Participation of NH1 receptors in nociceptin-induced modulation of rat knee joint mechanosensitivity

Nociceptin is known to act peripherally in the rat knee joint to modulate a rticular mechanosensitivity and it has been postulated that neurokinin-1 (N K1) receptors may be involved in this process. To test this hypothesis, sin gle unit extracellular recordings were made from knee joint primary afferen ts in response to normal and extreme rotation of the joint. Afferent firing rate was assessed following close intraarterial injection of the NK1 antag onist RP67580 followed by administration of 20 nmol nociceptin. With both n ormal and hyper-rotation of the knee, nociceptin was unable to elicit its u sual mechanomodulatory effect such that afferent activity was not significa ntly different from control (P=0.7572 and P=0.9182 for normal and hyper-rot ation of the joint, respectively). These data indicate that nociceptin-indu ced mechanosensitivity changes in the rat knee depend upon NK1 receptor act ivation possibly through secondary release of substance P.