Repetitive nerve stimulation

Presynaptic or prejunctional receptors are located on the presynaptic nerve endings and function to control the amount of transmitter released per nerve impulse and in some instances to affect the rate of transmitter synthesis through some as yet undetermined feedback mechanism. For instance, during repetitive nerve stimulation, when the concentration of transmitter released into the synaptic or junctional cleft is relatively high, the released transmitter may activate presynaptic receptors and thereby reduce the further release of transmitter. Such an action may prevent excessive and prolonged stimulation of the postsynaptic cell. In this case, the activation of the presynaptic receptor would be part of a negative feedback mechanism... 

Nerve conduction study. This tests for specific muscle fatigue by repetitive nerve stimulation. It should demonstrate decrements of the muscle action potential due to impaired nerve-to-muscle transmission. 

There was impaired neuromuscular transmission at high frequency repetitive nerve stimulation in two children who presented in coma with diffuse hjrpotonia and areflexia after carbamazepine overdose (82). Both recovered with supportive care. 

Reduced amplitude evoked potentials increased amplitude with rapid repetitive nerve stimulation... 

Tetanic contractions (Wedensky inhibition) induced by repetitive nerve stimulation in phrenic nerve-diaphragm preparations of mice was faded by 0.5-2 ijlM neostigmine (Chang ei al., 1986). The fade was brought about by failure to elicit muscle action potentials, which was due to end-plate depolarization and a decrease in transmitter release. Both effects were attributed to ACh accumulation as a result of ChE inhibition. 

Maselli, R, A and SoMven. B. C. (1991). Analysis of the organophosphate-induced electromyographic response to repetitive nerve stimulation Paradoxical response to edrophonium and D-tubocurarine. Mu.tcle Ner e 14, 1182-1188,... 

Our group compared in Wistar rats the acutely toxic organophosphate (OP) paraoxon with fenthion, one of the agents frequently involved in human IMS. The clinical symptoms, the occurrence of muscle fiber necrosis and histochemical assessment of neuromuscular junction AChE activity in muscle biopsies, biochemical assessment of brain AChE activity, and EMG parameters including repetitive nerve stimulation at various frequencies were studied at various lime points. 

Consecutive OP-poisoned patients admitted to our institution were prospectively studied. The protocol included a standard neurological examination at frequent prefixed time intervals, semm ChE and erythrocyte AChE activity, urinary OP metabolite excretion, and EMG with repetitive nerve stimulation. Some patients underwent a muscle biopsy. 

All patients had severe AChE inhibition during the entire period of IMS. OP metabolite excretion was also prolonged. Consecutive EMG Endings in the evolution of IMS were decrement, decrement-increment, increment, and eventually normal repetitive nerve stimulation studies. The... 

Repetitive nerve stimulation (RNS) records sequential muscle twitches as a result of repeated stimulation of its nerve supply. The difference in size of the initial and fourth twitch reflects efflcacy of neuromuscular transmission. 

However, in a study in 10 myasthenic patients with mild to moderate symptoms, intravenous propranolol 100 micrograms/kg did not result in a worsening of neuromuscular transmission (assessed by muscle function tests and repetitive nerve stimulation), even though 8 of those with mild symptoms had reduced their pyridostigmine dose during the study to allow the effects of the additional drug to be more readily seen. ... 

Studies Acetylcholine receptor binding and blocking antibodies were positive, as was the anti-striated-muscle antibody. Other immunological parameters were normal, as were thyroid function tests. Repetitive nerve stimulation at low-frequency (3 Hz) showed an 18% decremental response of the compound-motor-unit potential indicating MG (normal is < 11 % decrement). Nerve conduction studies were normal. Computed tomography (with contrast) of the mediastinum revealed a mass, presumably thymoma. 

Repetitive nerve stimulation is performed to exclude neuromuscular transmission defects, such as prolonged... 

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