Effect of nocistatin in pain modulation

Using tail-flick latency as the nociceptive index and von Frey hair to measure the mechanical allodynia, the aim of the present study is to determine whether nocistatin, injected intracerebroventricularly (i.c.v.), would reverse the anti-morphine effect of orphanin FQ (OFQ), and, injected i.c.v. or intrathecally (Lt.), would inhibit the mechanical allodynia in a L5 and L6 spinal nerve ligation model of neuropathic pain in rats. The results show that i.c.v. injection of nocistatin produces no significant changes in the TFL, nor does it affect morphine analgesia. In addition, i.c.v. or i.t. nocistatin produces no significant changes in withdrawal threshold of the nerve-lesioned hind paw. However, nocistatin significantly reverses the antagonistic effect of OFQ on morphine analgesia when it was coinjected i.c.v. with OFQ. The results suggest that nocistatin can reverse the anti-morphine effect of OFQ in rat brain, but cannot inhibit the mechanical allodynia of neuropathic pain in rat brain and spinal cord.