Changes in the effectiveness of the blood-brain and blood-spinal cord barriers in experimental allergic encephalomyelitis.

Experimental allergic encephalomyelitis (EAE) was induced In Lewis rats by the intradermal inoculation of an homogenate of guinea pig spinal cord in complete Freund's adjuvant. In these animals the effectiveness with which the capillary barrier excluded mannitol (a substance which normally only crosses this barrier very slowly) from the brain and spinal cord involvement were at their height, 14 days after the inoculation, the effectiveness of the barrier was reduced since the rate of diffusion of the mannitol out of the blood into the brain-stem and spinal cord was approximately doubled. Even as early as 7 days after inoculation, before any clinical signs had appeared, the rate of diffusion was significantly increased in the region of the lumbo-sacral cord. These changes roughly paralleled the histological changes seen in many of the small vessels. We believe that the changes are due to an increase in the permeability of the vessels to mannitol. The bearing of these findings on multiple sclerosis is discussed.