Chronic co-exposure to low levels of brominated flame retardants and heavy metals induces reproductive toxicity in zebrafish.

Brominated flame retardants (BFRs) and heavy metals (HMs) are two main types of pollutants in electronic waste recycling sites, which are also ubiquitously detectable in environmental media and human tissues. However, the adverse health effects of exposure to the mixture of these types of pollutants are unknown. In this study, we investigated the reproductive toxicity of a mixture of decabromodiphenyl ether (BDE-209), tetrabromobisphenol A, cadmium chloride, and lead acetate (PbAc) at the environmental relevant levels. Zebrafish were waterborne and exposed to chemical mixtures for one generation. The reproductive effects were evaluated for F0 adults and F1 offspring. Chemical residues were also analyzed in the exposed adults and their eggs at the end of exposure. Our findings demonstrated that exposure to the chemical mixture for 150 days had no effect on the survival rate of zebrafish, but it decreased body length and weight in females and increased body weight and condition factor in males. The mixture exposure resulted in a female-biased sex ratio in adults and decreased sperm density and motility in males and egg production in females. For the F1 offspring, decreased fertilization, delayed hatching, and increased malformation were found in all exposure groups. In conclusion, chronic co-exposure to BFRs and HMs at the environmental relevant levels not only affected growth, sex ratio, and sperm quantity/quality and egg production in adults but also reduced the reproductive success in the offspring, implying that multi-pollutants in the environmental media may pose a public health risk to other exposed organisms or human beings.

Benzoquinone induces ROS-dependent mitochondria-mediated apoptosis in HL-60 cells.

Benzene exposure affects the hematopoietic system and leads to the occurrence of various types of leukemia and hematotoxicity. It has been confirmed that active metabolites of benzene, including 1,4-benzoquinone (1,4-BQ), can induce reactive oxygen species (ROS) and apoptosis in the bone marrow, and recent studies have also suggested that benzene exposure can affect mitochondrial function in both experimental animals and cell lines. However, the potential relationship among ROS production, mitochondrial damages, and subsequent apoptosis following benzene exposure has not been well studied in detail. In the present study, we utilized HL-60 cells, a well-characterized human myeloid cell line, as an in vitro model and examined the effects of 1,4-BQ on intracellular ROS formation, mitochondria damage, and the occurrence of apoptotic events with or without using the ROS scavenger N-acetyl-l-cysteine (NAC). The results demonstrated that 1,4-BQ could dose-dependently induce production of ROS and mitochondrial damage as characterized by mitochondrial membrane potential disruption, mitochondrial ultrastructure alteration, and induced apoptosis and activated caspase-3 and caspase-9. Preincubation of HL-60 cells with NAC prior to 1,4-BQ treatment could block 1,4-BQ-induced production of ROS and the occurrence of apoptosis. These results demonstrated that 1,4-BQ induced apoptosis in HL-60 cells through a ROS-dependent mitochondrial-mediated pathway.

Chronic PFOS Exposure Disrupts Thyroid Structure and Function in Zebrafish.

Perfluorooctane sulfonic acid (PFOS), as a potential endocrine disrupting chemical, is widely detected in the environment, wildlife and human. Currently few studies have documented the effects of chronic PFOS exposure on thyroid in aquatic organisms and the underlying mechanisms are largely unknown. The present study assessed the effect of chronic PFOS exposure on thyroid structure and function using zebrafish model. Zebrafish at 8 h post fertilization (hpf) were exposed to PFOS (250 µg/l) until 120 d post fertilization (dpf). Thyroid hormone (T3 and T4) level, thyroid morphology and thyroid function related gene expression were evaluated in zebrafish at 120 dpf. Our findings demonstrated that chronic PFOS exposure altered thyroid hormone level, thyroid follicular cell structure and thyroid hormone related gene expression, suggesting the validity of zebrafish as an alternative model for PFOS chronic toxicity screening.

Dichlorvos exposure results in large scale disruption of energy metabolism in the liver of the zebrafish, Danio rerio.

BACKGROUND: Exposure to dichlorvos (DDVP), an organophosphorus pesticide, is known to result in neurotoxicity as well as other metabolic perturbations. However, the molecular causes of DDVP toxicity are poorly understood, especially in cells other than neurons and muscle cells. To obtain a better understanding of the process of non-neuronal DDVP toxicity, we exposed zebrafish to different concentrations of DDVP, and investigated the resulting changes in liver histology and gene transcription. RESULTS: Functional enrichment analysis of genes affected by DDVP exposure identified a number of processes involved in energy utilization and stress response in the liver. The abundance of transcripts for proteins involved in glucose metabolism was profoundly affected, suggesting that carbon flux might be diverted toward the pentose phosphate pathway to compensate for an elevated demand for energy and reducing equivalents for detoxification. Strikingly, many transcripts for molecules involved in ß-oxidation and fatty acid synthesis were down-regulated. We found increases in message levels for molecules involved in reactive oxygen species responses as well as ubiquitination, proteasomal degradation, and autophagy. To ensure that the effects of DDVP on energy metabolism were not simply a consequence of poor feeding because of neuromuscular impairment, we fasted fish for 29 or 50 h and analyzed liver gene expression in them. The patterns of gene expression for energy metabolism in fasted and DDVP-exposed fish were markedly different. CONCLUSION: We observed coordinated changes in the expression of a large number of genes involved in energy metabolism and responses to oxidative stress. These results argue that an appreciable part of the effect of DDVP is on energy metabolism and is regulated at the message level. Although we observed some evidence of neuromuscular impairment in exposed fish that may have resulted in reduced feeding, the alterations in gene expression in exposed fish cannot readily be explained by nutrient deprivation.

Polybrominated diphenyl ethers (PBDEs) in human serum from Southeast China.

Polybrominated diphenyl ethers (PBDEs) have been used extensively in electrical and electronic products, but little is known about the exposure level in the electrical appliance factories workers and nearby local residents. In this study, we assessed body burdens of PBDEs in 194 Chinese injection workers from electrical appliance factories and also measured 205 blood samples from catering workers, leather factory workers, umbilical cord and infertile men for comparison. Twelve PBDE congeners in serum samples were measured by GC-MS. The highest concentration for total PBDEs was found in injection workers, which is positively correlated to employment duration. BDE-209 was the most dominant congener followed by BDE-47, 28 and 99. We also found the presence of all twelve PBDEs in cord blood, suggesting an evidence of fetal exposure. Concentration of BDE-47 was particularly higher in serum samples from infertile men in comparison with that of catering workers and leather factory workers.

Epoxyeicosatrienoic acids enhance axonal growth in primary sensory and cortical neuronal cell cultures.

It has recently been reported that soluble epoxide hydrolase (sEH), the major enzyme that metabolizes epoxyeicosatrienoic acids (EETs), is expressed in axons of cortical neurons; however, the functional relevance of axonal sEH localization is unknown. Immunocytochemical analyses demonstrate predominant axonal localization of sEH in primary cultures of not only cortical but also sympathetic and sensory neurons. Morphometric analyses of cultured sensory neurons indicate that exposure to a regioisomeric mixture of EETs (0.01-1.0 µM) causes a concentration-dependent increase in axon outgrowth. This axon promoting activity is not a generalized property of all regioisomers of EETs as axonal growth is enhanced in sensory neurons exposed to 14,15-EET but not 8,9- or 11,12-EET. 14,15-EET also promotes axon outgrowth in cultured cortical neurons. Co-exposure to EETs and either of two structurally diverse pharmacological inhibitors of sEH potentiates the axon-enhancing activity of EETs in sensory and cortical neurons. Mass spectrometry indicates that sEH inhibition significantly increases EETs and significantly decreases dihydroxyeicosatrienoic acid metabolites in neuronal cell cultures. These data indicate that EETs enhance axon outgrowth and suggest that axonal sEH activity regulates EETs-induced axon outgrowth. These findings suggest a novel therapeutic use of sEH inhibitors in promoting nerve regeneration.

Chronic zebrafish low dose decabrominated diphenyl ether (BDE-209) exposure affected parental gonad development and locomotion in F1 offspring.

Polybrominated diphenyl ethers (PBDEs) are widely used as flame retardants around the world. Because of large production volumes, widespread usage and persistence, PBDEs are now ubiquitous environmental pollutants detected in a wide variety of environment media and human samples and therefore pose a significant public health concern. Deca-PBDE (BDE-209) is the only commercial PBDE mixture still allowed for use at present, and has been recently detected at high levels in human samples. However, few studies explore its effect on development, reproduction or neurobehavior with animal models. In particular, studies with long-term chronic exposure at relatively low doses are lacking. In this study, we utilize the zebrafish model to explore the developmental, reproductive, and behavioral toxicities associated with long-term chronic exposure to deca-PBDE (BDE-209). Our findings revealed that long-term chronic exposure to low dose of deca-BDE (ranging from 0.001 to 1 µM) affected overall fitness (measured by condition factor), gonad development, male gamete quantity and quality in F0 parental fish. For F1 offspring without continuous exposure to BDE-209, parental BDE treatment led to delayed hatch and motor neuron development, loose muscle fiber, slow locomotion behavior in normal conditions, and hyperactivity when subjected to light-dark photoperiod stimulation. In conclusion, parental chronic low dose BDE-209 exposure not only affects F0 growth and reproduction, but also elicits neurobehavior alternations in F1 offspring.

Coordinate control of axon defasciculation and myelination by laminin-2 and -8.

Schwann cells form basal laminae (BLs) containing laminin-2 (Ln-2; heterotrimer alpha2beta1gamma1) and Ln-8 (alpha4beta1gamma1). Loss of Ln-2 in humans and mice carrying alpha2-chain mutations prevents developing Schwann cells from fully defasciculating axons, resulting in partial amyelination. The principal pathogenic mechanism is thought to derive from structural defects in Schwann cell BLs, which Ln-2 scaffolds. However, we found loss of Ln-8 caused partial amyelination in mice without affecting BL structure or Ln-2 levels. Combined Ln-2/Ln-8 deficiency caused nearly complete amyelination, revealing Ln-2 and -8 together have a dominant role in defasciculation, and that Ln-8 promotes myelination without BLs. Transgenic Ln-10 (alpha5beta1gamma1) expression also promoted myelination without BL formation. Rather than BL structure, we found Ln-2 and -8 were specifically required for the increased perinatal Schwann cell proliferation that attends myelination. Purified Ln-2 and -8 directly enhanced in vitro Schwann cell proliferation in collaboration with autocrine factors, suggesting Lns control the onset of myelination by modulating responses to mitogens in vivo.

Developmental exposure to polychlorinated biphenyls influences stroke outcome in adult rats.

BACKGROUND: The "developmental origins of adult disease" hypothesis was originally derived from evidence linking low birth weight to cardiovascular diseases including stroke. Subsequently, it has been expanded to include developmental exposures to environmental contaminants as risk factors for adult onset disease. OBJECTIVE: Our goal in this study was to test the hypothesis that developmental exposure to poly-chlorinated biphenyls (PCBs) alters stroke outcome in adults. METHODS: We exposed rats to the PCB mixture Aroclor 1254 (A1254) at 0.1 or 1 mg/kg/day in the maternal diet throughout gestation and lactation. Focal cerebral ischemia was induced at 6-8 weeks of age via middle cerebral artery occlusion, and infarct size was measured in the cerebral cortex and striatum at 22 hr of reperfusion. PCB congeners were quantified in brain tissue by gas chromatography with microelectron capture detection, and cortical and striatal expression of Bcl2 and Cyp2C11 were quantified by quantitative reverse transcriptase-polymerase chain reaction. RESULTS: Developmental exposure to A1254 significantly decreased striatal infarct in females and males at 0.1 and 1 mg/kg/day, respectively. Predominantly ortho-substituted PCB congeners were detected above background levels in brains of adult females and males exposed to A1254 at 1 but not 0.1 mg/kg/day. Effects of developmental A1254 exposure on Bcl2 and Cyp2C11 expression did not correlate with effects on infarct volume. CONCLUSION: Our data provide proof of principle that developmental exposures to environmental contaminants influence the response of the adult brain to ischemic injury and thus represent potentially important determinants of stroke susceptibility.

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.

From the Cover: BDE-47 and BDE-49 Inhibit Axonal Growth in Primary Rat Hippocampal Neuron-Glia Co-Cultures via Ryanodine Receptor-Dependent Mechanisms.

Polybrominated diphenyl ethers (PBDEs) are widespread environmental contaminants associated with adverse neurodevelopmental outcomes in children and preclinical models; however, the mechanisms by which PBDEs cause developmental neurotoxicity remain speculative. The structural similarity between PBDEs and nondioxin-like (NDL) polychlorinated biphenyls (PCBs) suggests shared toxicological properties. Consistent with this, both NDL PCBs and PBDEs have been shown to stabilize ryanodine receptors (RyRs) in the open configuration. NDL PCB effects on RyR activity are causally linked to increased dendritic arborization, but whether PBDEs similarly enhance dendritic growth is not known. In this study, we quantified the effects of individual PBDE congeners on not only dendritic but also axonal growth since both are regulated by RyR-dependent mechanisms, and both are critical determinants of neuronal connectivity. Neuronal-glial co-cultures dissociated from the neonatal rat hippocampus were exposed to BDE-47 or BDE-49 in the culture medium. At concentrations ranging from 20 pM to 2 µM, neither PBDE congener altered dendritic arborization. In contrast, at concentrations ≥ 200 pM, both congeners delayed neuronal polarization resulting in significant inhibition of axonal outgrowth during the first few days in vitro. The axon inhibitory effects of these PBDE congeners occurred independent of cytotoxicity, and were blocked by pharmacological antagonism of RyR or siRNA knockdown of RyR2. These results demonstrate that the molecular and cellular mechanisms by which PBDEs interfere with neurodevelopment overlap with but are distinct from those of NDL PCBs, and suggest that altered patterns of neuronal connectivity may contribute to the developmental neurotoxicity of PBDEs.

Subchronic perfluorooctanesulfonate (PFOS) exposure induces elevated mutant frequency in an in vivo λ transgenic medaka mutation assay.

Perfluorooctanesulfonate (PFOS) has been widely detected in the environment, wildlife and humans, but few studies have ever examined its mutagenic effect in vivo. In the present study, we use a transgenic fish model, the λ transgenic medaka, to evaluate the potential mutagenicity of PFOS in vivo following a subchronic exposure of 30 days. The mutant frequency of cII target gene was 3.46 × 10-5 in liver tissue from control fish, which increased by 1.4-fold to 4.86 × 10-5 in fish exposed to 6.7 µg/L PFOS, 1.55-fold to 5.36 × 10-5 in fish exposed to 27.6 µg/L PFOS, and 2.02-fold to 6.99 × 10-5 in fish exposed to 87.6 µg/L PFOS. This dose-dependent increase of mutant frequency was also accompanied with mutational spectrum changes associated with PFOS exposure. In particular, PFOS-induced mutation was characterized by +1 frameshift mutations, which increased from 0% in control fish to 13.2% in fish exposed to 27.6 µg/L PFOS and 14.6% in fish exposed to 87.6 µg/L PFOS. Our findings provide the first evidence of PFOS's mutagenicity in an aquatic model system. Given the fact that most conventional mutagenic assays were negative for PFOS, we propose that PFOS-induced mutation in liver tissue of λ transgenic medaka may be mediated through compromised liver function.

Chronic perfluorooctane sulfonate (PFOS) exposure induces hepatic steatosis in zebrafish.

Perfluorooctane sulfonate (PFOS), one persistent organic pollutant, has been widely detected in the environment, wildlife and human. Currently few studies have documented the effects of chronic PFOS exposure on lipid metabolism, especially in aquatic organisms. The underlying mechanisms of hepatotoxicity induced by chronic PFOS exposure are still largely unknown. The present study defined the effects of chronic exposure to low level of PFOS on lipid metabolism using zebrafish as a model system. Our findings revealed a severe hepatic steatosis in the liver of males treated with 0.5µM PFOS as evidenced by hepatosomatic index, histological assessment and liver lipid profiles. Quantitative PCR assay further indicated that PFOS significantly increase the transcriptional expression of nuclear receptors (nr1h3, rara, rxrgb, nr1l2) and the genes associated with fatty acid oxidation (acox1, acadm, cpt1a). In addition, chronic PFOS exposure significantly decreased liver ATP content and serum level of VLDL/LDL lipoprotein in males. Taken together, these findings suggest that chronic PFOS exposure induces hepatic steatosis in zebrafish via disturbing lipid biosynthesis, fatty acid ß-oxidation and excretion of VLDL/LDL lipoprotein, and also demonstrate the validity of using zebrafish as an alternative model for PFOS chronic toxicity screening.

Functional changes of nicotinic acetylcholine receptor in muscle and lymphocyte of myasthenic rats following acute dimethoate poisoning.

The mechanism underlying intermediate myasthenia syndrome (IMS) following acute organophosphate poisoning remains largely unknown. Previous studies indicated that the mechanism of myasthenia in rats and IMS patients is most likely due to a postsynaptic neurotransmission blocking at neuromuscular junctions (NMJ). Nicotinic acetylcholine receptor (nAChR) is a key postsynaptic component at NMJ. Whether functional changes of nAChR are related to the development of myasthenia has not been demonstrated and addressed in vivo so far. In this study, we attempted to investigate temporal and spatial changes of nAChR in the blood lymphocyte, muscle and brain of rats during the course of myasthenia after acute dimethoate poisoning by using radioligand-binding assay. We found that specific nAChR binding activity in the gastrocnemius muscle and blood lymphocytes of myasthenia rats was significantly increased at 48h after dimethoate poisoning. However, no changes of nAChR binding activity were found in the lymphocytes and muscle of non-myasthenia rats which were sacrificed at 1h after intoxication. Interestingly, no changes of nAChR and muscarinic acetylcholine receptor (mAChR) binding activity were found in the cerebrum and cerebellum of all rats after dimethoate intoxication either at 1 or 48h. The change of nAChR specific binding activity in the lymphocytes is parallel with that in the skeletal muscle during the development of myasthenia. This implied that the changes of nAChR receptor binding activity in the skeletal muscle and lymphocytes are highly associated with the development of myasthenia. The functional changes of nAChR at NMJ might play an important role in the paralysis of skeletal muscle following acute organophosphates (OPs) poisoning.

Using the Morris water maze to assess spatial learning and memory in weanling mice.

Mouse models have been indispensable for elucidating normal and pathological processes that influence learning and memory. A widely used method for assessing these cognitive processes in mice is the Morris water maze, a classic test for examining spatial learning and memory. However, Morris water maze studies with mice have principally been performed using adult animals, which preclude studies of critical neurodevelopmental periods when the cellular and molecular substrates of learning and memory are formed. While weanling rats have been successfully trained in the Morris water maze, there have been few attempts to test weanling mice in this behavioral paradigm even though mice offer significant experimental advantages because of the availability of many genetically modified strains. Here, we present experimental evidence that weanling mice can be trained in the Morris water maze beginning on postnatal day 24. Maze-trained weanling mice exhibit significant improvements in spatial learning over the training period and results of the probe trial indicate the development of spatial memory. There were no sex differences in the animals' performance in these tasks. In addition, molecular biomarkers of synaptic plasticity are upregulated in maze-trained mice at the transcript level. These findings demonstrate that the Morris water maze can be used to assess spatial learning and memory in weanling mice, providing a potentially powerful experimental approach for examining the influence of genes, environmental factors and their interactions on the development of learning and memory.

Ontogeny of biochemical, morphological and functional parameters of synaptogenesis in primary cultures of rat hippocampal and cortical neurons.

BACKGROUND: Synaptogenesis is a critical neurodevelopmental process whereby pre- and postsynaptic neurons form apposed sites of contact specialized for chemical neurotransmission. Many neurodevelopmental disorders are thought to reflect altered patterns of synaptic connectivity, including imbalances between excitatory and inhibitory synapses. Developing rapid throughput approaches for assessing synaptogenesis will facilitate toxicologic and drug screening studies of neurodevelopmental disorders. The current study describes the use of high-content imaging to quantify the ontogeny of excitatory and inhibitory synapses using in vitro models of neurodevelopment. These data are compared to biochemical and functional measures of synaptogenesis. RESULTS: The ontogenetic patterns of synapse formation were compared between primary rodent hippocampal and cortical neurons over 28 days in vitro (DIV). As determined by ELISA, the increase in synaptophysin expression levels as cultures matured was similar between hippocampal and cortical cultures. High-content imaging of immunoreactivity of excitatory and inhibitory synaptic biomarkers demonstrated an overall greater number of synapses in hippocampal relative to cortical neurons with marked differences in the pattern of inhibitory synapse development between these two neuronal cell types. Functional assays revealed that both the mean firing rates and mean bursting rates were significantly increased in cortical cultures relative to hippocampal cultures. This difference may reflect decreased inhibitory synaptic tone in cortical versus hippocampal cultures. CONCLUSIONS: These data demonstrate differences and similarities in the ontogeny of synaptogenesis between hippocampal and cortical neurons, depending on the biological level examined. Assessment of synaptophysin protein levels by ELISA showed a general increase in synapse formation in both cell types with increasing time in culture, while high-content imaging was able to delineate cell type-dependent differences in formation of excitatory versus inhibitory synapses. The functional significance of differences in the balance of excitatory to inhibitory synapses was confirmed by the assessment of network activity using microelectrode arrays. These results suggest that high-content imaging and microelectrode arrays provide complementary approaches for quantitative assessment of synaptogenesis, which should provide a robust readout of toxicologic and pharmacologic effects on this critical neurodevelopmental event.

Biochemical changes in primary culture of skeletal muscle cells following dimethoate exposure.

In order to investigate the cellular mechanism of muscular weakness in the Intermediate Myasthenia Syndrome (IMS) following acute organophosphate poisoning, we studied the cytotoxicity of dimethoate and its effects on the activity of acetylcholine esterase (AChE), Na+-K+-ATPase, succinate dehydrogenase (SDH), and Ca2+-ATPase in primary cultured skeletal muscle cells. The results showed that the activity of AChE was significantly inhibited in a dose and time-dependent manner when cells were exposed to dimethoate for 2 h, but the expression of heat-shock protein (HSP70) in muscle cells was significantly increased in a time-dependent manner following dimethoate exposure. Dimethoate can significantly increase the activity of Na+-K+-ATPase in the mitochondrial and cytoplasm fraction of muscle cells, and inhibit the activity of Ca2+-ATPase. This study suggests that the disruption of intracellular homeostasis and energy metabolism of the muscle cells may play a role in the etiology of IMS.

Early life perfluorooctanesulphonic acid (PFOS) exposure impairs zebrafish organogenesis.

As a persistent organic contaminant, perfluorooctanesulphonic acid (PFOS) has been widely detected in the environment, wildlife, and humans. The present study revealed that zebrafish embryos exposed to 16 µM PFOS during a sensitive window of 48-96 hour post-fertilization (hpf) disrupted larval morphology at 120 hpf. Malformed zebrafish larvae were characterized by uninflated swim bladder, less developed gut, and curved spine. Histological and ultrastructural examination of PFOS-exposed larvae showed structural alterations in swim bladder and gut. Whole genome microarray was used to identify the early transcripts dysregulated following exposure to 16 µM PFOS at 96 hpf. In total, 1278 transcripts were significantly misexpressed (p<0.05) and 211 genes were changed at least two-fold upon PFOS exposure in comparison to the vehicle-exposed control group. A PFOS-induced network of perturbed transcripts relating to swim bladder and gut development revealed that misexpression of genes were involved in organogenesis. Taken together, early life stage exposure to PFOS perturbs various molecular pathways potentially resulting in observed defects in swim bladder and gut development.

PCB 136 atropselectively alters morphometric and functional parameters of neuronal connectivity in cultured rat hippocampal neurons via ryanodine receptor-dependent mechanisms.

We recently demonstrated that polychlorinated biphenyl (PCB) congeners with multiple ortho chlorine substitutions sensitize ryanodine receptors (RyRs), and this activity promotes Ca²âº-dependent dendritic growth in cultured neurons. Many ortho-substituted congeners display axial chirality, and we previously reported that the chiral congener PCB 136 (2,2',3,3',6,6'-hexachlorobiphenyl) atropselectively sensitizes RyRs. Here, we test the hypothesis that PCB 136 atropisomers differentially alter dendritic growth and other parameters of neuronal connectivity influenced by RyR activity. (-)-PCB 136, which potently sensitizes RyRs, enhances dendritic growth in primary cultures of rat hippocampal neurons, whereas (+)-PCB 136, which lacks RyR activity, has no effect on dendritic growth. The dendrite-promoting activity of (-)-PCB 136 is observed at concentrations ranging from 0.1 to 100 nM and is blocked by pharmacologic RyR antagonism. Neither atropisomer alters axonal growth or cell viability. Quantification of PCB 136 atropisomers in hippocampal cultures indicates that atropselective effects on dendritic growth are not due to differential partitioning of atropisomers into cultured cells. Imaging of hippocampal neurons loaded with Ca²âº-sensitive dye demonstrates that (-)-PCB 136 but not (+)-PCB 136 increases the frequency of spontaneous Ca²âº oscillations. Similarly, (-)-PCB 136 but not (+)-PCB 136 increases the activity of hippocampal neurons plated on microelectrode arrays. These data support the hypothesis that atropselective effects on RyR activity translate into atropselective effects of PCB 136 atropisomers on neuronal connectivity, and suggest that the variable atropisomeric enrichment of chiral PCBs observed in the human population may be a significant determinant of individual susceptibility for adverse neurodevelopmental outcomes following PCB exposure.

Bisphenol A affects axonal growth, musculature and motor behavior in developing zebrafish.

Bisphenol A (BPA) is a ubiquitous contaminant in environment and human body. The reproductive and developmental effects of BPA exposure in aquatic and laboratory animals have been extensively studied. However, BPA exposure on the nervous system and motor behavior development are not well understood. In this study, we utilized zebrafish embryo as a model system to investigate the effect of developmental BPA exposure on larval teratology, motor behaviors, axonal growth of spinal motoneurons and muscle structure at various developmental stages. Our findings revealed that BPA exposure altered spontaneous movement, significantly decreased touch response and swimming speed in response to light stimulation in developing zebrafish. These effects were observed at the concentrations that did not yield any significant teratogenic effects. Correlated with those changes in swimming activity, BPA-induced axial muscle damage occurred at the same concentration range (1-15 µM), but disruption of axonal growth of primary and secondary motoneuron occurred only at higher concentration (15 µM). BPA-induced apoptotic cell death subsequent to initial ROS formation and oxidative DNA damage may be the underlying mechanism for axial muscle damage, suggesting the functional relevance of muscle structural changes and the observed deficits in swimming activity.