Behavioral effects following single and combined maternal exposure to PCB 77 (3,4,3',4'-tetrachlorobiphenyl) and PCB 47 (2,4,2',4'-tetrachlorobiphenyl) in rats

Contamination of food crops by unintentionally released PCB 47, PCB 51 and PCB 68 in the vicinity of silicone production sites and their relevance for human health assessment

Since it was shown that silicone rubber production can unintentionally release PCBs, these production sites have become a focus of investigation. The use of the cross-linking agent bis(2,4)-dichlorobenzoylperoxide (2,4-DCBP) can lead to emissions of the PCB congeners PCB 47, PCB 51 and PCB 68 into the environment and cause their accumulation e. g. in food crops. To determine the presence and extent of this uptake, we used the newly developed method dandelion screening. Samples were taken from wild dandelion plants near nine production sites in North Rhine-Westphalia, Germany, and analysed for PCBs. In some cases, the regional orientation values for the maximum background level (OMB) were exceeded by up to nine times. Overall, background levels were exceeded at seven of the nine sites investigated and mitigation measures were initiated at the production sites. In order to validate the dandelion screening results, kale was exposed, which allowed for a health assessment. A wide-ranging consumption recommendation was then issued in four out of nine study areas. At this point in the investigations, risk reduction measures had already been implemented at all production sites investigated, so it can be assumed that the exposures at sites not yet in focus are significantly greater. This is a globally relevant problem, as 2,4-DCBP is used in many countries.

Evidence Implicating Non-Dioxin-Like Congeners as the Key Mediators of Polychlorinated Biphenyl (PCB) Developmental Neurotoxicity

Despite being banned from production for decades, polychlorinated biphenyls (PCBs) continue to pose a significant risk to human health. This is due to not only the continued release of legacy PCBs from PCB-containing equipment and materials manufactured prior to the ban on PCB production, but also the inadvertent production of PCBs as byproducts of contemporary pigment and dye production. Evidence from human and animal studies clearly identifies developmental neurotoxicity as a primary endpoint of concern associated with PCB exposures. However, the relative role(s) of specific PCB congeners in mediating the adverse effects of PCBs on the developing nervous system, and the mechanism(s) by which PCBs disrupt typical neurodevelopment remain outstanding questions. New questions are also emerging regarding the potential developmental neurotoxicity of lower chlorinated PCBs that were not present in the legacy commercial PCB mixtures, but constitute a significant proportion of contemporary human PCB exposures. Here, we review behavioral and mechanistic data obtained from experimental models as well as recent epidemiological studies that suggest the non-dioxin-like (NDL) PCBs are primarily responsible for the developmental neurotoxicity associated with PCBs. We also discuss emerging data demonstrating the potential for non-legacy, lower chlorinated PCBs to cause adverse neurodevelopmental outcomes. Molecular targets, the relevance of PCB interactions with these targets to neurodevelopmental disorders, and critical data gaps are addressed as well.

Delayed effects of developmental exposure to low levels of the aryl hydrocarbon receptor agonist 3,3',4,4',5-pentachlorobiphenyl (PCB126) on adult zebrafish behavior

Polychlorinated biphenyls (PCBs) are ubiquitous environmental contaminants. The most toxic PCBs are the non-ortho-substituted ("dioxin-like") congeners that act through the aryl hydrocarbon receptor (AHR) pathway. In humans, perinatal exposure to dioxin-like PCBs is associated with neurodevelopmental toxicity in children. Yet, the full potential for later-life neurobehavioral effects that result from early-life low level exposure to dioxin-like PCBs is not well understood. The objective of this study was to determine the effects of developmental exposure to low levels of dioxin-like PCBs on early- and later-life behavioral phenotypes using zebrafish as a model system. We exposed zebrafish embryos to either vehicle (DMSO) or low concentrations of PCB126 (0.3, 0.6, 1.2nM) for 20h (4-24h post fertilization), and then reared them to adulthood in clean water. Locomotor activity was tested at two larval stages (7 and 14 days post fertilization). Adult fish were tested for anxiety-related behavior using the novel tank and shoaling assays. Adult behavioral assays were repeated several times on the same group of fish and effects on intra- and inter-trial habituation were determined. While there was no effect of PCB126 on larval locomotor activity in response to changes in light conditions, developmental exposure to PCB126 resulted in impaired short- and long-term habituation to a novel environment in adult zebrafish. Cyp1a induction was measured as an indicator for AHR activation. Despite high induction at early stages, cyp1a expression was not induced in the brains of developmentally exposed adult fish that showed altered behavior, suggesting that AHR was not activated at this stage. Our results demonstrate the effectiveness of the zebrafish model in detecting subtle and delayed behavioral effects resulting from developmental exposure to an environmental contaminant.

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.

Toxicological profile of ultrapure 2,2',3,4,4',5,5'-heptachlorbiphenyl (PCB 180) in adult rats

PCB 180 is a persistent non-dioxin-like polychlorinated biphenyl (NDL-PCB) abundantly present in food and the environment. Risk characterization of NDL-PCBs is confounded by the presence of highly potent dioxin-like impurities. We used ultrapure PCB 180 to characterize its toxicity profile in a 28-day repeat dose toxicity study in young adult rats extended to cover endocrine and behavioral effects. Using a loading dose/maintenance dose regimen, groups of 5 males and 5 females were given total doses of 0, 3, 10, 30, 100, 300, 1000 or 1700 mg PCB 180/kg body weight by gavage. Dose-responses were analyzed using benchmark dose modeling based on dose and adipose tissue PCB concentrations. Body weight gain was retarded at 1700 mg/kg during loading dosing, but recovered thereafter. The most sensitive endpoint of toxicity that was used for risk characterization was altered open field behavior in females; i.e. increased activity and distance moved in the inner zone of an open field suggesting altered emotional responses to unfamiliar environment and impaired behavioral inhibition. Other dose-dependent changes included decreased serum thyroid hormones with associated histopathological changes, altered tissue retinoid levels, decreased hematocrit and hemoglobin, decreased follicle stimulating hormone and luteinizing hormone levels in males and increased expression of DNA damage markers in liver of females. Dose-dependent hypertrophy of zona fasciculata cells was observed in adrenals suggesting activation of cortex. There were gender differences in sensitivity and toxicity profiles were partly different in males and females. PCB 180 adipose tissue concentrations were clearly above the general human population levels, but close to the levels in highly exposed populations. The results demonstrate a distinct toxicological profile of PCB 180 with lack of dioxin-like properties required for assignment of WHO toxic equivalency factor. However, PCB 180 shares several toxicological targets with dioxin-like compounds emphasizing the potential for interactions.

Impact of lycopene on epididymal androgen and estrogen receptors' expression in polychlorinated biphenyls-exposed rat

The aim of the study was to evaluate the androgen (AR) and estrogen receptors' (ER) expression in epididymis of polychlorinated biphenyls (PCBs)-exposed rats. The rats were assigned to groups. Group I controls were treated with corn oil 80 µL/d intraperitoneally (ip), group II were treated with 2 mg/kg/d of A1254 ip; and group III were treated with 2 mg/kg/d of A1254 ip along with simultaneous oral supplementation of 4 mg/kg/d lycopene . The treatment was given daily for 30 days. After 24 hours of treatment, the rats were killed, and the epididymal regions (caput, corpus, and cauda) were dissected out, weighed, and prepared to estimate the levels of sialic acid, glyceryl phosphoryl choline (GPC), hydrogen peroxide (H2O2), and lipid peroxidation (LPO). The messenger RNA (mRNA) expressions of AR, ERα, and ERβ were analyzed by reverse transcriptase-polymerase chain reaction, and ERα and ERβ protein expressions were analyzed by immunoblotting. The toxicity of PCBs was also confirmed by histology. There was a marked decrease in epididymal weight, sialic acid, and GPC levels, while oxidative stress markers H2O2 and LPO were increased in PCBs-treated rats. The mRNA and protein expression of AR, ERα, and ERβ were decreased in PCBs-treated groups, and the histology confirms the cytoplasmic damage in the regions of caput, corpus, and cauda in PCBs-treated rats. Simultaneous supplementation of lycopene to PCBs-exposed rats resulted in significant decrease in the oxidative stress markers as that of control, while the AR, ERα, and ERβ gene expressions were near to control. The results suggest that lycopene has ameliorative effect against PCBs-induced toxicity in epididymis.

Prenatal exposure to polychlorinated biphenyls and child neuropsychological development in 4-year-olds: an analysis per congener and specific cognitive domain

Polychlorinated biphenyls (PCB) are synthetic organochlorine compounds with potential neurotoxic effects. Although negative effects on neuropsychological development have been observed in previous studies on PCB exposure, there are inconsistencies in these effects at current exposure levels of these compounds which are much lower than for previous generations. This study aimed to disentangle the effects of prenatal and postnatal PCB exposure on neuropsychological development at 4 years of age. This study is based on a population-based birth cohort design established in Menorca (Spain) as part of the INMA [Environment and Childhood] Project. We assessed general neuropsychological development using the McCarthy Scales of Children's Abilities (MCSA). A total of 422 4-year old children were assessed with the MCSA. Levels of PCBs were measured in cord blood (n=405) and in blood samples taken at 4 years (n=285). We found no statistically significant effects of the sum of prenatal PCBs on MCSA scores. Nevertheless, individual congener analyses yielded significant detrimental effects of prenatal PCB153 on the majority of MCSA scores, while no effects were reported for other congeners. The levels of PCBs at 4 years of age were not associated with neuropsychological development. Thus, prenatal exposure to low-level concentrations of PCBs, particularly PCB153, was associated with an overall deleterious effect on neuropsychological development at 4 years of age, including negative effects on executive function, verbal functions and visuospatial abilities, but not on motor development.

Mother counts: how effects of environmental contaminants on maternal care could affect the offspring and future generations

Various compounds of anthropogenic origin represent environmental contaminants (EC) that penetrate the food chain and are frequently detected in human milk and maternal blood at the time of delivery. These ECs can affect the development of the fetus and can be transferred to the newborn during lactation. Many studies have used animal models to study the impact of ECs on the development of the nervous system and have reported effects of early exposure on neural and neuroendocrine systems and on behavior, when the exposed animals are tested as adults. Some of these effects persist across generations and may involve epigenetic mechanisms. The majority of these studies in developmental toxicology treat the pregnant or lactating animal with ECs in order to deliver the contaminants to the developing offspring. Almost universally, the mother is viewed as a passive conduit for the ECs, and maternal behavior is rarely assessed. Here we review the literature on the effects of ECs on maternal care and find mounting evidence that important components of the care given to the offspring are affected by maternal exposure to different ECs. Some of these changes in maternal behavior appear to be secondary to changes in the behavior and/or stimulus properties of the exposed offspring, but others are likely to be direct effects of the ECs on the maternal nervous and endocrine systems. Considering the extent to which the quality of maternal care affects the development of the offspring, it becomes imperative to determine the contributions that changes in maternal behavior make to the deficits traditionally ascribed solely to direct effects of ECs on the developing organism. Given the complexity and importance of mother-infant interactions, future research on developmental toxicology must consider the effects of ECs not only on the offspring, but also on the mother and on the interactions and social bond between mother and infant.

Development of TEFs for PCB congeners by using an alternative biomarker--thyroid hormone levels

Polychlorinated biphenyls (PCBs) are ubiquitous toxic contaminants. Health risk assessment for this class of chemicals is complex: the current toxic equivalency factor (TEF) method covers dioxin-like (DL-) PCBs, dibenzofurans, and dioxins, but excludes non-DL-PCBs. To address this deficiency, we evaluated published data for several PCB congeners to determine common biomarkers of effect. We found that the most sensitive biomarkers for DL-non-ortho-PCB 77 and PCB 126 are liver enzyme (e.g., ethoxyresorufin-O-deethylase, EROD) induction, circulating thyroxine (T4) decrease, and brain dopamine (DA) elevation. For DL-ortho-PCB 118 and non-DL-ortho-PCB 28 and PCB 153, the most sensitive biomarkers are brain DA decrease and circulating T4 decrease. The only consistent biomarker for both DL- and non-DL-PCBs is circulating T4 decrease. The calculated TEF-(TH), based on the effective dose to decrease T4 by 30% (ED(30)) with reference to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), is identical to both TEF-(WHO98) and TEF-(WHO05) for TCDD and DL-PCBs (correlation coefficients are r=1.00, P<0.001; and r=0.99, P<0.001, respectively). We conclude that T4 decrease is a prospective biomarker for generating a new TEF scheme which includes some non-DL-congeners. The new TEF-(TH) parallels the TEF-(WHO) for DL-PCBs and, most importantly, is useful for non-DL-PCBs in risk assessment to address thyroid endocrine disruption and potentially the neurotoxic effects of PCBs.

Altered stress-induced cortisol levels in goats exposed to polychlorinated biphenyls (PCB 126 and PCB 153) during fetal and postnatal development

Short-term stress exposure is associated with activation of the hypothalamic-pituitary-adrenal (HPA) axis and a consequent rise in blood glucocorticoids and catecholamines, from the adrenal cortex and medulla, respectively. The HPA axis is a potential target for some persistent organic pollutants, among which polychlorinated biphenyls (PCB) were found to be modulators of the mammalian endocrine system. PCB are distributed globally in the environment, in food chains, and are transferred to the fetuses of pregnant animals and via mother's milk to suckling offspring. In the present study it was postulated that intrauterine and lactational exposure to either of two single congeners of PCB (PCB 153 and PCB 126, respectively) might affect basal cortisol concentrations, and also the cortisol response to short-term stress in adulthood. Thus, pregnant goats were orally exposed to one of these PCB congeners from d 60 of gestation until delivery, and their offspring studied. Low-dose exposure to PCB 153 and PCB 126 resulted in significantly lower mean basal cortisol concentrations in goat offspring during certain periods of pubertal development and their first breeding season. Male goat kids exposed to either PCB congener showed a greater and more prolonged rise in plasma cortisol levels than controls when animals were subjected to mild stress at 9 mo of age using frequent blood sampling. Neither the basal maternal cortisol plasma level nor goat kid adrenal masses were affected by PCB exposure.

Immunologic and neurodevelopmental susceptibilities of autism

Symposium 5 focused on research approaches that are aimed at understanding common patterns of immunological and neurological dysfunction contributing to neurodevelopmental disorders such as autism and ADHD. The session focused on genetic, epigenetic, and environmental factors that might act in concert to influence autism risk, severity and co-morbidities, and immunological and neurobiological targets as etiologic contributors. The immune system of children at risk of autism may be therefore especially susceptible to psychological stressors, exposure to chemical triggers, and infectious agents. Identifying early biomarkers of risk provides tangible approaches toward designing studies in animals and humans that yield a better understanding of environmental risk factors, and can help identify rational intervention strategies to mitigate these risks.

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.

Effects of polychlorinated biphenyls on maternal odor conditioning in rat pups

Polychlorinated biphenyls (PCBs) are pervasive environmental contaminants that can have damaging effects on physiologic, motoric and cognitive function. Results from studies on PCBs and behavior have shown that exposure can alter learning and memory processes and that these shifts in cognitive abilities can be related to changes in hormonal and neural function. Little experimentation has been done on the impact of exposure to PCBs on social and emotional development. Previous work has shown that exposure to PCBs in children can alter play behavior. Importantly, exposure to PCBs has been found to change aspects of maternal-offspring interactions in rodents. The present study examined the impact of PCBs on maternal odor conditioning in rat pups 12-14 days of age. A modified version of the conditioned place preference paradigm was used that incorporated a maternal-associated odor cue (lemon scent) as the conditioned stimulus. PCBs significantly depressed the preference for the maternal-associated cue but did not impair discrimination for a novel odor. These effects could arise due to changes in the social dynamics between the dam and offspring after co-exposure to PCBs. For example, dams exposed to PCBs during gestation have been found to show elevated grooming directed towards pups exposed to PCBs. This change in maternal care can have dramatic effects on behavioral and hormonal systems in the developing rat pup. In conclusion, perinatal PCBs alter important social behaviors of both the mother and pup, and these alterations could have long-lasting effects on behavioral, cognitive and emotional development.

Effects of prenatal chlordecone on sexually differentiated behavior in adult rats

In rodents, exposure to estrogens during early development masculinizes the structure and function of the brain. The effects of early exposure to estrogens or estrogenic compounds can be evaluated by neurobehavioral testing after puberty. In this study, the effect of developmental exposure to the chlorinated pesticide, chlordecone (CD) on sexually differentiated behaviors in adults was investigated because CD binds to estrogen receptors and causes estrogenic effects in the reproductive tract of humans and rodents at relatively high doses. Pregnant Sprague-Dawley rats were exposed to 5 mg/kg CD by intraperitoneal injection on gestation day 16 (GD 16). Offspring were gonadectomized on postnatal day 50 (PN 50) to remove the effects of circulating hormones and were sequentially tested for sex-typic spontaneous behaviors in an open field and elevated plus maze, and for male and female mating behavior following the appropriate steroid regimen. Female rats exposed in utero to CD showed an increased ratio of inner to total crossings in the open field and significantly increased lordosis and male mounting as compared to female control rats. Male rats exposed in utero to CD showed significantly increased lordosis as compared to male control rats and no change in male mating behaviors. Permanent changes in adult behavior were consistent with both estrogenic and anti-estrogenic actions following developmental exposure to CD at the dose tested.

Neurochemical targets and behavioral effects of organohalogen compounds: an update

Organohalogen compounds (OHCs) have been used and still are used extensively as pesticides, flame retardants, hydraulic fluids, and in other industrial applications. These compounds are stable, most often lipophilic, and may therefore easily biomagnify. Today these compounds are found distributed both in human tissue, including breast milk, and in wildlife animals. In the late 1960s and early 1970s, high levels of the polychlorinated biphenyls (PCBs) and the pesticide dichlorodiphenyl trichloroethane (DDT) were detected in the environment. In the 1970s it was discovered that PCBs and some chlorinated pesticides, such as lindane, have neurotoxic potentials after both acute and chronic exposure. Although the use of PCBs, DDT, and other halogenated pesticides has been reduced, and environmental levels of these compounds are slowly diminishing, other halogenated compounds with potential of toxic effects are being found in the environment. These include the brominated flame retardants, chlorinated paraffins (PCAs), and perfluorinated compounds, whose levels are increasing. It is now established that several OHCs have neurobehavioral effects, indicating adverse effects on the central nervous system (CNS). For instance, several reports have shown that OHCs alter neurotransmitter functions in CNS and Ca2+ homeostatic processes, induce protein kinase C (PKC) and phospholipase A2 (PLA2) mobilization, and induce oxidative stress. In this review we summarize the findings of the neurobehavioral and neurochemical effects of some of the major OHCs with our main focus on the PCBs. Further, we try to elucidate, on the basis of available literature, the possible implications of these findings on human health.

Motor function following developmental exposure to PCBS and/or MEHG

Recent studies raise concern for combined exposure to polychlorinated biphenyls (PCBs) and methylmercury (MeHg), two environmental contaminants that are found in fish and seafood. Past accidental poisonings in humans show that exposure to high levels of either contaminant is associated with motor impairments, including alterations in cerebellar functions such as balance and coordination. Epidemiological studies of lower level exposures suggest some neuromotor impairment in exposed children, but the majority of these studies have focused on cognitive endpoints rather than examining a full-range of motor function. In particular, the cerebellum could be a sensitive target for combined PCB and MeHg toxicity. MeHg exposure during development damages the cerebellum along with cortical areas, and PCBs may also cause cerebellar damage via thyroid hormone disruption during development. In addition, in vitro studies report interactive effects of PCBs and MeHg on ryanodine-sensitive calcium signaling. Ryanodine receptors are found especially within the cerebellum, and alterations in calcium signaling within the cerebellum could impair long-term depression and subsequent motor learning. This article reviews the motor impairments reported in humans and laboratory animals following exposure to PCBs and/or MeHg during development. There is need for a better understanding of the interactive effects of PCBs and MeHg, especially in regard to motor function.

Maternal-fetal distribution and transfer of dioxins in pregnant women in Japan, and attempts to reduce maternal transfer with Chlorella (Chlorella pyrenoidosa) supplements

Dioxins can be transferred from mother to fetus via the placenta, or to nursing infants via breast milk, potentially causing developmental health problems in children. To assess pediatric health risks from dioxins, exposure of mothers and children to dioxins must be clarified. Methods of reducing maternal transfer of dioxins should also be investigated. Concentrations of 28 dioxin (polychlorinated dibenzo-p-dioxins, polychlorinated dibenzofurans, and co-planar polychlorinated biphenyls) congeners in blood, adipose tissue, breast milk, cord blood and placenta collected from 44 pregnant Japanese women were measured. In addition, to investigate potential reductions in maternal transfer of dioxins, 23 pregnant women were instructed to take Chlorella pyrenoidosa supplements during pregnancy. Correlations were observed between dioxin total toxic equivalents (total TEQ) in blood and total TEQ in adipose tissue (r=0.913, P<0.0001), breast milk (r=0.695, P=0.0007), and cord blood (r=0.759, P<0.0001). Dioxin levels transferred to fetuses and nursing infants reflect cumulative maternal concentrations of dioxins. A linear regression equation was introduced to predict total TEQ in breast milk and cord blood from dioxin levels in maternal blood, which should prove useful in evaluating fetal and infant risk of dioxin exposure. Total TEQ in cord blood were approximately 26% lower than in maternal blood (P<0.0001). The results of this study suggest that transplacental transfer differs depending on the dioxin congener. Total TEQ in breast milk were approximately 30% lower in the Chlorella group than in controls (P=0.0113). This finding suggests that maternal transfer of dioxins can be reduced using dietary measures such as Chlorella supplements.

Toxicological Effects of Gestational and Lactational Exposure to a Mixture of Persistent Organochlorines in Rats: Systemic Effects

A large multi-disciplinary study was conducted to investigate the systemic, neurodevelopmental, neurochemical, endocrine, and molecular pathological effects of a mixture of reconstituted persistent organochlorine pollutants (POP) based on the blood profiles of Canadians residing in the Great Lakes/St. Lawrence region. This report outlines the overall study design and describes the systemic effects in rat offspring perinatally exposed to the POP mixture. Maternal rats were administered orally 0, 0.013, 0.13, 1.3, or 13 mg/kg bw/day of the mixture from gestational day (GD) 1 to postnatal day (PND) 23. Positive and negative controls were given Aroclor 1254 (15 mg/kg bw/day) and corn oil (vehicle), respectively. The rat pups were reared, culled to 8 per litter, and killed on postnatal days 35, 70, and 350, at which time tissues were collected for analysis. Exposure to high doses of the mixture elicited clinical, biochemical, and pathological changes and high mortality rates in rat offspring. Aroclor 1254 produced similar effects but a lower mortality than was seen in POP mixture groups. Biochemical changes consisted of increased liver microsomal activities and elevated serum cholesterol. Hepatomegaly was observed in the highest dose group of the mixture and in the positive control. Liver, thymus, and spleen were the target organs of action. Microscopic changes in the liver consisted of vacuolation and hypertrophy, and those in the thymus were characterized by reduced cortical and medullary volume. The spleen showed a treatment-related reduction in lymphocyte density and lymphoid areas. This study demonstrates that exposure to the POP mixture up to 13 mg/kg/day perinatally produced growth suppression, elevated serum cholesterol, increased liver microsomal enzyme activities, and immunopathological changes in the thymus and spleen, and lethality. Most of the effects were seen at dose levels much higher than expected human exposure.

Formulation and characterization of an experimental PCB mixture designed to mimic human exposure from contaminated fish

Each environmental exposure matrix contains a unique mixture of PCB congeners. Since several congener types have multiple and distinct biological actions, it is important to characterize congener profiles in exposure sources. The Fox River Environment and Diet Study (FRIENDS) is assessing the human health effects of consumption of PCB-contaminated fish from the Fox River in northeastern Wisconsin. Concurrent laboratory studies required the formulation of a dosing solution which closely mimicked the human PCB exposure from fish. PCB congener profiles from Fox River walleye were compared to profiles for various theoretical mixtures having different relative percentages of Aroclors by weight. The theoretical mixture which provided the best approximation of the Fox River fish PCB profile contained 35% 1242, 35% 1248, 15% 1254, and 15% 1260. A PCB mixture was formulated to match this theoretical construct, and the congener profile for the mixture of Aroclors was determined by capillary column gas chromatography with electron capture detection (GC/ECD). The relative percent of each congener was compared to the PCB congener profile of the theoretical Aroclor mixture and that for Fox River walleye. The specific congeners differed on average by 17% from the theoretical Aroclor mixture predicted values, and the specific congeners measured in the mixture were on average within 71% of those reported for Fox River fish. The mixture was found to have relatively low AhR activity but high RyR activity. Indirect comparisons suggest that in vivo toxicity was slightly greater than that for Aroclor 1254. This illustrates that Aroclor mixtures are useful for formulating dosing solutions which closely approximate actual environmental exposures.

Perinatal exposure to polychlorinated biphenyls differentially affects cerebellar development and motor functions in male and female rat neonates

Perinatal exposure to polychlorinated biphenyls (PCBs) interacts with genetics and impacts the course of the central nervous system (CNS) development in both humans and animals. To test the hypothesis that the neurobehavioral impairments, and specifically motor dysfunctions following perinatal PCB exposure in rats are associated with changes in a specific brain region, the cerebellum, we compared neurodevelopment, motor behavior, cerebellar structure, and protein expression in rat neonates exposed to the PCB mixture Aroclor 1254 (A1254, 10.0 mg/kg/day) from gestational day 11 until postnatal day (P) 21 with that of controls. Body mass of PCB-exposed pups was not affected at birth, but was significantly lower than that of controls between birth and weaning; by P21 the difference was greater in females than in males. A1254 exposure delayed ear unfolding and impaired performance on the following behavioral tests: (1) righting response on P3-P6; (2) negative geotaxis on P5-P7; (3) startle response on P10-P12; and (4) a rotorod on P12, with PCB-male pups more severely affected than female. Changes in the behavior of PCB pups were associated with changes in cerebellar structure and protein expression. Cerebellar mass was more reduced in PCB-male than PCB-female pups. Analysis of selected cerebellar proteins revealed an increase in GFAP expression, greater in male than in female, and a decrease in L1 expression in both sexes. These results suggest that PCB exposure affects behavior and cerebellar development differently in male and female rat neonates, with greater effects in males. Further studies of neonatal PCB exposure will establish whether the environmental pollutants can contribute to the sex-related preponderance of certain neuropsychiatric disorders.

Developmental neurotoxicity of PHAHs: Endocrine-mediated and general behavioral endpoints in adult male rats

During development, gonadal steroids exert effects on the nervous system which are long-lasting or organizational, in contrast to the transient activational actions in adulthood. Therefore, disturbance of neuroendocrine functions by developmental exposure to polyhalogenated aromatic hydrocarbons (PHAHs) is likely to affect sex-dependent behavior in adults. Our previous data revealed effects of maternal PCB exposure on sexual differentiation of the brain and subsequent sweet preference as sexually dimorphic behavior in adult offspring. Present research is focused on brominated flame retardants because of their wide-spread use and accumulation in human breast milk. Pregnant Long Evans rats were SC injected with PBDE 99 (2,2',4,4',5-PBDE) daily from gestational day 10 to 18. For comparison, an additional group was exposed to Aroclor 1254. Preliminary results indicate a dose-related increase in sweet preference in adult male offspring exposed to PBDE. Exposure also led to decreases in testosterone and estradiol serum levels. Additional decreases were detected in male anogenital distance. There were no changes of locomotor activity in the open field. On haloperidol-induced catalepsy, latencies were prolonged in all exposed males. In summary, PBDE induced endocrine effects and concomitant changes of sex-dependent behavior similar to PCBs. Outcome of general behavior suggests an involvement of dopaminergic processes in developmental PBDE exposure.

Coplanar PCB congeners increase uterine weight and frontal cortical dopamine in the developing rat: implications for developmental neurotoxicity

We show that developmental exposure of the laboratory rat to the coplanar polychlorinated biphenyl (PCB) congener 3,4,3',4'-tetrachlorobiphenyl (TCB) and the structurally similar congener 3,4,5,3',4'-pentachlorobiphenyl (PtCB) elevates dopamine (DA) concentrations in the prefrontal cortex (PFC). To determine whether these coplanar congeners are estrogenic, and may thus contribute to the elevations in PFC DA, we measured uterine wet weight (UWW) in prepubertal rats exposed to TCB or PtCB. For comparison, additional animals were exposed to either the ortho-substituted congener 2,4,2',4'-tetrachlorobiphenyl (o-TCB) or 3,4,5,3',4',5'-hexachlorobiphenyl (HCB), a coplanar congener highly resistant to metabolism. Both TCB and PtCB increased UWW, but this effect was blocked after exposure to the anti-estrogen ICI 182,780. Neither o-TCB nor HCB altered UWW. These results demonstrate that certain coplanar PCB congeners and/or their metabolites, are estrogenic, and suggest that exposure during critical periods of neuronal development may increase central DA concentrations, and by inference, alter behavior.

Hippocampal long-term potentiation (LTP) is reduced by a coplanar PCB congener

Neurotoxicity of polychlorinated biphenyls (PCBs) is usually ascribed to the ortho-substituted congeners. We have examined the effects of acute perfusion of 3,3',4,4'-tetrachlorobiphenyl (PCB 77), a coplanar, dioxin-like congener, on long-term potentiation (LTP) in the Schaffer collateral-CA1 and the mossy fiber-CA3 pathways in mouse hippocampus. LTP in both pathways was blocked by PCB 77, with a threshold effect at a concentration of 1 microM. LTP is a useful model of learning and memory function in which a patterned stimulation of an afferent pathway produces a persistent increase in the efficacy of synaptic transmission. LTP is reduced by PCB mixtures and ortho-substituted congeners at concentrations comparable to those studied here. These observations provide evidence in support of the hypothesis that dioxin-like and non-dioxin-like PCB congeners are equally potent in causing the cognitive decrements seen in children exposed prenatally to PCBs.

Sexual dimorphism in cerebellar structure, function, and response to environmental perturbations

Sexual dimorphism of CNS structure and function has been observed in humans and animals, but remains relatively unrecognized in the context of the cerebellum. Recent research in our laboratory has examined whether these gender differences extend to cerebellar structure and function, as well as the impact of environmental factors on the developing cerebellum. Perinatal exposure to both chemical and physical perturbations in the environment (in our experiments, PCBs or hypergravity) affects growth, neurodevelopment, and motor coordination differently in males and females. These neurodevelopmental and behavioral effects are accompanied by sex-related changes in cerebellar mass and cerebellar protein expression. Exposure to chemical toxins (PCBs) resulted in more dramatic neurodevelopmental and behavioral changes in male neonates. It is possible that gender-related differences in male and female cerebellar structure and function are related to sex-specific development of the cerebellum and sex-specific distribution of specific receptors, local synthesis of trophic factors, and maturation of the pituitary hypophesial axis. These sex-related differences may underlie the sex-specific preponderance of certain neuropsychiatric disorders, and must be incorporated in the design of future basic and clinical investigations.

Exposure to PCB 77 affects the maternal behavior of rats

Polychlorinated biphenyls are environmental contaminants known to affect neurobehavioral development in many laboratory studies using different animal models. Because of their bioaccumulation and long half-life they are a serious concern for our own species. The dioxin-like PCB congener 3,4,3',4'-tetrachlorobiphenyl (PCB 77) has estrogenic and anti-estrogenic properties, and has been shown to affect brain chemistry and behavior of developing rats when administered during gestation. Since many developmental outcomes in mammals depend upon the type of maternal care provided by the dams, we investigated the effects of two doses of PCB 77 (2 and 4 mg/kg administered during gestational days 6-18) on the maternal behavior of the treated dams. Both doses of PCB 77 reduced the amount of nursing time in which the dams displayed the high-crouch posture over postnatal days 1-6. In addition, the high dose increased the amount of maternal licking and grooming of the litters and the amount of time the dams spent on the nest. The high dose also increased pup mortality, and both doses reduced the weight gain of the litters during the first 6 days of life. These results document effects of PCB 77 on maternal behavior and serve to raise questions about the importance of maternal contributions to the developmental effects of this and similar contaminants.

Chronic exposure to trichloroethylene affects neuronal plasticity in rat hippocampal slices

Inhalational exposure to organic solvents is known to exert neurotoxic effects. Using the new multielectrode dish system (Panasonic) the effects of chronic exposure to trichloroethylene (TCE) on neuronal plasticity were assessed in different regions of the adult rat brain. Two groups of Long-Evans rats were exposed to 0 ppm or 500 ppm TCE, respectively, 6 h/day, 5 days/week for 6 months. Long-term potentiation (LTP) as well as paired-pulse potentiation/inhibition were assessed in slices from the visual cortex and the hippocampus. In addition, several behavioral tests were performed. Trichloroethanol concentrations were measured in blood and trichloroacetic acid concentrations were determined in urine. While TCE exposure impaired LTP as well as paired-pulse potentiation in hippocampal slices, no effects were seen in cortical slices. Our data demonstrate brain region specific functional changes following TCE exposure with the hippocampus being more vulnerable than the visual cortex. The behavioral measurements revealed no TCE related effects.

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.

Developmental exposure to polychlorinated biphenyls affects sexual behavior of rats

Polychlorinated biphenyls (PCBs) are persistent environmental contaminants that have the potential to disrupt reproduction through a variety of different pathways. In the present study, we investigated the effects of fetal and lactational PCB exposure on reproductive behavior in male and female laboratory rats. These pregnant rats were injected daily with either 2,4,2',4'-tetrachlorobiphenyl (PCB 47) at the dosage of 1 or 20 mg/kg body weight or 3,4,3',4'-tetrachlorobiphenyl (PCB 77) at the dosage of 0.25 or 1 mg/kg body weight or sesame oil (control group) from gestational days 7 to 18. Offspring were then tested for sexual behavior as adults. Exposure to both PCB 77 and PCB 47 reduced the level of sexual receptivity in the female offspring, but had no detectable effects on the sexual behavior of the male offspring. In addition to changes in adult sexual behavior in the females, both PCBs produced a significant increase in the females' anogenital distance, suggesting a modification of androgen responsiveness in females resulting from PCB exposure during development. Similar effects were not seen with the males.

EthoVision: a versatile video tracking system for automation of behavioral experiments

The need for automating behavioral observations and the evolution of systems developed for that purpose is outlined. Video tracking systems enable researchers to study behavior in a reliable and consistent way and over longer time periods than if they were using manual recording. To overcome limitations of currently available systems, we have designed EthoVision, an integrated system for automatic recording of activity, movement, and interactions of animals. The EthoVision software is presented, highlighting some key features that separate EthoVision from other systems: easy file management, independent variable definition, flexible arena and zone design, several methods of data acquisition allowing identification and tracking of multiple animals in multiple arenas, and tools for visualization of the tracks and calculation of a range of analysis parameters. A review of studies using EthoVision is presented, demonstrating the system's use in a wide variety of applications. Possible future directions for development are discussed.

Neurotransmitter concentrations and binding at dopamine receptors in rats after maternal exposure to 3,4,3',4'-tetrachlorobiphenyl: the role of reduced thyroid hormone concentrations

Polychlorinated biphenyls (PCBs) are environmental contaminants, which accumulate in the food chain and are transferred to the offspring during prenatal development through the placenta and postnatally via breast milk. It is reported that PCBs exert effects on thyroid hormone levels and brain neurotransmitter levels. Both actions may alter neuronal development. The aim of the present study was to investigate, if PCB-induced effects on concentrations of catecholamines and serotonin can be attributed to PCB-induced reductions in thyroid hormone concentrations. In addition, binding to dopamine D(1) and D(2) receptors was examined. Time-mated Wistar rats were treated prenatally with 1 mg 3,4,3',4'-tetrachlorobiphenyl (PCB 77)/kg bodyweight or the vehicle. A third group serving as the positive control received perinatally 5 mg propylthiouracil (PTU)/l drinking water. There were no overt toxic signs in dams or offspring. Thyroid hormone measurements demonstrated effects in dams and offspring up to postnatal day 40. In particular, total T(4) in serum and in the thyroid were decreased in PCB- and PTU-treated dams and offspring. Only PTU exposed rats exhibited significantly increased concentrations of TSH in the serum and pituitary. Measurement of neurotransmitters revealed changes in the PCB-exposed offspring at PND 40, while PTU-treatment was without effect. Dopamine and DOPAC were increased in the medial prefrontal cortex. In adulthood, there were no PCB-related effects on thyroid hormones and neurotransmitters. Binding studies of dopamine D1 and D2 receptors demonstrated that PCB and PTU had no influence on receptor concentration and affinity. Comparison of PCB 77 exposed offspring to PTU exposed offspring demonstrated differential effects on TSH and neurotransmitter levels, the latter result indicating that not all PCB-induced effects on the nervous system can be ascribed to decreases in thyroid hormone concentrations.

2,2',4,6,6'-pentachlorobiphenyl induces apoptosis in human monocytic cells

Polychlorinatedbiphenyls (PCBs) are a group of persistent and widely dispersed environmental pollutants, some of which may be immunotoxic. In the present study, we investigated the effect of PCBs on immune system by assessing apoptotic cell death in human monocytic U937 cells. Among the various congeners tested, 2,2',4,6, 6'-pentachlorobiphenyl (PeCB), a highly ortho-substituted congener, specifically induced DNA fragmentation, a hallmark of apoptosis, while the other examined di-, tri-, tetra-, and pentachlorobiphenyls did not. To further study the 2,2',4,6,6'-PeCB-induced cell death, various features of apoptosis were examined. 2,2',4,6,6'-PeCB caused a decrease in cell viability and induced cellular morphologic features characteristic of apoptosis such as chromatin aggregation and apoptotic bodies. In addition, caspase-3, an executioner of apoptosis, was activated and its substrate, poly(ADP-ribose) polymerase (PARP), was cleaved during 2,2',4,6,6'-PeCB-induced apoptosis. In contrast, 3,3',4,4',5-PeCB, a congener of coplanar structure, as well as 2,3,7,8-TCDD did not induce apoptosis in these human monocytic cells, although they potently induced CYP 1A1 in human hepatoma Hep G2 cells. Taken together, the data indicate that 2,2',4,6,6'-PeCB induces apoptosis in human monocytic cells through a mechanism that is independent of the arylhydrocarbon receptor. This suggests a possibly separate mechanism by which PCBs cause immunosuppression.

Role of protein phosphorylation in activation of phospholipase A2 by the polychlorinated biphenyl mixture Aroclor 1242

Polychlorinated biphenyls (PCBs) activate neutrophils to induce degranulation and undergo superoxide production through a mechanism that involves stimulation of phospholipase A(2) (PLA(2)). Since the biochemical processes leading to the PCB-induced activation of this enzyme are unknown, the objective of this study was to determine whether protein phosphorylation has a role in this mechanism. Isolated rat neutrophils were labeled with [(3)H]-arachidonic acid ([(3)H]-AA), and activation of PLA(2) was determined from release of radioactivity into the medium. Exposure to the PCB mixture Aroclor 1242 induced release of [(3)H]-AA, and pretreatment with bromoenol lactone (BEL), an inhibitor of calcium-independent PLA(2), diminished release by 80%. Genistein, an inhibitor of tyrosine kinases, caused a small but significant decrease in Aroclor 1242-stimulated release of [(3)H]-AA. Daidzein, a genistein analog with no activity to inhibit tyrosine kinases, had no effect on [(3)H]-AA release. An inhibitor of p38 mitogen-activated protein kinase (MAPK), SB203580, did not affect Aroclor 1242-induced PLA(2) activity at concentrations selective for p38 MAPK; however, PD 98059, which inhibits MAPK kinase (MEK), decreased [(3)H]-AA release to about the same extent as genistein. Treatment of neutrophils with Aroclor 1242 induced phosphorylation of p44 MAPK, and this phosphorylation was unaffected by BEL but was inhibited by PD 98059. Staurosporine, a nonselective inhibitor of protein kinase C (PKC), inhibited PCB-induced release of [(3)H]-AA. Ro 32-0432, a selective inhibitor of PKC(alpha) and PKC(beta1), produced the greatest degree of inhibition (40%) among the tested protein kinase inhibitors. These results suggest that tyrosine kinases, PKC, and the MEK/MAPK pathway are involved in a fraction of Aroclor 1242-induced activation of PLA(2).

Neurotoxic effects of endocrine disruptors

Endocrine disrupting chemicals are a newly defined category of environmental contaminants that may affect animal and human populations by interfering with normal hormone action. There is substantial concern that these agents could have a range of subtle and long-lasting effects. Because of the sensitivity of the developing central nervous system to low levels of endogenous gonadal hormones during development, the central nervous system may be a target for the action of endocrine disrupting chemicals.

Developmental exposure of rats to a reconstituted PCB mixture or aroclor 1254: effects on organ weights, aromatase activity, sex hormone levels, and sweet preference behavior

Polychlorinated biphenyls (PCBs) are lipophilic industrial chemicals which are regularly detected in human breast milk, serum, and tissues. They possess hormone-modulating properties, and, when transferred transplacentally to the developing fetus, PCBs have been shown to induce persistent sex-specific neurobehavioral deficits. Interactions of PCBs with sex steroid-modulated neural differentiation could in part account for such effects. To test this hypothesis, female Long-Evans rats were exposed via food containing 40 mg/kg of either a reconstituted PCB mixture (RM), composed according to the congener-pattern in human breast milk, or the technical PCB mixture Aroclor 1254 (A1254). The exposure period started 50 days prior to mating and was terminated at birth (postnatal day 0: PND 0). Aromatase (CYP 19) activity was determined in hypothalamus/preoptic area (HPOA) brain-sections from newborn male pups. This enzyme converts testosterone (T) to 17beta-estradiol (E(2)) and plays a key role in sexual brain differentiation. Moreover, serum concentrations of T and E(2), physical development, organ weights, exposure levels, and sex-specific behavior were evaluated at different life stages. On PND 0, a reduced aromatase activity was detected in the HPOA of male RM-pups compared to controls. Female RM-weanlings exhibited significantly elevated uterine wet weights on PND 21, which is a marker for estrogenic activity. In the adult stage (PND 170), male offspring with maternal exposure to either PCB mixture showed markedly reduced testes weights and serum testosterone levels, thus demonstrating persistent antiandrogenic effects. On PND 180, male RM-rats exhibited a behavioral feminization in a sweet preference test, suggesting long-lasting changes in neuronal brain organization caused by the perinatally suppressed aromatase activity. The results suggest that maternal exposure to the RM, the pattern of which is similar to the PCB spectrum in human milk, results in more distinct effects on sex steroid-dependent processes and behavior than the technical PCB mixture A1254. PCB levels in brain and adipose tissue of the exposed offspring lay within 1-2 orders of magnitude above background concentrations in humans.