DISTRIBUTION OF VESICULAR STOMATITIS-VIRUS PROTEINS IN THE BRAINS OF BALB/C MICE FOLLOWING INTRANASAL INOCULATION - AN IMMUNOHISTOCHEMICAL ANALYSIS

Earlier studies have shown that intranasal instillation of vesicular stomatitis virus (VSV), a negative-sense RNA virus, in mice and rats can result in infection of the brain, hind-limb paralysis and death. Using an antiserum directed against VSV proteins, we sought to determine the potential neuronal and non-neuronal pathways VSV utilize, for central nervous system dissemination in BALB/c mice. Within 12 h following intranasal inoculation of VSV, VSV antigen could be detected in the olfactory nerve layer of the ipsilateral olfactory bulb. Within 3-4 days post-inoculation (p.i.), VSV had disseminated into the glomeruli of the olfactory bulb as well as the anterior olfactory nuclei that were ipsilateral to the VSV instillation. Within the glomeruli, VSV antigen was more prevalent in the granule cells than in the mitral cells. Correspondingly, the lateral olfactory tract, where axons of mitral cells course, remained VSV negative throughout 7 days p.i. By 7 days p.i., viral proteins were detected in several additional regions extending to the brainstem. These included regions involved in theta-rhythm generation during exploration and REM sleep, i.e. the septal nuclei, the supramammilary body, and the hippocampal formation, as well as the amygdaloid complex and brainstem neuromodulatory centers, such as the dorsal raphe and locus coeruleus. Structures abutting the ventricular surfaces, such as the dorsal cochlear nucleus, were also labeled. Tracts immunoreactive to VSV included the dorsal tegmental tract, fascia retroflexus, Probst tract, and mesencephalic tract of the trigeminal motor nerve. Besides the lateral olfactory tract, tracts that remained VSV negative included the anterior commissure, the corpus callosum and the mammillary peduncle. The pattern of VSV immunoreactivity supports the idea that following infection of the olfactory bulb glomeruli, VSV spreads via both ventricular surfaces and retrograde transport within axons of neuromodulatory transmitter systems innervating the olfactory bulb. Conversely, regions exhibiting low levels of VSV antigen are not likely to be involved in VSV dissemination. In particular, the paucity of VSV antigen in some of the terminal fields of neuromodulatory systems indicate that anterograde transport is more selective than retrograde transport. Surprisingly, the principal neurons of the olfactory glomeruli, thalamus, cerebral cortex and the hippocampus, all of which use L-glutamate as the excitatory neurotransmitter, are much less involved in viral dissemination.