Mechanisms of spinal reflex depressant effects of CS-722, a newly synthesized centrally acting muscle relaxant, in spinal rats

The mechanisms of the depressant action of ( R )-4-chloro-2-(2-hydroxy-3-morpholinopropyl)-5-phenyl-4-isoxazolin-3-one hydrochloride (CS-722), a newly synthesized centrally acting muscle relaxant, on spinal reflexes were investigated in spinal rats. The drug CS-722 (50 solmg/kg, i.v.) depressed the polysynaptic reflex but was less effective on the monosynaptic reflex. Eperisone-HCl (10 solmg/kg, i.v.) and baclofen (2 solmg/kg, i.v.) markedly decreased the monosynaptic and polysynaptic reflexes, with longer durations than CS-722; CS-722, eperisone and baclofen depressed the dorsal root reflex. The excitability of the motoneurone was reduced by CS-722 and eperisone. Excitability of the primary afferent fibres was reduced by CS-722, while eperisone and baclofen had no effect. Both CS-722 and eperisone did not have a depressant influence on the focal synaptic potential. These results suggest that CS-722 and eperisone but not baclofen, have a common motoneurone-membrane-stabilizing action and that this action may contribute, in part, to the spinal reflex depressant effects of CS-722 and eperisone.