Effects of intrathecal and i.c.v. administration of neuropeptide W-23 and neuropeptide B on the mechanical allodynia induced by partial sciatic nerve ligation in rats.

Neuropeptide W-23 and neuropeptide B are each an endogenous ligand of GPR7. GPR7 mRNA has been detected in regions of the cortex, the hippocampus, the hypothalamus and the spinal cord in the rat. GPR7 receptor has structural features in common with both opioid and somatostatin receptors. In the present study, the effects of intrathecal and i.c.v. application of neuropeptide W-23 and neuropeptide B on the level of mechanical allodynia induced by partial sciatic nerve ligation were tested in rats. The level of mechanical allodynia was measured using von Frey filaments. Intrathecal injection of either neuropeptide W-23 or neuropeptide B attenuated the level of mechanical allodynia in a dose dependent manner at a dose between 0.1 and 10 microg, but i.c.v. injection of either neuropeptide W-23 or neuropeptide B had no effect on the level of mechanical allodynia at a dose between 3 and 30 microg. The effect of intrathecal administration of either 10 microg of neuropeptide W-23 or 10 microg of neuropeptide B was not antagonized by i.p. injection of 1 mg/kg of naloxone. Immunohistochemical examination revealed that neuropeptide W-23 was expressed mainly in the small- to medium-sized neuronal profiles in the dorsal root ganglion and that partial sciatic nerve injury decreased the percentage of neuropeptide W-23-like immunoreactivity positive neuronal profiles that were labeled by IB4. These data suggest that neuropeptide W-23 is involved in the nociceptive transmission in spinal cord and that both spinally-applied neuropeptide W-23 and spinally-applied neuropeptide B produce anti-allodynic effects in the partial sciatic nerve ligation model in rat.