| Lead is a heavy metal element primarily for neurotoxicity, which has obvious and sure damage to nervous system. Children's nervous system is under rapid and perfecting period, sensitive to lead poisoning . And it is known that subclinical lead poisoning might do harm to children's intelligence as well as memories ability. Nitric oxide (NO) is regarded as typical retrograde messenger, important in learning and memory. Its biosynthesis is modulated by nitric oxide synthase (NOS). At present, the level of NO is reflected mainly by NOS activity. Lead can inhibit NOS activity and therefore reduce NO. By means of establishing a series of rat models exposed to different low level lead during developing period, we observed effects of developmental lead exposure on nitric oxide synthase activity in different brain regions (hippocampus, cerebellum, cerebral cortical, brain stem)of rat, researched the relationship between NOS activity and lead level , time of exposure, and provided experiment evidence on how lead harms learning and memory function. Methods:Twenty-nine Female SD rats were randomly assigned to distilled water containing 0, 0.025%, 0.05%, 0/075% lead acetate (PbAc-3H2O). Treatment was started two weeks prior to mating. Pups were weaned at 21 day of age andfed the same diet as the dams. At each developmental time point (7,14,21 and 28 days age), pups were euthanized by decapitation and hippocampus, cerebellum, cerebral cortical, brain stem were dissected on an ice-chilled plate, stored at -70C until used for NOS activity studies. Blood samples of pups for lead analysis were obtained by heart puncture, and the samples of dams were obtained by thigh venous puncture. Analysis of Pb concentrations in blood was performed by graphite furnace atomic absorption spectrometry. Statistical analysis:All values were expressed as mean ?SD. All statistical comparisons among groups were conducted using one way analysis of variance (ANOVA). All statistical comparisons in different brain regions were also conducted using analysis of covariance. Results:(1) No differences in body weight of dams were measured between any two groups (P>0.05). The blood lead level of Pb-exposed dams were higher than those of control group (PO.05)(2) There were no differences in body weight of pups between any two groups at nay age (P>0.05). The blood lead level of Pb-exposed pups were higher, having significant difference with control, and the exposed groups have significant difference with one another (P<0.05). As lead increased in dam's drinking water, the blood lead in pups increased correspondingly and changed regularly: at age of 14th day, it was lower than that of 7th day, and increased to a highest level at 21st day, then returned to lower level at 28th day.(3) NOS activity in hippocampus showed: NOS activity of 0.05% and 0.075% groups were higher than that of 0.025% group, but on the 7th day and 14th day of the birth, the three groups showed no difference, and no significant difference compared with control (P>0.05). While on the 21st and 28th day, NOS activity of each experiment group were obviously higher than that ofcontrol group (P<0.01). On the 21st day 0.075%group had higher NOS activity than 0.025% group. While on the 28th day, NOS activity of both 0.05% and 0.075% groups were higher than that of 0.025% group, having significant difference by testing.(4) On the 7th day and 14th day after birth, NOS activity in cerebellums from each group had no difference by comparison (P>0.05). While on the 21st day and 28th day, each group had obvious difference in NOS activity (P<0.01). On the 28th day, NOS activity of 0.075% and 0.05% groups were higher than that of 0.025% group, having significant difference by testing (P<0.05).(5) NOS activity in cerebral cortical showed: on different time points, NOS activity of 0.075% group was obviously lower than that of control, 0.025% group and 0.05%group (P<0.05). While the last three groups had no significant difference compared with each other on the same time p...
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