A comparison of physostigmine and soman using taste aversion and nociception

Area of Science:

• Neuroscience
• Pharmacology
• Toxicology

Background:

• Acetylcholinesterase inhibitors are crucial in understanding neurological functions and potential toxicities.
• Physostigmine (reversible) and soman (irreversible) represent distinct classes of these inhibitors.
• Evaluating their behavioral effects, particularly on nociception and taste aversion, is vital for safety assessments.

Purpose of the Study:

• To compare the nociceptive effects of physostigmine and soman in rats.
• To assess the stimulus properties of these acetylcholinesterase inhibitors using conditioned taste aversion (CTA).
• To determine the utility of the tail flick (TF), hot plate (HP), and CTA tests for evaluating the behavioral toxicity of physostigmine and soman.

Main Methods:

• Rats were administered varying doses of physostigmine salicylate or soman via intramuscular injection.
• Nociception was measured using the rat tail flick (TF) and hot plate (HP) tests 40 minutes post-injection.
• Conditioned taste aversion (CTA) was induced by pairing a novel saccharin solution with drug administration, followed by a choice test between saccharin and water.

Main Results:

• Both physostigmine and soman produced dose-dependent increases in nociceptive thresholds in TF and HP tests.
• Median effective doses (ED50) for nociception were 0.27 mg/kg (physostigmine) and 54 µg/kg (soman) on TF, and 0.55 mg/kg (physostigmine) and 52 µg/kg (soman) on HP.
• Both drugs induced dose-related conditioned taste aversions, with ED50 values of 0.05 mg/kg for physostigmine and 59 µg/kg for soman.

Conclusions:

• Physostigmine and soman exhibit significant dose-dependent effects on nociception and induce conditioned taste aversions in rats.
• The tail flick, hot plate, and conditioned taste aversion procedures are suitable for evaluating the behavioral toxicity of physostigmine and soman.
• These findings highlight the utility of behavioral assays in characterizing the toxicological profiles of acetylcholinesterase inhibitors.