 5dpf and 14 dpf zebrafish and resulted in: significant decrease in expression of slco2b1 for both sexes in PFNA and PFOS treated groups, significant decrease of slco1d1 in all treatment groups for females and PFOS and PFOA exposed males, significant increase of tgfb1a in males treated with PFOS and PFNA, and a significant increase of bdnf in all PFAS male groups. This study demonstrates that acute, embryonic exposure (5days) to individual PFASs result in significant biochemical and behavioral changes in young adult zebrafish 6 months after exposure. These three PFASs have long term and persistent impacts following short term embryonic exposure that persists into adulthood.

PFOS, PFNA, and PFOA sub-lethal exposure to embryonic zebrafish have different toxicity profiles in terms of morphometrics, behavior and gene expression

Polyfluorinated compounds (PFC) are a class of anthropogenic, persistent and toxic chemicals. PFCs are detected worldwide and consist of fluorinated carbon chains of varying length, terminal groups, and industrial uses. Previous zebrafish studies in the literature as well as our own studies have shown that exposure to these chemicals at a low range of concentrations (0.02-2.0μM; 20-2000ppb) resulted in chemical specific developmental defects and reduced post hatch survival. It was hypothesized that sub-lethal embryonic exposure to perfluorooctanesulfonic acid (PFOS), perfluorononanoic acid (PFNA), or perfluorooctanoic acid (PFOA) would result in different responses with regard to morphometric, behavior, and gene expression in both yolk sac fry and larval zebrafish. Zebrafish were exposed to PFOS, PFOA, and PFNA (0.02, 0.2, 2.0μM) for the first five days post fertilization (dpf) and analyzed for morphometrics (5 dpf, 14 dpf), targeted gene expression (5 dpf, 14 dpf), and locomotive behavior (14 dpf). All three PFCs commonly resulted in a decrease in total body length, increased tfc3a (muscle development) expression and decreased ap1s (protein transport) expression at 5dpf, and hyperactive locomotor activity 14 dpf. All other endpoints measured at both life-stage time points varied between each of the PFCs. PFOS, PFNA, and PFOA exposure resulted in significantly altered responses in terms of morphometric, locomotion, and gene expression endpoints, which could be manifested in field exposed teleosts.

Long-term consequences of prenatal stress and neurotoxicants exposure on neurodevelopment

There is a large consensus that the prenatal environment determines the susceptibility to pathological conditions later in life. The hypothesis most widely accepted is that exposure to insults inducing adverse conditions in-utero may have negative effects on the development of target organs, disrupting homeostasis and increasing the risk of diseases at adulthood. Several models have been proposed to investigate the fetal origins of adult diseases, but although these approaches hold true for almost all diseases, particular attention has been focused on disorders related to the central nervous system, since the brain is particularly sensitive to alterations of the microenvironment during early development. Neurobiological disorders can be broadly divided into developmental, neurodegenerative and neuropsychiatric disorders. Even though most of these diseases share genetic risk factors, the onset of the disorders cannot be explained solely by inheritance. Therefore, current understanding presumes that the interactions of environmental input, may lead to different disorders. Among the insults that can play a direct or indirect role in the development of neurobiological disorders are stress, infections, drug abuse, and environmental contaminants. Our laboratories have been involved in the study of the neurobiological impact of gestational stress on the offspring (Dr. Antonelli's lab) and on the effect of gestational exposure to toxicants, mainly methyl mercury (MeHg) and perfluorinated compounds (PFCs) (Dr. Ceccatelli's lab). In this focused review, we will review the specialized literature but we will concentrate mostly on our own work on the long term neurodevelopmental consequences of gestational exposure to stress and neurotoxicants.

Automated, high-throughput, in vivo analysis of visual function using the zebrafish

BACKGROUND

Modern genomics has enabled the identification of an unprecedented number of genetic variants, which in many cases are extremely rare, associated with blinding disorders. A significant challenge will be determining the pathophysiology of each new variant. The Zebrafish is an excellent model for the study of inherited diseases of the eye. By 5 days post-fertilization (dpf), they have quantifiable behavioral responses to visual stimuli. However, visual behavior assays can take several hours to perform or can only be assessed one fish at a time.

RESULTS

To increase the throughput for vision assays, we used the Viewpoint Zebrabox to automate the visual startle response and created software, Visual Interrogation of Zebrafish Manipulations (VIZN), to automate data analysis. This process allows 96 Zebrafish larvae to be tested and resultant data to be analyzed in less than 35 minutes. We validated this system by disrupting function of a gene necessary for photoreceptor differentiation and observing decreased response to visual stimuli.

CONCLUSIONS

This automated method along with VIZN allows rapid, high-throughput, in vivo testing of Zebrafish's ability to respond to light/dark stimuli. This allows the rapid analysis of novel genes involved in visual function by morpholino, CRISPRS, or small-molecule drug screens. Developmental Dynamics 245:605-613, 2016. © 2016 Wiley Periodicals, Inc.

Comparability of behavioural assays using zebrafish larvae to assess neurotoxicity

Testing of compounds for neurotoxicity has become increasingly important in recent years. It has been shown that neurological disorders like autism may be related to chemical exposures, which may play a crucial role in the progression of these diseases. Special attention has been be given to the substances causing developmental neurotoxicity as the developing nervous system is more vulnerable to impacts by chemicals than the adult nervous system. The zebrafish (Danio rerio) is a well-established model species in developmental biology and an emerging model in behavioural and neurological studies. Zebrafish larvae display numerous behavioural patterns highly similar to rodents and humans. Their physical characteristics make them well suited for automated high-throughput screening. In the last years, the number of behavioural studies conducted with zebrafish larvae has increased notably. The goal of this review is to provide an overview of behavioural assays commonly used to test substances for developmental neurotoxicity. Literature from 1995 to 2014 was reviewed and focussed on assays performed with zebrafish larvae younger than 7 days post fertilization (dpf). The behavioural tests were scrutinized, and parameters describing the different experimental setups were defined. In the next step, we investigated if differences in the experimental parameters alter the outcome of the test. In order to test the comparability of behavioural assays, we analysed several studies using ethanol, valproate and pentylenetetrazole as model substances. Based on our findings, we provide recommendations which could help improve future behavioural studies performed with zebrafish larvae.

Behavior, metabolism and swimming physiology in juvenile Spinibarbus sinensis exposed to PFOS under different temperatures

The harmful effects of perfluorooctane sulfonate (PFOS) are of growing international concern. This paper aimed to gain an integrated understanding of fitness-related ecological end points, such as behavior, metabolism and swimming physiology, in juvenile Spinibarbus sinensis in response to PFOS toxicity at different temperatures. The fish were exposed to a range of PFOS concentrations (0, 0.32, 0.8, 2 and 5 mg/L) at different temperatures (18 and 28 °C) for 30 days. The effects on fish behavior, metabolic characteristics and aerobic swimming performance caused by PFOS at different temperatures were investigated. Our results showed that both PFOS and temperature had important influences on spontaneous swimming behavior, social interactions, routine metabolic rate (RMR), net energetic cost of transport (COTnet) and critical swimming speed (U crit) in fish. The lowest observed effect concentration for both U crit and RMR was 5 and 0.8 mg/L at 18 and 28 °C, respectively. We found that PFOS affected various behavioral and social end points and also appeared to affect metabolic rates and reduced U crit, likely as a result of increased COTnet, and that many of these effects also changed with respect to temperature. Our results further the understanding of the metabolic and behavioral toxicity of PFOS to aquatic organisms.

Alterations in circadian entrainment precede the onset of depression-like behavior that does not respond to fluoxetine

Growing evidence links adverse prenatal conditions to mood disorders. We investigated the long-term behavioral alterations induced by prenatal exposure to excess glucocorticoids (dexamethasone--DEX). At 12 months, but not earlier, DEX-exposed mice displayed depression-like behavior and impaired hippocampal neurogenesis, not reversible by the antidepressant fluoxetine (FLX). Concomitantly, we observed arrhythmic glucocorticoid secretion and absent circadian oscillations in hippocampal clock gene expression. Analysis of spontaneous activity showed progressive alterations in circadian entrainment preceding depression. Circadian oscillations in clock gene expression (measured by means of quantitative PCR) were also attenuated in skin fibroblasts before the appearance of depression. Interestingly, circadian entrainment is not altered in a model of depression (induced by methylmercury prenatal exposure) that responds to FLX. Altogether, our results suggest that alterations in circadian entrainment of spontaneous activity, and possibly clock gene expression in fibroblasts, may predict the onset of depression and the response to FLX in patients.

Tissue uptake, distribution and elimination of (14)C-PFOA in zebrafish (Danio rerio)

Perfluorooctanoic acid (PFOA) is a long-chain perfluorinated chemical that has been shown to be non-degradable and persistent in the environment. Laboratory studies on bioconcentration and compound-specific tissue distribution in fish can be valuable for prediction of the persistence and environmental effects of the chemicals. In the present study male and female zebrafish (Danio rerio) were continuously exposed to 10μg/L of radiolabeled perfluorooctanoic acid ((14)C-PFOA) for 40 days, after which the exposed fish were transferred to fresh clean water for another 80 days wash-out period. At defined periodic intervals during the uptake and wash-out, fish were sampled for liquid scintillation counting and whole body autoradiography to profile the bioconcentration and tissue distribution of PFOA. The steady-state concentration of (14)C-PFOA in the zebrafish was reached within 20-30 days of exposure. The concentration-time course of (14)C-PFOA displayed a bi-exponential decline during washout, with a terminal half-life of approximately 13-14 days. At steady-state the bioconcentration of (14)C-PFOA into whole-body fish was approximately 20-30 times greater than that of the exposure concentration, with no differences between females and males. The bioconcentration factors for liver and intestine were approximately 100-fold of the exposure medium, while in brain, ovary and gall bladder the accumulation factors were in the range 15-20. Whole-body autoradiograms confirmed the highest labeling of PFOA in bile and intestines, which implies enterohepatic circulation of PFOA. The (14)C-PFOA was also observed in maturing vitellogenic oocytes, suggesting chemical accumulation via yolk proteins into oocytes with plausible risk for adverse effects on early embryonic development and offspring health. The bioconcentration at several (14)C-PFOA exposure concentrations were also investigated (0.3-30μg/L). This showed that bioconcentration increased linearly with tank exposure in the present in vivo model under steady-state conditions. From this model tissue concentrations of PFOA can be predicted when the external exposure level is known. The present study has generated experimental data on PFOA kinetics in zebrafish that can be valuable for aquatic environmental risk assessment.

Molecular psychiatry of zebrafish

Due to their well-characterized neural development and high genetic homology to mammals, zebrafish (Danio rerio) have emerged as a powerful model organism in the field of biological psychiatry. Here, we discuss the molecular psychiatry of zebrafish, and its implications for translational neuroscience research and modeling central nervous system (CNS) disorders. In particular, we outline recent genetic and technological developments allowing for in vivo examinations, high-throughput screening and whole-brain analyses in larval and adult zebrafish. We also summarize the application of these molecular techniques to the understanding of neuropsychiatric disease, outlining the potential of zebrafish for modeling complex brain disorders, including attention-deficit/hyperactivity disorder (ADHD), aggression, post-traumatic stress and substance abuse. Critically evaluating the advantages and limitations of larval and adult fish tests, we suggest that zebrafish models become a rapidly emerging new field in modern molecular psychiatry research.

Sex-specific enhanced behavioral toxicity induced by maternal exposure to a mixture of low dose endocrine-disrupting chemicals

Humans are increasingly and consistently exposed to a variety of endocrine disrupting chemicals (EDCs), chemicals that have been linked to neurobehavioral disorders such as ADHD and autism. Many of such EDCs have been shown to adversely influence brain mesocorticolimbic systems raising the potential for cumulative toxicity. As such, understanding the effects of developmental exposure to mixtures of EDCs is critical to public health protection. Consequently, this study compared the effects of a mixture of four EDCs to their effects alone to examine potential for enhanced toxicity, using behavioral domains and paradigms known to be mediated by mesocorticolimbic circuits (fixed interval (FI) schedule controlled behavior, novel object recognition memory and locomotor activity) in offspring of pregnant mice that had been exposed to vehicle or relatively low doses of four EDCs, atrazine (ATR - 10mg/kg), perfluorooctanoic acid (PFOA - 0.1mg/kg), bisphenol-A (BPA - 50 μg/kg), 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD - 0.25 μg/kg) alone or combined in a mixture (MIX), from gestational day 7 until weaning. EDC-treated males maintained significantly higher horizontal activity levels across three testing sessions, indicative of delayed habituation, whereas no effects were found in females. Statistically significant effects of MIX were seen in males, but not females, in the form of increased FI response rates, in contrast to reductions in response rate with ATR, BPA and TCDD, and reduced short term memory in the novel object recognition paradigm. MIX also reversed the typically lower neophobia levels of males compared to females. With respect to individual EDCs, TCDD produced notable increases in FI response rates in females, and PFOA significantly increased ambulatory locomotor activity in males. Collectively, these findings show the potential for enhanced behavioral effects of EDC mixtures in males and underscore the need for animal studies to fully investigate mixtures, including chemicals that converge on common physiological substrates to examine potential mechanisms of toxicity with full dose effect curves to assist in interpretations of relevant mechanisms.