Repetitive nerve stimulation vs. twitch tension in rats with EAMG

Two methods were compared with regard to their ability to detect acetylcholine receptor-dependent neuromuscular dysfunction in rats with experimental autoimmune myasthenia gravis. In both cases, detection of AChR impairment required amplification of symptoms by administration of the AChR antagonist curare and appeared to be directly related to increasing levels of circulating anti-AChR antibodies. First, in vivo evaluations of decremental compound motor action potentials following repetitive nerve stimulation were performed by electromyography. Impaired neuromuscular function (i.e., greater than 10% decrement) was noted only after rats had been immunized twice with AChR, requiring levels of circulating anti-AChR antibody greater than about 200 micrograms/mL in serum. In contrast, the direct in vitro evaluation of stimulated isometric twitch tension appeared to be more sensitive in that impaired AChR-dependent muscle contraction was clearly observed following a single AChR immunization, and, as shown previously, required anti-AChR antibody levels of about 50 micrograms/mL in serum. Further discussion is presented concerning the advantages and disadvantages associated with each method of monitoring disease.