Abstract
The analgesic mechanism of morphine on the spinal nociceptive transmission was compared in rabbits with the intact and cold-blocked states of the spinal cord. The degree of the suppressive effect of morphine (2 mg/kg) on the bradykinin-induced activity was significantly greater in the intact than in the coldblocked states. Morphine (4 mg/kg) suppressed the nociceptive responses to similar levels in both states. These results suggest that in a small dose, the indirect suppressive action is more important than the direct action. In a larger dose, the suppressive action is probably exerted primarily by the direct spinal action.
