Evidence for different pre-and post-junctional receptors for neuropeptide Y and related peptides

Illuminating the neuropeptide Y4 receptor and its ligand pancreatic polypeptide from a structural, functional, and therapeutic perspective

The neuropeptide Y4 receptor (Y4R), a rhodopsin-like G protein-coupled receptor (GPCR) and the hormone pancreatic polypeptide (PP) are members of the neuropeptide Y family consisting of four receptors (Y1R, Y2R, Y4R, Y5R) and three highly homologous peptide ligands (neuropeptide Y, peptide YY, PP). In this family, the Y4R is of particular interest as it is the only subtype with high affinity to PP over NPY. The Y4R, as a mediator of PP signaling, has a pivotal role in appetite regulation and energy homeostasis, offering potential avenues for the treatment of metabolic disorders such as obesity. PP as anorexigenic peptide is released postprandial from the pancreas in response to food intake, induces satiety signals and contributes to hamper excessive food intake. Moreover, this system was also described to be associated with different types of cancer: overexpression of Y4R have been found in human adenocarcinoma cells, while elevated levels of PP are related to the development of pancreatic endocrine tumors. The pharmacological relevance of the Y4R advanced the search for potent and selective ligands for this receptor subtype, which will be significantly progressed through the elucidation of the active state PP-Y4R cryo-EM structure. This review summarizes the development of novel PP-derived ligands, like Obinepitide as dual Y2R/Y4R agonist in clinical trials or UR-AK86c as small hexapeptide agonist with picomolar affinity, as well as the first allosteric modulators that selectively target the Y4R, e.g. VU0506013 as potent Y4R positive allosteric modulator or (S)-VU0637120 as allosteric antagonist. Here, we provide valuable insights into the complex physiological functions of the Y4R and PP and the pharmacological relevance of the system in appetite regulation to open up new avenues for the development of tool compounds for targeted therapies with potential applications in metabolic disorders.

Neuropeptide Y Signaling Regulates Recurrent Excitation in the Auditory Midbrain

Neuropeptides play key roles in shaping the organization and function of neuronal circuits. In the inferior colliculus (IC), which is in the auditory midbrain, Neuropeptide Y (NPY) is expressed by a class of GABAergic neurons that project locally and outside the IC. Most neurons in the IC have local axon collaterals; however, the organization and function of local circuits in the IC remain unknown. We previously found that excitatory neurons in the IC can express the NPY Y1 receptor (Y1R+) and application of the Y1R agonist, [Leu31, Pro34]-NPY (LP-NPY), decreases the excitability of Y1R+ neurons. As NPY signaling regulates recurrent excitation in other brain regions, we hypothesized that Y1R+ neurons form interconnected local circuits in the IC and that NPY decreases the strength of recurrent excitation in these circuits. To test this hypothesis, we used optogenetics to activate Y1R+ neurons in mice of both sexes while recording from other neurons in the ipsilateral IC. We found that nearly 80% of glutamatergic IC neurons express the Y1 receptor, providing extensive opportunities for NPY signaling to regulate local circuits. Additionally, Y1R+ neuron synapses exhibited modest short-term synaptic plasticity, suggesting that local excitatory circuits maintain their influence over computations during sustained stimuli. We further found that application of LP-NPY decreased recurrent excitation in the IC, suggesting that NPY signaling strongly regulates local circuit function in the auditory midbrain. Our findings show that Y1R+ excitatory neurons form interconnected local circuits in the IC, and their influence over local circuits is regulated by NPY signaling.SIGNIFICANCE STATEMENT Local networks play fundamental roles in shaping neuronal computations in the brain. The IC, localized in the auditory midbrain, plays an essential role in sound processing, but the organization of local circuits in the IC is largely unknown. Here, we show that IC neurons that express the Neuropeptide Y1 receptor (Y1R+ neurons) make up most of the excitatory neurons in the IC and form interconnected local circuits. Additionally, we found that NPY, which is a powerful neuromodulator known to shape neuronal activity in other brain regions, decreases the extensive recurrent excitation mediated by Y1R+ neurons in local IC circuits. Thus, our results suggest that local NPY signaling is a key regulator of auditory computations in the IC.

Morphological study of neuropeptide Y expression in human and mouse anterior insular cortex: Overexpression in the insular cortex and nucleus accumbens in obese mice on a long-term obesogenic diet

BACKGROUND

The anterior lobe of the insular cortex (aINS) is a cortical region that has reciprocal connections with limbic centers such as the anterior cingulate cortex, prefrontal cortex, amygdala and nucleus accumbens (NAc). In fact, the aINS has been involved in the integration of autonomic information for emotional and motivational functions. The compulsive consumption of drugs or high-fat foods induces alterations at both behavioural and brain levels. Brain reward circuits are altered in response to continued intake, in particular the dopaminergic projections from the ventral tegmental area (VTA) to the NAc. The aINS has multiple connections with the components of this system. In recent years, efforts have been made to better understand the fundamental role of the aINS in addiction, making it one of the key centres of interest for research into new treatments for addiction.

OBJECTIVES

The present work focuses on studying 1.- whether the human aINS expresses orexigenic peptides such as neuropeptide Y (NPY), a peptide known to induce hyperphagia, and which has been implicated in the onset and development of obesity, 2.- the long-term effect of an obesogenic diet on NPY expression in the aINS and NAc of C57BL/6 mice.

METHODS

A total of 17 female C57BL/6 J mice were used in this study. Female mice were fed ad libitum with water and, either a standard diet (SD) or a high-fat diet (HFD) to induce obesity. There were seven female mice on the SD and ten on the HFD. The duration of the experiment was 180 days. We also studied 3 human adult brains (1 male and 2 females, mean age 55.7 ± 5.2 years). The morphological study was performed using immunohistochemistry and double immunofluorescence techniques to study the neurochemical profile of NPY neurons of the aINS and NAc of humans and mice.

RESULTS

Our morphological analysis demonstrates for the first time the basal expression of NPY in different layers of the human cortex (II, III, IV, V/VI), in a pattern similar to previous studies in other species. Furthermore, we observed an increase in the number of NPY-positive cells and their intracytoplasmic signal in the aINS and NAc of the obese mice subjected to a long-term obesogenic diet.

CONCLUSIONS

To our knowledge, this is the first study to show the distribution and expression of NPY in the human INS and how its expression is altered after prolonged treatment with an obesogenic diet in obese mice. Our findings may contribute to the understanding of the pathophysiological mechanisms underlying obesity in regions related to the reward system and associated with uncontrolled intake of high-fat foods, thus facilitating the identification of novel therapeutic targets.

Pigment-dispersing factor is present in circadian clock neurons of pea aphids and may mediate photoperiodic signalling to insulin-producing cells

The neuropeptide pigment-dispersing factor (PDF) plays a pivotal role in the circadian clock of most Ecdysozoa and is additionally involved in the timing of seasonal responses of several photoperiodic species. The pea aphid, Acyrthosiphon pisum, is a paradigmatic photoperiodic species with an annual life cycle tightly coupled to the seasonal changes in day length. Nevertheless, PDF could not be identified in A. pisum so far. In the present study, we identified a PDF-coding gene that has undergone significant changes in the otherwise highly conserved insect C-terminal amino acid sequence. A newly generated aphid-specific PDF antibody stained four neurons in each hemisphere of the aphid brain that co-express the clock protein Period and have projections to the pars lateralis that are highly plastic and change their appearance in a daily and seasonal manner, resembling those of the fruit fly PDF neurons. Most intriguingly, the PDF terminals overlap with dendrites of the insulin-like peptide (ILP) positive neurosecretory cells in the pars intercerebralis and with putative terminals of Cryptochrome (CRY) positive clock neurons. Since ILP has been previously shown to be crucial for seasonal adaptations and CRY might serve as a circadian photoreceptor vital for measuring day length, our results suggest that PDF plays a critical role in aphid seasonal timing.

Neuropeptide Y signaling regulates recurrent excitation in the auditory midbrain

Neuropeptides play key roles in shaping the organization and function of neuronal circuits. In the inferior colliculus (IC), which is located in the auditory midbrain, Neuropeptide Y (NPY) is expressed by a large class of GABAergic neurons that project locally as well as outside the IC. The IC integrates information from numerous auditory nuclei making the IC an important hub for sound processing. Most neurons in the IC have local axon collaterals, however the organization and function of local circuits in the IC remains largely unknown. We previously found that neurons in the IC can express the NPY Y1 receptor (Y 1 R + ) and application of the Y 1 R agonist, [Leu 31 , Pro 34 ]-NPY (LP-NPY), decreases the excitability of Y 1 R + neurons. To investigate how Y 1 R + neurons and NPY signaling contribute to local IC networks, we used optogenetics to activate Y 1 R + neurons while recording from other neurons in the ipsilateral IC. Here, we show that 78.4% of glutamatergic neurons in the IC express the Y1 receptor, providing extensive opportunities for NPY signaling to regulate excitation in local IC circuits. Additionally, Y 1 R + neuron synapses exhibit modest short-term synaptic plasticity, suggesting that local excitatory circuits maintain their influence over computations during sustained stimuli. We further found that application of LP-NPY decreases recurrent excitation in the IC, suggesting that NPY signaling strongly regulates local circuit function in the auditory midbrain. Together, our data show that excitatory neurons are highly interconnected in the local IC and their influence over local circuits is tightly regulated by NPY signaling.

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).

DPP4 (Dipeptidyl Peptidase-4) Inhibition Increases Catecholamines Without Increasing Blood Pressure During Sustained ACE (Angiotensin-Converting Enzyme) Inhibitor Treatment

BACKGROUND

DPP4 (dipeptidyl peptidase-4) inhibitors comprise a class of oral diabetes medication that have the potential for off-target cardiovascular effects. We previously showed that DPP4 inhibition attenuates the hypotensive effect of acute ACE (angiotensin-converting enzyme) inhibition and increases norepinephrine. Here, we investigated the effects of DPP4 during sustained ACE inhibition compared with during therapy with an ARB (angiotensin receptor blocker) or calcium channel blocker (neutral comparator) in a randomized, double-blinded crossover study.

METHODS

We enrolled 106 adults with type 2 diabetes and hypertension and 100 received intervention. Subjects were randomized to one of 3 blood pressure arms: ramipril, valsartan, or amlodipine for a total of 15 weeks and received 3 one-week crossover therapies in random order: placebo + placebo, sitagliptin + placebo, and sitagliptin + aprepitant separated by 4-week washout.

RESULTS

We found that DPP4 inhibition increased norepinephrine during ramipril but did not increase blood pressure. Aprepitant, a NK1 (substance P) receptor blocker, lowered standing heart rate during renin-angiotensin-aldosterone system blockade with ramipril or valsartan.

CONCLUSIONS

Increased catecholamines during concurrent ACE and DPP4 inhibition may contribute to cardiovascular complications in patients predisposed to heart failure.

Regulation of neuropeptide Y in body microenvironments and its potential application in therapies: a review

Neuropeptide Y (NPY), one of the most abundant neuropeptides in the body, is widely expressed in the central and peripheral nervous systems and acts on the cardiovascular, digestive, endocrine, and nervous systems. NPY affects the nutritional and inflammatory microenvironments through its interaction with immune cells, brain-derived trophic factor (BDNF), and angiogenesis promotion to maintain body homeostasis. Additionally, NPY has great potential for therapeutic applications against various diseases, especially as an adjuvant therapy for stem cells. In this review, we discuss the research progress regarding NPY, as well as the current evidence for the regulation of NPY in each microenvironment, and provide prospects for further research on related diseases.

NPY and Gene Therapy for Epilepsy: How, When,... and Y

Neuropeptide Y (NPY) is a neuropeptide abundantly expressed in the mammalian central and peripheral nervous system. NPY is a pleiotropic molecule, which influences cell proliferation, cardiovascular and metabolic function, pain and neuronal excitability. In the central nervous system, NPY acts as a neuromodulator, affecting pathways that range from cellular (excitability, neurogenesis) to circuit level (food intake, stress response, pain perception). NPY has a broad repertoire of receptor subtypes, each activating specific signaling pathways in different tissues and cellular sub-regions. In the context of epilepsy, NPY is thought to act as an endogenous anticonvulsant that performs its action through Y2 and Y5 receptors. In fact, its overexpression in the brain with the aid of viral vectors can suppress seizures in animal models of epilepsy. Therefore, NPY-based gene therapy may represent a novel approach for the treatment of epilepsy patients, particularly for pharmaco-resistant and genetic forms of the disease. Nonetheless, considering all the aforementioned aspects of NPY signaling, the study of possible NPY applications as a therapeutic molecule is not devoid of critical aspects. The present review will summarize data related to NPY biology, focusing on its anti-epileptic effects, with a critical appraisal of key elements that could be exploited to improve the already existing NPY-based gene therapy approaches for epilepsy.

Contribution of NPY Y5 Receptors to the Reversible Structural Remodeling of Basolateral Amygdala Dendrites in Male Rats Associated with NPY-Mediated Stress Resilience

Endogenous neuropeptide Y (NPY) and corticotrophin-releasing factor (CRF) modulate the responses of the basolateral amygdala (BLA) to stress and are associated with the development of stress resilience and vulnerability, respectively. We characterized persistent effects of repeated NPY and CRF treatment on the structure and function of BLA principal neurons in a novel organotypic slice culture (OTC) model of male rat BLA, and examined the contributions of specific NPY receptor subtypes to these neural and behavioral effects. In BLA principal neurons within the OTCs, repeated NPY treatment caused persistent attenuation of excitatory input and induced dendritic hypotrophy via Y5 receptor activation; conversely, CRF increased excitatory input and induced hypertrophy of BLA principal neurons. Repeated treatment of OTCs with NPY followed by an identical treatment with CRF, or vice versa, inhibited or reversed all structural changes in OTCs. These structural responses to NPY or CRF required calcineurin or CaMKII, respectively. Finally, repeated intra-BLA injections of NPY or a Y5 receptor agonist increased social interaction, a validated behavior for anxiety, and recapitulated structural changes in BLA neurons seen in OTCs, while a Y5 receptor antagonist prevented NPY's effects both on behavior and on structure. These results implicate the Y5 receptor in the long-term, anxiolytic-like effects of NPY in the BLA, consistent with an intrinsic role in stress buffering, and highlight a remarkable mechanism by which BLA neurons may adapt to different levels of stress. Moreover, BLA OTCs offer a robust model to study mechanisms associated with resilience and vulnerability to stress in BLA.SIGNIFICANCE STATEMENT Within the basolateral amygdala (BLA), neuropeptide Y (NPY) is associated with buffering the neural stress response induced by corticotropin releasing factor, and promoting stress resilience. We used a novel organotypic slice culture model of BLA, complemented with in vivo studies, to examine the cellular mechanisms associated with the actions of NPY. In organotypic slice cultures, repeated NPY treatment reduces the complexity of the dendritic extent of anxiogenic BLA principal neurons, making them less excitable. NPY, via activation of Y5 receptors, additionally inhibits and reverses the increases in dendritic extent and excitability induced by the stress hormone, corticotropin releasing factor. This NPY-mediated neuroplasticity indicates that resilience or vulnerability to stress may thus involve neuropeptide-mediated dendritic remodeling in BLA principal neurons.

Small-Molecule Agonists of Ae. aegypti Neuropeptide Y Receptor Block Mosquito Biting

Female Aedes aegypti mosquitoes bite humans to obtain blood to develop their eggs. Remarkably, their strong attraction to humans is suppressed for days after the blood meal by an unknown mechanism. We investigated a role for neuropeptide Y (NPY)-related signaling in long-term behavioral suppression and discovered that drugs targeting human NPY receptors modulate mosquito host-seeking. In a screen of all 49 predicted Ae. aegypti peptide receptors, we identified NPY-like receptor 7 (NPYLR7) as the sole target of these drugs. To obtain small-molecule agonists selective for NPYLR7, we performed a high-throughput cell-based assay of 265,211 compounds and isolated six highly selective NPYLR7 agonists that inhibit mosquito attraction to humans. NPYLR7 CRISPR-Cas9 null mutants are defective in behavioral suppression and resistant to these drugs. Finally, we show that these drugs can inhibit biting and blood-feeding on a live host, suggesting a novel approach to control infectious disease transmission by controlling mosquito behavior. VIDEO ABSTRACT.

Contribution of Baroreflex Afferent Pathway to NPY-Mediated Regulation of Blood Pressure in Rats

Neuropeptide Y (NPY), a metabolism-related cardiovascular factor, plays a crucial role in blood pressure (BP) regulation via peripheral and central pathways. The expression of NPY receptors (Y₁R/Y₂R) specific to baroreflex afferents impacts on the sexually dimorphic neural control of circulation. This study was designed to investigate the expression profiles of NPY receptors in the nodose ganglion (NG) and nucleus tractus solitary (NTS) under hypertensive conditions. To this end, rats with hypertension induced by N^G-nitro-L-arginine methylester (L-NAME) or high fructose drinking (HFD), and spontaneously hypertensive rats (SHRs) were used to explore the effects/mechanisms of NPY on BP using functional, molecular, and electrophysiological approaches. The data showed that BP was elevated along with baroreceptor sensitivity dysfunction in model rats; Y₁R was up- or down-regulated in the NG or NTS of male and female HFD/L-NAME groups, while Y₂R was only down-regulated in the HFD groups as well as in the NG of the male L-NAME group. In SHRs, Y₁R and Y₂R were both down-regulated in the NTS, and not in the NG. In addition to NPY-mediated energy homeostasis, leptin-melanocortin activation may be essential for metabolic disturbance-related hypertension. We found that leptin and α-melanocyte stimulating hormone (α-MSH) receptors were aberrantly down-regulated in HFD rats. In addition, α-MSH concentrations were reduced and NPY concentrations were elevated in the serum and NTS at 60 and 90 min after acute leptin infusion. Electrophysiological recordings showed that the decay time-constant and area under the curve of excitatory post-synaptic currents were decreased by Y₁R activation in A-types, whereas, both were increased by Y₂R activation in Ah- or C-types. These results demonstrate that sex- and afferent-specific NPY receptor expression in the baroreflex afferent pathway is likely to be a novel target for the clinical management of metabolism-related and essential hypertension.

Pharmacological characterization, cellular localization and expression profile of NPY receptor subtypes Y2 and Y7 in large yellow croaker, Larimichthys crocea

Neuropeptide Y (NPY) receptors are suggested to mediate the multi-physiological functions of NPY family peptides, such as food intake, in teleost fish. However, the structure and signaling of fish NPY receptors are yet to be fully elucidated. In this study, we report the cloning and characterization of two neuropeptide Y receptor subtypes, Y2 (NPY2R) and Y7 (NPY7R), in yellow croaker Larimichthys crocea (L. crocea) (LcNPY2R, LcNPY7R). The gene structure, pharmacological characterization, cell location, and tissue expression of these two receptors were explored. The phylogenetic results showed that LcNPY2R and LcNPY7R had typical G protein-coupled receptor profiles, associated with the Y2 subfamily, with coding sequences that are highly conserved in vertebrates. The expression of both LcNPY2R and LcNPY7R could be activated by LcNPY in HEK293 cells. However, truncated LcNPY_18-36 was only able to activate LcNPY2R at the same level as full length LcNPY. Expression analysis revealed that LcNPY2R mRNA was predominantly expressed in the intestine and liver, whereas LcNPY7R was expressed in the stomach, which indicated that both receptors were related to the digestive system. Overall, our data establishes a molecular basis to determine the actions of LcNPY2R and LcNPY7R, which could be used to elucidate the conserved roles of these receptor-ligand pairs in vertebrates.

Actions of Neuropeptide Y on Synaptic Transmission in the Lateral Habenula

Neuropeptide Y is a peptide neuromodulator with protective roles including anxiolytic and antidepressant-like effects in animal models of depression and post-traumatic stress disorder. The lateral habenula (LHb) is a brain region that encodes aversive information and is closely related with mood disorders. Although LHb neurons express NPY receptors, the physiological roles of NPY in this region remain uninvestigated. In this study, we examined the actions of NPY on synaptic transmission in the LHb using whole cell patch clamp recording. We observed that NPY inhibited excitatory neurotransmission in a subset of LHb neurons whereas potentiating in a small population of neurons. Inhibitory transmission remained unchanged by NPY application in a subset of neurons but was reduced in the majority of LHb neurons recorded. The overall outcome of NPY application was a decrease in the spontaneous firing rate of the LHb, leading to hypoactivation of the LHb. Our observations indicate that although NPY has divergent effects on excitatory and inhibitory transmission, NPY receptor activation decreases LHb activity, suggesting that the LHb may partly mediate the protective roles of NPY in the central nervous system.

Dipeptidyl Peptidase 4 Inhibition Increases Postprandial Norepinephrine via Substance P (NK1 Receptor) During RAAS Inhibition

Context

Dipeptidyl peptidase 4 (DPP4) inhibitors may increase the risk of heart failure. Decreased degradation of vasoactive peptides like substance P [also degraded by angiotensin-converting enzyme (ACE)] and Y1 agonists peptide YY (PYY 1-36) and neuropeptide Y (NPY 1-36) could contribute.

Objective

This study tested the hypothesis that there is an interactive effect of DPP4 inhibition and ACE inhibition (vs antihypertensive control subjects) on vasoactive peptides after a mixed meal.

Participants and Design

Fifty-three patients with type 2 diabetes and hypertension were randomized to double-blind treatment with ramipril, valsartan, or amlodipine for 15 weeks in parallel groups. During the 5th, 10th, and 15th weeks, participants also received placebo + placebo, sitagliptin 100 mg/d + placebo, and sitagliptin + aprepitant 80 mg/d in random order. On the last day of each crossover treatment, participants underwent a mixed-meal study.

Results

Sitagliptin increased postprandial glucagon-like peptide-1 and decreased glucose in all antihypertensive groups. Sitagliptin increased NPY 1-36 and decreased Y2 agonists NPY 3-36 and PYY 3-36 in all groups. During ramipril or valsartan, but not amlodipine, sitagliptin increased postprandial norepinephrine; substance P receptor blockade with aprepitant prevented this effect. Despite increased norepinephrine, sitagliptin decreased postprandial blood pressure during ACE inhibition.

Conclusion

DPP4 inhibition increases postprandial concentrations of the Y1 agonist NPY 1-36. During treatment with an ACE inhibitor or angiotensin receptor blocker, DPP4 inhibition increased postprandial norepinephrine through a substance P receptor–dependent mechanism. Increased NPY 1-36 and norepinephrine could increase risk of heart failure but did not result in higher postprandial blood pressure.

Calcium Signaling Pathways: Key Pathways in the Regulation of Obesity

Nowadays, high epidemic obesity-triggered hypertension and diabetes seriously damage social public health. There is now a general consensus that the body's fat content exceeding a certain threshold can lead to obesity. Calcium ion is one of the most abundant ions in the human body. A large number of studies have shown that calcium signaling could play a major role in increasing energy consumption by enhancing the metabolism and the differentiation of adipocytes and reducing food intake through regulating neuronal excitability, thereby effectively decreasing the occurrence of obesity. In this paper, we review multiple calcium signaling pathways, including the IP3 (inositol 1,4,5-trisphosphate)-Ca²⁺ (calcium ion) pathway, the p38-MAPK (mitogen-activated protein kinase) pathway, and the calmodulin binding pathway, which are involved in biological clock, intestinal microbial activity, and nerve excitability to regulate food intake, metabolism, and differentiation of adipocytes in mammals, resulting in the improvement of obesity.

The intersection of stress and reward: BNST modulation of aversive and appetitive states

The bed nucleus of the stria terminalis (BNST) is widely acknowledged as a brain structure that regulates stress and anxiety states, as well as aversive and appetitive behaviours. The diverse roles of the BNST are afforded by its highly modular organisation, neurochemical heterogeneity, and complex intrinsic and extrinsic circuitry. There has been growing interest in the BNST in relation to psychopathologies such as anxiety and addiction. Although research on the human BNST is still in its infancy, there have been extensive preclinical studies examining the molecular signature and hodology of the BNST and their involvement in stress and reward seeking behaviour. This review examines the neurochemical phenotype and connectivity of the BNST, as well as electrophysiological correlates of plasticity in the BNST mediated by stress and/or drugs of abuse.

The C-terminal flanking peptide of neuropeptide Y (NPY) is not essential for seizure-suppressant actions of prepro-NPY overexpression in male rats

The full coding sequence of neuropeptide Y (NPY), prepro-NPY, is sequentially metabolized into three peptides; an N-terminus 28-amino acid signaling peptide, the NPY peptide itself (NPY1-36), and a 30-amino acid C-terminus peptide, known as the C-terminal flanking peptide of neuropeptide-Y (CPON). While the signaling peptide directs intracellular trafficking and NPY1-36 is well characterized, the biological function of CPON is unknown. This is noteworthy because CPON is co-stored and co-released along with NPY1-36 and could thus potentially serve important functions. To assess the role of CPON, we adapted a viral genetic approach using two different vector designs encoding NPY, but where the CPON coding sequence was excluded from one of the vectors. Thus, the effect of CPON was indirectly assessed. Male rats received intrahippocampal injections of either a vector encoding NPY1-39 whose metabolism yields NPY1-36 and not CPON, or a prepro-NPY vector encoding both NPY1-36 and CPON. A third vector encoding EGFP served as control. We subsequently studied to what extent CPON might affect seizure susceptibility and memory performance, respectively, to address two important questions to evaluate the potential of NPY gene therapy in epilepsy. Both NPY vectors, as compared to EGFP control, were found to be equally effective at suppressing acute kainate-induced seizures, and both did not influence learning and memory performance in the Morris water maze. Thus CPON itself does not appear to aid actions governed by vector-mediated overexpression of NPY1-36 within the hippocampus. Whether CPON serves other important functions remains to be determined.

Chronic subcutaneous infusion of neurosecretory protein GM increases body mass gain in chicks

Recently we discovered a small hypothalamic protein in the chicken, named neurosecretory protein GL (NPGL), which is associated with body growth and energy metabolism in birds and rodents. Genome database analysis suggested that the NPGL gene has a paralogous gene in vertebrates, named neurosecretory protein GM (NPGM). However, the biological action of NPGM remains unclear. In this study, we investigated whether NPGM affects body growth in chicks. We found that subcutaneous infusion of NPGM for six days increased body mass gain in a dose-dependent manner. Despite the observed increase in body mass, infusion of NPGM did not alter food and water intake. Of note, we observed tendency of mass increase of several peripheral tissues, specifically. When we compared several tissue types, NPGM seemed to induce the largest growth increase in white adipose tissue mass. These results suggest that NPGM may accelerate fat accumulation and body growth. In addition, we analyzed whether NPGM increases body growth through the action of pituitary hormones. However, we observed no significant changes in mRNA expression of pituitary hormones or plasma levels of growth hormone in NPGM-treated chicks. This is the first report describing the biological action of NPGM in vertebrates.

Neuropeptide Y Y2 antagonist treated ovariectomized mice exhibit greater bone mineral density

Osteoporosis, a disease characterized by progressive bone loss and increased risk of fracture, often results from menopausal loss of estrogen in women. Neuropeptide Y has been shown to negatively regulate bone formation, with amygdala specific deletion of the Y2 receptor resulting in increased bone mass in mice. In this study, ovariectomized (OVX) mice were injected once daily with JNJ-31020028, a brain penetrant Y2 receptor small molecule antagonist to determine the effects on bone formation. Antagonist treated mice had reduced weight and showed increased whole-body bone mineral density compared to vehicle-injected mice. Micro computerized tomography (micro-CT) demonstrated increased vertebral trabecular bone volume, connectivity density and trabecular thickness. Femoral micro-CT analysis revealed increased bone volume within trabecular regions and greater trabecular number, without significant difference in other parameters or within cortical regions. A decrease was seen in serum P1NP, a measure used to confirm positive treatment outcomes in bisphosphonate treated patients. C-terminal telopeptide 1 (CTX-1), a blood biomarker of bone resorption, was decreased in treated animals. The higher bone mineral density observed following Y2 antagonist treatment, as determined by whole-body DEXA scanning, is indicative of either enhanced mineralization or reduced bone loss. Additionally, our findings that ex vivo treatment of bone marrow cells with the Y2 antagonist did not affect osteoblast and osteoclast formation suggests the inhibitor is not affecting these cells directly, and suggests a central role for compound action in this system. Our results support the involvement of Y2R signalling in bone metabolism and give credence to the hypothesis that selective pharmacological manipulation of Y2R may provide anabolic benefits for treating osteoporosis.

Spinal activation of the NPY Y1 receptor reduces mechanical and cold allodynia in rats with chronic constriction injury

Neuropeptide tyrosine (NPY) and its associated receptors Y1R and Y2R have been previously implicated in the spinal modulation of neuropathic pain induced by total or partial sectioning of the sciatic nerve. However, their role in chronic constrictive injuries of the sciatic nerve has not yet been described. In the present study, we analyzed the consequences of pharmacological activation of spinal Y1R, by using the specific Y1R agonist Leu³¹Pro³⁴-NPY, in rats with chronic constriction injury (CCI). CCI and sham-injury rats were implanted with a permanent intrathecal catheter (at day 7 after injury), and their response to the administration of different doses (2.5, 5, 7, 10 or 20μg) of Leu³¹Pro³⁴-NPY (at a volume of 10μl) through the implanted catheter, recorded 14days after injury. Mechanical allodynia was tested by means of the up-and-down method, using von Frey filaments. Cold allodynia was tested by application of an acetone drop to the affected hindpaw. Intrathecal Leu³¹Pro³⁴-NPY induced an increase of mechanical thresholds in rats with CCI, starting at doses of 5μg and becoming stronger with higher doses. Intrathecal Leu³¹Pro³⁴ also resulted in reductions in the frequency of withdrawal to cold stimuli, although the effect was somewhat more moderate and mostly observed for doses of 7μg and higher. We thus show that spinal activation of the Y1R is able to reduce neuropathic pain due to a chronic constrictive injury and, together with other studies, support the use of a spinal Y1R agonist as a therapeutic agent against chronic pain induced by peripheral neuropathy.

C-terminal amidation of PACAP-38 and PACAP-27 is dispensable for biological activity at the PAC1 receptor

PACAP-27 and PACAP-38 are the exclusive physiological ligands for the mammalian PAC1 receptor. The role of C-terminal amidation of these ligands at that receptor was examined in neuroendocrine cells expressing the PAC1 receptor endogenously and in non-neuroendocrine cells in which the human and rat PAC1 receptors were expressed from stable single-copy genes driven by the CMV promoter, providing stoichiometrically appropriate levels of this Gs-coupled GPCR in order to examine the potency and intrinsic activity of PACAP ligands and their des-amidated congeners. We found that replacement of the C-terminal glycine residues of PACAP-27 and -38 with a free acid; or extension of either peptide with the two to three amino acids normally found at these positions in PACAP processing intermediates in vivo following endoproteolytic cleavage and after exoproteolytic trimming and glycine-directed amidated, were equivalent in potency to the fully processed peptides in a variety of cell-based assays. These included real-time monitoring of cyclic AMP generation in both NS-1 neuroendocrine cells and non-neuroendocrine HEK293 cells; PKA-dependent gene activation in HEK293 cells; and neuritogenesis and cell growth arrest in NS-1 cells. The specific implications for the role of amidation in arming of secretin-related neuropeptides for biological function, and the general implications for neuropeptide-based delivery in the context of gene therapy, are discussed.

Stress induced obesity: lessons from rodent models of stress

Stress was once defined as the non-specific result of the body to any demand or challenge to homeostasis. A more current view of stress is the behavioral and physiological responses generated in the face of, or in anticipation of, a perceived threat. The stress response involves activation of the sympathetic nervous system and recruitment of the hypothalamic-pituitary-adrenal (HPA) axis. When an organism encounters a stressor (social, physical, etc.), these endogenous stress systems are stimulated in order to generate a fight-or-flight response, and manage the stressful situation. As such, an organism is forced to liberate energy resources in attempt to meet the energetic demands posed by the stressor. A change in the energy homeostatic balance is thus required to exploit an appropriate resource and deliver useable energy to the target muscles and tissues involved in the stress response. Acutely, this change in energy homeostasis and the liberation of energy is considered advantageous, as it is required for the survival of the organism. However, when an organism is subjected to a prolonged stressor, as is the case during chronic stress, a continuous irregularity in energy homeostasis is considered detrimental and may lead to the development of metabolic disturbances such as cardiovascular disease, type II diabetes mellitus and obesity. This concept has been studied extensively using animal models, and the neurobiological underpinnings of stress induced metabolic disorders are beginning to surface. However, different animal models of stress continue to produce divergent metabolic phenotypes wherein some animals become anorexic and lose body mass while others increase food intake and body mass and become vulnerable to the development of metabolic disturbances. It remains unclear exactly what factors associated with stress models can be used to predict the metabolic outcome of the organism. This review will explore a variety of rodent stress models and discuss the elements that influence the metabolic outcome in order to further extend our understanding of stress-induced obesity.

The role of neuropeptide Y and aquaporin 4 in the pathogenesis of intestinal dysfunction caused by traumatic brain injury

BACKGROUND

Although the exact incidence is unknown, traumatic brain injury (TBI) can lead to intestinal dysfunction. It has important influence on the early nutrition and prognosis of TBI patients. Experiments were designed to study the roles of neuropeptide Y (NPY) and aquaporin 4 (AQP4) in the pathogenesis of intestinal dysfunction caused by TBI and to find some new solutions for the treatment of intestinal dysfunction after TBI.

METHODS

Forty adult male Wistar rats were randomly divided into control, mild trauma, moderate trauma, and severe trauma groups. TBI was induced by Feeney's impact method. Control animals were sham operated but not subjected to the impact test. All rats were killed 24 h after surgery. Blood samples were obtained from the abdominal aorta for enzyme-linked immunosorbent assay measurement of NPY concentrations. Jejunum segments 15 cm distal to the Treitz ligament were taken for analysis of NPY and AQP4 expression by polymerase chain reaction, Western blot, and immunohistochemistry. Pathologic changes in intestinal cell structure and ultrastructure were studied by light microscopy and transmission electron microscopy.

RESULTS

The specimens from different groups showed different degrees of structural changes, ranging from swelling and degeneration of villous epithelial cells to extensive denudation and collapse of the villi. The more severe the trauma, the more serious the degree of intestinal mucosal injury. Intestinal smooth muscle also showed varying degrees of edema and structural disorder. Electron microscopy showed that intestinal mitochondria had varying degrees of swelling and the structure of mitochondrial crista was disordered and even fractured. Plasma concentrations of NPY and jejunal gene and protein expressions of NPY and AQP4 increased significantly following TBI (P < 0.05), with greater increases at higher levels of injury. Moreover, there were positive correlations between NPY and AQP4 (P < 0.05).

CONCLUSIONS

Increasing grades of TBI caused increasing degrees of intestinal ischemia and edema, and thus caused increasingly severe intestinal dysfunction. AQP4 and NPY may be involved in the pathogenesis of intestinal dysfunction after TBI. Increased NPY levels may be responsible for intestinal ischemia and hypoxia, and AQP4 may play an important role in intestinal edema. Increased NPY levels may be one of the main causes for the increase in AQP4 after TBI.

Neuropeptide Y receptors: how to get subtype selectivity

The neuropeptide Y (NPY) system is a multireceptor/multiligand system consisting of four receptors in humans (hY(1), hY(2), hY(4), hY(5)) and three agonists (NPY, PYY, PP) that activate these receptors with different potency. The relevance of this system in diseases like obesity or cancer, and the different role that each receptor plays influencing different biological processes makes this system suitable for the design of subtype selectivity studies. In this review we focus on the latest findings within the NPY system, we summarize recent mutagenesis studies, structure activity relationship studies, receptor chimera, and selective ligands focusing also on the binding mode of the native agonists.

Cell-specific expression of calcineurin immunoreactivity within the rat basolateral amygdala complex and colocalization with the neuropeptide Y Y1 receptor

Neuropeptide Y (NPY) produces potent anxiolytic effects via activation of NPY Y1 receptors (Y1r) within the basolateral amygdaloid complex (BLA). The role of NPY in the BLA was recently expanded to include the ability to produce stress resilience and long-lasting reductions in anxiety-like behavior. These persistent behavioral effects are dependent upon activity of the protein phosphatase, calcineurin (CaN), which has long been associated with shaping long-term synaptic signaling. Furthermore, NPY-induced reductions in anxiety-like behavior persist months after intra-BLA delivery, which together indicate a form of neuronal plasticity had likely occurred. To define a site of action for NPY-induced CaN signaling within the BLA, we employed multi-label immunohistochemistry to determine which cell types express CaN and if CaN colocalizes with the Y1r. We have previously reported that both major neuronal cell populations in the BLA, pyramidal projection neurons and GABAergic interneurons, express the Y1r. Therefore, this current study evaluated CaN immunoreactivity in these cell types, along with Y1r immunoreactivity. Antibodies against calcium-calmodulin kinase II (CaMKII) and GABA were used to identify pyramidal neurons and GABAergic interneurons, respectively. A large population of CaN immunoreactive cells displayed Y1r immunoreactivity (90%). Nearly all (98%) pyramidal neurons displayed CaN immunoreactivity, while only a small percentage of interneurons (10%) contained CaN immunoreactivity. Overall, these anatomical findings provide a model whereby NPY could directly regulate CaN activity in the BLA via activation of the Y1r on CaN-expressing, pyramidal neurons. Importantly, they support BLA pyramidal neurons as prime targets for neuronal plasticity associated with the long-term reductions in anxiety-like behavior produced by NPY injections into the BLA.

Central neuropeptide Y modulates binge-like ethanol drinking in C57BL/6J mice via Y1 and Y2 receptors

Frequent binge drinking has been linked to heart disease, high blood pressure, type 2 diabetes, and the development of ethanol dependence. Thus, identifying pharmaceutical targets to treat binge drinking is of paramount importance. Here we employed a mouse model of binge-like ethanol drinking to study the role of neuropeptide Y (NPY). To this end, the present set of studies utilized pharmacological manipulation of NPY signaling, immunoreactivity (IR) mapping of NPY and NPY receptors, and electrophysiological recordings from slice preparations of the amygdala. The results indicated that central infusion of NPY, a NPY Y1 receptor (Y1R) agonist, and a Y2R antagonist significantly blunted binge-like ethanol drinking in C57BL/6J mice (that achieved blood ethanol levels >80 mg/dl in control conditions). Binge-like ethanol drinking reduced NPY and Y1R IR in the central nucleus of the amygdala (CeA), and 24 h of ethanol abstinence after a history of binge-like drinking promoted increases of Y1R and Y2R IR. Electrophysiological recordings of slice preparations from the CeA showed that binge-like ethanol drinking augmented the ability of NPY to inhibit GABAergic transmission. Thus, binge-like ethanol drinking in C57BL/6J mice promoted alterations of NPY signaling in the CeA, and administration of exogenous NPY compounds protected against binge-like drinking. The current data suggest that Y1R agonists and Y2R antagonists may be useful for curbing and/or preventing binge drinking, protecting vulnerable individuals from progressing to the point of ethanol dependence.

NPY receptors as potential targets for anti-obesity drug development

The neuropeptide Y system has proven to be one of the most important regulators of feeding behaviour and energy homeostasis, thus presenting great potential as a therapeutic target for the treatment of disorders such as obesity and at the other extreme, anorexia. Due to the initial lack of pharmacological tools that are active in vivo, functions of the different Y receptors have been mainly studied in knockout and transgenic mouse models. However, over recent years various Y receptor selective peptidic and non-peptidic agonists and antagonists have been developed and tested. Their therapeutic potential in relation to treating obesity and other disorders of energy homeostasis is discussed in this review.

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.

Neuropeptide Y overflow and metabolism in skeletal muscle arterioles

The purpose of this study was to characterize neuropeptide Y (NPY) overflow and metabolism from isolated skeletal muscle arterioles of female rats. Gastrocnemius first-order arterioles were removed from young (2 months), young adult (6 months) and middle-aged (12 months) F344 female rats. Arterioles were isolated, cannulated and pressurized in a microvessel bath with field stimulation electrodes. NPY overflow from isolated arterioles was assessed at 0 s and 30 s post-field stimulation. Dipeptidyl peptidase IV (DPPIV) activity was quantified via fluorometric assay of whole vessel homogenate. In young adult and middle-aged rats, NPY overflow increased 0 s and 30 s following field stimulation. In young adult rats, DPPIV inhibition resulted in an increase in NPY overflow at 30 s, while middle-aged rats had no increase in NPY overflow with DPPIV inhibition (P <0.05). DPPIV activity was influenced by factors such as age, vessel type, and endothelium (P <0.05). The present data suggest that DPPIV plays a significant role in modulating the actions of NPY in arterioles of young adult females; however, this role appears to diminish with age.

Pulmonary delivery of peptide YY for food intake suppression and reduced body weight gain in rats

AIMS

Peptide YY (PYY) is an endogenous anorectic gut-secreted peptide that has been shown to suppress appetite in animals and humans, when given by injection. This study tested if needle-free pulmonary delivery of PYY enables food intake suppression and reduced body weight gain in rats. The PYY pharmacokinetics and effects on brain neuropeptide levels were also examined.

METHODS

Rats received single or once-daily 7-day pulmonary administration of saline or PYYs. Food intake and body weight gain were monitored to study the effects of different doses (0.08-0.90 mg/kg) of PYY3-36, PYY1-36 and PYY13-36. Plasma PYY pharmacokinetics were determined via enzyme-linked immunosorbent assay. Changes in orexigenic neuropeptide Y (NPY) and c-Fos protein levels in the hypothalamus arcuate nucleus (ARC) were measured by immunofluorescence microscopy.

RESULTS

PYY3-36 caused dose-dependent and 4- to 6-h food intake suppression following pulmonary delivery. At 0.80 mg/kg, the effect was significant with 35.1 ± 5.7 and 19.7 ± 4.2% suppression at 4 and 6 h, respectively. Repeated administration for 7 days reduced cumulative body weight gain by 39.4 ± 11.0%. PYY1-36, but not PYY13-36, was equipotent to PYY3-36 in food intake suppression. The plasma PYY concentration reached its peak at 10 min following pulmonary delivery with 12-14% of bioavailability. Increased c-Fos and reduced NPY expressions were observed in the hypothalamus ARC, consistent with the magnitude of food intake suppression by each of the PYYs.

CONCLUSIONS

Pulmonary delivery of PYY enabled significant 4- to 6-h food intake suppression via 12-14% of lung absorption and hypothalamic ARC interaction, leading to reduced body weight gain in rats.

Neuropeptide Y receptors: ligand binding and trafficking suggest novel approaches in drug development

NPY, PYY and PP constitute the so-called NPY hormone family, which exert its biological functions in humans through YRs (Y₁, Y₂, Y₄ and Y₅). Systematic modulation of YR function became important as this multireceptor/multiligand system is known to mediate various essential physiological key functions and is involved in a variety of major human diseases such as epilepsy, obesity and cancer. As several YRs have been found to be overexpressed on different types of malignant tumors they emerge as promising target in modern drug development. Here, we summarize the current understanding of YRs function and the molecular mechanisms of ligand binding and trafficking. We further address recent advances in YR-based drug design, the development of promising future drug candidates and novel approaches in YR-targeted tumor diagnostics and therapy opportunities.

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.

In vitro effects of neuropeptide Y in rat neocortical and hippocampal tissue

Neuropeptide Y (NPY) network effects in hippocampus and frontal cortex and its impact on epileptiform neocortical discharges were investigated in rat juvenile brain slices. NPY (1 μM) reduced amplitudes of paired pulse stimulation in hippocampal brain tissue (p<0.05) whereas NPY (1 nM-2 μM) had no effect in neocortex. Late stage epileptiform activity in the neocortex was unaffected by NPY (1 μM). Our results point to a region dependent effect of NPY with a high impact on hippocampal and minimal impact on neocortical networks.

Brain neuropeptide Y and corticotropin-releasing hormone in mediating stress and anxiety

Neuropeptides such as neuropeptide Y (NPY) and corticotropin-releasing hormone (CRH) have been implicated not only in acute regulation of stress/anxiety-related behaviors, but adaptations and changes in these neuropeptide systems may also participate in the regulation of behavior and endocrine responses during chronic stress. NPY is an endogenous anxiolytic neuropeptide, while CRH has anxiogenic properties upon central administration. Changes in these neuropeptide systems may contribute to disease states and give us indications for putative treatment targets for stress/anxiety disorders as well as alcohol/drug dependence. In this review, we briefly present these two systems and review their involvement in mediating the responses to acute and chronic stressors, as well as their possible roles in the development and progression of stress/anxiety disorders. We suggest that neuropeptides may be attractive in treatment development for stress/anxiety disorders, as well as for alcohol/drug dependence, based on their specificity and activity following exposure to external challenges, i.e. stressors, and their differential adaptations during transition from an acute to a chronic stress exposure state.

Stress-related neuropeptides and alcoholism: CRH, NPY, and beyond

This article summarizes the proceedings of a symposium held at the conference on "Alcoholism and Stress: A Framework for Future Treatment Strategies" in Volterra, Italy, May 6-9, 2008. Chaired by Markus Heilig and Roberto Ciccocioppo, this symposium offered a forum for the presentation of recent data linking neuropetidergic neurotransmission to the regulation of different alcohol-related behaviors in animals and in humans. Dr. Donald Gehlert described the development of a new corticotrophin-releasing factor receptor 1 antagonist and showed its efficacy in reducing alcohol consumption and stress-induced relapse in different animal models of alcohol abuse. Dr. Andrey Ryabinin reviewed recent findings in his laboratory, indicating a role of the urocortin 1 receptor system in the regulation of alcohol intake. Dr. Annika Thorsell showed data supporting the significance of the neuropeptide Y receptor system in the modulation of behaviors associated with a history of ethanol intoxication. Dr. Roberto Ciccocioppo focused his presentation on the nociceptin/orphanin FQ (N/OFQ) receptors as treatment targets for alcoholism. Finally, Dr. Markus Heilig showed recent preclinical and clinical evidence suggesting that neurokinin 1 antagonism may represent a promising new treatment for alcoholism. Collectively, these investigators highlighted the significance of neuropeptidergic neurotransmission in the regulation of neurobiological mechanisms of alcohol addiction. Data also revealed the importance of these systems as treatment targets for the development of new medication for alcoholism.

Selective and brain penetrant neuropeptide y y2 receptor antagonists discovered by whole-cell high-throughput screening

The role of neuropeptide Y Y2 receptor (Y2R) in human diseases such as obesity, mood disorders, and alcoholism could be better resolved by the use of small-molecule chemical probes that are substantially different from the currently available Y2R antagonist, 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) (BIIE0246). Presented here are five potent, selective, and publicly available Y2R antagonists identified by a high-throughput screening approach. These compounds belong to four chemical scaffolds that are structurally distinct from the peptidomimetic BIIE0246. In functional assays, IC(50) values between 199 and 4400 nM against the Y2R were measured, with no appreciable activity against the related NPY-Y1 receptor (Y1R). Compounds also displaced radiolabeled peptide YY from the Y2R with high affinity (K(i) values between 1.55 and 60 nM) while not displacing the same ligand from the Y1R. In contrast to BIIE0246, Schild analysis with NPY suggests that two of the five compounds behave as competitive antagonists. Profiling against a panel of 40 receptors, ion channels, and transporters found in the central nervous system showed that the five Y2R antagonists demonstrate greater selectivity than BIIE0246. Furthermore, the ability of these antagonists to penetrate the blood-brain barrier makes them better suited for pharmacological studies of Y2R function in both the brain and periphery.

Towards understanding the free and receptor bound conformation of neuropeptide Y by fluorescence resonance energy transfer studies

Despite a considerable sequence identity of the three mammalian hormones of the neuropeptide Y family, namely neuropeptide Y, peptide YY and pancreatic polypeptide, their structure in solution is described to be different. A so-called pancreatic polypeptide-fold has been identified for pancreatic polypeptide, whereas the structure of the N-terminal segment of neuropeptide Y is unknown. This element is important for the binding of neuropeptide Y to two of its relevant receptors, Y(1) and Y(5), but not to the Y(2) receptor subtype. In this study now, three doubly fluorescent-labeled analogs of neuropeptide Y have been synthesized that still bind to the Y(5) receptor with high affinity to investigate the conformation in solution and, for the first time, to probe the conformational changes upon binding of the ligand to its receptor in cell membrane preparations. The results obtained from the fluorescence resonance energy transfer investigations clearly show considerable differences in transfer efficiency that depend both on the solvent as well as on the peptide concentration. However, the studies do not support a pancreatic polypeptide-like folding of neuropeptide Y in the presence of membranes that express the human Y(5) receptor subtype.

Effect of pharmacological manipulations of neuropeptide Y and corticotropin-releasing factor neurotransmission on incubation of conditioned fear

We recently developed a procedure to study fear incubation in which rats given 100 tone-shock pairings over 10 days show low fear 2 days after conditioned fear training and high fear after 30 or 60 days. Here, we studied the role of the stress-related peptides, neuropeptide Y (NPY) and corticotropin-releasing factor (CRF), in fear incubation. We gave rats either 10 or 100 30-s tone-0.5-s footshock pairings over 1 day (short training) or 10 days (long training) and then assessed tone-cue-induced conditioned suppression of lever responding 2 days after short training or 2 days and 1 month after long training. Prior to testing, we injected NPY (5-10 microg, i.c.v.), the NPY Y1 receptor antagonist BIBO3304 (20-40 microg, i.c.v.), the NPY Y2 receptor antagonist BIIE0246 (2.5-5 mg/kg s.c.), the non-selective CRF receptor antagonist D-Phe CRF(12-41) (10 microg, i.c.v.), or the CRF1 receptor antagonist MTIP (10-20 mg/kg s.c.). Conditioned suppression after long training was higher after 1 month than after 2 days (fear incubation); conditioned suppression was robustly expressed 2 days after short training (non-incubated fear). Both incubated and non-incubated fear responses were attenuated by NPY. In contrast, D-Phe CRF(12-41), MTIP, BIBO3304, or BIIE0246 had no effect on conditioned fear at the different time points. Results confirm previous work on the potent effect of exogenous NPY administration on conditioned fear, but the negative results with BIBO3304 and BIIE0246 question whether endogenous NPY contributes to incubated (or non-incubated) fear. Results also suggest that CRF receptors are not involved in cue-induced fear in the conditioned suppression procedure.

Effect of neuropeptide Y Y2 receptor deletion on emotional stress-induced neuronal activation in mice

In different behavioral paradigms including the elevated plus maze (EPM), it was observed previously that deletion of the neuropeptide Y Y2 receptor subtype results in potent suppression of anxiety-related and stress-related behaviors. To identify neurobiological correlates underlying this behavioral reactivtiy, expression of c-Fos, an established early marker of neuronal activation, was examined in Y2 receptor knockout (Y2(-/-)) vs. wildtype (WT) mice. Mice were placed on the open arm (OA) or closed arm (CA) of the EPM for 10 min and the effect on regional c-Fos expression in the brain was investigated. The number of c-Fos positive neurons was significantly increased in both WT and Y2(-/-) lines after OA and CA exposure in 51 of 54 regions quantified. These regions included various cortical, limbic, thalamic, hypothalamic, and hindbrain regions. Genotype influenced c-Fos responses to arm exposures in 6 of the 51 activated regions: the cingulate cortex, barrel field of the primary somatosensory cortex, nucleus accumbens, dorsal lateral septum, amygdala and lateral periaqueductal gray. These differences in neuronal activity responses to the novel environments were more pronounced after OA than after CA exposure. Mice lacking Y2 receptors exhibited reduced neuronal activation when compared to WT animals in response to the emotional stressors. Reduced neuronal excitability in the identified brain areas relevant to the processing of motivated, explorative as well as anxiety-related behaviors is suggested to contribute to the reduced anxiety-related behavior observed in Y2(-/-) mice.

Central neuropeptide Y in anxiety- and stress-related behavior and in ethanol intake

One of the most profound properties of central neuropeptide Y (NPY) is its anxiolytic, or anti-anxiety, effect. This has been demonstrated repeatedly in a number of animal models. In addition, stressors affect NPY expression in the central nervous system, with acute and repeated (chronic) stress having differential effects. Here, a brief summary of some work performed in our laboratory is presented that supports a role for NPY in regulation of stress responses and behaviors.

Pyridone dipeptide backbone scan to elucidate structural properties of a flexible peptide segment

Whereas the C-terminal fragment of neuropeptide Y (NPY) has been structurally well-defined both in solution and as membrane-bound, detailed structural information regarding the proline-rich N-terminus is still missing. The systematic variation of each position by a conformationally constrained pyridone dipeptide building block within the amino terminal segment of NPY leads to a systematic receptor subtype selectivity of the neuropeptide. Thereby, the systematic dipeptide scan proved superior to the traditional L-Ala scan because it showed how to modify the N-terminus in order to obtain increasingly more Y1 or Y5 receptor selective ligands. NMR and CD spectroscopic analyses were used to characterize the stepwise rigidification of the N-terminus of NPY when up to three dipeptide building blocks were incorporated by solid-phase peptide synthesis. The pyridone dipeptide increases the hydrophobicity of the amino terminus of NPY, and this allows the tuning of the membrane affinity of NPY. The amphiphilic C-terminal helix of 3-fold-substituted NPY thus becomes visible by selective line broadening in the (1)H NMR. Accordingly, we could structurally characterize protein segments that are too flexible for other methods.