Opposing interplay between Neuropeptide FF and nitric oxide in antinociception and hypothermia

This study examined the ability of the anti-opioid Neuropeptide FF (NPFF) to modify the endogenous activity of nitric oxide (NO). Antinociceptive and hypothermic effects of 1DMe (D.Tyr-Leu-(N.Me)Phe-Gln-Pro-Gln-Arg-Phe-NH 2), an NPFF agonist, and of l-NAME (N ωnitro- l-arginine methyl ester), an inhibitor of nitric oxide synthase, were investigated in mice. Intraperitoneal (i.p.) injection of l-NAME induced, in the hot plate test, a dose-dependent antinociception not reversed by naloxone, an opioid antagonist, but inhibited by l-Arg, the NO synthesis precursor. Intracerebroventricular (i.c.v.) injections of 1DMe inhibit the antinociceptive activity of l-NAME in a dose-dependent manner. On the contrary, l-NAME markedly potentiated hypothermia induced by 1DMe injected in the third ventricle. These data show that Neuropeptide FF receptors exert a dual effect on endogenous NO functions and could modulate pain transmission independently of opioids.