لخّصلي

The brain of adults exposed to increased lead levels during their childhood also shows a decreased volume, especiallyin the prefrontal cortex on MRI . Lead is able to pass through the endothelial cells at the blood brain barrier because it can substitute for calcium ions and be taken up by calcium-ATPase pumps, thereby interfering with synapse formation. Children with blood lead concentration greater than 10μg/dL are at higher risk for developmental disabilities . The effect of lead on children´s cognitive abilities takes place at very low levels . There is apparently no lower threshold to the dose-response relationship below which lead exposure is treated as safe.Blood lead levels lower than 5 μg/dL were found to be associated with reduced academic performance . Blood lead levels below 10 μg/dL were reported to be associated with lower IQ and behaviour problems such as aggression, in proportion with the given blood lead level . Between the blood lead levels of 5 and 35 μg/dL, an IQ decrease of 2–4 points for each μg/dL increase was reported in children . Increased blood lead levels are also associated with a decrease in cognitive performance and with other psychiatric conditions like depression and anxiety . An increase in the blood lead levels from 50 to about 100 μg/dL in adults was found to be associated with more severe conditions, like permanent impairment of central nervous system function . With increased lead exposure in children, an increase in neuropsychiatric disorders like attention deficit hyperactivity disorder and antisocial behaviour were found . Prenatal and early childhood lead exposure was reported in correlation with violent crimes in adulthood. The highest lead levels in the air were also shown to deviate normal behaviour and turn to become aggressive and violent, thus for example the highest murder rates were found in countries with high levels of lead in the air . One study theorizes that lead exposure explains 65% to 90% of the variation in violent crime rates in the US . Another study showed a strong association between preschool blood lead levels and subsequent crime rate trends over several decades across nine countries . The hippocampus is a part of the brain involved in learning and memory. The main reasons for lead interfering with learning particularly in children is that it damages the cells within the hippocampus. In rats exposed to lead, structural damage such as irregular nuclei and denaturation of myelin were reported . Lead is also involved in interfering with the release of neurotransmitters . Neurotransmitters are chemicals used by neurons to send signals to other cells. This interference leads to the disruption of communication between cells. Lead usually interferes with the neurotransmitter glutamate which is important for many functions, like learning. It operates by blocking NMDA receptors. Blocking of such receptors is thought to be the main target of lead toxicity. One study found that in addition to inhibition of the NMDA receptor, lead exposure also decreased the amount of gene for this receptor in part of the brain .