Identification and characterization of novel mammalian neuropeptide FF-like peptides that attenuate morphine-induced antinociception

Prolactin releasing peptide has high affinity and efficacy at neuropeptide FF2 receptors

Neuropeptide FF (NPFF) and prolactin-releasing peptide (PrRP) are two members of the RFamide peptide family. In this study we investigated whether these RFamide peptides, which have common structural features in their C-terminal RFamide motif and share several physiologically important functions, could exert their effects through the same set of receptors. The affinity and functional activity of several related RFamide peptides were determined at the human neuropeptide FF receptor subtype 2 (hNPFF2) and the human prolactin-releasing peptide (hPrRP) receptors. The full-length human prolactin releasing peptide 31 (hPrRP31) had significantly higher efficacy compared with NPFF and its stable analog, (1DMe)Y8Fa, at the hNPFF2 receptor. In contrast, NPFF and (1DMe)Y8Fa were not efficacious at the hPrRP receptor. Our study indicated a generally relatively low level of discrimination for RFamide peptides at the NPFF receptor, whereas the hPrRP receptor clearly preferred PrRP or very closely related peptides. The seemingly promiscuous binding of the RFamide peptides to the NPFF receptor was further confirmed by receptor autoradiography. PrRP may thus signal through the NPFF receptors in vivo.

Characterization of endothelin-converting enzyme-2. Implication for a role in the nonclassical processing of regulatory peptides

Most neuroendocrine peptides are generated by proteolysis of the precursors at basic residue cleavage sites. Prohormone convertases belonging to the subtilisin family of serine proteases are primarily responsible for processing at these "classical sites." In addition to the classical cleavages, a subset of bioactive peptides is generated by processing at "nonclassical" sites. The proteases responsible for these cleavages have not been well explored. Members of several metalloprotease families have been proposed to be involved in nonclassical processing. Among them, endothelin-converting enzyme-2 (ECE-2) is a good candidate because it exhibits a neuroendocrine distribution and an acidic pH optimum. To examine the involvement of this protease in neuropeptide processing, we purified the recombinant enzyme and characterized its catalytic activity. Purified ECE-2 efficiently processes big endothelin-1 to endothelin-1 by cleavage between Trp(21) and Val(22) at acidic pH. To characterize the substrate specificity of ECE-2, we used mass spectrometry with a panel of 42 peptides as substrates to identify the products. Only 10 of these 42 peptides were processed by ECE-2. A comparison of residues around the cleavage site revealed that ECE-2 exhibits a unique cleavage site selectivity that is related to but distinct from that of ECE-1. ECE-2 tolerates a wide range of amino acids in the P1-position and prefers aliphatic/aromatic residues in the P1'-position. However, only a small fraction of the aliphatic/aromatic amino acid-containing sites were cleaved, indicating that there are additional constraints beyond the P1- and P1'-positions. The enzyme is able to generate a number of biologically active peptides from peptide intermediates, suggesting an important role for this enzyme in the biosynthesis of regulatory peptides. Also, ECE-2 processes proenkephalin-derived bovine adrenal medulla peptides, and this processing leads to peptide products known to have differential receptor selectivity. Finally, ECE-2 processes PEN-LEN, an endogenous inhibitor of prohormone convertase 1, into products that do not inhibit the enzyme. Taken together, these results are consistent with an important role for ECE-2 in the processing of regulatory peptides at nonclassical sites.

Distribution of a novel avian gonadotropin-inhibitory hormone in the quail brain

We recently identified a novel hypothalamic neuropeptide inhibiting gonadotropin release in the quail brain and termed it gonadotropin inhibitory hormone (GnIH). In this study, we investigated the localization and distribution of GnIH in both sexes of adult quails by immunohistochemistry with a specific antiserum against GnIH and in situ hybridization. Quantitative analysis demonstrated that the concentration of GnIH in the diencephalon was greater than that in the mesencephalon without sex difference. GnIH concentrations in the cerebrum and cerebellum were below the level of detectability. Clusters of GnIH-like immunoreactive (GnlH-ir) cell bodies were localized in the paraventricular nucleus (PVN) of the hypothalamus. There was no significant difference in the number of GnlH-ir cells in the PVN between males and females. By double immunostaining with antisera reacting with GnIH or avian posterior pituitary hormones (vasotocin and mesotocin), GnIH-ir cells were found to be parvocellular neurons in the ventral portion of PVN, which showed no immunoreaction with the antisera against vasotocin and mesotocin. In situ hybridization revealed the cellular localization of GnIH mRNA in the PVN. GnIH-ir nerve fibers were however widely distributed in the diencephalic and mesencephalic regions. Dense networks of immunoreactive fibers were found in the ventral paleostriatum, septal area, preoptic area, hypothalamus, and optic tectum. The most prominent fibers were seen in the median eminence of the hypothalamus and the dorsal motor nucleus of the vagus in the medulla oblongata. Thus, GnIH may participate not only in neuroendocrine functions, but also in behavioral and autonomic mechanisms.

Molecular properties of endogenous RFamide-related peptide-3 and its interaction with receptors

Based on database searches of DNA sequences, we previously reported a gene encoding peptides possessing Arg-Phe-NH(2) (RFamide) at their C termini. This gene, RFamide-related peptide (RFRP), was expected to encode several different peptides (i.e., RFRP-1, -2, and -3). In the present study, we purified endogenous RFRP-3 from bovine hypothalamus, and demonstrated that it consisted of 28 amino acid residues. After constructing a sandwich enzyme immunoassay for RFRP-3, we analyzed the tissue distribution of endogenous RFRP-3 in rats and found its concentration to be highest in the hypothalamus. In binding assays, [125I]-labeled RFRP-3 bound to OT7T022 with high affinity, but its binding affinity to HLWAR77 was low. On the other hand, [125I]-labeled neuropeptide FF (NPFF) bound to both OT7T022 and HLWAR77 with high affinity. By serial deletion in the N-terminal portions of RFRP-3 and NPFF, we found that four C-terminal amino acid residues (i.e., PQRFamide), which were common between the two peptides, comprised a core sequence responsible for binding with the receptors, whereas three amino acid residues (i.e., PNL in RFRP-3 and LFQ in NPFF) added to the N terminus of PQRFamide played crucial roles in the agonistic activities of RFRP-3 and NPFF for OT7T022 and HLWAR77, respectively.

Scintillation proximity assay of inositol phosphates in cell extracts: high-throughput measurement of G-protein-coupled receptor activation

The phosphatidylinositol turnover assay is used widely to measure activation, and inhibition, of G(q)-linked G-protein-coupled receptors. Cells expressing the receptor of interest are labeled by feeding with tritiated myo-inositol. The label is incorporated into cellular phosphatidylinositol 4,5-bisphosphate, which, upon agonist binding to the receptor, is hydrolyzed by phospholipase C to inositol 1,4,5-trisphosphate (IP(3)) and diacylglycerol. In the presence of Li(+), dephosphorylation of IP(3) to inositol is blocked, and the mass of soluble inositol phosphates is a quantitative readout of receptor activation. Current protocols for this assay all involve an anion-exchange chromatography step to separate radiolabeled inositol phosphates from radiolabeled inositol, making the assay cumbersome and difficult to automate. We now describe a scintillation proximity assay to measure soluble inositol phosphate mass in cell extracts, thus obviating the need for the standard chromatography step. The method uses positively charged yttrium silicate beads that bind inositol phosphates, but not inositol. We have used this assay to measure activation of recombinant and endogenous muscarinic acetylcholine receptors and activation of recombinant neuropeptide FF2 receptor coupled to IP(3) production by coexpression of a chimeric G protein. Further, we demonstrate the use and functional validity of this assay in a semiautomated, 384-well format, by characterizing the muscarinic receptor antagonists pirenzepine and atropine.

Identification of a novel frog RFamide and its effect on the latency of the tail-flick response of the newt

Neuropeptide FF, one of the mammalian PQRFamides, has been reported to affect the latency of the tail-flick response in rat. We intended to examine the nociceptive effect by the peptide PQRFamides from the comparative aspect. Using the dot immunoblot method with antiserum to FMRFamide as an assay system, a peptide (frog's nociception-related peptide, fNRP) which has the C-terminal sequence PQRFamide was isolated from the brain of the frog, Rana catesbeiana. The determined sequence, SIPNLPQRF-NH(2), is the same as that named first (frog growth hormone-releasing peptide-gene-related peptide-1: fGRP-RP-1, which is encoded in the cDNA of the fGRP precursor. Since the peptide was isolated from the frog brain, we tested another amphibian, the newt, which has a tail, by the hot beam tail-flick test. Intraperitoneal injection of fNRP significantly increased the latency of the pain response (tail-flick) 90 min after administration. The effect was blocked by simultaneous administration of 5 mM naloxone. The result provides evidence for the interaction of fNRP and opioid steps in the analgesia pathways in the newt.

Quantitative autoradiographic distribution of NPFF1 neuropeptide FF receptor in the rat brain and comparison with NPFF2 receptor by using [125I]YVP and [(125I]EYF as selective radioligands

The selectivity of two new radioligands, [(125)I]YVP ([(125)I]YVPNLPQRF-NH(2)) and [(125)I]EYF ([(125)I]EYWSLAAPQRF-NH(2)), for neuropeptide FF (NPFF) receptor subtypes was determined using HEK293 cells expressing hNPFF(1) and CHO cells expressing hNPFF(2) receptors. Saturation binding and displacement experiments showed that [(125)I]YVP and [(125)I]EYF bound selectively with a very high affinity, K(D)=0.18 nM and 0.06 nM, to NPFF(1) and NPFF(2) receptors respectively. By using in vitro autoradiography with these radioligands and frog pancreatic polypeptide (PP) as selective unlabelled competitor of NPFF(2) binding sites, NPFF(1) and NPFF(2) receptor distribution was analyzed throughout the rat CNS. The highest densities of [(125)I]EYF binding sites were seen in the most external layers of the dorsal horn of the spinal cord, the parafascicular thalamic nucleus, laterodorsal thalamic nucleus and presubiculum of hippocampus. All specific binding of this radioligand was inhibited by 200 nM frog PP. The density of 0.1 nM [(125)I]YVP binding was much smaller in all brain areas and frog PP-insensitive binding sites (NPFF(1) receptor subtype) were detected in septal, thalamic and hypothalamic areas but were absent in the spinal cord. The restricted distribution of NPFF(1) receptors in the CNS supports its specific role in a limited number of neuronal functions. In contrast to the rat spinal cord where the NPFF(1) system is absent, there is no strict separation between NPFF(1) and NPFF(2) system at the supraspinal level.

Central administration of neuropeptide FF causes activation of oxytocin paraventricular hypothalamic neurones that project to the brainstem

Neuropeptide FF (NPFF), a morphine modulatory peptide, is emerging as an important neuromodulator in the context of central autonomic and neuroendocrine regulation. NPFF immunoreactivity and receptors have been identified in discrete autonomic regions within the brain and spinal cord, including the hypothalamic paraventricular nucleus (PVN). In this study, we examined the effects of intracerebroventricular (i.c.v.) administration of NPFF on activation of chemically identified PVN neurones that project to the brainstem nucleus of the solitary tract (NTS). In conscious rats, i.c.v. NPFF at a dose of 10 micro g, but not 8 micro g, caused an increase in arterial blood pressure. Immunohistochemical analysis revealed a dose-dependent increase in activated (Fos positive) PVN neurones following i.c.v. NPFF administration compared to controls receiving i.c.v. saline. Activated PVN neurones were located predominantly in the parvocellular compartment of the nucleus with relatively few Fos positive cells in the magnocellular subdivision. Chemical identification of activated neurones revealed significant number of activated cells to be oxytocin positive, whereas only few vasopressin, tyrosine hydroxylase (TH) or corticotrophin-releasing factor (CRF) neurones were double-labelled. Injection of the retrograde tracer fluorogold into the NTS resulted in labelling of significant numbers of parvocellular oxytocin, but not vasopressin, TH or CRF, PVN neurones. We conclude that centrally administered NPFF stimulates brainstem-projecting oxytocin PVN neurones. Oxytocin released from terminals within the NTS oxytocin thus modulate the activity of ascending visceral autonomic pathways that synapse initially within the NTS.

Identification of neuropeptide FF-related peptides in human cerebrospinal fluid by mass spectrometry

Several neuropeptide FF (NPFF)-related peptides, known as modulators of the opioid system, have been previously characterized in bovine and rodent brain. Reverse-phase high pressure liquid chromatography (HPLC) fractions of a human with normal pressure hydrocephalus cerebrospinal fluid (CSF), co-migrating with NPFF-related synthetic peptides, were characterized by capillary HPLC coupled on-line to nanospray ion trap tandem mass spectrometry. Two peptides present in the pro-NPFF(A) precursor, NPAF (AGEGLNSQFWSLAAPQRF-NH2) and NPSF (SLAAPQRF-NH2), were identified. The monitoring of NPFF-related peptides in human CSF can be helpful to understand their roles in pain sensitivity.

Novel fish hypothalamic neuropeptide

Recently, we identified novel avian and amphibian hypothalamic neuropeptides that inhibited gonadotropin release and stimulated growth hormone release. They were characterized by a similar structure including the C-terminal LPLRF-NH2 motif. To clarify that the expression of these novel hypothalamic neuropeptides is a conserved property in vertebrates, we characterized a cDNA encoding a similar novel peptide, having LPLRF-NH2 from the goldfish brain, by a combination of 3' and 5' rapid amplification of cDNA ends (RACE). The deduced peptide precursor consisted of 197 amino acid residues, encoding three putative peptide sequences that included -LPXRF (where X is L or Q) at their C-termini. Mass spectrometric analyses revealed that a tridecapeptide (SGTGLSATLPQRF-NH2) was derived from the precursor in the brain as an endogenous ligand. Southern blotting analysis of reverse-transcriptase-mediated PCR products demonstrated a specific expression of the goldfish peptide gene in the diencephalon. In situ hybridization revealed the cellular localization of goldfish peptide mRNA in the nucleus posterioris periventricularis in the hypothalamus. Immunoreactive cell bodies were also restricted to the the nucleus posterioris periventricularis and the nervus terminalis and immunoreactive fibers were distributed in several brain regions including the nucleus lateralis tuberis pars posterioris and pituitary. Thus, the goldfish hypothalamus expresses a novel neuropeptide containing the C-terminal -LPQRF-NH2 sequence, which may possess multiple regulatory functions and act, at least partly, on the pituitary to regulate pituitary hormone release.

Endogenous opiates and behavior: 2001

This paper is the twenty-fourth installment of the annual review of research concerning the opiate system. It summarizes papers published during 2001 that studied the behavioral effects of the opiate peptides and antagonists. The particular topics covered this year include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors (Section 2), and the roles of these opioid peptides and receptors in pain and analgesia (Section 3); stress and social status (Section 4); tolerance and dependence (Section 5); learning and memory (Section 6); eating and drinking (Section 7); alcohol and drugs of abuse (Section 8); sexual activity and hormones, pregnancy, development and endocrinology(Section 9); mental illness and mood (Section 10); seizures and neurologic disorders (Section 11); electrical-related activity and neurophysiology (Section 12); general activity and locomotion (Section 13); gastrointestinal, renal and hepatic functions (Section 14); cardiovascular responses (Section 15); respiration and thermoregulation (Section 16); and immunological responses (Section 17).

Neuropeptide AF and FF modulation of adipocyte metabolism. Primary insights from functional genomics and effects on beta-adrenergic responsiveness

The presence of a neuropeptide AF and FF receptor (NPFF-R2) mRNA in human adipose tissue (Elshourbagy, N. A., Ames, R. S., Fitzgerald, L. R., Foley, J. J., Chambers, J. K., Szekeres, P. G., Evans, N. A., Schmidt, D. B., Buckley, P. T., Dytko, G. M., Murdock, P. R., Tan, K. B., Shabon, U., Nuthulaganti, P., Wang, D. Y., Wilson, S., Bergsma, D. J., and Sarau, H. M. (2000) J. Biol. Chem. 275, 25965-25971) suggested these peptides, principally recognized for their pain modulating effects, may also impact on adipocyte metabolism, an aspect that has not been explored previously. Our aim was thus to obtain more insights into the actions of these peptides on adipocytes, an approach initially undertaken with a functional genomic assay. First we showed that 3T3-L1 adipocytes express both NPFF-R1 and NPFF-R2 transcripts, and that NPAF binds adipocyte membranes with a nanomolar affinity as assessed by surface plasmon resonance technology. Then, and following a 24-h treatment with NPFF or NPAF (1 microm), we have measured using real-time quantitative reverse transcriptase-PCR the mRNA steady state levels of already well characterized genes involved in key pathways of adipose metabolism. Among the 45 genes tested, few were modulated by NPFF ( approximately 10%) and a larger number by NPAF ( approximately 27%). Interestingly, NPAF increased the mRNA levels of beta2- and beta3-adrenergic receptors (AR), and to a lesser extent those of beta1-ARs. These variations in catecholamine receptor mRNAs correlated with a clear induction in the density of beta2- and beta3-AR proteins, and in the potency of beta-AR subtype-selective agonists to stimulate adenylyl cyclase activity. Altogether, these data show that NPFF-R1 and NPFF-R2 are functionally present in adipocytes and suggest that besides their well described pain modulation effects, NPAF and to a lesser extent NPFF, may have a global impact on body energy storage and utilization.

A neuropeptide FF-related gene is expressed selectively in neurons of the terminal nerve in Danio rerio

RFamides constitute a large family of neuromodulatory peptides. We have cloned a zebrafish gene, which is presumably a homologue to the mammalian PQRF subfamily of RFamides, and named it zfPQRF for its species and subfamily allocation. We report that in contrast to its mammalian counterparts zfPQRF is expressed in the olfactory bulb and the nucleus olfactoretinalis in the telencephalon, but absent in more caudal regions, including hypothalamus, brain stem and spinal cord. zfPQRF-expressing neurons originate in the vicinity of the olfactory placode and populate the nuclei of the terminal nerve during later development, as demonstrated by co-expression of zebrafish salmon-type gonadotropin releasing hormone, which was found to exclusively label terminal nerve neurons.

Pharmacological characterization of human NPFF1 and NPFF2 receptors expressed in CHO cells by using NPY Y1 receptor antagonists

Neuropeptide FF (NPFF) belongs to an opioid-modulatory system including two precursors (pro-NPFF(A) and pro-NPFF(B)) and two G-protein coupled receptors (NPFF(1) and NPFF(2)). The pharmacological and functional profiles of human NPFF(1) and NPFF(2) receptors expressed in Chinese hamster ovary (CHO) cells were compared by determining the affinity of several peptides derived from both NPFF precursors and by measuring their abilities to inhibit forskolin-induced cAMP accumulation. Each NPFF receptor recognizes peptides from both precursors with nanomolar affinities, however, with a slight preference of pro-NPFF(A) peptides for NPFF(2) receptors and of pro-NPFF(B) peptides for NPFF(1) receptors. BIBP3226 ((R)-N(2)-(diphenylacetyl)-N-[(4-hydroxyphenyl)-methyl]-argininamide) and BIBO3304 ((R)-N(2)-(diphenylacetyl)-N-[4-(aminocarbonylaminomethyl)-benzyl]-argininamide trifluoroacetate), two selective neuropeptide Y (NPY) Y(1) receptor antagonists, display relative high affinities for NPFF receptors and exhibit antagonist properties towards hNPFF(1) receptors. The structural determinants responsible for binding of these molecules to NPFF receptors were investigated and led to the synthesis of hNPFF(1) receptor antagonists with affinities from 40 to 80 nM. Our results demonstrate differences in pharmacological characteristics between NPFF(1) and NPFF(2) receptors and the feasibility of subtype-selective antagonists.

Analysis of human neuropeptide FF gene expression

As an initial step to study the function of the gene encoding the human neuropeptide FF (NPFF), we cloned a 4.7-kb sequence from the promoter region. Primer extension and 5'-rapid amplification of cDNA ends revealed multiple transcription initiation sites. Northern blot analysis of the mRNA expression revealed a specific signal only in poly(A) + RNA from medulla and spinal cord. Chimeric luciferase reporter gene constructs were transiently transfected in A549, U-251 MG, SK-N-SH, SK-N-AS and PC12 cells. The promoter activity was directly comparable with the level of endogenous NPFF mRNA as determined by real-time quantitative RT-PCR. The highest promoter activity was measured when a region from - 552 to - 830 bp of the 5'-flanking region was fused to the constructs, and a potential silencer element was localized between nucleotides -220 and -551. A twofold increase in NPFF mRNA was observed after 72 h of nerve growth factor stimulation of PC12 cells and the region between - 61 and - 214 bp of the 5'-flanking region was found to be responsive to this stimulation. We postulate that control of human NPFF gene expression is the result of both positive and negative regulatory elements and the use of multiple transcription initiation sites.

Dissociation of pharmacological pro- and anti-opioid effects by neuropeptide FF analogs

Neuropeptide FF (NPFF) and its analog 1DMe ([D-Tyr(1),(NMe)Phe(3)]NPFF) have been shown to reverse or potentiate morphine analgesia in rat depending on the supraspinal or spinal site of injection. The properties, in the mouse tail-flick test, of 1DMe and its related compound Nic-1DMe (Nicotinoyl-Pro-1DMe) were investigated after their local (i.c.v. and i.t.) and systemic administration. Whereas Nic-1DMe and 1DMe exhibit the same affinity and selectivity towards NPFF(1) and NPFF(2) receptors, Nic-1DMe, in contrast to 1DMe, is unable to inhibit morphine-induced analgesia after i.c.v. and i.p. administration. Conversely, after i.t. and i.p. administration, both neuropeptide FF analogs could potentiate morphine analgesia. Differences in disposition parameters between 1DMe and Nic-1DMe are evidenced, suggesting that the two neuropeptide FF analogs could stimulate differentially supraspinal neuropeptide FF receptors. The predominant activation of spinal neuronal pathways by Nic-1DMe could explain the selective pro-opioid action of this compound after i.t., i.c.v. and i.p. administration.

Central administration of neuropeptide FF (NPFF) causes increased neuronal activation and up-regulation of NPFF gene expression in the rat brainstem

Neuropeptide FF (NPFF) is a morphine modulatory peptide that plays an important role in a wide variety of physiological functions, including those related to nociception and central autonomic regulation. NPFF fibers and cells have been shown to be discretely localized in key autonomic centers within the brain, including the brainstem nucleus of the solitary tract (NTS). Central applications of NPFF evoke a number of important biological effects through activation of central neuronal circuits whose identities remain unknown at present. NPFF administered in this manner may also be capable of up- or down-regulating its own gene expression. In this study, we investigated the effects of intracerebroventricular (i.c.v.) administration of NPFF on the activation and the gene expression of NPFF in NTS neurons. Conscious rats received saline or NPFF (8 or 10 microg i.c.v.), with concomitant monitoring of arterial blood pressure. Brains were prepared for Fos immunohistochemistry to identify neuronal activation and NPFF in situ hybridization to determine cells expressing NPFF mRNA in the NTS. At a dose of 8 microg, i.c.v., NPFF did not evoke alterations in blood pressure, but, at 10 microg, there was an increase in arterial blood pressure of 30-40 mmHg. Image analysis showed a dose-dependent increase in number of NPFF neurons that were activated in rats receiving i.c.v. NPFF compared with saline controls. NPFF gene expression in the NTS showed a similar dose-dependent increase following i.c.v. administration of either 8 or 10 microg of NPFF. Significantly greater numbers of activated neurons expressing the NPFF gene (double labeled) were observed in the NTS at the level of the area postrema in animals receiving i.c.v. NPFF compared with saline controls. These data indicate that centrally administered NPFF is capable of up-regulating its own gene expression in the NTS and that this effect appears in part to be independent of elevations in arterial blood pressure that this peptide can evoke when administered i.c.v. at the higher dose. The up-regulation of NPFF may play a homeostatic role in response to specific cardiovascular challenges, such as hypotension.

Novel G-protein-coupled receptor genes expressed in the brain: continued discovery of important therapeutic targets

The rhodopsin family of G-protein-coupled receptors (GPCRs) is the largest known group of cell-surface mediators of signal transduction. The vast majority of these receptors were discovered by methods based upon shared sequence homologies found throughout this family. While such efforts identified a multitude of receptor subtypes for previously known ligands, numerous receptors have been discovered for which endogenous ligands were unknown. These receptors are commonly referred to as orphan receptors. One of the most important tasks of modern pharmacology lies in elucidating the functions of these receptors. Of particular interest are receptors with recognised expression in the central nervous system, given that many psychiatric and neurodegenerative disorders are mediated by unknown mechanisms. Hence, this collection of putative neurotransmitter and neuromodulator signal mediators represents a substantial and untapped resource for novel drug discovery. Recently, various methodologies have accelerated the discovery of novel ligands for these orphan receptors, identifying the basic components required for further physiological ligand/receptor system characterisation. Equipped with proven ligand identification strategies, the characterisation of all orphan GPCRs and the exploitation of their exciting potential as targets for the discovery of novel drugs is anticipated.

Descending control of pain

Upon receipt in the dorsal horn (DH) of the spinal cord, nociceptive (pain-signalling) information from the viscera, skin and other organs is subject to extensive processing by a diversity of mechanisms, certain of which enhance, and certain of which inhibit, its transfer to higher centres. In this regard, a network of descending pathways projecting from cerebral structures to the DH plays a complex and crucial role. Specific centrifugal pathways either suppress (descending inhibition) or potentiate (descending facilitation) passage of nociceptive messages to the brain. Engagement of descending inhibition by the opioid analgesic, morphine, fulfils an important role in its pain-relieving properties, while induction of analgesia by the adrenergic agonist, clonidine, reflects actions at alpha(2)-adrenoceptors (alpha(2)-ARs) in the DH normally recruited by descending pathways. However, opioids and adrenergic agents exploit but a tiny fraction of the vast panoply of mechanisms now known to be involved in the induction and/or expression of descending controls. For example, no drug interfering with descending facilitation is currently available for clinical use. The present review focuses on: (1) the organisation of descending pathways and their pathophysiological significance; (2) the role of individual transmitters and specific receptor types in the modulation and expression of mechanisms of descending inhibition and facilitation and (3) the advantages and limitations of established and innovative analgesic strategies which act by manipulation of descending controls. Knowledge of descending pathways has increased exponentially in recent years, so this is an opportune moment to survey their operation and therapeutic relevance to the improved management of pain.

A novel rat hypothalamic RFamide-related peptide identified by immunoaffinity chromatography and mass spectrometry

Recently, cDNAs encoding novel RFamide-related peptides (RFRPs) have been reported in the mammalian brains by a gene database search and the deduced RFRPs have been suggested to participate in neuroendocrine and pain mechanisms in the rat. Two peptides have been predicted to be encoded in the cDNA of rodent RFRPs. To assess precise functions of rodent RFRPs in the brain, in the present study we identified a naturally occurring RFRP in the rat hypothalamus by immunoaffinity purification combined with mass spectrometry (MS). The affinity chromatography showed that the rat hypothalamus contained RFRP-like immunoreactivity. The immunoreactive material was analyzed by a nanoflow electrospray ionization time-of-flight MS followed by tandem MS analysis. The mass peak corresponding to octadecapeptide was detected at 1010.54 m/z ([M+2H](2+)) and its sequence, ANMEAGTMSHFPSLPQRF-NH(2), was revealed by the fragmentation, showing a mature form encoded in the cDNA sequence of RFRPs. The identified endogenous RFRP will aid not only in defining its physiological roles but also facilitate the development of its agonists and antagonists in the rodent brain.