Serotonin immunoreactivity in spinal cord axons and terminals of rodents with experimental allergic encephalomyelitis

Spinal cord axons and terminals stained for serotonin-like immunoreactivity were examined in rats and guinea-pigs with experimental allergic encephalomyelitis, an animal disease model for multiple sclerosis. During the paraplegic stage of experimental allergic encephalomyelitis, many serotonin-positive axons in the ventral and lateral funiculi of both rats and guinea-pigs were found to be grossly distorted, often appearing to end in bulbous enlargements. Serotonin-immunoreactive terminal varicosities in the gray matter were swollen and diminished in number in paraplegic rats with experimental allergic encephalomyelitis. In addition, the intervaricose segments which were observed in control rats appeared to be missing in rats with experimental allergic encephalomyelitis. Depletion of serotonin-positive terminals was much more pronounced in paraplegic guinea-pigs with experimental allergic encephalomyelitis than in rats with experimental allergic encephalomyelitis, but those terminals which remained in the guinea-pigs were morphologically similar to those of control guinea-pigs. The greater depletion of serotonin-positive terminals in guinea-pigs may reflect a more severe disease state in this species, as none of the guinea-pigs survived the acute stage of paralysis. As the time period between recovery from paralysis and sacrifice increased in rats with experimental allergic encephalomyelitis, serotonin-positive terminals in the gray matter became increasingly more normal in appearance. Even by the first day of recovery, some intervaricose segments could again be observed, and after two weeks of recovery, the terminals were much more numerous and less swollen than during the paraplegic stage of disease.(ABSTRACT TRUNCATED AT 250 WORDS)