BIIE0246, a potent and highly selective non-peptide neuropeptide Y Y(2) receptor antagonist

Neuropeptide Y: Direct vasoconstrictor and facilitatory effects on P2X1 receptor-dependent vasoconstriction in human small abdominal arteries

Neuropeptide Y (NPY) is co-released with norepinephrine and ATP by sympathetic nerves innervating arteries. Circulating NPY is elevated during exercise and cardiovascular disease, though information regarding the vasomotor function of NPY in human blood vessels is limited. Wire myography revealed NPY directly stimulated vasoconstriction (EC50 10.3 ± 0.4 nM; N = 5) in human small abdominal arteries. Maximum vasoconstriction was antagonised by both BIBO03304 (60.7 ± 6%; N = 6) and BIIE0246 (54.6 ± 5%; N = 6), suggesting contributions of both Y1 and Y2 receptor activation, respectively. Y1 and Y2 receptor expression in arterial smooth muscle cells was confirmed by immunocytochemistry, and western blotting of artery lysates. α,β-meATP evoked vasoconstrictions (EC50 282 ± 32 nM; N = 6) were abolished by suramin (IC50 825 ± 45 nM; N = 5) and NF449 (IC50 24 ± 5 nM; N = 5), suggesting P2X1 mediates vasoconstriction in these arteries. P2X1, P2X4 and P2X7 were detectable by RT-PCR. Significant facilitation (1.6-fold) of α,β-meATP-evoked vasoconstrictions was observed when submaximal NPY (10 nM) was applied between α,β-meATP applications. Facilitation was antagonised by either BIBO03304 or BIIE0246. These data reveal NPY causes direct vasoconstriction in human arteries which is dependent upon both Y1 and Y2 receptor activation. NPY also acts as a modulator, facilitating P2X1-dependent vasoconstriction. Though in contrast to the direct vasoconstrictor effects of NPY, there is redundancy between Y1 and Y2 receptor activation to achieve the facilitatory effect.

Agrp-negative arcuate NPY neurons drive feeding under positive energy balance via altering leptin responsiveness in POMC neurons

Neuropeptide Y (NPY) in the arcuate nucleus (ARC) is known as one of the most critical regulators of feeding. However, how NPY promotes feeding under obese conditions is unclear. Here, we show that positive energy balance, induced by high-fat diet (HFD) or in genetically obese leptin-receptor-deficient mice, leads to elevated Npy2r expression especially on proopiomelanocortin (POMC) neurons, which also alters leptin responsiveness. Circuit mapping identified a subset of ARC agouti-related peptide (Agrp)-negative NPY neurons that control these Npy2r expressing POMC neurons. Chemogenetic activation of this newly discovered circuitry strongly drives feeding, while optogenetic inhibition reduces feeding. Consistent with that, lack of Npy2r on POMC neurons leads to reduced food intake and fat mass. This suggests that under energy surplus conditions, when ARC NPY levels generally drop, high-affinity NPY2R on POMC neurons is still able to drive food intake and enhance obesity development via NPY released predominantly from Agrp-negative NPY neurons.

Neuropeptide Y Y2 and Y5 receptors as potential targets for neuroprotective and antidepressant therapies: Evidence from preclinical studies

There is currently no effective treatment either for neurological illnesses (ischemia and neurodegenerative diseases) or psychiatric disorders (depression), in which the Glu/GABA balance is disturbed and accompanied by significant excitotoxicity. Therefore, the search for new and effective therapeutic strategies is imperative for these disorders. Studies conducted over the last several years indicate that the neuropeptide Y (NPY)-ergic system may be a potential therapeutic target for neuroprotective or antidepressant compounds. This review focuses on the neuroprotective roles of Y2 and Y5 receptors (YRs) in neurological disorders such as ischemia, Alzheimer's disease, Parkinson's disease, Huntington's disease, and in psychiatric disorders such as depression. It summarizes current knowledge on the possible mechanisms underlying the neuroprotective or antidepressant-like actions of Y2R and Y5R ligands. The review also discusses ligands acting at Y2R and Y5R and their limitations as in vivo pharmacological tools. The results from the preclinical studies discussed here may be useful in developing effective therapeutic strategies to treat neurological diseases on the one hand and psychiatric disorders on the other, and may pave the way for the development of novel Y2R and Y5R ligands as candidate drugs for the treatment of these diseases.

Y1 receptors modulate taste-related behavioral responsiveness in male mice to prototypical gustatory stimuli

Mammalian taste bud cells express receptors for numerous peptides implicated elsewhere in the body in the regulation of metabolism, nutrient assimilation, and satiety. The perturbation of several peptide signaling pathways in the gustatory periphery results in changes in behavioral and/or physiological responsiveness to subsets of taste stimuli. We previously showed that Peptide YY (PYY) - which is present in both saliva and in subsets of taste cells - can affect behavioral taste responsiveness and reduce food intake and body weight. Here, we investigated the contributions of taste bud-localized receptors for PYY and the related Neuropeptide Y (NPY) on behavioral taste responsiveness. Y1R, but not Y2R, null mice show reduced responsiveness to sweet, bitter, and salty taste stimuli in brief-access taste tests; similar results were seen when wildtype mice were exposed to Y receptor antagonists in the taste stimuli. Finally, mice in which the gene encoding the NPY propeptide was deleted also showed reduced taste responsiveness to sweet and bitter taste stimuli. Collectively, these results suggest that Y1R signaling, likely through its interactions with NPY, can modulate peripheral taste responsiveness in mice.

Intracolonic Neuropeptide Y Y1 Receptor Inhibition Attenuates Intestinal Inflammation in Murine Colitis and Cytokine Release in IBD Biopsies

We have demonstrated that neuropeptide Y (NPY) can regulate pro-inflammatory signaling in the gut via cross-talk with the pro-inflammatory cytokine tumor necrosis factor (TNF). Here, we investigated if selective blocking of NPY receptors, NPY1R or NPY2R, using small molecule non-peptide antagonists (BIBP-3222 for NPY1R and BIIE-0246 for NPY2R) in the colon could attenuate intestinal inflammation by lowering TNF levels (BIBP - N-[(1R)]-4-[(Aminoiminomethyl)amino-1-[[[(4-hydroxyphenyl)methyl]amino]carbonyl]butyl-α-phenylbenzeneacetamide; BIIE - N-[(1S)-4-[(Aminoiminomethyl)amino]-1-[[[2-(3,5-dioxo-1,2-diphenyl-1,2,4-triazolidin-4-yl)ethyl]amino]carbonyl]butyl]-1-[2-[4-(6,11-dihydro-6-oxo-5H-dibenz[b,e]azepin-11-yl)-1-piperazinyl]-2-oxoethyl]-cyclopentaneacetamide). Colitis was induced using dextran sodium sulfate in drinking water for 7 days, or by adoptive T-cell transfer in RAG-/- mice. Colonic biopsies from healthy subjects (n = 10) and IBD patients (n = 34, UC = 20, CD = 14) were cultured ex vivo in presence or absence of NPY antagonists (100 µM, 20 h), and cytokine release into culture supernatants was measured by ELISA. Intracolonic administration of BIBP (but not BIIE) significantly reduced clinical, endoscopic, and histological scores, and serum TNF, interleukin (IL)-6, and IL-12p70 in DSS colitis; it also significantly attenuated histological damage and serum IL-6 in T-cell colitis (P < .05). Intracolonic administration of BIBP significantly reduced TNF and interferon (IFN)-γ release from UC biopsies, whereas BIIE downregulated only IFN-γ (P < .05). BIBP significantly reduced TNF and interferon (IFN)-γ release from UC biopsies, whereas BIIE downregulated only IFN-γ (P < .05). Our data suggest a promising therapeutic value for NPY1R inhibition in alleviating intestinal inflammation in UC, possibly as enemas to IBD patients.

Neuropeptide Y facilitates P2X1 receptor-dependent vasoconstriction via Y1 receptor activation in small mesenteric arteries during sympathetic neurogenic responses

ATP, norepinephrine and NPY are co-released by sympathetic nerves innervating arteries. ATP elicits vasoconstriction via activation of smooth muscle P2X receptors. The functional interaction between neuropeptide Y (NPY) and P2X receptors in arteries is not known. In this study we investigate the effect of NPY on P2X1-dependent vasoconstriction in mouse mesenteric arteries. Suramin or P2X1 antagonist NF449 abolished α,β-meATP evoked vasoconstrictions. NPY lacked any direct vasoconstrictor effect but facilitated the vasoconstrictive response to α,β-meATP. Mesenteric arteries expressed Y1 and Y4 receptors, but not Y2 or Y5. Y1 receptor inhibition (BIBO3304) reversed NPY facilitation of the α,β-meATP-evoked vasoconstriction. L-type Ca2+ channel antagonism (nifedipine) had no effect on α,β-meATP-evoked vasoconstrictions, but completely reversed NPY facilitation. Electrical field stimulation evoked sympathetic neurogenic vasoconstriction. Neurogenic responses were dependent upon dual α1-adrenergic (prazosin) and P2X1 (NF449) receptor activation. Y1 receptor antagonism partially reduced neurogenic vasoconstriction. Isolation of the P2X1 component by α1-adrenergic blockade allowed faciliatory effects of Y1 receptor activation to be explored. Y1 receptor antagonism reduced the P2X1 receptor component during neurogenic vasoconstriction. α1-adrenergic and P2X1 receptors are post-junctional receptors during sympathetic neurogenic vasoconstriction in mesenteric arteries. In conclusion, we have identified that NPY lacks a direct vasoconstrictor effect in mesenteric arteries but can facilitate vasoconstriction by enhancing the activity of P2X1, following activation by exogenous agonists or during sympathetic nerve stimulation. The mechanism of P2X1 facilitation by NPY involved activation of the NPY Y1 receptor and the L-type Ca2+ channel.

Design and Evaluation of Peptide Dual-Agonists of GLP-1 and NPY2 Receptors for Glucoregulation and Weight Loss with Mitigated Nausea and Emesis

There is a critical unmet need for therapeutics to treat the epidemic of comorbidities associated with obesity and type 2 diabetes, ideally devoid of nausea/emesis. This study developed monomeric peptide agonists of glucagon-like peptide 1 receptor (GLP-1R) and neuropeptide Y2 receptor (Y2-R) based on exendin-4 (Ex-4) and PYY_3–36. A novel peptide, GEP44, was obtained via in vitro receptor screens, insulin secretion in islets, stability assays, and in vivo rat and shrew studies of glucoregulation, weight loss, nausea, and emesis. GEP44 in lean and diet-induced obese rats produced greater reduction in body weight compared to Ex-4 without triggering nausea associated behavior. Studies in the shrew demonstrated a near absence of emesis for GEP44 in contrast to Ex-4. Collectively, these data demonstrate that targeting GLP-1R and Y2-R with chimeric single peptides offers a route to new glucoregulatory treatments that are well-tolerated and have improved weight loss when compared directly to Ex-4.

Metaplastic contribution of neuropeptide Y receptors to spatial memory acquisition

Neuropeptide Y (NPY) is highly abundant in the brain and is released as a co-transmitter with plasticity-related neurotransmitters such as glutamate, GABA and noradrenaline. Functionally, its release is associated with appetite, anxiety, and stress regulation. NPY acting on Y2 receptors (Y₂R), facilitates fear extinction, suggesting a role in associative memory. Here, we explored to what extent NPY action at Y₂R contributes to hippocampus-dependent spatial memory and found that dorsal intrahippocampal receptor antagonism improved spatial reference memory acquired in a water maze in rats, without affecting anxiety levels, or spontaneous motor activity. Water maze training resulted in an increase of Y₂R, but not Y₁R expression in the hippocampus. By contrast, in the prefrontal cortex there was a decrease in Y₂R, and an increase of Y₁R expression. Our results indicate that neuropeptide Y₂R are significantly involved in hippocampus-dependent spatial memory and that receptor expression is dynamically regulated by this learning experience. Effects are consistent with a metaplastic contribution of NPY receptors to cumulative spatial learning.

NPY2R signaling gates spontaneous and mechanical, but not thermal, pain transmission

Neuropeptide Y signaling plays an important role in inhibiting chronic pain in the spinal cord of mice. However, little is known about the respective roles of two major neuropeptide Y receptors, Y1R and Y2R, in evoked and spontaneous pain behavior under normal physiological condition. Using intrathecal administration approach, we found that pharmacological inhibition of Y2R, unexpectedly, gave rise to spontaneous pain behavior. In addition, Y2R antagonism also resulted in long-lasting mechanical but not thermal hypersensitivity. By contrast, neither overt spontaneous pain behavior nor mechanical and thermal hypersensitivity were detected after pharmacological inhibition of Y1R. Remarkably, the activation of Y1R produced powerful analgesic effect: blocking both evoked and spontaneous pain behavior resulted from Y2R antagonism. These findings highlight the pivotal role of endogenous Y2R in gating mechanical and spontaneous pain transmission. Importantly, our results suggest that Y1R could be a therapeutic target that may be exploited for alleviating spontaneous pain without affecting acute pain transmission.

Nonconventional glucagon and GLP-1 receptor agonist and antagonist interplay at the GLP-1 receptor revealed in high-throughput FRET assays for cAMP

G protein-coupled receptors (GPCRs) for glucagon (GluR) and glucagon-like peptide-1 (GLP-1R) are normally considered to be highly selective for glucagon and GLP-1, respectively. However, glucagon secreted from pancreatic α-cells may accumulate at high concentrations to exert promiscuous effects at the β-cell GLP-1R, as may occur in the volume-restricted microenvironment of the islets of Langerhans. Furthermore, systemic administration of GluR or GLP-1R agonists and antagonists at high doses may lead to off-target effects at other receptors. Here, we used molecular modeling to evaluate data derived from FRET assays that detect cAMP as a read-out for GluR and GLP-1R activation. This analysis established that glucagon is a nonconventional GLP-1R agonist, an effect inhibited by the GLP-1R orthosteric antagonist exendin(9-39) (Ex(9-39)). The GluR allosteric inhibitors LY2409021 and MK 0893 antagonized glucagon and GLP-1 action at the GLP-1R, whereas des-His¹-[Glu⁹]glucagon antagonized glucagon action at the GluR, while having minimal inhibitory action versus glucagon or GLP-1 at the GLP-1R. When testing Ex(9-39) in combination with des-His¹-[Glu⁹]glucagon in INS-1 832/13 cells, we validated a dual agonist action of glucagon at the GluR and GLP-1R. Hybrid peptide GGP817 containing glucagon fused to a fragment of peptide YY (PYY) acted as a triagonist at the GluR, GLP-1R, and neuropeptide Y2 receptor (NPY2R). Collectively, these findings provide a new triagonist strategy with which to target the GluR, GLP-1R, and NPY2R. They also provide an impetus to reevaluate prior studies in which GluR and GLP-1R agonists and antagonists were assumed not to exert promiscuous actions at other GPCRs.

Platelet Lysate-Derived Neuropeptide y Influences Migration and Angiogenesis of Human Adipose Tissue-Derived Stromal Cells

Neuropeptide Y (NPY), a powerful neurotransmitter of the central nervous system, is a key regulator of angiogenesis and biology of adipose depots. Intriguingly, its peripheral vascular and angiogenic powerful activity is strictly associated to platelets, which are source of clinical hemoderivates, such as platelet lysate (PL), routinely employed in several clinical applications as wound healing, and to preserve ex vivo the progenitor properties of the adipose stromal cells pool. So far, the presence of NPY in PL and its biological effects on the adipose stromal cell fraction (ASCs) have never been investigated. Here, we aimed to identify endogenous sources of NPY such as PL-based preparations and to investigate which biological properties PL-derived NPY is able to exert on ASCs. The results show that PL contains a high amount of NPY, which is in part also excreted by ASCs when stimulated with PL. The protein levels of the three main NPY subtype receptors (Y1, Y2, Y5) are unaltered by stimulation of ASCs with PL, but their inhibition through selective pharmacological antagonists, considerably enhances migration, and a parallel reduction of angiogenic features of ASCs including decrease in VEGF mRNA and intracellular calcium levels, both downstream targets of NPY. The expression of VEGF and NPY is enhanced within the sites of neovascularisation of difficult wounds in patients after treatment with leuco-platelet concentrates. Our data highlight the presence of NPY in PL preparations and its peripheral effects on adipose progenitors.

Appetite-associated responses to central neuropeptide Y injection in quail

The appetite-associated effects of neuropeptide Y (NPY) have been extensively studied in mammalian models. Less knowledge exists for other vertebrate species including birds. The aim of this study was to determine the effects of central injection of NPY on feeding behavior and hypothalamic physiology in 7 day-old Japanese quail (Coturnix japonica). During the light cycle, intracerebroventricular injection of 1.9 pmol, 0.5, and 1.0 nmol doses of NPY did not affect food intake, 0.031 to 0.13 nmol increased food intake, and 2.0 nmol NPY decreased food intake, in comparison to vehicle injection. Multiple doses of NPY stimulated water intake, but when food was not available, water intake was not affected. When injected during the dark cycle, NPY did not influence food intake. NPY-injected chicks had more c-Fos immunoreactive cells in the arcuate nucleus of the hypothalamus (ARC) and greater hypothalamic agouti-related peptide and neuropeptide Y receptors 1 and 2 (NPYR1 and NPYR2, respectively) mRNA than vehicle-injected chicks. Within the ventromedial hypothalamus, NPY-treated chicks expressed less NPYR1 mRNA, within the dorsomedial hypothalamus less NPY mRNA, and in the ARC greater NPYR2 mRNA than vehicle-injected chicks. Lastly, quail injected with NPY increased feeding pecks, escape attempts, and time spent preening, while locomotion, the number of steps, and time spent perching decreased compared to chicks injected with the vehicle. Results demonstrate that NPY stimulates food intake in quail, consistent with mammals and other avian species, but with some unique responses at the molecular level that are not documented in other species.

Chimeric peptide EP45 as a dual agonist at GLP-1 and NPY2R receptors

We report the design and target validation of chimeric peptide EP45, a novel 45 amino acid monomeric dual agonist peptide that contains amino acid sequence motifs present within the blood glucose-lowering agent exendin-4 (Ex-4) and the appetite-suppressing agent PYY(3-36). In a new high-throughput FRET assay that provides real-time kinetic information concerning levels of cAMP in living cells, EP45 recapitulates the action of Ex-4 to stimulate cAMP production via the glucagon-like peptide-1 receptor (GLP-1R), while also recapitulating the action of PYY(3-36) to inhibit cAMP production via the neuropeptide Y2 receptor (NPY2R). EP45 fails to activate glucagon or GIP receptors, whereas for cells that co-express NPY2R and adenosine A2B receptors, EP45 acts in an NPY2R-mediated manner to suppress stimulatory effects of adenosine on cAMP production. Collectively, such findings are remarkable in that they suggest a new strategy in which the co-existing metabolic disorders of type 2 diabetes and obesity will be treatable using a single peptide such as EP45 that lowers levels of blood glucose by virtue of its GLP-1R-mediated effect, while simultaneously suppressing appetite by virtue of its NPY2R-mediated effect.

Ligands of the neuropeptide Y Y2 receptor

Neuropeptide Y (NPY) is one of the most abundant neuropeptides in the mammalian brain and exerts a variety of physiological processes in humans via four different receptor subtypes Y1, Y2, Y4 and Y5. Y2 receptor is the most abundant Y subtype receptor in the central nervous system and implicated with food intake, bone formation, affective disorders, alcohol and drugs of abuse, epilepsy, pain, and cancer. The lack of small molecule non-peptidic Y2 receptor modulators suitable as in vivo pharmacological tools hampered the progress to uncover the precise pharmacological role of Y2. Only in recent years, several potent, selective and non-peptidic Y2 antagonists have been discovered providing the tools to validate Y2 receptor as a therapeutic target. This Letter reviews Y2 receptor modulators mainly non-peptidic antagonists and their structure-activity relationships.

Neuropeptide y gates a stress-induced, long-lasting plasticity in the sympathetic nervous system

Acute stress evokes the fight-or-flight reflex, which via release of the catecholamine hormones affects the function of every major organ. Although the reflex is transient, it has lasting consequences that produce an exaggerated response when stress is reexperienced. How this change is encoded is not known. We investigated whether the reflex affects the adrenal component of the sympathetic nervous system, a major branch of the stress response. Mice were briefly exposed to the cold-water forced swim test (FST) which evoked an increase in circulating catecholamines. Although this hormonal response was transient, the FST led to a long-lasting increase in the catecholamine secretory capacity measured amperometrically from chromaffin cells and in the expression of tyrosine hydroxylase. A variety of approaches indicate that these changes are regulated postsynaptically by neuropeptide Y (NPY), an adrenal cotransmitter. Using immunohistochemistry, RT-PCR, and NPY(GFP) BAC mice, we find that NPY is synthesized by all chromaffin cells. Stress failed to increase secretory capacity in NPY knock-out mice. Genetic or pharmacological interference with NPY and Y1 (but not Y2 or Y5) receptor signaling attenuated the stress-induced change in tyrosine hydroxylase expression. These results indicate that, under basal conditions, adrenal signaling is tonically inhibited by NPY, but stress overrides this autocrine negative feedback loop. Because acute stress leads to a lasting increase in secretory capacity in vivo but does not alter sympathetic tone, these postsynaptic changes appear to be an adaptive response. We conclude that the sympathetic limb of the stress response exhibits an activity-dependent form of long-lasting plasticity.

Aging and long-term caloric restriction regulate neuropeptide Y receptor subtype densities in the rat brain

The effects of aging and long-term caloric restriction (LTCR), on the regulation of neuropeptide Y (NPY) Y1, Y2 and Y5 receptors subtypes, was studied in 20-month-old male rats fed ad libitum (AL) or submitted to a 40% caloric restriction for 12 months. [(125)I]GR231118, a Y1 antagonist was used as Y1 receptor radioligand. [(125)I][Leu(31), Pro(34)]PYY, a high affinity agonist of Y1 and Y5 subtypes was used in the absence or presence of 100 nM BIBO3304 (a highly selective Y1 receptor antagonist) to assess the apparent levels of [(125)I][Leu(31), Pro(34)]PYY/BIBO3304 insensitive sites (Y5-like) from [(125)I][Leu(31), Pro(34)]PYY/BIBO3304 sensitive sites (Y1). [(125)I]PYY(3-36) was used to label the Y2 receptor. In the brain of 3-month-old AL rats, the distribution and densities of Y1, Y2 and Y5 receptors were in agreement with previous reports. In the brain of 20AL rats, a decrease of NPY receptor subtype densities in regions having important physiological functions such as the cingulate cortex, hippocampus and dentate gyrus, thalamus and hypothalamus was observed. In contrast, LTCR had multiple effects. It induced specific decreases of Y1-receptor densities in the dentate gyrus, thalamic and hypothalamic nuclei and lateral hypothalamic area and Y2-receptor densities in the suprachiasmatic nucleus of hypothalamus. Moreover, it prevented the age-induced increase in Y1-receptor densities in the ventromedial hypothalamic nucleus and decrease in the mediodorsal thalamic nucleus, and increased Y2-receptor densities in the CA2 subfield of the hippocampus. These results indicate that LTCR not only counteracts some of the deleterious effects of aging on NPY receptor subtype densities but exerts specific effects of its own. The overall impact of the regulation of NPY receptor subtypes in the brain of old calorie-restricted rats may protect the neural circuits involved in pain, emotions, feeding and memory functions.

Chronic administration of the Y2 receptor antagonist, JNJ-31020028, induced anti-depressant like-behaviors in olfactory bulbectomized rat

Recent studies from our groups have shown that BIIE0246, a Y2 receptor antagonist, has antidepressant effect in olfactory bulbectomized (OBX) rat. However, its complex structure and high molecular weight limit its usefulness as an in vivo pharmacological tool. Alternatively, the novel and brain penetrant Y2 receptor antagonist, JNJ-31020028 is a useful tool to investigate the in vivo function of the Y2 receptor. In the present study, we evaluated the effect of chronic intracerebroventricular (icv) administration of JNJ-31020028 in a battery of behavioral tests in an animal model that mimics several deficits observed in the human depression, the OBX rat. Chronic administration of JNJ-31020028 induced a decrease in immobility time in the forced swim test in OBX while had no effect in control animals. Additionally, it decreased number of grooming events in OBX animals, but had no effects on some other behavioral deficits observed such as rearing and hyperlocomotion. Furthermore, JNJ-31020028 had no effect on behavior tests that are commonly used to evaluate anxiety, namely the social interaction test in both OBX and control animals. These data indicate that similar to BIIE0246, JNJ-31020028 also has antidepressant like effects in the OBX model.

Differences in neuropeptide Y-induced secretion of endothelin-1 in left and right human endocardial endothelial cells

The aim of the study was to test the hypothesis that neuropeptide Y (NPY) may induce endothelin-1 (ET-1) secretion in left (hLEECs) and right (hREECs) human endocardial endothelial cells. Furthermore, the type of NPY receptor implicated could be different in NPY-induced secretion in hLEECs and hREECs. Using immunofluorescence coupled to real 3D confocal microscopy and ELISA, our results showed that stimulation of secretion by NPY induced the release of ET-1 from both right and left human ventricular endocardial endothelial cells (hEECs) in a time-dependent manner. Furthermore, the secretory capacity of hREECs was higher than that of hLEECs. In addition, our results showed that the effect of NPY on ET-1 secretion in hLEECs was only due to activation of Y(5) receptors. However, the effect of NPY on ET-1 secretion in hREECs was due to mainly Y(2) and partially Y(5) receptors activation. In conclusion, our results suggest that differences in excitation-secretion coupling exist between hREECS and hLEECs which may contribute to the functional differences between right and left ventricular muscle. Furthermore, high NPY level contributes to ET-1 release by hEECs and Y(2) and Y(5) receptors antagonists may be used for regulation of ET-1 secretion in the heart.

Methamphetamine-induced changes in the mice hippocampal neuropeptide Y system: implications for memory impairment

Methamphetamine (METH) is a psychostimulant drug that causes irreversible brain damage leading to several neurological and psychiatric abnormalities, including cognitive deficits. Neuropeptide Y (NPY) is abundant in the mammalian central nervous system (CNS) and has several important functions, being involved in learning and memory processing. It has been demonstrated that METH induces significant alteration in mice striatal NPY, Y(1) and Y(2) receptor mRNA levels. However, the impact of this drug on the hippocampal NPY system and its consequences remain unknown. Thus, in this study, we investigated the effect of METH intoxication on mouse hippocampal NPY levels, NPY receptors function, and memory performance. Results show that METH increased NPY, Y(2) and Y(5) receptor mRNA levels, as well as total NPY binding accounted by opposite up- and down-regulation of Y(2) and Y(1) functional binding, respectively. Moreover, METH-induced impairment in memory performance and AKT/mammalian target of rapamycin pathway were both prevented by the Y(2) receptor antagonist, BIIE0246. These findings demonstrate that METH interferes with the hippocampal NPY system, which seems to be associated with memory failure. Overall, we concluded that Y(2) receptors are involved in memory deficits induced by METH intoxication.

Activation of NPY receptors suppresses excitatory synaptic transmission in a taste-feeding network in the lower brain stem

Consummatory responses to taste stimuli are modulated by visceral signals processed in the caudal nucleus of the solitary tract (cNST) and ventrolateral medulla. On the basis of decerebrate preparations, this modulation can occur through local brain stem pathways. Among the large number of neuropeptides and neuromodulators implicated in these visceral pathways is neuropeptide Y (NPY), which is oftentimes colocalized in catecholaminergic neurons themselves implicated in glucoprivic-induced feeding and satiety. In addition to the cNST and ventrolateral medulla, noradrenergic and NPY receptors are found in circumscribed regions of the medullary reticular formation rich in preoromotor neurons. To test the hypothesis that NPY may act as a neuromodulator on preoromotor neurons, we recorded the effects of bath application of NPY and specific Y1 and Y2 agonists on currents elicited from electrical stimulation of the rostral (taste) NST in prehypoglossal neurons in a brain stem slice preparation. A high proportion of NST-driven responses were suppressed by NPY, as well as Y1 and Y2 agonists. On the basis of paired pulse ratios and changes in membrane resistance, we concluded that Y1 receptors influence these neurons both presynaptically and postsynaptically and that Y2 receptors have a presynaptic locus. To test the hypothesis that NPY may act in concert with norepinephrine (NE), we examined neurons showing suppressed responses in the presence of a Y2 agonist and demonstrated a greater degree of suppression to a Y2 agonist/NE cocktail. These suppressive effects on preoromotoneurons may reflect a satiety pathway originating from A2 neurons in the caudal brain stem.

The cardiac sympathetic co-transmitter galanin reduces acetylcholine release and vagal bradycardia: implications for neural control of cardiac excitability

The autonomic phenotype of congestive cardiac failure is characterised by high sympathetic drive and impaired vagal tone, which are independent predictors of mortality. We hypothesize that impaired bradycardia to peripheral vagal stimulation following high-level sympathetic drive is due to sympatho-vagal crosstalk by the adrenergic co-transmitters galanin and neuropeptide-Y (NPY). Moreover we hypothesize that galanin acts similarly to NPY by reducing vagal acetylcholine release via a receptor mediated, protein kinase-dependent pathway. Prolonged right stellate ganglion stimulation (10 Hz, 2 min, in the presence of 10 μM metoprolol) in an isolated guinea pig atrial preparation with dual autonomic innervation leads to a significant (p < 0.05) reduction in the magnitude of vagal bradycardia (5 Hz) maintained over the subsequent 20 min (n = 6). Immunohistochemistry demonstrated the presence of galanin in a small number of tyrosine hydroxylase positive neurons from freshly dissected stellate ganglion tissue sections. Following 3 days of tissue culture however, most stellate neurons expressed galanin. Stellate stimulation caused the release of low levels of galanin and significantly higher levels of NPY into the surrounding perfusate (n = 6, using ELISA). The reduction in vagal bradycardia post sympathetic stimulation was partially reversed by the galanin receptor antagonist M40 after 10 min (1 μM, n = 5), and completely reversed with the NPY Y₂ receptor antagonist BIIE 0246 at all time points (1 μM, n = 6). Exogenous galanin (n = 6, 50–500 nM) also reduced the heart rate response to vagal stimulation but had no effect on the response to carbamylcholine that produced similar degrees of bradycardia (n = 6). Galanin (500 nM) also significantly attenuated the release of ³H-acetylcholine from isolated atria during field stimulation (5 Hz, n = 5). The effect of galanin on vagal bradycardia could be abolished by the galanin receptor antagonist M40 (n = 5). Importantly the GalR₁ receptor was immunofluorescently co-localised with choline acetyl-transferase containing neurons at the sinoatrial node. The protein kinase C inhibitor calphostin (100 nM, n = 6) abolished the effect of galanin on vagal bradycardia whilst the protein kinase A inhibitor H89 (500 nM, n = 6) had no effect. These results demonstrate that prolonged sympathetic activation releases the slowly diffusing adrenergic co-transmitter galanin in addition to NPY, and that this contributes to the attenuation in vagal bradycardia via a reduction in acetylcholine release. This effect is mediated by GalR₁ receptors on vagal neurons coupled to protein kinase C dependent signalling pathways. The role of galanin may become more important following an acute injury response where galanin expression is increased.

The role of NPY in hypothalamic mediated food intake

Neuropeptide Y (NPY) is a highly conserved neuropeptide with orexigenic actions in discrete hypothalamic nuclei that plays a role in regulating energy homeostasis. NPY signals via a family of high affinity receptors that mediate the widespread actions of NPY in all hypothalamic nuclei. These actions are also subject to tight, intricate regulation by numerous peripheral and central energy balance signals. The NPY system is embedded within a densely-redundant network designed to ensure stable energy homeostasis. This redundancy may underlie compensation for the loss of NPY or its receptors in germline knockouts, explaining why conventional knockouts of NPY or its receptors rarely yield a marked phenotypic change. We discuss insights into the hypothalamic role of NPY from studies of its physiological actions, responses to genetic manipulations and interactions with other energy balance signals. We conclude that numerous approaches must be employed to effectively study different aspects of NPY action.

Anticonvulsant neuropeptides as drug leads for neurological diseases

Anticonvulsant neuropeptides are best known for their ability to suppress seizures and modulate pain pathways. Galanin, neuropeptide Y, somatostatin, neurotensin, dynorphin, among others, have been validated as potential first-in-class anti-epileptic or/and analgesic compounds in animal models of epilepsy and pain, but their therapeutic potential extends to other neurological indications, including neurodegenerative and psychatric disorders. Disease-modifying properties of neuropeptides make them even more attractive templates for developing new-generation neurotherapeutics. Arguably, efforts to transform this class of neuropeptides into drugs have been limited compared to those for other bioactive peptides. Key challenges in developing neuropeptide-based anticonvulsants are: to engineer optimal receptor-subtype selectivity, to improve metabolic stability and to enhance their bioavailability, including penetration across the blood–brain barrier (BBB). Here, we summarize advances toward developing systemically active and CNS-penetrant neuropeptide analogs. Two main objectives of this review are: (1) to provide an overview of structural and pharmacological properties for selected anticonvulsant neuropeptides and their analogs and (2) to encourage broader efforts to convert these endogenous natural products into drug leads for pain, epilepsy and other neurological diseases.

In vitro and in vivo characterization of JNJ-31020028 (N-(4-{4-[2-(diethylamino)-2-oxo-1-phenylethyl]piperazin-1-yl}-3-fluorophenyl)-2-pyridin-3-ylbenzamide), a selective brain penetrant small molecule antagonist of the neuropeptide Y Y(2) receptor

RATIONALE

The lack of potent, selective, brain penetrant Y(2) receptor antagonists has hampered in vivo functional studies of this receptor.

OBJECTIVE

Here, we report the in vitro and in vivo characterization of JNJ-31020028 (N-(4-{4-[2-(diethylamino)-2-oxo-1-phenylethyl]piperazin-1-yl}-3-fluorophenyl)-2-pyridin-3-ylbenzamide), a novel Y(2) receptor antagonist.

METHODS

The affinity of JNJ-31020028 was determined by inhibition of the PYY binding to human Y(2) receptors in KAN-Ts cells and rat Y(2) receptors in rat hippocampus. The functional activity was determined by inhibition of PYY-stimulated calcium responses in KAN-Ts cells expressing a chimeric G protein Gqi5 and in the rat vas deferens (a prototypical Y(2) bioassay). Ex vivo receptor occupancy was revealed by receptor autoradiography. JNJ-31020028 was tested in vivo with microdialysis, in anxiety models, and on corticosterone release.

RESULTS

JNJ-31020028 bound with high affinity (pIC(50) = 8.07 +/- 0.05, human, and pIC(50) = 8.22 +/- 0.06, rat) and was >100-fold selective versus human Y(1), Y(4), and Y(5) receptors. JNJ-31020028 was demonstrated to be an antagonist (pK(B) = 8.04 +/- 0.13) in functional assays. JNJ-31020028 occupied Y(2) receptor binding sites (approximately 90% at 10 mg/kg) after subcutaneous administration in rats. JNJ-31020028 increased norepinephrine release in the hypothalamus, consistent with the colocalization of norepinephrine and neuropeptide Y. In a variety of anxiety models, JNJ-31020028 was found to be ineffective, although it did block stress-induced elevations in plasma corticosterone, without altering basal levels, and normalized food intake in stressed animals without affecting basal food intake.

CONCLUSION

These results suggest that Y(2) receptors may not be critical for acute behaviors in rodents but may serve modulatory roles that can only be elucidated under specific situational conditions.

Neuroprotective effects of neuropeptide Y-Y2 and Y5 receptor agonists in vitro and in vivo

It is generally assumed that neurodegeneration is connected with glutamatergic hyperactivity, and that neuropeptide Y (NPY) inhibits glutamate release. Some earlier studies indicated that NPY may have neuroprotective effect; however, the results obtained so far are still divergent, and the role of different Y receptors remains unclear. Therefore in the presented study we investigated the neuroprotective potential of NPY and its Y2, Y5 or Y1 receptor (R) ligands against the kainate (KA)-induced excitotoxicity in neuronal cultures in vitro, as well as in vivo after intrahippocampal KA injection and also in an ischemic middle cerebral artery occlusion model after intraventricular injection of Y2R agonist. NPY compounds were applicated 30 min, 1, 3 or 6 h after the start of the exposure to KA, or 30 min after the onset of ischemia. Our results indicate the neuroprotective activity of NPY and its Y2R and Y5R ligands against the kainate-induced excitotoxicity in primary cortical and hippocampal cultures. Importantly, NPY was effective when given as late as 6 h, while Y2R or Y5R agonists 3 h, after starting the exposure to KA. In in vitro studies those protective effects were inhibited by the respective receptor antagonists. Neuroprotection was also observed in vivo after intrahippocampal injection of Y2R and Y5R agonists 30 min or 1 h after KA. No protection was found either in vitro or in vivo after the Y1R agonist. The Y2R agonist also showed neuroprotective activity in the ischemic model. The obtained results indicate that neuropeptide Y produces neuroprotective effect via Y2 and Y5 receptors, and that the compounds may be effective after delayed application.

Endogenous PYY and NPY mediate tonic Y1- and Y2-mediated absorption in human and mouse colon

Objective

To establish the functional significance of endogenous peptide YY (PYY) and neuropeptide Y (NPY) as mediators of Y₁ and Y₂ absorptive tone in colonic mucosa.

Methods

Functional studies utilized descending colon from adult mice (wild type [WT] and peptide nulls) and ex vivo human colonic tissue (from patients undergoing bowel resections) measuring changes in basal ion transport. Peak increases in ion transport to Y₁ or Y₂ antagonists (BIBO3304 300 nM; BIIE0246 1 μM) were pooled (mean ± SEM) and compared using Student's unpaired t test (P ≤ 0.05); some tissues received tetrodotoxin (TTX; 100 nM). PYY-positive L-cell numbers and NPY innervation were also compared.

Results

Y₁ and Y₂ tones were present in human and WT mouse colon mucosa and only the latter was TTX sensitive. Y₁ tone was unchanged in NPY^−/− but was ∼90% inhibited in PYY^−/− and abolished in PYYNPY^−/− colon mucosa. Y₂ tone was reduced ∼50% in NPY^−/− and PYY^−/− tissues and was absent from PYYNPY^−/− colon. Residual Y₂ and Y₁ tones present in PYY^−/− mucosa were abolished by TTX. PYY ablation had no apparent effect on NPY innervation and PYY-positive cells were observed at the same frequency in NPY^−/− (56.7 ± 6.8 cells/section) and WT (55.0 ± 4.6 cells/section) colons. Double knockouts lacked PYY and NPY expression, but endocrine cells and enteric nerves were present with similar frequencies to those of WT mice.

Conclusion

Endogenous PYY mediates Y₁ absorptive tone that is epithelial in origin, whereas Y₂ tone is a combination of PYY and NPY mediation.

Sigma 1 receptor-mediated increase in hippocampal extracellular dopamine contributes to the mechanism of the anticonvulsant action of neuropeptide Y

The potent anticonvulsant properties of neuropeptide Y (NPY) are generally attributed to a Y2 receptor-mediated inhibition of glutamatergic synaptic transmission. Independent studies have shown that NPY increases brain dopamine content, possibly via interaction with sigma 1 receptors. Recently, we showed that increased extracellular hippocampal dopamine attenuates pilocarpine-induced limbic seizures via activation of hippocampal D2 receptors. Our aim in this study was to elucidate the role of increased hippocampal dopamine in the mechanism of the anticonvulsant action of NPY and to investigate the involvement of Y2 and sigma 1 receptors in this process. Limbic seizures were evoked in freely moving rats by intrahippocampal administration of pilocarpine via a microdialysis probe. NPY was administered intracerebroventricularly, intrahippocampally via the microdialysis probe, or coadministered intrahippocampally with the D2 receptor antagonist remoxipride, the Y2 receptor antagonist BIIE0246 or the sigma 1 receptor antagonist BD1047. Changes in hippocampal extracellular dopamine were monitored, and behavioural changes indicative of seizure activity were scored. Intracerebroventricular (10 nmol/3 microL) and intrahippocampal (20-50 microm) NPY administration increased hippocampal dopamine and attenuated pilocarpine-induced seizures. Hippocampal D2 receptor blockade (4 microm remoxipride) reversed the anticonvulsant effect of NPY. Y2 receptor blockade (1 microm BIIE0246) reversed the anticonvulsant effect of NPY but did not prevent NPY-induced increases in hippocampal dopamine. Sigma 1 receptor blockade (10 microm BD1047) abolished NPY-induced increases in hippocampal dopamine and reversed the anticonvulsant effect of NPY. Our results indicate that NPY-induced increases in hippocampal dopamine are mediated via sigma 1 receptors and contribute to the anticonvulsant effect of NPY via increased activation of hippocampal D2 receptors. This novel mechanism of anticonvulsant action of NPY is separate from, and may be complementary to, the well established Y2 receptor-mediated inhibition of hippocampal excitability.

Neuropeptide Y reduces acetylcholine release and vagal bradycardia via a Y2 receptor-mediated, protein kinase C-dependent pathway

The co-transmitter neuropeptide Y (NPY), released during prolonged cardiac sympathetic nerve stimulation, can attenuate vagal-induced bradycardia. We tested the hypothesis that NPY reduces acetylcholine release, at similar concentrations to which it attenuates vagal bradycardia, via pre-synaptic Y2 receptors modulating a pathway that is dependent on protein kinase A (PKA) or protein kinase C (PKC). The Y2 receptor was immunofluorescently colocalized with choline acetyl-transferase containing neurons at the guinea pig sinoatrial node. The effect of NPY in the presence of various enzyme inhibitors was then tested on the heart rate response to vagal nerve stimulation in isolated guinea pig sinoatrial node/right vagal nerve preparations and also on (3)H-acetylcholine release from right atria during field stimulation. NPY reduced the heart rate response to vagal stimulation at 1, 3 and 5 Hz (significant at 100 nM and reaching a plateau at 250 nM NPY, p<0.05, n=6) but not to the stable analogue of acetylcholine, carbamylcholine (30, 60 or 90 nM, n=6) which produced similar degrees of bradycardia. The reduced vagal response was abolished by the Y2 receptor antagonist BIIE 0246 (1 microM, n=4). NPY also significantly attenuated the release of (3)H-acetylcholine during field stimulation (250 nM, n=6). The effect of NPY (250 nM) on vagal bradycardia was abolished by the PKC inhibitors calphostin C (0.1 microM, n=5) and chelerythrine chloride (25 microM, n=6) but not the PKA inhibitor H89 (0.5 microM, n=6). Conversely, the PKC activator Phorbol-12-myristate-13-acetate (0.5 microM, n=7) mimicked the effect of NPY and significantly reduced (3)H-acetylcholine release during field stimulation. These results show that NPY attenuates vagal bradycardia via a pre-synaptic decrease in acetylcholine release that appears to be mediated by a Y2 receptor pathway involving modulation of PKC.

Neuropeptide y receptor selective ligands in the treatment of obesity

Obesity is a serious public health problem throughout the world, affecting both developed societies and developing countries. The central nervous system has developed a meticulously interconnected circuitry in order to keep us fed and in an adequate nutritional state. One of these consequences is that an energy-dense environment favors the development of obesity. Neuropeptide Y (NPY) is one of the most abundant and widely distributed peptides in the central nervous system of both rodents and humans and has been implicated in a variety of physiological actions. Within the hypothalamus, NPY plays an essential role in the control of food intake and body weight. Centrally administered NPY causes robust increases in food intake and body weight and, with chronic administration, can eventually produce obesity. NPY activates a population of at least six G protein-coupled Y receptors. NPY analogs exhibit varying degrees of affinity and specificity for these Y receptors. There has been renewed speculation that ligands for Y receptors may be of benefit for the treatment of obesity. This review highlights the therapeutic potential of Y(1), Y(2), Y(4), and Y(5) receptor agonists and antagonists as additional intervention to treat human obesity.

Peptide YY3–36-induced inhibition of food intake in female monkeys

Peptide YY (PYY) is produced in L cells of the intestine and is released after eating. PYY circulates in a truncated form designated PYY(3-36). PYY(3-36) is thought to be a physiologic anorexigenic peptide. The objective of the current study was to test the effect of exogenous PYY(3-36) on food intake in non-human primates exposed to different ovarian steroid milieus. The study was conducted in four ovariectomized cynomolgus monkeys replaced with estrogen alone for 2 weeks followed by estrogen in combination with progesterone for 2 weeks to mimic the menstrual cycle. The effect of PYY(3-36) on food intake was tested during each week of the simulated menstrual cycle by comparing the 2 h food intake following intracerebroventricular (icv) injection of artificial cerebrospinal fluid (aCSF) or PYY(3-36). Despite considerable variation in food intake following aCSF, PYY(3-36) consistently inhibited food consumption, except during week 2 of estrogen plus progesterone replacement. PYY(3-36) reduced food consumption by 16.2 g (95% confidence interval (CI)=4.5-27.9 g) and 26.6 g (95% CI=7.3-45.9 g) in weeks 1 and 2 respectively of estrogen only treatment and by 38.2 g (95% CI=26.1-50.2 g) in week 1 of estrogen plus progesterone treatment. In contrast, PYY(3-36) injected in week 2 of estrogen plus progesterone did not consistently inhibit food intake (13.1 g; CI=-49.5-75.7). This is the first study to report the effect of PYY(3-36) on food consumption in female monkeys. We conclude that icv administration of PYY(3-36) has a strong anorexic effect in female cynomolgus monkeys and that sensitivity to PYY(3-36) may be influenced by the ovarian steroid milieu.

Adeno-associated virus-mediated expression and constitutive secretion of NPY or NPY13-36 suppresses seizure activity in vivo

Neuropeptide Y (NPY) is a 36-amino-acid peptide that attenuates seizure activity following direct infusion or adeno-associated virus (AAV)-mediated expression in the central nervous system. However, NPY activates all NPY receptor subtypes, potentially causing unwanted side effects. NPY13-36 is a C-terminal peptide fragment of NPY that primarily activates the NPY Y2 receptor, thought to mediate the antiseizure activity. Therefore, we investigated if recombinant adeno-associated virus-mediated expression and constitutive secretion of NPY or NPY13-36 could alter limbic seizure sensitivity. Rats received bilateral piriform cortex infusions of AAV vectors that express and constitutively secrete full-length NPY (AAV-FIB-NPY) or NPY13-36 (AAV-FIB-NPY13-36). Control rats received no infusion, as we have previously shown that vectors expressing and secreting reporter genes like GFP (AAV-FIB-EGFP), as well as vectors expressing peptides that lack secretion sequences (AAV-GAL) have no effect on seizures. One week later, all animals received kainic acid (10 mg kg(-1), intraperitoneally), and the latencies to wet dog shakes and limbic seizure behaviors were determined. Although both control and vector-treated rats developed wet dog shake behaviors with similar latencies, the latencies to class III and class IV limbic seizures were significantly prolonged in both NPY- and NPY13-36-treated groups. Thus, AAV-mediated expression and constitutive secretion of NPY and NPY13-36 is effective in attenuating limbic seizures, and provides a platform for delivering therapeutic peptide fragments with increased receptor selectivity.

Neuropeptide Y-induced enhancement of the evoked release of newly synthesized dopamine in rat striatum: Mediation by Y2 receptors

The purpose of the present study was to determine whether or not activation of neuropeptide Y (NPY) receptors resulted in an enhancement or attenuation of the KCl (50 mM) evoked release of [3H]dopamine newly synthesized from [3H]tyrosine in superfused striatal slices and, if so to identify the NPY receptor subtype mediating the effect. Rat striatal slices were prepared and placed in microsuperfusion chambers and continuously superfused with physiological buffer containing 50 microCi/ml of l-3-5-[3H]tyrosine. Superfusate effluents were collected and analyzed for [3H]dopamine by liquid scintillation spectrometry following amberlite CG50 and alumina chromatography. NPY agonists (NPY and PYY3-36) were added 6 min prior to the addition of KCl, while the Y1, Y2, and Y5 antagonist BIBO3304, BIIE0246 and CGP71683A, respectively were added 6 min prior to the agonists. Continuous superfusion with [3H]tyrosine resulted in the production of [3H]dopamine which reached a steady state at approximately 48 min. Depolarization with KCl resulted in a 2- to 3-fold increase in [3H]dopamine overflow. NPY and PYY3-36 produced a concentration dependent enhancement in the KCl induced increase in newly synthesized [3H]dopamine overflow. The Y2 antagonist BIIE0246 produced an attenuation of both the NPY and PYY3-36 induced enhancement while the Y1 antagonist BIBO3304 and theY5 antagonist CGP71683A failed to alter the NPY or PYY3-36 induced enhancement. These results are consistent with the NPY-Y2 receptor subtype mediating the facilitatory effect.

Ventricular fibrillation induced by ischemia-reperfusion is not prevented by the NPY Y2 receptor antagonist BIIE0246

Neuropeptide Y is released together with norepinephrine from sympathetic nerve terminals during conditions of increased sympathetic activity. Neuropeptide Y is known to inhibit vagal activity, and accordingly, it might increase the risk for ventricular fibrillation during myocardial ischemia-reperfusion, with concomitant sympathetic stimulation. Counteracting the inhibiting effect of neuropeptide Y by the specific neuropeptide Y2 antagonist, BIIE0246, we expected occurrence of ventricular fibrillation in association with repeated periods of myocardial ischemia-reperfusion to decrease. The midleft anterior descending coronary artery was repeatedly occluded in 16 open-chest pigs. Eight pigs received BIIE0246, and the controls received the vehicle only. Ventricular fibrillation developed in 2 animals of the control group, but in 4 pigs receiving BIIE0246. Occurrence of ventricular fibrillation and ventricular tachycardia did not differ significantly between the 2 groups, and in association with repeated periods of regional myocardial ischemia, did not decline in pigs treated by the specific neuropeptide Y2-receptor antagonist BIIE0246.

Neuropeptide Y: potential role in recurrent developmental seizures

Seizures induce profound plastic changes in the brain, including altered expression of neuropeptide Y (NPY) and its receptors. Here, I discuss a potential role of NPY plasticity in the developmental brain: in a rat model of febrile seizures (FS), the most common type of seizures in infants and young children, NPY expression was up-regulated in hippocampus after experimentally induced FS. Interestingly, NPY up-regulation was associated with an increased seizure threshold for additional (recurrent) FS, and this effect was abolished when an antagonist against NPY receptor type 2 was applied. These findings suggest that inhibitory actions of NPY, released after seizures, exert a protective effect that reduces the risk of seizure recurrence in the developing brain.

Peptide YY: a neuroendocrine neighbor of note

Endocrine cells, enteric neurons and enterocytes provide an integrated functional defense against luminal factors, including nutrients, microbes and toxins. Prominent among intrinsic mediators is peptide YY (PYY) which is present in approximately 50% of colorectal endocrine cells and neuropeptide Y (NPY), a neurotransmitter expressed in submucous and myenteric nerves. Both peptides and their long fragments (PYY(3-36) and NPY(3-36)) are potent, long-lasting anti-secretory agents in vitro and in vivo and, they provide significant Y receptor-mediated absorptive tone in human and mouse colon mucosa. The main function of the colon is to absorb 90% of approximately 2l of daily ileal effluent (in adult humans) and Y-absorptive tone can contribute significantly to this electrolyte absorption. Blockade or loss of this mucosal Y-absorptive tone (i.e. with Y(1) or Y(2) antagonists) leads to hypersecretion and potentially to diarrhea, so Y agonists are predicted to rescue absorption by mimicking endogenous neuroendocrine PYY or neuronal NPY.

Protein kinase C activity blocks neuropeptide Y-mediated inhibition of glutamate release and contributes to excitability of the hippocampus in status epilepticus

The unbalanced excitatory/inhibitory neurotransmitter function in the neuronal network afflicted by seizures is the main biochemical and biophysical hallmark of epilepsy. The aim of this work was to identify changes in the signaling mechanisms associated with neuropeptide Y (NPY)-mediated inhibition of glutamate release that may contribute to hyperexcitability. Using isolated rat hippocampal nerve terminals, we showed that the KCl-evoked glutamate release is inhibited by NPY Y2 receptor activation and is potentiated by the stimulation of protein kinase C (PKC). Moreover, we observed that immediately after status epilepticus (6 h postinjection with kainate, 10 mg/kg), the functional inhibition of glutamate release by NPY Y2 receptors was transiently blocked concomitantly with PKC hyperactivation. The pharmacological blockade of seizure-activated PKC revealed again the Y2 receptor-mediated inhibition of glutamate release. The functional activity of PKC immediately after status epilepticus was assessed by evaluating phosphorylation of the AMPA receptor subunit GluR1 (Ser-831), a substrate for PKC. Moreover, NPY-stimulated [35S]GTPgammaS autoradiographic binding studies indicated that the common target for Y2 receptor and PKC on the inhibition/potentiation of glutamate release was located downstream of the Y2 receptor, or its interacting G-protein, and involves voltage-gated calcium channels.

Neuropeptide Y (NPY) modulates oxidative burst and nitric oxide production in carrageenan-elicited granulocytes from rat air pouch

We studied the effects of neuropeptide Y (NPY) and NPY-related receptor specific peptides on functions of carrageenan-elicited granulocytes in vitro and ability of NPY to modulate carrageenan-induced air pouch inflammation in rats in vivo. Anti-inflammatory effect of NPY comprises reduced granulocyte accumulation into the air pouch, to some extent attenuation of phagocytosis, attained via Y1 receptor, and considerable decrease in peroxide production, albeit mediated via Y2 and Y5 receptors activation. Conversely, NPY increases nitric oxide production and this potentiation is mediated via Y1 receptor. It is concluded that NPY Y1 and Y2/Y5 receptors' interaction participates in NPY-induced modulation of granulocyte functions related to inflammation.

Neuropeptide Y receptors; antisecretory control of intestinal epithelial function

This paper reviews the cellular localisation, mechanisms of release and intestinal absorptive actions of neuropeptide Y and its related peptides, peptide YY, pancreatic polypeptide and major fragments NPY(3-36) and PYY(3-36). While NPY is commonly found in inhibitory enteric neurons that can be interneurons, motor neurons or secretomotor-nonvasodilator in nature, its analogue, peptide YY in contrast, is located in neuroendocrine L-cells that predominate in the colorectal mucosa. Peptide YY is released from these cells when nutrients arrive in the small or large bowel, exerting paracrine as well as hormonal actions. Pancreatic polypeptide is found in relatively few, scattered intestinal endocrine cells, the majority of this peptide being produced by, and released from pancreatic islet F-cells in response to food intake. An introduction to the current pharmacology of this family of peptides is provided and the different types of neuropeptide Y (termed Y) receptors, their agonist preferences, antagonism, and preferred signalling pathways, are described. Our current understanding of specific Y receptor localisation within the intestine as determined by immunohistochemistry, is presented as a prelude to an assessment of functional studies that have monitored ion transport across isolated mucosal preparations. It is becoming clear that three Y receptor types are significant functionally in human colon, as well as particular rodent models (e.g. mouse) and these, namely the Y(1), Y(2) and Y(4) receptors, are discussed in detail. Their presence within the basolateral aspect of the epithelial layer (Y(1) and Y(4) receptors) or on enteric neurons (Y(1) and Y(2) receptors) and their activation by endogenous neuropeptide Y, peptide YY (Y(1) and Y(2) receptors) or pancreatic polypeptide (which prefers Y(4) receptors) results consistently in antisecretory/absorptive responses. The recent use of novel mouse knockouts has helped establish loss of specific intestinal functions including Y(1) and Y(2) receptor-mediated absorptive tone in colon mucosa. Progress in this field has been rapid recently, aided by the availability of selective antagonists and mutant mice lacking either one (e.g. Y(4)-/-, for which no antagonists exist at present) or more Y receptor types. It is therefore timely to review this work and present a rational basis for developing stable synthetic Y receptor agonists as novel anti-diarrhoeals.

Neuropeptide Y regulates recurrent mossy fiber synaptic transmission less effectively in mice than in rats: Correlation with Y2 receptor plasticity

A unique feature of temporal lobe epilepsy is the formation of recurrent excitatory connections among granule cells of the dentate gyrus as a result of mossy fiber sprouting. This novel circuit contributes to a reduced threshold for granule cell synchronization. In the rat, activity of the recurrent mossy fiber pathway is restrained by the neoexpression and spontaneous release of neuropeptide Y (NPY). NPY inhibits glutamate release tonically through activation of presynaptic Y2 receptors. In the present study, the effects of endogenous and applied NPY were investigated in C57Bl/6 mice that had experienced pilocarpine-induced status epilepticus and subsequently developed a robust recurrent mossy fiber pathway. Whole cell patch clamp recordings made from dentate granule cells in hippocampal slices demonstrated that, as in rats, applied NPY inhibits recurrent mossy fiber synaptic transmission, the Y2 receptor antagonist (S)-N2-[[1-[2-[4-[(R,S)-5,11-dihydro-6(6H)-oxodibenz[b,e]azepin-11-yl]-1-piperazinyl]-2-oxoethyl]cyclopentyl]acetyl]-N-[2-[1,2-dihydro-3,5(4H)-dioxo-1,2-diphenyl-3H-1,2,4-triazol-4-yl]ethyl]-argininamide (BIIE0246) blocks its action and BIIE0246 enhances synaptic transmission when applied by itself. Y5 receptor agonists had no significant effect. Thus spontaneous release of NPY tonically inhibits synaptic transmission in mice and its effects are mediated by Y2 receptor activation. However, both NPY and BIIE0246 were much less effective in mice than in rats, despite apparently equivalent expression of NPY in the recurrent mossy fibers. Immunohistochemistry indicated greater expression of Y2 receptors in the mossy fiber pathway of normal mice than of normal rats. Pilocarpine-induced status epilepticus markedly reduced the immunoreactivity of mouse mossy fibers, but increased the immunoreactivity of rat mossy fibers. Mossy fiber growth into the inner portion of the dentate molecular layer was associated with increased Y2 receptor immunoreactivity in rat, but not in mouse. These contrasting receptor changes can explain the quantitatively different effects of endogenously released and applied NPY on recurrent mossy fiber transmission in mice and rats.

Neuropeptide Y Induced Attenuation of Catecholamine Synthesis in the Rat Mesenteric Arterial Bed

The effect of neuropeptide Y (NPY) on the basal and nerve stimulation-induced increase in norepinephrine synthesis was studied in the isolated and perfused mesenteric arterial bed of the rat. Tyrosine hydroxylation, the rate-limiting step in catecholamine (CA) biosynthesis, was assessed by measuring the accumulation of DOPA in the perfusate/superfusate overflow after perfusion of the mesenteric arterial bed with the decarboxylase inhibitor m-hydroxybenzyl hydralazine (NSD-1015). Treatment with NDS-1015 resulted in a time-dependent increase in DOPA production and nerve stimulation (8 Hz, supramaximal voltage, 2 ms duration) increased DOPA production even further. NPY 1 to 100 nM was observed to produce a concentration-dependent attenuation in both the basal and nerve stimulation-induced increase in DOPA formation. To come to an understanding of the NPY receptor subtype mediating the inhibition of CA synthesis, the rank order of potency of a series of NPY analogs with varying selectivity for NPY receptor subtypes including intestinal polypeptide (PYY), PYY 13-36, Leu36 Pro34 NPY, human pancreatic polypeptide (h-PP), and rat pancreatic polypeptide (r-PP) were determined. In addition, the effect of various selective NPY antagonists on the inhibitory effect of NPY was also examined. These included the Y1 antagonist BIB03304, the Y2 antagonist BIIE0246, and the Y5 antagonist CGP71683. The IC50's for NPY, PYY, PYY13-36, Leu31 Pro34 NPY, and hPP in inhibiting CA synthesis were 5, 7, 15, 30, and 33 nM respectively. rPP failed to inhibit CA synthesis. All 3 of the NPY antagonists produced attenuation of the NPY-induced inhibition of CA synthesis, but it took a combination of all 3 to completely block the effect of a maximal inhibitory concentration of NPY. These results demonstrate that NPY inhibits CA synthesis in the perfused mesenteric arterial bed and can do so by activation of a variety of receptors including the Y1, Y2, and Y5.

Influence of endogenous neuropeptide Y (NPY) on the sympathetic-parasympathetic interaction in the canine heart

The purpose of this study was to examine the sympathetic-parasympathetic interactions on heart rate through release of neuropeptide Y (NPY) and its action on prejunctional NPY Y2 receptors on vagal and sympathetic nerve fibers. In other studies on various preparations and in various organs, attenuation of transmitter release has in fact been demonstrated through activation of the NPY Y2 receptor. In the present study on anesthetized dogs we examine, however, for the first time if vagal bradycardia is attenuated by endogenous NPY released during intense cardiac sympathetic stimulation. In addition, we explore if sympathetic transmitter release and heart rate, during moderate sympathetic stimulation, are affected through this receptor system. The significance of the NPY Y2 receptor was revealed by performing experiments before and after administration of its specific receptor antagonist BIIE0246. We found that attenuation of the bradycardia during vagal nerve stimulation was dose-dependently counteracted by BIIE0246 and that the tachycardia elicited by sympathetic stimulation remained unaffected after NPY Y2 receptor blockade. Thus, endogenous NPY appears to attenuate vagal bradycardia by stimulating prejunctional NPY Y2 receptors on cardiac vagal nerve terminals and, less efficiently, to attenuate transmitter release and tachycardia through a feedback loop on the cardiac sympathetic nerve fibers.

Neuropeptide Y modulates excitatory synaptic transmission in the olfactory bulb

Although the olfactory bulb contains one of the highest concentrations of neuropeptide Y in the CNS, its function in the bulb remains unclear. In this study, we used whole-cell electrophysiological, molecular, and primary culture techniques to investigate neuropeptide Y gene expression and neuromodulatory actions of neuropeptide Y on rat olfactory bulb neurons. Northern analysis showed that neuropeptide Y mRNA increases with animal age or time in culture, in a parallel manner. In electrophysiology experiments, agonists that activate neuropeptide Y receptors (whole neuropeptide Y) and the Y2 receptor subtype (neuropeptide Y 13-36) reduced spontaneous excitatory activity in bulb interneurons. In investigating potential presynaptic effects, both agonists reduced the amplitude of calcium channel currents in the presynaptic (mitral/tufted) cell. Also consistent with a presynaptic effect, both agonists reduced the frequency but not the amplitude of miniature excitatory postsynaptic currents (or "minis") in interneurons. In examining potential postsynaptic effects, both agonists slightly increased membrane resistance but had no effect on currents evoked by glutamate. Together, these data suggest that neuropeptide Y inhibits excitatory neurotransmission between olfactory bulb neurons via a presynaptic effect on transmitter (glutamate) release.

Spontaneous release of neuropeptide Y tonically inhibits recurrent mossy fiber synaptic transmission in epileptic brain

In the pilocarpine model of temporal lobe epilepsy, mossy fibers coexpress the inhibitory transmitter neuropeptide Y (NPY) with glutamate. The effects of endogenous and applied NPY on recurrent mossy fiber synaptic transmission were investigated with the use of whole-cell voltage-clamp and field recordings in rat hippocampal slices. Applied NPY reversibly inhibited synaptic transmission at recurrent mossy fiber synapses on dentate granule cells but not at perforant path or associational-commissural synapses. It also reduced the frequency of miniature EPSCs (mEPSCs) in granule cells from epileptic, but not control, rats and depressed granule cell epileptiform activity dependent on the recurrent mossy fiber pathway. These actions of NPY were mediated by activation of presynaptic Y2 receptors. The Y2 receptor antagonist (S)-N2-[[1-[2-[4-[(R,S)-5,11-dihydro-6(6H)-oxodibenz[b,e]azepin-11-yl]-1-piperazinyl]-2-oxoethyl]cyclopentyl]acetyl]-N-[2-[1,2-dihydro-3,5(4H)-dioxo-1,2-diphenyl-3H-1,2,4-triazol-4-yl]ethyl]argininamide (BIIE0246) not only blocked the effects of NPY but also enhanced recurrent mossy fiber synaptic transmission, the frequency of mEPSCs, and the magnitude of mossy fiber-evoked granule cell epileptiform activity when applied by itself. Several observations supported the selectivity of BIIE0246. These results suggest that even the spontaneous release of NPY (or an active metabolite) from recurrent mossy fibers is sufficient to depress glutamate release from this pathway. Tonic release of NPY accounts at least partially for the low probability of glutamate release from recurrent mossy fiber terminals, impedes the ability of these fibers to synchronize granule cell discharge, and may protect the hippocampus from seizures that involve the entorhinal cortex. This pathway may synchronize granule cell discharge more effectively in human brain than in rat because of its lower expression of NPY.

High expression of neuropeptide y receptors in tumors of the human adrenal gland and extra-adrenal paraganglia

PURPOSE

Recently, a role of neuropeptide Y (NPY) in tumor biology was suggested based on the high density of NPY receptors in breast and ovarian cancers. The high frequency of NPY receptors in steroid hormone-producing ovarian sex cord-stromal tumors, together with the known influence of NPY on steroid hormone and catecholamine secretion in the rodent adrenal gland, led to the investigation of NPY receptor expression in the human adrenal gland and related tumors.

EXPERIMENTAL DESIGN

Fifteen adrenal cortical tumors, 20 paragangliomas, 23 pheochromocytomas, 20 neuroblastomas, and 8 normal adrenal glands were investigated by in vitro NPY receptor autoradiography using 125I-labeled peptide YY in competition experiments with receptor subtype selective analogs.

RESULTS

Ninety three percent of cortical tumors express Y1, 35% of pheochromocytomas and 61% of paragangliomas express Y1 and Y2, and 90% of neuroblastomas express Y2 receptors. The NPY receptors in pheochromocytomas, paragangliomas, and neuroblastomas are often expressed concomitantly with the NPY hormone detected immunohistochemically. The adrenal cortex strongly expresses Y1, whereas no NPY receptors are found in the adrenal medulla.

CONCLUSIONS

These receptor data suggest a role of NPY in adrenal cortical tumors and, together with the strong NPY innervation of the cortex, a physiologic role in the adrenal gland, mediated by Y1 receptors. These NPY receptors are a potential new molecular target for the therapy of malignant tumors.

Role of serotonin (5-HT) in the antidepressant-like properties of neuropeptide Y (NPY) in the mouse forced swim test

Neuropeptide Y (NPY) is thought to be implicated in depressive disorders. The mouse forced swim test (FST) is an animal model widely used as a predictor of the efficacy of antidepressant drugs. The present study was undertaken to explore the possible contribution of endogenous serotonin (5-HT) systems in the behavioral effects elicited by NPY in this model. The selective serotonin re-uptake inhibitor (SSRI), fluoxetine, was also tested for comparison. 5-HT was depleted prior to testing by the administration of the tryptophan hydroxylase inhibitor p-chlorophenylalanine (PCPA; 300 mg/kg, i.p., each day for 3 days; control mice received saline-vehicle over the same period). On the fourth day, mice received NPY (3 nmol, I.C.V.), fluoxetine (16 mg/kg, i.p.) or saline injections before testing in the FST. Both NPY and fluoxetine significantly reduced immobility time in saline-treated control animals. Pre-treatment with PCPA significantly blocked the effects of fluoxetine in the FST, confirming the role of endogenous 5-HT. Similarly, pre-treatment with PCPA also significantly attenuated the anti-immobility effects of NPY, thus suggesting a role for 5-HT in the effects of NPY in the FST. Quantitative receptor autoradiography revealed increases in specific [125I][Leu31, Pro34]PYY sites that were sensitive to BIBP3226 (Y1-like sites) in various brain regions. Specific [125I]GR231118 and [125I]PYY(3-36) binding levels were not changed following PCPA treatment, suggesting that depletion of endogenous 5-HT resulted in an apparent increase in the level of Y1 sites in their high-affinity state. Taken together, these results suggest a role for 5-HT-related systems in the antidepressant-like properties of NPY.