Blocks, Pins, and Heavy Metal: Optimized Sample Preparation for Volume EM of Myelin in Mouse Central Nervous System

Volume electron microscopy is a widely used technique to image complex tissue architecture at high resolution for 3D reconstruction. Originally developed for brain connectomics, this technology has proven important for other applications as well. Here we describe protocols established in our laboratories for the visualization of myelin in the mouse central nervous system. The main purpose of the protocol is the optimized preparation of small samples such as vibratome slices or optic nerves. We include possible substitutions for toxic chemicals in commonly used protocols. Tannic acid and neodymium acetate turned out suitable for the replacement of thiocarbohydrazide and uranyl acetate.