Depression of muscle spindle activity--a new type of pharmacological action?

The effect of 2,4-di(diethylamino)-6-(2-phenylacetylhydrazino)-1,3,5-triazine (Ciba 28882-Ba) injected intravenously on the activity of de-efferented muscle spindles of the tibialis anterior and extensor digitorum longus muscles of anaesthetized cats, and on gamma-motoneurones of decerebrate cats, was investigated. The drug depressed both the static activity of muscle spindles and the spontaneous activity of gamma-motoneurones. In contrast, the response of muscle spindles to rapid stretch was not affected. The effect of 28882-Ba on the activity of the muscle spindles resembled that of progressive unloading or shortening of the muscle. 28882-Ba antagonized excitation of the muscle spindle by suxamethonium. The effect of 28882-Ba on the response of the gamma-motoneurones to various driving stimuli was not predictable.