Effects of perinatal PCB exposure on discrimination-reversal learning in monkeys

Adipose Tissue Transcriptome Is Related to Pollutant Exposure in Polar Bear Mother-Cub Pairs from Svalbard, Norway

Being at the food chain apex, polar bears (Ursus maritimus) are highly contaminated with persistent organic pollutants (POPs). Females transfer POPs to their offspring through gestation and lactation; therefore, young cubs present higher POPs concentrations than their mothers. Recent studies suggest that POPs affect the lipid metabolism in female polar bears; however, the mechanisms and impact on their offspring remain unknown. Here, we hypothesized that exposure to POPs differentially alters genome-wide gene transcription in the adipose tissue from mother polar bears and their cubs, highlighting molecular differences in response between adults and young. Adipose tissue biopsies were collected from 13 adult female polar bears and their twin cubs in Svalbard, Norway, in April 2011, 2012, and 2013. Total RNA extracted from biopsies was subjected to next-generation RNA sequencing. Plasma concentrations of summed polychlorinated biphenyls, organochlorine pesticides, and polybrominated diphenyl ethers in mothers ranged from 897 to 13620 ng/g wet weight and were associated with altered adipose tissue gene expression in both mothers and cubs. In mothers, 2502 and 2586 genes in total were positively and negatively, respectively, correlated to POP exposure, whereas in cubs, 2585 positively and 1690 negatively genes. Between mothers and cubs, 743 positively and negatively genes overlapped between mothers and cubs suggesting partially shared molecular responses to ΣPOPs. ΣPOP-associated genes were involved in numerous metabolic pathways in mothers and cubs, indicating that POP exposure alters the energy metabolism, which, in turn, may be linked to metabolic dysfunction.

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

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

A Systematic Review on the Influences of Neurotoxicological Xenobiotic Compounds on Inhibitory Control

Background: Impulsive and compulsive traits represent a variety of maladaptive behaviors defined by the difficulties to stop an improper response and the control of a repeated behavioral pattern without sensitivity to changing contingencies, respectively. Otherwise, human beings are continuously exposed to plenty neurotoxicological agents which have been systematically linked to attentional, learning, and memory dysfunctions, both preclinical and clinical studies. Interestingly, the link between both impulsive and compulsive behaviors and the exposure to the most important xenobiotic compounds have been extensively developed; although the information has been rarely summarized. For this, the present systematic review schedule and analyze in depth the most important works relating different subtypes of the above-mentioned behaviors with 4 of the most important xenobiotic compounds: Lead (Pb), Methylmercury (MeHg), Polychlorinated biphenyls (PCB), and Organophosphates (OP) in both preclinical and clinical models.

Methods: Systematic search strategy on PubMed databases was developed, and the most important information was structured both in text and in separate tables based on rigorous methodological quality assessment.

Results: For Lead, Methylmercury, Polychlorinated biphenyls and organophosphates, a total of 44 (31 preclinical), 34 (21), 38 (23), and 30 (17) studies were accepted for systematic synthesis, respectively. All the compounds showed an important empirical support on their role in the modulation of impulsive and, in lesser degree, compulsive traits, stronger and more solid in animal models with inconclusive results in humans in some cases (i.e., MeHg). However, preclinical and clinical studies have systematically focused on different subtypes of the above-mentioned behaviors, as well as impulsive choice or habit conformations have been rarely studied.

Discussion: The strong empirical support in preclinical studies contrasts with the lack of connection between preclinical and clinical models, as well as the different methodologies used. Further research should be focused on dissipate these differences as well as deeply study impulsive choice, decision making, risk taking, and cognitive flexibility, both in experimental animals and humans.

Exposure to endocrine disrupting chemicals and neurodevelopmental alterations

The developing brain is remarkably malleable as neural circuits are formed and these circuits are strongly dependent on hormones for their development. For those reasons, the brain is very vulnerable to the effects of endocrine-disrupting chemicals (EDCs) during critical periods of development. This review focuses on three ubiquitous endocrine disruptors that are known to disrupt the thyroid function and are associated with neurobehavioral deficits: polychlorinated biphenyls, polybrominated diphenyl ethers, and bisphenol A. The human and rodent data suggesting effects of those EDCs on memory, cognition, and social behavior are discussed. Their mechanisms of action go beyond relative hypothyroidism with effects on neurotransmitter release and calcium signaling.

L-Theanine alleviates the neuropathological changes induced by PCB (Aroclor 1254) via inhibiting upregulation of inflammatory cytokines and oxidative stress in rat brain

The present study is aimed at evaluating the protective role of L-theanine on aroclor 1254-induced oxidative stress in rat brain. Intraperitoneal administration of Aroclor 1254 (2 mg/kg b.wt. for 30 days) caused oxidative stress in rat brain and also caused neurobehavioral changes. Oxidative stress was assessed by determining the levels of lipid peroxide (LPO), protein carbonyl content, and changes in activities of creatine kinase (CK), acetylcholinesterase (AchE), and ATPases in the hippocampus, cerebellum and cerebral cortex of control and experimental rats. Histopathological results showed that PCB caused neuronal loss in all three regions. PCB upregulated the mRNA expressions of inflammatory cytokines. Oral administration of L-theanine (200 mg/kg b.wt.) increased the status of antioxidants, decreased the levels of LPO, nitric oxide (NO) and increased the activities of CK, AchE and ATPases. L-Theanine restored normal architecture of brain regions and downregulated the expression of inflammatory cytokines. In conclusion, L-theanine shows a protective role against PCBs-induced oxidative damage in rat brain.

Effects of embryonic exposure to polychlorinated biphenyls (PCBs) on anxiety-related behaviors in larval zebrafish

The zebrafish (Danio rerio) is an excellent model system for assessing the effects of toxicant exposure on behavior and neurodevelopment. In the present study, we examined the effects of sub-chronic embryonic exposure to polychlorinated biphenyls (PCBs), a ubiquitous anthropogenic pollutant, on anxiety-related behaviors. We found that exposure to the PCB mixture, Aroclor (A) 1254, from 2 to 26h post-fertilization (hpf) induced two statistically significant behavioral defects in larvae at 7 days post-fertilization (dpf). First, during 135min of free swimming, larvae that had been exposed to 2ppm, 5ppm or 10ppm A1254 exhibited enhanced thigmotaxis (edge preference) relative to control larvae. Second, during the immediately ensuing 15-min visual startle assay, the 5ppm and 10ppm PCB-exposed larvae reacted differently to a visual threat, a red 'bouncing' disk, relative to control larvae. These results are consistent with the anxiogenic and attention-disrupting effects of PCB exposure documented in children, monkeys and rodents and merit further investigation.

A hypothesis about how early developmental methylmercury exposure disrupts behavior in adulthood

Events that disrupt the early development of the nervous system have lifelong, irreversible behavioral consequences. The environmental contaminant, methylmercury (MeHg), impairs neural development with effects that are manifested well into adulthood and even into aging. Noting the sensitivity of the developing brain to MeHg, the current review advances an argument that one outcome of early MeHg exposure is a distortion in the processing of reinforcing consequences that results in impaired choice, poor inhibition of prepotent responding, and perseveration on discrimination reversals (in the absence of alteration of extradimensional shifts). Neurochemical correlates include increased sensitivity to dopamine agonists and decreased sensitivity to gamma-aminobutyric acid (GABA) agonists. This leads to a hypothesis that the prefrontal cortex or dopamine neurotransmission is especially sensitive to even subtle gestational MeHg exposure and suggests that public health assessments of MeHg based on intellectual performance may underestimate the impact of MeHg in public health. Finally, those interested in modeling neural development may benefit from MeHg as an experimental model.

Endocrine-disrupting chemicals: elucidating our understanding of their role in sex and gender-relevant end points

Endocrine-disrupting chemicals (EDCs) are diverse and pervasive and may have significant consequence for health, including reproductive development and expression of sex-/gender-sensitive parameters. This review chapter discusses what is known about common EDCs and their effects on reproductively relevant end points. It is proposed that one way that EDCs may exert such effects is by altering steroid levels (androgens or 17-estradiol, E₂) and/or intracellular E₂ receptors (ERs) in the hypothalamus and/or hippocampus. Basic research findings that demonstrate developmentally sensitive end points to androgens and E₂ are provided. Furthermore, an approach is suggested to examine differences in EDCs that diverge in their actions at ERs to elucidate their role in sex-/gender-sensitive parameters.

Effects of condensed organic matter on PCBs bioavailability in juvenile swine, an animal model for young children

The exposure assessment of polychlorinated biphenyls (PCBs) contaminated soils is a critical issue in terms of human health, especially since little reliable information on transfer of PCBs to humans via involuntary soil ingestion is available. Indeed, young children with their hand-to-mouth activity may be exposed to contaminated soils. The current study addresses the impact of soil organic matter (OM) condensation on bioavailability of sequestrated NDL-PCBs. Three artificial soils (ASs) were prepared according to OECD guideline 207. One standard soil (SS), devoid of OM, and two amended versions of this SS with fulvic acid (FA) or activated carbon (AC) were prepared to obtain 1% organic mass. This study involved fourteen juvenile male swine as a digestive physiology model of young children. Animals were randomly distributed into 4 contaminated groups (3 replicates) and a control one (2 replicates). During 10d, the piglets were fed AS or a corn oil spiked with 19200 ng of Aroclor 1254 per g of dry matter (6000 ng g(-1) of NDL-PCBs) to achieve an exposure dose of 1200 ng NDL-PCBskg(-1) of body weight per day. After 10d of oral exposure, NDL-PCBs in adipose tissue, liver and muscles were analyzed by GC-MS, after extraction and purification. Two distinct groups of treatments were found: on the one hand oil, SS and FA, on the other hand C and AC. This study highlights that condensed OM (AC) strongly reduces bioavailability whereas the less condensed one (FA) does not seem to have a significant effect. This result has to be considered as a first major step for further relative bioavailability studies involving mixture of different humic substances.

Neuronal connectivity as a convergent target of gene × environment interactions that confer risk for Autism Spectrum Disorders

Evidence implicates environmental factors in the pathogenesis of Autism Spectrum Disorders (ASD). However, the identity of specific environmental chemicals that influence ASD risk, severity or treatment outcome remains elusive. The impact of any given environmental exposure likely varies across a population according to individual genetic substrates, and this increases the difficulty of identifying clear associations between exposure and ASD diagnoses. Heritable genetic vulnerabilities may amplify adverse effects triggered by environmental exposures if genetic and environmental factors converge to dysregulate the same signaling systems at critical times of development. Thus, one strategy for identifying environmental risk factors for ASD is to screen for environmental factors that modulate the same signaling pathways as ASD susceptibility genes. Recent advances in defining the molecular and cellular pathology of ASD point to altered patterns of neuronal connectivity in the developing brain as the neurobiological basis of these disorders. Studies of syndromic ASD and rare highly penetrant mutations or CNVs in ASD suggest that ASD risk genes converge on several major signaling pathways linked to altered neuronal connectivity in the developing brain. This review briefly summarizes the evidence implicating dysfunctional signaling via Ca(2+)-dependent mechanisms, extracellular signal-regulated kinases (ERK)/phosphatidylinositol-3-kinases (PI3K) and neuroligin-neurexin-SHANK as convergent molecular mechanisms in ASD, and then discusses examples of environmental chemicals for which there is emerging evidence of their potential to interfere with normal neuronal connectivity via perturbation of these signaling pathways.

Behavioral toxicology of cognition: extrapolation from experimental animal models to humans: behavioral toxicology symposium overview

A variety of behavioral instruments are available for assessing important aspects of cognition in both animals and humans and, in many cases, the same instruments can be used in both. While nonhuman primates are phylogenetically closest to humans, rodents, pigeons and other animals also offer behaviors worthy of note. Delay Discounting procedures are as useful as any in studies of impulsivity and may have utility in shedding light on processes associated with drug abuse. Specific memory tests such as Visual Paired Comparisons tasks (similar to the Fagan test of infant intelligence) can be modified to allow for assessment of different aspects of memory such as spatial memory. Use of these and other specific memory tasks can be used to directly monitor aspects of cognitive development in infant animals, particularly in nonhuman primates such as monkeys, and children and to draw inferences with respect to possible neuroanatomical substrates sub-serving their functions. Tasks for assessing working memory such as Variable Delayed Response (VDR), modified VDR and Spatial Working Memory tasks are now known to be affected in Parkinson's disease (PD). These and other cognitive function tasks are being used in a monkey model of PD to assess the ability of anti-Parkinson's disease therapies to ameliorate these cognitive deficits without diminishing their therapeutic effects on motor dysfunction. Similarly, in a rat model of the cognitive deficits associated with perinatal exposure to polychlorinated biphenyls (PCBs), clear parallels with children can be seen in at least two areas of executive function: cognitive flexibility and response inhibition. In the rat model, discrimination reversal tasks were utilized to assess cognitive flexibility, a function often assessed in humans using the Wisconsin Card Sorting Task. Response inhibition was assessed using performance in a Differential Reinforcement of Low Response Rates (DRL) task. As the data continue to accumulate, it becomes more clear that our attempts to adapt animal-appropriate tasks for the study of important aspects of human cognition have proven to be very fruitful.

Do Thyroid Disrupting Chemicals Influence Foetal Development during Pregnancy?

Maternal euthyroidism during pregnancy is crucial for normal development and, in particular, neurodevelopment of the foetus. Up to 3.5 percent of pregnant women suffer from hypothyroidism. Industrial use of various chemicals—endocrine disrupting chemicals (EDCs)—has been shown to cause almost constant exposure of humans with possible harmful influence on health and hormone regulation. EDCs may affect thyroid hormone homeostasis by different mechanisms, and though the effect of each chemical seems scarce, the added effects may cause inappropriate consequences on, for example, foetal neurodevelopment. This paper focuses on thyroid hormone influence on foetal development in relation to the chemicals suspected of thyroid disrupting properties with possible interactions with maternal thyroid homeostasis. Knowledge of the effects is expected to impact the general debate on the use of these chemicals. However, more studies are needed to elucidate the issue, since human studies are scarce.

In utero and lactational exposure to PCBs in mice: adult offspring show altered learning and memory depending on Cyp1a2 and Ahr genotypes

BACKGROUND

Both coplanar and noncoplanar polychlorinated biphenyls (PCBs) exhibit neurotoxic effects in animal studies, but individual congeners do not always produce the same effects as PCB mixtures. Humans genetically have > 60-fold differences in hepatic cytochrome P450 1A2 (CYP1A2)-uninduced basal levels and > 12-fold variability in aryl hydrocarbon receptor (AHR)affinity; because CYP1A2 is known to sequester coplanar PCBs and because AHR ligands include coplanar PCBs, both genotypes can affect PCB response.

OBJECTIVES

We aimed to develop a mouse paradigm with extremes in Cyp1a2 and Ahr genotypes to explore genetic susceptibility to PCB-induced developmental neurotoxicity using an environmentally relevant mixture of PCBs.

METHODS

We developed a mixture of eight PCBs to simulate human exposures based on their reported concentrations in human tissue, breast milk, and food supply. We previously characterized specific differences in PCB congener pharmacokinetics and toxicity, comparing high-affinity-AHR Cyp1a2 wild-type [Ahrb1_Cyp1a2(+/+)], poor-affinity-AHR Cyp1a2 wild-type [Ahrd_Cyp1a2(+/+)], and high-affinity-AHR Cyp1a2 knockout [Ahrb1_Cyp1a2(-/-)] mouse lines [Curran CP, Vorhees CV, Williams MT, Genter MB, Miller ML, Nebert DW. 2011. In utero and lactational exposure to a complex mixture of polychlorinated biphenyls: toxicity in pups dependent on the Cyp1a2 and Ahr genotypes. Toxicol Sci 119:189-208]. Dams received a mixture of three coplanar and five noncoplanar PCBs on gestational day 10.5 and postnatal day (PND) 5. In the present study we conducted behavioral phenotyping of exposed offspring at PND60, examining multiple measures of learning, memory, and other behaviors.

RESULTS

We observed the most significant deficits in response to PCB treatment in Ahrb1_Cyp1a2(-/-) mice, including impaired novel object recognition and increased failure rate in the Morris water maze. However, all PCB-treated genotypes showed significant differences on at least one measure of learning or behavior.

CONCLUSIONS

High levels of maternal hepatic CYP1A2 offer the most important protection against deficits in learning and memory in offspring exposed to a mixture of coplanar and noncoplanar PCBs. High-affinity AHR is the next most important factor in protection of offspring.

Lead and PCBs as risk factors for attention deficit/hyperactivity disorder

OBJECTIVES

Attention deficit/hyperactivity disorder (ADHD) is the most frequently diagnosed neurobehavioral disorder of childhood, yet its etiology is not well understood. In this review we present evidence that environmental chemicals, particularly polychlorinated biphenyls (PCBs) and lead, are associated with deficits in many neurobehavioral functions that are also impaired in ADHD.

DATA SOURCES

Human and animal studies of developmental PCB or lead exposures that assessed specific functional domains shown to be impaired in ADHD children were identified via searches of PubMed using "lead" or "PCB exposure" in combination with key words, including "attention," "working memory," "response inhibition," "executive function," "cognitive function," "behavior," and "ADHD."

DATA SYNTHESIS

Children and laboratory animals exposed to lead or PCBs show deficits in many aspects of attention and executive function that have been shown to be impaired in children diagnosed with ADHD, including tests of working memory, response inhibition, vigilance, and alertness. Studies conducted to date suggest that lead may reduce both attention and response inhibition, whereas PCBs may impair response inhibition to a greater degree than attention. Low-level lead exposure has been associated with a clinical diagnosis of ADHD in several recent studies. Similar studies of PCBs have not been conducted.

CONCLUSIONS

We speculate that exposures to environmental contaminants, including lead and PCBs, may increase the prevalence of ADHD.

Comparing Mini-Mental State Examination and Attention and Digit Span in elderly exposed to polychlorinated biphenyls and polychlorinated dibenzofurans

BACKGROUND

Polychlorinated biphenyls (PCB)/polychlorinated dibenzofurans (PCDF) are known to affect central nervous functioning. In recent studies, elderly patients who have been exposed to these have been noted to have psychological deficits. There is little known about which test is sensitive to neurotoxins in cognitive evaluation. The objective of the present study was to compare the significance between selective psychological tests in cognitive assessment in PCB-laden elderly.

METHODS

A retrospective PCB/PCDF exposed cohort was observed. Exposed elderly aged ≥ 60 years and registered in Central Health Administration were enrolled, and similar age- and sex-matched subjects served as non-exposed controls. The Mini-Mental State Examination (MMSE) and Attention and Digit Span (ADS) were tested in both groups. Student's t-test, χ(2) -test and linear regression models were used for statistical analysis.

RESULTS

 A total of 165 exposed patients and 151 controls were analyzed. The exposed group included 49% men, a mean age of 69.3 ± 6.4 years and an education level of 4.0 ± 3.9 years. The controls included 52% men, a mean age of 69.9 ± 5.5 years and an education level of 4.5 ± 3.2 years. There was no statistical difference in MMSE before and after adjusting for the confounding variables of age, sex and education (P= 0.16 vs P= 0.12). However, ADS-forward and ADS-total scores showed a significant decline in the exposed subjects (P= 0.0001 vs P= 0.001). Using a linear regression among stratified PCB and cognitive functioning (≤30 ppb; 31-89; ≥90), a dose effect was found at the medium (31-89 ppb) and high exposure (≧90 ppb) levels.

CONCLUSION

Our observations showed attention and short-term memory were impaired in PCB-laden elderly patients. Higher exposure level showed lower cognitive functioning in ADS. The MMSE was insensitive to neurotoxins. The present study shows that the selective test has a decisive role in toxic-related cognitive assessments.

Neuroendocrine actions of organohalogens: thyroid hormones, arginine vasopressin, and neuroplasticity

Organohalogen compounds are global environmental pollutants. They are highly persistent, bioaccumulative, and cause adverse effects in humans and wildlife. Because of the widespread use of these organohalogens in household items and consumer products, indoor contamination may be a significant source of human exposure, especially for children. One significant concern with regard to health effects associated with exposure to organohalogens is endocrine disruption. This review focuses on PCBs and PBDEs as old and new organohalogens, respectively, and their effects on two neuroendocrine systems; thyroid hormones and the arginine vasopressin system (AVP). Regarding neuroendocrine effects of organohalogens, there is considerable information on the thyroid system as a target and evidence is now accumulating that the AVP system and associated functions are also susceptible to disruption. AVP-mediated functions such as osmoregulation, cardiovascular function as well as social behavior, sexual function and learning/memory are discussed. For both thyroid and AVP systems, the timing of exposure seems to play a major role in the outcome of adverse effects. The mechanism of organohalogen action is well understood for the thyroid system. In comparison, this aspect is understudied in the AVP system but some similarities in neural processes, shown to be targeted by these pollutants, serve as promising possibilities for study. One challenge in understanding modes of action within neuroendocrine systems is their complexity stemming, in part, from interdependent levels of organization. Further, because of the interplay between neuroendocrine and neural functions and behavior, further investigation into organohalogen-mediated effects is warranted and may yield insights with wider scope. Indeed, the current literature provides scattered evidence regarding the role of organohalogen-induced neuroendocrine disruption in the neuroplasticity related to both learning functions and brain structure but future studies are needed to establish the role of endocrine disruption in nervous system function and development.

Minding the calcium store: Ryanodine receptor activation as a convergent mechanism of PCB toxicity

Chronic low-level polychlorinated biphenyl (PCB) exposures remain a significant public health concern since results from epidemiological studies indicate that PCB burden is associated with immune system dysfunction, cardiovascular disease, and impairment of the developing nervous system. Of these various adverse health effects, developmental neurotoxicity has emerged as a particularly vulnerable endpoint in PCB toxicity. Arguably the most pervasive biological effects of PCBs could be mediated by their ability to alter the spatial and temporal fidelity of Ca2+ signals through one or more receptor-mediated processes. This review will focus on our current knowledge of the structure and function of ryanodine receptors (RyRs) in muscle and nerve cells and how PCBs and related non-coplanar structures alter these functions. The molecular and cellular mechanisms by which non-coplanar PCBs and related structures alter local and global Ca2+ signaling properties and the possible short and long-term consequences of these perturbations on neurodevelopment and neurodegeneration are reviewed.

Behavioral changes in aging but not young mice after neonatal exposure to the polybrominated flame retardant decaBDE

BACKGROUND

After several decades of commercial use, the flame-retardant chemicals polybrominated diphenyl ethers (PBDEs) and their metabolites are pervasive environmental contaminants and are detected in the human body. Decabrominated diphenyl ether (decaBDE) is currently the only PBDE in production in the United States.

OBJECTIVES

Little is known about the health effects of decaBDE. In the present study we examined the effects of neonatal decaBDE exposure on behavior in mice at two ages.

METHODS

Neonatal male and female C57BL6/J mice were exposed to a daily oral dose of 0, 6, or 20 mg/kg decaBDE from postnatal days 2 through 15. Two age groups were examined: a cohort that began training during young adulthood and an aging cohort of littermates that began training at 16 months of age. Both cohorts were tested on a series of operant procedures that included a fixed-ratio 1 schedule of reinforcement, a fixed-interval (FI) 2-min schedule, and a light-dark visual discrimination.

RESULTS

We observed minimal effects on the light-dark discrimination in the young cohort, with no effects on the other tasks. The performance of the aging cohort was significantly affected by decaBDE. On the FI schedule, decaBDE exposure increased the overall response rate. On the light-dark discrimination, older treated mice learned the task more slowly, made fewer errors on the first-response choice of a trial but more perseverative errors after an initial error, and had lower latencies to respond compared with controls. Effects were observed in both dose groups and sexes on various measures.

CONCLUSIONS

These findings suggest that neonatal decaBDE exposure produces effects on behavioral tasks in older but not younger animals. The behavioral mechanisms responsible for the pattern of observed effects may include increased impulsivity, although further research is required.

Alterations in male infant behaviors towards its mother by prenatal exposure to bisphenol A in cynomolgus monkeys (Macaca fascicularis) during early suckling period

Bisphenol A (BPA) is an environmental chemical with physiological potencies that cause adverse effects, even at environmentally relevant exposures, on the basis of a number of studies in experimental rodents. Thus, there is an increasing concern about environmental exposure of humans to BPA. In the present study, we used experimentally controlled cynomolgus monkeys (Macaca fascicularis) to assess the influence of prenatal exposure to BPA (10 microg/(kg day)) via subcutaneously implanted pumps and examined social behaviors between infants and their mothers during the suckling period. Mother-infant interactions in cynomolgus monkeys had behavioral sexual dimorphism associated with sex of infant from early suckling period. Prenatal exposure to BPA altered the behaviors of male infants significantly; BPA-exposed male infants behaved as female infants. And it also affected some of female infant behaviors. Consequently, gestational BPA exposure altered some behaviors of their mothers, mainly in male-nursing mothers. These results suggest that BPA exposure affects behavioral sexual differentiation in male monkeys, which promotes the understanding of risk of BPA exposure in human.

Neurocognitive changes among elderly exposed to PCBs/PCDFs in Taiwan

BACKGROUND

In 1979 approximately 2,000 people were exposed to polychlorinated biphenyls (PCBs) and polychlorinated dibenzofurans (PCDFs) due to ingestion of contaminated cooking oil in Taiwan. Although a previous study has shown delayed developmental milestones and poorer neurocognitive functioning in children born to exposed mothers, it is unclear whether neurocognitive functioning was impaired in people who were directly exposed to the PCBs and PDCFs.

OBJECTIVE

The objective of this study was to compare neurocognitive functioning in people exposed to PCBs and PCDFs with that of unexposed sex- and age-matched neighbors.

METHODS

We conducted a retrospective cohort study among exposed and unexposed subjects > or =60 years of age using prospective outcome measurements. We evaluated neurocognitive tests including cognition, memory modalities, learning, motor and sensory function, mood, and daily activity.

RESULTS

In total, 162 (59%) exposed and 151 (55%) reference subjects completed this study. In exposed men, all test results were similar to the reference group; however, exposed women had reduced functioning in attention and digit span (ADS), visual memory span (VMS), and verbal memory recalls (VMR), especially learning ability. We also found a borderline reduction in the Mini-Mental State Examination. The digit symbol, motor, sensory, depression (determined by the Geriatric Depression Scale-Short Form), and activity of daily life were not different between the exposed and reference groups. A significant dose-response relationship was found for VMR, ADS, and VMS.

CONCLUSION

Our study showed dose-dependent neurocognitive deficits in certain aspects of attention, visual memory, and learning ability in women previously exposed to PCBs and PCDFs, but not in exposed men.

Associations between prenatal exposure to polychlorinated biphenyls and neonatal thyroid-stimulating hormone levels in a Mexican-American population, Salinas Valley, California

BACKGROUND

Studies have reported that prenatal exposure to polychlorinated biphenyls (PCBs) may alter neurodevelopment in both humans and animals. Furthermore, prenatal exposure to some PCB congeners and commercial mixtures has been shown to decrease free and total thyroxine (T(4)) blood levels in animals. Because thyroid hormones (TH) are essential for normal neurologic development, it has been suggested that the deleterious neurodevelopmental effect of PCBs may occur through TH disruption. PCBs may in turn affect TH levels by inducing the microsomal enzyme uridinediphosphate glucuronosyltransferase (UDP-GT), which is involved in TH elimination.

OBJECTIVES

Our goals were to group PCB congeners based on their potential to induce microsomal enzymes in animals, and to examine the relationship between neonatal TSH levels and prenatal exposure to PCB congeners grouped according to their structure and potential mechanisms of action.

METHODS

We measured the concentration of 34 PCB congeners in serum samples collected from 285 pregnant women and the thyroid-stimulating hormone (TSH) levels in their children's blood collected shortly after birth.

RESULTS

We found no association between the sum of PCB congeners, the toxic equivalents, or structure-based groupings (mono- or di-ortho substituted congeners), and TSH blood concentration. However, we found a positive association between the sum of congeners suspected to be UDP-GT inducers (more specifically cytochrome P450 2B inducers) in animals and neonatal TSH levels. In individual congener analyses, PCBs 99, 138, 153, 180, 183, 187, 194, and 199 were positively associated with neonatal TSH levels after adjustment for covariates. PCBs 194 and 199 remained significant after adjustment for multiple hypothesis testing.

CONCLUSIONS

Our results support grouping PCB congeners based on their potential mechanism of action of enzyme induction when investigating associations with TH. Findings also suggest that PCBs affect TH homeostasis even at the low background level of exposure found in the CHAMA-COS (Center for the Health Assessment of Mothers and Children of Salinas) population.

Ontogenetic alterations in molecular and structural correlates of dendritic growth after developmental exposure to polychlorinated biphenyls

OBJECTIVE

Perinatal exposure to polychlorinated biphenyls (PCBs) is associated with decreased IQ scores, impaired learning and memory, psychomotor difficulties, and attentional deficits in children. It is postulated that these neuropsychological deficits reflect altered patterns of neuronal connectivity. To test this hypothesis, we examined the effects of developmental PCB exposure on dendritic growth.

METHODS

Rat dams were gavaged from gestational day 6 through postnatal day (PND) 21 with vehicle (corn oil) or the commercial PCB mixture Aroclor 1254 (6 mg/kg/day). Dendritic growth and molecular markers were examined in pups during development.

RESULTS

Golgi analyses of CA1 hippocampal pyramidal neurons and cerebellar Purkinje cells indicated that developmental exposure to PCBs caused a pronounced age-related increase in dendritic growth. Thus, even though dendritic lengths were significantly attenuated in PCB-treated animals at PND22, the rate of growth was accelerated at later ages such that by PND60, dendritic growth was comparable to or even exceeded that observed in vehicle controls. Quantitative reverse transcriptase polymerase chain reaction analyses demonstrated that from PND4 through PND21, PCBs generally increased expression of both spinophilin and RC3/neurogranin mRNA in the hippocampus, cerebellum, and cortex with the most significant increases observed in the cortex.

CONCLUSIONS

This study demonstrates that developmental PCB exposure alters the ontogenetic profile of dendritogenesis in critical brain regions, supporting the hypothesis that disruption of neuronal connectivity contributes to neuropsychological deficits seen in exposed children.

Development of a neurotoxic equivalence scheme of relative potency for assessing the risk of PCB mixtures

PCBs produce adverse effects in humans and animals by several modes of action. The first mode of action is binding of coplanar or mono-ortho-PCBs to the aryl hydrocarbon (Ah) receptor leading to effects associated with the activation of this receptor. The remaining PCB congeners do not activate this receptor and have different modes of action underlying their toxic effects. One mode of action that has been shown for di-ortho-substituted non-coplanar PCBs (PCB congeners with two or more chlorines in the ortho-positions) is the interference with intracellular signaling pathways dependent on Ca(2+) homeostasis and the resulting cellular, organ-level and organismal effects. The ortho-substituted non-coplanar congeners produce other cellular or organ-level effects including changes in protein kinase C translocation, changes in cellular dopamine (DA) uptake, formation of reactive oxygen species, and thyroid effects. Here, we propose a scheme for developing relative potency estimates (REP) for the PCB congeners not considered in the TEF scheme used to assess the toxicity of coplanar and mono-ortho-PCBs and chlorinated dioxins and furans. Because a number of the modes of action listed here for the ortho-substituted non-coplanar PCB congeners have been implicated in the neurotoxic effects of these PCBs congeners, this relative potency scheme is referred to here as the Neurotoxic Equivalent (NEQ) scheme for estimating toxicity of PCB mixtures. The Neurotoxic Equivalent (NEQ) values are developed in a way similar in concept to the derivation of the well-known TEF congener values. Although this scheme is in its infancy and the set of NEQ values are limited by the current data, there are several compelling reasons for proposing such a scheme now. First, it should open discussions as to how different modes of action can be utilized to predict congener potency differences for the effects they produce. Second, consideration and evaluation of the ability of the proposed NEQ scheme to predict the toxicity of PCB mixtures will assist in the identification of the specific modes of action relevant to the effects produced by non-coplanar PCBs. If other modes of action are suggested and subsequently identified, then other schemes of relative potency could be developed specifically for those modes of action, distinct from either the TEF scheme or the NEQ scheme. Knowing these other modes of action and the relative toxicity of the various congeners would advance our understanding of PCB toxicology and thereby ultimately improve our ability to estimate the toxic potency of PCB mixtures for each identified mode of action. Third, a quantitative scheme for assessing the toxicity of the non-coplanar PCB congeners present in a mixture has the potential to improve significantly future risk assessments of PCB mixtures.

Neurotoxicity of persistent organic pollutants: possible mode(s) of action and further considerations

Persistent organic pollutants (POPs) are long-lived toxic organic compounds and are of major concern for human and ecosystem health. Although the use of most POPs is banned in most countries, some organochlorine pesticides are still being used in several parts of the world. Although environmental levels of some POPs such as polychlorinated biphenyls (PCBs) have declined, newly emerging POPs such as polybrominated diphenyl ethers (PBDEs) have been increasing considerably. Exposure to POPs has been associated with a wide spectrum of effects including reproductive, developmental, immunologic, carcinogenic, and neurotoxic effects. It is of particular concern that neurotoxic effects of some POPs have been observed in humans at low environmental concentrations. This review focuses on PCBs as a representative chemical class of POPs and discusses the possible mode(s) of action for the neurotoxic effects with emphasis on comparing dose-response and structure-activity relationships (SAR) with other structurally related chemicals. There is sufficient epidemiological and experimental evidence showing that PCB exposure is associated with motor and cognitive deficits in humans and animal models. Although several potential mode(s) of actions were postulated for PCB-induced neurotoxic effects, changes in neurotransmitter systems, altered intracellular signalling processes, and thyroid hormone imbalance are predominant ones. These three potential mechanisms are discussed in detail in vitro and in vivo. In addition, SAR was conducted on other structurally similar chemicals to see if they have a common mode(s) of action. Relative potency factors for several of these POPs were calculated based on their effects on intracellular signalling processes. This is a comprehensive review comparing molecular effects at the cellular level to the neurotoxic effects seen in the whole animal for environmentally relevant POPs.

Genetic Differences in Lethality of Newborn Mice Treated In Utero with Coplanar versus Non-Coplanar Hexabromobiphenyl

Polybrominated biphenyl (PBB) exposure in humans is known to cause immunotoxicity and disorders related to the central nervous system. Coplanar PBBs bind to the aryl hydrocarbon receptor (AHR) in vertebrates. We compared the coplanar PBB, 3,3',4,4',5,5'-hexabromobiphenyl (cHBB), with its stereoisomer, the non-coplanar PBB, 2,2',4,4'6,6'-hexabromobiphenyl (ncHBB), using C57BL/6J (B6) inbred mice (having the high-affinity AHR) and congenic B6.D2-Ahr d mice (having the low-affinity AHR in a >99.8% C57BL/6J genetic background). Pregnant dams were treated i.p. with vehicle alone, cHBB, or ncHBB on gestational day 5 (GD 5). Unexpectedly, neonatal lethality within the first 72 h postpartum was significant in cHBB-treated B6 mice at doses as low as 2.5 mg/kg, whereas no deaths were seen in B6 pups whose mother had received ncHBB 100 mg/kg or in either B6.D2-Ahr d or Ahr(-/-) knockout mice whose mother had received cHBB 100 mg/kg. Histological and gross anatomical analyses of a battery of tissues in the mother or fetus at GD 18, as well as 24 h postpartum, revealed no significant differences, except for decreased thymus and spleen weights in cHBB-treated B6 GD 18 fetuses. Cross-fostering and genetics experiments confirmed the association of neonatal deaths principally with in utero (rather than lactational) exposure to cHBB, and also no paternal effect. For the end points of mouse neonatal lethality and immunotoxicity, cHBB appears to act through the high-affinity AHR receptor. Although dioxin in utero is well known to cause AHR-dependent cleft palate and hydronephrosis, cHBB did not; thus, chronic activation of the AHR appears to be necessary but not sufficient for AHR-mediated teratogenicity.

Polybrominated diphenyl ether (PBDE) effects in rat neuronal cultures: 14C-PBDE accumulation, biological effects, and structure-activity relationships

Polybrominated diphenyl ethers (PBDEs), widely used as flame-retardants, are now recognized as globally distributed pollutants, and are detected in most environmental and biological samples, including human blood, adipose tissue, and breast milk. Due to their wide use in commercial products and their persistent nature, long-term exposure to PBDEs may pose a human health risk, especially to children. Our previous reports showed that the commercial PBDE mixture, DE-71, affected protein kinase C (PKC) and calcium homeostasis in a similar way to those of a structurally-related polychlorinated biphenyl (PCB) mixture. These intracellular signaling events are associated with neuronal development and learning and memory function. The objectives of the present study were to test whether environmentally relevant PBDE congeners, with different position and number of bromines, affected PKC translocation in cerebellar granule neuronal cultures and compare the potency and efficacy of PBDE congeners with their 14C-accumulation. All the tested PBDE congeners increased 3H-phorbol ester (PDBu) binding, and a significant effect was seen as low as 10 microM. Among the congeners tested, 2,2',4,4'-tetrabromodiphenyl ether (PBDE 47) increased 3H-PDBu binding in a concentration-dependent manner and to a greater extent than other congeners. These effects were seen at concentrations and exposure times where no cytotoxicity was observed. The efficacy of PBDE congeners varied with their structural composition, and the effects seen on 3H-PDBu binding with some PBDE congeners are similar to those of PCB congeners. Cerebellar granule neurons accumulated all three PBDE congeners (PBDEs 47, 99, and 153) following exposure. At the lowest concentration (0.67 microM), about 13-18% of the total dose of 14C-PBDE congeners was accumulated by these neurons. There were distinct differences in the pattern of 14C-PBDE accumulation among the PBDE congeners. The 14C-PBDE accumulation, either represented as percent basis or nanomole basis, was much lower for the 30.69 microM PBDE 99 and 10.69-30.69 microM PBDE 153 than at the lower concentrations, which may be due to low solubility of these congeners. The accumulation pattern with PBDE 47 did not vary with concentration. On a nanomole accumulation basis, PBDEs 47, 99, and 153 accumulation was linear with time. While the nanomole accumulation was linear with concentration for PBDE 47, it is nonlinear for PBDEs 99 and 153. The pattern of PBDE accumulation seems to correlate with the effects on PKC translocation, with regression values of 0.773-0.991. These results indicate that PBDEs affected PKC translocation in neurons in a similar way to those of other organohalogens, some PBDE congeners are equally efficacious as the respective PCB congeners, and PBDE accumulation correlated well with PKC translocation, suggesting a common mode of action for this group of chemicals.

Attention-deficit and hyperactive neurobehavioural characteristics induced by perinatal hypothyroidism in rats

Thyroid hormone is essential for the proper development of the mammalian central nervous system (CNS). In the present study, we examined behavioural alterations caused by transient perinatal hypothyroidism induced by an anti-thyroid drug, propylthiouracil (PTU). This drug produces perinatal disruption of the thyroid system and subsequent behavioural changes, which we investigated using a series of behavioural tests and focusing particularly on attention-deficit/hyperactivity disorder (ADHD)-like behaviours. In the open field test, both male and female rats that had experienced perinatal hypothyroidism (HT rats) showed an increased percent of locomotion behaviour and reduced grooming behaviour, suggesting that HT rats may be hyperactive and show fewer anxiety characteristics. Neither male nor female HT rats showed retention in the passive avoidance test. Male HT rats showed a significantly lower rate of correct avoidance responses than control rats in earlier sessions in the active avoidance test. In addition, we observed significant increases in the number of times that rats crossed the partition during inter-trial intervals and the percent of failure of avoidance during 5 s electrical stimuli in HT rats, suggesting that HT rats are restless, have a shortened attention span and panic easily. In measuring spontaneous motor activity during a period of darkness, male HT rats appeared to plunge into active phase with short, quick steps, while male control rats showed only long active phases during a stress-free period of darkness. These abnormal behavioural characteristics in HT rats might coincide with those found in some cases of ADHD.

Perinatal exposure to polychlorinated biphenyls alters excitatory synaptic transmission and short-term plasticity in the hippocampus of the adult rat

Developmental exposure to polychlorinated biphenyls (PCBs) has been associated with cognitive deficits in humans and laboratory animals. Previous work has demonstrated a reduced capacity to support long-term potentiation (LTP) in animals exposed to a PCB mixture, Aroclor 1254 (A1254) via the dam in utero and throughout the preweaning period [Brain Res. 850;1999:87-95; Toxicol. Sci. 57;2000:102-11]. Assessment of normalized input/output (I/O) functions collected prior to LTP induction failed to reveal consistent differences in baseline synaptic transmission between control and PCB-exposed groups. The present study was designed to systematically evaluate excitatory and inhibitory synaptic transmission using a more extensive I/O analysis and paired pulse functions to assess short-term plasticity. Pregnant Long-Evans rats were administered either corn oil (control) or 6 mg/kg per day of A1254 by gavage from gestational day (GD) 6 until pups were weaned on postnatal day (PND) 21. In adult male offspring (5-11 months of age), field potentials evoked by perforant path stimulation were recorded in the dentate gyrus under urethane anesthesia. Detailed I/O functions were assessed by averaging the responses evoked in the dentate gyrus to stimulus pulses delivered to the perforant path in an extensive ascending intensity series. Population spike (PS) and postsynaptic potential (PSP) amplitudes recorded in the dentate gyrus were significantly enhanced in PCB-exposed animals relative to controls at midrange intensities. No group differences were observed in EPSP slope amplitudes. Short-term plasticity was assessed by delivering pairs of stimulus pulses at interpulse intervals (IPIs) ranging from 10 to 70 ms. In the dentate gyrus this range of intervals activates both inhibitory and excitatory mechanisms leading to a pattern of depression at brief intervals (<30 ms) followed by facilitation as the interval between pulses is extended. Paired pulse depression was decreased at an intermediate IPI (30 ms) with submaximal stimulus intensities. These data augment previous work demonstrating persistent changes in hippocampal plasticity as a result of exposure to PCBs during development. Furthermore, as increases in field potential amplitudes were observed, these findings support previous conclusions that A1254-induced LTP deficits are not readily attributable to reductions in synaptic excitability. Thus, in addition to impairment in use-dependent synaptic plasticity reported previously, the present report reveals that basic components of information processing within the hippocampus are permanently altered as a result of perinatal exposure to PCBs.

Effects of Perinatal Exposure to PCBs on Neuropsychological Functions in the Rotterdam Cohort at 9 Years of Age

PCBs are known for their neurotoxic properties, especially on the developing brain. To increase insight into the neurotoxic effects of PCB exposure, the authors studied the effects of perinatal exposure to environmental levels of these compounds on different neuropsychological domains. In 9-year-old children of the Rotterdam PCB--dioxin cohort, higher prenatal PCB levels were associated with longer response times (RTs), more variation in RTs, and lower scores on the Tower of London (TOL; Shallice, 1982). A longer breast-feeding duration was associated with lower TOL scores and with better spatial organizational skills. There was some evidence of negative effects of lactational exposure to PCBs on scores on the TOL.

Up-regulation of methionine-enkephalin-like immunoreactivity by 2,3,7,8-tetrachlorodibenzo-p-dioxin treatment in the forebrain of the Long-Evans rat

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is considered to be one of the most toxic environmental contaminants, named dioxin. Exposure to TCDD induces a plethora of intoxication symptoms, including anorexia and hypothermia, in several mammals and human. Enkephalin, an endogenous pentapeptide, is an important neuroregulator of autonomic functions, such as food intake and body temperature. In this study, we investigated the effects of TCDD gastric administration on methionine-enkephalin (MEK) immunoreactivity in the brain of the Long-Evans rat, the species strain considered to be the most TCDD-susceptible, using immunohistochemical staining. A single dose of TCDD (dissolved in olive oil, 50 microg/kg) or olive oil alone was administrated to the rats by gavage. Compared with the vehicle-treated rat, a marked increase in the density of MEK immunoreactive cell bodies, fibers and terminals was found 2 weeks after TCDD treatment in the forebrain of the TCDD-treated rat, i.e. the central amygdaloid nucleus, field CA3 of the hippocampus, paraventricular hypothalamic nucleus, medial preoptic nucleus, interstitial nucleus of the posterior limb of the anterior commissure, lateral globus pallidus, ventral pallidum and lateral division of the bed nucleus of the stria terminalis. These results demonstrated for the first time a site-specific increased enkephalinergic activity in certain brain regions of the Long-Evans rat. It is suggested that the increased MEK immunoreactivity may act as a compensatory adaptation for the pathophysiological alterations caused by TCDD exposure.

Cognitive development in preschool children prenatally exposed to PCBs and MeHg

A number of epidemiological studies have shown predictive relationships between prenatal exposure to polychlorinated biphenyls (PCBs) and subtle deficits in cognitive development in infancy through the preschool years [Child Dev. 56 (1985) 853; J. Pediatr. 116 (1990) 38; J. Pediatr. 134 (1999) 33; Toxicol. Lett. 102-103 (1998) 423; Neurotox. 21 (6) (2000) 1029-1038]. However, since not all studies have demonstrated these relationships (J. Pediatr. 119 (1991) 58-63), debate regarding the role of prenatal PCB exposure in cognitive development continues. The current study was designed to provide additional data to assist in resolving this question. Two hundred twelve children enrolled in the Oswego Newborn and Infant Development Project were assessed using the McCarthy Scales of Children's Abilities at 38 months of age, followed by a reassessment at 54 months of age. The relationship between prenatal exposure to PCBs (cord blood PCBs) and McCarthy performance was assessed at both ages after first controlling for a wide range of important predictors of cognitive development, including socioeconomic status (SES), maternal IQ, maternal education, home environment, cigarette smoking, and many others. Cord blood PCBs were statistically significant predictors of small but measurable deficits in McCarthy performance at 38 months of age. Moreover, a significant interaction between cord blood PCBs and maternal hair mercury (MeHg) was found, such that negative associations between prenatal MeHg exposure and McCarthy performance were found in subjects with higher levels of prenatal PCB exposure. No relationship between PCBs and/or MeHg and McCarthy performance was observed when the children were reassessed almost 1.5 years later (54 months of age). Inspection of the age-related trajectory of McCarthy performance revealed that the more highly exposed children caught up with the least exposed children by 54 months. Although the current data partially replicate the findings of Jacobson et al., Patandin et al., and Walkowiak et al. [J. Pediatr. 116 (1990) 38; J. Pediatr. 134 (1999) 33; Lancet 358 (2001) 1602], results reported here suggest that functional recovery may occur. Moreover, the interaction between PCB and MeHg cannot be considered conclusive until it has been replicated in subsequent investigations.

Neurobehavioral toxicity of methylmercury and PCBs Effects-profiles and sensitive populations

A large and growing body of literature is available on the neurotoxicity of methylmercury and PCBs as expressed in the behavior of both humans and laboratory animals. Methylmercury and PCBs will be compared with PCBs with attention directed at overlaps and distinctions in their profiles of neurotoxicity. It is possible with methylmercury and, to a lesser extent, with PCBs to characterize the sensory, motor, and cognitive consequences of exposure. Methylmercury is emerging as a life-span developmental neurotoxicant: adverse effects of exposure have been identified in development and during aging in human populations as well as in laboratory animals. Less is known about the PCBs on this count. While the mechanisms of neurotoxicity are not understood for either class of compounds, emerging clues are pointing to the possibility of overlap in some mechanisms of neurotoxicity.

Impaired cued delayed alternation behavior in adult rat offspring following exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin on gestation day 15

This investigation used random ratio (RR) and cued delayed alternation procedures to examine the operant behavior of adult male and female rats following prenatal 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Offspring were exposed to a single maternal dose of 0.0, 0.06, 0.18 or 0.54 microg/kg po of TCDD on gestation day (GD) 15. For RR, adult subjects were trained to respond on one lever in a two-lever chamber for food reinforcement. The response requirement was increased across sessions. Male offspring responded at higher rates than females regardless of RR value and prenatal exposure history. For delayed alternation, animals were required to alternate responses on both apparatus levers and to inhibit responding during randomly interpolated delay intervals. The performance of male and female offspring exposed to 0.18-microg/kg TCDD was significantly less accurate and this group committed more errors by responding during the delay intervals than the other exposure groups. A similar trend was observed in the 0.54- microg/kg group. Overall, response accuracy during the delayed alternation procedure was inversely related to delay length and tended to improve with experience. Interpretations of these outcomes include the possibility that TCDD interfered with the development of attentional processes, impaired response inhibition or promoted response perseveration despite the presence of cues, indicating changes in reinforcement contingencies.

Spatial reversal learning in Aroclor 1254-exposed rats: sex-specific deficits in associative ability and inhibitory control

Polychlorinated biphenyls (PCBs) are ubiquitous environmental contaminants that have been associated with cognitive deficits in children exposed in utero. Cognitive deficits due to PCB exposure have also been documented in animal models, but the underlying behavioral mechanisms responsible for those deficits remain to be elucidated. The current study examined the effects of gestational and lactational exposure to PCBs on spatial discrimination-reversal learning (spatial RL) in rats using standard two-lever operant testing chambers. Pregnant Long-Evans rats (10/dose) received either 0 or 6 mg/kg Aroclor 1254 (A1254) po in corn oil from gestational day 6 to postnatal day 21. One male and one female from each litter were tested on spatial RL beginning at 190-220 days of age. Animals were reinforced with a 45-mg food pellet for pressing the lever associated with the correct spatial location (either left or right). After reaching 85% correct performance for 2 consecutive days, the opposite spatial location was reinforced. Five of these position reversals were given. Male rats exposed to A1254 made significantly more total errors (121.6 +/- 12.5) on the first reversal than controls (90.7 +/- 5.8). In contrast, female rats exposed to A1254 exhibited deficits on the fourth and fifth reversals (23.6 +/- 4.2, 17.0 +/- 2.8 and 36.7 +/- 4.7, 26.8 +/- 2.5 for control and exposed animals, respectively). Response-pattern analyses in the A1254-exposed male and female rats revealed fundamental differences in the underlying behavioral mechanisms responsible for the deficits. A1254-exposed males exhibited an increased tendency to incorrectly respond to the previously correct stimulus (i.e., perseverate) following a reversal while A1254-exposed females exhibited impairments in their ability to make new associations with a reinforced spatial location (i.e., associative deficit). These data provide new insights into the underlying behavioral mechanisms that may be responsible for the spatial learning deficits observed in PCB-exposed rodents and monkeys.

Effects of polychlorinated biphenyl 19 (2,2',6-trichlorobiphenyl) on contraction, Ca2+ transient, and Ca2+ current of cardiac myocytes

Polychlorinated biphenyls (PCBs) have been known as serious environmental pollutants, causing developmental delays, motor dysfunction, and decrease in brain dopamine level in humans and animals. We have investigated the effects of a PCB congener, 2,2',6-trichlorobiphenyl (PCB 19) on contractile force, Ca2+ transient, and L-type Ca2+ current (I(Ca,L)) in guinea pig ventricular myocytes stimulated at a rate of 0.25-0.33 Hz. PCB 19 decreased contractile force in a concentration-dependent manner. During the negative inotropic response, the action potential duration at 20% (APD20), 90% of repolarization (APD90), and the action potential amplitude (APA) were decreased concentration dependently: 30 microM PCB 19 reduced APD20, APD90 and APA by 36.7 +/- 3.5%, 22.6 +/- 3.9%, and 2.4 +/- 0.6%, respectively (n = 11, p < 0.01). PCB 19 30 microM decreased the Ca2+ transient and the I(Ca,L) by 46.8 +/- 1.8% (n = 9, p < 0.01) and 47.1 +/- 3.1% (n = 9, p < 0.01), respectively. The results suggest that PCB 19 decreased the Ca2+ transient through inhibition of L-type Ca2+ channels and that the decreased Ca2+ transient consequently caused a negative inotropic effect in cardiac myocytes.

Perinatal exposure to polychlorinated biphenyls Aroclor 1016 or 1254 did not alter brain catecholamines nor delayed alternation performance in Long-Evans rats

Several reports have indicated that polychlorinated biphenyls (PCB) altered development of biogenic amine systems in the brain, impaired behavioral performances, and disrupted maturation of the thyroid axis. The current study examines whether these developmental effects of PCB are correlated. Timed-pregnant Long-Evans rats were gavaged with the PCB mixture Aroclor 1016 (A-1016, 10 mg/kg) from gestation day (GD) 6 to parturition. Some pups continued to receive daily oral administration of PCB (10 mg/kg) until weaning at postnatal day (PD) 21. Another group of pregnant rats was given Aroclor 1254 (A-1254, 8 mg/kg) daily from GD 6 to weaning. At various age intervals, rats were sacrificed and six brain regions (prefrontal cortex, striatum, hippocampus, diencephalon, cerebellum, midbrain + brain stem) were removed and analyzed for dopamine (DA) and norepinephrine (NE) levels by high-performance liquid chromatography. In addition, transmitter turnover rates were determined after an acute treatment of alpha-methyl-p-tyrosine. Serum samples were collected and analyzed for triiodothyronine (T(3)) and thyroxine (T(4)) by radioimmunoassay. Behaviorally, rats were evaluated for spatial learning and memory by means of T-maze delayed alternation and Morris maze tasks on PD 23 and PD 70, respectively. A-1016 treatment produced only small and transient reductions in body weight gain, and generally did not alter the thyroid status of the developing rats. It did not cause any significant changes in DA or NE level, or turnover rate in any of the brain regions examined, nor did it affect behavioral measures of cognitive development. In contrast, perinatal exposure to A-1254 led to marked deficits of growth, and sharply reduced serum T(4), although T(3) remained largely unaffected. Accompanying this hormonal imbalance, brain NE contents in the A-1254-exposed pups were reduced, although brain DA was not significantly affected; no demonstrable neurobehavioral deficits were seen in the T-maze or Morris maze tests. These results indicated that development of central noradrenergic neurons was compromised by perinatal exposure to A-1254 but not A-1016, and both PCB mixtures failed to alter behavioral performances.

Effects of polychlorinated biphenyls on development and reproduction

As part of its mandate, the Agency for Toxic Substances and Disease Registry (ATSDR) prepares toxicological profiles on hazardous chemicals found at Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) National Priorities List (NPL) sites that have the greatest public health impact. These profiles comprehensively summarize toxicological and environmental information. This article, which constitutes the release of an important section of the Toxicological Profile for Polychlorinated Biphenyls (ATSDR 2000) into the scientific literature, focuses on the developmental and reproductive effects of this group of synthetic organic chemicals (PCBs) in humans and animals. Information on other health effects, toxicokinetics, mechanisms of toxicity, biomarkers, interactions, chemical and physical properties, potential for human exposure, and regulations and advisories is detailed in the profile. Interested readers are encouraged to consult the original toxicological profile for more information. Profiles can be requested from ATSDR's Information Center by telephone (1-888-42-ATSDR [1-888-422-8737] or E-mail: (atsdric@cdc.gov).

Determination of a site-specific reference dose for methylmercury for fish-eating populations

Environmental risk-management decisions in the U.S. involving potential exposures to methylmercury currently use a reference dose (RfD) developed by the U.S. Environmental Protection Agency (USEPA). This RfD is based on retrospective studies of an acute poisoning incident in Iraq in which grain contaminated with a methylmercury fungicide was inadvertently used in the baking of bread. The exposures, which were relatively high but lasted only a few months, were associated with neurological effects in both adults (primarily paresthesia) and infants (late walking, late talking, etc.). It is generally believed that the developing fetus represents a particularly sensitive subpopulation for the neurological effects of methylmercury. The USEPA derived an RfD of 0.1 microg/kg/day based on benchmark dose (BMD) modeling of the combined neurological endpoints reported for children exposed in utero. This RfD included an uncertainty factor of 10 to consider human pharmacokinetic variability and database limitations (lack of data on multigeneration effects or possible long-term sequelae of perinatal exposure). Alcoa signed an Administrative Order of Consent for the conduct of a remedial investigation/feasibility study (RI/FS) at their Point Comfort Operations and the adjacent Lavaca Bay in Texas to address the effects of historical discharges of mercury-containing wastewater. In cooperation with the Texas Natural Resource Conservation Commission and USEPA Region VI, Alcoa conducted a baseline risk assessment to assess potential risk to human health and the environment. As a part of this assessment. Alcoa pursued the development of a site-specific RfD for methylmercury to specifically address the potential human health effects associated with the ingestion of contaminated finfish and shellfish from Lavaca Bay. Application of the published USEPA RfD to this site is problematic; while the study underlying the RfD represented acute exposure to relatively high concentrations of methylmercury, the exposures of concern for the Point Comfort site are from the chronic consumption of relatively low concentrations of methylmercury in fish. Since the publication of the USEPA RfD, several analyses of chronic exposure to methylmercury in fish-eating populations have been reported. The purpose of the analysis reported here was to evaluate the possibility of deriving an RfD for methylmercury, specifically for the case of fish ingestion, on the basis of these new studies. In order to better support the risk-management decisions associated with developing a remediation approach for the site in question, the analysis was designed to provide information on the distribution of acceptable ingestion rates across a population, which could reasonably be expected to be consistent with the results of the epidemiological studies of other fish-eating populations. Based on a review of the available literature on the effects of methylmercury, a study conducted with a population in the Seychelles Islands was selected as the critical study for this analysis. The exposures to methylmercury in this population result from chronic, multigenerational ingestion of contaminated fish. This prospective study was carefully conducted and analyzed, included a large cohort of mother-infant pairs, and was relatively free of confounding factors. The results of this study are essentially negative, and a no-observed-adverse-effect level (NOAEL) derived from the estimated exposures has recently been used by the Agency for Toxic Substances and Disease Registry (ATSDR) as the basis for a chronic oral minimal risk level (MRL) for methylmercury. In spite of the fact that no statistically significant effects were observed in this study, the data as reported are suitable for dose-response analysis using the BMD method. Evaluation of the BMD method used in this analysis, as well as in the current USEPA RfD, has demonstrated that the resulting 95% lower bound on the 10% benchmark dose (BMDL) represents a conservative estimate of the traditional NOAEL, and that it is superior to the use of "average" or "grouped" exposure estimates when dose-response information is available, as is the case for the Seychelles study. A more recent study in the Faroe Islands, which did report statistically significant associations between methylmercury exposure and neurological effects, could not be used for dose-response modeling due to inadequate reporting of the data and confounding from co-exposure to polychlorinated biphenyls (PCBs). BMD modeling over the wide range of neurological endpoints reported in the Seychelles study yielded a lowest BMDL for methylmercury in maternal hair of 21 ppm. This BMDL was then converted to an expected distribution of daily ingestion rates across a population using Monte Carlo analysis with a physiologically based pharmacokinetic (PBPK) model to evaluate the impact of interindividual variability. The resulting distribution of ingestion rates at the BMDL had a geometric mean of 1.60 microg/kg/day with a geometric standard deviation of 1.33; the 1st, 5th, and 10th percentiles of the distribution were 0.86, 1.04, and 1.15 microg/kg/day. In place of the use of an uncertainty factor of 3 for pharmacokinetic variability, as is done in the current RfD, one of these lower percentiles of the daily ingestion rate distribution provides a scientifically based, conservative basis for taking into consideration the impact of pharmacokinetic variability across the population. On the other hand, it was felt that an uncertainty factor of 3 for database limitations should be used in the current analysis. Although there can be high confidence in the benchmark-estimated NOAEL of 21 ppm in the Seychelles study, some results in the New Zealand and Faroe Islands studies could be construed to suggest the possibility of effects at maternal hair concentrations below 10 ppm. In addition, while concerns regarding the possibility of chronic sequelae are not supported by the available data, neither can they be absolutely ruled out. The use of an uncertainty factor of 3 is equivalent to using a NOAEL of 7 ppm in maternal hair, which provides additional protection against the possibility that effects could occur at lower concentrations in some populations. Based on the analysis described above, the distribution of acceptable daily ingestion rates (RfDs) recommended to serve as the basis for site-specific risk-management decisions at Alcoa's Point Comfort Operations ranges from approximately 0.3 to 1.1 microg/kg/day, with a population median (50th percentile) of 0.5 microg/kg/day. By analogy with USEPA guidelines for the use of percentiles in applications of distributions in exposure assessments, the 10th percentile provides a reasonably conservative measure. On this basis, a site-specific RfD of 0.4 microg/kg/day is recommended.

Effects of polychlorinated biphenyls on the nervous system

The neurological effects of polychlorinated biphenyls (PCBs) have been extensively investigated in humans and in animals. The main focus in human studies has been on the effects in neonates and young children, although studies of adults have also been conducted. A great deal of concern exists that even low levels of PCBs transferred to the fetus across the placenta may induce long-lasting neurological damage. Because PCBs are lipophilic substances, there is also concem that significant amounts might be transferred to nursing infants via breast milk. Studies in humans who consumed large amounts of Great Lakes fish contaminated with environmentally persistent chemicals, including PCBs. have provided evidence that PCBs are important contributors to subtle neurobehavioral alterations observed in newborn children and that some of these alterations persist during childhood. Some consistent observations at birth have been motor immaturity and hyporeflexia and lower psychomotor scores between 6 months and 2 years old. There is preliminary evidence that highly chlorinated PCB congeners, which accumulate in certain fish, are associated with neurobehavioral alterations seen in some newbom children. Subtle neurobehavioral alterations have also been observed in children bom to mothers in the general population with the highest PCB body burdens. Because of the limitations of epidemiological studies, these effects cannot be attributed entirely to PCB exposure. In one general population study, there was strong evidence that dioxins, as well as PCBs, were contributors to the neurobehavioral effects seen in exposed children. Children born to women who accidentally consumed rice oil contaminated with relatively high amounts of PCBs and chlorinated dibenzofurans (CDFs) during pregnancy also had neurodevelopmental changes. Studies in animals support the human data. Neurobehavioral alterations have been also observed in rats and monkeys following prenatal and/or postnatal exposure to commercial Aroclor mixtures, defined experimental congener mixtures, single PCB congeners, and Great Lakes contaminated fish. In addition, monkeys exposed postnatally to PCB mixtures of congeneric composition and concentration similar to that found in human breast milk showed learning deficits long after exposure had ceased. A few other generalizations can be made from the data in animals. It appears that ortho-substituted PCB congeners are more active than coplanar PCBs in modifying cognitive processes. In addition, one effect observed in both rats and monkeys--deficits on delayed spatial alternation--has been known to be induced by exposure to ortho-substituted PCBs, defined experimental mixtures, and commercial Aroclors. Both dioxin-like and non-dioxin-like PCB congeners have been shown to induce neurobehavioral alterations in animals. Changes in levels of neurotransmitters in various brain areas have also been observed in monkeys, rats, and mice. Of all the observed changes, the most consistent has been a decrease in dopamine content in basal ganglia and prefrontal cortex, but further research is needed before specific neurobehavioral deficits can be correlated with PCB-induced changes in specific neurotransmitters in specific brain areas.

Methods for studying nonhuman primates in neurobehavioral toxicology and teratology

The behavioral repertoire of nonhuman primates is highly evolved and includes advanced problem-solving capabilities, complex social relationships, and sensory acuity equal or superior to humans. These factors make nonhuman primates valuable animal models for studies of the functional effects of neurotoxicants. This review provides descriptions of tests designed to study learning, memory, schedule-controlled behavior, information processing, social behavior, sensory functioning, and visual-motor coordination and/or visuospatial orientation in macaque monkeys. Whenever possible, the results of studies in primate behavioral toxicology are provided for individual test measures. The primate model is especially useful for studies of developmental exposures because monkeys, like humans, have relatively prolonged periods of gestation, infancy, and adolescence. In recognition of this, a special section is provided for tasks that are specifically designed to study behavioral processes in infant monkeys.

Developmental exposure to a commercial PCB mixture (Aroclor 1254) produces a persistent impairment in long-term potentiation in the rat dentate gyrus in vivo

Developmental exposure to polycholorinated biphenyls (PCBs) has been associated with cognitive deficits in humans and laboratory animals. The present study sought to examine synaptic plasticity in the hippocampus, a brain region critical for some types of memory function, in animals exposed to PCBs early in development. Pregnant Long-Evans rats were administered either corn oil (control) or 6 mg/kg/day of a commercial PCB mixture, Aroclor 1254 (A1254) by gavage from gestational day (GD) 6 until pups were weaned on postnatal day (PND) 21. In adult male offspring (3-6 months of age), field potentials evoked by perforant path stimulation were recorded in the dentate gyrus under urethane anesthesia. Input/output (I/O) functions were assessed by averaging the response evoked in the dentate gyrus to stimulus pulses delivered to the perforant path in an ascending intensity series. Long-term potentiation (LTP) was induced by delivering a series of brief high frequency (400 Hz) train bursts to the perforant path at a moderate stimulus intensity and I/O functions were reassessed 1 h later. No differences in baseline synaptic population spike (PS) and minor effects on excitatory postsynaptic potential (EPSP) slope amplitudes were discerned between the groups prior to train delivery. Post-train I/O functions, however, revealed a 50% decrement in the magnitude of LTP in PCB-exposed animals. These data are the first to demonstrate persistent decrements in hippocampal synaptic plasticity in the intact animal following developmental exposure to PCBs. Disruption of early brain ontogeny due to developmental PCB exposure may underlie perturbations in the neurological substrates that support synaptic plasticity and contribute to deficits in LTP and learning that persist into adulthood.

Dose- and age-dependent alterations in choline acetyltransferase (ChAT) activity, learning and memory, and thyroid hormones in 15- and 30-day old rats exposed to 1.25 or 12.5 PPM polychlorinated biphenyl (PCB) beginning at conception

1. Polychlorinated biphenyls (PCB) were released into the environment through improper disposal for decades, causing widespread contamination. Slow biodegradation and lipophilic properties of PCB caused its persistence and concentration through food webs. Exposure to these environmental contaminants through maternal transfer during early development has been associated with neurological and endocrinological alterations in several different organisms. 2. The present study extended a preliminary investigation which suggested low level exposure to PCB altered acetylcholine biosynthesis enzyme, choline acetyltransferase (ChAT), activity in the hippocampus and basal forebrain and caused aberrations in thyroid hormone and behavior. 3. Dietary exposure of 15-day-old animals to 1.25 ppm of Aroclor 1254 (LPCB) during gestation and lactation significantly elevated ChAT activity in both areas of the brain. Animals exposed to 12.5 ppm of Aroclor 1254 (HPCB) until 15 days of age demonstrated significant elevations of ChAT activity in the basal forebrain. Thyroxine (T4) concentrations were slightly elevated in 15-day-old LPCB animals and significantly depressed in HPCB exposed pups; triiodothyronine (T3) concentrations were not altered. 4. At 30 days both LPCB and HPCB treatment groups displayed significantly depressed ChAT activity in both areas of the brain. T3 and T4 concentrations were subnormal, although T4 was not significantly depressed in LPCB animals. 5. In the Morris water maze all animals, when tested between 25 and 29 days of age, improved their latency time to the platform over 10 spatial learning trials. However, when combined means of trials 8-10 were compared, HPCB exposed animals had significantly increased latency time to the podium compared to control and LPCB animals.

Urban anglers' perception of risk from contaminated fish

The Newark Bay Complex includes the Newark Bay, tidal portions of the Hackensack River, Passaic River, Arthur Kill, and Kill van Kull. It is a highly industrialized urban area including five counties and more than 20 local governments with a large racially-mixed population of more than 3 million people. In 1982, research conducted by the New Jersey Department of Environmental Protection (NJDEP) showed elevated levels of chemical contaminants in five species of fish and one type of crab in the Newark Bay Complex. Subsequently, the State of New Jersey adopted advisories to guide citizens on safe consumption practices for fish and crabs. Since then, fish consumption advisories have been issued primarily through the Fish and Game Digest, a publication distributed by the state to licensed anglers. However, anglers in the Complex are not required to have a fishing license because the waters are marine. Therefore, most anglers in this area do not receive advisory information. To gain greater insight into the information sources and risk perceptions of urban anglers, a survey was conducted of 300 anglers at 26 fishing and crabbing locations in the Newark Bay Complex during the summer and early fall of 1995. The objectives of the study were to learn anglers': (1) knowledge of fish consumption advisories; (2) belief in the advisories; (3) perception of how safe fish are to eat; (4) sources for information about fish and fishing; and (5) sources for information on fish consumption advisories. The study concluded that while 60% had heard about advisories, they either did not believe or were unconcerned about health effects from eating contaminated species. In addition, the most used source for information about fish and fishing was other fishermen, while newspapers were selected as a source for information about community news, health, and food safety.