Sites of action of CS-722, a newly synthesized centrally acting muscle relaxant

Sites of the muscle relaxant action of CS-722 were investigated in rats. Doses injected intra-4th ventricularly (i.c.v.) or intrathecally (i.t.) were determined according to measurements of CS-722 concentration in the brain stem and the spinal cord after systemic administration. When administered i.c.v. (50 and 100 micrograms) or i.t. (200 and 400 micrograms), CS-722 reduced the radio frequency decerebrate rigidity, although the effect after i.c.v. injection was transient. These results indicate that CS-722 exerts its muscle relaxant action by affecting both the supraspinal structure and the spinal cord. Spinal reflexes were not affected by CS-722 injected i.c.v. It seems that muscle relaxation is not always accompanied by impairment of the spinal reflex.