Emerging evidence has suggested that neurokinin 1 receptor (NK1R) is important in the development of visceral pain and hyperalgesia, however, whether NK1R exists in the CSF‑CN and its exact role in visceral pain remain to be fully elucidated.
Injection of the selective NK-1 receptor agonist Sar9,Met(O<sub>2</sub>)<sup>11</sup>-substance P (SSP) into the RVM produced dose-dependent mechanical and heat hyperalgesia that was blocked by coadministration of the selective NK-1 receptor antagonist L-733,060.
Here, the role of NK-1 receptor expressing cells in the spinal dorsal horn in morphine-induced hyperalgesia and spinal antinociceptive tolerance was assessed by ablating these cells with intrathecal injection of SP-saporin (SP-SAP).