Effects of tizanidine, eperisone and afloqualone on feline dorsal horn neuronal responses to peripheral cutaneous noxious and innocuous stimuli.

The effects of eperisone and afloqualone have been compared with those of tizanidine on excitatory responses of spinal dorsal horn neurones, evoked by noxious and innocuous peripheral stimuli. Tizanidine, administered intravenously or iontophoretically, resulted in a profound, long-lasting and selective depression of the responses to noxious stimuli. In contrast, intravenous injection of eperisone produced either a rapidly reversible depression of responses to both noxious and innocuous stimuli or had no effect on these responses. Iontophoretic administration of eperisone also reduced neuronal responses to both forms of peripheral stimuli and that induced by quisqualate. This depressant action of eperisone was rapidly reversible but was often accompanied by a reduction of the amplitude of the action potentials. Afloqualone had no depressant action on any evoked response when administered iontophoretically. However, intravenous injection of this agent resulted in weak depressant effects on responses to noxious, innocuous or both types of stimuli, of a few of the neurones tested. This effect of afloqualone was not dose-dependent and was mimicked by control injections of the vehicle in which it was suspended. It is suggested that the muscle relaxants, eperisone and afloqualone, in contrast to tizanidine, do not possess any direct spinal antinociceptive activity.