Effects of succinylcholine in an organotypic spinal cord-skeletal muscle coculture of embryonic mice

• Simple in vitro-systems for testing drug effects on muscle activity are lacking.
• A crucial question is the sensitivity of nicotinic acetylcholine receptors.
• Nerve-muscle cocultures are tested using di-acetylcholine (succinylcholine).
• The EC50 of succinylcholine in cocultures is close to the EC50 in adult humans.
• Nerve-muscle cocultures are a valuable tool for testing drugs on muscle activity.

Intoxication with organophosphorus compounds is an important clinical problem worldwide. Although the core treatments – atropine, oximes and diazepam – are defined, high case fatalities were reported for intoxication with organophosphorus insecticides. In particular the role of oximes is not completely understood since they might benefit only patients poisoned by specific pesticides or patients with moderate poisoning and few randomised trials of such poisoning have been performed. This justifies the need for new in vitro test-systems like cocultures of spinal cord and muscle tissue, which have been recently introduced. However this test-system is not yet fully characterized. In order to estimate the applicability of cocultures of spinal cord and muscle tissue their sensitivity to succinylcholine (di-acetylcholine), a depolarizing muscle relaxant in clinical use, was tested.The test-system evaluated in the current study showed sensitivity to succinylcholine with an EC50 as low as 1 μM thereby being close to the EC50 value in adult human patients (2.6 μM). Furthermore, action potential activity of spinal ventral horn neurons was not altered by succinylcholine. The latter observations strongly suggest that our preparation well predicts the qualitative and quantitative actions of novel drugs targeting the neuromuscular system in vivo. In summary, cocultures of spinal cord and muscle tissue seem to be a valid test-system for the development and investigation of new oximes. Moreover, practical aspects like transport over long distances to further laboratories, the opportunity to conduct long-term studies and the reduction of animal usage display further advantages of its use.