Reed Miranda N, Banna Kelly M, Donlin Wendy D, Newland M Christopher
Department of Neurology and Neuroscience, University of Minnesota Medical School, 420 Delaware St., Minneapolis, MN 55455, USA.
Neurotoxicol Teratol. 2008 Jan-Feb;30(1):29-37. doi: 10.1016/j.ntt.2007.10.003. Epub 2007 Nov 1.
It has recently been demonstrated that developmental exposure to methylmercury (MeHg) is associated with perseveration on operant tasks. An understanding of the behavioral mechanisms underlying this phenomenon may improve human testing of MeHg exposures and could provide insight into clinical syndromes that include perseveration as a component. One possible mechanism is that MeHg-induced enhancement of reinforcer efficacy produces a "reinforcement trap" that inhibits change in novel situations. Rats were exposed gestationally to 0, 0.5 or 5 ppm mercury (Hg) as MeHg via maternal drinking water. They also received a diet during gestation and throughout life that was marginal (0.06 ppm) or rich (0.6 ppm) in selenium (Se), a nutrient believed to protect against MeHg's toxicity. Reinforcer efficacy was evaluated using a progressive ratio schedule of reinforcement during adulthood. Maximum ratio obtained (MRO) was determined using 20 or 60 mg sucrose pellets and with ratio requirements that increased at 5% or 20% per reinforcer. MRO was related to the rate at which the ratio increased, reinforcer magnitude, sex, and exposure regimen; MRO was increased for the 0.6 ppm Se, 5 ppm Hg group. This extends an earlier observation that developmental MeHg exposure enhances reinforcer efficacy, an effect that could be related to reports of perseveration.
最近有研究表明，发育期接触甲基汞（MeHg）与操作性任务中的持续性行为有关。了解这一现象背后的行为机制，可能会改进对人类接触MeHg的测试，并有助于深入了解包含持续性行为这一组成部分的临床综合征。一种可能的机制是，MeHg诱导的强化物效力增强会产生一个“强化陷阱”，从而抑制在新情境中的行为改变。通过给孕鼠饮用含0、0.5或5 ppm汞（Hg）的甲基汞水溶液，使其在孕期接触甲基汞。在孕期及整个生命过程中，它们还分别摄入了含硒（Se）量低（0.06 ppm）或高（0.6 ppm）的食物，硒是一种被认为可抵御MeHg毒性的营养素。成年后，使用渐进比率强化程序评估强化物效力。使用20或60毫克蔗糖颗粒，且每次强化的比率要求以5%或20%的幅度递增，来确定最大获得比率（MRO）。MRO与比率增加的速率、强化物大小、性别及接触方案有关；0.6 ppm Se、5 ppm Hg组的MRO有所增加。这扩展了早期的一项观察结果，即发育期接触MeHg会增强强化物效力，这一效应可能与持续性行为的报告有关。
