[Effects of muscle relaxant E.M.P.P. on afferent discharges of muscle spindle in man--an microneurographic analysis (author's transl)].

Effects of a new muscle relaxant E.M.P.P.(4'-ethyl-2-methyl-3-piperidino-propiophenone . hydrochloride) on afferent discharges of muscle spindle were studied in 10 healthy volunteer subjects. Single unit afferent discharges of muscle spindle were recorded microneurographically from the median or tibial nerve using a tungsten microelectrode with a tip diameter of about 1 micrometer (impedence: about 10 M omega). Effects of an oral administration of 150--300 mg of E.M.P.P. on spontaneous afferent discharges as well as dynamic and static responses of muscle spindle were analysed in the present study. 1. E.M.P.P. suppressed remarkably the frequency of spontaneous afferent discharges of muscle spindle. Meanwhile, mental activations such as speech of mental arithmetic recovered temporarily the frequency of afferent discharges to that before E.M.P.P. administration. 2. E.M.P.P. suppressed the dynamic and static responses of muscle spindle to stretch. It also suppressed the dynamic responses of muscle spindle in the decontraction phase of electrically-induced twitch contractions of the receptor-bearing muscle. Based on these results, it is concluded that E.M.P.P. suppresses the static and dynamic activities of muscle spindle in man. These effects seem to be due to modifications of descending influences from central structures on the static and dynamic gamma motoneurons which innervate the muscle spindle.