Evidence for Y1 and Y2 subtypes of neuropeptide Y receptors linked to opposing postjunctional effects observed in rat cardiac myocytes

Exploring the Therapeutic Effect of Neurotrophins and Neuropeptides in Neurodegenerative Diseases: at a Glance

Neurotrophins and neuropeptides are the essential regulators of peripheral nociceptive nerves that help to induce, sensitize, and maintain pain. Neuropeptide has a neuroprotective impact as it increases trophic support, regulates calcium homeostasis, and reduces excitotoxicity and neuroinflammation. In contrast, neurotrophins target neurons afflicted by ischemia, epilepsy, depression, and eating disorders, among other neuropsychiatric conditions. Neurotrophins are reported to inhibit neuronal death. Strategies maintained for "brain-derived neurotrophic factor (BDNF) therapies" are to upregulate BDNF levels using the delivery of protein and genes or compounds that target BDNF production and boosting BDNF signals by expanding with BDNF mimetics. This review discusses the mechanisms of neurotrophins and neuropeptides against acute neural damage as well as highlighting neuropeptides as a potential therapeutic agent against Parkinson's disease (PD), Huntington's disease (HD), Alzheimer's disease (AD), and Machado-Joseph disease (MJD), the signaling pathways affected by neurotrophins and their receptors in both standard and diseased CNS systems, and future perspectives that can lead to the potent application of neurotrophins and neuropeptides in neurodegenerative diseases (NDs).

Co-transmission of neuropeptides and monoamines choreograph the C. elegans escape response

Co-localization and co-transmission of neurotransmitters and neuropeptides is a core property of neural signaling across species. While co-transmission can increase the flexibility of cellular communication, understanding the functional impact on neural dynamics and behavior remains a major challenge. Here we examine the role of neuropeptide/monoamine co-transmission in the orchestration of the C. elegans escape response. The tyraminergic RIM neurons, which coordinate distinct motor programs of the escape response, also co-express the neuropeptide encoding gene flp-18. We find that in response to a mechanical stimulus, flp-18 mutants have defects in locomotory arousal and head bending that facilitate the omega turn. We show that the induction of the escape response leads to the release of FLP-18 neuropeptides. FLP-18 modulates the escape response through the activation of the G-protein coupled receptor NPR-5. FLP-18 increases intracellular calcium levels in neck and body wall muscles to promote body bending. Our results show that FLP-18 and tyramine act in different tissues in both a complementary and antagonistic manner to control distinct motor programs during different phases of the C. elegans flight response. Our study reveals basic principles by which co-transmission of monoamines and neuropeptides orchestrate in arousal and behavior in response to stress.

Neuropeptide Y (NPY) inhibits spontaneous contraction of the mouse atrium by possible activation of the NPY1 receptor

Neuropeptide Y (NPY) causes various central and peripheral actions through activation of G-protein-coupled NPY receptors. Although a species-dependent difference in cardiac actions of NPY has been reported, the responses to NPY have not been examined in mice, widely used experimental animals. This study aimed to clarify the responses to NPY and the receptor subtype involved in the responses in mouse atrium. Neuropeptide Y caused negative inotropic and negative chronotropic actions in spontaneous beating right atria. Negative inotropic actions were more marked than negative chronotropic actions. Therefore, negative inotropic actions were studied in detail for evaluation of the NPY-induced cardiac actions in mouse atrium. Neuropeptide Y-induced negative inotropic actions were not affected by atropine but were abolished in the atria from pertussis toxin-treated mice. In isolated atrial preparations from reserpine-treated mice, NPY-induced negative inotropic actions were significantly attenuated. [Leu31, Pro34]-NPY, but not peptide YY, was effective in decreasing spontaneous contraction in atrial preparations. Although Y₁ , Y₂ , Y₄ and Y₅ receptor mRNAs were expressed almost equally in the brain, NPY₁ receptor mRNA was dominantly expressed in the atrium. In conclusion, NPY caused negative inotropic and chronotropic actions through activation of the Y₁ receptor in the mouse atrium. A high expression level of Y₁ mRNA in the atrium suggests a functional role of NPY in the regulation of mouse cardiac contraction.

Neuropeptide Y and its receptors in ventricular endocardial endothelial cells

Endocardial endothelial cells (EECs) constitute an important component of the heart. These cells form a monolayer that covers the cavities of the right (EECRs) and left (EECLs) ventricles. They play an important role in cardiac excitation-contraction coupling via their secretion of cardioactive factors such as neuropeptide Y (NPY). They also contribute to cardiac pathology such as arrhythmia, hypertrophy, and heart failure. Differences between EECRs and EECLs contribute to tuning of circulating factors at the entry and exit of the ventricles. NPY, via activation of its receptors, modulates the excitation-secretion coupling of EECs, thus, indirectly modulating cardiac function and remodeling.

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.

Therapeutic potential of neuropeptide Y (NPY) receptor ligands

Neuropeptide Y (NPY) is widely distributed in the human body and contributes to a vast number of physiological processes. Since its discovery, NPY has been implicated in metabolic regulation and, although interest in its role in central mechanisms related to food intake and obesity has somewhat diminished, the topic remains a strong focus of research concerning NPY signalling. In addition, a number of other uses for modulators of NPY receptors have been implied in a range of diseases, although the development of NPY receptor ligands has been slow, with no clinically approved receptor therapeutics currently available. Nevertheless, several interesting small molecule compounds, notably Y2 receptor antagonists, have been published recently, fueling optimism in the field. Herein we review the role of NPY in the pathophysiology of a number of diseases and highlight instances where NPY receptor signalling systems are attractive therapeutic targets.

Neuropeptide Y (NPY) and NPY receptors in the cardiovascular system: implication in the regulation of intracellular calcium

The 3-dimensional confocal microscopy technique has allowed us to identify the presence of yet another cardioactive factor and its receptor, namely neuropeptide Y (NPY) and its Y1 receptor, at the level of vascular smooth muscle cells and heart cells including endocardial endothelial cells (EECs). Using this technique, we also demonstrated that NPY is able to induce an increase in both cytosolic and nuclear calcium in all these cell types. Furthermore, besides being expressed at the level of EECs, NPY is also released from these cells following a sustained increase of intracellular Ca2+. This suggests the ability of NPY to contribute to the regulation of the excitation-secretion coupling of EECs and the excitation-contraction coupling of cardiomyocytes and vascular smooth muscle cells.

Modulation of contractile function through neuropeptide Y receptors during development of cardiomyocyte hypertrophy

Severity of left ventricular hypertrophy (LVH) correlates with elevated plasma levels of neuropeptide Y (NPY) in hypertension. NPY elicits positive and negative contractile effects in cardiomyocytes through Y(1) and Y(2) receptors, respectively. This study tested the hypothesis that NPY receptor-mediated contraction is altered during progression of LVH. Ventricular cardiomyocytes were isolated from spontaneously hypertensive rats (SHRs) pre-LVH (12 weeks), during development (16 weeks), and at established LVH (20 weeks) and age-matched normotensive Wistar Kyoto (WKY) rats. Electrically stimulated (60 V, 0.5 Hz) cell shortening was measured using edge detection and receptor expression determined at mRNA and protein level. The NPY and Y(1) receptor-selective agonist, Leu(31)Pro(34)NPY, stimulated increases in contractile amplitude, which were abolished by the Y(1) receptor-selective antagonist, BIBP3226 [R-N(2)-(diphenyl-acetyl)-N-(4-hydroxyphenyl)methyl-argininamide)], confirming Y(1) receptor involvement. Potencies of both agonists were enhanced in SHR cardiomyocytes at 20 weeks (2300- and 380-fold versus controls). Maximal responses were not attenuated. BIBP3226 unmasked a negative contraction effect of NPY, elicited over the concentration range (10(-12) to 3 x 10(-9) M) in which NPY and PYY(3-36) attenuated the positive contraction effects of isoproterenol, the potencies of which were increased in cardiomyocytes from SHRs at 20 weeks (175- and 145-fold versus controls); maximal responses were not altered. Expression of NPY-Y(1) and NPY-Y(2) receptor mRNAs was decreased (55 and 69%) in left ventricular cardiomyocytes from 20-week-old SHRs versus age-matched WKY rats; parallel decreases (32 and 80%) were observed at protein level. Enhancement of NPY potency, producing (opposing) contractile effects on cardiomyocytes together with unchanged maximal response despite reduced receptor number, enables NPY to contribute to regulating cardiac performance during compensatory LVH.

Roles of nuclear NPY and NPY receptors in the regulation of the endocardial endothelium and heart functionThis paper is one of a selection of papers published in this Special issue, entitled Second Messengers and Phosphoproteins—12th International Conference

It is now well accepted that the heart is a multifunctional organ in which endothelial cells, and more particularly endocardial endothelial cells (EECs), seem to play an important role in regulating and maintaining cardiac excitation–contraction coupling. Even if major differences exist between vascular endothelial cells (VECs) and EECs, all endothelial cells including EECs release a variety of auto- and paracrine factors such as nitric oxide, endothelin-1, angiotensin II, and neuropeptide Y. All these factors were reported to affect cardiomyocyte contractile performance and rhythmicity. In this review, findings on the morphology of EECs, differences between EECs and other types of endothelial cells, interactions between EECs and the adjacent cardiomyocytes, and effects of NPY on the heart will be presented. We will also show evidence on the presence and localization of NPY and the Y1receptor in the endocardial endothelium and discuss their role in the regulation of cytosolic and nuclear free calcium.

Presence of neuropeptide Y and the Y1 receptor in the plasma membrane and nuclear envelope of human endocardial endothelial cells: modulation of intracellular calcium

The aims of the present study were to investigate the presence and distribution of NPY and the Y1 receptor in endocardial endothelial cells (EECs), to verify if EECs can release NPY, and to determine if the effect of NPY on intracellular calcium is mediated via the Y1 receptor. Immunofluorescence, 3-D confocal microscopy and radioimmunoassay techniques were used on 20-week-old human fetal EECs. Our results showed that NPY and the Y1 receptor are present in human EECs (hEECs) and that their distributions are similar, the fluorescence labelling being higher in the nucleus and more particularly at the level of the nuclear envelope when compared with the cytosol. Using radioimmunoassay, we demonstrated that EECs are a source of NPY and can secrete this peptide upon a sustained increase of intracellular calcium ([Ca]i). Using fluo-3 and 3-D confocal microscopy technique, superfusion of hEECs as well as EECs isolated from rat adult hearts with increasing concentrations of NPY induced a dose-dependent, sustained increase in free cytosolic and nuclear Ca2+ levels. This effect of NPY on EEC [Ca]i was completely reversible upon washout of NPY and was partially blocked by BIBP3226, a selective Y1 receptor antagonist. The results suggest that NPY and Y1 receptors are present in the EECs of 20-week-old human fetal heart and they share the same distribution and localization inside the cell. In addition, EECs are able to secrete NPY in response to an increase in [Ca]i, and the Y1 receptor as well as other NPY receptors seem to participate in mediating the effects of NPY on [Ca]i in these cells. Thus, NPY released by EECs may modulate excitation-secretion coupling of these cells.

Distribution of neuropeptide Y Y1 and Y2 receptors in the postmortem human heart

In the present study, we present for the first time the presence and distribution of neuropeptide Y (NPY) receptors Y1 and Y2 in the human postmortem heart using specific antibodies raised against extracellular parts of the receptors. A more intensive staining against the Y2 than against the Y1 receptors was detected on both atrial and ventricular cardiomyocytes. Immunoreactivity against both receptors was identified on both conducting fibers and cardiac nerves. More vessels stained positively for the Y2 than for the Y1 receptor, but the Y1 receptors were more abundant in subendocardial than subepicardial vessels of the left ventricular wall.

Induction of hypertrophic responsiveness of cardiomyocytes to neuropeptide Y in response to pressure overload

To determine whether neuropeptide Y (NPY)-related mechanisms become activated with progression of cardiac hypertrophy in vivo, protein mass and de novo protein synthesis (incorporation of [(14)C]Phe, 0.1 muCi ml(-1)) were assessed in cardiomyocytes, obtained from spontaneously hypertensive rats (SHRs) and normotensive Wistar Kyoto rats (8, 12, 16, 20, and 24 weeks of age), and cultured for 24 h. NPY (10(-8) M) increased protein mass of cardiomyocytes from 16-week-old SHRs by 9.2 +/- 2.1% (n = 8, P < 0.05). De novo protein synthesis was increased maximally in SHRs at 12, 16, and 20 weeks (P < 0.05, n = 8) in response to NPY by 12.6 +/- 2.1% (10(-6) M), 20.1 +/- 4.2% (10(-8) M), and 9.4 +/- 1.8% (10(-7) M), respectively. Peptide YY(3-36), (PYY(3-36)), which displays selectivity for NPY Y(2) and NPY Y(5) receptors, and the NPY Y(5)-selective agonist [D-Trp(34)]-NPY increased de novo protein synthesis maximally by 16.2 +/- 5.1% (10(-7) M; n = 4, P < 0.05) and 17.8 +/- 5.2% (10(-6) M; n = 7, P < 0.05), respectively, in SHRs at 16 weeks, whereas [Leu(31)Pro(34)]-NPY (< or =10(-6) M), which displays some activity at NPY Y(1) and NPY Y(4) receptors, did not. The NPY Y(1)-selective antagonist BVD-42 (2 x 10(-7) M) and the NPY Y(2)-selective antagonist BIIE0246 (2 x 10(-7) M) did not attenuate responses to NPY (10(-7) M) and PPY(3-36) (10(-7) M). These data indicate that hypertrophic responsiveness to NPY, mediated via NPY Y(5) receptors, is induced transiently in SHR cardiomyocytes subsequent to onset of cardiomyocyte hypertrophy in response to pressure overload.

Effects of ACE inhibitor and beta-adrenergic blocker on plasma NPY and NPY receptors in aortic vascular smooth muscle cells from SHR and WKY rats

To investigate the effects of the angiotensin-converting enzyme (ACE) inhibitor, peridopril, and the beta-adrenergic blocker, metoprolol, on plasma neuropeptide Y (NPY), and NPY receptors in aortic vascular smooth muscle cells (VSMCs) from normotensive Wistar-Kyoto (WKY) rats and spontaneously hypertensive rats (SHR), both strains of rats were fed with different doses of the drugs (peridopril or metoprolol) for 7 days to get the optimal dosages. After that, 18 male SHR and 18 male age-matched WKY rats were divided into three groups: control, peridopril (2mg/kg/day) and metoprolol (2mg/kg/day). After two months of treatment, VSMCs were isolated from the media layer of the aortic wall. Results showed that the SHRs had higher plasma concentrations and binding sites/affinity for NPY as compared to WKY rats. Peridopril dose-dependently decreased plasma NPY concentrations in WKY rats, and the absolute changes of plasma NPY were greater in SHRs than in WKY rats. Metoprolol showed none of these changes. Metoprolol decreased while peridopril increased NPY binding sites/affinity in SHRs. This indicated that lowered plasma NPY concentration and decreased NPY receptor in VSMCs, might play some roles in the anti-hypertensive mechanisms mediated by ACE inhibitor and beta-adrenergic blockers.

The direct stimulation of Gi proteins by neuropeptide Y (NPY) in the rat left ventricle

Neuropeptide Y (NPY) is a neuropeptide with high distribution in the cardiovascular system of mammals, where it modulates heart and vessel contractility. In the rat heart, the presence of at least three different NPY receptor subtypes has been hypothesised. Notwithstanding this, receptor activation might not be the only mechanism responsible for the complex cardiac effects of the peptide. In this study, we investigated the effect of NPY on the GTPase activity of G-proteins in the rat left ventricle as a possible alternative mechanism of action for the peptide in the rat heart. Our results show that NPY, but also the neuropeptide fragment (18-36) (NPY (18-36)), stimulated the basal, spontaneous GTPase activity of ventricle membranes only when it was measured under the condition of an absence of Mg2+. This stimulation was resistant to BIBP3226 a non-peptidergic antagonist at Y1 receptors, but it was significantly reduced in membranes treated with selective antibodies against the Gialpha subunits. NPYs effect was concentration-dependent with a maximum of activity at 10nM. At this concentration, NPY (and NPY 18-36) was able to inhibit forskolin (FSK)-induced cyclic adenosine-5'-monophosphate (cAMP) elevation in rat left ventricle slices. Our results assess that NPY in the rat heart is able to activate the GTPase activity of Gi proteins, in a receptor-independent way.

Neuropeptide Y Y(1) receptor regulates protein turnover and constitutive gene expression in hypertrophying cardiomyocytes

Increased levels of neuropeptide Y correlate with severity of left ventricular hypertrophy in vivo. At cardiomyocyte level, hypertrophy is characterised by increased mass and altered phenotype. The aims were to determine the contributions of increased synthesis and reduced degradation of protein to neuropeptide Y-mediated increase in mass, assess effects on gene expression, and characterise neuropeptide Y Y receptor subtype involvement. Neuropeptide Y (10 nM) increased protein mass of adult rat ventricular cardiomyocytes maintained in culture (24 h) (16%>basal) and de novo protein synthesis (incorporation of [(14)C]phenylalanine) (18%>basal). Neuropeptide Y (100 nM) prevented degradation of existing protein at 8 h. Actinomycin D (5 microM) attenuated increases in protein mass to neuropeptide Y (< or = 1 nM) but not to neuropeptide Y (10 nM). [Leu(31), Pro(34)]neuropeptide Y (10 nM), an agonist at neuropeptide Y Y(1) receptors, increased protein mass (25%>basal) but did not stimulate protein synthesis. Neuropeptide Y-(3-36) (10 nM), an agonist at neuropeptide Y Y(2) receptors, increased protein mass (29%>basal) and increased protein synthesis (13%>basal), respectively. Actinomycin D (5 microM) abolished the increase in protein mass elicited by neuropeptide Y-(3-36) but not that by [Leu(31), Pro(34)]neuropeptide Y. BIBP3226 [(R)-N2-(diphenylacetyl)-N-(4-hydroxyphenylmethyl)-D-arginine amide] (1 microM), a neuropeptide Y Y(1) receptor subtype-selective antagonist, and T(4) [neuropeptide Y-(33-36)](4), a neuropeptide Y Y(2) receptor subtype-selective antagonist, attenuated the increase in protein mass to 100 nM neuropeptide Y by 68% and 59%, respectively. Neuropeptide Y increased expression of the constitutive gene, myosin light chain-2 (MLC-2), maximally at 12 h (4.7-fold>basal) but did not induce (t< or = 36 h) expression of foetal genes (atrial natriuretic peptide (ANP), skeletal-alpha-actin and myosin heavy chain-beta). This increase was attenuated by 86% and 51%, respectively, by BIBP3226 (1 microM) and T(4) [neuropeptide Y-(33-36)](4) (100 nM). [Leu(31), Pro(34)]neuropeptide Y (100 nM) (2.4-fold>basal) and peptide YY-(3-36) (100 nM) (2.3 fold>basal) increased expression of MLC-2 mRNA at 12 h. In conclusion, initiation of cardiomyocyte hypertrophy by neuropeptide Y requires activation of both neuropeptide Y Y(1) and neuropeptide Y Y(2) receptors and is associated with enhanced synthesis and attenuated degradation of protein together with increased expression of constitutive genes but not reinduction of foetal genes.

Neuropeptide Y increases 4-aminopyridine-sensitive transient outward potassium current in rat ventricular myocytes

1. The modulation of 4-aminopyridine sensitive transient outward potassium current (4-AP I(to)) by neuropeptide Y (NPY) (100 nM) in rat ventricular myocytes was examined using the whole cell voltage-clamp technique. 2. Continuous exposure to NPY (100 nM) for 3 - 6 h significantly increased 4-AP I(to) density. The stimulation of 4-AP I(to) density by NPY was concentration-dependent (EC(50)=10 nM). 3. In the presence of BIBP 3226, an NPY receptor antagonist that binds selectively to NPY Y1-receptors, the effect of NPY on 4-AP I(to) density was maintained. However, in the presence of BIIE 0246, a highly selective non-peptide NPY Y2-receptor antagonist, NPY was unable to increase 4-AP I(to) density. 4. The effect of NPY on 4-AP I(to) density was prevented by pretreatment with 500 ng ml(-1) pertussis toxin (PTX) and by the specific protein kinase C (PKC) inhibitor, calphostin C (100 nM). 5. Thus, short term exposure to NPY induces an increase of 4-AP I(to) density in rat ventricular myocytes mediated by Y2-receptors and involving the action of PKC via a PTX-sensitive signalling cascade.

The signal transduction pathway causing the synergistic hypertrophic effects of neuropeptide Y and norepinephrine on primary cardiomyocyte

To investigate the synergistic hypertrophic effects of neuropeptide Y (NPY) and norepinephrine (NE) and its possible signal transduction pathway on primary cardiomyocytes, neonatal cardiomyocytes were exposed to NPY, NE or angiotensin II (AnII). All three agonists induced hypertrophic effects, stimulated protein kinase C (PKC) and activated mitogen-activated protein kinase (MAPK). Moreover, NPY at sub-optimal concentration potentiated NE-, not AnII-, induced all of the above effects. Pretreatment with phorbol 12-myristate 13-acetate (PMA) completely abolished these effects for both NE and NPY. NPY potentiation was calcium-independent and pertussis toxin (PTX)-sensitive, and was different from NPY direct hypertrophic effect on cardiomyocyte, as PTX only partially abolished NPY-induced hypertrophic effects. Taken together, NPY participated in the development of cardiac hypertrophy by potentiating NE effects. The signal pathway involves PTX-sensitive G protein, PKC, MAPK, and does not require the presence of calcium.

Neuropeptide Y regulates intracellular calcium through different signalling pathways linked to a Y(1)-receptor in rat mesenteric small arteries

Simultaneous measurements of intracellular calcium concentration ([Ca(2+)](i)) and tension were performed to clarify whether the mechanisms which cause the neuropeptide Y (NPY)-elicited contraction and potentiation of noradrenaline contractions, and the NPY inhibition of forskolin responses are linked to a single or different NPY receptor(s) in rat mesenteric small arteries. In resting arteries, NPY moderately elevated [Ca(2+)](i) and tension. These effects were antagonized by the selective Y(1) receptor antagonist, (R)-N(2)-(diphenacetyl)-N-[(4-hydroxyphenyl)methyl]-D-argininea mide (BIBP 3226) (apparent pK(B) values of 8.54+/-0.25 and 8.27+/-0.17, respectively). NPY (0.1 microM) caused a near 3 fold increase in sensitivity to noradrenaline but did not significantly modify the tension-[Ca(2+)](i) relationship for this agonist. BIBP 3226 competitively antagonized the contractile response to NPY in arteries submaximally preconstricted with noradrenaline (pA(2) 7.87+/-0.20). In arteries activated by vasopressin, the adenylyl cyclase activator forskolin (3 microM) induced a maximum relaxation and a return of [Ca(2+)](i) to resting levels. NPY completely inhibited these effects. The contractile responses to NPY in arteries maximally relaxed with either sodium nitroprusside (SNP) or nifedipine were not significantly higher than those evoked by the peptide at resting tension, in contrast to the contractions to NPY in forskolin-relaxed arteries. BIBP 3226 competitively antagonized the contraction to NPY in forskolin-relaxed arteries with a pA(2) of 7.92+/-0.29. Electrical field stimulation (EFS) at 8-32 Hz caused large contractions in arteries relaxed with either forskolin or noradrenaline in the presence of phentolamine. These responses to EFS were inhibited by BIBP 3226. Similar EFS in resting, non-activated arteries did not produce any response. The present results suggest that different intracellular pathways are linked to a single NPY Y(1) receptor in intact rat mesenteric small arteries, and provide little support for involvement of other postjunctional NPY receptors in the contractile responses to NPY. Neurally released NPY also seems to act through Y(1) receptors, and may serve primarily as an inhibitor of vasodilatation.

Normal feeding behavior, body weight and leptin response require the neuropeptide Y Y2 receptor

Neuropeptide Y (NPY), a 36-amino-acid peptide widely expressed in the brain is involved in many physiological responses, including hypothalamic control of food intake and cardiovascular homeostasis. NPY mediates its effects through binding to the Y1, Y2 and Y5 G-protein-coupled receptors. Little is known of the role of the Y2 receptor in mediating the different NPY effects. We inactivated the Y2 receptor subtype in mice and found that these mice developed increased body weight, food intake and fat deposition. The null mutant mice showed an attenuated response to leptin administration but a normal response to NPY-induced food intake and intact regulation of re-feeding and body weight after starvation. An absence of the Y2 receptor subtype also affected the basal control of heart rate, but did not influence blood pressure. These findings indicate an inhibitory role for the Y2 receptor subtype in the central regulation of body weight and control of food intake.

Neuropeptide Y contributes to innervation-dependent increase in I(Ca, L) via ventricular Y2 receptors

The developmental increase in L-type Ca current (I(Ca,L)) density in the rat ventricle is reproduced in vitro by culturing neonatal myocytes with sympathetic neurons. We tested whether this effect of sympathetic innervation results from a chronic or sustained action of neurally released neuropeptide Y (NPY). Ventricular myocytes from newborn rats were cultured in serum-free medium with or without sympathetic neurons, NPY, or NPY analogs. Ca currents were measured in single myocytes at room temperature using the perforated patch clamp. In all cell groups (control, innervated, or NPY treated), the current-voltage relation for I(Ca,L) was represented by a bell-shaped curve with maximal value near 0 mV. The current density at 0 mV normalized to that of corresponding mean control values was 1.63 +/- 0.12 and 1.52 +/- 0.16 for innervated and NPY-treated myocytes, respectively. Both groups differed significantly from control (P < 0.05). NPY analogs exhibited the following rank order of effectiveness: NPY >/= NPY-(13-36) >/= PYY >> [Leu31Pro34]NPY, suggesting that the NPY effect occurs via a Y2-receptor subtype. In confirmation, chronic treatment of innervated cultures with a Y2-selective NPY antagonist prevented the innervation-dependent increase in I(Ca,L). These results indicate that sympathetic innervation contributes to the developmental increase in I(Ca,L) via neurally released NPY acting at Y2 receptors on the ventricular myocytes.

Neuropeptide Y is a prejunctional inhibitor of vagal but not sympathetic inotropic responses in guinea-pig isolated left atria

1. The effects of NPY and related peptides were examined on basal contractile force and nerve-mediated inotropic responses to electrical field stimulation of the guinea-pig isolated left atrium. 2. Electrical field stimulus (EFS)-inotropic response curves were constructed by applying 1-64 trains of four field pulses (200 Hz, 0.1 ms duration, 100 V) across isolated left atria (paced at 4 Hz, 2 ms, 1-4 V) within the atrial refractory period. Curves were constructed in presence of vehicle, propranolol (1 microM) or atropine (1 microM) to determine appropriate stimulus conditions. 3. The effects of PYY (1-10,000 nM), NPY (0.01-10 microM), N-Ac-[Leu28,31]NPY(24-36) (N-A[L]NPY(24-36); 0.01-10 microM) and clonidine (0.1-1000 nM) were examined on the positive and negative inotropic responses to EFS (eight trains, four pulses per refractory period). 4. NPY-related peptides had no effect on basal force of contraction nor on the inotropic concentration-response curves to bethanechol or isoprenaline. All three peptides inhibited vagally-mediated negative inotropic responses; rank order of potency PYY>NPY> or =N-A[L]NPY(24-36) was consistent with an action at prejunctional Y2-receptors. Clonidine concentration-dependently inhibited sympathetic inotropic responses. However, PYY, NPY and N-A[L]NPY(24-36) failed to mediate any significant inhibition of the positive inotropic response to EFS. 5. These data demonstrate that NPY is an effective inhibitor of vagal but not sympathetically-mediated inotropic responses in the guinea-pig isolated left atria. This may suggest that endogenously co-released NPY is important in mediating cross talk between efferent components of the autonomic nervous system modulating cardiac contractility, acting overall to sustain positive inotropic responses.