Valentine Holly L, Does Mark D, Marshall Vivian, Tonkin Elizabeth G, Valentine William M
Department of Pathology, Vanderbilt University Medical Center, 21st Avenue S., Nashville, TN 37232, USA.
Neurotoxicology. 2007 May;28(3):645-54. doi: 10.1016/j.neuro.2007.01.009. Epub 2007 Feb 2.
Standard light microscope histological evaluation of peripheral nerve lesions has been used routinely to assess peripheral nerve demyelination; however, the development of magnetic resonance (MR) methodology for assessing peripheral nerve may provide complementary information, with less expense and in less time than nerve histology methods. In this study, the utility of multicomponent NMR T(2) relaxation analysis for assessing myelin injury in toxicology studies was examined using two dithiocarbamates, N,N-diethyldithiocarbamate (DEDC) and pyrrolidine dithiocarbamate (PDTC), known to produce myelin injury and elevate copper in the nervous system. T(2) analysis was used in conjunction with standard histological methods to assess myelin injury and determine if dithiocarbamate-mediated copper accumulation in peripheral nerve was associated with more severe myelin lesions. Male Sprague-Dawley rats were administered i.p. DEDC for 8 weeks and maintained on either a diet containing normal (13 ppm) or elevated (200 ppm) copper. Another group of male Sprague-Dawley rats was administered oral PDTC and a 200 ppm copper diet, with controls given only the 200 ppm copper diet, for 47 weeks. Following exposures, the morphology of sciatic nerve was evaluated using light microscopy and multicomponent T(2) analysis of excised fixed nerves; and copper levels in sciatic nerve were determined using ICP-AES. Light microscopy demonstrated the presence of a primary myelinopathy in dithiocarbamate-exposed rats characterized by intramyelinic edema, demyelination, and secondary axonal degeneration. Both the nerve copper level and number of degenerated axons, as ascertained by ICP-AES and microscopy, respectively, were augmented by dietary copper supplementation in conjunction with administration of DEDC or PDTC. T(2) analysis revealed a decreased contribution from the shortest T(2) component in multicomponent T(2) spectra obtained from animals administered DEDC or PDTC, consistent with decreased myelin content; and the decrease of the myelin water component was inversely correlated to the levels of nerve copper and myelin lesion counts. Also, the T(2) analysis showed reduced variability compared to histological assessment. These studies support multicomponent T(2) analysis as a complementary method to light microscopic evaluations that may also be applicable to in vivo assessments.
外周神经损伤的标准光学显微镜组织学评估一直被常规用于评估外周神经脱髓鞘；然而，用于评估外周神经的磁共振（MR）方法的发展可能会提供补充信息，且成本低于神经组织学方法，耗时也更短。在本研究中，使用两种已知会导致髓鞘损伤并使神经系统中铜含量升高的二硫代氨基甲酸盐，即N，N - 二乙基二硫代氨基甲酸盐（DEDC）和吡咯烷二硫代氨基甲酸盐（PDTC），来检验多组分核磁共振T(2)弛豫分析在毒理学研究中评估髓鞘损伤的效用。T(2)分析与标准组织学方法结合使用，以评估髓鞘损伤，并确定二硫代氨基甲酸盐介导的外周神经铜积累是否与更严重的髓鞘病变相关。给雄性Sprague-Dawley大鼠腹腔注射DEDC，持续8周，并维持在含正常（13 ppm）或高铜（200 ppm）的饮食上。另一组雄性Sprague-Dawley大鼠口服PDTC并给予200 ppm铜的饮食，对照组仅给予200 ppm铜的饮食，持续47周。暴露后，使用光学显微镜和对切除的固定神经进行多组分T(2)分析来评估坐骨神经的形态；并使用电感耦合等离子体发射光谱法（ICP-AES）测定坐骨神经中的铜含量。光学显微镜显示，在暴露于二硫代氨基甲酸盐的大鼠中存在原发性髓鞘病，其特征为髓鞘内水肿、脱髓鞘和继发性轴突变性。通过ICP-AES和显微镜分别确定的神经铜水平和变性轴突数量，在给予DEDC或PDTC的同时补充膳食铜后均有所增加。T(2)分析显示，从给予DEDC或PDTC的动物获得的多组分T(2)光谱中最短T(2)成分的贡献降低，这与髓鞘含量降低一致；髓鞘水成分的降低与神经铜水平和髓鞘病变计数呈负相关。此外，与组织学评估相比，T(2)分析显示变异性降低。这些研究支持多组分T(2)分析作为光学显微镜评估的补充方法，该方法也可能适用于体内评估。
