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Intranuclear inclusions found in glial cells of two cases of subacute sclerosing leukoencephalitis have been examined in the electron microscope. The inclusions are composed of filamentous tubules 170 to 230 angstroms in diameter, which bear a general resemblance to the intranuclear structures observed in cells infected with measles virus. This finding provides further suggestive evidence that a virus may be involved in the pathogenesis of subacute sclerosing leukoencephalitis.

In dengue type-2 virus-infected neurones of suckling mice, formation of single-membrane vesicles is observed in the distended cisternae of the endoplasmic reticulum mostly of the perinuclear zone around 72 h after inoculation. Electron-dense 50-nm virus particles are arranged in chains in these distended cisternae; some form small crystalloid aggregates. Aberrant particles of different shapes are also seen in the distended cisternae about the same time that the virus particles appear. Parallel filamentous structures are occasionally observed in the cisternae that contain very few virions, either characteristic or aberrant. Increasing cytopathic changes are present after 75 to 96 h. There is an intense vesicular formation. Large numbers of virions and aberrant particles are seen either in the endoplasmic reticulum cisternae or smooth membrane vesicles. They are spread throughout the neurocytoplasm, extending into the dendrites. Dengue virions which are enclosed in fairly intact membrane-bound vesicles are released during cytolysis of the neurones. Morphogenesis of dengue virus type 2 is discussed.

Astrocytes in cultures of brain cells from fetal or newborn hamsters undergo neoplastic transformation after infection with simian virus 40 or polyoma virus. Subcutaneous or intracerebral inoculation of the transformed brain cells into newborn or adult hamsters produces progressively enlarging astrocytomas at the sites of injection. Astrocytomas produced by polyomatransformed cell lines are histologically better differentiated, but grow more rapidly and metastasize more frequently, than astrocytomas produced by cell lines transformed by simian virus 40. These observations make available in vitro models of virus-induced oncogenesis in astrocytes and provide simple techniques for obtaining astrocytoma cell lines suitable for screening studies of chemical agents effective against astrocytomas.