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Updated: Jul 17, 2026
In Vivo Electrophysiological Measurement of the Rat Ulnar Nerve with Axonal Excitability Testing
Published on: February 6, 2018
Reevaluation of indirect field stimulation technique to demonstrate oxime effectiveness in OP-poisoning in muscles in
1Bundeswehr Institute of Pharmacology and Toxicology, Neuherbergstrasse 11, 80937 Munich, Germany. ThomasSeeger@bundeswehr.org
Abstract:
Organophosphorus (OP) pesticides or nerve agents cause severe intoxication by inhibition of acetylcholinesterase, finally resulting in death due to respiratory failure. The phrenic nerve diaphragm preparation is considered as the classic model to investigate the effect of OP intoxications and oxime treatment at the neuromuscular junction. However, this preparation is unsuitable for larger species or for muscle strips from biopsies where no nerve is available for stimulation. An alternative technique is the indirect field stimulation of muscles containing intramuscular nerve branches only. The proposed method by Wolthuis et al. [Wolthuis, O.L., Vanwersch, R.A.P., Van Der Wiel, H.J., 1981. The efficacy of some bis-pyridinium oximes as antidotes to soman in isolated muscles of several species including man. Eur. J. Pharmacol. 70, 355-369] was modified and experimentally reevaluated in isolated mouse diaphragms. To confirm that electrical field stimulation technique induced muscle contraction only via the neuromuscular endplate the nicotinic antagonists pancuronium or d-tubocurarine (1microM) were given. In the presence of a nicotinic antagonist hardly any contraction was blocked after indirect field stimulation technique with very short pulses (5micros, <0.6A), in contrast to direct muscle stimulation (broader pulse width, or higher amplitude >0.6A). During paraoxon circumfusion (20min, 1micromol/l) muscle force generation by indirect stimulation was almost completely blocked. Restoration of paralyzed muscle function to 80% of initial values could be achieved after paraoxon wash out (20min) and circumfusion with obidoxime (1micromol/l, 20min). This data correspond quite well to data shown earlier when using conventional nerve stimulation techniques.
Insights
Organophosphorus pesticide intoxication can be studied using a novel indirect field stimulation technique on isolated muscles. This method effectively models neuromuscular junction blockade and oxime antidote efficacy, offering an alternative to traditional nerve stimulation.
Area of Science:
- Pharmacology
- Neuroscience
- Toxicology
Background:
- Organophosphorus (OP) pesticides and nerve agents cause fatal intoxication via acetylcholinesterase inhibition.
- The phrenic nerve diaphragm preparation is a classic model for studying OP intoxication and oxime antidotes.
- This traditional model is limited for larger species or nerve-less muscle biopsies.
Purpose of the Study:
- To modify and reevaluate indirect electrical field stimulation for studying neuromuscular junction function in isolated muscles.
- To confirm that indirect field stimulation targets the neuromuscular endplate.
- To assess the efficacy of oxime antidotes in a model of OP intoxication.
Main Methods:
- Isolated mouse diaphragms were used to test indirect electrical field stimulation.
- Nicotinic antagonists (pancuronium, d-tubocurarine) were employed to verify stimulation specificity.
- Paraoxon was used to induce OP intoxication, followed by oxime (obidoxime) treatment.
Main Results:
- Indirect field stimulation with short pulses (<0.6A, 5µs) selectively activated the neuromuscular junction, unlike direct muscle stimulation.
- Paraoxon (1µmol/l) exposure for 20 minutes nearly abolished muscle force generated by indirect stimulation.
- Obidoxime (1µmol/l) treatment for 20 minutes restored muscle function to 80% of initial levels after paraoxon washout.
Conclusions:
- Indirect electrical field stimulation is a viable alternative to conventional nerve stimulation for studying neuromuscular junction dynamics.
- This technique accurately models OP intoxication and the therapeutic effects of oxime antidotes.
- The findings support the use of this modified method for research involving larger species or clinical muscle samples.
