Depressive effects of mu and delta opioid receptor agonists on activities of dorsal horn neurones are enhanced by dibencozide.

The effects on C fiber evoked activity in lumbar dorsal horn convergent neurones of i.v. morphine alone, of Tyr-D-Thr-Gly-Phe-Leu-Thr (DTLET) alone or of either of these drugs in association with 5-deoxyadenosylcobalamine (dibencozide) were investigated in anesthetized rats. Both morphine and DTLET depressed the neuronal responses in a dose-related fashion, with the former requiring lower doses. Although dibencozide alone was devoid of any effect, it significantly enhanced the depressive effects of all doses of morphine tested and of the lower two doses of DTLET. It is concluded that dibencozide enhances the spinal depression of nociceptive information elicited by mu and delta opioid agonists. This drug could provide a useful tool for the study of interactions between opioids and opioids receptors. It is also suggested that dibencozide could be useful in clinical practice for reducing the dosage of opioids.