EXPERIMENTAL STUDIES ON PARALYSIS AFTER ANTIRABIES VACCINATION

I. HISTOLOGICAL STUDIES ON ACUTE DEMYELINATING ENCEPHALOMYELITIS IN GUINEA PIGS

Abstract

1. Approximately 3 weeks after a single injection of Freund's adjuvant and homologous brain emulsion into muscle or the foot pad of guinea pigs, symptoms of meningoencephalitis occurred.
2. Histologic changes occurred soon after injection and before onset of clinical symptoms. The intensity of inflammatory changes did not always parallel the severity of the illness.
3. In paralyzed guinea pigs meningitis was followed by perivascular infiltration of round cells which in severe cases was accompanied by the destruction of myelin. However, demylination was generally mild.
4. Differences in the intensity and localization of pathological changes in the central nervous tissues was correlated with site of inoculation. Guinea pigs injected into the lumber region showed lesions in the spinal cord, while those injected in the neck showed lesions localized in the brain. Inflammatory reactions in groups injected into the thigh muscles and into the food pad were equally intense in the brain and spinal cord.
5. Histological observations of the tissue sections including the site of injection and surrounding bony structures revealed that in some cases the granulomatous tissues from the injection infiltrated into the vertebral canal and resulted in meningitis. Accordingly, the injection into the foot pad is considered the most suitable method to avoid this artifact.
6. Not all components of the adjuvant were equally effective in producing encephalomyelitis. Inoculurn without lanolin showed typical histological changes. However, owing to the decrease of the inoculum, there is a tendency for infiltration into vertebral canal. The injection of inoculum without tubercle bacilli induces a slight degree of menigitis but not the characteristic changes. Each group of guinea pigs injected with the inoculum without the paraffin oil or brain tissue was entirely free of the pathological changes.
7. Pathological changes of the other visceral organs were caused by tubercle bacilli.
8. There were no significant histological differences at the site of the injection or of the adjacent lymph node between the paralyzed and non-paralyzed guinea pigs.