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Single Fiber Electromyographic Jitter to Detect Acute Changes in Neuromuscular Function in Young and Adult Rats
Citation:
FINLEY, D. B., X. WANG, J. GRAFF, AND D. W. HERR. Single Fiber Electromyographic Jitter to Detect Acute Changes in Neuromuscular Function in Young and Adult Rats. JOURNAL OF PHARMACOLOGICAL & TOXICOLOGICAL METHODS. Elsevier Science Ltd, New York, NY, 59(2):108-119, (2009).
Impact/Purpose:
This manuscript describes a method to quantify neuromuscular jitter in adult and juvenile animals using single fiber electromyography (SFEMG). The effects of different needle placement and criterion amplitude used in calculating the mean consecutive difference (MCD) did not alter the results. Disruption of neuromuscular transmission with decamethonium did change MCD values in adult or juvenile rats. This result was found in the presence of an increased occurrence of blocking of muscle action potentials (MAP), and a greater decrease in MAP amplitude between the first and fourth responses. Treatment with the reversible cholinesterase (ChE) inhibitor physostigmine resulted in minimal changes in the MCD values in adult or juvenile animals, in the presence of at least 35% inhibition of muscle ChE activity. However, age- and stimulation frequency-related changes were observed. Control MCD values in adult and juvenile rats were determined. This technique described is adaptable to multiple ages and had direct clinical correlates with human measures, and will be a useful method to examine changes in neuromuscular function.
Description:
Introduction: Exposure to irreversible cholinesterase (ChE)-inhibiting compounds, such as organophosphates may produce neuromuscular dysfunction. However, less is known about changes in neuromuscular transmission after treatment with reversible ChE-inhibitors. These studies adapted single fiber electromyography techniques to quantify neuromuscular jitter in adult and juvenile rats after treatment with agents that alter cholinergic neurotransmission. Methods: Anesthetized adult and juvenile rats were tested using stimulation single fiber electromyography, recorded in the gastrocnemius muscle, after stimulation in the sciatic notch region. Muscle stretch was controlled using a plastic leg restraint. The influence of electrode placement, treatment with decamethonium (to disrupt neuromuscular transmission) or physostigmine (reversible cholinesterase (ChE) inhibitor), and the impact of varied stimulation frequency were quantified. Results: No significant effects of needle placement or criterion amplitude were observed when calculating the mean consecutive difference (MCD). Treatment with decamethonium did not alter MCD values in adult or juvenile rats. However, an increased blocking of muscle action potentials (MAP), and a greater decrease in MAP amplitude between the first and fourth responses, was observed. The larger decrease in MAP amplitude occurred when with stimulation at 9.09 Hz, but not 0.91 or 3.03 Hz. Treatment with physostigmine produced minimal changes in the MCD values in adults or juveniles, in the presence of at least 50% inhibition of muscle ChE activity. Age- and stimulation-related differences in the MCD values were detected. The neuromuscular jitter MCD was larger when faster stimulation rates were used, and was more evident in juveniles than in adult rats. Discussion: A technique was developed to record single fiber electromyography and neuromuscular jitter, in vivo, in adult and juvenile rats. Based on the literature and the current data, the technique appears to be more sensitive to prolonged inhibition of ChE enzymes than the reversible inhibition produced by physostigmine.
URLs/Downloads:
JOURNAL OF PHARMACOLOGICAL TOXICOLOGICAL METHODS
Single Fiber Electromyographic Jitter to Detect Acute Changes in Neuromuscular Function in Young and Adult Rats