Microtubules observed within the cistern of RER in neurons of the aged dog.

Twenty-seven randomly selected dogs ranging from 1 month to 16 years of age were examined light- and electron microscopically. An intraneuronal inclusion body was found im 13 of 27 cases. In particular, 12 of 13 positive cases were elderly dogs of over 8 years of age. The inclusions showed amphophilic violet color with H.-E. stain and measured 3--42 micrometer in diameter. Histochemically, they were thought to be a glycoprotein complex. The inclusions were characterized by the electron microscopy and composed of aggregated cistern of RER closely packed with tubular structures. The individual tubules measured about 24 nm in diameter and had 11--13 subunits forming their walls. These constituents were very similar to those of microtubules. The occurrence of the inclusion bodies showed an apparent age-dependency.