Correlation between single fibre EMG jitter and endplate potentials studied in mild experimental botulinum poisoning

To study the correlation between single fibre EMG jitter and endplate potential amplitude we examined neuromuscular transmission in rats paralysed with botulinum toxin type A with single fibre EMG (SFEMG) in vivo and with intracellular microelectrode techniques in vitro. In muscles that were not completely paralysed SFEMG showed an increased neuromuscular jitter on nerve stimulation and in these muscles endplate potentials were of reduced amplitude. When the nerve stimulation frequency increased the jitter decreased. Intravenous injection of drugs that increase the acetylcholine release and endplate potential amplitude markedly reduced the jitter and the frequency dependence disappeared.