Morphine sulphate was perfused between the third ventricle and cisterna magna in alpha-chloralose anaesthetized cats while recording from multireceptive dorsal horn neurones activated by peripheral noxious radiant heat. Morphine concentrations of 10(-5) and 10(-4) M were without effect, while 10(-3) M resulted in an increase in the spinal cord neuronal responses. The results do not support the notion that morphine activates a supraspinal mediated descending inhibition which antagonizes spinal cord nociceptive transmission.
Animals Cats