[Dependency of Japanese encephalitis virus neurotropism on neuronal immaturity of rat cerebral cortex].

It is generally accepted that, the younger an animal is, the more susceptible it is to Japanese encephalitis virus (JEV) infection. A time-kinetic study of JEV antigen in the developing rat brain after infection disclosed that in the motor cortex, neurons were diffusely infected with JEV until the age of 5 days. However, on exposure from the 6th to 7th day, only the neurons of the upper layers were infected; those of the deeper layers remained uninfected. On the 8th day, the infection was limited to the superficial neurons, and from the 9th day onward, no neurons were infected. Since neuronal maturation in the motor cortex begins in the deeper layers and extends to the upper layers, it seems that JEV targets immature neurons. Fifteen-day-old rats, which were resistant to JEV infection, received intracerebral transplants of neurons taken from 19th-day embryos. When these animals were infected with JEV at 3 days after transplantation, viral antigen was detected only in the transplanted neurons; the host neurons were negative. However, when animals were infected with JEV at 9 days after transplantation, neither host neurons nor donor neurons became infected. This showed that JEV attacked embryonal neurons only early after transplantation into young-adult brains. JEV infectivity limited to the immature neurons was also confirmed by in vitro explant culture experiments. It can be concluded from these experiments that the susceptibility to JEV infection in the rat brain is closely associated with neuronal immaturity.