Tubular profile of the Gallyas‐ and tau‐positive argyrophilic threads in corticobasal degeneration: An electronmicroscopic study

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Abstract
Two brains with corticobasal degeneration (CBD) were examined in order to elucidate the immunocytochemical and ultrastructural characteristics of argyrophilic threads (AT) and oligodendroglial cytoskeletal alterations. Gallyaspositive oligodendroglial perikaryal coiled bodies reacted positively with antibodies against tau and ubiquitin immunohistochemically, and consisted of 15 to 20 nm tubules with occasional irregular constrictions ultrastructurally. The present study demonstrated, for the first time, that (i) the tubular structure of the non‐physiological nature actually aggregated in the inner and outer loops of the myelin sheath, which corresponded to the histological AT; (ii) these tubules were 15 to 20 nm in diameter with occasional irregular constrictions ultrastructurally, coated with silver particles in Gallyas electronmicroscopy, positive for anti‐tau, and weakly positive for anti‐ubiquitin antibodies immunocytochemically; and (iii) the plasma membrane of the inner and outer loops that surrounded these abnormal tubules of AT was immunolabeled by both anti‐tau and anti‐ubiquitin antibodies. Argyrophilic threads and oligodendroglial perikaryal coiled bodies share the immunohistochemical, immunocytochemical, and electronmicroscopical characteristics. Therefore, it is considered that the common tau‐pathology may develop in the oligodendroglia from the perikarya throughout its process. In conclusion, the cytoskeletal pathology in oligodendroglial process is of significance in the pathoetiology of CBD.