Immunoelectron microscopy was performed in the Microscopy Core of the Center for Systems Biology/Program in Membrane Biology (MGH, Boston, USA). The sarkosyl-insoluble fractions were resuspended in PBS, placed on formvar-carbon coated Ni grids and allowed to adsorb for 10 minutes. They were placed on drops of tau46 antibody solution (1:25, Cell Signaling Technology) for 1 hour at room temp, then rinsed on drops of PBS and placed on drops of goat-anti-mouse 10 nm gold (Ted Pella, Redding, CA, USA) for 1 hour. They were rinsed on drops of distilled water and stained for 1 minute on drops of 2% phosphotungstic acid (Electron Microscopy Sciences, Hatfield, PA, USA). Grids were examined in a JEOL JEM 1011 transmission electron microscope at 80 kV. Images were collected using an AMT digital imaging system (Advanced Microscopy Techniques, Danvers, MA, USA).
