Excessive production of nitric oxide (NO) due to the overinduction of inducible nitric oxide synthase (iNOS) has a severe cytotoxic effect, which may relate to the pathogenesis of neurodegenerative disorders. In this study, we report the novel finding that iNOS is overinduced in a large number of bizarre astrocytes in the white matter of patients with panencephalopathic (PE)‐type Creutzfeldt–Jakob disease (CJD). This study was carried out on brain tissue from seven patients with PE‐type CJD. As controls, 12 normal individuals and nine patients with cerebral infarction were examined. We identified a large number of bizarre astrocytes in the degenerative cerebral white matter in PE‐type CJD. Using immunohistochemistry, only bizarre astrocytes in PE‐type CJD showed strong immunoreactivity for both iNOS and superoxide dismutase 1 (SOD1). Ultrastructural examination demonstrated that these bizarre astrocytes contained many free polyribosome‐like granules. No significant iNOS immunoreactivity was observed in either the astrocytes of patients with cerebral infarcts or in the normal controls. This study suggests that the iNOS‐overexpressing astrocytes, especially iNOS‐overexpressing bizarre astrocytes, could play an important role in the development of white matter lesions in PE‐type CJD. Our data also suggest that the bizarre astrocytes could be protecting themselves from the cytotoxicity of NO by producing SOD1. These immunohistochemical findings are supported by the ultrastructural observation of numerous polyribosome granules restricted to the cytoplasm of these bizarre astrocytes.

Niemann‐Pick disease type C (NPC) is a neurovisceral lipid‐storage disease. Although NPC patients show lipid storage in anterior horn cells of the spinal cord, little information is available regarding the electron microscopic analyses of the morphologies of intra‐endosomal lipid like‐materials in the anterior horn cells of NPC patients. In this study, we elucidated the intra‐endosomal ultrastructures in spinal anterior horn cells in an NPC patient, as well as in mutant BALB/c NPC1−/− mice with a retroposon insertion in the NPC1 gene. These morphologies were classified into four types: vesicle, multiple concentric sphere (MCS), membrane, and rose flower. The percentages of the composition in the NPC patient and NPC1−/− mice were: vesicle (55.5% and 14.9%), MCS (15.7% and 3.4%), membrane (23.6% and 57.1%), and rose flower (5.2% and 24.6%), respectively. Formation of the intra‐endosomal structures could proceed as follows: (i) a vesicle or MCS buds off the endosome into the lumen; (ii) when a vesicle breaks down, a membrane is formed; and (iii) after an MCS breaks down, a rose flower structure is formed. Our new finding in this study is that ultrastructural morphology is the same between the NPC patient and NPC1−/− mice, although there are differences in the composition.