Etifoxine does not impair muscle tone and motor function in rats as assessed by in vivo and in vitro methods.

The purpose of our study is to evaluate the effects of the translocator protein (TSPO) ligand etifoxine on muscle tone and locomotor activity. In addition, the mechanism of action of etifoxine on the presynaptic membrane and neuromuscular junction is investigated. These effects of etifoxine were examined employing the following methods: 1) in vivo experiments using bar holding test and activity cage test, and 2) comparative in vitro studies with nifedipine on indirectly-elicited twitches of striated abdominal muscle preparations. Etifoxine in doses 50 mg/kg and 100 mg/kg i.p. does not produce any significant changes in locomotor activity and muscle tone of intact rats. Nifedipine (10-5 М) induces a significant decrease in the muscle force of striated muscle preparations. Etifoxine (10-8-10-4 М) has no significant effect on indirectly-elicited twitch tension. Results show that the TSPO ligand etifoxine has no myorelaxant effect. The activation of TSPO is not associated with a reduction in muscle tone and motor impairment. Etifoxine does not affect the presynaptic membrane and its influence on L-type Ca2+-channels is insignificant. Etifoxine does not act as a competitive antagonist of acetylcholine and does not impair the impulse transmission in the neuromuscular junction.