Selective neuronal, dendritic, and postsynaptic localization of viral antigen in measles-infected mice

The pathology of acute disease produced by intracerebral inoculation of hamster neurotropic strain of measles virus was studied in adult BALB/c mice using immunolabeling techniques at a light and electron microscopic level. Brains of animals with acute disease showed an abundance of viral antigen but no inflammatory cells, giant cells, or inclusions. Infection was limited to neurons which were rarely necrotic, indicating that the process was not cytolytic. Mapping of infected neurons identified a consistent predilection to the rhinencephalon, other components of the limbic system, and the striatum. Ultrastructural examination revealed similar findings in all of the involved areas. No evidence of viral assembly at the cell membrane was found. Viral antigen was identified in neuronal perikaryon with somatofugal spread into dendritic and synaptic sites. Unlabeled smooth nucleocapsid and labeled tubular structures were detected both in the cytoplasm and nucleus of neurons. Dendritic labeling when present was occasionally associated with the neurotubules. The most remarkable and frequent finding was identification of viral antigen in postsynaptic endings. This consisted of clumps of viral antigen and occasional staining of the postsynaptic density. This localization of viral antigen may create dysfunction of synaptic transmission, and in the absence of overt pathology, may account for clinical disease.