[Effects of tizanidine, a central muscle relaxant, upon spinal reflexes]

Effects of intravenous administration of tizanidine upon spinal reflexes were studied in cats anesthetized with urethane-chloralose. Both extensor and flexor monosynaptic reflexes and polysynaptic flexor reflex were inhibited by intravenous administration of tizanidine in a dose of 10-50 micrograms.kg-1. The inhibition was dose-dependent. After strychnine administration, polysynaptic flexor reflex was augmented, but the inhibition by tizanidine administration was unaffected. In spinal cats, inhibitory effect of tizanidine upon monosynaptic reflex was weaker than in intact cats. Viscero-intercostal reflex elicited by electrical stimulation of A delta afferent fibers in the greater splanchnic nerve was also inhibited by intravenous tizanidine (25 micrograms.kg-1). The degree of inhibition decreased in parallel with increase in the intensity of stimulus applied to the greater splanchnic nerve.