Morphine and meperidine on bulbospinal inhibition of the monosynaptic reflex

The effects of morphine and meperidine were studied on the ventromedial bulbospinal inhibition of the monosynaptic reflex (MRS) in decerebrate unanesthetized cats. Administration of these agents in accumulative doses (0.5–16 mg/kg, i.v.) progressively blocked this inhibition. Meperidine was more potent in blocking this inhibition when administered by close-arterial injection to the spinal cord than when administered i.v. which suggests that the spinal cord is a major site of action. The results of this study are contrary to the suggestion made by Takagi et al. (1955), that these drugs enhance bulbospinal inhibition of the MSR.