Experiments were conducted to explore the effects of
Neuropeptide FF acting at spinal and supraspinal sites in models of chronic inflammatory or
neuropathic pain and of
acute pain.
Neuropeptide FF was administered intrathecally (i.t.; 10.0, 25.0 and 50.0 nmol) or intracerebroventricularly (i.c.v.; 10.0, 12.5 and 15.0 nmol) either 24 h after
inflammation-inducing
injections of Freund's Complete Adjuvant in one hind paw or 7 days after unilateral sciatic nerve constriction. Evoked
pain was assessed by measuring the withdrawal response threshold (in grams of pressure) to a mechanical stimulus applied to the plantar surface of the injured paw.
Neuropeptide FF dose-dependently attenuated the allodynic response (i.e., withdrawal from a normally innocuous stimulus) to mechanical stimulation in the inflammatory and neuropathic model following i.t. (ED50=20.86 nmol and ED50=18.91 nmol, respectively) and i.c.v. (ED50=12.31 nmol and ED50=11.68 nmol, respectively) administration. Pretreatment with
naloxone (2.0 mg/kg; s.c.) attenuated the anti-allodynic effect of i.t. or i.c.v.
Neuropeptide FF in rats experiencing inflammatory, but not
neuropathic pain. In contrast,
Neuropeptide FF administered i.t. (10.0, 25.0 and 50.0 nmol) or i.c.v. (10.0, 12.5 and 15.0 nmol) had no effect on the response to acute thermal or mechanical stimulation.
Neuropeptide FF injected i.t. or i.c.v. in inflamed or neuropathic rats did not produce any sign of motor dysfunction. These results suggest that
Neuropeptide FF acting at spinal and supraspinal sites plays a role in modulating chronic, but not
acute pain. Furthermore, the results suggest that the anti-allodynic effect of
Neuropeptide FF is mediated indirectly by
naloxone-sensitive
opioid mechanisms in rats subjected to inflammatory, but not
neuropathic pain.