HERPES-SIMPLEX ENCEPHALITIS IN THE TEMPORAL CORTEX AND LIMBIC SYSTEM AFTER TRIGEMINAL NERVE INOCULATION

Herpes simplex virus type 1 causes an encephalitis in humans that is p rimarily restricted to the temporal lobe and limbic system. The distri bution of lesions suggests that virus enters the brain from a single s ite and then spreads transneuronally to infect connected structures. T wo obvious sites of potential viral entry are the olfactory and trigem inal nerves. Trigeminal nerve entry is more likely because it innervat es the oral cavity, a common site of initial infection, and the trigem inal ganglion is the most common site of viral latency. In previous re ports, however, experimental trigeminal nerve infection has never led to the pattern of disease observed in humans. By directly inoculating virus into the murine tooth pulp, the mandibular division of the trige minal nerve was selectively infected. This division, which innervates the oral cavity, is the one most commonly infected in humans. Intrapun inoculation led to an encephalitis primarily affecting the temporal c ortex and limbic system. Thus, spread via the trigeminal nerve provide s an explanation for the distribution of herpes simplex virus observed in the human encephalitis.