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Effects of lead exposure at different developmental stages on spatial learning and memory in rats and its microstructural changes in the region CA1 of the hippocampus

FU Dagan,LI Huaqiang,SHI Yuan,et al. Department of Pediatrics, Daping Hospital, Third Military Medical University ,Chongqing 400042,P.R.China  
Objective To investigate the spatial learning and memory of adult rats which were exposed to lead at different developmental stages and to explore the microstructural changes in the region CA1 after lead exposure in the early development of the central nervous system.Methods Morris water maze and electron microscopy were applied to observe the spatial learning and memory of adult rats and the microstructural changes in the region CA1. Results The results showed that the scores of Morris water maze task were significantly reduced in the permanent group and perinatal group as compared to the control group(P0.05), while the postweaning group did not significantly differ from the control group (P0.05). Electron scopic observation:lead exposure in the early developing phases, in the region CA1, the changes including myelinic layer, neuropile vacuole and abnormal dense bodies in cytoplasm and lysosome in the peripheral vessels, pyknotic compact of gliocyte, peripheral interstitial edema, disorder of cytoplasmic collacin and mitochondrial compact. In fact, no significant change occurred in the structure of synapsis.Conclusions We may come to the conclusion that the vulnerability of the early developing central nervous system is higher than that of the mature central nervous system after chronic low lead exposure.That is to say , pregnant women and infants are high risk population and we should monitor their blood lead in time. In addition, microstructural changes indicate that in the early developing period of hippocampus, low level lead exposure may disturb the conduction of electro neuronal impulse and metabolism of neurons as well as structure of brain blood barrier. This may be one of the morphologic basis for the mechanism of its effect on learning and memory.
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