Developmental effects of PCBs and methylmercury

我们已经证明，共同暴露于多氯联苯（PCBs）和甲基汞(MeHg)-在福克斯河鱼类中发现的两种主要神经毒物-协同增加纹状体组织中多巴胺（DA）的释放，并改变培养细胞中的细胞内钙浓度。我们现在提出的实验将使我们能够验证以下假设：(i)发育过程中暴露于多氯联苯和甲基汞会引起与我们在成人中看到的相似的神经化学变化；（ii）这些变化是由于DA的释放增强和细胞内钙的改变；（iii）这些变化将诱发氧化应激，可能导致程序性细胞死亡增加；（iv）这种发育性神经元重塑将导致行为的持续变化。为了验证这些假设，我们将首先进行一系列体外实验，使用发育中的大鼠纹状体的完整脑切片和突触体来证实我们在成年动物身上得到的结果。在这些体外实验中，我们将测量培养基和细胞DA水平；细胞内钙浓度，羟基自由基形成和脂质过氧化。这些数据将有助于体内实验，在体内实验中，暴露于这些污染物的发育后果将被确定。在发育暴露的动物中，我们还将使用体内微透析测量额叶皮层和纹状体的细胞外DA和羟基自由基浓度，以及断奶前和成年动物黑质的凋亡指数（DNA链断裂、caspase-3、形态变化）。这些实验将：(1)有助于理解共同暴露于这些污染物改变行为的机制；（ii）提供发育数据，以证明目前基于单一污染物暴露的鱼类消费指南的修订是合理的；（iii）最重要的是提供干预/教育目的的信息，因为这些污染物定位于鱼类的不同组织，将允许改变物种的选择，以及福克斯河鱼类的制备和消费。

We have demonstrated that co-exposure to polychlorinated biphenyls (PCBs) and methylmercury (MeHg)-two of the major neurotoxicants found in fish from the Fox River-synergistically increases the release of dopamine (DA) in striatal tissue and alters intracellular calcium concentrations in cells in culture. The experiments we now propose will allow us to test the hypotheses that: (i) developmental exposure to PCBs and MeHg will induce neurochemical changes similar to those we have seen in the adult; (ii) these changes are due to enhanced release of DA and alterations in intracellular calcium; (iii) these changes will induce oxidative stress that may lead to increased programmed cell death and (iv) this developmental neuronal re-modeling will lead to persistent changes in behavior. In order to test these hypotheses we will first carry out a series of in-vitro experiments using intact brain slices and synaptosomes from developing rat striata to confirm results we obtained in the adult animal. In these in-vitro experiments we will measure media and cellular DA levels; intracellular calcium concentrations, hydroxyl radical formation and lipid peroxidation. These data will aid in the in- vivo in the in-vivo experiments in which the developmental consequences of exposure to these contaminants will be determined. In developmentally exposed animals we will also measure extracellular DA and hydroxyl radical concentrations in frontal cortex and striatum using in-vivo microdialysis, as well as indices of apoptosis (DNA strand breaks, caspase-3, morphological changes) in the substantia nigra of both pre- weaning and adult animals. These experiments will: (1) aid in understanding the mechanisms by which co-exposure to these contaminants alter behavior; (ii) provide developmental data that may justify revision of fish consumption guidelines currently based on exposure to single contaminants and (iii) and most importantly provide information for interventional/educational purposes since these contaminants, localized in different tissues within the fish will allow for changes in the choice of species and the preparation and consumption of fish from the Fox River.