Mammalian RF-
amide peptides are encoded by five different genes and act through five different
G protein-coupled receptors. RF-
amide-related peptides-1 and -3,
neuropeptides AF and FF,
Prolactin releasing
peptides,
Kisspeptins and RFa
peptides are currently considered endogenous
peptides for NPFF1, NPFF2, GPR10, GPR54 and GPR103 receptors, respectively. However, several studies suggest that the selectivity of these
peptides for their receptors is low and indicate that expression patterns for receptors and their corresponding
ligands only partially overlap. In this study, we took advantage of the cloning of the five human RF-
amide receptors to systematically examine their affinity for and their activation by all human RF-
amide peptides. Binding experiments, performed on membranes from CHO cells expressing GPR10, GPR54 and GPR103 receptors, confirmed their high affinity and remarkable selectivity for their cognate
ligands. Conversely, NPFF1 and NPFF2 receptors displayed high affinity for all RF-
amide peptides. Moreover, GTPĪ³S and cAMP experiments showed that almost all RF-
amide peptides efficiently activate NPFF1 and NPFF2 receptors. As
NPFF is known to modulate
morphine analgesia, we undertook a systematic analysis in mice of the hyperalgesic and anti
morphine-induced
analgesic effects of a representative set of endogenous RF-
amide peptides. All of them induced
hyperalgesia and/or prevented
morphine analgesia following intracerebroventricular administration. Importantly, these effects were prevented by administration of RF9, a highly selective NPFF1/NPFF2 antagonist. Altogether, our results show that all endogenous RF-
amide peptides display
pain-modulating properties and point to
NPFF receptors as essential players for these effects.