Grantee Research Project Results
2003 Progress Report: Developmental Effects of PCBs and Methylmercury
EPA Grant Number: R829390C004Subproject: 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
EPA Project Officer: Hahn, Intaek
Project Period: October 17, 2001 through October 16, 2002
Project Period Covered by this Report: October 17, 2002 through October 16, 2003
RFA: Centers for Children's Environmental Health and Disease Prevention Research (2001) RFA Text | Recipients Lists
Research Category: Children's Health , Human Health
Objective:
The objectives of this research project are to investigate the effects of exposure of organotypic striatal brain slices and synaptosomes to polychlorinated biphenyls (PCBs) and methylmercury (MeHg) on neuronal function, including changes in dopamine (DA) neurochemistry and intracellular calcium concentrations. Because of the complexity of the biochemical pathways, we have decided to examine: (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.
Progress Summary:
Effects of PCBs and MeHg on Striatal Synaptosomal Dopamine Function
PCBs and MeHg Elevate Media DA Concentrations. Purified striatal synaptosomes from adult rats were exposed to PCBs or MeHg. PCBs significantly elevated media DA concentrations, whereas MeHg induced similar although smaller changes. These effects are similar to those we previously reported in striatal organotypic cultures (Bemis and Seegal, 1999) and most likely are caused by inhibition of the DA transporter (DAT) responsible for the uptake of released DA from the synaptic cleft. Indeed, we have shown that the ortho-substituted congener 2,3,6,2',5'-pentachlorobiphenyl [C95] significantly inhibits uptake of labeled DA.
Donor Age Affects PCB-induced DAT inhibition. We demonstrated an age-dependent difference in the ability of PCBs to inhibit uptake of labeled DA in striatal synaptosomes derived from adult and postnatal day (PND) 7 and 14 rats (Figure 1). C95 inhibited DA uptake to a greater extent in tissue from PND 7 and 14 animals than in tissue from adult rats. Although elevations in media DA derived from synaptosomes from PND 7 and 14 animals were significantly increased, elevations in media DA were no greater than those seen in synaptosomes from adult rats. These results suggest that PCB-induced DAT inhibition (elevations in media DA concentrations) may not significantly affect tissue DA content.
Figure 1. Congener 95 Reduces Dopamine (DA) Uptake Into Striatal Synaptosomes in an Age-Dependent Manner
PCBs and MeHg Reduce Synaptosomal DA Content. PCBs, and to a lesser extent MeHg, also significantly reduced synaptosomal DA content. Although alterations in synaptic (i.e., media) DA concentrations play a critical role in regulating both pre- and postsynaptic neuronal activity, including de novo synthesis and further release of DA, data we have obtained recently bring into question the role that PCB-induced DAT inhibition plays in regulating tissue DA content. Using known pharmacologic antagonists of the DAT (nomifensine [NOM] and GBR 12935 [GBR]) we demonstrated that DAT inhibition and the resulting elevation in media DA are insufficient to explain the PCB-induced reductions in DA content because NOM and GBR, at doses that led to elevations in media DA similar to those seen with PCBs, failed to yield significant reductions in synaptosomal DA content. These illustrate the complex nature by which PCBs and MeHg influence DA content.
PCBs and MeHg Elevate Intrasynaptosomal Calcium Concentrations
Although we demonstrated previously that PCBs and MeHg elevate intracellular calcium concentrations ([Ca2+]i) in cerebellar granule cells (Bemis and Seegal, 2000), we have undertaken experiments using striatal synaptosomes because this latter model allows us to study the relationship between contaminant-induced changes in [Ca2+]i and alterations in neurochemical function.
Both PCBs and MeHg significantly elevate [Ca2+]i with PCBs again more active than MeHg. The relationship between changes in [Ca2+]i and DA function, however, are complex. By manipulating [Ca2+]i (i.e., using either media containing nominal concentrations of calcium or using the intracellular calcium chelator), we demonstrated that media DA concentrations were unaffected following exposure to PCBs, although synaptosomal DA content was reduced significantly. These results illustrate the important role that [Ca2+]i plays in regulating DA synthesis and further support our hypothesis that PCB-induced elevations in media DA (caused by DAT inhibition) play, at most, a minor role in regulating synaptosomal DA content.
Effects of PCBs and MeHg on Striatal Organotypic Dopamine Function Are Age-Dependent
We briefly described age-dependent differences in the response of organotypic striatal tissue to commercial PCB mixtures in the previous progress report. Additional experiments have allowed us to describe more completely the differential response of tissue derived from rats of different ages to PCBs. At low doses of PCBs (< to 20 ppm), tissue from PND 7 and 14 rats demonstrated greater decreases in DA content than tissue derived from PND 21 or adult rats. Most striking was the relative insensitivity of changes in tissue DA derived from PND 21 rats (the age at which weaning occurs) (Figure 2A, B). These changes were limited to PCB-induced reductions in DA content and were not seen either in elevations in media DA or following exposure of same aged tissue to MeHg.
Figure 2A. Effects of PCBs on Striatal Tissue | Figure 2B. Effects of PCBs on Dopamine Release From Striatal Tissue Into Media are Age Dependent |
Elevations in media DA cannot explain the insensitivity of the PND 21 tissue, and we currently are examining the consequences of PCB exposure on inhibition of the vesicular monoamine transporter (VMAT) in tissue derived from PND 21 and adult rats because Fonnum and coworkers have shown that VMAT is inhibited by ortho-substituted PCB congeners in tissue derived from the adult.
Future Activities:
We will continue to investigate the mechanisms responsible for the relative insensitivity of tissue derived from PND 21 rats. We will determine whether: (1) the insensitivity is caused by the weaning process or the chronological age of the animal; (2) the VMAT is less sensitive to PCB-induced inhibition; (3) changes in [Ca2+] are blunted in PND 21 animals; and (4) contaminant-induced increases in reactive oxygen species (ROS) formation play a role in this age-related insensitivity.
We will examine the role that PCBs, MeHg, and the two toxicants in combination play in inducing ROS formation.
We will examine the effects of PCBs and MeHg on synaptogenesis in organotypic culture of embryonic day 15 cocultures of substantia nigra and striatum. This model system will allow us to expose in utero either substantia nigra or striatum to the contaminants and determine whether toxicant-induced alterations in the target (striatum) or the substantia nigra influence axonal growth and synaptogenesis.
Journal Articles:
No journal articles submitted with this report: View all 7 publications for this subprojectSupplemental Keywords:
children’s health, disease and cumulative effects, ecological risk assessment, susceptibility, sensitive population, toxicology, Fox River, PCBs, exposure assessment, heavy metals, methylmercury, pesticides, fish consumption,, RFA, Scientific Discipline, Health, PHYSICAL ASPECTS, ENVIRONMENTAL MANAGEMENT, Toxicology, Health Risk Assessment, Risk Assessments, Susceptibility/Sensitive Population/Genetic Susceptibility, Physical Processes, Children's Health, Molecular Biology/Genetics, genetic susceptability, Risk Assessment, developmental neurotoxicology, neurotoxic, sensitive populations, childhood cancer, biomarkers, PCBs, animal model, developmental effects, exposure, Human Health Risk Assessment, children, methylmercury, assessment of exposure, children's vulnerablity, residential populations, PCB, neurodevelopmental toxicity, neurobehavioral effects, biological markers, toxicsRelevant Websites:
http://www.cvm.uiuc.edu/vb/friends_center/ Exit
Progress and Final Reports:
Original AbstractMain 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
The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.
Project Research Results
3 journal articles for this subproject
Main Center: R829390
40 publications for this center
23 journal articles for this center