Effects of maternal exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin on parvalbumin- and calbindin-immunoreactive neurons in the limbic system and superior colliculus in rat offspring

Adverse effects of dioxins on cognitive ability and motor performance of 5-year-old children residing in a hotspot of dioxin contamination originating from Agent Orange in Vietnam: A prospective cohort study

Bien Hoa airbase is the most dioxin-polluted hotspot in Vietnam. In 2012, a birth cohort living around Bien Hoa airbase was recruited for assessment of physical and neurological development. In the present study, neurodevelopment scores at 5 years of age were assessed by the Kaufman Assessment Battery for Children, Second Edition and the Movement Assessment Battery for Children, Second Edition for 185 children in Bien Hoa and 104 children in Ha Dong (unexposed control group) to clarify the effects of dioxin. 2,3,7,8-tetrachlorodibenzo-p-dioxin concentrations in breast milk of women in Bien Hoa were approximately three times higher than those of women in Ha Dong (2.33 vs. 0.69 pg/g fat, p < 0.001). In general, neurodevelopment scores were lower in Bien Hoa children than in Ha Dong children. In boys, scores differed for number recall (12.6 vs. 14.0, p = 0.036), triangles (10.7 vs. 12.4, p = 0.005), manual dexterity (8.3 vs. 9.7, p = 0.037), balance (7.4 vs. 10.3, p < 0.001), and total movement scores (8.0 vs. 10.1, p = 0.003). After adjusting for covariates, linear regression analysis indicated that the scores of the triangles, balance, and total movement tests were inversely associated with levels of 2,3,7,8-tetrachlorodibenzo-p-dioxin and of toxic equivalency of polychlorinated dibenzodioxins and polychlorinated dibenzofurans. In girls, scores differed for the triangles test (11.0 vs. 12.6, p = 0.005), hand movement test (9.6 vs. 11.3, p = 0.003), and balance test (9.1 vs. 10.7, p = 0.050); toxic equivalency of polychlorinated dibenzofurans was inversely associated with hand movement and balance scores. Overall, perinatal dioxin exposure appears to have a long-term impact on neurodevelopment.

Gestational and lactational exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin primes cortical microglia to tissue injury

Recent studies have shown that the aryl hydrocarbon receptor (AhR) is expressed in the brain's native immune cells, known as microglia. However, while the impact of exposure to AhR ligands is well studied in the peripheral immune system, the impact of such exposure on immune function in the brain is less well defined. Microglia serve dual roles in providing synaptic and immunological support for neighboring neurons and in mediating responses to environmental stimuli, including exposure to environmental chemicals. Because of their dual roles in regulating physiological and pathological processes, cortical microglia are well positioned to translate toxic stimuli into defects in cortical function via aberrant synaptic and immunological functioning, mediated either through direct microglial AhR activation or in response to AhR activation in neighboring cells. Here, we use gene expression studies, histology, and two-photon in vivo imaging to investigate how developmental exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), a high-affinity and persistent AhR agonist, modulates microglial characteristics and function in the intact brain. Whole cortical RT-qPCR analysis and RNA-sequencing of isolated microglia revealed that gestational and lactational TCDD exposure produced subtle, but durable, changes in microglia transcripts. Histological examination and two-photon in vivo imaging revealed that while microglia density, distribution, morphology, and motility were unaffected by TCDD exposure, exposure resulted in microglia that responded more robustly to focal tissue injury. However, this effect was rectified with depletion and repopulation of microglia. These results suggest that gestational and lactational exposure to AhR ligands can result in long-term priming of microglia to produce heightened responses towards tissue injury which can be restored to normal function through microglial repopulation.

Effects of perinatal dioxin exposure on mirror neuron activity in 9-year-old children living in a hot spot of dioxin contamination in Vietnam

BACKGROUND

For 8 years, we have followed up a birth cohort comprising 241 mother-and-infant pairs living around the Da Nang airbase, a hot spot of dioxin contamination in Vietnam, and have reported the impacts of perinatal dioxin exposure on the neurodevelopment of children at various ages. In the present study, 9 years after birth, we investigated the effects of perinatal dioxin exposure on mu and theta rhythms by analyzing EEG power during the execution and observation of hand movements, which indicate mirror neuron system activity.

METHODS

One hundred fifty-five 9-year-old children (86 boys and 69 girls) from the Da Nang birth cohort participated in the EEG examination with free viewing of hand movements. The dioxin levels in their mothers' breast milk, measured 1 month after birth, were used as perinatal dioxin exposure markers. A log transform of the ratio of EEG power during execution or observation of the hand movements relative to the power during observation of a bouncing ball for theta and mu rhythms was used to evaluate mirror neuron activity.

RESULTS

In both brain hemispheres, the log power ratio in the theta band was significantly higher (i.e., less reduction of power) during observation of hand movements in girls exposed to high levels of TCDD. In boys, however, dioxin congeners other than TCDD, including HxCDDs and several PCDF congeners, contributed to increased log power ratios in the theta band. Particularly for PCDF congeners, the log power ratios in the lowest group among 4 exposure groups were lowest and significantly increased (i.e., decreasing reduction of power) with increasing dose.

CONCLUSION

Perinatal TCDD exposure may influence the mirror neuron system of the brain, which plays an important role for social-emotional behavior in children, particularly in girls living in a hot spot of dioxin contamination in Vietnam.

Application of ImageJ software for quantification of Hand Joint Space Narrowing in Patients with Rheumatoid Arthritis

BACKGROUND

ImageJ software is used to quantify the joint space width (JSW) of hand and wrist in patients with rheumatoid arthritis (RA) as well as in the healthy control group.

METHOD

Forty-one RA patients and 31 healthy controls are included in this study. All of 72 participants underwent digital radiography of the bilateral hand and wrist, then all the images were opened by ImageJ software to measure the width of wrist and hand joint space (total 2160 joints). Joint space narrowing (JSN) was defined if the width was less than the mean - 2SD of the control group.

RESULT

The mean JSW of all sites of wrist and hand joints of RA patients was significantly reduced as compared to those in the control group (p<0.001). There were 37/41 (90.24%) RA patients who had JSN in at least one joint in hand or wrist. In total, 70.89% of joints on the right and 68.46% of joints on the left wrist and hand had JSN.

CONCLUSION

ImageJ software was simple and convenient , which helps rheumatologists quantify the width of joint space for diagnosis and follow-up in RA patients.

Persistent organic pollutants at the synapse: Shared phenotypes and converging mechanisms of developmental neurotoxicity

The developing nervous system is sensitive to environmental and physiological perturbations in part due to its protracted period of prenatal and postnatal development. Epidemiological and experimental studies link developmental exposures to persistent organic pollutants (POPs) including polychlorinated biphenyls, polychlorinated dibenzo-p-dioxins, polybrominated diphenyl ethers, and benzo(a)pyrene to increased risk for neurodevelopmental disorders in children. Mechanistic studies reveal that many of the complex cellular processes that occur during sensitive periods of rapid brain development are cellular targets for developmental neurotoxicants. One area of research interest has focused on synapse formation and plasticity, processes that involve the growth and retraction of dendrites and dendritic spines. For each chemical discussed in this review, we summarize the morphological and electrophysiological data that provide evidence that developmental POP exposure produces long-lasting effects on dendritic morphology, spine formation, glutamatergic and GABAergic signaling systems, and synaptic transmission. We also discuss shared intracellular mechanisms, with a focus on calcium and thyroid hormone homeostasis, by which these chemicals act to modify synapses. We conclude our review highlighting research gaps that merit consideration when characterizing synaptic pathology elicited by chemical exposure. These gaps include low-dose and nonmonotonic dose-response effects, the temporal relationship between dendritic growth, spine formation, and synaptic activity, excitation-inhibition balance, hormonal effects, and the need for more studies in females to identify sex differences. By identifying converging pathological mechanisms elicited by POP exposure at the synapse, we can define future research directions that will advance our understanding of these chemicals on synapse structure and function.

Effects of Low-Dose Gestational TCDD Exposure on Behavior and on Hippocampal Neuron Morphology and Gene Expression in Mice

BACKGROUND

2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) is a persistent and toxic environmental pollutant. Gestational exposure to TCDD has been linked to cognitive and motor deficits, and increased incidence of autism spectrum disorder (ASD) traits in children. Most animal studies of these neurodevelopmental effects involve acute TCDD exposure, which does not model typical exposure in humans.

OBJECTIVES

The aim of the study was to establish a dietary low-dose gestational TCDD exposure protocol and performed an initial characterization of the effects on offspring behavior, neurodevelopmental phenotypes, and gene expression.

METHODS

Throughout gestation, pregnant C57BL/6J mice were fed a diet containing a low dose of TCDD (9  ng TCDD/kg body weight per day) or a control diet. The offspring were tested in a battery of behavioral tests, and structural brain alterations were investigated by magnetic resonance imaging. The dendritic morphology of pyramidal neurons in the hippocampal Cornu Ammonis (CA)1 area was analyzed. RNA sequencing was performed on hippocampi of postnatal day 14 TCDD-exposed and control offspring.

RESULTS

TCDD-exposed females displayed subtle deficits in motor coordination and reversal learning. Volumetric difference between diet groups were observed in regions of the hippocampal formation, mammillary bodies, and cerebellum, alongside higher dendritic arborization of pyramidal neurons in the hippocampal CA1 region of TCDD-exposed females. RNA-seq analysis identified 405 differentially expressed genes in the hippocampus, enriched for genes with functions in regulation of microtubules, axon guidance, extracellular matrix, and genes regulated by SMAD3.

DISCUSSION

Exposure to 9  ng TCDD/kg body weight per day throughout gestation was sufficient to cause specific behavioral and structural brain phenotypes in offspring. Our data suggest that alterations in SMAD3-regulated microtubule polymerization in the developing postnatal hippocampus may lead to an abnormal morphology of neuronal dendrites that persists into adulthood. These findings show that environmental low-dose gestational exposure to TCDD can have significant, long-term impacts on brain development and function. https://doi.org/10.1289/EHP7352.

Nutritional Intervention with Dried Bonito Broth for the Amelioration of Aggressive Behaviors in Children with Prenatal Exposure to Dioxins in Vietnam: A Pilot Study

Dioxins have been suggested to induce inflammation in the intestine and brain and to induce neurodevelopmental disorders such as autism spectrum disorder (ASD) and attention deficit hyperactivity disorder (ADHD), partly due to deficits in parvalbumin-positive neurons in the brain that are sensitive to inflammatory stress. Previously, we reported ADHD traits with increased aggressiveness in children with prenatal exposure to dioxins in Vietnam, whereas dried bonito broth (DBB) has been reported to suppress inflammation and inhibit aggressive behavior in animal and human studies. In the present study, we investigated the association between dioxin exposure and the prevalence of children with highly aggressive behaviors (Study 1), as well as the effects of DBB on the prevalence of children with highly aggressive behaviors (Study 2). Methods: In Study 1, we investigated the effects of dioxin exposure on the prevalence of children with high aggression scores, which were assessed using the Children’s Scale of Hostility and Aggression: Reactive/Proactive (C-SHARP) in dioxin-contaminated areas. The data were analyzed using a logistic regression model after adjusting for confounding factors. In Study 2, we performed nutritional intervention by administering DBB for 60 days to ameliorate the aggressiveness of children with high scores on the C-SHARP aggression scale. The effects of DBB were assessed by comparing the prevalence of children with high C-SHARP scores between the pre- and post-intervention examinations. Results: In Study 1, only the prevalence of children with high covert aggression was significantly increased with an increase in dioxin exposure. In Study 2, in the full ingestion (>80% of goal ingestion volume) group, the prevalence of children with high covert aggression associated with dioxin exposure was significantly lower in the post-ingestion examination compared with in the pre-ingestion examination. However, in other ingestion (<20% and 20–79%) groups and a reference (no intervention) group, no difference in the prevalence of children with high covert aggression was found between the examinations before and after the same experimental period. Conclusions: The findings suggest that DBB ingestion may ameliorate children’s aggressive behavior, which is associated with perinatal dioxin exposure.

Dioxin exposure and sexual dimorphism of gaze behavior in prepubertal Vietnamese children living in Da Nang, a hot spot for dioxin contamination

Previous studies have reported that dioxin exposure alters sexual dimorphism of play behavior in pre-pubertal children. We aimed to investigate the effects of perinatal dioxin exposure, indicated by dioxins in breast milk, on sexual dimorphism of gaze behavior after adjusting for salivary testosterone (T). Participants were pre-pubertal children in a hot spot for dioxin contamination originating from herbicide spraying in Vietnam. We used eye tracking to assess gaze behavior in 172 children (100 boys and 72 girls) aged 8-9 years. Two sets of 15 pairs of pictures, one oriented towards boys and one oriented towards girls, containing 5 pairs of toy photos (non-biological stimuli) and 10 pairs of human line drawings (biological stimuli) were shown to all children. The total fixation duration for each picture was extracted using Tobii studio software and a feminine index of gaze behavior was defined as the ratio of the summed fixation duration for the girl- vs boy-oriented versions of each stimuli. When viewing non-biological stimuli, feminine index scores significantly increased with TCDD (β = 0.294) in girls only. For biological stimuli, however, feminine index scores significantly increased with TEQ-PCDD/Fs (β = 0.269) in boys and with TCDD in girls (β = 0.286). These associations were significant even after adjusting for salivary T levels, which were inversely associated with some dioxin congeners in girls. In addition, increased feminine index scores for biological stimuli were associated with lower cognitive scores for hand-movement and word-order tests in boys and for face-recognition tests in girls examined at 5 years of age. In conclusion, these results suggest that perinatal dioxin exposure may increase visual interest in girl-oriented objects through impairment of cognitive abilities in pre-pubertal Vietnamese children. PCDD congeners were associated with gaze behavior independently of T levels in boys, while this was only the case for TCDD levels in girls.

Review of the Effects of Perinatal Exposure to Endocrine-Disrupting Chemicals in Animals and Humans

Maternal exposure to endocrine-disrupting chemicals (EDCs) is associated with long-term hormone-dependent effects that are sometimes not revealed until maturity, middle age, or adulthood. The aim of this study was to conduct descriptive reviews on animal experimental and human epidemiological evidence of the adverse health effects of in utero and lactational exposure to selected EDCs on the first generation and subsequent generation of the exposed offspring. PubMed, Web of Science, and Toxline databases were searched for relevant human and experimental animal studies on 29 October 29 2018. Search results were screened for relevance, and studies that met the inclusion criteria were evaluated and qualitative data extracted for analysis. The search yielded 73 relevant human and 113 animal studies. Results from studies show that in utero and lactational exposure to EDCs is associated with impairment of reproductive, immunologic, metabolic, neurobehavioral, and growth physiology of the exposed offspring up to the fourth generation without additional exposure. Little convergence is seen between animal experiments and human studies in terms of the reported adverse health effects which might be associated with methodologic challenges across the studies. Based on the available animal and human evidence, in utero and lactational exposure to EDCs is detrimental to the offspring. However, more human studies are necessary to clarify the toxicological and pathophysiological mechanisms underlying these effects.

Loss of Tiparp Results in Aberrant Layering of the Cerebral Cortex

2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)-inducible poly-ADP-ribose polymerase (TIPARP) is an enzyme that adds a single ADP-ribose moiety to itself or other proteins. Tiparp is highly expressed in the brain; however, its function in this organ is unknown. Here, we used Tiparp^–/– mice to determine Tiparp’s role in the development of the prefrontal cortex.

2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)-inducible poly-ADP-ribose polymerase (TIPARP) is an enzyme that adds a single ADP-ribose moiety to itself or other proteins. Tiparp is highly expressed in the brain; however, its function in this organ is unknown. Here, we used Tiparp^–/– mice to determine Tiparp’s role in the development of the prefrontal cortex. Loss of Tiparp resulted in an aberrant organization of the mouse cortex, where the upper layers presented increased cell density in the knock-out mice compared with wild type. Tiparp loss predominantly affected the correct distribution and number of GABAergic neurons. Furthermore, neural progenitor cell proliferation was significantly reduced. Neural stem cells (NSCs) derived from Tiparp^–/– mice showed a slower rate of migration. Cytoskeletal components, such as α-tubulin are key regulators of neuronal differentiation and cortical development. α-tubulin mono-ADP ribosylation (MAR) levels were reduced in Tiparp^–/– cells, suggesting that Tiparp plays a role in the MAR of α-tubulin. Despite the mild phenotype presented by Tiparp^–/– mice, our findings reveal an important function for Tiparp and MAR in the correct development of the cortex. Unravelling Tiparp’s role in the cortex, could pave the way to a better understanding of a wide spectrum of neurological diseases which are known to have increased expression of TIPARP.

Perinatal dioxin exposure and neurodevelopment of 2-year-old Vietnamese children in the most contaminated area from Agent Orange in Vietnam

Bien Hoa airbase is the most contaminated area of dioxin contamination from Agent Orange in Vietnam, but little is known about the neurodevelopmental effects of perinatal dioxin exposure on children living nearby. We recruited 210 mother-newborn resident pairs in 2012 and 78 pairs in 2015 and followed them for 2 years to assess the children's neurodevelopment. As a control group, we used 120 mother-child pairs recruited in 2014 in the Ha Dong district of Ha Noi City, an unexposed area. Perinatal dioxin exposure levels were indicated by levels of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and toxic equivalency values of polychlorodibenzodioxins, polychlorodibenzofurans, and nonortho-polychlorinated biphenyls (TEQ-PCDD/Fs/noPCBs) in maternal breast milk. The Bayley Scales of Infant and Toddler Development, Third Edition (Bayley-III) were used to assess neurodevelopment, and scores in each domain were compared between children with different exposure levels using general linear regression models and stratification by sex. Decreased expressive and composite language scores in boys and gross motor scores in girls were found in children exposed to TCDD ≥ 5.5 (pg/g lipid) compared with children with TCDD < 1.8. However, in matched pair analysis between children with TCDD ≥ 5.5 and <1.8 (pg/g lipid), lower expressive and composite language scores in boys exposed to TCDD ≥ 5.5 were significant, but lower gross motor scores in girls did not reach statistical significance. In addition, significant association was found between levels of PCDD congeners other than TCDD and gross motor scores in boys. These findings suggest that perinatal exposure of TCDD and other PCDD congeners affects development of language and gross motor skills, respectively, in boys at 2 years of age exposed to dioxins originating from Agent Orange in Vietnam.

Maternal exposure to TCDD during gestation advanced sensory-motor development, but induced impairments of spatial learning and memory in adult male rat offspring

2,3,7,8-Tetrachlorodibenzo-p-Dioxin (TCDD) is an endocrine disrupting chemical (EDC) with high persistency. Even a low amount can pass the placental barrier during gestational exposure. Exposure to TCDD exposure can impair the development of the nervous system in children, leading to impaired learning ability in later-life. But the changes in neurobehavioral developments in infancy and childhood caused by TCDD are unknown. Pregnant Sprague-Dawley rats were given a consecutive daily dose of TCDD (200 or 800 ng/day/kg) or an equivalent volume of vehicle by gavage on gestational days 8-14 (GD 8-14) as the prenatal TCDD exposure model. In the offspring, early neurobehavioral development was assessed at postnatal day 5 (PND5) and eye-opening was monitored from PND10 onwards. Adult male offspring was tested by Morris Water Maze for spatial memory and learning ability evaluation. Hippocampus Nissl's staining and astrocyte GFAP immunohistochemistry were used to evaluate the activity of astrocytes. The results of the behavioral tests showed that gestational TCDD exposure induced premature motor activity and earlier eyes-opening, but lead to serious deficits of spatial memory and learning ability in the adult male offspring. Morphology and number of neurons in the hippocampus CA1 region was not affected, while the activity of astrocytes in the same region was significantly reduced. These data indicate that perinatal TCDD exposure induced premature neurobehavioral development but impaired the spatial learning and memory in adult male rat offspring. The decreased activity of astrocytes in the hippocampus may play a role in these adverse effects.

The Aryl Hydrocarbon Receptor and the Nervous System

The aryl hydrocarbon receptor (or AhR) is a cytoplasmic receptor of pollutants. It translocates into the nucleus upon binding to its ligands, and forms a heterodimer with ARNT (AhR nuclear translocator). The heterodimer is a transcription factor, which regulates the transcription of xenobiotic metabolizing enzymes. Expressed in many cells in vertebrates, it is mostly present in neuronal cell types in invertebrates, where it regulates dendritic morphology or feeding behavior. Surprisingly, few investigations have been conducted to unravel the function of the AhR in the central or peripheral nervous systems of vertebrates. In this review, we will present how the AhR regulates neural functions in both invertebrates and vertebrates as deduced mainly from the effects of xenobiotics. We will introduce some of the molecular mechanisms triggered by the well-known AhR ligand, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), which impact on neuronal proliferation, differentiation, and survival. Finally, we will point out the common features found in mice that are exposed to pollutants, and in AhR knockout mice.

Sex-specific effects of perinatal dioxin exposure on eating behavior in 3-year-old Vietnamese children

Background

We previously reported that perinatal dioxin exposure increased autistic traits in children living in dioxin-contaminated areas of Vietnam. In the present study, we investigated the impact of dioxin exposure on children’s eating behavior, which is often altered in those with developmental disorders.

Methods

A total of 185 mother-and-child pairs previously enrolled in a birth cohort in dioxin-contaminated areas participated in this survey, conducted when the children reached 3 years of age. Perinatal dioxin exposure levels in the children were estimated using dioxin levels in maternal breast milk after birth. Mothers were interviewed using the Children’s Eating Behaviour Questionnaire (CEBQ). A multiple linear regression model was used to analyze the association between dioxin exposure and CEBQ scores, after controlling for covariates such as location, parity, maternal age, maternal education, maternal body mass index, family income, children’s gestational age at delivery, and children’s age at the time of the survey. A general linear model was used to analyze the effects of sex and dioxin exposure on CEBQ scores.

Results

There was no significant association between most dioxin congeners or toxic equivalencies of polychlorinated dibenzo-p-dioxins/furans (TEQ-PCDDs/Fs) and CEBQ scores in boys, although significant associations between some eating behavior sub-scores and 1,2,3,4,6,7,8,9-octachlorodibenzofuran were observed. In girls, there was a significant inverse association between levels of TEQ-PCDFs and enjoyment of food scores and between levels of TEQ-PCDFs and TEQ-PCDDs/Fs and desire to drink scores. Two pentachlorodibenzofuran congeners and 1,2,3,6,7,8-hexachlorodibenzofuran were associated with a decreased enjoyment of food score, and seven PCDF congeners were associated with a decreased desire to drink score. The adjusted mean enjoyment of food score was significantly lower in children of both sexes exposed to high levels of TEQ-PCDFs. There was, however, a significant interaction between sex and TEQ-PCDF exposure in their effect on desire to drink scores, especially in girls.

Conclusions

Perinatal exposure to dioxin can influence eating behavior in children and particularly in girls. A longer follow-up study would be required to assess whether emotional development that affects eating styles and behaviors is related to dioxin exposure.

Electronic supplementary material

The online version of this article (10.1186/s12887-018-1171-2) contains supplementary material, which is available to authorized users.

Effects of high fat diet and perinatal dioxin exposure on development of body size and expression of platelet-derived growth factor receptor β in the rat brain

Environmental exposure to dioxins, consumption of a high fat diet, and platelet-derived growth factor receptor β signaling in the brain affect feeding behavior, which is an important determinant of body growth. In the present study, we investigated the effects of prenatal exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin and high fact diet after weaning on body growth and expression of platelet-derived growth factor receptor β in the brain in rat pups. Subjects from the control and dioxin exposure groups were assigned to 1 of 3 different diet groups: standard diet, high fat diet in the juvenile period, or high fat diet in adulthood. Body weight gain rate in the juvenile high fat diet group and the length gain rate in the adult high fat diet group were greater than the corresponding values in the standard diet group only in male offspring, although the effects of dioxin exposure on growth were not significant. Consumption of a high fat diet decreased platelet-derived growth factor receptor β levels in the amygdala and hippocampus in both sexes compared to control groups, while 2,3,7,8-tetrachlorodibenzo-p-dioxin decreased platelet-derived growth factor receptor platelet-derived growth factor receptor β levels in the amygdala and striatum only in females receiving an high fat diet. Furthermore, platelet-derived growth factor receptor β levels in the hippocampus and platelet-derived growth factor receptor β striatum were inversely correlated with increases in body length, while changes in platelet-derived growth factor receptor β in the amygdala and nucleus accumbens were significantly correlated to body weight gain or body mass index. In conclusion, these findings suggest that these 2,3,7,8-tetrachlorodibenzo-p-dioxin and high fat diet-induced changes in body growth and feeding behaviors might be partially mediated by changes in brain platelet-derived growth factor receptor β levels.

2,3,7,8-tetrachlorodibenzo-p-dioxin exposure influence the expression of glutamate transporter GLT-1 in C6 glioma cells via the Ca(2+) /protein kinase C pathway

The widespread environmental contaminant, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), is considered one of the most toxic dioxin-like compounds. Although epidemiological studies have shown that TCDD exposure is linked to some neurological and neurophysiological disorders, the underlying mechanism of TCDD-mediated neurotoxicity has remained unclear. Astrocytes are the most abundant cells in the nervous systems, and are recognized as the important mediators of normal brain functions as well as neurological, neurodevelopmental and neurodegenerative brain diseases. In this study, we investigated the role of TCDD in regulating the expression of glutamate transporter GLT-1 in astrocytes. TCDD, at concentrations of 0.1-100 nm, had no significantly harmful effect on the viability of C6 glioma cells. However, the expression of GLT-1 in C6 glioma cells was downregulated in a dose- and time-dependent manner. TCDD also caused activation of protein kinase C (PKC), as TCDD induced translocation of the PKC from the cytoplasm or perinuclear to the membrane. The translocation of PKC was inhibited by one Ca(2+) blocker, nifedipine, suggesting that the effects are triggered by the initial elevated intracellular concentration of free Ca(2+) . Finally, we showed that inhibition of the PKC activity reverses the TCDD-triggered reduction of GLT-1. In summary, our results suggested that TCDD exposure could downregulate the expression of GLT-1 in C6 via Ca(2+) /PKC pathway. The downregulation of GLT-1 might participate in TCDD-mediated neurotoxicity. Copyright © 2016 John Wiley & Sons, Ltd.

Impacts of Perinatal Dioxin Exposure on Motor Coordination and Higher Cognitive Development in Vietnamese Preschool Children: A Five-Year Follow-Up

Dioxin concentrations remain elevated in the environment and in humans residing near former US Air Force bases in South Vietnam. Our previous epidemiological studies showed adverse effects of dioxin exposure on neurodevelopment for the first 3 years of life. Subsequently, we extended the follow-up period and investigated the influence of perinatal dioxin exposure on neurodevelopment, including motor coordination and higher cognitive ability, in preschool children. Presently, we investigated 176 children in a hot spot of dioxin contamination who were followed up from birth until 5 years old. Perinatal dioxin exposure levels were estimated by measuring dioxin levels in maternal breast milk. Dioxin toxicity was evaluated using two indices; toxic equivalent (TEQ)-polychlorinated dibenzo-p-dioxins/furans (PCDDs/Fs) and concentration of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Coordinated movements, including manual dexterity, aiming and catching, and balance, were assessed using the Movement Assessment Battery for Children, Second Edition (Movement ABC-2). Cognitive ability was assessed using the nonverbal index (NVI) of the Kaufman Assessment Battery for Children, Second Edition (KABC-II). In boys, total test and balance scores of Movement ABC-2 were significantly lower in the high TEQ- PCDDs/Fs group compared with the moderate and low exposure groups. NVI scores and the pattern reasoning subscale of the KABC-II indicating planning ability were also significantly lower in the high TCDD exposure group compared with the low exposure group of boys. However, in girls, no significant differences in Movement ABC-2 and KABC-II scores were found among the different TEQ-PCDDs/Fs and TCDD exposure groups. Furthermore, in high risk cases, five boys and one girl highly exposed to TEQ-PCDDs/Fs and TCDD had double the risk for difficulties in both neurodevelopmental skills. These results suggest differential impacts of TEQ-PCDDs/Fs and TCDD exposure on motor coordination and higher cognitive ability, respectively. Moreover, high TEQ-PCDDs/Fs exposure combined with high TCDD exposure may increase autistic traits combined with developmental coordination disorder.

Perinatal dioxin exposure and the neurodevelopment of Vietnamese toddlers at 1 year of age

Dioxin concentrations remain elevated in both the environment and in humans residing near former US Air Force bases in South Vietnam. This may potentially have adverse health effects, particularly on infant neurodevelopment. We followed 214 infants whose mothers resided in a dioxin-contaminated area in Da Nang, Vietnam, from birth until 1 year of age. Perinatal exposure to dioxins was estimated from toxic equivalent (TEQ) levels of polychlorinated dibenzodioxins and polychlorinated dibenzofurans (PCDDs/Fs-TEQ), and 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TetraCDD) concentrations in breast milk. In infants, daily dioxin intake (DDI) was used as an index of postnatal exposure through breastfeeding. Neurodevelopment of toddlers was assessed using the Bayley Scales of Infant and Toddler Development, Third Edition (Bayley-III). No significant differences in neurodevelopmental scores were exhibited for cognitive, language or motor functions between four exposure groups of PCDDs/Fs-TEQ or 2,3,7,8-TetraCDD. However, social-emotional scores were decreased in the high PCDDs/Fs-TEQ group and the high 2,3,7,8-TetraCDD group compared with those with mild exposure, after adjusting for confounding factors. Cognitive scores in the mild, moderate, and high DDI groups were significantly higher than those in low DDI group, but there were no differences in cognitive scores among the three higher DDI groups. These results suggest that perinatal exposure to dioxins may affect social-emotional development of 1-year-old toddlers, without diminishing global neurodevelopmental function.

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.

Proteomic pathway analysis of the hippocampus in schizophrenia and bipolar affective disorder implicates 14-3-3 signaling, aryl hydrocarbon receptor signaling, and glucose metabolism: potential roles in GABAergic interneuron pathology

Neuropathological changes of the hippocampus have been associated with psychotic disorders such as schizophrenia and bipolar disorder. Recent work has particularly implicated hippocampal GABAergic interneurons in the pathophysiology of these diseases. However, the molecular mechanisms underlying structural and cellular hippocampal pathology remain poorly understood. We used data from comprehensive difference-in-gel electrophoresis (2-D DIGE) investigations of postmortem human hippocampus of people with schizophrenia and bipolar disorder, covering the acidic (isoelectric point (pI) between pH4 and 7) and, separately, the basic (pI between pH6 and 11) sub-proteome, for Ingenuity Pathway Analysis (IPA) of implicated protein networks and pathways. Comparing disease and control cases, we identified 58 unique differentially expressed proteins in schizophrenia, and 70 differentially expressed proteins in bipolar disorder, using mass spectrometry. IPA implicated, most prominently, 14-3-3 and aryl hydrocarbon receptor signaling in schizophrenia, and gluconeogenesis/glycolysis in bipolar disorder. Both disorders were characterized by alterations of proteins involved in the oxidative stress response, mitochondrial function, and protein-endocytosis, -trafficking, -degradation, and -ubiquitination. These findings are interpreted with a focus on GABAergic interneuron pathology in the hippocampus.

Aryl hydrocarbon receptor mediates both proinflammatory and anti-inflammatory effects in lipopolysaccharide-activated microglia

The aryl hydrocarbon receptor (AhR) regulates peripheral immunity; but its role in microglia-mediated neuroinflammation in the brain remains unknown. Here, we demonstrate that AhR mediates both anti-inflammatory and proinflammatory effects in lipopolysaccharide (LPS)-activated microglia. Activation of AhR by its ligands, formylindolo[3,2-b]carbazole (FICZ) or 3-methylcholanthrene (3MC), attenuated LPS-induced microglial immune responses. AhR also showed proinflammatory effects, as evidenced by the findings that genetic silence of AhR ameliorated the LPS-induced microglial immune responses and LPS-activated microglia-mediated neurotoxicity. Similarly, LPS-induced expressions of tumor necrosis factor α (TNFα) and inducible nitric oxide synthase (iNOS) were reduced in the cerebral cortex of AhR-deficient mice. Intriguingly, LPS upregulated and activated AhR in the absence of AhR ligands via the MEK1/2 signaling pathway, which effects were associated with a transient inhibition of cytochrome P450 1A1 (CYP1A1). Although AhR ligands synergistically enhance LPS-induced AhR activation, leading to suppression of LPS-induced microglial immune responses, they cannot do so on their own in microglia. Chromatin immunoprecipitation results further revealed that LPS-FICZ co-treatment, but not LPS alone, not only resulted in co-recruitment of both AhR and NFκB onto the κB site of TNFα gene promoter but also reduced LPS-induced AhR binding to the DRE site of iNOS gene promoter. Together, we provide evidence showing that microglial AhR, which can be activated by LPS, exerts bi-directional effects on the regulation of LPS-induced neuroinflammation, depending on the availability of external AhR ligands. These findings confer further insights into the potential link between environmental factors and the inflammatory brain disorders.

2,3,7,8-Tetrachlorodibenzo-p-dioxin in breast milk increases autistic traits of 3-year-old children in Vietnam

Dioxin levels in the breast milk of mothers residing near a contaminated former airbase in Vietnam remain much higher than in unsprayed areas, suggesting high perinatal dioxin exposure for their infants. The present study investigated the association of perinatal dioxin exposure with autistic traits in 153 3-year-old children living in a contaminated area in Vietnam. The children were followed up from birth using the neurodevelopmental battery Bayley-III. The high-2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) exposed groups (⩾3.5 pg per g fat) showed significantly higher Autism Spectrum Rating Scale (ASRS) scores for both boys and girls than the mild-TCDD exposed groups, without differences in neurodevelopmental scores. In contrast, the high total dioxin-exposed group, indicated by polychlorinated dibenzo-p-dioxins/furans (PCDDs/Fs)--the toxic equivalents (TEQ) levels⩾17.9 pg-TEQ per g fat, had significantly lower neurodevelopmental scores than the mild-exposed group in boys, but there was no difference in the ASRS scores. The present study demonstrates a specific impact of perinatal TCDD on autistic traits in childhood, which is different from the neurotoxicity of total dioxins (PCDDs/Fs).