Study of the effect of 26RF- and 43RF-amides on testosterone and prolactin secretion in the adult male rhesus monkey (Macaca mulatta)

The Arg-Phe-amide peptide 26RFa/glutamine RF-amide peptide and its receptor: IUPHAR Review 24

The RFamide neuropeptide 26RFa was first isolated from the brain of the European green frog on the basis of cross-reactivity with antibodies raised against bovine neuropeptide FF (NPFF). 26RFa and its N-terminally extended form glutamine RF-amide peptide (QRFP) have been identified as cognate ligands of the former orphan receptor GPR103, now renamed glutamine RF-amide peptide receptor (QRFP receptor). The 26RFa/QRFP precursor has been characterized in various mammalian and non-mammalian species. In the brain of mammals, including humans, 26RFa/QRFP mRNA is almost exclusively expressed in hypothalamic nuclei. The 26RFa/QRFP transcript is also present in various organs especially in endocrine glands. While humans express only one QRFP receptor, two isoforms are present in rodents. The QRFP receptor genes are widely expressed in the CNS and in peripheral tissues, notably in bone, heart, kidney, pancreas and testis. Structure-activity relationship studies have led to the identification of low MW peptidergic agonists and antagonists of QRFP receptor. Concurrently, several selective non-peptidic antagonists have been designed from high-throughput screening hit optimization. Consistent with the widespread distribution of QRFP receptor mRNA and 26RFa binding sites, 26RFa/QRFP exerts a large range of biological activities, notably in the control of energy homeostasis, bone formation and nociception that are mediated by QRFP receptor or NPFF2. The present report reviews the current knowledge concerning the 26RFa/QRFP-QRFP receptor system and discusses the potential use of selective QRFP receptor ligands for therapeutic applications.

Anxiolytic effect of the GPR103 receptor agonist peptide P550 (homolog of neuropeptide 26RFa) in mice. Involvement of neurotransmitters

The GPR103 receptor is a G protein-coupled receptor, which plays a role in several physiological functions. However, the role of the GPR103 receptor in anxiety has not been clarified. The first aim of our study was to elucidate the involvement of the GPR103 receptor in anxious behavior. Mice were treated with peptide P550, which is the mouse homolog of neuropeptide 26RFa and has similar activity for the GPR103 receptor as neuropeptide 26RFa. The anxious behavior was investigated using an elevated plus-maze paradigm. The second aim of our study was to investigate the underlying neurotransmissions. Accordingly, mice were pretreated with a nonselective muscarinic acetylcholine receptor antagonist, atropine, a γ-aminobutyric acid subunit A (GABAA) receptor antagonist, bicuculline, a non-selective 5-HT2 serotonergic receptor antagonist, cyproheptadine, a mixed 5-HT1/5-HT2 serotonergic receptor antagonist, methysergide, a D2, D3, D4 dopamine receptor antagonist, haloperidol, a nonselective α-adrenergic receptor antagonist, phenoxybenzamine and a nonselective β-adrenergic receptor antagonist, propranolol. Our results demonstrated that peptide P550 reduces anxious behavior in elevated plus maze test in mice. Our study shows also that GABAA-ergic, α- and β-adrenergic transmissions are all involved in this action, whereas 5-HT1 and 5-HT2 serotonergic, muscarinic cholinergic and D2, D3, D4 dopaminergic mechanisms may not be implicated.

RF-amide neuropeptides and their receptors in Mammals: Pharmacological properties, drug development and main physiological functions

RF-amide neuropeptides, with their typical Arg-Phe-NH2 signature at their carboxyl C-termini, belong to a lineage of peptides that spans almost the entire life tree. Throughout evolution, RF-amide peptides and their receptors preserved fundamental roles in reproduction and feeding, both in Vertebrates and Invertebrates. The scope of this review is to summarize the current knowledge on the RF-amide systems in Mammals from historical aspects to therapeutic opportunities. Taking advantage of the most recent findings in the field, special focus will be given on molecular and pharmacological properties of RF-amide peptides and their receptors as well as on their implication in the control of different physiological functions including feeding, reproduction and pain. Recent progress on the development of drugs that target RF-amide receptors will also be addressed.

Molecular evolution of GPCRs: 26Rfa/GPR103

Neuropeptides possessing the Arg-Phe-NH2 (RFamide) motif at their C-termini (designated as RFamide peptides) have been characterized in a variety of animals. Among these, neuropeptide 26RFa (also termed QRFP) is the latest member of the RFamide peptide family to be discovered in the hypothalamus of vertebrates. The neuropeptide 26RFa/QRFP is a 26-amino acid residue peptide that was originally identified in the frog brain. It has been shown to exert orexigenic activity in mammals and to be a ligand for the previously identified orphan G protein-coupled receptor, GPR103 (QRFPR). The cDNAs encoding 26RFa/QRFP and QRFPR have now been characterized in representative species of mammals, birds, and fish. Functional studies have shown that, in mammals, the 26RFa/QRFP-QRFPR system may regulate various functions, including food intake, energy homeostasis, bone formation, pituitary hormone secretion, steroidogenesis, nociceptive transmission, and blood pressure. Several biological actions have also been reported in birds and fish. This review summarizes the current state of identification, localization, and understanding of the functions of 26RFaQRFP and its cognate receptor, QRFPR, in vertebrates.

Identification, localization and function of a novel neuropeptide, 26RFa, and its cognate receptor, GPR103, in the avian hypothalamus

Several neuropeptides possessing the RFamide motif at their C-termini (designated RFamide peptides) have been characterized in the hypothalamus of a variety of vertebrates. Since the discovery of the 26-amino acid RFamide peptide (termed 26RFa) from the frog brain, 26RFa has been shown to exert orexigenic activity in mammals and to be a ligand of the previously identified orphan G protein-coupled receptor GPR103. Recently, we have identified 26RFa in the avian brain by molecular cloning of the cDNA encoding the 26RFa precursor and mass spectrometry analysis of the mature peptide. 26RFa-producing neurons are exclusively located in the hypothalamus whereas GPR103 is widely distributed in the avian brain. Furthermore, avian 26RFa stimulates feeding behavior in broiler chicks. This review summarizes the advances in the identification, localization, and functions of 26RFa and its cognate receptor GPR103 in vertebrates and highlights recent progress made in birds.