Neuronal cell cultures as a model for assessing neurotoxicity induced by encephalitic viruses

Primary dispersed and organotypic cultures were prepared from selected brain areas and spinal cords of rat (Sprague-Dawley) and mouse (SJL/OLA(F) Ness-Ziona) fetuses and neonates. Following fiber regeneration, synapse formation and myelination, cultures were infected with one of the following viruses: Rabies CVS-21 strain, Sindbis Alphavirus, West-Nile Flavivirus and Theiler Murine Encephalomyelitis virus. Light and electron microscopical studies showed clear differences in the target cells for virus infection; time of viral replication and in the intensity and specificity of the cytopathic effects induced by these viruses. Thus, Sindbis and Theiler viruses induced severe cytotoxicity and demyelination due to rapid viral replication in both neurons and all glial cell types. Rabies and West-Nile viruses, on the other hand, replicated mainly in neurons and at a much slower rate, causing only mild damage to the cells and the myelin sheath. A very specific alignment of West-Nile virions was observed along the interperiod lines of the myelin sheath in several myelinated axons. This peculiar arrangement of the virions, entrapped between the myelin lamellae may lead to a novel concept in the understanding of viral infection.