2004 Progress Report: Developmental Effects of PCBs and MethylmercuryEPA Grant Number: R829390C004
Subproject: this is subproject number 004 , established and managed by the Center Director under grant R829390
(EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).
Center: CECEHDPR - University of Illinois FRIENDS Children’s Environmental Health Center
Center Director: Schantz, Susan L.
Title: Developmental Effects of PCBs and Methylmercury
Investigators: Seegal, Richard F.
Institution: New York State Department of Health - Wadsworth Center
EPA Project Officer: Louie, Nica
Project Period: October 17, 2001 through October 16, 2002
Project Period Covered by this Report: October 17, 2003 through October 16, 2004
RFA: Centers for Children's Environmental Health and Disease Prevention Research (2001) RFA Text | Recipients Lists
Research Category: Children's Health , Health Effects , Health
The objective of this research project is to investigate the effects of exposure of organotypic striatal brain slices and synaptosomes to polychlorinated biphenyls (PCBs) and methyl mercury (MeHg) on neuronal function at various developmental ages, including changes in dopamine (DA) neurochemistry and reactive oxygen species (ROS) generation. Because of the complexity of the biochemical pathways, we have examined: (1) the actions of each contaminant prior to examining the consequences of simultaneous exposure to PCBs and MeHg and (2) the consequences and mechanisms of action of the contaminants in tissue derived from adult animals before using tissue from developing animals. We have begun to study the effects of PCBs on synaptogenesis in organotypic cocultures of embryonic substantia nigra and striatum.
Effects of PCBs and MeHg on Striatal Synaptosomal Dopamine Function
We have expanded our study of the effects of PCBs and MeHg, alone or in combination, on striatal neuronal function by using purified striatal synaptosomes from developing rats at postnatal days (PND) 7, 14, and 21. Both PCBs and MeHg reduce synaptosomal DA content with the greatest effects seen in tissue from PND 7 animals (Figures 1 and 2). The Fox River PCB Mixture used in these studies is a mixture of PCB congeners similar to those found in fish from the Fox River near Green Bay, Wisconsin, the site of ongoing epidemiological studies conducted by Drs. Schantz and Sweeney.
Figure 1. PCBs and MeHg Reduce Synaptosomal DA Content With the Greatest Effects Seen in Tissue From PND 7 Animals
Figure 2. PCBs and MeHg Reduce Synaptosomal DA Content With the Greatest Effects Seen in Tissue From PND 7 Animals
Taken together, these data strongly suggest that, at least for ex vivo exposure, tissue derived from PND 7 animals is uniquely sensitive, which might be caused by higher oxidative stress in tissue. Co-exposure of PND 7 striatal synaptosomes to PCBs and MeHg antagonized the reductions in synaptosomal DA seen following exposure to PCBs only (Figure 3). These results stand in sharp contrast to the synergism seen in adult synaptosomes following exposure to PCBs and MeHg (Bemis and Seegal, 1999).
PCBs Decrease Dopamine and Tyrosine Positive Neurons in Coculture
We also are examining the biochemical consequences of PCBs using an organotypic coculture model using tissue from embryonic day (ED) 14 substantia nigra and ED 21 striatum from rats. This culture system will allow us to determine the effects of PCBs and MeHg on DA innervation of the striatum from DA cell bodies located in the substantia nigra in a similar fashion to what is seen in vivo during development. In preliminary experiments, we have demonstrated that 10-day exposure to micromolar concentrations of the Fox River PCB Mixture reduces DA concentrations in the striatum (Figure 4) and reduces the number of tyrosine-positive cell bodies in the substantia nigra (Figure 5).
Figure 3. Co-Exposure of PND7 Striatal Synaptosomes to PCBs and MeHg
Figure 4. DA Concentrations in the Striatum
Figure 5. Tyrosine-Positive Cell Bodies in the Substantia Nigra
Methylmercury Induces Reactive Oxygen Species Formation Synaptosomes from Developing Animals and Reduces Mitochondrial Function
We are assessing the role of MeHg in inducing ROS formation in synaptosomes, using the fluorescent probe dichlorofluorescin (DCFH), from adult rats as well as from PND 7, 14, and 21 rats (Figure 6). The effects were greater in tissue from young rats than in the adult synaptosomes. Despite background ROS levels being higher in synaptosomes from the youngest animals, the response to hydrogen peroxide was the same in tissue from all ages, indicating that the differences in MeHg response is not simply caused by differences in uptake, deesterification, or retention of DCFH. MeHg and H2O2 both reduced mitochondrial function in synaptosomes from adult animals, measured by the conversion of the dye methylthiazoletetrazolium to formazan by intracellular dehydrogenases, indicating that an increase in ROS may lead to mitochondrial damage (Figure 7). These experiments will be expanded to include the Fox River PCB Mixture and combinations of PCBs and MeHg.
Figure 6. Role of MeHg in Inducing ROS Formation in Synaptosomes
Figure 7. Increase in ROS May Lead to Mitochondrial Damage
We will continue to investigate the effects of exposure of synaptosomes to PCBs and MeHg on DA neuronal function at various developmental ages, expanding the studies to include tissue from early post-weaning animals. Parallel studies will be undertaken in tissue derived from animals exposed in utero to these contaminants either alone or in combination.
We will continue to examine the role that PCBs, MeHg, and the two toxicants in combination play in inducing ROS formation using synaptosomes and organotypic cocultures exposed to the above contaminants. These studies also will be expanded to include the determination of ROS formation in tissue from rats exposed in utero.
We will continue to examine the effects of PCBs and MeHg on synaptogenesis in organotypic culture of embryonic cocultures of substantia nigra and striatum. The use of tissue exposed in utero from either substantia nigra or striatum will allow us to determine whether toxicant-induced alterations in the “target” (striatum) or the substantia nigra influence axonal growth, synaptogenesis, and contaminant-induced apoptotic cell death.
We will begin studies using in vivo microdialysis to examine the developmental neurochemical consequences of exposure to PCBs and MeHg following in utero exposure in post-weaning animals.
Journal Articles on this Report : 1 Displayed | Download in RIS Format
|Other subproject views:||All 7 publications||3 publications in selected types||All 3 journal articles|
|Other center views:||All 38 publications||22 publications in selected types||All 21 journal articles|
||Bemis JC, Seegal RF. PCB-induced inhibition of the vesicular monoamine transporter predicts reductions in synaptosomal dopamine content. Toxicological Sciences 2004;80(2):288-295.||
Supplemental Keywords:children’s health, disease and cumulative effects, ecological risk assessment, susceptibility, sensitive population, toxicology, Fox River, PCBs, exposure assessment, heavy metals, methylmercury, neurotoxicity, pesticides, fish consumption,, RFA, Health, Scientific Discipline, PHYSICAL ASPECTS, ENVIRONMENTAL MANAGEMENT, Toxicology, Health Risk Assessment, Risk Assessments, Susceptibility/Sensitive Population/Genetic Susceptibility, Physical Processes, Children's Health, genetic susceptability, Molecular Biology/Genetics, Risk Assessment, sensitive populations, neurotoxic, developmental neurotoxicology, biomarkers, childhood cancer, exposure, PCBs, animal model, developmental effects, children, Human Health Risk Assessment, methylmercury, residential populations, PCB, children's vulnerablity, assessment of exposure, neurodevelopmental toxicity, neurobehavioral effects, biological markers, toxics
Progress and Final Reports:Original Abstract
Main Center Abstract and Reports:R829390 CECEHDPR - University of Illinois FRIENDS Children’s Environmental Health Center
Subprojects under this Center: (EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).
R829390C001 Neurobehavioral Effects of PCBs and Methylmercury in Rats
R829390C002 Perinatal PCB Exposure and Neuropsychological/Auditory Function
R829390C003 FRIENDS Analytical Toxicology Core Facility
R829390C004 Developmental Effects of PCBs and Methylmercury