Schwann cell and glial responses in beta, beta'-iminodipropionitrile intoxication. I. Schwann cell and oligodendrocyte ingrowths.

In rats continuously exposed to beta, beta'-iminodipropionitrile (DPN) for long periods, numerous Schwann cell and oligodendrocyte ingrowths extending into giant axonal swellings were found. These ingrowths, cytoplasmic processes of the Schwann cells and oligodendrocytes which deeply indented the axon, regularly arose from Schmidt-Lanterman clefts in the internodes. They dissected along an intra-axonal 'cleavage plane' which separated the giant axonal swellings into two compartments: an inner central channel of relatively normal axoplasm and an outer 'axoplasmic pad' comprised of circularly or spirally-arranged masses of neurofilaments. Multiple ingrowths often arose within a single internode, resulting in nearly complete segregation of the axoplasmic pad from the central channel over long distances. At the interface between the two axoplasmic compartments, internal myelin sheaths were occasionally found. The distinctive ingrowths found in this study appear to represent unusual responses of the Schwann cells and oligodendrocytes to the primary neurofilamentous axonal pathology produced by IDPN.