Electron microscopy of massive cerebrocortical necrosis in suckling rats inoculated intracerebrally with mouse hepatitis virus, A59 strain.

Cerebrocortical lesions produced in suckling rats by intracerebral inoculation with MHV-A59 was studied by electron microscopy. Many cytoplasmic vesicles and irregular patterns of the nuclear membrane were observed in infected neurons at 48 h post-inoculation (p.i.). The abnormally electron-lucent or -dense neurons were seen at 72 h p.i., and in the formers, many virions were detected between the outer and inner nuclear membranes as well as in the dilated endoplasmic reticulum cisternae. Both reticular and tubular inclusion bodies appeared in the cytoplasm and some virions seemed to be associated with an end of the latter. Many virions were also seen in the intercellular spaces. At 96 h p.i. many virions were present not only in the cytoplasm of degenerated neurons but also in astrocytes appearing in the spongy lesions. There was also degeneration of oligodendrocytes while having no virions. In rats which survived the acute phase of infection and were killed at 8 days or 14 days p.i., many macrophages and fibroblasts were accumulated in the thickened leptomeninges and submeningeal area. At 22 days p.i., atrophied electron-dense neurons having no virions were scattered throughout the cerebral cortex.