An interaction of opioids and galanin in dorsal horn of the spinal cord in mononeuropathic rats.

The present study was performed in rats with experimentally induced mononeuropathy after common sciatic nerve ligation. The hind-paw withdrawal latencies to thermal and mechanical stimulation were increased significantly after intrathecal injection of 3 nmol of galanin. The increased hind-paw response latencies induced by galanin were attenuated by following intrathecal injection of 22 nmol, but not 11 or 2.75 nmol of the opioid receptor antagonist naloxone. Further, the increased hind-paw response latencies induced by galanin were prevented by following intrathecal injection of 10 nmol of mu-opioid receptor antagonist, beta-funaltrexamine (beta-FNA), but not by 10 nmol of delta-opioid receptor antagonist, natrindole or 10 nmol of kappa-opioid receptor antagonist, nor-binaltorphimine (nor-BNI). Intrathecal 10 nmol of beta-FNA alone had no significant effects on the hind-paw withdrawal responses. These results demonstrate the existence of a specific interaction between galanin and opioids in the transmission of presumed nociceptive information in the spinal cord of mononeuropathic rats. This interaction involves the activation of mu-opioid receptor.