Intracytoplasmic hyaline inclusions in the hippocampal neurons of two cattle.

This report deals with the large intracytoplasmic hyaline inclusions observed in hippocampal large pyramidal cells of two Holstein-Friesian cattle. These inclusions were round to elongated polyhedral in shape with consistently homogeneous glassy appearance; they varied in size and were positive for the periodic acid-Schiff reaction and silver impregnation. Electron microscopic examination revealed that the inclusions consisted of granular materials showing moderate electron density and were bounded by a unit membrane. On the external surface of the unit membrane, there were direct connections to cellular organelles, including ribosome, rough endoplasmic reticulum, and mitochondria. These findings suggest that the inclusions might be derived from neuronal endoplasmic reticulum.