Abstract

The effect of orphenadrine on motor systems was studied in anesthetized, spinal and decerebrate cats. Orphenadrine was found to block facilitation of the knee jerk induced by electrical stimulation of the facilitatory reticular formation or the contralateral sciatic nerve. This blockade occurred at a dose which did not block inhibition of the reflex induced by stimulation of inhibitory reticular, cerebellar, caudate or cortical regions or the ipsilateral sciatic nerve. Orphenadrine also relieved the increased extensor tonus and clonus in cats decerebrated by intercollicular section. The action does not depend on the presence of an anesthetic such as chloralose or pentobarbital and is not secondary to gross cardiovascular effects. The anticholinergic and antihistaminic properties of the drug are not likely to play an essential role in its blocking effect on facilitation or decerebrate rigidity. Conversely, cholinergic synapses are not likely to be present within the facilitatory reticulospinal pathway. The evidence presented provides a basis for the understanding of the efficacy of orphenadrine in various forms of skeletal muscle spasm and prompts the classification of the drug as a centrally acting muscle relaxant. The possible site and mechanism of the antifacilitatory action of orphenadrine is discussed.