Retro is the new modern: Contemporary application of gold impregnation staining on brain cryosections for digital image analysis

Background and purpose: Since the times of Golgi and Cajal, impregnation with gold or silver has been used to visualize microscopic details of the nervous tissue. Although immunohistochemistry has largely replaced impregnation techniques, they are still used, and there is a growing interest in combining them with modern image analysis methods for quantitative studies in neuroscience. The aim of this research was to modify the gold chloride impregnation method published by Schmued to improve consistency of staining, to be adequate for digital image analysis. Materials and methods: Brains of 8 six-month-old female Wistar rats were fixed in 4% PFA, cryoprotected in sucrose and flash-frozen in liquid nitrogen. Neighboring sets of coronal sections were chosen for gold impregnation, Nissl staining and MAP2 immunohistochemistry. Whole-slide images and images of specific regions were taken for analysis. Results: Myelinated fibers were stained dark reddish to brown on gold stained sections, and other tissue was yellowish, which gave an excellent contrast for digital image analysis. Gold staining was consistent in all regions, and no major artifacts were noticed. When compared to Nissl and MAP2, only myelinated structures were stained with gold impregnation. Conclusions: Modified gold impregnation method is an alternative that's on par with traditional myelin staining methods. The new, modified gold impregnation method gives a consistent and reproducible staining suitable for digital image analysis. It can be useful in morphometric evaluation of nervous tissue and investigation of neuropathological changes in nervous tissue, especially for quantitative studies.