Summary of Study Results
Parkinson’s Disease, Dopamine and PCBs
Each entry below represents one finding in a brain chemistry study, unless otherwise noted. Some studies had multiple findings. For additional information, see Parkinson's Table of Contents.
Keep in mind that not all of the 38 studies are equal in size or quality. Some examine the effects of old PCB commercial mixtures (which had variable composition), or just one or two individual types of PCBs (out of 209 possible.) This accounts for some of the varying results. It’s clear that not all PCBs have the same effects. Some studies used high and some used low doses of PCBs. Some tested adult exposure to PCBs, others tested offspring of PCB exposed mothers.
- diortho-substituted PCBs may contribute to the pathogenesis of Parkinson's disease
- Parkinson’s victims had significantly higher concentrations of total PCBs, and PCBs 153 and 180 in their brain tissue
- low PCB doses reduce serotonergic cell numbers (1 ppm PCB levels --- and much higher --- have been commonly found in fish along the Fox River, Green Bay and Lake Michigan)
- PCBs cause dose-dependent decreases in dopamine (6 studies)
- PCB levels higher than 100 micrograms per milliliter (.1 ppm) caused 85% mortality of dopaminergic cells [Note: Parkinson’s Disease symptoms begin at 85% mortality of dopaminergic cells in the brain.]
- cells showed increasing sensitivity over time to lower doses of PCBs
- PCBs cause neurite elongation and decreased cellular dopamine levels
- PCBs and mercury are much more potent together in decreasing dopamine than if they were separate [Note: Fox River and Green Bay fish contain both PCBs and mercury]
- significant synergism between these two contaminants may involve an elevation of free intracellular calcium
- fish-consumption guidelines may need to consider these interactions
- PCBs have long-lasting effects on dopamine and serotonin producing processes
- PCB exposure results in alterations in serotonin metabolism but not dopamine metabolism in offspring of PCB exposed mothers, which differs from PCB induced neurotoxicity in adult animals
- low doses of PCBs inhibit dopamine (2 studies)
- inhibition of vesicular uptake may contribute to the decrease of dopamine
- PCBs affect dopamine and serotonin processes
- PCBs induce serotonin release
- PCB levels in the brain dropped after PCB exposures stopped
- long term dysfunction that results in lowered brain dopamine is probably due to initial PCB damage
- both lightly and highly chlorinated PCBs are responsible for changes in neurochemical function
- PCBs induce permanent functional and neurochemical changes in adults when given to newborns during the peak of rapid brain growth genetic factors may alter the susceptibility to the effects of PCBs on dopamine synthesis
- PCBs may inhibit tyrosine-hydroxylase activity and dopamine synthesis through an indirect mechanism
- ortho-chlorinated PCBs reduced dopamine levels by decreasing potassium ions through non Ah receptor mechanisms
- inhibition of tyrosine uptake was not the primary mechanism by which PCBs reduce dopamine levels
- low PCB exposures to adults decreased dopamine concentrations in adults
- 3 ortho-substituted types of PCBs decreased dopamine concentrations
- some PCBs increase dopamine, others decrease dopamine
- behavioral abnormalities
- reduced concentrations of catecholamines such as norepinephrine and dopamine
- non-dioxin-like PCBs have a high potency for decreasing brain dopamine levels
- interfered with calcium homeostatic mechanisms and intracellular second messenger systems
- only non-coplanar PCB congeners reduce dopamine content in the adult central nervous system
- both coplanar and non-coplanar PCBs alter brain dopamine during development
- either increases or decreases in brain dopamine concentrations induce deficits in working memory
- one dose of modest PCB levels during pregnancy effects dopamine regulation in the offspring
- altered locomotor activity and decreased brain dopamine function
- dopamine function in offspring is altered by PCBs in both the womb and/or through breastfeeding
- dopamine changes persist even when PCBs are no longer found in the brain
- lower-chlorinated ortho-substituted PCBs affect dopamine levels (therefore, they’re not as "non-toxic" as some believed)
- ortho-substituted PCBs bind to (and interfere with) important sites for brain chemical formation, including dopamine
- PCB induced behavioral changes may in part be caused by an alteration in brain dopamine concentration.
- fetus or newborn PCB exposure results in increased neurotransmitter concentrations while adult exposure results in decreased concentrations
- PCB exposed monkeys were learning impaired on spatial tasks but facilitated learning on object tasks
- PCB effects are not easily comparable to dioxin --- therefore, toxic equivalency factors (TEFs) are not appropriate
- Great Lakes fish significantly reduce brain dopamine levels, causing deficits in brain function in children of fish-eating mothers
- PCBs reduce brain dopamine levels in the lab, but at much higher PCB doses than found in Great Lakes fish
- other contaminants present in Great Lakes fish may interact synergistically with PCBs to produce greater neurotoxicity
- PCBs may serve as a marker for other contaminants responsible for the observed effects
- PCBs decrease cell dopamine levels through interaction at brain sites which prefer ortho substituted or ortho,para substituted PCB congeners
- PCBs, and not their metabolites, are the toxicants
- PCBs inhibit tyrosine hydroxylase and L-aromatic amino acid decarboxylase, two enzymes involved in the synthesis of dopamine.
- PCBs did not appear to disrupt the pattern of receptor development, and did not appear to result in up regulation.
- females appear more sensitive than males
- PCBs reduce tissue dopamine and elevate media dopamine
- the mature mammalian nervous system is sensitive to a brief exposure to PCBs
- PCBs alter dopamine levels differently in different areas of the brain
- the variable composition of PCB residues in the environment and different PCB mechanisms of toxicity complicate the development of scientifically based regulations and risk assessments.
- PCBs block dopamine synthesis by inhibiting tyrosine hydroxylase (which is supposed to produce a chemical called L-dopa, which in turn stimulates production of dopamine.) (2 studies)
- PCBs may also interfere with vesicular monoamine transporter (affecting storage or release of dopamine)
- PCBs did not cause any significant changes in dopamine concentrations
- PCBs increased serum levels of dopamine
- cell suicide is a sensitive and early indicator of acute and chronic chemical stress, loss of cellular function and structure, and organismal health
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