Fluoro-Jade and silver methods: application to the neuropathology of scrapie, a transmissible spongiform encephalopathy

Abstract

Traditional methods for evaluating neurodegeneration include variations of Nauta’s selective silver-staining techniques. The Fluoro-Jade (FJ) method applies a novel fluorescent, anionic stain for localizing degenerating neurons. FJ has produced comparable results to the silver methods, when both have been applied to detect neurodegeneration in animals treated acutely with a variety of neurotoxins, including kainic acid (KA), ibogaine (IBO), 3-nitropropionic acid (3-NPA), domoic acid and others. The potential value of methods selective for neurodegeneration in elucidating the pathophysiology of transmissible spongiform encephalopathies (TSEs), such as the prion disease ‘scrapie’, has not yet been investigated. Using frozen or paraffin sections stained with FJ or silver, we evaluated the brains of hamsters inoculated with either the 263K or the 139H strains of scrapie, originally passaged from sheep into mice and then into hamsters. As a positive control, we also examined sections from IBO-treated rats, which experience degeneration restricted to small clusters of Purkinje neurons located in the paravermal region of the cerebellum. As expected, both FJ and silver methods delineated this identical pattern of neurodegeneration, characteristic of IBO exposure. Surprisingly, only a small number of FJ or silver-labeled cortical neurons were observed in scrapie-infected hamsters evaluated near the end of their incubation period but before obvious spongiform pathology. Instead, there was intense fluorescent staining of astrocytes in scrapie-infected hamsters, especially in the cortex, corpus callosum, and hypothalamus. Detailed protocols describing the application of the degeneration-selective methods we utilized are presented and compared.