International Union of Basic and Clinical Pharmacology. LXXVII. Kisspeptin receptor nomenclature, distribution, and function

Involvement of Mammalian RF-Amide Peptides and Their Receptors in the Modulation of Nociception in Rodents

Mammalian RF-amide peptides, which all share a conserved carboxyl-terminal Arg-Phe-NH2 sequence, constitute a family of five groups of neuropeptides that are encoded by five different genes. They act through five G-protein-coupled receptors and each group of peptide binds to and activates mostly one receptor: RF-amide related peptide group binds to NPFFR1, neuropeptide FF group to NPFFR2, pyroglutamylated RF-amide peptide group to QRFPR, prolactin-releasing peptide group to prolactin-releasing peptide receptor, and kisspeptin group to Kiss1R. These peptides and their receptors have been involved in the modulation of several functions including reproduction, feeding, and cardiovascular regulation. Data from the literature now provide emerging evidence that all RF-amide peptides and their receptors are also involved in the modulation of nociception. This review will present the current knowledge on the involvement in rodents of the different mammalian RF-amide peptides and their receptors in the modulation of nociception in basal and chronic pain conditions as well as their modulatory effects on the analgesic effects of opiates.

The Concise Guide to PHARMACOLOGY 2013/14: G protein-coupled receptors

The Concise Guide to PHARMACOLOGY 2013/14 provides concise overviews of the key properties of over 2000 human drug targets with their pharmacology, plus links to an open access knowledgebase of drug targets and their ligands (www.guidetopharmacology.org), which provides more detailed views of target and ligand properties. The full contents can be found at http://onlinelibrary.wiley.com/doi/10.1111/bph.12444/full. G protein-coupled receptors are one of the seven major pharmacological targets into which the Guide is divided, with the others being G protein-coupled receptors, ligand-gated ion channels, ion channels, catalytic receptors, nuclear hormone receptors, transporters and enzymes. These are presented with nomenclature guidance and summary information on the best available pharmacological tools, alongside key references and suggestions for further reading. A new landscape format has easy to use tables comparing related targets. It is a condensed version of material contemporary to late 2013, which is presented in greater detail and constantly updated on the website www.guidetopharmacology.org, superseding data presented in previous Guides to Receptors and Channels. It is produced in conjunction with NC-IUPHAR and provides the official IUPHAR classification and nomenclature for human drug targets, where appropriate. It consolidates information previously curated and displayed separately in IUPHAR-DB and the Guide to Receptors and Channels, providing a permanent, citable, point-in-time record that will survive database updates.

Kisspeptin/KISS1R System in Breast Cancer

Kisspeptins (KP), peptide products of the kisspeptin-1 (KISS1) gene are the endogenous ligands for a G protein-coupled receptor (GPCR) - KP receptor (KISS1R). KISS1R couples to the Gα_q/11 signaling pathway. KISS1 is a metastasis suppressor gene and the KP/KISS1R signaling has anti-metastatic and tumor-suppressant effects in numerous human cancers. On the other hand, recent studies indicate that KP/KISS1R pathway plays detrimental roles in breast cancer. In this review, we summarize recent developments in the understanding of the mechanisms regulating KP/KISS1R signaling in breast cancer metastasis.

Modulation of testicular and whole blood trace element concentrations in conjunction with testosterone release following kisspeptin administration in male rabbits (Oryctolagus cuniculus)

The present study investigated the role of kisspeptin-10 on reproductively significant trace elements in relation to testosterone release in male rabbits, Oryctolagus cuniculus. Groups of rabbits were exposed to single 1 μg kisspeptin dose (i.v., saphenous vein), while simultaneous groups were pretreated with a kisspeptin antagonist, peptide-234 (50 μg) 20 min before administering kisspeptin. Sequential blood sampling was done through marginal ear vein puncture at staggered time intervals: 0, 0.5, 1, 2, 4, and 24 h to determine serum testosterone. Testes and whole blood were collected at 4 and 24 h post dosage to determine trace element concentrations through atomic absorption spectrophotometry. In testes, zinc (Zn), manganese (Mn), and Fe concentrations showed significant increases at 24 h, while copper (Cu) concentration was found elevated at 4 and 24 h both (P < 0.001). In whole blood, Zn and Cu concentrations were significantly elevated at 4 and 24 h, while Mn and cobalt (Co) concentrations showed increases only at 24 h (P < 0.001). Blood iron concentration was not altered in the blood. In contrast, no change occurred in testicular Co, and chromium or nickel concentrations in either testes or blood. Compared to control and predose groups, serum testosterone levels increased gradually and peaked at 2 h (P < 0.001) post kisspeptin treatment but declined thereafter. Pretreatment with antagonist abolished all increases in trace elements and testosterone concentrations. The present study provides first evidence that reproduction- and fertility-related peptide "kisspeptin" modulates testicular and blood trace elements and that this action is likely GPR54-dependent.

The Role of Neurotransmitters in Protection against Amyloid- β Toxicity by KiSS-1 Overexpression in SH-SY5Y Neurons

Recent studies have suggested that the kisspeptin (KP) and kissorphin (KSO) peptides have neuroprotective actions against the Alzheimer's amyloid-β (Aβ) peptide. Overexpression of the human KiSS-1 gene that codes for KP and KSO peptides in SH-SY5Y neurons has also been shown to inhibit Aβ neurotoxicity. The in vivo actions of KP include activation of neuroendocrine and neurotransmitter systems. The present study used antagonists of KP, neuropeptide FF (NPFF), opioids, oxytocin, estrogen, adrenergic, cholinergic, dopaminergic, serotonergic, and γ-aminobutyric acid (GABA) receptors plus inhibitors of catalase, cyclooxygenase, nitric oxide synthase, and the mitogen activated protein kinase cascade to characterize the KiSS-1 gene overexpression neuroprotection against Aβ cell model. The results showed that KiSS-1 overexpression is neuroprotective against Aβ and the action appears to involve the KP or KSO peptide products of KiSS-1 processing. The mechanism of neuroprotection does not involve the activation of the KP or NPFF receptors. Opioids play a role in the toxicity of Aβ in the KiSS-1 overexpression system and opioid antagonists naloxone or naltrexone inhibited Aβ toxicity. The mechanism of KiSS-1 overexpression induced protection against Aβ appears to have an oxytocin plus a cyclooxygenase dependent component, with the oxytocin antagonist atosiban and the cyclooxygenase inhibitor SC-560 both enhancing the toxicity of Aβ.

International Union of Basic and Clinical Pharmacology. LXXXVIII. G protein-coupled receptor list: recommendations for new pairings with cognate ligands

In 2005, the International Union of Basic and Clinical Pharmacology Committee on Receptor Nomenclature and Drug Classification (NC-IUPHAR) published a catalog of all of the human gene sequences known or predicted to encode G protein-coupled receptors (GPCRs), excluding sensory receptors. This review updates the list of orphan GPCRs and describes the criteria used by NC-IUPHAR to recommend the pairing of an orphan receptor with its cognate ligand(s). The following recommendations are made for new receptor names based on 11 pairings for class A GPCRs: hydroxycarboxylic acid receptors [HCA₁ (GPR81) with lactate, HCA₂ (GPR109A) with 3-hydroxybutyric acid, HCA₃ (GPR109B) with 3-hydroxyoctanoic acid]; lysophosphatidic acid receptors [LPA₄ (GPR23), LPA₅ (GPR92), LPA₆ (P2Y5)]; free fatty acid receptors [FFA4 (GPR120) with omega-3 fatty acids]; chemerin receptor (CMKLR1; ChemR23) with chemerin; CXCR7 (CMKOR1) with chemokines CXCL12 (SDF-1) and CXCL11 (ITAC); succinate receptor (SUCNR1) with succinate; and oxoglutarate receptor [OXGR1 with 2-oxoglutarate]. Pairings are highlighted for an additional 30 receptors in class A where further input is needed from the scientific community to validate these findings. Fifty-seven human class A receptors (excluding pseudogenes) are still considered orphans; information has been provided where there is a significant phenotype in genetically modified animals. In class B, six pairings have been reported by a single publication, with 28 (excluding pseudogenes) still classified as orphans. Seven orphan receptors remain in class C, with one pairing described by a single paper. The objective is to stimulate research into confirming pairings of orphan receptors where there is currently limited information and to identify cognate ligands for the remaining GPCRs. Further information can be found on the IUPHAR Database website (http://www.iuphar-db.org).

KISS1R induces invasiveness of estrogen receptor-negative human mammary epithelial and breast cancer cells

Kisspeptins (KPs), peptide products of the KISS1 metastasis-suppressor gene, are endogenous ligands for a G protein-coupled receptor (KISS1R). KISS1 acts as a metastasis suppressor in numerous human cancers. However, recent studies have demonstrated that an increase in KISS1 and KISS1R expression in patient breast tumors correlates with higher tumor grade and metastatic potential. We have shown that KP-10 stimulates invasion of estrogen receptor α (ERα)-negative MDA-MB-231 breast cancer cells via transactivation of the epidermal growth factor receptor (EGFR). Here, we report that either KP-10 treatment of ERα-negative nonmalignant mammary epithelial MCF10A cells or expression of KISS1R in MCF10A cells induced a mesenchymal phenotype and stimulated invasiveness. Similarly, exogenous expression of KISS1R in ERα-negative SKBR3 breast cancer cells was sufficient to trigger invasion and induced extravasation in vivo. In contrast, KP-10 failed to transactivate EGFR or stimulate invasiveness in the ERα-positive MCF7 and T47D breast cancer cells. This suggested that ERα negatively regulates KISS1R-dependent breast cancer cell migration, invasion, and EGFR transactivation. In support of this, we found that these KP-10-induced effects were ablated upon exogenous expression of ERα in the MDA-MB-231 cells, by down-regulating KISS1R expression. Lastly, we have identified IQGAP1, an actin cytoskeletal binding protein as a novel binding partner of KISS1R, and have shown that KISS1R regulates EGFR transactivation in breast cancer cells in an IQGAP1-dependent manner. Overall, our data strongly suggest that the ERα status of mammary cells dictates whether KISS1R may be a novel clinical target for treating breast cancer metastasis.

Immunolocalization of Kisspeptin Associated with Amyloid-β Deposits in the Pons of an Alzheimer's Disease Patient

The pons region of the Alzheimer's disease (AD) brain is one of the last to show amyloid-β (Aβ) deposits and has been suggested to contain neuroprotective compounds. Kisspeptin (KP) is a hormone that activates the hypothalamic-pituitary-gonadal axis and has been suggested to be neuroprotective against Aβ toxicity. The localization of KP, plus the established endogenous neuroprotective compounds corticotropin releasing hormone (CRH) and catalase, in tissue sections from the pons region of a male AD subject has been determined in relation to Aβ deposits. Results showed Aβ deposits also stained with KP, CRH, and catalase antibodies. At high magnification the staining of deposits was either KP or catalase positive, and there was only a limited area of the deposits with KP-catalase colocalization. The CRH does not bind Aβ, whilst both KP and catalase can bind Aβ, suggesting that colocalization in Aβ deposits is not restricted to compounds that directly bind Aβ. The neuroprotective actions of KP, CRH, and catalase were confirmed in vitro, and fibrillar Aβ preparations were shown to stimulate the release of KP in vitro. In conclusion, neuroprotective KP, CRH, and catalase all colocalize with Aβ plaque-like deposits in the pons region from a male AD subject.

Organizational and activational effects of sex steroids on kisspeptin neuron development

Kisspeptin, encoded by the Kiss1 gene, is a neuropeptide required for puberty and adult reproductive function. Understanding the regulation and development of the kisspeptin system provides valuable knowledge about the physiology of puberty and adult fertility, and may provide insights into human pubertal or reproductive disorders. Recent studies, particularly in rodent models, have assessed how kisspeptin neurons develop and how hormonal and non-hormonal factors regulate this developmental process. Exposure to sex steroids (testosterone and estradiol) during critical periods of development can induce organizational (permanent) effects on kisspeptin neuron development, with respect to both sexually dimorphic and non-sexually dimorphic aspects of kisspeptin biology. In addition, sex steroids can also impart activational (temporary) effects on kisspeptin neurons and Kiss1 gene expression at various times during neonatal and peripubertal development, as they do in adulthood. Here, we discuss the current knowledge--and in some cases, lack thereof--of the influence of hormones and other factors on kisspeptin neuronal development.

Effects of kisspeptin-13 on the hypothalamic-pituitary-adrenal axis, thermoregulation, anxiety and locomotor activity in rats

Kisspeptin is a mammalian amidated neurohormone, which belongs to the RF-amide peptide family and is known for its key role in reproduction. However, in contrast with the related members of the RF-amide family, little information is available regarding its role in the stress-response. With regard to the recent data suggesting kisspeptin neuronal projections to the paraventricular nucleus, in the present experiments we investigated the effect of kisspeptin-13 (KP-13), an endogenous derivative of kisspeptin, on the hypothalamus-pituitary-adrenal (HPA) axis, motor behavior and thermoregulatory function. The peptide was administered intracerebroventricularly (icv.) in different doses (0.5-2 μg) to adult male Sprague-Dawley rats, the behavior of which was then observed by means of telemetry, open field and elevated plus maze tests. Additionally, plasma concentrations of corticosterone were measured in order to assess the influence of KP-13 on the HPA system. The effects on core temperature were monitored continuously via telemetry. The results demonstrated that KP-13 stimulated the horizontal locomotion (square crossing) in the open field test and decreased the number of entries into and the time spent in the open arms during the elevated plus maze tests. The peptide also caused marked elevations in the spontaneous locomotor activity and the core temperature recorded by the telemetric system, and significantly increased the basal corticosterone level. In conclusion, our data indicate that icv. administered KP-13 stimulates the HPA axis, induces hyperthermia, activates motor behavior and causes anxiety in rats.

Single-cell analyses reveal that KISS1R-expressing cells undergo sustained kisspeptin-induced signaling that is dependent upon an influx of extracellular Ca2+

The kisspeptin receptor (KISS1R) is a Gα(q/11)-coupled seven-transmembrane receptor activated by a group of peptides referred to as kisspeptins (Kps). The Kp/KISS1R signaling system is a powerful regulator of GnRH secretion, and inactivating mutations in this system are associated with hypogonadotropic hypogonadism. A recent study revealed that Kp triggers prolonged signaling; not from the inability of the receptor to undergo rapid desensitization, but instead from the maintenance of a dynamic and active pool of KISS1R at the cell surface. To investigate this further, we hypothesized that if a dynamic pool of receptor is maintained at the cell surface for a protracted period, chronic Kp-10 treatment would trigger the sustained activation of Gα(q/11) as evidenced through the prolonged activation of phospholipase C, protein kinase C, and prolonged mobilization of intracellular Ca(2+). Through single-cell analyses, we tested our hypothesis in human embryonic kidney (HEK) 293 cells and found that was indeed the case. We subsequently determined that prolonged KISS1R signaling was not a phenomenon specific to HEK 293 cells but is likely a conserved property of KISS1R-expressing cells because evidence of sustained KISS1R signaling was also observed in the GT1-7 GnRH neuronal and Chinese hamster ovary cell lines. While exploring the regulation of prolonged KISS1R signaling, we identified a critical role for extracellular Ca(2+). We found that although free intracellular Ca(2+), primarily derived from intracellular stores, was sufficient to trigger the acute activation of a major KISS1R secondary effector, protein kinase C, it was insufficient to sustain chronic KISS1R signaling; instead extracellular Ca(2+) was absolutely required for this.

Antiproliferative effects of kisspeptin‑10 depend on artificial GPR54 (KISS1R) expression levels

Kisspeptins are peptides derived from the metastasis suppressor gene KISS1 interacting with GPR54 as their corresponding receptor. The KISS1/GPR54 system is one regulator of cellular motility mechanisms leading to decreased migration and invasion. Its role in cell proliferation processes is not clearly understood. In this study, breast cancer cell lines, T47D, ZR75-1, MDA‑MB‑231, MDA‑MB‑435s, MDA‑MB‑453, HCC 70, HCC 1806, HCC 1937 and MCF‑7, were investigated for their endogenous GPR54 expression by immunocytochemistry, RT‑PCR and western blot analysis. The effect of kisspeptin‑10 on proliferation was measured in MDA‑MB‑231, MDA‑MB‑435s, HCC 1806 and MCF‑7 cells. Further experiments on proliferation were carried out with cells transfected with GPR54. All of the tested breast cancer cell lines expressed GPR54 in different amounts. No effects on proliferation were detected in the breast cancer cells expressing the receptor endogenously. In transfected neuronal cells overexpressing GPR54, proliferation was significantly inhibited by kisspeptin‑10. The results indicate that the antiproliferative action of kisspeptin depends on the nature of GPR54 expression. The effect was detected in an artificial system of cells transfected with GPR54 and not in cells expressing the receptor endogenously. Thus, the antiproliferative action of kisspeptin seems not to be important for pathophysiological processes.

Paradoxical effects of kisspeptin: it enhances oocyte in vitro maturation but has an adverse impact on hatched blastocysts during in vitro culture

Kisspeptin (Kp) is best known as a multifunctional peptide with roles in reproduction, the cardiovascular system and cancer. In the present study the expression of kisspeptin hierarchy elements (KISS1, GNRH1 and LHB) and their receptors (KISS1R, GNRHR and LHCGR, respectively) in porcine ovary and in cumulus-oocyte complexes (COCs) were investigated, as were its effects on the in vitro maturation (IVM) of oocytes and their subsequent ability to sustain preimplantation embryo competence after parthenogenetic electrical activation. Kp system elements were expressed and affected IVM of oocytes when maturation medium was supplemented with 10(-6)M Kp. Oocyte maturation, maternal gene expression (MOS, GDF9 and BMP15), blastocyst formation rate, blastocyst hatching and blastocyst total cell count were all significantly increased when oocytes were matured in medium containing Kp compared with the control group (without Kp). A Kp antagonist (p234) at 4×10(-6)M interfered with this hierarchy but did not influence the threshold effect of gonadotrophins on oocyte maturation. FSH was critical and permissive to Kp action on COCs by increasing the relative expression of KISS1R. In contrast, Kp significantly increased apoptosis, the expression of pro-apoptotic gene, BAK1, and suppressed trophoblast outgrowths from hatched blastocysts cultured on feeder cells. The present study provides the first functional evidence of the Kp hierarchy in porcine COCs and its role in enhancing oocyte maturation and subsequent developmental competence in an autocrine-paracrine manner. However, Kp supplementation may have a harmful impact on cultured hatched blastocysts reflecting systemic or local regulation during the critical early period of embryonic development.

Kiss of the mutant mouse: how genetically altered mice advanced our understanding of kisspeptin's role in reproductive physiology

The kisspeptin system has emerged as one of the most important circuits within the central network governing reproduction. Although kisspeptin physiology has been examined in many species, much of our understanding of this system has come from mice. Recently, the study of several innovative strains of genetically engineered mouse models has revealed intriguing and unexpected insights into the functions of kisspeptin signaling in the hypothalamus. Here, we review the advancements in our knowledge of the central kisspeptin system through the use of mutant mice.

Kisspeptin prevention of amyloid-β peptide neurotoxicity in vitro

Alzheimer's disease (AD) onset is associated with changes in hypothalamic-pituitary-gonadal (HPG) function. The 54 amino acid kisspeptin (KP) peptide regulates the HPG axis and alters antioxidant enzyme expression. The Alzheimer's amyloid-β (Aβ) is neurotoxic, and this action can be prevented by the antioxidant enzyme catalase. Here, we examined the effects of KP peptides on the neurotoxicity of Aβ, prion protein (PrP), and amylin (IAPP) peptides. The Aβ, PrP, and IAPP peptides stimulated the release of KP and KP 45-54. The KP peptides inhibited the neurotoxicity of Aβ, PrP, and IAPP peptides, via an action that could not be blocked by kisspeptin-receptor (GPR-54) or neuropeptide FF (NPFF) receptor antagonists. Knockdown of KiSS-1 gene, which encodes the KP peptides, in human neuronal SH-SY5Y cells with siRNA enhanced the toxicity of amyloid peptides, while KiSS-1 overexpression was neuroprotective. A comparison of the catalase and KP sequences identified a similarity between KP residues 42-51 and the region of catalase that binds Aβ. The KP peptides containing residues 45-50 bound Aβ, PrP, and IAPP, inhibited Congo red binding, and were neuroprotective. These results suggest that KP peptides are neuroprotective against Aβ, IAPP, and PrP peptides via a receptor independent action involving direct binding to the amyloid peptides.

Plasma Kisspeptin-54 levels in gastric cancer patients

BACKGROUND

Kisspeptin (Kisspeptin-54; KP-54) is a 54-amino acid peptide was originally known as metastin that was implicated in suppression of tumor metastasis and circulating kisspeptin has been proposed as a tumor marker for numerous cancers in humans. However, the plasma level of KP-54 in gastric cancer (GC) remains undetermined.

AIM

We aimed to investigate the plasma levels of KP-54 in patients with GC.

METHODS

Plasma KP-54 levels were quantified with enzyme-immunoassay from blood samples of 40 patients with GC at their initial staging and 59 age-matched controls.

RESULTS

Plasma KP-54 levels were significantly higher in GC patients (63.3±17.9) than in controls (49.0±12.7) (p=0.000). Cut-off value for KP-54 was determined as 44 ng/ml and sensitivity, specificity, positive predictive value and negative predictive value, were 60%, 78%, 63%, and 74% respectively. Plasma KP-54 levels were not correlated with any clinicopathological features of GC patients (p>0.05).

CONCLUSIONS

Result of our preliminary study suggest that plasma KP-54 levels might be a useful parameter in diagnosis of GC.

In Vitro Activities of Kissorphin, a Novel Hexapeptide KiSS-1 Derivative, in Neuronal Cells

The primary products of the metastasis-suppressor KiSS-1 gene are the kisspeptin (KP) peptides that stimulate gonadotrophin-releasing-hormone (GnRH) release via GPR-54 receptor activation. Recent studies have suggested that the KP-10 peptide also activates neuropeptide FF (NPFF) receptors. The aim of the current study was to determine the activities of the KiSS-1 derivative kissorphin (KSO), which contains the first six amino acids of the KP-10 peptide, is C-terminally amidated, and shares amino acid similarities with the biologically active NPFF 3–8 sequence. The KSO peptide inhibited forskolin-stimulated cyclic adenosine monophosphate (cAMP) production in ND7/23 neuroblastoma cells via an action that could be inhibited by the NPFF receptor antagonist RF9. Release of GnRH by LA-N-1 neuroblastoma cells was not altered by the KSO peptide. In ND7/23 neuroblastoma cells, the KSO peptide was able to reduce forskolin neuroprotection against H₂O₂ toxicity. The KSO peptide was also able to prevent prostaglandin E2-induced apoptosis in rat cortical neurons. The NPFF receptor antagonist RF9 could inhibit these actions of the KSO peptide in oxidative stress and apoptosis models. In conclusion, the kissorphin peptide, comprising the amino acid sequence Tyr-Asn-Trp-Asn-Ser-Phe-NH₂, has NPFF-like biological activity without showing any GnRH releasing activity and inhibits forskolin-activated cAMP release.

FMRFamide-related peptides: anti-opiate transmitters acting in apoptosis

Members of the FMRFamide-related peptide (FaRP) family are neurotransmitters, hormone-like substances and tumor suppressor peptides. In mammals, FaRPs are considered as anti-opiate peptides due to their ability to inhibit opioid signaling. Some FaRPs are asserted to attenuate opiate tolerance. A recently developed chimeric FaRP (Met-enkephalin-FMRFa) mimics the analgesic effects of opiates without the development of opiate-dependence, displaying a future therapeutical potential in pain reduction. In this review we support the notion, that opiates and representative members of the FaRP family show overlapping effects on apoptosis. Binding of FaRPs to opioid receptors or to their own receptors (G-protein linked membrane receptors and acid-sensing ion channels) evokes or suppresses cell death, in a cell- and receptor-type manner. With the dramatically increasing incidence of opiate abuse and addiction, understanding of opioid-induced cell death, and in this context FaRPs will deserve growing attention.

Co-localisation of kisspeptin with galanin or neurokinin B in afferents to mouse GnRH neurones

The gonadotrophin-releasing hormone (GnRH) secreting neurones, which form the final common pathway for the central regulation of reproduction, are directly targeted by kisspeptin (KP) via the G protein-coupled receptor, GPR54. In these multiple labelling studies, we used ovariectomised mice treated with 17β-oestradiol (OVX + E(2)) or vehicle (OVX + oil) to determine: (i) the ultrastructural characteristics of KP-immunoreactive (IR) afferents to GnRH neurones; (ii) their galanin or neurokinin B (NKB) content; and (iii) the co-expression of galanin or NKB with KP in the two major subpopulations of KP neurones located in the rostral periventricular area of the third ventricle (RP3V) and the arcuate nucleus (Arc). Electron microscopic investigation of the neuronal juxtapositions revealed axosomatic and axodendritic synapses; these showed symmetrical or asymmetrical characteristics, suggesting a phenotypic diversity of KP afferents. Heterogeneity of afferents was also demonstrated by differential co-expression of neuropeptides; in OVX + E(2) mice, KP afferents to GnRH neurones showed galanin-immunoreactivity with an incidence of 22.50 ± 2.41% and NKB-immunoreactivity with an incidence of 5.61 ± 2.57%. In OVX + oil animals, galanin-immunoreactivity in the KP afferents showed a major reduction, appearing in only 5.78 ± 1.57%. Analysis for co-localisation of galanin or NKB with KP was extended to the perikaryal level in animal models, which showed the highest KP incidence; these were OVX + E(2) females for the RP3V and OVX + oil females for the ARC. In the RP3V of colchicine-treated OVX + E(2) animals, 87.84 ± 2.65% of KP-IR neurones were galanin positive. In the Arc of the colchicine-treated OVX + oil animals, galanin immunoreactivity was detected in only 12.50 ± 1.92% of the KP expressing neurones. By contrast, the incidence of co-localisation with NKB in the Arc of those animals was 98.09 ± 1.30%. In situ hybridisation histochemistry of sections from OVX + E(2) animals identified galanin message in more than a third of the KP neurones in the RP3V (38.67 ± 11.57%) and in the Arc (42.50 ± 12.52%). These data suggest that GnRH neurones are innervated by chemically heterogeneous KP cell populations, with a small proportion deriving from the Arc group. The presence of galanin within KP axons innervating GnRH neurones and the oestrogen-dependent regulation of that presence add a new dimension to the roles played by galanin in the central regulation of reproduction.

Cellular localization of receptors using antibodies visualized by light and dual labeling confocal microscopy

Immunocytochemistry can be used to visualize the binding of specific site-directed antisera to receptors in tissue sections and permits the precise identification of cell types expressing a particular receptor when viewed using a conventional light microscope or by confocal microscopy. Protocols are also described for the dual labeling of cells in the same section using primary antisera raised in two different species (one to the receptor of interest, the second to an immunogen such as a cell-specific marker or the endogenous ligand) with the corresponding secondary antisera conjugated to different fluorescent dyes.The technique has a range of applications. Subtypes of receptors can be identified and distinguished prior to the development of selective agonists or antagonists, which is particularly important for mapping orphan receptors, where the identity of the endogenous ligand in not yet known. The deletion of genes encoding receptors, particularly in mice, has emerged as a powerful tool in understanding the role of a specific receptor in physiological processes. Receptor immunocytochemistry can be used to analyze the resulting phenotype in whole body sections of mice without preselection of the tissue to be studied.

Radioligand binding assays and their analysis

Radioligand binding is widely used to characterize receptors and determine their anatomical distribution, particularly the superfamily of seven transmembrane-spanning G protein-coupled receptors for both established transmitters such as endothelin-1 and an increasing number of orphan receptors recently paired with their cognate ligands. Three types of assay are described. In saturation experiments, tissue sections, cultured cells, or homogenates are incubated with an increasing concentration of a radiolabeled ligand, which can be a labeled analog of a naturally occurring transmitter, hormone, or synthetic drug. Analysis using iterative nonlinear curve-fitting programs, such as KELL, measures the affinity of the labeled ligand for a receptor (equilibrium dissociation constant, K ( D )), receptor density (B (max)), and Hill slope (nH). The affinity and selectivity of an unlabeled ligand to compete for the binding of a fixed concentration of a radiolabeled ligand to a receptor are determined using a competition binding assay. Kinetic assays measure the rate of association to or dissociation from a receptor from which a kinetic K ( D ) may be derived. Quantitative autoradiography and image analysis is a sensitive technique to detect low levels of radiolabeled ligands and determine the anatomical distribution of receptors in sections that retain the morphology of the tissue. The measurement of bound radioligand within discrete regions of autoradiographical images using -computer-assisted image analysis is described.

Inotropic action of the puberty hormone kisspeptin in rat, mouse and human: cardiovascular distribution and characteristics of the kisspeptin receptor

Kisspeptins, the ligands of the kisspeptin receptor known for its roles in reproduction and cancer, are also vasoconstrictor peptides in atherosclerosis-prone human aorta and coronary artery. The aim of this study was to further investigate the cardiovascular localisation and function of the kisspeptins and their receptor in human compared to rat and mouse heart. Immunohistochemistry and radioligand binding techniques were employed to investigate kisspeptin receptor localisation, density and pharmacological characteristics in cardiac tissues from all three species. Radioimmunoassay was used to detect kisspeptin peptide levels in human normal heart and to identify any pathological changes in myocardium from patients transplanted for cardiomyopathy or ischaemic heart disease. The cardiac function of kisspeptin receptor was studied in isolated human, rat and mouse paced atria, with a role for the receptor confirmed using mice with targeted disruption of Kiss1r. The data demonstrated that kisspeptin receptor-like immunoreactivity localised to endothelial and smooth muscle cells of intramyocardial blood vessels and to myocytes in human and rodent tissue. [¹²⁵I]KP-14 bound saturably, with subnanomolar affinity to human and rodent myocardium (K_D = 0.12 nM, human; K_D = 0.44 nM, rat). Positive inotropic effects of kisspeptin were observed in rat, human and mouse. No response was observed in mice with targeted disruption of Kiss1r. In human heart a decrease in cardiac kisspeptin level was detected in ischaemic heart disease. Kisspeptin and its receptor are expressed in the human, rat and mouse heart and kisspeptins possess potent positive inotropic activity. The cardiovascular actions of the kisspeptins may contribute to the role of these peptides in pregnancy but the consequences of receptor activation must be considered if kisspeptin receptor agonists are developed for use in the treatment of reproductive disorders or cancer.

Centrally injected kisspeptin reduces food intake by increasing meal intervals in mice

Kisspeptin is distributed not only in brain areas for regulating reproduction but also in nuclei involved in feeding control. Whether kisspeptin alters food intake is unknown in mice. We examined how kisspeptin-10 influences feeding after intracerebroventricular injection in mice using automated monitoring. Kisspeptin-10 (0.3, 1, and 3 μg/mouse) dose-dependently inhibited the feeding response to an overnight fast by 50, 95, and 90% respectively, during the 2-3 h period postinjection. The 1μg/mouse dose reduced the 4-h cumulative food intake by 28% whereas intraperitoneal injection (10 μg/mouse) did not. The decreased 4-h food intake was due to reduced meal frequency (-45%/4 h), whereas meal size and gastric emptying were not altered. These data suggest that kisspeptin may be a negative central regulator of feeding by increasing satiety.

RFamide Peptides: Structure, Function, Mechanisms and Pharmaceutical Potential

Different neuropeptides, all containing a common carboxy-terminal RFamide sequence, have been characterized as ligands of the RFamide peptide receptor family. Currently, five subgroups have been characterized with respect to their N-terminal sequence and hence cover a wide pattern of biological functions, like important neuroendocrine, behavioral, sensory and automatic functions. The RFamide peptide receptor family represents a multiligand/multireceptor system, as many ligands are recognized by several GPCR subtypes within one family. Multireceptor systems are often susceptible to cross-reactions, as their numerous ligands are frequently closely related. In this review we focus on recent results in the field of structure-activity studies as well as mutational exploration of crucial positions within this GPCR system. The review summarizes the reported peptide analogs and recently developed small molecule ligands (agonists and antagonists) to highlight the current understanding of the pharmacophoric elements, required for affinity and activity at the receptor family. Furthermore, we address the biological functions of the ligands and give an overview on their involvement in physiological processes. We provide insights in the knowledge for the design of highly selective ligands for single receptor subtypes to minimize cross-talk and to eliminate effects from interactions within the GPCR system. This will support the drug development of members of the RFamide family.