Clonus depression by propranolol

Propranolol administered i.v. to spastic patients was found to be capable of depressing clonus. The drug exerts its action on the spinal cord but does not influence dynamic spindle activity or alpha-motoneurone activity as tested by the T (Achilles tendon) and H reflexes. It may disinhibit the tonic stretch reflex. Thus, clonus is dependent not only on dynamic spindle activity but also on another, probably inhibitory, mechanism.