Neuronal degeneration in the brain of the brindled mouse. II. Ultrastructure of neuronal inclusions in the cerebral cortex.

Two types of intra-cytoplasmic inclusions were observed in many cortical neurons of hemizygous brindled mutant mice (MObr/Y) which survived for more than 1 month. One type is an electron-lucent vacuole containing numerous vesicles and membrane fragments, some arranged concentrically, and the other consisted of electron-dense matrix with myelin figures. These inclusions were, as a rule, found near the axonal hillock where abnormally enlarged mitochondria were often present. In view of the presence of many features suggestive of autophagic vacuoles and absence of such inclusions in the oldest mice (91 days old), we hypothesize that these inclusions probably represent a focal repairing process of neurons from the sublethal injury.