EFFECTS OF NK433, A NEW CENTRALLY ACTING MUSCLE-RELAXANT, ON MASTICATORY MUSCLE REFLEXES IN RATS

The effects of 3-(1-pyrrolidinyl)-4'-trifluoromethylpropiophenone mono hydrochloride (NK433), a novel centrally acting muscle relaxant, on ma sticatory muscle reflexes were investigated in rats. NK433 inhibited t he monosynaptic tonic vibration reflex of the masseter muscle and the polysynaptic tonic periodontal masseteric reflex. These reflexes are i ncreased by gamma-motor activity. NK433 had a weak inhibitory effect o n the polysynaptic jaw opening reflex evoked by electrical stimulation of the tooth pulp, which is little related with gamma-motor activity. Eperisone-HCl depressed the three types of masticatory muscle reflexe s. When intravenously administered, eperisone-HCl was equipotent to NK 433, but the effect of eperisone-HCl was shorter-lasting than that of NK433. The effect of intragastrically administered NK433 on the period ontal masseteric reflex was about three times stronger than that of ep erisone-HCl. These results suggest that NK433 inhibits masticatory mus cle reflexes controlled by the gamma-motor system and thus may amelior ate the temporomandibular joint syndrome in man.