Neuroplastic effects of pollution
Encyclopedia
Recent research indicates that living in areas of high pollution
has serious long term implications. Living in these areas during childhood and adolescence can lead to diminished mental capacity and increased risk for brain damage. People of all ages who live in high pollution areas for extended periods place themselves at increased risk for various neurological disorders. Both air pollution and heavy metal pollution have been implicated as having negative effects on central nervous system
functionality. Pollution's ability to affect individuals' neurophysiology after central nervous system structure is fairly stabilized is an example of negative neuroplasticity
.
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, causing neurons in the cerebral cortex
to degenerate, destroying glial cells found in white matter, and by causing neurofibrillary tangles . These changes can permanently alter brain structure and chemistry, resulting in various impairments and disorders. Sometimes, the effects of neural remodeling do not manifest for a prolonged period of time.
. According to this study, children raised in areas of higher pollution scored lower on IQ tests and showed signs of brain lesions when they underwent an MRI. The children from the low pollution area scored as expected on IQ tests and did not show any signs of being significantly at risk for brain lesions. This correlation was found to be statistically significant and shows that there is a relation between pollution levels and brain lesion formation and also a relation between IQ scores and pollution levels. The implication of these findings is that high pollution levels contribute to brain lesion formation which in turn manifests visibly as impaired intellectual capability. Living in high pollution areas thus places adolescents at risk of premature brain degeneration and improper neural development; these findings could have significant implications for future generations. Dogs which spent their lives in high pollution areas showed signs of restructured blood flow in the subcortical region of their brains when compared to dogs living in low pollution areas. The kind of restructuring that was observed was similar to that seen in Alzheimer's patients, suggesting that air pollution could possibly increase an individual's risk for Alzheimer's Disease or speed up the rate at which the disease progresses in already afflicted individuals. Unfortunately, it is impossible to be certain that the difference in lesion formation is only due to pollution; other variations between the two tested locations could serve as confounding factors leading to incorrect conclusions; correlation does not imply causation
.
using a 95% confidence interval
. These air pollutants that the researchers attempted to correlate with increased incidence of epilepsy were Carbon Monoxide
, Ozone
, Sulfur Dioxide
, Nitrogen Dioxide
, large particulate matter, and fine particulate matter. The researchers tested these pollutants across seven cities; in all but one case a correlation was found between pollutant levels and the occurrence of epilepsy. All of the correlations found were shown to be statistically significant. The researchers hypothesize that air pollutants increase epilepsy risk by providing inflammatory mediators and providing a source of oxidative stress
. They believe that these changes eventually alter the functioning of the blood-brain barrier, causing brain inflammation. Brain inflammation is known to be a risk factor for epilepsy; thus this sequence of events provides a plausible mechanism by which pollution may increase epilepsy risk in individuals who are genetically vulnerable to the disease.
levels, modified neurotransmitter functions in the central nervous system, and loss of pH maintenance . A study on 350 chemical plant employees exposed to a dioxin precursor for herbicides between 1965 and 1968 showed that 80 of the employees displayed signs of initial dioxin poisoning 15 of these 350 employees were contacted once again in 2004 to come in for neurological tests to assess whether the dioxin poisoning had any long term effects on neurological capability. The amount of time that had passed made it difficult to assemble a larger cohort. The results of the tests indicated that 8 of the 15 subjects exhibited central nervous system impairment and 9 showed signs of polyneuropathy
. Electroencephalography
showed various degrees of structural abnormalities. This study showed that the effects of dioxins were not limited to initial dysfunction. Dioxins, through neuroplastic effects, can cause long term damage that may not exhibit for years.
and lead
. The impact that these two metals will have is highly dependent upon the individual. This is due to genetic variation
amongst individuals. There are many reasons that mercury and lead are particularly neurotoxic. Mercury and lead easily cross cell membranes and have oxidative effects on cells; both metals also react with sulfur in the body leading to disturbances in the many bodily functions that rely upon sulfhydryl groups and reduce glutathione levels inside cells. Methylmercury
, in particular, has an extremely high affinity for sulfhydrl groups.. Organomercury is a particularly damaging form of mercury because of its high absorbability Lead also mimics calcium
, a very important mineral in the central nervous system. This mimicry has many adverse effects upon the central nervous system . Mercury's neuroplastic mechanisms work by affecting protein production. Elevated mercury levels increases glutathione levels by affecting gene expression
and this in turn affects two proteins, MT1 and MT2, that are contained in astrocytes and neurons. Lead's ability to imitate Calcium allows it to cross the blood-brain barrier. Lead also upregulates glutathione .
, such as oxidative stress, neuroinflammation, and mitochondrial dysfunction, could be byproducts of environmental stressors such as pollution. There have been reports of autism outbreaks occurring in specific locations . Since these cases of autism are related to geographic location, the implication is that something in the environment is complementing an at risk genotype
to cause autism in these vulnerable individuals. Mercury and lead both contribute to inflammation, leading scientists to speculate that these heavy metals could play a role in autism. These findings are controversial, however, with many researchers believing that increasing rates of autism are a byproduct of more accurate screening methods and not any sort of environmental factor.
, Parkinson's Disease
, Amyotrophic Lateral Sclerosis
,and Alzheimer's are all believed to be exacerbated by inflammatory processes, resulting in individuals displaying signs of these disease at an earlier age than is typically expected.. Multiple Sclerosis occurs when chronic inflammation leads to the compromise of oligodendrocytes. This in turn leads to the destruction of the myelin sheath. After this, axons will began exhibiting signs of damage, which in turn will lead to neuron death. Multiple Sclerosis has been correlated to living in areas with high particulate matter levels in the air . In Parkinson's Disease, inflammation leading to depletion of antioxidant stores will ultimately lead to dopaminergic neuron degeneration, causing a shortage of dopamine and contributing to the formation of Parkinson's Disease. Chronic glial activation as a result of inflammation causes motor neuron death and compromises astrocytes; these factors lead to the symptoms of Amyotrophic Lateral Sclerosis. In the case of Alzheimer's, inflammatory processes lead to neuron death by inhibiting growth at axons and activating astrocytes that produce proteoglycans; this product can only be deposited at the hippocampus and cortex, indicating that this may be the reason these two areas show the highest levels of degeneration in Alzheimer's.. Airborne metal particulates have been shown to directly access and affect the brain through olfactory pathways; this direct access allows a large amount of particulate matter to reach the blood-brain barrier . These facts, coupled with air pollution's link to neurofibrillary tangles and the observed subcortical vascular changes observed in dogs, imply that the negative neuroplastic effects of pollution could result in increased risk for Alzheimer's disease and could also implicate pollution as a cause of early onset Alzheimer's disease through multiple mechanisms. The general effect of pollution is to increase levels of inflammation levels. By doing this, pollution can significantly contribute to various neurological disorders that are caused by inflammatory processes.
Pollution
Pollution is the introduction of contaminants into a natural environment that causes instability, disorder, harm or discomfort to the ecosystem i.e. physical systems or living organisms. Pollution can take the form of chemical substances or energy, such as noise, heat or light...
has serious long term implications. Living in these areas during childhood and adolescence can lead to diminished mental capacity and increased risk for brain damage. People of all ages who live in high pollution areas for extended periods place themselves at increased risk for various neurological disorders. Both air pollution and heavy metal pollution have been implicated as having negative effects on central nervous system
Central nervous system
The central nervous system is the part of the nervous system that integrates the information that it receives from, and coordinates the activity of, all parts of the bodies of bilaterian animals—that is, all multicellular animals except sponges and radially symmetric animals such as jellyfish...
functionality. Pollution's ability to affect individuals' neurophysiology after central nervous system structure is fairly stabilized is an example of negative neuroplasticity
Neuroplasticity
Neuroplasticity is a non-specific neuroscience term referring to the ability of the brain and nervous system in all species to change structurally and functionally as a result of input from the environment. Plasticity occurs on a variety of levels, ranging from cellular changes involved in...
.
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Air pollution
Air pollution is known to have serious vascular effects throughout the body; high levels of air pollution are associated with increased risk for strokes and heart attacks. By permanently affecting vascular structure in the brain, air pollution can have serious effects on neural functioning. Air pollution can also seriously affect neural matter. Currently, air pollution is known to cause damage to the central nervous system by altering the blood-brain barrierBlood-brain barrier
The blood–brain barrier is a separation of circulating blood and the brain extracellular fluid in the central nervous system . It occurs along all capillaries and consists of tight junctions around the capillaries that do not exist in normal circulation. Endothelial cells restrict the diffusion...
, causing neurons in the cerebral cortex
Cerebral cortex
The cerebral cortex is a sheet of neural tissue that is outermost to the cerebrum of the mammalian brain. It plays a key role in memory, attention, perceptual awareness, thought, language, and consciousness. It is constituted of up to six horizontal layers, each of which has a different...
to degenerate, destroying glial cells found in white matter, and by causing neurofibrillary tangles . These changes can permanently alter brain structure and chemistry, resulting in various impairments and disorders. Sometimes, the effects of neural remodeling do not manifest for a prolonged period of time.
Effects in adolescents and canines
A recent study from 2008 compared children and dogs raised in Mexico City, an area known for its high pollution, with children and dogs raised in Polotitlán, a city whose pollution levels meet the current USA National Ambient Air Quality StandardsNational Ambient Air Quality Standards
The National Ambient Air Quality Standards are standards established by the United States Environmental Protection Agency under authority of the Clean Air Act that apply for outdoor air throughout the country...
. According to this study, children raised in areas of higher pollution scored lower on IQ tests and showed signs of brain lesions when they underwent an MRI. The children from the low pollution area scored as expected on IQ tests and did not show any signs of being significantly at risk for brain lesions. This correlation was found to be statistically significant and shows that there is a relation between pollution levels and brain lesion formation and also a relation between IQ scores and pollution levels. The implication of these findings is that high pollution levels contribute to brain lesion formation which in turn manifests visibly as impaired intellectual capability. Living in high pollution areas thus places adolescents at risk of premature brain degeneration and improper neural development; these findings could have significant implications for future generations. Dogs which spent their lives in high pollution areas showed signs of restructured blood flow in the subcortical region of their brains when compared to dogs living in low pollution areas. The kind of restructuring that was observed was similar to that seen in Alzheimer's patients, suggesting that air pollution could possibly increase an individual's risk for Alzheimer's Disease or speed up the rate at which the disease progresses in already afflicted individuals. Unfortunately, it is impossible to be certain that the difference in lesion formation is only due to pollution; other variations between the two tested locations could serve as confounding factors leading to incorrect conclusions; correlation does not imply causation
Correlation does not imply causation
"Correlation does not imply causation" is a phrase used in science and statistics to emphasize that correlation between two variables does not automatically imply that one causes the other "Correlation does not imply causation" (related to "ignoring a common cause" and questionable cause) is a...
.
Epilepsy
Researchers in Chile found statistically significant correlations between multiple air pollutants and risk for epilepsyEpilepsy
Epilepsy is a common chronic neurological disorder characterized by seizures. These seizures are transient signs and/or symptoms of abnormal, excessive or hypersynchronous neuronal activity in the brain.About 50 million people worldwide have epilepsy, and nearly two out of every three new cases...
using a 95% confidence interval
Confidence interval
In statistics, a confidence interval is a particular kind of interval estimate of a population parameter and is used to indicate the reliability of an estimate. It is an observed interval , in principle different from sample to sample, that frequently includes the parameter of interest, if the...
. These air pollutants that the researchers attempted to correlate with increased incidence of epilepsy were Carbon Monoxide
Carbon monoxide
Carbon monoxide , also called carbonous oxide, is a colorless, odorless, and tasteless gas that is slightly lighter than air. It is highly toxic to humans and animals in higher quantities, although it is also produced in normal animal metabolism in low quantities, and is thought to have some normal...
, Ozone
Ozone
Ozone , or trioxygen, is a triatomic molecule, consisting of three oxygen atoms. It is an allotrope of oxygen that is much less stable than the diatomic allotrope...
, Sulfur Dioxide
Sulfur dioxide
Sulfur dioxide is the chemical compound with the formula . It is released by volcanoes and in various industrial processes. Since coal and petroleum often contain sulfur compounds, their combustion generates sulfur dioxide unless the sulfur compounds are removed before burning the fuel...
, Nitrogen Dioxide
Nitrogen dioxide
Nitrogen dioxide is the chemical compound with the formula it is one of several nitrogen oxides. is an intermediate in the industrial synthesis of nitric acid, millions of tons of which are produced each year. This reddish-brown toxic gas has a characteristic sharp, biting odor and is a prominent...
, large particulate matter, and fine particulate matter. The researchers tested these pollutants across seven cities; in all but one case a correlation was found between pollutant levels and the occurrence of epilepsy. All of the correlations found were shown to be statistically significant. The researchers hypothesize that air pollutants increase epilepsy risk by providing inflammatory mediators and providing a source of oxidative stress
Oxidative stress
Oxidative stress represents an imbalance between the production and manifestation of reactive oxygen species and a biological system's ability to readily detoxify the reactive intermediates or to repair the resulting damage...
. They believe that these changes eventually alter the functioning of the blood-brain barrier, causing brain inflammation. Brain inflammation is known to be a risk factor for epilepsy; thus this sequence of events provides a plausible mechanism by which pollution may increase epilepsy risk in individuals who are genetically vulnerable to the disease.
Dioxin poisoning
Organohalogen compounds, commonly used in pesticides, can have significant impacts on neurobiology. Some observed effects of Dioxin exposure are altered astroglial intracellular Ca2+, decreased GlutathioneGlutathione
Glutathione is a tripeptide that contains an unusual peptide linkage between the amine group of cysteine and the carboxyl group of the glutamate side-chain...
levels, modified neurotransmitter functions in the central nervous system, and loss of pH maintenance . A study on 350 chemical plant employees exposed to a dioxin precursor for herbicides between 1965 and 1968 showed that 80 of the employees displayed signs of initial dioxin poisoning 15 of these 350 employees were contacted once again in 2004 to come in for neurological tests to assess whether the dioxin poisoning had any long term effects on neurological capability. The amount of time that had passed made it difficult to assemble a larger cohort. The results of the tests indicated that 8 of the 15 subjects exhibited central nervous system impairment and 9 showed signs of polyneuropathy
Polyneuropathy
Polyneuropathy is a neurological disorder that occurs when many peripheral nerves throughout the body malfunction simultaneously. It may be acute and appear without warning, or chronic and develop gradually over a longer period of time. Many polyneuropathies have both motor and sensory...
. Electroencephalography
Electroencephalography
Electroencephalography is the recording of electrical activity along the scalp. EEG measures voltage fluctuations resulting from ionic current flows within the neurons of the brain...
showed various degrees of structural abnormalities. This study showed that the effects of dioxins were not limited to initial dysfunction. Dioxins, through neuroplastic effects, can cause long term damage that may not exhibit for years.
Metal exposure
Heavy metal exposure can result in increased risk for various neurological diseases. Current research indicates that the two most neurotoxic heavy metals are mercuryMercury (element)
Mercury is a chemical element with the symbol Hg and atomic number 80. It is also known as quicksilver or hydrargyrum...
and lead
Lead
Lead is a main-group element in the carbon group with the symbol Pb and atomic number 82. Lead is a soft, malleable poor metal. It is also counted as one of the heavy metals. Metallic lead has a bluish-white color after being freshly cut, but it soon tarnishes to a dull grayish color when exposed...
. The impact that these two metals will have is highly dependent upon the individual. This is due to genetic variation
Genetic variation
Genetic variation, variation in alleles of genes, occurs both within and among populations. Genetic variation is important because it provides the “raw material” for natural selection. Genetic variation is brought about by mutation, a change in a chemical structure of a gene. Polyploidy is an...
amongst individuals. There are many reasons that mercury and lead are particularly neurotoxic. Mercury and lead easily cross cell membranes and have oxidative effects on cells; both metals also react with sulfur in the body leading to disturbances in the many bodily functions that rely upon sulfhydryl groups and reduce glutathione levels inside cells. Methylmercury
Methylmercury
Methylmercury is an organometallic cation with the formula . It is a bioaccumulative environmental toxicant.-Structure:...
, in particular, has an extremely high affinity for sulfhydrl groups.. Organomercury is a particularly damaging form of mercury because of its high absorbability Lead also mimics calcium
Calcium
Calcium is the chemical element with the symbol Ca and atomic number 20. It has an atomic mass of 40.078 amu. Calcium is a soft gray alkaline earth metal, and is the fifth-most-abundant element by mass in the Earth's crust...
, a very important mineral in the central nervous system. This mimicry has many adverse effects upon the central nervous system . Mercury's neuroplastic mechanisms work by affecting protein production. Elevated mercury levels increases glutathione levels by affecting gene expression
Gene expression
Gene expression is the process by which information from a gene is used in the synthesis of a functional gene product. These products are often proteins, but in non-protein coding genes such as ribosomal RNA , transfer RNA or small nuclear RNA genes, the product is a functional RNA...
and this in turn affects two proteins, MT1 and MT2, that are contained in astrocytes and neurons. Lead's ability to imitate Calcium allows it to cross the blood-brain barrier. Lead also upregulates glutathione .
Autism
Heavy metal exposure, when combined with certain genetic predispositions, can place individuals at increased risk for developing autism. Many examples of central nervous system pathophysiologyPathophysiology
Pathophysiology is the study of the changes of normal mechanical, physical, and biochemical functions, either caused by a disease, or resulting from an abnormal syndrome...
, such as oxidative stress, neuroinflammation, and mitochondrial dysfunction, could be byproducts of environmental stressors such as pollution. There have been reports of autism outbreaks occurring in specific locations . Since these cases of autism are related to geographic location, the implication is that something in the environment is complementing an at risk genotype
Genotype
The genotype is the genetic makeup of a cell, an organism, or an individual usually with reference to a specific character under consideration...
to cause autism in these vulnerable individuals. Mercury and lead both contribute to inflammation, leading scientists to speculate that these heavy metals could play a role in autism. These findings are controversial, however, with many researchers believing that increasing rates of autism are a byproduct of more accurate screening methods and not any sort of environmental factor.
Accelerated neural aging
Neuroinflammation is associated with increased rates of neurodegeneration . Inflammation tends to increase naturally with age. By facilitating inflammation, pollutants such as air particulates and heavy metals cause the central nervous system to age more quickly. Many late onset diseases are caused by neurodegeneration. Multiple SclerosisMultiple sclerosis
Multiple sclerosis is an inflammatory disease in which the fatty myelin sheaths around the axons of the brain and spinal cord are damaged, leading to demyelination and scarring as well as a broad spectrum of signs and symptoms...
, Parkinson's Disease
Parkinson's disease
Parkinson's disease is a degenerative disorder of the central nervous system...
, Amyotrophic Lateral Sclerosis
Amyotrophic lateral sclerosis
Amyotrophic lateral sclerosis , also referred to as Lou Gehrig's disease, is a form of motor neuron disease caused by the degeneration of upper and lower neurons, located in the ventral horn of the spinal cord and the cortical neurons that provide their efferent input...
,and Alzheimer's are all believed to be exacerbated by inflammatory processes, resulting in individuals displaying signs of these disease at an earlier age than is typically expected.. Multiple Sclerosis occurs when chronic inflammation leads to the compromise of oligodendrocytes. This in turn leads to the destruction of the myelin sheath. After this, axons will began exhibiting signs of damage, which in turn will lead to neuron death. Multiple Sclerosis has been correlated to living in areas with high particulate matter levels in the air . In Parkinson's Disease, inflammation leading to depletion of antioxidant stores will ultimately lead to dopaminergic neuron degeneration, causing a shortage of dopamine and contributing to the formation of Parkinson's Disease. Chronic glial activation as a result of inflammation causes motor neuron death and compromises astrocytes; these factors lead to the symptoms of Amyotrophic Lateral Sclerosis. In the case of Alzheimer's, inflammatory processes lead to neuron death by inhibiting growth at axons and activating astrocytes that produce proteoglycans; this product can only be deposited at the hippocampus and cortex, indicating that this may be the reason these two areas show the highest levels of degeneration in Alzheimer's.. Airborne metal particulates have been shown to directly access and affect the brain through olfactory pathways; this direct access allows a large amount of particulate matter to reach the blood-brain barrier . These facts, coupled with air pollution's link to neurofibrillary tangles and the observed subcortical vascular changes observed in dogs, imply that the negative neuroplastic effects of pollution could result in increased risk for Alzheimer's disease and could also implicate pollution as a cause of early onset Alzheimer's disease through multiple mechanisms. The general effect of pollution is to increase levels of inflammation levels. By doing this, pollution can significantly contribute to various neurological disorders that are caused by inflammatory processes.