Electroneurophysiological studies in rats of acute dimethoate poisoning.

In order to investigate the mechanism of muscular weakness in the intermediate myasthenia syndrome (IMS) following acute organophosphate poisoning, the effect of dimethoate on the neuromuscular transmission was studied in rats by using the electrical stimulation single fiber electromyography (SSFEMG) and repetitive nerve stimulation (RNS). The results showed that there was a prolongation of mean consecutive difference (MCD) of the latencies of single fiber potential shown by SSFEMG in dimethoate intoxicated rats during the presence of muscle weakness when the stimuli were given at 10 or 20 Hz, and there was a remarkable decrement of compound muscle action potential (CMAP) of gastrocnemius muscle evoked by RNS on the sciatic nerve at 20 Hz in some rats with myasthenia. The frequency of neuromuscular transmission abnormalities detected by SSFEMG was significantly higher than those detected by RNS. This study demonstrates that the SSFEMG is a more sensitive electrophysiological method in the detection of neuromuscular transmission block occurred in rats of acute organophosphate poisoning with muscle weakness.