Intraaxonal transport of Herpes simplex virus in the rat central nervous system.

Light and electron microscopic observation 3--4 days after microinjection of Herpes simplex virus (HSV) into the left neostriatum of rat demonstrated the following results. (1) Virus labeled nerve cells were found in the ipsilateral substantia nigra; a large number of infected neurons were in the zona compacta and some were in the zona reticulata. No virus infection was evident in the contralateral side. (2) Virus labeled neurons were found in the cortex, a greater number ipsilaterally than contralaterally, and in the dorsal raphé nuclei. Cortical microinjection of HSV led to infection of some cortical cells but no neostriatal cells. We conclude, therefore, that spread of the virus to the cortex, the substantia nigra and the dorsal raphé following neostriatal injection was by retrograde axonal transport. (3) The left neostriatum, where HSV was injected, showed a surprisingly small number of virus infected neurons. The infected neurons were mostly the large neurons; the majority of medium sized neurons were well preserved. There was massive degeneration of nerve terminals throughout the neuropil. Most of these degenerating nerve terminals are considered to be afferent fibers.