Cardiovascular actions of central neuromedin U in conscious rats

Bone mechanical loading reduces heart rate and increases heart rate variability in mice

Cardiovascular disease and osteoporosis are clinically associated. Bone adapts to mechanical forces by altering its overall structure and mass. In response to mechanical strain bone cells release signaling molecules and activate the nervous system. Bone also exhibits endocrine functions that modulate a number of tissues including the heart. We hypothesized that bone mechanical loading acutely alters cardiac function via neural and/or endocrine mechanisms. To test this hypothesis, we performed in vivo tibia mechanical loading in anesthetized mice while monitoring heart parameters using electrocardiogram (ECG). An immediate, transient reduction in resting heart rate was observed during tibial loading in both adult male and female mice (p < 0.01) with concurrent increases in heart rate variability (HRV) (p < 0.01). ECG intervals, PR, QRS and QTc were unaffected with loading. In further studies, we found that at least 3 N of load was necessary to elicit this heart response in adult mice. With aging to 11-12 months the responsiveness of the heart to loading was blunted, suggesting this bone-heart connection may weaken with age. Administration of lidocaine around the tibia significantly diminished the heart rate response to bone loading (p < 0.05). Moreover, pre-treatment with sympathetic antagonist propranolol inhibited this heart rate response to loading (p < 0.05), while parasympathetic antagonist atropine did not (p > 0.05). This suggests that a neuronal afferent pathway in the hindlimb and reduction in efferent sympathetic tone mediate this bone-neuro-heart reflex. In conclusion, the findings that tibia bone loading age-dependently modulates heart function support the concept of physiological coupling of the skeletal and cardiovascular systems.

The Aggravating Role of Failing Neuropeptide Networks in the Development of Sporadic Alzheimer's Disease

Alzheimer's disease imposes an increasing burden on aging Western societies. The disorder most frequently appears in its sporadic form, which can be caused by environmental and polygenic factors or monogenic conditions of incomplete penetrance. According to the authors, in the majority of cases, Alzheimer's disease represents an aggravated form of the natural aging of the central nervous system. It can be characterized by the decreased elimination of amyloid β1-42 and the concomitant accumulation of degradation-resistant amyloid plaques. In the present paper, the dysfunction of neuropeptide regulators, which contributes to the pathophysiologic acceleration of senile dementia, is reviewed. However, in the present review, exclusively those neuropeptides or neuropeptide families are scrutinized, and the authors' investigations into their physiologic and pathophysiologic activities have made significant contributions to the literature. Therefore, the pathophysiologic role of orexins, neuromedins, RFamides, corticotrope-releasing hormone family, growth hormone-releasing hormone, gonadotropin-releasing hormone, ghrelin, apelin, and natriuretic peptides are discussed in detail. Finally, the therapeutic potential of neuropeptide antagonists and agonists in the inhibition of disease progression is discussed here.

Unanticipated Characteristics of a Selective, Potent Neuromedin-U Receptor 2 Agonist

Neuromedin-U (NMU) mediates several physiological functions via its two cognate receptors, NMUR1 and NMUR2. Disentangling the individual roles of each receptor has largely been undertaken through the use of transgenic mice bearing a deletion in one of the two receptors or by testing native molecules (NMU or its truncated version NMU-8) in a tissue-specific manner, in effect, taking advantage of the distinct receptor expression profiles. These strategies have proved quite useful despite the inherent limitations of overlapping receptor roles and potential compensatory influences of germline gene deletion. With these considerations in mind, the availability of potent, selective NMU compounds with appropriate pharmacokinetic profiles would advance the capabilities of investigators undertaking such efforts. Here, we evaluate a recently reported NMUR2-selective peptide (compound 17) for its in vitro potency (mouse and human), binding affinity, murine pharmacokinetic properties, and in vivo effects. Despite being designed as an NMUR2 agonist, our results show compound 17 unexpectedly binds but does not have functional activity on NMUR1, thereby acting as an R1 antagonist while simultaneously being a potent NMUR2 agonist. Furthermore, evaluation of compound 17 across all known and orphan G-protein-coupled receptors demonstrates multiple receptor partners beyond NMUR2/R1 binding. These properties need to be appreciated for accurate interpretation of results generated using this molecule and may limit the broader ability of this particular entity in disentangling the physiological role of NMU receptor biology.

Peptide Tool-Driven Functional Elucidation of Biomolecules Related to Endocrine System and Metabolism

The enhancement of basic research based on biomolecule-derived peptides has the potential to elucidate their biological function and lead to the development of new drugs. In this review, two biomolecules, namely "neuromedin U (NMU)" and "myostatin," are discussed. NMU, a neuropeptide first isolated from the porcine spinal cord, non-selectively activates two types of receptors (NMUR1 and NMUR2) and displays a variety of physiological actions, including appetite suppression. The development of receptor-selective regulators helps elucidate each receptor's detailed biological roles. A structure-activity relationship (SAR) study was conducted to achieve this purpose using the amidated C-terminal core structure of NMU for receptor activation. Through obtaining receptor-selective hexapeptide agonists, molecular functions of the core structure were clarified. Myostatin is a negative regulator of skeletal muscle growth and has attracted attention as a target for treating atrophic muscle disorders. Although the protein inhibitors, such as antibodies and receptor-decoys have been developed, the inhibition by smaller molecules, including peptides, is less advanced. Focusing on the inactivation mechanism by prodomain proteins derived from myostatin-precursor, a first mid-sized α-helical myostatin-inhibitory peptide (23-mer) was identified from the mouse sequence. The detailed SAR study based on this peptide afforded the structural requirements for effective inhibition. The subsequent computer simulation proposed the docking mode at the activin type I receptor binding site of myostatin. The resulting development of potent inhibitors suggested the existence of a more appropriate binding mode linked to their β-sheet forming properties, suggesting that further investigations might be needed.

Moniezia benedeni infection enhances neuromedin U (NMU) expression in sheep (Ovis aries) small intestine

BACKGROUND

Neuromedin U (NMU) plays an important role in activating the group 2 innate lymphoid cells (ILC2s) and initiating the host's anti-parasitic immune responses. It is aimed to explore the distribution characteristics of NMU in the sheep small intestine and the influence of Moniezia benedeni infection on them. In the present study, the pET-28a-NMU recombinant plasmids were constructed, and Escherichia coli. BL21 (DE3) were induced to express the recombinant protein. And then, the rabbit anti-sheep NMU polyclonal antibody was prepared and immunofluorescence staining was performed with it. The expression levels of NMU in the intestine of normal and Moniezia benedeni-infected sheep were detected by ELISA.

RESULTS

The results showed that the molecular weight of the obtained NMU recombinant protein was consistent with the expected molecular (13 kDa) and it was expressed in the form of inclusion body. The titer and specificity of obtained rabbit anti-sheep NMU polyclonal antibody were good. The results of immunofluorescence analysis showed that the nerve fibers which specifically expressed NMU mainly extended from the ganglion in the submucosal to lamina propria (LP) in the sheep small intestine, and the expression level was relatively high; especially on the nerve fibers of LP around the intestinal glands. The expression levels were gradually increased from the duodenum to the ileum, and the levels in the jejunum and ileum were significantly higher than that in the duodenum (P < 0.05). In addition, scattered NMU positive cells were distributed in the epithelium of the jejunal crypts. Moniezia benedeni infection increased the expression of NMU in each intestinal segment, especially in the jejunum and ileum there were significant increase (P < 0.05).

CONCLUSIONS

It was suggested that Moniezia benedeni infection could be detected by the high expression of NMU in sheep enteric nervous, and which laid the foundation for further studies on whether NMU exerts anti-parasitic immunity by activating ILC2s. In addition, NMU was expressed in some intestinal gland epitheliums, which also provided a basis for studying its roles in regulation of the immune homeostasis. The present study laid the foundation for further revealing the molecular mechanism of sheep's neural-immune interaction network perceiving the colacobiosis of parasites.

Neuromedins NMU and NMS: An Updated Overview of Their Functions

More than 35 years have passed since the identification of neuromedin U (NMU). Dozens of publications have been devoted to its physiological role in the organism, which have provided insight into its occurrence in the body, its synthesis and mechanism of action at the cellular level. Two G protein-coupled receptors (GPCRs) have been identified, with NMUR1 distributed mainly peripherally and NMUR2 predominantly centrally. Recognition of the role of NMU in the control of energy homeostasis of the body has greatly increased interest in this neuromedin. In 2005 a second, structurally related peptide, neuromedin S (NMS) was identified. The expression of NMS is more restricted, it is predominantly found in the central nervous system. In recent years, further peptides related to NMU and NMS have been identified. These are neuromedin U precursor related peptide (NURP) and neuromedin S precursor related peptide (NSRP), which also exert biological effects without acting via NMUR1, or NMUR2. This observation suggests the presence of another, as yet unrecognized receptor. Another unresolved issue within the NMU/NMS system is the differences in the effects of various NMU isoforms on diverse cell lines. It seems that development of highly specific NMUR1 and NMUR2 receptor antagonists would allow for a more detailed understanding of the mechanisms of action of NMU/NMS and related peptides in the body. They could form the basis for attempts to use such compounds in the treatment of disorders, for example, metabolic disorders, circadian rhythm, stress, etc.

Neuromedin U precursor-related peptide (NURP) exerts neuromedin U-like sympathetic nerve action in the rat

It has been suggested that novel peptide that is produced from the neuromedin U (NMU) precursor may exist, as this precursor contains multiple consensus sequences for proteolytic processing. Recently, we identified two mature novel peptides comprising 33 and 36 residues in the rat brain, which were designated neuromedin U precursor-related peptide (NURP) 33 and 36. In the present study, we compared the roles of NURP33 and 36 with that of NMU, as neither activates the NMU receptors. Immunoreactivity for NMU and NURPs was widely present in the central nervous system and showed a similar distribution. Intracerebroventricular (icv) injection of NURP33 in rats increased locomotor activity, energy expenditure, heart rate and back surface temperature (BS-T), similarly to NMU or NURP36. NMU treatment reduced food intake, but NURP33 did not. Pretreatment with the β3 blocker, SR59230A, and the cyclooxygenase blocker, indomethacin, inhibited the NURP33- or NMU-induced increase of BS-T. In addition, icv injection of NURP33 or NMU increased the expression of mRNA for cyclooxygenase 2 in the hypothalamus and for uncoupling protein 1 in the brown adipose tissue. These results suggest that although NURP33 and 36 do not activate the NMU receptors, they might exert NMU-like sympathetic nerve action in the brain.

Neuromedin: An insight into its types, receptors and therapeutic opportunities

Neuropeptides are small protein used by neurons in signal communications. Neuromedin U was the first neuropeptide discovered from the porcine spinal and showed its potent constricting activities on uterus hence was entitled with neuromedin U. Following neuromedin U another of its isoform was discovered neuromedin S which was observed in suprachiasmatic nucleus hence was entitled neuromedin S. Neuromedin K and neuromedin L are of kanassin class which belong to tachykinin family. Bombesin family consists of neuromedin B and neuromedin C. All these different neuromedins have various physiological roles like constrictive effects on the smooth muscles, control of blood pressure, pain sensations, hunger, bone metastasis and release and regulation of hormones. Over the years various newer physiological roles have been observed thus opening ways for various novel therapeutic treatments. This review aims to provide an overview of important different types of neuromedin, their receptors, signal transduction mechanism and implications for various diseases.

Involvement of endogenous neuromedin U and neuromedin S in thermoregulation

We investigated the possible involvement of neuromedin U (NMU) and neuromedin S (NMS) in thermoregulation in rats. Intracerebroventricular (icv) injection of NMU or NMS increased the back surface temperature (BS-T) in a dose-dependent manner during both the light and dark periods. Pre-treatment with the β3 blocker SR59230A, and the cyclooxygenase blocker indomethacin, inhibited the increase in BS-T induced by NMS. Icv injection of NMS and NMU increased the expression of mRNAs for prostaglandin E synthase and cyclooxygenase 2 (COX2) in the hypothalamus, and that of mRNA for uncoupling protein 1 (UCP1) in the brown adipose tissue. Comparison of thermogenesis in terms of body temperature under normal and cold conditions revealed that NMS-KO and double-KO mice had a significantly low BS-T during the active phase, whereas NMU-KO mice did not. Exposure to low temperature decreased the BS temperature in all KO mice, but BS-T was lower in NMS-KO and double-KO mouse than in NMU-KO mice. Calorie and oxygen consumption was also significantly lower in all KO mice than in wild-type mice during the dark period. These results suggest that NMU and NMS are involved in thermoregulation via the prostaglandin E2 and β3 adrenergic receptors, but that endogenous NMS might play a more predominant role than NMU.

Neuromedin U: a multifunctional neuropeptide with pleiotropic roles

BACKGROUND

Neuromedin U (NmU) belongs to the neuromedin family, comprising a series of neuropeptides involved in the gut-brain axis and including neuromedins B and C (bombesin-like), K (neurokinin B), L (neurokinin A or neurotensin), N, S, and U.

CONTENT

Although initially isolated from porcine spinal cord on the basis of their ability to induce uterine smooth muscle contraction, these peptides have now been found to be expressed in several different tissues and have been ascribed numerous functions, from appetite regulation and energy balance control to muscle contraction and tumor progression. NmU has been detected in several species to date, particularly in mammals (pig, rat, rabbit, dog, guinea pig, human), but also in amphibian, avian, and fish species. The NmU sequence is highly conserved across different species, indicating that this peptide is ancient and plays an important biological role. Here, we summarize the main structural and functional characteristics of NmU and describe its many roles, highlighting the jack-of-all-trades nature of this neuropeptide.

SUMMARY

NmU involvement in key processes has outlined the possibility that this neuropeptide could be a novel target for the treatment of obesity and cancer, among other disorders. Although the potential for NmU as a therapeutic target is obvious, the multiple functions of this molecule should be taken into account when designing an approach to targeting NmU and/or its receptors.

Mediators involved in the hyperthermic action of neuromedin U in rats

Neuromedin U (NmU), first was isolated from the porcine spinal cord, has subsequently been demonstrated in a number of species, in which it is present in the periphery and also the brain. Two receptors have been identified: NmU1R is mainly present in peripheral tissues, and Nmu2R in the central nervous system. NmU, a potent endogenous anorectic, serves as a catabolic signaling molecule in the brain; it inhibits food uptake, increases locomotion, activates stress mechanism, having cardiovasscular effects and, causes hyperthermia. The mechanism of this hyperthermia is unknown. In the present experiments, the effects of NmU on the colon temperature following i.c.v administration were studied in rats. For an investigation of the possible role of receptors in mediating hyperthermia, the animals were treated simultaneously with CRF 9-41 and antalarmin, a CRH1 receptor inhibitors, astressin 2B, a CRH2 receptor antagonist, haloperidol a dopamine receptor antagonist, atropine a muscarinic cholinergic receptor antagonist, noraminophenazone a cyclooxygenase inhibitor or isatin, a prostaglandin receptor antagonist. NmU increased the colon temperature, maximal action being observed at 2-3h. CRF 9-41, antalarmin, astressin 2B haloperidol, atropine, noraminophenazone and isatin prevented the NmU-induced increase in colon temperature. The results demonstrated that, when injected into the lateral brain ventricle NmU increased the body temperature, mediated by CRHR1 and CRHR2, dopamine and muscarinic cholinergic receptors. The final pathway involves prostaglandin.

Anxiolytic action of neuromedin-U and neurotransmitters involved in mice

Peptide Neuromedin-U (NmU) is widely distributed in the central nervous system and the peripheral tissues. Its physiological effects include the regulation of blood pressure, heart rate, and body temperature, and the inhibition of gastric acid secretion. The action of NmU in rats is mediated by two G-protein-coupled receptors, NmU-1R and NmU-2R. NmU-2R is present mainly in the brain, and NmU-1R mainly in the periphery. Despite the great variety of the physiological action of NmU, little is known about its possible effects in different forms of behavior, such as anxiety. In the present work, NmU-23 (the rodent form of the peptide) was tested for its effect on anxiety in elevated plus maze test in mice. For detection of the possible involvement of neurotransmitters, the mice were pretreated with receptor blockers: haloperidol (a D2, dopamine receptor antagonist), propranolol (a β-adrenergic receptor antagonist), atropine (a nonselective muscarinic acetylcholine receptor antagonist), phenoxybenzamine (a nonselective α-adrenergic receptor antagonist) or nitro-l-arginine (a nitric oxide synthase inhibitor). The peptide and nitro-l-arginine were administered into the lateral brain ventricle, while the receptor blockers were applied intraperitoneally. An NmU-23 dose 0.5μg elicited anxiolytic action, whereas this action is faded away when the dose was increased. For further testing therefore 0.5μg i.c.v. was used. Propranolol and atropine fully blocked the NmU-induced anxiolytic action, while haloperidol, phenoxybenzamine and nitro-l-arginine were ineffective. The results suggest that β-adrenergic and cholinergic mechanisms are involved in the anxiolytic action of NmU.

Neuromedin U causes biphasic cardiovascular effects and impairs baroreflex function in rostral ventrolateral medulla of spontaneously hypertensive rat

Neuromedin U (NMU) causes biphasic cardiovascular and sympathetic responses and attenuates adaptive reflexes in the rostral ventrolateral medulla (RVLM) and spinal cord in normotensive animal. However, the role of NMU in the pathogenesis of hypertension is unknown. The effect of NMU on baseline cardiorespiratory variables in the RVLM and spinal cord were investigated in urethane-anaesthetized, vagotomized and artificially ventilated male spontaneously hypertensive rats (SHR) and Wistar-Kyoto rats (WKY). Experiments were also conducted to determine the effects of NMU on somatosympathetic and baroreceptor reflexes in the RVLM of SHR and WKY. NMU injected into the RVLM and spinal cord elicited biphasic response, a brief pressor and sympathoexcitatory response followed by a prolonged depressor and sympathoinhibitory response in both hypertensive and normotensive rat models. The pressor, sympathoexcitatory and sympathoinhibitory responses evoked by NMU were exaggerated in SHR. Phrenic nerve amplitude was also increased following intrathecal or microinjection of NMU into the RVLM of both strains. NMU injection into the RVLM attenuated the somatosympathetic reflex in both SHR and WKY. Baroreflex sensitivity was impaired in SHR at baseline and further impaired following NMU injection into the RVLM. NMU did not affect baroreflex activity in WKY. The present study provides functional evidence that NMU can have an important effect on the cardiovascular and reflex responses that are integrated in the RVLM and spinal cord. A role for NMU in the development and maintenance of essential hypertension remains to be determined.

Functional genomics of the rat neuromedin U receptor 1 reveals a naturally occurring deleterious allele

Neuromedin U (NMU) plays an important role in a number of physiological processes, but the relative contribution of its two known receptors, NMUR1 and NMUR2, is still poorly understood. Here we report the existence of a SNP T1022→A (Val341→Glu) in the third exon of the rat Nmur1 gene that leads to an inactive receptor. This SNP is present within the coding region of the highly conserved NPXXY motif found within all class A type G protein-coupled receptors and translates to an NMUR1 receptor that is not expressed on the cell surface. Genetic analysis of the Nmur1 gene in a population of Sprague-Dawley rats revealed that this strain is highly heterogeneous for the inactivating polymorphism. The loss of functional NMUR1 receptors in Sprague-Dawley rats homozygous for the inactive allele was confirmed by radioligand binding studies on native tissue expressing NMUR1. The physiological relevance of this functional genomics finding was examined in two nociceptive response models. The pronociceptive effects of NMU were abolished in rats lacking functional NMUR1 receptors. The existence of naturally occurring NMUR1-deficient rats provides a novel and powerful tool to investigate the physiological role of NMU and its receptors. Furthermore, it highlights the importance of verifying the NMUR1 single nucleotide polymorphism status for rats used in physiological, pharmacological or toxicological studies conducted with NMUR1 modulators.

Ghrelin does not affect gastrointestinal contractility in rainbow trout and goldfish in vitro

Ghrelin has been identified in rainbow trout and goldfish, and it has been shown to regulate growth hormone release and food intake in these species as seen in mammals. The aim of this study was to investigate the functional role of ghrelin in regulation of gastrointestinal contractility in both fishes. Neither rainbow trout ghrelin nor rat ghrelin affected the contractility of gastrointestinal strips of rainbow trout. Similarly, goldfish ghrelin-17 and rat ghrelin did not cause marked contraction in the goldfish intestinal bulb. Detail examinations using the goldfish intestine revealed that human neurotensin, substance-P, goldfish neuromedine-U and carbachol showed apparent contractile activities in the intestinal strips. Electrical field stimulation (EFS, 1-20 Hz) caused a frequency-dependent contraction of the intestinal bulb. Atropine partially inhibited and tetrodotoxin abolished the EFS-induced contraction. Pretreatments with goldfish ghrelin-17 and rat ghrelin did not modify the EFS-induced contraction. The mRNAs of two types of growth hormone secretagogue receptor (GHS-R), GHS-R1a-1 and GHS-R1a-2, were detected in the goldfish intestine, and the expression level of GHS-R1a-2 was 4-times higher than that of GHS-R1a-1. The expression levels of GHS-R1a-1 and GHS-R1a-2 in four regions of the goldfish intestine (intestinal bulb, intestine-1, intestine-2 and intestine-3) were almost the same. In conclusion, ghrelin does not affect gastrointestinal contractility of the rainbow trout and goldfish, although GHSR-like receptor/GHS-R1a is expressed entire intestine. These results suggest diversity of ghrelin function in vertebrates.

Differential cardiorespiratory and sympathetic reflex responses to microinjection of neuromedin U in rat rostral ventrolateral medulla

The rostral ventrolateral medulla (RVLM) regulates sympathetic vasomotor outflow and reflexes. Intracerebroventricular neuromedin U (NMU) increases sympathetic nerve activity (SNA), mean arterial pressure (MAP), and heart rate (HR), but the central nuclei that mediate these effects are unknown. In urethane-anesthetized, vagotomized, and artificially ventilated male Sprague-Dawley rats (n = 36) the effects of bilateral microinjection of NMU (50 nl, each side) into RVLM on cardiorespiratory variables, somatosympathetic reflex, arterial baroreflex, and chemoreflex were investigated. Microinjection of NMU into RVLM elicited a hypertension, tachycardia, and an increase in splanchnic SNA (SSNA) and lumbar SNA (LSNA) at lower doses (25 and 50 pmol). At higher dose (100 pmol), NMU caused a biphasic response, a brief hypertension and sympathoexcitation followed by prolonged hypotension and sympathoinhibition. The peak excitatory and inhibitory response was found at 100 pmol NMU with an increase in MAP, HR, SSNA, and LSNA of 36 mm Hg, 20 beats per minute, 34%, and 89%, respectively, and a decrease of 33 mm Hg, 25 beats per minute, 42%, and 52%, respectively, from baseline. NMU, in the RVLM, also increased phrenic nerve amplitude and the expiratory period and reduced the inspiratory period. NMU (100 pmol) attenuated the somatosympathetic reflex and the sympathoexcitatory and respiratory responses to hypoxia and hypercapnia. After NMU injection in RVLM, the maximum gain of the SSNA baroreflex function curve was increased, but that of the LSNA was reduced. The present study provides functional evidence for a complex differential modulatory activity of NMU on the cardiovascular and reflex responses that are integrated in the RVLM.

Intrathecal neuromedin U induces biphasic effects on sympathetic vasomotor tone, increases respiratory drive and attenuates sympathetic reflexes in rat

BACKGROUND

Neuromedin U (NMU) is a brain-gut peptide that plays regulatory roles in feeding, anxiety, smooth muscle contraction, blood flow, pain and adrenocortical function via two receptors, the NMU receptor 1 and NMU receptor 2. NMU has several known functions in the periphery, but its role in central cardiorespiratory regulation remains poorly understood.

EXPERIMENTAL APPROACH

Experiments were conducted on urethane-anaesthetized, vagotomized and artificially ventilated male Sprague-Dawley rats (n= 42) to determine if NMU modulates sympathetic vasomotor output at the spinal level or modulates baro-, chemo- and somato-sympathetic reflexes.

KEY RESULTS

Intrathecal (i.t.) injections of NMU (2.5-20 nmol) caused a dose-dependent biphasic response, initially a brief period of hypertension and sympatho-excitation followed by prolonged hypotension and sympatho-inhibition. Peak excitatory as well as inhibitory responses were observed at 20 nmol. NMU (20 nmol) initially increased mean arterial pressure and splanchnic sympathetic nerve activity by 24 mmHg and 27% and then reduced these by 37 mmHg and 47%, respectively. NMU also dose-dependently increased respiratory drive, as indicated by a rise in phrenic nerve amplitude, an increase in neural minute ventilation and a shortening of the inspiratory period. Both sympatho-excitatory peaks of the somato-sympathetic reflex were abolished by i.t. NMU. Pressor, sympatho-excitatory and tachycardiac responses to chemoreceptor activation (100% N₂) were blocked or significantly reduced following i.t. NMU. NMU also reduced barosensitivity.

CONCLUSIONS

The data demonstrate that NMU, acting in the spinal cord, differentially contributes to the control of sympathetic tone and adaptive sympathetic reflexes.

Corticotrophin-releasing factor inhibits neuromedin U mRNA expressing neuron in the rat hypothalamic paraventricular nucleus in vitro

In the present study, we examined the effects of corticotrophin-releasing factor (CRF) on neuromedin U (NMU) mRNA-expressing neurons in the rat paraventricular nucleus (PVN) by whole-cell patch-clamp recordings and single-cell reverse transcription-multiplex polymerase chain reaction (single-cell RT-mPCR) techniques. In total, of 116 PVN putative parvocellular neurons screened for NMU mRNA, 14.7% (17/116) of them expressed NMU mRNA. The electrophysiological properties observed in the NMU mRNA-expressing neurons were generation of a low-threshold Ca(2+) spike (LTS) and robust low voltage-activated (T-type) Ca(2+) currents. Under current-clamp conditions, CRF (100 nM) induced a reversible decrease in spike firing and significantly diminished the LTS in 88.2% (15/17) of NMU mRNA-expressing neurons. Extracellular application of 1 μM α-helical CRF-(9-14) (α-hCRF), a selective CRF receptor antagonist, completely blocked the CRF-induced decrease in spike firing in the NMU mRNA-expressing neurons. Under voltage-clamp conditions, CRF (100 nM) significantly decreased the peak value of the T-type Ca(2+) currents by 35.6±7.8%. These findings suggest that CRF decreases neuronal excitability and diminishes T-type Ca(2+) currents in a population of rat PVN NMU phenotype neurons in vitro.

Neuromedin S regulates cardiovascular function through the sympathetic nervous system in mice

Intracerebroventricular (icv) injection of neuromedin S (NMS) in mice increased the heart rate in a dose-dependent manner. On the other hand, genetically NMS deficient mice (NMS-KO mice) exhibited a decreased heart rate and significant extension of the QRS and PR interval in the electrocardiogram complex. Although treatment with a parasympathetic nerve blocker, methylscopolamine, and a sympathetic nerve blocker, timolol, respectively increased and decreased the heart rate in both NMS-KO and wild-type mice, the extent of the decrease induced by timolol was smaller in NMS-KO than in wild-type mice. In addition, pretreatment with timolol completely inhibited the NMS-induced heart rate increase in wild-type mice. No expression of mRNA for NMS or the NMS receptor was evident in the heart by RT-PCR analysis. These results suggest that endogenous NMS may regulate cardiovascular function by activating the sympathetic nervous system.

Neuromedin U(2) receptor signaling mediates alteration of sleep-wake architecture in rats

Growing evidence indicates that neuromedin U (NmU) neuropeptide system plays an integral role in mediating the stress response through the corticotrophin-releasing factor (CRF) pathways. Stress is often associated with alteration in sleep-wake architecture both in human and laboratory animals. Here, we investigated whether activation of the NmU₂ receptor, a major high affinity receptor for NmU predominantly expressed in the brain, affects sleep behavior in rats. Effects of single (acute) intracebroventricular (icv) infusion of 2.5 nmol of the full agonists porcine NmU8 and rat NmU23 were assessed on sleep-wake architecture in freely moving rats, which were chronically implanted with EEG and EMG electrodes. In addition, repeated once daily administration of NmU8 at 2.5 nmol during 8 consecutive days (sub-chronic) was studied. Acute icv infusion of NmU23 elicited a robust alteration in sleep-wake architecture, namely enhanced wakefulness and suppressed sleep during the first 4h after administration. Acute infusion NmU8 had no effect on spontaneous sleep-wake architecture. However, sub-chronic icv infusion of NmU8 increased the amount of rapid eye movement (REM) sleep and intermediate stage (IS), while decreased light sleep. Additionally, NmU8 increased transitions from sleep states towards wakefulness suggesting a disruption in sleep continuity. The present results show that central-activation of NmU₂ receptor markedly reduced sleep duration and disrupted the mechanisms underlying NREM-REM sleep transitions. Given that sleep-wakefulness cycle is strongly influenced by stress and the role of NmU/NmU₂ receptor signaling in stress response, the disruption in sleep pattern associated with peptides species may support at least some signs of stress.

Neuromedin U: physiology, pharmacology and therapeutic potential

Neuromedin U (NmU), a multifunctional neuropeptide, belongs to a family of neuropeptides, the neuromedins. It is ubiquitously distributed with highest levels found in the gastrointestinal tract and pituitary. The conservation of structural elements of NmU across species, the widespread distribution of NmU and its receptors throughout the body point to a fundamental role in key physiological processes. Two G protein coupled receptors for NmU have been cloned NmU R1 and NmU R2. NmU R1 is expressed pre-dominantly in the periphery especially the gastrointestinal tract whereas NmU R2 is expressed pre-dominantly in the central nervous system. Current evidence suggests a role of NmU in pain, in regulation of feeding and energy homeostasis, stress, cancer, immune mediated inflammatory diseases like asthma, inflammatory diseases, maintaining the biological clock, in the regulation of smooth muscle contraction in the gastrointestinal and genitourinary tract, and in the control of blood flow and blood pressure. With the development of drugs selectively acting on receptors and knockout animal models, exact pathophysiological roles of NmU will become clearer.

Emerging pharmacology and physiology of neuromedin U and the structurally related peptide neuromedin S

Neuromedin U (NMU) has been paired with the G-protein-coupled receptors (GPRs) NMU(1) (formerly designated as the orphan GPR66 or FM-3) and NMU(2) (FM-4 or hTGR-1). Recently, a structurally related peptide, neuromedin S (NMS), which shares an amidated C-terminal heptapeptide motif, has been identified in both rat and human, and has been proposed as a second ligand for these receptors. Messenger RNA encoding NMU receptor subtypes shows differential expression: NMU(1) is predominantly expressed in peripheral tissues, particularly the gastrointestinal tract, whereas NMU(2) is abundant within the brain and spinal cord. NMU peptide parallels receptor distribution with highest expression in the gastrointestinal tract and specific structures within the brain, reflecting its major role in the regulation of energy balance. The NMU knockout mouse has an obese phenotype and, in agreement, the Arg165Trp amino acid variant of NMU-25 in humans, which is functionally inactive, co-segregated with childhood-onset obesity. Emerging physiological roles for NMU include vasoconstriction mediated predominantly via NMU(1) with nociception and bone remodelling via NMU(2). The NMU system has also been implicated in the pathogenesis of septic shock and cancers including bladder carcinoma and acute myeloid leukaemia. Intriguingly, NMS is more potent at NMU(2) receptors in vivo where it has similar central actions in suppression of feeding and regulation of circadian rhythms to NMU. Taken together with its vascular actions, NMU may be a functional link between energy balance and the cardiovascular system and may provide a future target for therapies directed against the disorders that comprise metabolic syndrome.

Autonomic and cardiovascular effects of central neuromedin U in rats

Previous studies have demonstrated that neuromedin U (NMU) affects cardiovascular functions such as blood pressure (BP) or heart rate (HR) in rats. Here, we examined the effects of the lateral cerebral ventricular (ICV) injection of various doses of NMU on renal sympathetic nerve activity (RSNA) and BP in urethane-anesthetized rats. ICV injection of NMU elevated RSNA, BP and HR in a dose-dependent manner. Moreover, neither ICV pretreatment of thioperamide, an antagonist of histaminergic H3-receptor, or of diphenhydramine, an antagonist of histaminergic H1-receptor, abolished increasing effects of NMU on RSNA, BP and HR In addition, ICV injection of NMU suppressed gastric vagal nerve activity (GVNA) and activated brown adipose tissue sympathetic nerve activity (BAT-SNA) of anesthetized rats, and elevated brown adipose tissue temperature (BAT-T) of conscious rats. Thus, these evidence suggest that NMU affects neural activities of autonomic nerves containing RSNA, GVNA or BAT-SNA, and BP by mediating central mechanism.

Centrally administered neuromedin U elevates plasma adrenaline by brain prostanoid TP receptor-mediated mechanisms in rats

Neuromedin U is a hypothalamic peptide involved in energy homeostasis and stress responses. The peptide, when administered intracerebroventricularly (i.c.v.), decreases food intake and body weight while increasing body temperature and heat production. We examined the effect of i.c.v. administered neuromedin U on plasma catecholamines with regard to the brain prostanoid using anesthetized rats. Neuromedin U (0.1, 0.5 and 1 nmol/animal, i.c.v.) effectively elevated plasma adrenaline (a maximal response was obtained at 0.5 nmol/animal), but had little effect on plasma noradrenaline. However, intravenously administered neuromedin U (0.5 nmol/animal) had no effect on plasma catecholamines. Neuromedin U (0.5 nmol/animal, i.c.v.)-induced elevation of plasma adrenaline was effectively reduced by intracerebroventricular pretreatments with indomethacin (an inhibitor of cyclooxygenase) (0.6 and 1.2 micromol/animal), furegrelate (an inhibitor of thromboxane A2 synthase) (0.9 and 1.8 micromol/animal) and (+)-S-145 (a blocker of prostanoid TP receptors) (250 and 625 nmol/animal), respectively. The neuromedin U-induced adrenaline response was also abolished by acute bilateral adrenalectomy. These results suggest that centrally administered neuromedin U evokes the secretion of adrenaline from the adrenal medulla by brain prostanoid TP receptor-mediated mechanisms in rats.

Paradoxical behavior of neuromedin U in isolated smooth muscle cells and intact tissue

Neuromedin U (NmU) is a neuropeptide showing high levels of structural conservation across different species. Since its discovery in 1985, NmU has been implicated in numerous physiological roles, including smooth muscle contraction, energy homeostasis, stress, intestinal ion transport, pronociception, and circadian rhythm. Two G-protein-coupled receptors have been identified for NmU and cloned from humans, rats, and mice. Recombinantly expressed NmU receptors couple to both Galpha(q/11) and Galpha(i) G-proteins, and NmU binds essentially irreversibly, preventing signaling to repetitive applications of NmU. However, it is unclear whether these properties reflect those of endogenously expressed NmU receptors or how these properties influence the functional consequences of NmU receptor signaling. Here, we have explored the signaling by rat NmU receptors expressed endogenously in cultured rat colonic smooth muscle cells and explore the functional consequence of this signaling by investigating the NmU-mediated contraction of ex vivo rat colonic smooth muscle preparations. We demonstrate that endogenous rat NmU receptors couple to both Galpha(q/11) and Galpha(i) G-proteins. Furthermore, we show complex patterns of Ca(2+) signaling, including oscillations, and provide evidence of essentially irreversible binding of NmU to smooth muscle cells. Challenge of either circular or longitudinal rat isolated colonic smooth muscle preparations with NmU resulted in robust contractions. Stimulation was direct, and paradoxically, repetitive applications of NmU mediated repetitive contractions with no evidence of desensitization, highlighting a major discrepancy in the behavior of NmU in single cells and in intact tissues. The reason for this discrepancy is presently unknown.

Endocrine and behavioral effects of neuromedin S

The present experiments focused on the effects of neuromedin S on hypothalamic-pituitary-adrenal (HPA) activation and behavior. The peptide (0.25-1 nmol) was administered intracerebroventricularly to rats, the behavior of which was monitored by means of telemetry, open field observations and an elevated plus-maze (EPM) test. Autonomic functions such as the temperature and the heart rate were recorded by telemetry. The action on the HPA axis was assessed via measurements of the plasma corticosterone and ACTH levels. To reveal the transmission of the endocrine responses, animals were pretreated with corticotrophin releasing hormone receptor (CRHR) antagonists (1 nmol). In the open field test, the animals were pretreated with either a CRHR(1) antagonist (antalarmin) or haloperidol (10 microg/kg), while in the EPM test they were pretreated with antalarmin or diazepam (1 mg/kg). The dopamine release from striatal and amygdala slices after peptide treatment was measured with a superfusion apparatus. Neuromedin S exerted dose-dependent effects on the HPA system, which were inhibited by antalarmin. It also activated grooming and decreased the entries to and time spent in the open arms during the EPM test. The grooming response was abolished by haloperidol and antalarmin pretreatment, while diazepam and antalarmin showed a tendency to attenuate the response evoked in the EPM test. In the superfusion studies, neuromedin S enhanced the dopamine release from the amygdala slices. These results demonstrate that neuromedin S stimulates the HPA axis through the CRHR(1) pathway and evokes stereotyped behavior and anxiety through mesolimbic dopamine and corticotrophin releasing hormone release.

Central control of bone remodeling by neuromedin U

Bone remodeling, the function affected in osteoporosis, the most common of bone diseases, comprises two phases: bone formation by matrix-producing osteoblasts and bone resorption by osteoclasts. The demonstration that the anorexigenic hormone leptin inhibits bone formation through a hypothalamic relay suggests that other molecules that affect energy metabolism in the hypothalamus could also modulate bone mass. Neuromedin U (NMU) is an anorexigenic neuropeptide that acts independently of leptin through poorly defined mechanisms. Here we show that Nmu-deficient (Nmu-/-) mice have high bone mass owing to an increase in bone formation; this is more prominent in male mice than female mice. Physiological and cell-based assays indicate that NMU acts in the central nervous system, rather than directly on bone cells, to regulate bone remodeling. Notably, leptin- or sympathetic nervous system-mediated inhibition of bone formation was abolished in Nmu-/- mice, which show an altered bone expression of molecular clock genes (mediators of the inhibition of bone formation by leptin). Moreover, treatment of wild-type mice with a natural agonist for the NMU receptor decreased bone mass. Collectively, these results suggest that NMU may be the first central mediator of leptin-dependent regulation of bone mass identified to date. Given the existence of inhibitors and activators of NMU action, our results may influence the treatment of diseases involving low bone mass, such as osteoporosis.

Identification and functional analysis of a novel ligand for G protein-coupled receptor, Neuromedin S

We identified a novel 36-amino acid neuropeptide in rat brain as an endogenous ligand for the G protein-coupled receptors FM-3/GPR66 and FM-4/TGR-1, which were identified to date as the neuromedin U (NMU) receptors, and designated this peptide neuromedin S (NMS) because it was specifically expressed in the suprachiasmatic nucleus (SCN) of the hypothalamus. NMS shared a C-terminal core structure with NMU. NMS mRNA was highly expressed in the central nervous system, spleen and testis. In rat brain, NMS expression was restricted to the ventrolateral portion of the SCN and has a diurnal peak under light/dark cycling, but remains stable under constant darkness. Intracerebroventricular (ICV) administration of NMS in rats induced nonphotic type phase shifts in the circadian rhythm of locomotor activity. ICV injection of NMS also decreased 12-h food intake during the dark period in rats. This anorexigenic effect was more potent than that observed with the same dose of NMU. ICV administration of NMS increased proopiomelanocortin (POMC) mRNA expression in the arcuate nucleus (Arc) and corticotropin-releasing hormone mRNA in the paraventricular nucleus, and induced c-Fos expression in the POMC neurons in the Arc. These findings suggest that NMS is implicated in the regulation of circadian rhythm and feeding behavior.

Cardiovascular actions of central neuropeptide W in conscious rats

Neuropeptide W (NPW) is a novel hypothalamic peptide that activates the orphan G protein-coupled receptors, GPR7 and GPR8. Two endogenous molecular forms of NPW that consist of 23- and 30-amino acid residues were identified. Intracerebroventricular (i.c.v.) administration of NPW is known to suppress spontaneous-feeding at dark-phase and fasting-induced food intake and to decrease body weight and plasma growth hormone and to increase prolactin and corticosterone; however, little is known about its effect on other physiological functions. We examined the effects of i.c.v. administration of NPW30 (0.3 and 3 nmol) on the mean arterial pressure (MAP), heart rate (HR), and plasma norepinephrine and epinephrine in conscious rats. NPW30 (3 nmol) provoked increases in MAP (85.12+/-3.16 to 106.26+/-2.66 mm Hg) and HR (305.75+/-13.76 to 428.45+/-26.82 beats/min) and plasma norepinephrine (138.1+/-18.1 to 297.2+/-25.9 pg/ml) and epinephrine (194.6+/-21.4 to 274.6+/-22.7 pg/ml). Intravenously administered NPW30 (3 nmol) had no significant effects on MAP and HR. These results indicate that central NPW30 increases sympathetic nervous outflow and affects cardiovascular function.

Species-dependent smooth muscle contraction to Neuromedin U and determination of the receptor subtypes mediating contraction using NMU1 receptor knockout mice

The peptide ligand neuromedin U (NMU) has been implicated in an array of biological activities, including contraction of uterine, intestinal and urinary bladder smooth muscle. However, many of these responses appear to be species-specific. This study was undertaken to fully elucidate the range of smooth muscle-stimulating effects of NMU in rats, mice and guinea-pigs, and to examine the extent of the species differences. In addition, the NMU1 receptor knockout mouse was used to determine which receptor subtype mediates the contractile responses generated by NMU in the mouse. A range of isolated organ in vitro bioassays were carried out, which were chosen to re-confirm previous literature reports (uterine and stomach fundus contraction) and also to explore potentially novel smooth muscle responses to NMU. This investigation uncovered a number of previously unidentified NMU-mediated responses: contraction of rat lower esophageal sphinster (LES), rat ileum, mouse gallbladder, enhancement of electrically evoked contractions in rat and mouse vas deferens, and a considerable degree of cross-species differences. Studies using the NMU1 receptor knockout mice revealed that in the mouse fundus and gallbladder assays the NMU contractile response was mediated entirely through the NMU1 receptor subtype, whereas, in assays of mouse uterus and vas deferens, the response to NMU was unchanged in the NMU1 receptor knockout mouse, suggesting that the NMU response may be mediated through the NMU2 receptor subtype. NMU receptor subtype-selective antagonists are required to further elucidate the role of the individual receptor subtypes.

Neuromedin U stimulates contraction of human long saphenous vein and gastrointestinal smooth muscle in vitro

The neuropeptide Neuromedin U (NMU) stimulates smooth muscle contraction, and modulates local blood flow and adrenocortical function via two endogenous receptors, NMU1 and NMU2. Although its amino-acid sequence is highly conserved across species, the physiological effects of NMU are variable between species and little is known of its effects on human tissues. We have examined the contractile effects of NMU-25 on human smooth muscles of the gastrointestinal (GI) tract (ascending colon, gallbladder) and long saphenous vein (LSV) using in vitro organ bath bioassays. From LSV, ileum, gallbladder, caecum and colon, NMU receptor transcripts were amplified by RT-PCR and expression levels were determined by semi-quantitative scanning densitometry. NMU-25 produced a concentration-dependent, sustained contraction of isolated smooth muscle (p[A](50)+/-s.e.m., ascending colon, 8.93+/-0.18; gallbladder, 7.01+/-0.15; LSV, 8.67+/-0.09). NMU1 and NMU2 receptor transcription was detected in all tissues; transcription of both receptors was similar in gallbladder, but NMU1 receptor transcription was predominant in the sigmoid colon and LSV. In summary, these studies indicate that NMU may control tone in the human GI tract and LSV through an action on smooth muscle. Development of NMU receptor subtype-selective ligands will aid the further elucidation of the physiological roles of NMU and its two receptors.

Chemical genetic analysis reveals the effects of NMU2R on the expression of peptide hormones

Neuromedin U 2 receptor (NMU2R) plays important roles for the regulation of food intake and body weight. However, the molecular mechanism underlying the action of NMU2R has not been clearly defined. We have taken chemical genetic approach to examine the involvement of peptides in the regulation of NMU2R effects. A cell-based reporter gene assay has been developed and used for the screening of human NMU2R agonist. Three natural product compounds, EUK2010, EUK2011 and EUK2012, were identified that could activate the reporter gene expression in the cell-based functional assay. Although these compounds showed high EC50 at hundreds micro-molar range, in vitro pharmacological analysis suggested that they were specific agonists for the human NMU2R. The natural compounds could decrease food intake and lead to the reduction of body weight in different animal models. To understand the molecular basis of the NMU2R regulation of food intake and body weight, we examined the expression of a number of key genes in hypothalamus and adipose tissues after oral administration of EUK2010 in mice. Our results demonstrated that the expression levels of a number of neuropeptide genes were altered after the treatment of EUK2010. Interestingly, EUK2010 increased the expression of Leptin in white fat. These results suggested that these peptides may participate in the regulation of NMU2R effects in mice.

Neuromedin U has a physiological role in the regulation of food intake and partially mediates the effects of leptin

Intracerebroventricular (ICV) administration of Neuromedin U (NMU), a hypothalamic neuropeptide, or leptin, an adipostat hormone released from adipose tissue, reduces food intake and increases energy expenditure. Leptin stimulates the release of NMU in vitro, and NMU expression is reduced in models of low or absent leptin. We investigated the role of NMU in mediating leptin-induced satiety. ICV administration of anti-NMU immunoglobulin G (IgG) (5 nmol) to satiated rats significantly increased food intake 4 h after injection, an effect seen for </=8 h after injection. ICV administration of NMU (1 nmol) to fasted rats reduced food intake 1 h after injection compared with control, an effect attenuated by pretreatment with anti-NMU IgG. ICV administration of leptin (0.625 nmol) reduced 24-h food intake. This was partially attenuated by the administration of anti-NMU IgG [24 h after onset of dark phase: vehicle, 22.5 +/- 2.0 g; leptin, 13.7 +/- 2.3 g (P < 0.005 vs. vehicle), leptin/NMU IgG, 19.4 +/- 1.3 g (P < 0.05 vs. leptin)]. Intraperitoneal administration of leptin (1.1 mg/kg body wt) reduced 24-h food intake. This was partially attenuated by ICV administration of anti-NMU IgG [24 h after onset of dark phase: vehicle, 31.4 +/- 4.9 g; leptin, 20.8 +/- 2.6 g (P < 0.01 vs. vehicle); leptin/NMU IgG, 28.7 +/- 1.1 g (P < 0.01 vs. leptin)]. These results suggest that NMU plays a physiological role in the regulation of appetite and partially mediates the leptin-induced satiety.

Neuromedin-U is regulated by the circadian clock in the SCN of the mouse

Neuromedin-U (NMU) has been reported to drive several physiological or behavioural responses following i.c.v. injection of the peptide into the third ventricle of rodent brains. Many of these responses are mediated through a change in corticotrophin-releasing factor (CRF) output from the paraventricular nucleus (PVN). A number of the physiological or behavioural responses are regulated in a circadian manner, e.g. feeding. We have previously reported NMU gene expression in the suprachiasmatic nucleus (SCN) and NMU-2 receptor expression in the PVN, dorsal medial hypothalamus (DMH) and other regions of the mouse brain. We therefore hypothesized that NMU would be regulated by the circadian clock and may consequently drive a circadian rhythm of CRF expression in the PVN. Here we report that NMU is regulated in a circadian manner with peak expression during the light phase of a light-dark cycle. In C3H mice held in constant darkness, the NMU rhythm free runs with a period predicted by the free running period of locomotor activity in this mouse. The NMU mRNA transcript colocalizes with cells expressing AVP in the SCN and shows a coincident rhythm of expression with AVP. On the other hand, CRF did not express a circadian rhythm of expression in a light-dark cycle, although a rhythm was evident in constant darkness with a peak of expression prior to the rise of NMU in the same conditions. This would suggest that the circadian rhythm in NMU expression in the SCN does not drive a circadian rhythm in CRF in the PVN to be translated into physiological and behavioural responses mediated by NMU.

Neuromedin U receptor-2 mRNA and HCN channels mRNA expression in NMU-sensitive neurons in rat hypothalamic paraventricular nucleus

We have characterized the neuromedin U (NMU)-sensitive neurons in the rat paraventricular nucleus (PVN) using whole-cell patch-clamp recordings and single-cell reverse transcription-multiplex polymerase chain reaction (single-cell RT-mPCR). Following completion of whole-cell recording, the NMU-sensitive neurons were examined for oxytocin (OT), vasopressin (VP), and corticotrophin-releasing hormone (CRH) mRNA expression using single-cell RT-mPCR. Of the NMU-sensitive neurons (n=23), 82% expressed OT mRNA, 9% expressed VP mRNA, 9% did not express the detected specific phenotypes mRNA. Further, the NMU-sensitive neurons (23/23) predominantly expressed NMU-receptor 2 (NMUR-2) mRNA, co-expressed HCN1 channel mRNA, HCN2 channel mRNA, and HCN3 channel mRNA but not HCN4 channel mRNA. These results suggest that NMU modulates the function of the PVN putative parvocellular neurons and is involved in the regulation of OTergic and VPergic neurons by enhanced HCN ion channels activity via NMU-receptor 2.

Neuromedin U elicits cytokine release in murine Th2-type T cell clone D10.G4.1

Neuromedin U (NmU), originally isolated from porcine spinal cord and later from other species, is a novel peptide that potently contracts smooth muscle. NmU interacts with two G protein-coupled receptors designated as NmU-1R and NmU-2R. This study demonstrates a potential proinflammatory role for NmU. In a mouse Th2 cell line (D10.G4.1), a single class of high affinity saturable binding sites for (125)I-labeled NmU (K(D) 364 pM and B(max) 1114 fmol/mg protein) was identified, and mRNA encoding NmU-1R, but not NmU-2R, was present. Competition binding analysis revealed equipotent, high affinity binding of NmU isopeptides to membranes prepared from D10.G4.1 cells. Exposure of these cells to NmU isopeptides resulted in an increase in intracellular Ca(2+) concentration (EC(50) 4.8 nM for human NmU). In addition, NmU also significantly increased the synthesis and release of cytokines including IL-4, IL-5, IL-6, IL-10, and IL-13. Studies using pharmacological inhibitors indicated that maximal NmU-evoked cytokine release required functional phospholipase C, calcineurin, MEK, and PI3K pathways. These data suggest a role for NmU in inflammation by stimulating cytokine production by T cells.

Identification of neuromedin S and its possible role in the mammalian circadian oscillator system

The discovery of neuropeptides has resulted in an increased understanding of novel regulatory mechanisms of certain physiological phenomena. Here we identify a novel neuropeptide of 36 amino-acid residues in rat brain as an endogenous ligand for the orphan G protein-coupled receptor FM-4/TGR-1, which was identified to date as the neuromedin U (NMU) receptor, and designate this peptide 'neuromedin S (NMS)' because it is specifically expressed in the suprachiasmatic nuclei (SCN) of the hypothalamus. NMS shares a C-terminal core structure with NMU. The NMS precursor contains another novel peptide. NMS mRNA is highly expressed in the central nervous system, spleen and testis. In rat brain, NMS expression is restricted to the core of the SCN and has a diurnal peak under light/dark cycling, but remains stable under constant darkness. Intracerebroventricular administration of NMS in rats activates SCN neurons and induces nonphotic type phase shifts in the circadian rhythm of locomotor activity. These findings suggest that NMS in the SCN is implicated in the regulation of circadian rhythms through autocrine and/or paracrine actions.

Signaling and ligand binding by recombinant neuromedin U receptors: evidence for dual coupling to Galphaq/11 and Galphai and an irreversible ligand-receptor interaction

The neuropeptide neuromedin U (NmU) shows considerable structural conservation across species. Within the body, it is widely distributed and in mammals has been implicated in physiological roles, including the regulation of feeding, anxiety, pain, blood flow, and smooth muscle contraction. Human NmU-25 (hNmU-25) and other NmU analogs were recently identified as ligands for two human orphan G protein-coupled receptors, subsequently named hNmU-R1 and hNmU-R2. These receptors have approximately 50% amino acid homology, and, at least in mammalian species, NmU-R1 and NmU-R2 are expressed predominantly in the periphery and central nervous system, respectively. Here, we have characterized signaling mediated by hNmU-R1 and hNmU-R2 expressed as recombinant proteins in human embryonic kidney 293 cells, particularly to define their G protein coupling and the activation and regulation of signal transduction pathways. We show that these receptors couple to both Galpha(q/11) and Galpha(i). Activation of either receptor type causes a pertussis toxin-insensitive activation of both phospholipase C and mitogen activated-protein kinase and a pertussis toxin-sensitive inhibition of adenylyl cyclase with subnanomolar potency for each. Activation of phospholipase C is sustained, but despite this capacity for prolonged receptor activation, repetitive application of hNmU-25 does not cause repetitive intracellular Ca2+ signaling by either recombinant receptors or those expressed endogenously in isolated smooth muscle cells from rat fundus. Using several strategies, we show this to be a consequence of essentially irreversible binding of hNmU-25 to its receptors and that this is followed by ligand internalization. Despite structural differences between receptors, there were no apparent differences in their activation, coupling, or regulation.

Chronic administration of NMU into the paraventricular nucleus stimulates the HPA axis but does not influence food intake or body weight

Hypothalamic neuromedin U (NMU) appears to have a role in the regulation of appetite and the hypothalamo-pituitary-adrenal (HPA) axis. Acute administration of NMU into the paraventricular nuclei (iPVN) increases plasma adrenocorticotrophic hormone and corticosterone, and inhibits food intake in fasted rats. No studies have as yet investigated the chronic effects of centrally administered NMU. We investigated the effect of twice-daily iPVN injections of 0.3 nmol NMU for 7 days on food intake, body weight, the HPA axis, and behavior in freely fed rats. Chronic iPVN NMU was not associated with a decrease in food intake or body weight. Chronic iPVN NMU produced a typical behavioral response on day 1 and day 4 of the study, and resulted in the elevation of plasma corticosterone present 18 h after the final injection. These results suggest NMU may have a role in the regulation of the HPA axis and behavior.

The gut-brain peptide neuromedin U is involved in the mammalian circadian oscillator system

Immunohistochemical analysis revealed the presence of a gut-brain peptide, neuromedin U (NMU), in the suprachiasmatic nucleus (SCN), which is the site of the master circadian oscillator. The expression of NMU mRNA exhibited a circadian rhythm, with the peak expression in the SCN occurring at CT4-8h. The two NMU-binding receptors (NMU-R1 and NMU-R2) were also expressed in the SCN, but their phase angles were different. Intracerebroventricular injection (ICV) of NMU induced the expression of Fos protein in the SCN cells and caused a phase-dependent phase shift of the circadian locomotor activity rhythm. The magnitude of the phase shift was dose dependent. This NMU-induced phase shift was of the nonphotic type. Quantitative reverse transcriptase-polymerase chain reaction (RT-PCR) analysis revealed increases in the expression in the SCN of immediate early genes, such as c-fos, NGFI-A, NGFI-B, and JunB. Furthermore, ICV injection of NMU increased the expression of Per1, but not Per2, in the SCN. These results indicate that NMU may play some important role in the circadian oscillator by exerting an autocrine or paracrine action in the SCN.

Neuromedin U and its receptors: structure, function, and physiological roles

Neuromedin U (NmU) is a structurally highly conserved neuropeptide. It is ubiquitously distributed, with highest levels found in the gastrointestinal tract and pituitary. Originally isolated from porcine spinal cord, it has since been isolated and sequenced from several species. Amino acid alignment of NmU from different species reveals a high level of conservation, and particular features within its structure are important for bioactivity. Specifically, the C terminus, including a terminal asparagine-linked amidation, is essential for activity. The conservation of NmU across a wide range of species indicates a strong evolutionary pressure to conserve this peptide and points to its physiological significance. Despite this, the precise physiological and indeed pathophysiological roles of NmU have remained elusive. NmU was first isolated based on its ability to contract rat uterine smooth-muscle (hence the suffix "U") and has since been implicated in the regulation of smooth-muscle contraction, blood pressure and local blood flow, ion transport in the gut, stress responses, cancer, gastric acid secretion, pronociception, and feeding behavior. Two G-protein-coupled receptors for NmU have recently been cloned. These receptors are widespread throughout the body but have differential distributions suggesting diverse but specific roles for the receptor subtypes. Here we detail the isolation and characterization of NmU, describe the discovery, cloning, distribution, and structure of its two receptors, and outline its possible roles in both physiology and pathophysiology. Ultimately the development of receptor-specific ligands and the generation of animals in which the receptors have been selectively knocked out will hopefully reveal the true extent of the biological roles of NmU and suggest novel therapeutic indications for selective activation or blockade of either of its receptors.

Fos expression in CRF-containing neurons in the rat paraventricular nucleus after central administration of neuromedin U

We examined the effects of centrally administered neuromedin U (NMU) on corticotrophin-releasing factor (CRF)-containing neurons in the hypothalamic paraventricular nucleus (PVN) of rats, using double immunohistochemistry for CRF and Fos. Almost all CRF-containing neurons in the parvocellular divisions of the PVN expressed Fos-like immunoreactivity 90 min after intracerebroventricular administration of NMU (3 nmol/rat). This results suggest the possibility that central NMU may be involved in stress-induced activation of CRF-containing neurons in the PVN.

Hypotensive effects of neuromedin U microinjected into the cardiovascular-related region of the rat nucleus tractus solitarius

Neuromedin U (NMU) is a brain-gut peptide with potent contractile effects on the uterus and smooth muscle. Intracerebroventricular injection of NMU reportedly decreased food intake and body-weight gain in the rat. We evaluated the effects of NMU delivered by microinjection into the rat nucleus tractus solitarius (NTS) on cardiovascular responses. At the concentrations used (5, 10 or 50 pmol), the intra-NTS injection of NMU in artificial cerebrospinal fluid produced a significant reduction in both the mean arterial pressure and heart rate. The hypotensive responses were dose dependent. Our findings suggest that NMU may act as a neurotransmitter or neuromodulative substance that causes excitation of neurons in the NTS and that it may play a role in cardiovascular regulation in vivo.

Pro-nociceptive effects of neuromedin U in rat

The neuropeptide neuromedin U (NMU) has been shown to have significant effects on cardiovascular, gastrointestinal and CNS functions. The peptide was first isolated from the porcine spinal cord and later shown to be present in spinal cords of other species. Little is known about the distribution of neuromedin U receptors (NMURs) in the spinal cord and the spinal action of the peptide. Here we report on the expression of NMURs and a potential role in nociception in the rat spinal cord using a combination of behavioral and electrophysiological studies. Receptor autoradiography showed that NMU-23 binding was restricted to the superficial layers of spinal cord, a region known to be involved in the control of nociception. In situ hybridization analysis indicated the mRNA of NMUR2 was located in the same region (laminae I and IIo) as NMU-23 binding, while the mRNA for NMU receptor 1 was observed in a subpopulation of small diameter neurons of dorsal root ganglia. Intrathecal (i.t.) administration of neuromedin U-23 (0.4-4.0 nmol/10 microl) dose-dependently decreased both the mechanical threshold to von Frey hair stimulation and the withdrawal latency to a noxious thermal stimulus. Mechanical allodynia was observed between 10 and 120 min, peaking at 30 min and heat hyperalgesia was observed 10-30 min after i.t. administration of NMU-23. A similar mechanical allodynia was also observed following i.t. administration of NMU-8 (0.4-4 nmol/10 microl). A significant enhancement of the excitability of flexor reflex was induced by intrathecal administration of NMU-23 (4 nmol/10 microl). Evoked responses to touch and pinch stimuli were increased by 439+/-94% and 188+/-36% (P<0.01, n=6) respectively. The behavioral and electrophysiological data demonstrate, for the first time, a pro-nociceptive action of NMU. The restricted distribution of NMU receptors to a region of the spinal cord involved in nociception suggests that this peptide receptor system may play a role in nociception.