Failure of 5-hydroxytryptophan to increase lumbar MSR amplitude in rats paralyzed with experimental allergic encephalomyelitis.

Doses of the 5-hydroxytryptamine precursor, 5-hydroxytryptophan, which markedly increased lumbar monosynaptic response (MSR) amplitude in control rats failed to do so in rats paralyzed with experimental allergic encephalomyelitis (EAE). However, lumbar MSR amplitude could be increased in EAE rats just as in control rats by tetanically stimulating the dorsal root. Post-tetanic potentiation of MSR amplitude occurred in the EAE paralyzed rats both prior to and following 5-hydroxytryptophan injection. It was concluded that, as has been reported for the peripheral system in EAE guinea pigs, central nervous system 5-hydroxytryptamine neurotransmission is impaired, at least in the lumbar spinal cord, in EAE rats with hindlimb paralysis.