Morphine Modulating Neuropeptides
A-18F-NH₂ and NPFF (F-8-F-NH₂) are found in relatively high concentrations in the periaqueductal grey and dorsal spinal cord of the mammalian nervous system. Both peptides have been shown to attenuate the analgesic effect of morphine. NPFF was shown to exhibit antiopiate activity by inhibiting a variety of morphine-induced effects. For example, NPFF opposes the antinociceptive properties of morphine and the development of morphine tolerance and dependence, in addition to precipating withdrawal in morphine-dependent animals. Its antiopiate effects appear to be mediated via a single class of specific NPFF receptors, which are localized in spinal and supraspinal regions enriched with endogenous opioids. NPFF antagonizes morphine effects via binding to nonopioid (NPFF) receptors, not binding to opioid receptors.