Although Neurotropin® (NTP) has been used clinically as an analgesic in Japan for many years, its effect on neuropathic pain in animal models has not been examined in detail. Its main effect has been indicated to be activation of the descending monoaminergic pain inhibitory systems. To study the effect of NTP on neuropathic pain, we subjected mice to spinal nerve ligation. NTP inhibited both tactile allodynia and mechanical and thermal hyperalgesia in a dose-dependent manner. When the effect of NTP was examined after depletion of monoamines in the spinal cord by intrathecal neurotoxins, the antiallodynic and antihyperalgesic effects were still observed after serotonergic denervation, but not after noradrenergic denervation. In addition, intracerebroventricular NTP increased withdrawal threshold and latency although intrathecal or local administration of NTP did not. These results suggest that the antiallodynic and antihyperalgesic effect of NTP on neuropathic pain induced by spinal nerve ligation is mediated principally through the action at supraspinal sites and through activation of spinal noradrenergic systems, possibly via the descending inhibitory pathway.
IMPLICATIONS: We investigated the analgesic effect of Neurotropin® in mice with fifth lumber nerve ligation. Neurotropin® dose-dependently showed antiallodynic and antihyperalgesic effects via action at the supraspinal site and activation of spinal noradrenergic systems.
Department of Anesthesiology, Osaka University Medical School, Osaka, Japan
This study was supported in part by Grants-in-Aid for Scientific Research from the Ministry of Education, Science, and Culture of Japan.
Accepted for publication February 11, 2005.
Address correspondence and reprint requests to Takahiro Suzuki, MD, Department of Anesthesiology, Osaka University Medical School, 2-2 Yamadaoka, Suita, Osaka, Japan 565-0871. Address e-mail to firstname.lastname@example.org.