Intraspinal nerve terminals immunoreactive for tyrosine hydroxylase, serotonin and substance P in guinea-pigs with acute experimental allergic encephalomyelitis.

Spinal cord axons and terminals stained for tyrosine hydroxylase-, serotonin- and substance P-like immunoreactivity were examined in guinea-pigs in the paraplegic phase of acute experimental allergic encephalomyelitis, an animal disease model for multiple sclerosis. Fibers positive for monoamine and substance P-like staining that terminated in the lumbar ventral horn appeared to be markedly damaged during the disease. However, no changes were detected in those substance P-containing fibers that terminated in the dorsal horn. It was concluded that small diameter, thinly myelinated or unmyelinated axons that course for long distances in the spinal cord, and, therefore, have a high probability for encountering inflammatory foci, are particularly vulnerable to damage during experimental allergic encephalomyelitis. Damage to these monoaminergic and peptidergic fibers may contribute to the neurological deficits that are associated with this autoimmune nervous system disease.