Depression of neuromuscular transmission in methylmercury-poisoned rats: a glass microelectrode and single fiber electromyography study

Changes in neuromuscular transmission were examined in methylmercury (MeHg)-poisoned rats, given a total oral dose of 60 mg CH₃HgCl at 5 mg/kg/day. A microelectrode study was done on the 21st day. The mean quantal content and mean values of the immediately available pool of ACh in the MeHg-poisoned rats were reduced as compared to those in the control rats, but the mean values for the release probability of ACh did not differ significantly. Stimulation single fiber electromyography (SFEMG) was done on the biceps femoris muscle at 1,5, 10 and 20 Hz on the 28th day. Both a significant and consistent increase in jitter were found at increasing stimulation rates in the MeHg-poisoned rats. The SFEMG findings suggest presynaptic involvement due to accelerated depletion of ACh. We confirmed that neuromuscular transmission is depressed in MeHg-poisoned rats in vivo and in vitro.