Jett David A, Beckles Rondell A, Navoa Ryman V, McLemore Gabrielle L
Department of Environmental Health Science, Johns Hopkins University Bloomberg School of Public Health, Baltimore, MD 21205, USA.
Neurotoxicol Teratol. 2002 Nov-Dec;24(6):805-11. doi: 10.1016/s0892-0362(02)00314-8.
Receptor autoradiography and membrane radioligand-binding assays were used to determine the expression of nicotinic cholinergic receptors in the brains of weanling rats exposed to low-levels of lead (Pb) during development. Nicotinic receptors were identified with the frog toxin epibatidine (EB) that binds with high affinity to a variety of receptors containing alpha and beta subunits. Rat pups were exposed to Pb from their mothers given 750-ppm Pb in the diet beginning on gestational day 0 through postnatal day (PN) 21. Blood Pb levels ranged from 36.5 to 46.5 microg/dl in the PN21 pups, and this exposure did not alter their body weight when compared to control rats. Several brain regions identified by autoradiographic studies as having significant binding of EB were dissected from control and Pb-treated pups and used in saturation-binding experiments with membrane preparations to determine the affinity constant (K(d)) and maximal-binding capacity (B(max)) of [3H]EB. Results indicate that the B(max) of [3H]EB was increased in several brain regions in Pb-treated rat pups, without a significant effect on K(d) estimates. [3H]EB-binding to membranes from untreated rats was not affected by in vitro exposure to 20-microM Pb, indicating that the effect of Pb on [3H]EB-binding in vivo was not likely due to direct influence of free Pb remaining in the tissue at the time of assay. The data therefore suggest that expression of nicotinic receptors that bind [3H]EB were increased by developmental exposure to Pb. Several possible mechanisms for these effects and the potential toxicological significance are discussed.
采用受体放射自显影术和膜放射配体结合分析法，以确定在发育过程中暴露于低水平铅（Pb）的断奶大鼠大脑中烟碱型胆碱能受体的表达情况。用蛙毒素埃博霉素（EB）鉴定烟碱型受体，该毒素能与多种含有α和β亚基的受体高亲和力结合。从妊娠第0天至出生后第21天，给孕鼠喂食含750 ppm Pb的饲料，使其幼崽暴露于Pb。出生后第21天的幼崽血铅水平在36.5至46.5微克/分升之间，与对照大鼠相比，这种暴露并未改变它们的体重。通过放射自显影研究确定的几个对EB有显著结合的脑区，从对照和Pb处理的幼崽中分离出来，用于与膜制剂进行饱和结合实验，以确定[3H]EB的亲和常数（K(d)）和最大结合容量（B(max)）。结果表明，在Pb处理的大鼠幼崽的几个脑区中，[3H]EB的B(max)增加，而对K(d)估计值无显著影响。未处理大鼠的膜与[3H]EB的结合不受体外暴露于20 μM Pb的影响，这表明Pb对体内[3H]EB结合的影响不太可能是由于测定时组织中残留的游离Pb的直接影响。因此，数据表明发育过程中暴露于Pb会增加与[3H]EB结合的烟碱型受体的表达。讨论了这些效应的几种可能机制及其潜在的毒理学意义。
