Nociceptin (1–7) antagonizes nociceptin-induced hyperalgesia in mice

Abstract

Nociceptin and its N-terminal fragment, nociceptin (1–7), were administered intrathecally (i.t.) into conscious mice. Nociceptin (3.0 fmol) produced a significant reduction in the nociceptive thermal threshold (hyperalgesia) measured as the tail-flick and paw-withdrawal responses. Nociceptin (1–7), injected i.t., at 150–1200 fmol had no significant effect. However, when nociceptin (1–7) (150–1200 fmol) was injected simultaneously with nociceptin (3.0 fmol), nociceptin-induced hyperalgesia was significantly reduced. Analgesia induced by a high dose (1200 pmol) of nociceptin was not antagonized by co-administration of nociceptin (1–7) (1200 fmol). These results suggest that N-terminal fragments of nociceptin formed endogenously could modulate the hyperalgesic action of nociceptin in the spinal cord