The Effect Of Chronic Lead Exposure On The Leaning And Momory And Expression Of PI3K/PKB Of The Neurons In Cerebral Cortex Of Mice

ObjectiveLead is a strong nerve development toxicant.Even exposure to low levels of lead, it will damage the developing central nerve system and impair of learning and memory and mentality functions in children.Because of incompletely developed blood brain barrier,children who are exposure to lead as low as 100μg/L(blood lead level) show significant deficits of learning and memory and significant behavioral abnormal.And cause apparently irreversible damage to the nervous system.It is a matter of great import to prevent and treat lead poisoning,which related to three hundred millions children body and mind health in China and our offspring's wealthy and strong.So it is urgent to probe into lead nerve poisoning.Now,the mechanism of lead induced neurotoxic is not clarity.protein kinase B(PKB) has thorough homology with protein kinase A and protein kinase C.Because of the homology with human virus ono V-Akt,it is named as Akt. PKB/Akt pass road could active multiplicate substrate and regulate the survival,differentiation,multiplication and metabolize of cells.Erin et al.has proved that PKB/Akt could participate in the survival,differentiation and apoptosis of nerve and astroglia cells.Some studies indicate that PI3K could active downstream PKB/Akt and participate the expression of LTP in hippocampus CA1 region but have nothing to do with the inducing of LTP.The character of LTP expression is that the functions of AMPA receptor persistent strengthen.PI3K could promote the functions of AMPA receptor on the membrane and the increasing of receptor quantity.PI3K is the first factor found which would affect the expression of LTP.So people are interested in the function of PI3K.Lead is an important and strong nerve development toxicant.Even exposure to low levels of lead,it will damage the developing central nerve system and impair of learning and memory and mentality functions in people.Studies indicate that manifold protein kinases participate the process of learning and memory.There is no report about that lead affect the expression of PKB in the neuron in cerebral cortex of mice.The paper investigates the biochemistry mechanism of the effects of lead exposure on learning and memory from the view of cell signal transduction.Observe that lead of different concentrations affect to the expressions of PI3K/PKB signal molecules.Discuss the relationship between PI3K/PKB signal molecules and abnormity of learning and memory induced by lead.It's the foundation before discussing the mechanism of PI3K/PKB in survival,differentiation,apoptosis and LTP for nerve and astroglia cells.Materials and MethodsThe protocols for chronic exposure to lead were as follow:Kunming mice were purchased from animal department of china medical university and were individually housed in plastic cages and one male mouse was mated with two female mice of same strain.Mice were randomly and equally divided into four groups.On postnatal day 1, the dam began to be exposed to lead at 2.4,4.8,9.6mmol/L in their drinking water. Since weaning at postnatal 21d,the pups were directly provided lead in drinking water. Food and water were free provided to all animals.At postnatal 42d individually the hippocampus and cortex were got from mice in different groups and stored at fluid nitrogen and then stored at -70℃refrigerator.Since postnatal 42d the mice began to train in a spatial learning task using a water maze paradigm and in a passive escape reaction task using jumping paradigm.Results1.Effect of chronic Lead exposure on concentrations in blood and brain in mice.Since postnatal 42d,the concentrations in blood and brain in mice were detected. Compare with the control,the concentrations in blood and brain in mice who were exposed to chronic lead are higher evidently(P＜0.01).The level of increasing is positive correlation with the concentration of lead in drinking water.2.Chronic Lead exposure impairs spatial and passive-avoidance learning and memory in miceIn the Morris water maze task,results indicated that mice having drink lead water displayed significant impairment in their performance,and this extent of impairment showed in lead concentration dependent manner.In the jumping stand test,results suggested that lead exposure significantly reduced ability of acquiring and maintaining passive-avoidance reaction and that was correlated with concentration of drinking lead.3.Effect of chronic lead exposure on the signal molecular PI3K/PKBThe results of western blot display:The differences of expressions of PI3K between 4.8 and 9.6 mmol/L of Pb(AC)2 are meaningful(P＜0.01).Pearson results show that the expression of PI3K is negative correlation with the concentration in blood (r=—0.82,P＜0.01).The expression of PI3K is negative correlation with deficits of learning and memory(r=—0.671,P＜0.01).Compare with the control,the difference expression of total PKB(t-PKB) in lead exposure group is no significant meaningful(P＞0.05).Lead induced the decreasing of p-PKB protein expression dose dependently(P＜0.01).The levels of t-ERK showed no significant changes under different experimental conditions(P＞0.05).Pearson results show that the expression of p-PKB is negative correlation with the concentration in blood(r=—0.82,P＜0.01).The expression of p-PKB is negative correlation with deficits of learning and memory(r=—0.671,P＜0.01).Conclusion1.Chronic Lead exposure increasing the concentrations in blood and brain comparing with the control.The level of increasing is positive correlation with the concentration of lead in drinking water.2.Chronic Lead exposure impairs the ability of spatial learning and memory and passive-avoidance reaction learning.3.Chronic lead exposure could remarkable decrease expression of PI3K/PKB signal pathyway which maybe the reason for impairing learning and memory induced by lead exposure.