He T, Hirsch H V B, Ruden D M, Lnenicka G A
Department of Biological Sciences, University at Albany, SUNY, Albany, NY 12222, USA.
Neurotoxicology. 2009 Sep;30(5):777-84. doi: 10.1016/j.neuro.2009.08.007. Epub 2009 Sep 2.
Prolonged exposure to inorganic lead (Pb(2+)) during development has been shown to influence activity-dependent synaptic plasticity in the mammalian brain, possibly by altering the regulation of intracellular Ca(2+) concentration (Ca(2+)). To explore this possibility, we studied the effect of Pb(2+) exposure on Ca(2+) regulation and synaptic facilitation at the neuromuscular junction of larval Drosophila. Wild-type Drosophila (CS) were raised from egg stages through the third larval instar in media containing either 0 microM, 100 microM or 250 microM Pb(2+) and identified motor terminals were examined in late third-instar larvae. To compare resting Ca(2+) and the changes in Ca(2+) produced by impulse activity, the motor terminals were loaded with a Ca(2+) indicator, either Oregon Green 488 BAPTA-1 (OGB-1) or fura-2 conjugated to a dextran. We found that rearing in Pb(2+) did not significantly change the resting Ca(2+) nor the Ca(2+) transient produced in synaptic boutons by single action potentials (APs); however, the Ca(2+) transients produced by 10 Hz and 20 Hz AP trains were larger in Pb(2+)-exposed boutons and decayed more slowly. For larvae raised in 250 microM Pb(2+), the increase in Ca(2+) during an AP train (20 Hz) was 29% greater than in control larvae and the Ca(2+) decay tau was 69% greater. These differences appear to result from reduced activity of the plasma membrane Ca(2+) ATPase (PMCA), which extrudes Ca(2+) from these synaptic terminals. These findings are consistent with studies in mammals showing a Pb(2+)-dependent reduction in PMCA activity. We also observed a Pb(2+)-dependent enhancement of synaptic facilitation at these larval neuromuscular synapses. Facilitation of EPSP amplitude during AP trains (20 Hz) was 55% greater in Pb(2+)-reared larvae than in controls. These results showed that Pb(2+) exposure produced changes in the regulation of Ca(2+) during impulse activity, which could affect various aspects of nervous system development. At the mature synapse, this altered Ca(2+) regulation produced changes in synaptic facilitation that are likely to influence the function of neural networks.
研究表明，发育过程中长时间暴露于无机铅（Pb(2+)）会影响哺乳动物大脑中依赖活动的突触可塑性，这可能是通过改变细胞内钙离子浓度（Ca(2+)）的调节来实现的。为了探究这种可能性，我们研究了铅暴露对果蝇幼虫神经肌肉接头处Ca(2+)调节和突触易化的影响。野生型果蝇（CS）从卵期饲养至三龄幼虫，饲养培养基中分别含有0微摩尔、100微摩尔或250微摩尔的Pb(2+)，并在三龄晚期幼虫中检查已识别的运动终末。为了比较静息Ca(2+)以及冲动活动所产生的Ca(2+)变化，运动终末被加载了一种钙离子指示剂，即 Oregon Green 488 BAPTA-1（OGB-1）或与葡聚糖偶联的fura-2。我们发现，在含铅环境中饲养并不会显著改变静息Ca(2+)，也不会改变单个动作电位（AP）在突触小体中产生的钙离子瞬变；然而，在10赫兹和20赫兹AP串刺激下，铅暴露组突触小体产生的钙离子瞬变更大，且衰减更慢。对于在250微摩尔Pb(2+)环境中饲养的幼虫，AP串（20赫兹）刺激期间Ca(2+)的增加比对照组幼虫高29%，Ca(2+)衰减时间常数大69%。这些差异似乎是由于质膜钙离子ATP酶（PMCA）活性降低所致，该酶负责将钙离子从这些突触终末排出。这些发现与哺乳动物的研究结果一致，即显示出铅依赖的PMCA活性降低。我们还观察到，在这些幼虫神经肌肉突触处，铅暴露会导致突触易化增强。在AP串（20赫兹）刺激期间，铅暴露组幼虫的兴奋性突触后电位（EPSP）幅度易化比对照组高55%。这些结果表明，铅暴露会在冲动活动期间改变Ca(2+)的调节，这可能会影响神经系统发育的各个方面。在成熟突触处，这种改变的Ca(2+)调节会导致突触易化发生变化，这可能会影响神经网络的功能。
