The association of actin with Hirano bodies.

Ultrastructural studies of the rod-shaped eosinophilic inclusions of the hippocampus (Hirano bodies) have demonstrated thin, filamentous components. The size of the filaments suggests that actin polymers (microfilaments) might form part of the Hirano body. To investigate this possibility, sections of human hippocampus and neocortex were stained, using a peroxidase-antiperoxidase (PAP) technique, with an antiserum against actin. Dense reaction product was seen over rod-shaped bodies, the location and morphology of which were typical of Hirano bodies. Immunocytochemical reactions on tissue previously stained with hematoxylin and eosin allowed a direct comparison between Hirano bodies, identified by their shape and eosinophilia, and the PAP reaction product. These results suggest an abnormal organization of a major cytoskeletal protein in hippocampal neurons, especially those of aged brains.