Central serotonin receptor sensitivity in rats with experimental allergic encephalomyelitis.
Serotonin mediated bulbospinal motor activities were examined in rats with experimental allergic encephalomyelitis (EAE)-induced-paraplegia. Treatment with monoamine oxidase inhibitors and L-tryptophan failed to elicit the components of the serotonin syndrome which involved levels of the neuraxis manifesting flaccid paralysis. Straub tail, hindlimb abduction and hindlimb rigidity did not occur. The motor responses represented at spinal segments just above the level of paraplegia, lateral head weaving and forepaw treading, were present but altered in the diseased rats. No impairment was evident in the production of head tremor or hyper-reactivity to accoustic and tactile stimuli. Similarly, in urethane-anesthetized EAE rats, serotonergically-evoked automatic swallowing activity was unchanged as judged by the effects of serotonin receptor agonists, and a serotonin precursor, a reuptake blocker and an antagonist. Our data support the conclusion that EAE-induced impairment of serotonergic neurotransmission is correlated with motor deficits manfested during the acute paralytic stage of the disease.