Central muscle relaxant effects of diazepam.

Motor depressant effects of diazepam were studied in the intact, decerebrate and high spinal cat. Diazepam (0.125516 mg/kg, i.v.) produced a depression of both the patellar and linguomandibular reflexes in the intact cat. In the high spinal (Cl) cat only the linguomandibular reflex was depressed. Facilitation and inhibition of the patellar reflex elicited in both intact and high spinal (Cl) cats were reduced by diazepam. No depression was observed in the in viva neuromuscular preparation of the tibialis anticus muscle. Small doses of diazepam (0.125 mg/kg, i.v.) abolished the rigidity of the mid-collicular decerebrate cat. Mean arterial blood pressure was initially depressed in all animals (0.125-2 mg/kg) with an intact medullary vasomotor outflow. Larger doses (4-16 mg/kg) tended to return the blood pressure toward control levels. The present study presents evidence for both a brain stem reticular and a spinal cord site of action of diazepam on motor systems. Possible mechanisms of action of diazepam on motor systems are discussed.