| ObjectiveLead (Pb2+) is one of the oldest poison,which is a xaenobiotic metal with no known essential function in cellular grown,proliferation,or signaling.low-level lead exposure can also lead to the damage of nervous system,including the reduce of intelligence quotient,hearing,vision and the damage of function of peripheral nerve.Developmental nervous system is more vulnerable to lead toxicity,though nervous system can be damaged with blood lead levels below 10 ug/dl that is the lower limit of lead poisoning in children.It is associated with incompletely developed blood brain barrier, Gastrointestinal high absorptivity and low capacity of the Excretion of lead. Infant' exposure to lead can lead to irreversible damage to the nervous system,mainly showing the reduce of the ability of learning and memory and neurobehavioral abnormalities,and the damage can continue to the adulthood,even the whole life. Researchers have also confirmed that lead is by way of acting on the hippocampus that is one of the key limbic regions involved in learning and memory to influence the learning and memory function.In recent years, the influence of lead on learning and memory function and its cellular and molecular mechanism have been researched widely.However, the specific mechanism is still unclear,so it is significant to study correlative mechanisms.Neuronal growth associated protein (GAP-43) plays a significant role in the process of learning and memory. Whether low-level lead exposure at developmental stage could influence the expression of GAP-43 in hippocampus and cerebral cortex? And what is the influence mechanism? Investigation is necessary to answer these questions. Hereby, in this paper, we built a model of lead poisoning of pup rats at developmental stage by exposing the female rats to lead from the beginning of pregnancy, by which the GAP-43 expression in hippocampus and cerebral cortex at different time points and the state of learning and memory were researched, and the mechanism of the influence that low-level lead exposure exerted on learning and memory function of rats at developmental stage was explored, in order to provide a theoretical basis and an experimental basis for the prevention of lead poisoning of children.MethodsFemale Wistar rats (n=30) aging 2 were randomly divided into three group: control group, low-dose group1(0.05% PbAc), low-dose group2(0.2% PbAc).All the groups were fed normal feeds and double distilled water. After one week adaptive feed, the rats mate according to the pattern in which a female rat mate with one male, and the next morning when vaginal plug appears or sperm was found in vaginal secretion by means of microscopic examination,it was designated as gestation day 0, denoted as GDO. Since the first day of pregnancy, low-dose group 1,2 of lead were consumed 0.05%,0.2%lead acetate solution, until the postnatal day 28 (PN28) of the pups.The control group continued to drink double distilled water with no lead. Pre-weaning the offspring of lead-exposed group drank lead acetate through breast milk,and they continued to drink the same concentration of lead acetate after weaning.At PN1,PN3,PN7,PN14,PN21,PN28,individually the hippocampus and cerebral cortex were got from pups in different groups and stored at fluid nitrogen and then stored at-70℃refrigerator;At PN28,we measured the brain lead and blood lead;Since PN56 the pups began to train in a spatial learning tast using a water maze paradigm.Removing the speciments of the hippocampus and cerebral cortex,we detected the chang of expression of the neuronal growth associated protein using Immunohistochemistry and Western blot.Results1,Effect of chronic developmental low-level lead exposure on the blood lead and brain(hippocampus and cerebral cortex)lead in rat.lead levels in blood and brain of the groups of offspring in those two different lead-exposed groups were obviously higher than that in the control group,and the difference was statistically significant (P<0.01),and the extent of increasing showed in lead concentraion dependent manner.2,Effect of chronic developmental low-level lead exposure on spatial learning and memory in rats at the developmental stageIn the Morris water maze task, results indicated that rats having drunk lead water diplayed significant impairment in their performance,and this extent of impairment showed in lead concentration dependent manner.3,Effect of chronic developmental low-level lead exposure on GAP-43 expression in rat hippocampus and cerebral cortex(1) Immunohistochemistry showed:there was statistical significance (P＜0.01) in terms of the difference between the lead-exposed groups and the control group on the integral optical density (IOD) of hippocampal CA1 and CA3 areas, of cerebral cortex on PN7, PN14, PN 21 and PN28 and of DG area on PN7, PN14 and PN21, that was, the content of the protein expression of the lead-exposed groups was lower than that of the control group, compareing that of cerebral hippocampal CA1, and of cerebral cortex on PN1, PN3 and of DG area on PN28, the difference between low dose group 2 and the control group had statistical significance(P＜0.05 or P＜0.01), as well as the difference between the lead-exposed groups and the control group but that of cerebral hippocampal CA3 on PN1, PN3(P<0.01).(2)Western Blot showed:Rat pups exposed to chronic level-lead during development did express lower levels of GAP-43 expression in hippocampus and cerebral cortex than of the control group and this exhibited in a dose-dependentand developmental expressed differences manner.Conclusion1,Immunohistochemistry and Western Blot results showed that chronic developmental low-level lead exposure reduced the expression of GAP-43 in the hippocampus and cerebral cortex.2,Lead poisoning reduced the ability of learning and memory.3,Lead on the impact of GAP-43 could be a mechanism that lead poisoning lead to a decreased capacity for learning and memory mechanism.
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