A non-protein extract isolated from the inflamed skin of rabbits inocu
lated with vaccinia virus (Neurotropin, NTP), has been clinically used
in Japan for the treatment of chronic painful conditions such as low
back pain, osteoarthritis, postherpetic neuralgia, subacute myelo-opti
coneuropathy, and so on, Recent studies have shown its efficacy on pat
ients with complex regional pain syndrome (CRPS). The chronic constric
tion injury (CCl) model described by Bennett and Xie has been thought
to show similar painful conditions to those seen in CRPS patients. Thu
s, the antinociceptive effects of NTP were tested in CCl model. In rat
s with mechanical hyperalgesia 2 weeks after nerve injury, i.p, inject
ion of NTP (100 Neurotropin Unit, NU/kg) produced an analgesic effect
that lasted for at least 50 min. An analgesic effect lasting up to 30
min. was observed in rats with heat hyperalgesia 2 weeks after nerve i
njury. Seven daily i.p, injections (50 NU/kg) of NTP commencing 1 week
after surgery produced an early recovery from heat hyperalgesia. Prio
r studies suggest that NTP produces analgesia by activation of a desce
nding pain inhibitory system. Thus, our findings suggest the possibili
ty that the dysfunction of the descending pain inhibitory system could
be related to the hyperalgesia in the nerve injury model, and perhaps
also in people who suffer from painful peripheral neuropathies.