Light and electron microscope localization of the microtubule-associated tau protein in rat brain.

We have studied the distribution of microtubule-associated tau proteins in rat brain using monoclonal and affinity-purified polyclonal antibodies. Tau staining is prominent in axons in white matter areas of brain, as reported by Binder et al. (1985). In addition, we also find tau protein in neuron cell bodies, especially in the brain stem and basal ganglia and in the cell bodies of interfascicular oligodendroglia. Using electron microscopy, tau antibodies and colloidal gold-labeled second antibodies, gold particles are found associated with microtubules in axons and in the cytoplasm of cell bodies, while the nuclei, mitochondria, and myelin remain unlabeled. In double-staining experiments, tau staining co-localizes with that of tubulin. Our studies indicate that tau proteins are more widely distributed in brain than previously reported and cannot be used as an exclusive marker for axons.