Any damage occur in the central or peripheral nervous system due to toxins or artificial poisons called neurotoxicity, these poisons can stop or delay the action of nerves system in transmitting signal to different nerves in different body organs. There are to many substances that affect the nervous system and cause problems like insecticides, pesticides, mercury, lead, phenol, formaldehyde, chlorine, although there is naturally toxins in brain that cause toxicity like oxygen radicals that cause disorders in movement, autonomic nervous sytem dysfunction and diseases like Alzheimer, these all neurotoxins and poisons affect the nervous system variously, some affect it immediately and others take long time to start its activity.
There are many factors that affect the effect of poison, like nature of poison and ability in metabolisation and excretion, the dose that affect the body, poisons and neuron toxins can cause many symptoms. Some of symptoms that noticed in the infected person is, loss of circulation, imbalance, depression, headache, vision loss, weakness and paralysis of limbs, loss of memory, change of behaviour and sexual problems, although there is some problem that can be noticed like extreme fatigue, asthma, hyperactivity disorders, autoimmune disorders and rheumatoid arthiritis.
There are some tests that take place for neurotoxicity and poisoning diagnosis, an example pupilography that is used for detection of brain damage, brain imaging with SPECT camera, and measurement of heart rate variability although neuropshycological tests are effective in these cases. The treatment plans in such cases of neurotoxicity and poisoning depend on delaying the action of the toxin or poison, the symptoms although needs therapy there is some type of treatment includes massage and exercise, although eating and drinking organic products.
The predictable results in that cases depend on the time of exposure to poison, and degree of damage to the nervous system, in that article we will discuss some poisons and its effect on nervous system.
Methyl mercury
It is the most toxic compound of mercury group, it enter the body through ingestion of food or water contaminated with it, it is foundd in air and being dissolved in fresh water sources then contamination of food and water occurs, it is found in air in inorganic form, but the organic form which is taken from eating fish is organic. The methyl mercury is a very poisonus matter that affect the body according to its form, the way it enter the body and the amount entered the body, an example if a pregnant woman has been exposed to methyl mercury, it results in abortion or babies that have deformaties or nervous sytem serious problems.
Mercury which is a metal has two forms, the organic form and the inorganic form, organic compounds are those which are formed from hydrogen and carbon, the organic mercury is calssified into two classifications, which are allylmercury and alkylmercury, allylmercury compounds are phenylacetate mercury and mercurochrome, while alkylmercury compounds are methylmercury and ethylmercury, the inorganic mercury came from different contaminants flows into seas, rivers, and streams, is converted to methylmercury by bacteria and plankton in water.
Methyl mercury is a very strong poison, by a little exposure to it very serious problems to nervous system occurred like, dysfunction of mitochondria, migration of cell in brain which is growing, transportation of amino acids, and other motor problems like tremors, ataxia and impaired vision. Although methyl mercury affect the fetal brains, pregnant woman who is exposed to methyl mercury may do not show any symptoms, but the infants show very serious nervous problems like paralysis and disorders in intelligence.
In japan it has been recorded poisoning with methyl mercury in Minamata, children has been exposed to high concentration of methyl mercury, it results in very serious nerves problem like mental retardation, cerebellar ataxia, physical growth disorder, dysarthria, and limb deformities. Althought it has been recorded in iraq at 1970, children was exposed to methyl mercury more than the percentage that is recorded in minamata by eating bread which the grain made of it is contaminated by it, the children shows dysesthesia, paralysis, cerebral palsy and mental disorder symptoms.
Lead poisoning
As we writing in our essay about the poisons that affect nervous system we will write about lead poisoning, firstly the individual is exposed to lead then it is strongly binds to protein in different organs had been exposed to it, it binds especially in the sulfhydrl group as it is a divalent cation. The most affected part is central nervous system, as the danger of lead summarized in competeing with calcium and binding to binding sites in cereberal phosphokinase C, although it destroys proteins and enzymes of different organs, it causes inhibition to the cellular respiration and insertion of calcium to cells, stopping energy metabolism and enter the mitochondria causing welling the distortion.
When lead affect the peripheral nervous system, it causes dangerous changes to axons as it cause axonal degeneration and demyelination of segments, drop in the wrist and ankle due to pathological changes in the extensor muscles, it has been found that lead toxicity cause changes in the function of peripheral nervous system. Lead poisoning causes slowing in the velocity of motor nerves, although changes of behaviour has been noticed in primates that had been exposed to lead, there is disability in learning and the alteration is delayed, in children it causes difficulty in reading and failure in graduation.
It has been found in some experiments on newly born children that have high lead percentage in blood some problems like attention span and reaction time is low and low rate of intelligence, although exposing to lead for long time causes neurologic and psychiatric problems, although it causes some disease like Parkinson disease, motoneuron disease and dementia. First step of management of lead toxicity is to reduce the exposure to lead, although chelatin therapy is good in that cases and reduce the percentage of lead in blood, although Calcium disodium edathamil and dimercaptosuccinic acid had been found to reduce the lead percentage in blood.
Although there have been plans to reduce the lead in environment to reduce lead toxicity, an 1973 lead has been removed from gasoline in industrial big factories and companies although in 1977 it was based that the percentage of lead in air is 1.5 µg/M3.
Pesticides
Pesticides are chemicals that has a function in killing pests including insects, insects and microbes that affect mammles, birds, fish and human, the can spread for long distances, and can take any animal as a vector, it competes with human in its food and water, pesticides although includes disinfectant, rodenticides, nematocides and fungicides. The organophosphate pesticides are the most common pesticides known, it is the most type of pesticide causing death due to pesticide ingesion, when ingesion of organophosphate pesticide occur, it inhibits acetylcholinestrase enzyme which hydrolise acetyl choline, ai affect both sympathetic and parasympathetic nerve endings as acetyl choline is the neurotransmitter to that nerve endings.
The inhibition of acetylcholinestrase enzyme results in accumulation of acetyl choline at nerve endings and myoneural junctions of skeletal muscle, the released acetyl choline acts on the muscarinic receptors on the smooth muscles, The postsynaptic sites of preganglionic fibres and neuromuscular junctions have nicotinic receptors but the central neurons have both muscarinic and nicotinic receptors. Phosphorylation to the acetylcholinestrase enzyme takes place due to binding of organophosphorus to acetyl choline, this reaction is not reversible in easy way, reactivation of acetylcholine is slow in diethyl but fast in dimethyl organophosphorus.
Arsenic poisoning
It has been recorded in different health organizations the effect of exposure to arsenic in different pathways as contaminated water sources or coal, so let us talk about the ways of exposure to arsenic and its effect on different body organs especially nervous system. Ground water has high concentration of arsenic due to geological formations, although using of pesticides and fertilizers containing arsenic, industrial , mining activities and metal processing, all of these are sources of contamination of water with arsenic.
By long periods of drinking water contain arsenic – which is a carcinogenic matter – very serious problem occur as pigmentation of the skin, obesity, cardiovascular disease, diabetes, anemia, fertility symptoms, developmental effects and neurological diseases. Accumulation of arsenic through years in body affect the behaviour, this effect increase if there is exposure to lead although due to synergetic effect, when experiments have been done on children exposed to arsenic, the show delayed alteration, disabilities in learning.
Although arsenic has been found to have dangerous effect on neurotransmittors, on an experiment done on rats exposed to arsenic, it has been found that there is increase in levels of dopamine, serotonin and its metabolites, although it has been noticed that there is a decrease in norepinephrine although as in pesticides toxicity there is a decrease in acetylcholinetrase enzyme which is responsible for metabolization of acetyl choline neurotransmitter. The hippocampus which is the part responsible for memory is effected by arsenic according to the dose exposed to, ultrastrucural and molecular changes occur to the hippocampal region as a result of exposure to a little dose of arsenic, it causes neurobehavioural changes including problems in learning as we discussed before.
It has been found that exposing to arsenic causes serious problems to brain cell, it induces apoptosis to astrocytes, reduced astrocyticexpression of glial fibrillary acidic protein, which is important to astrocytes for keeping its shape and strength, there is no treatment for arsenic poisoning, but using therapy like chelatin therapy reduces its symptoms, although it can stop the out comes like cancer.
Summarization
At the beginning of our article we wrote about the neurotoxicity and the matters responsible for that like mercury, pesticides, lead and arsenic, and the results of poisoning by these matters, like delaying of nervous system action of transmitting signals to different body organs. We firstly wrote about methyl mercury which poisoning by it happens due to ingestion of food or water contaminated with it, exposing to methyl mercury cause many problems to nervous system like , dysfunction of mitochondria, migration of cell in brain which is growing, transportation of amino acids, and other motor problems like tremors, ataxia and impaired vision.
And then we wrote about lead that causes very serious problems to nervous system by exposing to it, like degeneration and demyelination of segments in peripheral nervous system, although competeing with calcium and binding to binding sites in cereberal phosphokinase C in central nervous system. Although pesticides which enter the body like mercury by ingestion contaminated food and water, pesticedes affect nervous system especially neurotransmittors it causes inhibition to acetylcholinestrase enzyme which hydrolise acetyl choline, and then accumulation of acetyl choline and cause many problems at nerve endings.
And then we wrote about arsenic which exposure to arsenic happens through different pathways like drinking water contaminated by arsenic or workers in coal mines it is like pesticides causes problems to neurotransmittors, increase in levels of dopamine, serotonin and its metabolites, although it has been noticed that there is a decrease in norepinephrine, although it cause change in hippocampal region in brain causing problems in memory result in problems in learning.
References
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Herbert Needleman Professor of Psychiatry and Pediatrics, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15213; email: hlnlead@pitt.edu
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Molly Tolins, MD, Mathuros Ruchirawat, PhD, and Philip Landrigan, MD, MSc
ARTICLES AND REVIEWSThe Developmental Neurotoxicity of Arsenic:Cognitive and Behavioral Consequences of EarlyLife Exposure