Nihei M K, Guilarte T R
Department of Environmental Health Sciences, The Johns Hopkins University, Room 2001, School of Hygiene and Public Health, 615 North Wolfe Street, Baltimore, MD, USA.
Brain Res Mol Brain Res. 1999 Mar 20;66(1-2):42-9. doi: 10.1016/s0169-328x(99)00005-4.
Chronic exposure to lead (Pb2+) produces deficits of learning and memory in children and spatial learning deficits in developing rats. The N-methyl-D-aspartate receptor (NMDAR) has been identified as a principal target for Pb2+-induced neurotoxicity. Age-dependent changes in NMDAR subunit gene expression were observed in hippocampi of rats chronically exposed to Pb2+ during development [T.R. Guilarte, J.L. McGlothan, Hippocampal NMDA receptor mRNA undergoes subunit specific changes during developmental lead exposure, Brain Res. 790 (1998) 98-107]. These changes were present at blood Pb2+ levels ranging from 20-60 microg/dl. Littermates were used in the present study to determine whether the changes in gene expression were reflected in protein levels. NR1, NR2A, and NR2B subunit protein levels were measured in rat hippocampus and cortex at post-natal days (PND) 7, 14, 21, and 28 by Western blot and densitometric analysis. A treatment effect was apparent for NR2A subunit protein expression in the hippocampus (F1,28=10.224, p<0.01). NR2A subunit protein was reduced by 40%, 19%, and 27% from control levels in PND14, 21, and 28 Pb2+-exposed rats, respectively. Mean comparisons indicated that rats at PND14 exhibited the most significant reduction of NR2A (p<0.001). These data concur with our previous finding of reduced NR2A mRNA found in hippocampal pyramidal and granule cells of Pb2+-exposed rats. Pb2+ exposure during development had no effect on NR1 or NR2B subunit protein expression in the hippocampus at any age. No effect was observed on any subunit in the cortex at any age. The developmental profile of the NMDAR-2A subunit protein in the hippocampus is specifically changed by chronic exposure to Pb2+. These data suggest that composition of subunits comprising NMDAR may be altered in Pb2+-exposed rats.
长期接触铅（Pb2+）会导致儿童学习和记忆能力下降，以及发育中的大鼠出现空间学习缺陷。N-甲基-D-天冬氨酸受体（NMDAR）已被确定为Pb2+诱导神经毒性的主要靶点。在发育过程中慢性暴露于Pb2+的大鼠海马中观察到NMDAR亚基基因表达的年龄依赖性变化[T.R.吉拉特，J.L.麦格洛坦，发育性铅暴露期间海马NMDA受体mRNA经历亚基特异性变化，《脑研究》790（1998）98 - 107]。这些变化出现在血铅水平为20 - 60微克/分升的情况下。本研究使用同窝出生的动物来确定基因表达的变化是否反映在蛋白质水平上。通过蛋白质印迹法和光密度分析在出生后第7、14、21和28天测量大鼠海马和皮质中NR1、NR2A和NR2B亚基蛋白质水平。海马中NR2A亚基蛋白质表达存在明显的处理效应（F1,28 = 10.224，p < 0.01）。在出生后第14、21和28天暴露于Pb2+的大鼠中，NR2A亚基蛋白质分别比对照水平降低了40%、19%和27%。均值比较表明，出生后第14天的大鼠NR2A降低最为显著（p < 0.001）。这些数据与我们之前在暴露于Pb2+的大鼠海马锥体细胞和颗粒细胞中发现NR2A mRNA减少的结果一致。发育过程中暴露于Pb2+对海马中任何年龄的NR1或NR2B亚基蛋白质表达均无影响。在任何年龄对皮质中的任何亚基均未观察到影响。海马中NMDAR - 2A亚基蛋白质的发育概况因长期暴露于Pb2+而发生特异性改变。这些数据表明，在暴露于Pb2+的大鼠中，构成NMDAR的亚基组成可能会发生改变。
