The dual nature of the tachykinin NK1 receptor

Sleep disturbance associated with the menopause

IMPORTANCE AND OBJECTIVES

Sleep disturbance is one of the most common and debilitating symptoms experienced by women during the menopause transition. However, there are currently no therapies specifically approved for sleep disturbance associated with the menopause. Here, we consider how to characterize sleep disturbance associated with the menopause and discuss its etiology, including the latest advances in our understanding of the neuronal circuits that regulate reproduction, body temperature, sleep, and mood; and reflect on its impact on women's health and well-being. We also examine the current treatment landscape and look to the future of treatment for this condition.

METHODS

We conducted a review of the literature and combined this with discussion with experts in the fields of sleep and menopause as well as experiences from our own clinical practices.

DISCUSSION AND CONCLUSIONS

Sleep disturbance associated with the menopause is characterized by frequent night-time awakenings and increased awake time after sleep onset. Its impacts are wide-ranging, negatively affecting health as well as personal and social relationships, productivity, and work performance. There is currently an unmet need for effective, safe, and well-tolerated treatments to address this important symptom, and wider recognition of the association between sleep disturbances and the menopause is needed. Sleep disturbances associated with the menopause can result from hormone changes as well as vasomotor and mood symptoms. Growing research has contributed to our knowledge of the role of hypothalamic estrogen-sensitive kisspeptin/neurokinin B/dynorphin neurons. These neurons are thought to integrate the gonadotropin-releasing hormone pathway and the pathways responsible for the homeostatic control of body temperature and the circadian regulation of sleep-wake cycles. Understanding these neurons offers the potential to create treatments that target a key cause of sleep disturbance associated with the menopause. Further research to understand their etiology and characterize the neuronal circuits responsible could benefit the development of these targeted treatment approaches.

Review of human genetic and clinical studies directly relevant to GnRH signalling

GnRH is the pivotal hormone in controlling the hypothalamic-pituitary gonadal (HPG) axis in humans and other mammalian species. GnRH function is influenced by a multitude of known and still unknown environmental and genetic factors. Molecular genetic studies on human families with hypogonadotropic hypogonadism over the past two decades have been instrumental in delineating the kisspeptin and neurokinin B signalling, which integrally modulates GnRH release from the hypothalamus. The identification of kisspeptin and neurokinin B ligand-receptor gene pair mutations in patients with absent puberty have paved the way to a greater understanding of the central regulation of the HPG cascade. In this article, we aim to review the literature on the genetic and clinical aspects of GnRH and its receptor, as well as the two ligand-receptor sets directly pertinent to the function of GnRH hormone signalling, kisspeptin/ kisspeptin receptor and NKB/NK3R.

Selective G protein signaling driven by substance P-neurokinin receptor dynamics

The neuropeptide substance P (SP) is important in pain and inflammation. SP activates the neurokinin-1 receptor (NK1R) to signal via Gq and Gs proteins. Neurokinin A also activates NK1R, but leads to selective Gq signaling. How two stimuli yield distinct G protein signaling at the same G protein-coupled receptor remains unclear. We determined cryogenic-electron microscopy structures of active NK1R bound to SP or the Gq-biased peptide SP6-11. Peptide interactions deep within NK1R are critical for receptor activation. Conversely, interactions between SP and NK1R extracellular loops are required for potent Gs signaling but not Gq signaling. Molecular dynamics simulations showed that these superficial contacts restrict SP flexibility. SP6-11, which lacks these interactions, is dynamic while bound to NK1R. Structural dynamics of NK1R agonists therefore depend on interactions with the receptor extracellular loops and regulate G protein signaling selectivity. Similar interactions between other neuropeptides and their cognate receptors may tune intracellular signaling.

The efficacy of a newly developed neurokinin 3 receptor agonist B21-750 on luteinizing hormone secretion in cycling goats

This study aimed to investigate the efficacy of a newly developed NK3 receptor agonist (B21-750) on the secretion of luteinizing hormone (LH) in association with ovarian steroid hormones during the follicular phase (FP, n = 5) and luteal phase (LP, n = 5) of Shiba goats. The FP group was treated with both prostaglandin F_2α and progesterone-controlled internal drug release (CIDR) inserts for 10 d, and B21-750 (200 nmol) was injected 12 h after removing the CIDR. Meanwhile, the LP group received B21-750 injections on a day during the mid-luteal phase. LH secretion increased at 1 h after B21-750 injection in both groups. The percent changes in the area under the curve of LH was higher during the hour after injection than during the hour before injection in both groups. Thus, this study demonstrated that B21-750 induces rapid LH secretion for a short period during both the follicular and luteal phases.

Molecular imaging probes derived from natural peptides

Covering: up to the end of 2015.Peptides are naturally occurring compounds that play an important role in all living systems and are responsible for a range of essential functions. Peptide receptors have been implicated in disease states such as oncology, metabolic disorders and cardiovascular disease. Therefore, natural peptides have been exploited as diagnostic and therapeutic agents due to the unique target specificity for their endogenous receptors. This review discusses a variety of natural peptides highlighting their discovery, endogenous receptors, as well as their derivatization to create molecular imaging agents, with an emphasis on the design of radiolabelled peptides. This review also highlights methods for discovering new and novel peptides when knowledge of specific targets and endogenous ligands are not available.

The role of neuropeptides in adverse myocardial remodeling and heart failure

In addition to traditional neurotransmitters of the sympathetic and parasympathetic nervous systems, the heart also contains numerous neuropeptides. These neuropeptides not only modulate the effects of neurotransmitters, but also have independent effects on cardiac function. While in most cases the physiological actions of these neuropeptides are well defined, their contributions to cardiac pathology are less appreciated. Some neuropeptides are cardioprotective, some promote adverse cardiac remodeling and heart failure, and in the case of others their functions are unclear. Some have both cardioprotective and adverse effects depending on the specific cardiac pathology and progression of that pathology. In this review, we briefly describe the actions of several neuropeptides on normal cardiac physiology, before describing in more detail their role in adverse cardiac remodeling and heart failure. It is our goal to bring more focus toward understanding the contribution of neuropeptides to the pathogenesis of heart failure, and to consider them as potential therapeutic targets.

Substance P Depolarizes Lamprey Spinal Cord Neurons by Inhibiting Background Potassium Channels

Substance P is endogenously released in the adult lamprey spinal cord and accelerates the burst frequency of fictive locomotion. This is achieved by multiple effects on interneurons and motoneurons, including an attenuation of calcium currents, potentiation of NMDA currents and reduction of the reciprocal inhibition. While substance P also depolarizes spinal cord neurons, the underlying mechanism has not been resolved. Here we show that effects of substance P on background K⁺ channels are the main source for this depolarization. Hyperpolarizing steps induced inward currents during whole-cell voltage clamp that were reduced by substance P. These background K⁺ channels are pH sensitive and are selectively blocked by anandamide and AVE1231. These blockers counteracted the effect of substance P on these channels and the resting membrane potential depolarization in spinal cord neurons. Thus, we have shown now that substance P inhibits background K⁺ channels that in turn induce depolarization, which is likely to contribute to the frequency increase observed with substance P during fictive locomotion.

Neurokinin receptors in the gastrointestinal muscle wall: cell distribution and possible roles

The neurokinin receptors are G-protein-linked receptors; three distinct molecules, called neurokinin-1, neurokinin-2, and neurokinin-3 receptors, have been identified. Their physiological ligands are the tachykinins, which, in the mammalian gut, correspond to substance P, neurokinin A, and neurokinin B. In this apparatus, the main source of tachykinins is represented by intrinsic neurons located either in the myenteric plexus and projecting mainly to the muscle coat, or in the submucous plexus and projecting to the mucosa and submucosal blood vessels. The availability of specific antibodies has allowed identifying the sites of distribution of the neurokinin receptors in the gut, and important differences have been found among cell types and animal species. The complexity of the receptor distribution, either intraspecies or interspecies, is in agreement with the variegated picture coming out from physiological and pharmacological experiments. Interestingly, most of the knowledge on the tachykinin systems has been obtained from pathological conditions. Here, we tried to collect the main information available on the cellular distribution of the neurokinin receptors in the gut wall in the attempt to correlate their cell location with the several roles the tachykinins seem to play in the gastrointestinal apparatus.

Mapping substance P binding sites on the neurokinin-1 receptor using genetic incorporation of a photoreactive amino acid

Substance P (SP) is a neuropeptide that mediates numerous physiological responses, including transmission of pain and inflammation through the neurokinin-1 (NK1) receptor, a G protein-coupled receptor. Previous mutagenesis studies and photoaffinity labeling using ligand analogues suggested that the binding site for SP includes multiple domains in the N-terminal (Nt) segment and the second extracellular loop (ECLII) of NK1. To map precisely the NK1 residues that interact with SP, we applied a novel receptor-based targeted photocross-linking approach. We used amber codon suppression to introduce the photoreactive unnatural amino acid p-benzoyl-l-phenylalanine (BzF) at 11 selected individual positions in the Nt tail (residues 11-21) and 23 positions in the ECLII (residues 170(C-10)-193(C+13)) of NK1. The 34 NK1 variants were expressed in mammalian HEK293 cells and retained the ability to interact with a fluorescently labeled SP analog. Notably, 10 of the receptor variants with BzF in the Nt tail and 4 of those with BzF in ECLII cross-linked efficiently to SP, indicating that these 14 sites are juxtaposed to SP in the ligand-bound receptor. These results show that two distinct regions of the NK1 receptor possess multiple determinants for SP binding and demonstrate the utility of genetically encoded photocross-linking to map complex multitopic binding sites on G protein-coupled receptors in a cell-based assay format.

Role of neurokinin 1 receptors in dextran sulfate-induced colitis: studies with gene-deleted mice and the selective receptor antagonist netupitant

OBJECTIVE AND DESIGN

The function of the neurokinin 1 (NK1) receptor was investigated in the DSS-induced mouse colitis model using NK1 receptor-deficient mice and the selective antagonist netupitant.

SUBJECTS

Colitis was induced by oral administration of 20 mg/ml DSS solution for 7 days in C57BL/6 and Tacr1 KO animals (n = 5-7).

TREATMENT

During the induction, one-half of the C57BL/6 and Tacr1 KO group received one daily dose of 6 mg/kg netupitant, administered intraperitoneally, the other half of the group received saline, respectively.

METHODS

Disease activity index (DAI), on the basis of stool consistency, blood and weight loss, was determined over 7 days. Histological evaluation, myeloperoxidase (MPO) measurement, cytokine concentrations and receptor expression analysis were performed on the colon samples.

RESULTS

NK1 receptors are up-regulated in the colon in response to DSS treatment. DSS increased DAI, histopathological scores, BLC, sICAM-1, IFN-γ, IL-16 and JE in wildtype mice, which were significantly reduced in NK1 receptor-deficient ones. NK1 receptor antagonism with netupitant significantly diminished DAI, inflammatory histopathological alterations, BLC, IFN-γ, IL-13 and IL-16 in wildtype mice, but not in the NK1-deficient ones. MPO was similarly elevated and netupitant significantly decreased its activity in both groups.

CONCLUSIONS

NK1 receptor antagonism could be beneficial for colitis via inhibiting different inflammatory mechanisms.

Targeted liquid chromatography quadrupole ion trap mass spectrometry analysis of tachykinin related peptides reveals significant expression differences in a rat model of neuropathic pain

Animal models are widely used to perform basic scientific research in pain. The rodent chronic constriction injury (CCI) model is widely used to study neuropathic pain. Animals were tested prior and after CCI surgery using behavioral tests (von Frey filaments and Hargreaves test) to evaluate pain. The brain and the lumbar enlargement of the spinal cord were collected from neuropathic and normal animals. Tachykinin related peptides were analyzed by high performance liquid chromatography quadrupole ion trap mass spectrometry. Our results reveal that the β-tachykinin₅₈₋₇₁, SP and SP₃₋₁₁ up-regulation are closely related to pain behavior. The spinal β-tachykinin₅₈₋₇₁, SP and SP₃₋₁₁ concentrations were significantly up-regulated in neuropathic animals compared with normal animals (p<0.001; p<0.001 and p<0.05, respectively). In contrast, the spinal SP5₅₋₁₁ concentration in neuropathic animals revealed a significant down-regulation compared with normal animals (p<0.05). The brain β-tachykinin₅₈₋₇₁ and SP concentrations were significantly up-regulated (p<0.05 and p<0.001, respectively). Interestingly, no significant concentration differences were observed in the spinal cord and brain for NKA, β-tachykinin₅₈₋₇₁, SP₁₋₇ and SP₆₋₁₁ (p>0.05). The β-tachykinin₅₈₋₇₁, SP and C-terminal SP metabolites could potentially serve as biomarkers in early drug discovery.

Role of Pituitary Adenylate-Cyclase Activating Polypeptide and Tac1 gene derived tachykinins in sensory, motor and vascular functions under normal and neuropathic conditions

Pituitary Adenylate-Cyclase Activating Polypeptide (PACAP) and Tac1 gene-encoded tachykinins (substance P: SP, neurokinin A: NKA) are expressed in capsaicin-sensitive nerves, but their role in nociception, inflammation and vasoregulation is unclear. Therefore, we investigated the function of these neuropeptides and the NK1 tachykinin receptor (from Tacr1 gene) in the partial sciatic nerve ligation-induced traumatic mononeuropathy model using gene deficient (PACAP(-/-), Tac1(-/-), and Tacr1(-/-)) mice. Mechanonociceptive threshold of the paw was measured with dynamic plantar aesthesiometry, motor coordination with Rota-Rod and cutaneous microcirculation with laser Doppler imaging. Neurogenic vasodilation was evoked by mustard oil stimulating sensory nerves. In wildtype mice 30-40% mechanical hyperalgesia developed one week after nerve ligation, which was not altered in Tac1(-/-) and Tacr1(-/-) mice, but was absent in PACAP(-/-) animals. Motor coordination of the PACAP(-/-) and Tac1(-/-) groups was significantly worse both before and after nerve ligation compared to their wildtypes, but it did not change in Tacr1(-/-) mice. Basal postoperative microcirculation on the plantar skin of PACAP(-/-) mice did not differ from the wildtypes, but was significantly lower in Tac1(-/-) and Tacr1(-/-) ones. In contrast, mustard oil-induced neurogenic vasodilation was significantly smaller in PACAP(-/-) mice, but not in Tacr1(-/-) and Tac1(-/-) animals. Both PACAP and SP/NKA, but not NK1 receptors participate in normal motor coordination. Tachykinins maintain basal cutaneous microcirculation. PACAP is a crucial mediator of neuropathic mechanical hyperalgesia and neurogenic vasodilation. Therefore identifying its target and developing selective, potent antagonists, might open promising new perspectives for the treatment of neuropathic pain and vascular complications.

Are biological actions of neurokinin A in the adult brain mediated by a cross-talk between the NK1 and NK2 receptors?

Mice lacking the NK(1) receptor (NK(1)R-/- mice) and selective, high-affinity, non-peptide, NK(1), NK(2) and NK(3) receptor antagonists were used to identify the tachykinin receptor subtype(s) mediating the central responses induced by neurokinin A (NKA). The peptides, substance P (SP), NKA and senktide and the antagonists were injected intracerebroventricularly (ICV) through an implanted cannula. NKA (50 pmol) was as potent as SP (50 pmol) in inducing grooming behaviour (face washing and hind limb grooming) in wild-type mice, but both peptides failed to induce behavioural responses in NK(1)R-/- mice. In wild-type mice, the NK(1) receptor antagonist, RP 67580 (2 nmol), effectively inhibited grooming behaviour elicited by SP, but was inactive against grooming induced by NKA, which in turn was abolished after pre-treatment with the selective NK(2) receptor agonist, SR 48968 (2 nmol). Unlike NKA, the selective NK(2) receptor agonists, (β Ala(8)) NKA 4-10 and (NLeu(10)) NKA 4-10, injected ICV at doses of 50 or 100 pmol did not elicit any behavioural response in wild-type mice. The NK(3) receptor antagonist, SR 142801, inhibited behaviours induced by the NK(3) receptor agonist, senktide, but did not alter behavioural responses to either SP or NKA in wild-type mice. The present findings demonstrate that central biological actions of SP and senktide are mediated by activation of NK(1) and NK(3) receptors, respectively. Our results also indicate that NK(1) receptors are essential for generating central actions induced by NKA, which are most probably mediated by a cross-talk between the NK(1) and NK(2) receptors.

New understandings of the genetic basis of isolated idiopathic central hypogonadism

Idiopathic hypogonadotropic hypogonadism is a rare disease that is characterized by delayed/absent puberty and/or infertility due to an insufficient stimulation of an otherwise normal pituitary-gonadal axis by gonadotrophin-releasing hormone (GnRH) action. Because reduced or normal luteinizing hormone (LH)/follicle-stimulating hormone (FSH) levels may be observed in the affected patients, the term idiopathic central hypogonadism (ICH) appears to be more appropriate. This disease should be distinguished from central hypogonadism that is combined with other pituitary deficiencies. Isolated ICH has a complex pathogenesis and is fivefold more prevalent in males. ICH frequently appears in a sporadic form, but several familial cases have also been reported. This finding, in conjunction with the description of numerous pathogenetic gene variants and the generation of several knockout models, supports the existence of a strong genetic component. ICH may be associated with several morphogenetic abnormalities, which include osmic defects that, with ICH, constitute the cardinal manifestations of Kallmann syndrome (KS). KS accounts for approximately 40% of the total ICH cases and has been generally considered to be a distinct subgroup. However, the description of several pedigrees, which include relatives who are affected either with isolated osmic defects, KS, or normo-osmic ICH (nICH), justifies the emerging idea that ICH is a complex genetic disease that is characterized by variable expressivity and penetrance. In this context, either multiple gene variants or environmental factors and epigenetic modifications may contribute to the variable disease manifestations. We review the genetic mechanisms that are presently known to be involved in ICH pathogenesis and provide a clinical overview of the 227 cases that have been collected by the collaborating centres of the Italian ICH Network.

Neurokinin B signalling in the human reproductive axis

Recent human genetic studies have established that neurokinin B (NKB) signalling via the neurokinin 3 receptor (NK3R) is required for normal developmental activation of pulsatile GnRH secretion from the hypothalamus. As increasing numbers of patients with loss-of-function mutations have been described, evidence has emerged that peripheral NKB is not necessary for normal pregnancy despite high placental expression and high plasma levels of NKB in late gestation. Nevertheless many key questions about the role of NKB in the function of the GnRH pulse generator remain to be answered. Differences in requirement for NKB/NK3R for hypothalamic-pituitary-gonadal (HPG) maturation amongst different species, and their varied responses to stimulation with NKB represent a challenge for higher resolution studies. Neuroanatomical investigation has, however, identified key "KNDy" (Kisspeptin, Neurokinin B, Dynorphin) arcuate neurones that are conserved amongst different species and that are intimately connected both to each other and to the GnRH nerve termini. Several lines of evidence suggest that these may be the core of the GnRH pulse generator, and with experimental tools now in place in humans, monkeys and other experimental animals to pursue the function of these interconnected neurones and the functional hierarchy of their neuroendocrine inputs, understanding of the enigmatic GnRH pulse generator may at last be within reach.

Neurokinin-1 receptor: functional significance in the immune system in reference to selected infections and inflammation

The G protein-coupled receptor (GPCR), neurokinin-1 receptor (NK1R), and its preferred ligand, substance P (SP), are reviewed in relationship to the immune system and selected infections. NK1R and SP are ubiquitous throughout the animal kingdom. This important pathway has unique functions in numerous cells and tissues. The interaction of SP with its preferred receptor, NK1R, leads to the activation of nuclear factor-kappa B (NF-κB) and proinflammatory cytokines. NK1R has two isoforms, both a full-length and a truncated form. These isoforms have different functional significances and differ in cell signaling capability. The proinflammatory signals modulated by SP are important in bacterial, viral, fungal, and parasitic diseases, as well as in immune system function. The SP-NK1R system is a major class 1, rhodopsin-like GPCR ligand-receptor interaction.

Involvement of preprotachykinin A gene-encoded peptides and the neurokinin 1 receptor in endotoxin-induced murine airway inflammation

Tachykinins encoded by the preprotachykinin A (TAC1) gene such as substance P (SP) and neurokinin A (NKA) are involved in neurogenic inflammatory processes via predominantly neurokinins 1 and 2 (NK1 and NK2) receptor activation, respectively. Endokinins and hemokinins encoded by the TAC4 gene also have remarkable selectivity and potency for the NK1 receptors and might participate in inflammatory cell functions. The aim of the present study was to investigate endotoxin-induced airway inflammation and consequent bronchial hyper-reactivity in TAC1(-/-), NK1(-/-) and also in double knockout (TAC1(-/-)/NK1(-/-)) mice. Sub-acute interstitial lung inflammation was evoked by intranasal Escherichia coli lipopolysaccharide (LPS) in the knockout mice and their wildtype C57BL/6 counterparts 24 h before measurement. Respiratory parameters were measured with unrestrained whole body plethysmography. Bronchoconstriction was induced by inhalation of the muscarinic receptor agonist carbachol and Penh (enhanced pause) correlating with airway resistance was calculated. Lung interleukin-1beta (IL-1beta) and tumor necrosis factor-alpha (TNF-alpha) concentrations were measured with ELISA. Histological evaluation was performed and a composite morphological score was determined. Myeloperoxidase (MPO) activity in the lung was measured with spectrophotometry to quantify the number of infiltrating neutrophils/macrophages. Airway hyper-reactivity was significantly reduced in the TAC1(-/-) as well as the TAC1(-/-)/NK1(-/-) groups. However, LPS-induced histological inflammatory changes (perivascular/peribronchial oedema, neutrophil infiltration and goblet cell hyperplasia), MPO activity and TNF-alpha concentration were markedly diminished only in TAC1(-/-) mice. Interestingly, the concentrations of both cytokines, IL-1beta and TNF-alpha, were significantly greater in the NK1(-/-) group. These data clearly demonstrated on the basis of histology, MPO and cytokine measurements that TAC1 gene-derived tachykinins, SP and NKA, play a significant role in the development of endotoxin-induced murine airway inflammation, but not solely via NK1 receptor activation. However, in inflammatory bronchial hyper-responsiveness other tachykinins, such as hemokinin-1 acting through NK1 receptors also might be involved.

Neurokinin B signaling in puberty: human and animal studies

Recent reports of humans who have normosmic idiopathic hypogonadotropic hypogonadism due to TAC3 or TACR3 (encoding neurokinin B and its receptor, NK3R, respectively) mutations provided compelling evidence for the involvement of neurokinin B (NKB) signaling in puberty. This apparently stimulated the field to understand the exact mechanism through which NKB signaling exerts its effects. With the important findings from these recent studies a sketch of GnRH pulse generator has emerged in which NKB signaling appears to play a key role. In this communication, NKB involvement in puberty is reviewed from the perspective of the fundamental question of "what controls puberty?"

The recent genetics of hypogonadotrophic hypogonadism - novel insights and new questions

The complex organization and regulation of the human hypothalamic-pituitary-gonadal axis render it susceptible to dysfunction in the face of a variety of genetic insults, leading to different degrees of hypogonadotrophic hypogonadism (HH). Although the genetic basis of some HH was recognized more than 60 years ago the first specific pathogenic defect, in the KAL1 gene, was only identified within the last 20 years. In the past decade, the rate of genetic discovery has dramatically accelerated, with defects in more than 10 genes now associated with HH. Several themes have emerged as the genetic basis of HH has gradually been uncovered, including the association of some genes such as FGFR1, FGF8, PROK2 and PROKR2, both with HH in association with hyposmia/anosmia (Kallmann syndrome) and with normosmic HH, thus blurring the clinical distinction between ontogenic and purely functional defects in the axis. Many examples of digenic inheritance of HH have also been reported, sometimes producing variable reproductive and accessory phenotypes within a family with non-Mendelian inheritance patterns. In strictly normosmic HH, human genetics has made a particularly dramatic impact in the past 6 years through homozygosity mapping in consanguineous families, first through identification of a key role for kisspeptin in triggering GnRH release, and very recently through demonstration of a critical role for neurokinin B in normal sexual maturation. This review summarises current understanding of the genetic architecture of HH, as well as its diagnostic and mechanistic implications.

The cytomegalovirus UL146 gene product vCXCL1 targets both CXCR1 and CXCR2 as an agonist

Large DNA viruses, such as herpesvirus and poxvirus, encode proteins that target and exploit the chemokine system of their host. UL146 and UL147 in the cytomegalovirus (CMV) genome encode the two CXC chemokines vCXCL1 and vCXCL2. In this study, vCXCL1 was probed against a panel of the 18 classified human chemokine receptors. In calcium mobilization assays vCXCL1 acted as an agonist on both CXCR1 and CXCR2 but did not activate or block any of the other 16 chemokine receptors. vCXCL1 was characterized and compared with CXCL1/GROalpha, CXCL2/GRObeta, CXCL3/GROgamma, CXCL5/ENA-78, CXCL6/GCP-2, CXCL7/NAP-2 and CXCL8/IL-8 in competition binding, calcium mobilization, inositol triphosphate turnover, and chemotaxis assays using CXCR1- and CXCR2-expressing Chinese hamster ovary, 300.19, COS7, and L1.2 cells. The affinities of vCXCL1 for the CXCR1 and CXCR2 receptors were 44 and 5.6 nm, respectively, as determined in competition binding against radioactively labeled CXCL8. In calcium mobilization, phosphatidylinositol turnover, and chemotaxis assays, vCXCL1 acted as a highly efficacious activator of both receptors, with a rather low potency for the CXCR1 receptor but comparable with CXCL5 and CXCL7. It is suggested that CMV uses the UL146 gene product expressed in infected endothelial cells to attract neutrophils by activating their CXCR1 and CXCR2 receptors, whereby neutrophils can act as carriers of the virus to uninfected endothelial cells. In that way a lasting pool of CMV-infected endothelial cells could be maintained.

Tachykinin-related peptides and their receptors in invertebrates: a current view

Members of the tachykinin peptide family have been well conserved during evolution and are mainly expressed in the central nervous system and in the intestine of both vertebrates and invertebrates. In these animals, they act as multifunctional messengers that exert their biological effects by specifically interacting with a subfamily of structurally related G protein-coupled receptors. Despite the identification of multiple tachykinin-related peptides (TKRPs) in species belonging to the insects, crustaceans, mollusks and echiuroid worms, only five invertebrate receptors harboring profound sequence similarities to mammalian receptors for tachykinins have been functionally characterized to date. Three of these have been cloned from dipteran insect species, i.e. NKD (neurokinin receptor from Drosophila), DTKR (Drosophila tachykinin receptor) and STKR (tachykinin-related peptide receptor from the stable fly, Stomoxys calcitrans). In addition, two receptors from non-insect species, present in echiuroid worms and mollusks, respectively have been identified as well. In this brief review, we will survey some recent findings and insights into the signaling properties of invertebrate tachykinin-related peptides via their respective receptors. In this context, we will also point out the necessity to take into account differences in signaling mechanisms induced by distinct TKRP isoforms in insects.

Tachykinin receptor assays

Described in this unit are methods for obtaining, preparing, and testing smooth muscle preparations bearing tachykinin receptors to study the agonist or antagonist properties of test compounds. Concentration-response curves to agonists are constructed to measure their ability to produce smooth muscle contractions and thus evaluate the potency and efficacy of the agonists. Antagonists are tested for their ability to shift the agonist concentration-response curve and to calculate their potency. Two different protocols are described for each of the three tachykinin receptors (NK(1), NK(2), and NK(3)). The NK(1) receptor assays use guinea pig ileum longitudinal muscle myenteric plexus (GPI) and rat urinary bladder (RUB), the NK(2) receptor assays use isolated endothelium-deprived rabbit pulmonary artery (RPA) and hamster trachea (HT), and the NK(3) receptor assays use GPI and rat portal vein (RPV).

Effects of Endokinin A/B and Endokinin C/D on the modulation of pain in mice

Endokinins are novel tachykinins encoded on the human TAC4 and consist of Endokinin A (EKA), B (EKB), C (EKC) and D (EKD). To date, the function of Endokinins in pain processing was not fully understood. Therefore the aim of this study was to investigate the effects of Endokinin A/B (EKA/B, the common C-terminal decapeptide in EKA and EKB) and Endokinin C/D (EKC/D, the common C-terminal duodecapeptide in EKC and EKD) on pain modulation at supraspinal level in mice. Intracerebroventricular (i.c.v.) administration of EKA/B (1, 3, 12, 20nmol/mouse) dose dependently induced potent analgesic effect. This effect could be fully antagonized by SR140333B but not SR48968C or SR142801. Naloxone could also block the analgesic effect, suggesting that this analgesic effect is related to opioid receptors. However, i.c.v. administration of EKA/B (10, 30, 100pmol/mouse) caused hyperalgesic effect significantly, with a "U" shape curve. Interestingly, the hyperalgesic effect induced by EKA/B could be attenuated by SR140333B, SR142801 but not SR48968C. I.c.v. administration of EKC/D (1, 3, 12, 20nmol/mouse) also dose dependently induced analgesic effect, which could not be blocked by SR48968C or SR142801 or naloxone. But to our astonishment, it could be significantly enhanced by SR140333B. More interestingly, the hyperalgesic effect induced by EKA/B could be significantly attenuated by EKC/D. In addition, the analgesic effect induced by co-administration of EKA/B and EKC/D was much less stronger than the effect of either EKA/B or EKC/D.

Endocannabinoids Mediate Tachykinin-Induced Effects in the Lamprey Locomotor Network

The spinal network underlying locomotion in lamprey is composed of excitatory and inhibitory interneurons mediating fast ionotropic action. In addition, several modulator systems are activated as locomotion is initiated, including the tachykinin system and the metabotropic glutamate receptor 1 (mGluR1), the latter operating partially via the endocannabinoid system. The effects of mGluR1 agonists and tachykinins resemble each other. Like mGluR1 agonists, the tachykinin substance P accelerates the burst rate and reduces the crossed inhibition in an activity-dependent fashion. The present study therefore explores whether tachykinins also use the endocannabinoid system to modulate the locomotor frequency. By monitoring fictive locomotion, we were able to compare the facilitatory effects exerted by applying substance P (1 μM, 20 min), on the burst frequency before and during application of the endocannabinoid CB1 receptor antagonist AM251 (2–5 μM). By using two different lamprey species, we showed that the response to substance P on the burst frequency is significantly reduced during the application of AM251. To examine whether endocannabinoids are involved in the substance P–mediated modulation of reciprocal inhibition, the commissural axons were stimulated, while recording intracellularly from motoneurons. We compare the effect of substance P on the amplitude of the contralateral compound glycinergic inhibitory postsynaptic potential (IPSP) in control and in the presence of AM251. The blockade of CB1 receptors reduced the substance P–mediated decrease in the amplitude by 29%. The present findings suggest that the effects of substance P on the increase in the locomotor burst frequency and depression of IPSPs are mediated partially via release of endocannabinoids acting through CB1 receptors.

Tachykinin receptor modulation of cyclooxygenase-2 expression in human polymorphonuclear leucocytes

BACKGROUND AND PURPOSE

We investigated the ability of natural and synthetic selective NK receptors agonists and antagonists to modulate cyclooxygenase-2 (COX-2) expression in human polymorphonuclear leucocytes (PMNs).

EXPERIMENTAL APPROACH

The presence of all three tachykinin in PMNs was assessed by Western blot and PCR techniques. Natural and synthetic ligands selective for the tachykinin receptors were used to modulate COX-2 protein (measured with Western blotting) and activity [as prostaglandin E(2) (PGE(2)) output]. Effects of substance P (SP) on phosphorylation of mitogen-activated protein kinases (MAPKs) and nuclear factor-kappa B (NF-kappaB) activation were studied to analyse the signalling pathway involved in COX-2 up-regulation mediated by SP.

KEY RESULTS

Stimulation of NK receptors with the natural ligands SP, neurokinin A (NKA) and neurokinin B, in the pmol.L(-1)-micromol.L(-1) concentration range, modulated COX-2 expression and PGE(2) release in a concentration- and time-dependent manner. Experiments with synthetic selective agonists [Sar(9), Met(O(2))(11)]SP, [beta-Ala(8)] NKA(4-10), senktide or selective antagonists L703,606, SR48,968 or SR142801, confirmed that COX-2 up-regulation was mediated by NK receptors. We found that mainly p38, p42 and p46 MAPKs were phosphorylated by SP and SB202190, PD98059 and SP600125, which are selective inhibitors of these kinases, blocked SP-induced COX-2 expression. SP also induced nuclear translocation of NF-kappaB concentration-dependently, with a maximum effect at 1 nmol.L(-1).

CONCLUSIONS AND IMPLICATIONS

Human PMNs possess functional NK(1), NK(2) and NK(3) receptors, which mediate the induction of COX-2 expression and NF-kappaB activation by SP.

Docking studies suggest ligand-specific delta-opioid receptor conformations

An automated docking procedure was used to study binding of a series of delta-selective ligands to three models of the delta-opioid receptor. These models are thought to represent the three ligand-specific receptor conformations. Docking results are in agreement with point mutation studies and suggest that different ligands--agonists and antagonists--may bind to the same binding site under different receptor conformations. Docking to different receptor models (conformations) also suggests that by changing to a receptor-specific conformation, the receptor may open or close different binding sites to other ligands.

Characterization of a conformationally sensitive TOAC spin-labeled substance P

To probe the binding of a peptide agonist to a G-protein coupled receptor in native membranes, the spin-labeled amino acid analogue 4-amino-4-carboxy-2,2,6,6-tetramethylpiperidino-1-oxyl (TOAC) was substituted at either position 4 or 9 within the substance P peptide (RPKPQQFFGLM-NH2), a potent agonist of the neurokinin-1 receptor. The affinity of the 4-TOAC analog is comparable to the native peptide while the affinity of the 9-TOAC derivative is approximately 250-fold lower. Both peptides activate receptor signaling, though the potency of the 9-TOAC peptide is substantially lower. The utility of these modified ligands for reporting conformational dynamics during the neurokinin-1 receptor activation was explored using EPR spectroscopy, which can determine the real-time dynamics of the TOAC nitroxides in solution. While the binding of both the 4-TOAC substance P and 9-TOAC substance P peptides to isolated cell membranes containing the neurokinin-1 receptor is detected, a bound signal for the 9-TOAC peptide is only obtained under conditions that maintain the receptor in its high-affinity binding state. In contrast, 4-TOAC substance P binding is observed by solution EPR under both low- and high-affinity receptor states, with evidence of a more strongly immobilized peptide in the presence of GDP. In addition, to better understand the conformational consequences of TOAC substitution into substance P as it relates to receptor binding and activation, atomistic models for both the 4- and 9-TOAC versions of the peptide were constructed, and the molecular dynamics calculated via simulated annealing to explore the influence of the TOAC substitutions on backbone structure.

Disruption of the neurokinin-3 receptor (NK3) in mice leads to cognitive deficits

RATIONALE

The structurally related neuropeptides, substance P, neurokinin A, and neurokinin B, belong to a family of molecules termed tachykinins and are widely distributed in the central and peripheral nervous systems. These peptides mediate their effects through three G protein coupled receptor subtypes, the neurokinin-1, neurokinin-2 and neurokinin-3 receptors, respectively.

OBJECTIVE

To study the physiological functions of NK3, a line of NK3 knockout mice were generated and characterized in a broad spectrum of well-established behavioral tests.

RESULTS

In several tests, including spontaneous locomotor activity, elevated plus maze, forced swim, and hot plate, wild-type and knockout mice performed similarly. However, in several cognition tests, including passive avoidance, acquisition of conditioned avoidance responding (CAR), and the Morris water maze, NK3 knockout mice displayed deficits compared to wild-type mice. Although NK3 wild-type and knockout mice performed similarly in the training phase of the passive avoidance test, knockout mice had shorter latencies to enter the dark compartment on days 3 and 4, suggesting impaired retention. In the acquisition phase of the conditioned avoidance responding assay, NK3 knockout mice acquired the CAR task at a slower rate than wild-type mice. Once the CAR test was acquired, both NK3 wild-type and knockout mice responded similarly to clozapine and risperidone, drugs which suppress responding in this test. In the Morris water maze, NK3 knockout mice showed increased latencies to find the escape platform on day 3 of training, suggesting a modest, but significant delay in acquisition compared to wild-type mice.

CONCLUSION

These studies suggest a role for NK3 in learning and memory in mice.

Evidence for a role of caveolin-1 in neurokinin-1 receptor plasma-membrane localization, efficient signaling, and interaction with beta-arrestin 2

This study was focused on the relationship between the plasma-membrane localization of neurokinin-1 receptor (NK1-R) and its endocytic and signaling properties. First, we employed electron paramagnetic resonance (EPR) to study the domain structure of HEK-293 cells and NK1-R microlocalization. EPR spectra and the GHOST condensation routine demonstrated that NK1-R was distributed in a well-ordered domain of HEK-293 cells possibly representing lipid raft/caveolae microdomains, whereas the impairment of caveolae changed the NK1-R plasma-membrane distribution. Internalization and second messenger assays combined with bioluminescence resonance energy transfer were employed subsequently to evaluate the functional importance of the NK1-R microlocalization in lipid raft/caveolae microdomains. The internalization pattern was delineated through the use of dominant-negative mutants (DNM) of caveolin-1 S80E (Cav1 S80E), dynamin-1 K44A (Dyn K44A), and beta-arrestin (beta-arr 319-418) and by means of cell lines that expressed various endogenous levels of beta-arrestins. NK1-R displayed rapid internalization that was substantially reduced by DNMs of dynamin-1 and beta-arrestin and even more profoundly in cells lacking both beta-arrestin1 and beta-arrestin2. These internalization data were highly suggestive of the predominant use of the clathrin-mediated pathway by NK1-R, even though NK1-R tended to reside constitutively in lipid raft/caveolae microdomains. Evidence was also obtained that the proper clustering of the receptor in these microdomains was important for effective agonist-induced NK1-R signaling and for its interaction with beta-arrestin2.

Endogenous Tachykinin Release Contributes to the Locomotor Activity in Lamprey

Tachykinins are present in lamprey spinal cord. The goal of this study was to investigate whether an endogenous release of tachykinins contributes to the activity of the spinal network generating locomotor activity. The locomotor network of the isolated lamprey spinal cord was activated by bath-applied N-methyl-d-aspartate (NMDA) and the efferent activity recorded from the ventral roots. When spantide II, a tachykinin receptor antagonist, was bath-applied after reaching a steady-state burst frequency (>2 h), it significantly lowered the burst rate compared with control pieces from the same animal. In addition, the time to reach the steady-state burst frequency (>2 h) was lengthened in spantide II. These data indicate that an endogenous tachykinin release contributes to the ongoing activity of the locomotor network by modulating the glutamate–glycine neuronal network responsible for the locomotor pattern. We also explored the effects of a 10-min exogenous application of substance P (1 μM), a tachykinin, and showed that its effect on the burst rate depended on the initial NMDA induced burst frequency. At low initial burst rates (∼0.5 Hz), tachykinins caused a marked further slowing to 0.1 Hz, whereas at higher initial burst rates, it instead caused an enhanced burst rate as previously reported, and in addition, a slower modulation (0.1 Hz) of the amplitude of the motor activity. These effects occurred during an initial period of ∼1 h, whereas a modest long-lasting increase of the burst rate remained after >2 h.

Substance P in traumatic brain injury

Recent evidence has suggested that neuropeptides, and in particular substance P (SP), may play a critical role in the development of morphological injury and functional deficits following acute insults to the brain. Few studies, however, have examined the role of SP, and more generally, neurogenic inflammation, in the pathophysiology of traumatic brain injury and stroke. Those studies that have been reported suggest that SP is released following injury to the CNS and facilitates the increased permeability of the blood brain barrier, the development of vasogenic edema and the subsequent cell death and functional deficits that are associated with these events. Inhibition of the SP activity, either through inhibition of the neuropeptide release or the use of SP receptor antagonists, have consistently resulted in profound decreases in edema formation and marked improvements in functional outcome. The current review summarizes the role of SP in acute brain injury, focussing on its properties as a neurotransmitter and the potential for SP to adversely affect outcome.

Conserved amino acid residues that are important for ligand binding in the type I gonadotropin-releasing hormone (GnRH) receptor are required for high potency of GnRH II at the type II GnRH receptor

GnRH I regulates reproduction. A second form, designated GnRH II, selectively binds type II GnRH receptors. Amino acids of the type I GnRH receptor required for binding of GnRH I (Asp2.61(98), Asn2.65(102), and Lys3.32(121)) are conserved in the type II GnRH receptor, but their roles in receptor function are unknown. We have delineated their functions using mutagenesis, signaling and binding assays, immunoblotting, and computational modeling. Mutating Asp2.61(97) to Glu or Ala, Asn2.65(101) to Ala, or Lys3.32(120) to Gln decreased potency of GnRH II-stimulated inositol phosphate production. Consistent with proposed roles in ligand recognition, mutations eliminated measurable binding of GnRH II, whereas expression of mutant receptors was not decreased. In detailed analysis of how these residues affect ligand-dependent signaling, [Trp2]-GnRH I showed lesser decreases in potency than GnRH I at the Asp2.61(97)Glu mutant. In contrast, [Trp2]-GnRH II showed the same loss of potency as GnRH II at this mutant. This suggests that Asp2.61(97) contributes to recognition of His2 of GnRH I, but not of GnRH II. GnRH II showed a large decrease in potency at the Asn2.65(101)Ala mutant compared with analogs lacking the CO group of Gly10NH2. This suggests that Asn2.65(101) recognizes Gly10NH2 of GnRH II. GnRH agonists showed large decreases in potency at the Lys3.32(120)Gln mutant, but antagonist activity was unaffected. This suggests that Lys3.32(120) recognizes agonists, but not antagonists, as in the type I receptor. These data indicate that roles of conserved residues are similar, but not identical, in the type I and II GnRH receptors.

The role of substance P in stress and anxiety responses

Substance P (SP) is one of the most abundant peptides in the central nervous system and has been implicated in a variety of physiological and pathophysiological processes including stress regulation, as well as affective and anxiety-related behaviour. Consistent with these functions, SP and its preferred neurokinin 1 (NK1) receptor has been found within brain areas known to be involved in the regulation of stress and anxiety responses. Aversive and stressful stimuli have been shown repeatedly to change SP brain tissue content, as well as NK1 receptor binding. More recently it has been demonstrated that emotional stressors increase SP efflux in specific limbic structures such as amygdala and septum and that the magnitude of this effect depends on the severity of the stressor. Depending on the brain area, an increase in intracerebral SP concentration (mimicked by SP microinjection) produces mainly anxiogenic-like responses in various behavioural tasks. Based on findings that SP transmission is stimulated under stressful or anxiety-provoking situations it was hypothesised that blockade of NK1 receptors may attenuate stress responses and exert anxiolytic-like effects. Preclinical and clinical studies have found evidence in favour of such an assumption. The status of this research is reviewed here.

How important are NK1 receptors for influencing microvascular inflammation and itch in the skin? Studies using Phoneutria nigriventer venom

Pain and itch sensations are induced by depolarization of C-fibre nerves and possibly other types of fibres. We have evidence from several species, including mice, that skin plasma extravasation induced by the Phoneutria nigriventer spider venom (PNV) is dependent on tachykinin NK(1) receptors. We have now investigated the itching measured as bouts of scratching in response to intradermal (i.d.) PNV in wildtype (NK(1)(+/+)) and NK(1) receptor knockout (NK(1)(-/-)) mice. Mice, either NK(1)(+/+) or NK(1)(-/-), were given a single i.d. injection (0.05 ml) of test agent or vehicle into the shaved dorsal skin, in the intercostal region, in a randomized way. The bouts of scratching were recorded in a blinded manner for 60 min. Oedema formation was concomitantly assessed by the extravascular accumulation of i.v. injected (125)I-albumin. The i.d. injection of either substance P (at a high dose of 100 nmol/site), or PNV (0.3-10 microg/site) induced oedema formation in NK(1)(+/+) but substantially less was observed in NK(1)(-/-) mice, as previously reported. PNV also induced scratching, but significantly less scratching was observed in NK(1)(-/-) compared with NK(1)(+/+) mice. In contrast, SP did not induce significant scratching at amounts up to 100 nmol in NK(1)(+/+) mice. Experiments with an NK(1) receptor antagonist SR140333 (at doses that blocked PNV-induced oedema) revealed that whilst a local co-injection i.d. (1 nmol) in NK(1)(+/+) mice had no effect on PNV (3 microg/site)-induced scratching (18.5+/-3.7 vs. 14.4+/-3.5 bouts, mean+/-S.E.M., n=5-7), systemic treatment with SR140333 (120 nmol/kg, i.v.) significantly inhibited scratching (14+/-3.5 vs. 3.1+/-1.2 bouts, n=4-6; P<0.05). These results indicate that NK(1) receptors are involved in mediating PNV-induced scratching and that the location of the receptors is unlikely to be skin. Thus, a distinct separation between endogenous microvascular and PNV nociceptive NK(1)-dependent effects is suggested.

Characteristics of substance P transport across the blood-brain barrier

PURPOSE

Substance P (SP; NH3(+)-Arg(+)-Pro-Lys(+)-Pro-Gln-Gln-Phe-Phe-Gly-Leu-Met-NH2) belongs to a group of neurokinins that are widely distributed in the central nervous system and peripheral nervous system. The biological effects mediated by SP in the central nervous system include regulation of affective behavior, emesis, and nociception. Many of these actions are believed to be the result of the binding of SP to the neurokinin-1 (NK-1) receptor and subsequent transport across the blood-brain barrier (BBB). The objective of the study was to investigate the involvement of the NK-1 receptor in the permeation of SP across the BBB.

METHODS

Transport of 3H SP (1-13 nM) was investigated using BBMEC monolayers grown on polycarbonate membranes mounted on a Side-bi-Side diffusion apparatus. 3H SP samples were analyzed by scintillation spectrometry. Liquid chromatography-tandem mass spectrometry was used to monitor the transport at higher concentrations (micromolar).

RESULTS

SP transport across BBMEC monolayers was found to be saturable (Km = 8.57 +/- 1.59 nM, Vmax = 0.017 +/- 0.005 pmol min(-1) mg(-1) protein) in the concentration range of 0-13 nM. Significant (p < 0.05) decline in 3H SP permeation was observed in the presence of unlabeled SP and at 4 degrees C, indicating that the transport process is carrier-mediated. High-performance liquid chromatography analysis showed no significant metabolism of 3H SP in either the donor or receiver chambers. 3H SP transport was inhibited by 2-11 SP (p < 0.05) but not by any other fragments, indicating that both the C- and N-terminal regions are essential for molecular recognition by the receptor. Endocytic inhibitors (chloroquine, phenylarsine oxide, monensin, and brefeldin) did not inhibit SP transport, suggesting the involvement of a nonendocytic mechanism in SP permeation. Pro(9) SP, a high-affinity substrate for the NK-1 major subtype receptor, significantly (p < 0.05) inhibited the transport of SP. However, Sar(9)Met(O2)(11) SP, a high-affinity substrate for the NK-1 minor subtype receptor, septide, and neurokinin A, inhibitors of NK-1 and neurokinin-2 (NK-2) receptors, respectively, did not produce any inhibition of SP transport. Western blot analysis confirmed the presence of the NK-1 receptor in BBMEC monolayers.

CONCLUSIONS

The above results provide functional and molecular evidence for the existence of a carrier-mediated mechanism in the transport of SP across the BBB. The effects of specific inhibitors and the results of Western blot analyses demonstrate the involvement of the NK-1 receptor in the transport of SP across the BBB.

Tachykinins and tachykinin receptors in the gut, with special reference to NK2 receptors in human

Tachykinins (TKs), substance P (SP), neurokinin A (NKA) and B (NKB) are important peptide modulators of intestinal motility in animal species studied so far, including humans. Modulation of motility by TKs can occur at various levels, since these peptides are expressed in cholinergic excitatory motor neurons projecting to both circular and longitudinal muscle, interneurons, and intramural and extramural sensory neurons. The effects of SP, NKA and NKB are preferentially mediated through the stimulation of NK1, NK2 and NK3 receptors, respectively; however, the selectivity of natural TKs for their preferred receptors is relative. In addition, SP and NKA are expressed in similar quantities in the human intestine and adequate stimuli can release similar amount of these TKs from enteric nerves. Furthermore, a single anatomical substrate can express more than one TK receptor type, so that the blockade of a single receptor type may not reveal functional effects in integrated models of motility. In isolated human small intestine and colon circular muscle strips, both NK1 and NK2 receptors mediate contractile effects. Indeed, in the human small intestine, smooth muscle electrical and motor events induced by electrical field stimulation (EFS) can involve either or both NK1 and NK2 receptors or these latter receptors predominantly, depending on the experimental conditions. In contrast, in the human colonic smooth muscle, only the NK2 receptor-mediated component of the response to EFS is prominent and some evidence would suggest that this component is the main excitatory motor mechanism at this level. Furthermore, a NK2 receptor-mediated secretory component in the human colonic mucosa has been recently demonstrated. Thus, it could be speculated that the blockade of both NK1 and NK2 receptors will be necessary to antagonise motor effects induced by exogenous administration or endogenous release of TKs in the small intestine, whereas the blockade of the NK2 receptors would be sufficient to disrupt physiological motor and, possibly, secretory activity at the colonic level. Available evidence indicates that, in healthy volunteers, the infusion of NKA (25 pmol/kg/min i.v.) stimulated small intestine motility and precipitated a series of intestinal and non-intestinal adverse events. Nepadutant (8 mg i.v.), a selective NK2 receptor antagonist, antagonised small intestine motility induced by NKA and prevented associated intestinal adverse events. In another study, the same dose of nepadutant increased colo-rectal compliance during isobaric balloon distension in healthy volunteers pretreated with a glycerol enema, disclosing a NK2 receptor-mediated component in the regulation of colonic smooth muscle tone. However, the prolonged blockade of NK2 receptors by nepadutant (16 mg i.v. b.i.d. for 8 days) did not affect bowel habits, neither in term of movements nor of stool consistency. Altogether, these results indicate that, even when there is a significant redundance in the effects of TKs and in the role of their receptors, the selective blockade of tachykinin NK2 receptors can have functional consequences on human intestinal motility and perception, but this can occur without the disruption of the physiological functions.

G protein-coupled receptors in haematopoietic disruption

Haematopoiesis is the process by which blood and immune cells are replenished from a finite number of resident bone marrow (BM) haematopoietic stem cells (HSCs). Regulatory molecules within the BM microenvironment contribute developmental signals to an interactive network capable of ensuring ordered biological processes. Many bioactive molecules contribute to the network through G protein-coupled receptors (GPCRs). GPCRs are seven-transmembrane receptors that, following ligand binding, signal by activating coupled heterotrimeric G proteins. This review focuses on those bioactive molecules that regulate haematopoietic development through GPCRs. Chemokines (SDF-1alpha, MIP-1), opioids and tachykinins (SP, NK-A) are important G protein-coupled haematopoietic regulators. Their biology in normal and diseased haematopoiesis is discussed below, as well as their potential as therapeutic targets.

Species differences in tachykinin receptor distribution: further evidence that the substance P (NK1) receptor predominates in human brain

Marked species differences in the distribution of central tachykinin receptors are reported but uncertainty remains about the ability of available ligands to detect NK2 and NK3 receptors in human brain. We compared the distribution of NK1, NK2, and NK3 receptors in sections from rodent, primate, and human brain using the 125I-labeled ligands substance P (SP) for the NK1 receptor, neurokinin A (NKA) for the NK2 receptor, and neurokinin B (NKB) and eledoisin for NK3 receptors. Duration of exposure to autoradiographic film was from 7 days for [125I]SP up to 90 days for the other ligands. High levels of specific [125I]SP binding were seen throughout the brains of all species studied. Specific [125I]NKA binding was detected in brains from neonatal rat, and to a lesser level in adult rat, gerbil, and guinea pig; it was not detected in monkey or human brain, but was present in circular muscle of human duodenum, confirming that this ligand binds to human NK2 receptors under our experimental conditions. Specific [125I]NKB and [125I]eledoisin binding was widespread in brain sections from rats, gerbils, and guinea pigs, and very low levels were also detected in marmoset, squirrel monkey, and rhesus monkey brain after prolonged (up to 90 days) exposure. We failed to identify specific eledoisin binding in human brain, even after prolonged exposures. These findings demonstrate that the NK1 receptor is the predominant tachykinin receptor expressed in primate and human brain, but that low levels of NK3 receptor are present in nonhuman, primate brain.

Functional characterisation of tachykinin receptors in the circular muscle layer of the mouse ileum

OBJECTIVES

Tachykinins are important mediators in neuromuscular signalling but have not been thoroughly characterised in the mouse gut. We investigated the participation of tachykinin receptors in contractility of circular muscle strips of the mouse ileum.

RESULTS

Electrical field stimulation (EFS) of excitatory nonadrenergic noncholinergic (NANC) nerves induced frequency-dependent contractions which were mimicked by substance P (SP). Desensitisation of SP and NK(1), NK(2) or NK(3) receptors significantly reduced contractions to EFS. The NK(1) receptor blocker RP67580 significantly inhibited NANC contractions to EFS. The NK(2) and NK(3) receptor blockers nepadutant and SR142801 did not affect NANC contractions per se but increased the RP67580-induced inhibition of NANC contractions to EFS. Contractions to SP were significantly reduced by RP67580 but not affected by nepadutant or SR142801. The NK(1) and NK(2) receptor agonists, septide and [beta-ala(8)]-NKA 4-10 (beta-A-NKA), respectively, but not the NK(3) receptor agonist senktide-induced dose-dependent contractions. Atropine inhibited and l-NNA augmented contractions to septide. Contractions to beta-A-NKA were insensitive to atropine but augmented by l-NNA.

CONCLUSIONS

Tachykinins mediate NANC contractions to EFS in the mouse small intestine. Endogenously released tachykinins activate mainly NK(1) receptors, located on cholinergic nerves and smooth muscle cells and, to a lesser degree, NK(2) and NK(3) receptors, most likely located presynaptically.

Effect of neurokinin-1 receptor antagonists on serotoninergic, noradrenergic and hippocampal neurons: comparison with antidepressant drugs

Neurokinin-1 (NK1) receptor antagonists have been reported to possess antidepressant and anxiolytic properties in controlled trials. Since antidepressant and anxiolytic drugs act mainly by enhancing serotonin (5-HT) and norepinephrine (NE) neurotransmission in forebrain areas, the main focus of the present review is to critically examine the electrophysiological effects of NK1 receptor antagonists on serotoninergic and noradrenergic neurons, and then hippocampal neurons. It is concluded that NK1 antagonists increase the firing and burst activity of 5-HT neurons, increase burst activity of NE neurons, and modulate postsynaptic transmission at the hippocampus level. Further research is needed in order to develop more selective ligands for the human NK1 receptor and to gain better knowledge of required brain penetration and optimal pharmacodynamic conditions for their use in patients.

Tachykinins and kinins in airway allergy

Using models of airway diseases, our understanding of the role of tachykinins and kinins in airway pathophysiology has been greatly enhanced by the recent development of a large series of peptide, peptoid and non-peptide antagonists for tachykinin and kinin receptors. This article reviews the experimental findings of the contribution of kinins and tachykinins and their respective receptors, in models of airway inflammation in response to agents known to trigger or worsen asthma attacks, such as antigen and cold air. Some new antagonists, mostly of a non-peptide nature, exhibit excellent pharmacodynamic and pharmacokinetic profiles; a brief account of early clinical studies in which they have been used is also given.

Insect Neuropeptide and Peptide Hormone Receptors: Current Knowledge and Future Directions

Peptides form a very versatile class of extracellular messenger molecules that function as chemical communication signals between the cells of an organism. Molecular diversity is created at different levels of the peptide synthesis scheme. Peptide messengers exert their biological functions via specific signal-transducing membrane receptors. The evolutionary origin of several peptide precursor and receptor gene families precedes the divergence of the important animal Phyla. In this chapter, current knowledge is reviewed with respect to the analysis of peptide receptors from insects, incorporating many recent data that result from the sequencing of different insect genomes. Therefore, detailed information is provided on six different peptide receptor families belonging to two distinct receptor categories (i.e., the heptahelical and the single transmembrane receptors). In addition, the remaining problems, the emerging concepts, and the future prospects in this area of research are discussed.

Morphologic evidence that neurokinin B modulates gonadotropin-releasing hormone secretion via neurokinin 3 receptors in the rat median eminence

Recent studies suggest that arcuate neurokinin B (NKB) neurons play a role in the regulation of gonadotropin secretion, but there is little information on the relationship between these neurons and the hypothalamic reproductive axis. In the present study, dual-label fluorescent immunohistochemistry was used to visualize the relationship between gonadotropin-releasing hormone (GnRH) neurons and either proNKB or NK3 receptor (NK3R) immunoreactivity. Immunocytochemistry was also combined with i.p. injections of the fluorescent retrograde tracer aminostilbamidine to determine whether arcuate neuroendocrine neurons expressed either proNKB or NK3R. A dense interweaving and close apposition of GnRH and proNKB-immunoreactive (ir) fibers was observed within the rat median eminence, where GnRH axons expressed NK3R immunoreactivity. These data provide morphological evidence that NKB neurons could influence GnRH secretion via interaction with NK3R in the rat median eminence. Colocalization of GnRH and NK3R was also identified in fiber tracts converging within the organum vasculosum of the lamina terminalis. In contrast, only a small number (16%) of GnRH-ir somata exhibited NK3R staining. ProNKB and NK3R-ir somata were identified within the arcuate nucleus, but none of these neurons were labeled by aminostilbamidine. Thus, we found no evidence that arcuate NKB neurons project to the primary capillary plexus of the portal system. Arcuate neuroendocrine neurons, however, were surrounded and closely apposed by proNKB-ir puncta and fibers. These data suggest that NKB neurons could indirectly influence anterior pituitary function by inputs to arcuate neuroendocrine neurons, but through a receptor other than NK3R. Our results provide an anatomic framework for putative interactions between NKB neurons and the hypothalamic reproductive axis.