MORPHINE ANTINOCICEPTION - EVIDENCE FOR THE RELEASE OF ENDOGENOUS SUBSTANCE(S)

Complete blockade of both the neural and the humoral pathways by spinal ligations at a low thoracic level (T11-T13) abolished morphine induced antinociception in mice. However, when only the humoral pathway was maintained, i.e. spinalization at T12 with the dura mater intact, the antinociceptive effect of morphine was not reduced. Furthermore, blocking only the humoral pathway, i.e. removal of the dura mater at T11-T13 without damaging spinal neurons, or making a leakage of CSF through an opening in the cisterna magna reduced morphine antinociception. These findings indicate that morphine antinociceptive effects in mice are mainly mediated by substance(s) released from supraspinal structures and transported in the CSF. © 1979.