Neuropeptide Y inhibits potassium-stimulated glutamate release through Y2 receptors in rat hippocampal slices in vitro

The antidepressant-like and glioprotective effects of the Y2 receptor antagonist SF-11 in the astroglial degeneration model of depression in rats: Involvement of glutamatergic inhibition

In this study, we explored the potential antidepressant-like properties of the brain-penetrant Y2 receptor (Y2R) antagonist SF-11 [N-(4-ethoxyphenyl)- 4-(hydroxydiphenylmethyl)- 1-piperidinecarbothioamide] in the astroglial degeneration model of depression with an emphasis on checking the possible mechanisms implicated in this antidepressant-like effect. The model of depression relies on the loss of astrocytes in the medial prefrontal cortex (mPFC) in Sprague-Dawley rats after administering the gliotoxin L-alpha-aminoadipic acid (L-AAA). SF-11 was administered intraperitoneally (i.p.) once (10 mg/kg) or for three consecutive days (10 mg/kg/day), and the effects of L-AAA and SF-11 injected alone or in combination were investigated using the forced swim test (FST), sucrose intake test (SIT), Western blotting, immunohistochemical staining, and microdialysis. SF-11 produced an antidepressant-like effect after single or three-day administration in rats subjected to astrocyte impairment, as demonstrated by the FST and SIT, respectively. Immunoblotting and immunohistochemical analyses showed that SF-11 reversed the L-AAA-induced astrocyte cell death in the mPFC, suggesting it is glioprotective. Microdialysis studies showed that SF-11 decreased extracellular glutamate (Glu) levels compared to basal value when administered alone and compared to the basal value and control group in LAAA-treated rats. The results from immunoblotting analysis indicated the involvement of Y2Rs in the astrocyte ablation model of depression and the antidepressant-like effect of SF-11. In addition, we observed the participation of the caspase-3 apoptotic pathway in the mechanism of gliotoxin action induced by L-AAA. These findings demonstrate that SF-11, a Y2R antagonist, elicited a rapid antidepressant-like response, possibly linked to its ability to inhibit glutamatergic neurotransmission.

Combinatorial gene therapy for epilepsy: Gene sequence positioning and AAV serotype influence expression and inhibitory effect on seizures

Gene therapy with AAV vectors carrying genes for neuropeptide Y and its receptor Y2 has been shown to inhibit seizures in multiple animal models of epilepsy. It is however unknown how the AAV serotype or the sequence order of these two transgenes in the expression cassette affects the actual parenchymal gene expression levels and the seizure-suppressant efficacy. To address these questions, we compared three viral vector serotypes (AAV1, AAV2 and AAV8) and two transgene sequence orders (NPY-IRES-Y2 and Y2-IRES-NPY) in a rat model of acutely induced seizures. Wistar male rats were injected bilaterally with viral vectors and 3 weeks later acute seizures were induced by a subcutaneous injection of kainate. The latency until 1st motor seizure, time spent in motor seizure and latency to status epilepticus were measured to evaluate the seizure-suppressing efficacy of these vectors compared to an empty cassette control vector. Based on the results, the effect of the AAV1-NPY-IRES-Y2 vector was further investigated by in vitro electrophysiology, and its ability to achieve transgene overexpression in resected human hippocampal tissue was evaluated. The AAV1-NPY-IRES-Y2 proved to be better to any other serotype or gene sequence considering both transgene expression and ability to suppress induced seizures in rats. The vector also demonstrated transgene-induced decrease of glutamate release from excitatory neuron terminals and significantly increased both NPY and Y2 expression in resected human hippocampal tissue from patients with drug-resistant temporal lobe epilepsy. These results validate the feasibility of NPY/Y2 receptor gene therapy as a therapeutic opportunity in focal epilepsies.

[Gene Therapy for Epilepsy: Clinical Studies are on the Road]

For more than 10 years, research has been conducted on gene therapies for the most severe forms of epilepsy, which until now have proven resistant to treatment. First gene therapies are now in clinical trials for pharmacoresistant focal epilepsies and Dravet syndrome. In this article, we describe how these and many more gene therapies work and what they target.

Seizure-induced overexpression of NPY induces epileptic tolerance in a mouse model of spontaneous recurrent seizures

Epileptic seizures result in pronounced over-expression of neuropeptide Y (NPY). In vivo and in vitro studies revealed that NPY exerts potent anticonvulsive actions through presynaptic Y2 receptors by suppressing glutamate release from principal neurons. We now investigated whether seizure-induced over-expression of NPY contributes to epileptic tolerance induced by preceding seizures. We used a previously established animal model based on selective inhibition of GABA release from parvalbumin (PV)-containing interneurons in the subiculum in mice. The animals present spontaneous recurrent seizures (SRS) and clusters of interictal spikes (IS). The frequency of SRS declined after five to six weeks, indicating development of seizure tolerance. In interneurons of the subiculum and sector CA1, SRS induced over-expression of NPY that persisted there for a prolonged time despite of a later decrease in SRS frequency. In contrast to NPY, somatostatin was not overexpressed in the respective axon terminals. Contrary to interneurons, NPY was only transiently expressed in mossy fibers. To demonstrate a protective function of endogenous, over-expressed NPY, we injected the selective NPY-Y2 receptor antagonist JNJ 5207787 simultaneously challenging the mice by a low dose of pentylenetetrazol (PTZ, 30 or 40 mg/kg, i.p.). In control mice, neither PTZ nor PTZ plus JNJ 5207787 induced convulsions. In mice with silenced GABA/PV neurons, PTZ alone only modestly enhanced EEG activity. When we injected JNJ 5207787 together with PTZ (either dose) the number of seizures, however, became significantly increased. In addition, in the epileptic mice CB1 receptor immunoreactivity was reduced in terminal areas of basket cells pointing to reduced presynaptic inhibition of GABA release from these neurons. Our experiments demonstrate that SRS result in overexpression of NPY in hippocampal interneurons. NPY overexpression persists for several weeks and may be related to later decreasing SRS frequency. Injection of the Y2 receptor antagonist JNJ 5207787 prevents this protective action of NPY only when release of the peptide is triggered by injection of PTZ and induces pronounced convulsions. Thus, over-expressed NPY released “on demand” by seizures may help terminating acute seizures and may prevent from recurrent epileptic activity.

Neuropeptides: Potential neuroprotective agents in ischemic injury

AIM

Ischemic damage to the brain is linked to an increased rate of morbidity and mortality worldwide. In certain parts of the world, it remains a leading cause of mortality and the primary cause of long-term impairment. Ischemic injury is exacerbated when particular neuropeptides are removed, or their function in the brain is blocked, whereas supplying such neuropeptides lowers ischemic harm. Here, we have discussed the role of neuropeptides in ischemic injury.

MATERIALS & METHODS

Numerous neuropeptides had their overexpression following cerebral ischemia. Neuropeptides such as NPY, CGRP, CART, SP, BK, PACAP, oxytocin, nociception, neurotensin and opioid peptides act as transmitters, documented in several "in vivo" and "in vitro" studies. Neuropeptides provide neuroprotection by activating the survival pathways or inhibiting the death pathways, i.e., MAPK, BDNF, Nitric Oxide, PI3k/Akt and NF-κB.

KEY FINDINGS

Neuropeptides have numerous beneficial effects in ischemic models, including antiapoptotic, anti-inflammatory, and antioxidant actions that provide a powerful protective impact in neurons when combined. These innovative therapeutic substances have the potential to treat ischemia injury due to their pleiotropic modes of action.

SIGNIFICANCE

This review emphasizes the neuroprotective role of neuropeptides in ischemic injury via modulation of various signalling pathways i.e., MAPK, BDNF, Nitric Oxide, PI3k/Akt and NF-κB.

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.

Naturally Occurring HMGB1 Inhibitor, Glycyrrhizin, Modulates Chronic Seizures-Induced Memory Dysfunction in Zebrafish Model

Glycyrrhizin (GL) is a well-known pharmacological inhibitor of high mobility group box 1 (HMGB1) and is abundantly present in the licorice root (Glycyrrhiza radix). HMGB1 protein, a key mediator of neuroinflammation, has been implicated in several neurological disorders, including epilepsy. Epilepsy is a devastating neurological disorder with no effective disease-modifying treatment strategies yet, suggesting a pressing need for exploring novel therapeutic options. In the current investigation, using a second hit pentylenetetrazol (PTZ) induced chronic seizure model in adult zebrafish, regulated mRNA expression of HMGB1 was inhibited by pretreatment with GL (25, 50, and 100 mg/kg, ip). A molecular docking study suggests that GL establishes different binding interactions with the various amino acid chains of HMGB1 and Toll-like receptor-4 (TLR4). Our finding suggests that GL pretreatment reduces/suppresses second hit PTZ induced seizure, as shown by the reduction in the seizure score. GL also regulates the second hit PTZ induced behavioral impairment and rescued second hit PTZ related memory impairment as demonstrated by an increase in the inflection ratio (IR) at the 3 h and 24 h T-maze trial. GL inhibited seizure-induced neuronal activity as demonstrated by reduced C-fos mRNA expression. GL also modulated mRNA expression of BDNF, CREB-1, and NPY. The possible mechanism underlying the anticonvulsive effect of GL could be attributed to its anti-inflammatory activity, as demonstrated by the downregulated mRNA expression level of HMGB1, TLR4, NF-kB, and TNF-α. Overall, our finding suggests that GL exerts an anticonvulsive effect and ameliorates seizure-related memory disruption plausibly through regulating of the HMGB1-TLR4-NF-kB axis.

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.

Increase in neuropeptide Y activity impairs social behaviour in association with glutamatergic dysregulation in diabetic mice

BACKGROUND AND PURPOSE

Patients with diabetes mellitus are reported to show a raised prevalence of mental disorders, which may be reflected in impaired social interaction. However, the mechanisms underlying such impairment in diabetes are unknown.

EXPERIMENTAL APPROACH

The present study investigated whether social interaction is impaired in diabetic mice and whether central neuropeptide Y (NPY) and glutamatergic function are involved in such impairment.

KEY RESULTS

In the three-chamber test, social novelty preference, but not sociability, was impaired in streptozotocin (STZ)-induced diabetic mice. The mRNA level of NPY in the hypothalamus was increased in STZ-induced diabetic mice. Injection of the NPY Y₂ receptor agonist NPY 13-36 into naïve mice impaired social novelty preference, but not sociability, and this effect was inhibited by the Y₂ receptor antagonist BIIE 0246. BIIE 0246 also reversed the impairment of social novelty preference in STZ-induced diabetic mice. Similarly, injection of the AMPA receptor agonist AMPA into naïve mice impaired social novelty preference, but not sociability, and this effect was inhibited by the AMPA receptor antagonist NBQX. Impairment of social novelty preference induced by NPY 13-36 was inhibited by NBQX, whereas impairment of social novelty preference induced by AMPA was not inhibited by BIIE 0246. Finally, impairment of social novelty preference in STZ-induced diabetic mice was reversed by NBQX.

CONCLUSION AND IMPLICATIONS

These findings suggest that NPY neurons are activated in diabetic mice and that this may impair social novelty preference by promoting glutamatergic function through Y₂ receptors.

Sex Differences in the Neuropeptide Y System and Implications for Stress Related Disorders

The neuropeptide Y (NPY) system is emerging as a promising therapeutic target for neuropsychiatric disorders by intranasal delivery to the brain. However, the vast majority of underlying research has been performed with males despite females being twice as susceptible to many stress-triggered disorders such as posttraumatic stress disorder, depression, anorexia nervosa, and anxiety disorders. Here, we review sex differences in the NPY system in basal and stressed conditions and how it relates to varied susceptibility to stress-related disorders. The majority of studies demonstrate that NPY expression in many brain areas under basal, unstressed conditions is lower in females than in males. This could put them at a disadvantage in dealing with stress. Knock out animals and Flinders genetic models show that NPY is important for attenuating depression in both sexes, while its effects on anxiety appear more pronounced in males. In females, NPY expression after exposure to stress may depend on age, timing, and nature and duration of the stressors and may be especially pronounced in the catecholaminergic systems. Furthermore, alterations in NPY receptor expression and affinity may contribute to the sex differences in the NPY system. Overall, the review highlights the important role of NPY and sex differences in manifestation of neuropsychiatric disorders.

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.

Inhibition of epileptiform activity by neuropeptide Y in brain tissue from drug-resistant temporal lobe epilepsy patients

In epilepsy patients, drug-resistant seizures often originate in one of the temporal lobes. In selected cases, when certain requirements are met, this area is surgically resected for therapeutic reasons. We kept the resected tissue slices alive in vitro for 48 h to create a platform for testing a novel treatment strategy based on neuropeptide Y (NPY) against drug-resistant epilepsy. We demonstrate that NPY exerts a significant inhibitory effect on epileptiform activity, recorded with whole-cell patch-clamp, in human hippocampal dentate gyrus. Application of NPY reduced overall number of paroxysmal depolarising shifts and action potentials. This effect was mediated by Y2 receptors, since application of selective Y2-receptor antagonist blocked the effect of NPY. This proof-of-concept finding is an important translational milestone for validating NPY-based gene therapy for targeting focal drug-resistant epilepsies, and increasing the prospects for positive outcome in potential clinical trials.

Regenerative Adaptation to Electrochemical Perturbation in Planaria: A Molecular Analysis of Physiological Plasticity

Anatomical homeostasis results from dynamic interactions between gene expression, physiology, and the external environment. Owing to its complexity, this cellular and organism-level phenotypic plasticity is still poorly understood. We establish planarian regeneration as a model for acquired tolerance to environments that alter endogenous physiology. Exposure to barium chloride (BaCl₂) results in a rapid degeneration of anterior tissue in Dugesia japonica. Remarkably, continued exposure to fresh solution of BaCl₂ results in regeneration of heads that are insensitive to BaCl₂. RNA-seq revealed transcriptional changes in BaCl₂-adapted heads that suggests a model of adaptation to excitotoxicity. Loss-of-function experiments confirmed several predictions: blockage of chloride and calcium channels allowed heads to survive initial BaCl₂ exposure, inducing adaptation without prior exposure, whereas blockade of TRPM channels reversed adaptation. Such highly adaptive plasticity may represent an attractive target for biomedical strategies in a wide range of applications beyond its immediate relevance to excitotoxicity preconditioning.

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Exposure to BaCl₂ causes the heads of Dugesia japonica to degenerate

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Prolonged exposure to BaCl₂ results in regeneration of a BaCl₂-insensitive head

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Ion channel expression is altered in the head to compensate for excitotoxic stress

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TRPMa is upregulated in BaCl₂-treated animals; blocking TRPM prevents adaptation

Neuroendocrine modulation of predator avoidance/prey capture tradeoffs: Role of tectal NPY2R receptors

The optic tectum rapidly inhibits food intake when a visual threat is present. Anatomical and electrophysiological evidence support a role for neuropeptide Y (NPY), originating from cells in the thalamus, in the tectal inhibition of prey capture. Here we test the hypothesis that tectal NPY receptor type 2 (NPY2R) influences prey-capture and predator-avoidance responses in the African clawed frog, Xenopus laevis. We tested two questions: 1) Does tectal NPY administration decrease food intake and alter prey-capture behavior? 2) Does tectal administration of a NPY2R antagonist increase food intake, alter prey-capture behavior, and alter predator avoidance behavior? NPY microinjected bilaterally into the tecta failed to significantly alter food intake at any dose tested, although predator presence significantly reduced food intake. However, NPY differentially altered discrete components of prey capture including increasing the latency to contact food and reducing the amount of time in contact with food. These effects were blocked by the NPY2R antagonist BIIE0246. Additionally, BIIE0246 elevated food intake on its own after bilateral tectal microinjection. Furthermore, BIIE0246 reversed the reduction of food intake caused by exposure to a predator. Overall, these findings indicate that tectal NPY2R activation causes frogs to consume food more quickly, which may be adaptive in predator-rich environments. Blocking tectal NPY2R increases baseline food intake and reduces or eliminates predator-induced changes in prey capture and food intake.

NPY2 Receptors Reduce Tonic Action Potential-Independent GABAB Currents in the Basolateral Amygdala

Although NPY has potent anxiolytic actions within the BLA, selective activation of BLA NPY Y₂ receptors (Y₂Rs) acutely increases anxiety by an unknown mechanism. Using ex vivo male rat brain slice electrophysiology, we show that the selective Y₂R agonist, [ahx^5-24]NPY, reduced the frequency of GABA_A-mediated mIPSCs in BLA principal neurons (PNs). [ahx^5-24]NPY also reduced tonic activation of GABA_B receptors (GABA_BR), which increased PN excitability through inhibition of a tonic, inwardly rectifying potassium current (K_IR ). Surprisingly, Y₂R-sensitive GABA_BR currents were action potential-independent, persisting after treatment with TTX. Additionally, the Ca²⁺-dependent, slow afterhyperpolarizing K⁺ current (I_sAHP ) was enhanced in approximately half of the Y₂R-sensitive PNs, possibly from enhanced Ca²⁺ influx, permitted by reduced GABA_BR tone. In male and female mice expressing tdTomato in Y₂R-mRNA cells (tdT-Y₂R mice), immunohistochemistry revealed that BLA somatostatin interneurons express Y₂Rs, as do a significant subset of BLA PNs. In tdT-Y₂R mice, [ahx^5-24]NPY increased excitability and suppressed the K_IR in nearly all BLA PNs independent of tdT-Y₂R fluorescence, consistent with presynaptic Y₂Rs on somatostatin interneurons mediating the above effects. However, only tdT-Y₂R-expressing PNs responded to [ahx^5-24]NPY with an enhancement of the I_sAHP Ultimately, increased PN excitability via acute Y₂R activation likely correlates with enhanced BLA output, consistent with reported Y₂R-mediated anxiogenesis. Furthermore, we demonstrate the following: (1) a novel mechanism whereby activity-independent GABA release can powerfully dampen BLA neuronal excitability via postsynaptic GABA_BRs; and (2) that this tonic inhibition can be interrupted by neuromodulation, here by NPY via Y₂Rs.SIGNIFICANCE STATEMENT Within the BLA, NPY is potently anxiolytic. However, selective activation of NPY₂ receptors (Y₂Rs) increases anxiety by an unknown mechanism. We show that activation of BLA Y₂Rs decreases tonic GABA release onto BLA principal neurons, probably from Y₂R-expressing somatostatin interneurons, some of which coexpress NPY. This increases principal neuron excitability by reducing GABA_B receptor (GABA_BR)-mediated activation of G-protein-coupled, inwardly rectifying K⁺ currents. Tonic, Y₂R-sensitive GABA_BR currents unexpectedly persisted in the absence of action potential firing, revealing, to our knowledge, the first report of substantial, activity-independent GABA_BR activation. Ultimately, we provide a plausible explanation for Y₂R-mediated anxiogenesis in vivo and describe a novel and modulatable means of damping neuronal excitability.

Peptide YY (3-36) modulates intracellular calcium through activation of the phosphatidylinositol pathway in hippocampal neurons

Peptide YY (PYY) belongs to the neuropeptide Y (NPY) family, which also includes the pancreatic polypeptide (PP) and NPY. PYY is secreted by the intestinal L cells, being present in the blood stream in two active forms capable of crossing the blood brain barrier, PYY (1-36) and its cleavage product, PYY (3-36). PYY is a selective agonist for the Y2 receptor (Y2R) and these receptors are abundant in the hippocampus. Here we investigated the mechanisms by which PYY (3-36) regulates intracellular Ca²⁺ concentrations ([Ca²⁺]_i) in hippocampal neurons by employing a calcium imaging technique in hippocampal cultures. Alterations in [Ca²⁺]_i were detected by changes in the Fluo-4 AM reagent emission. PYY (3-36) significantly increased [Ca²⁺] from the concentration of 10^-11M as compared to the controls (infusion of HEPES-buffered solution (HBS) solution alone). The PYY (3-36)-increase in [Ca²⁺]_i remained unchanged even in Ca²⁺-free extracellular solutions. Sarcoplasmic/endoplasmic reticulum Ca²⁺-ATPase pump (SERCA pump) inhibition partially prevent the PYY (3-36)-increase of [Ca²⁺]_i and inositol 1,4,5-triphosphate receptor (IP3R) inhibition also decreased the PYY (3-36)-increase of [Ca²⁺]_i. Taken together, our data strongly suggest that PYY (3-36) mobilizes calcium from the neuronal endoplasmic reticulum (ER) stores towards the cytoplasm. Next, we showed that PYY (3-36) inhibited high K⁺-induced increases of [Ca²⁺]_i, suggesting that PYY (3-36) could also act by activating G-protein coupled inwardly rectifying potassium K⁺ channels. Finally, the co-infusion of the Y2 receptor (Y2R) antagonist BIIE0246 with PYY (3-36) abolished the [Ca²⁺]_i increase induced by the peptide, suggesting that PYY (3-36)-induced [Ca²⁺]_i increase in hippocampal neurons occurs via Y2Rs.

Epilepsy-associated alterations in hippocampal excitability

The hippocampus exhibits a wide range of epilepsy-related abnormalities and is situated in the mesial temporal lobe, where limbic seizures begin. These abnormalities could affect membrane excitability and lead to overstimulation of neurons. Multiple overlapping processes refer to neural homeostatic responses develop in neurons that work together to restore neuronal firing rates to control levels. Nevertheless, homeostatic mechanisms are unable to restore normal neuronal excitability, and the epileptic hippocampus becomes hyperexcitable or hypoexcitable. Studies show that there is hyperexcitability even before starting recurrent spontaneous seizures, suggesting although hippocampal hyperexcitability may contribute to epileptogenesis, it alone is insufficient to produce epileptic seizures. This supports the concept that the hippocampus is not the only substrate for limbic seizure onset, and a broader hyperexcitable limbic structure may contribute to temporal lobe epilepsy (TLE) seizures. Nevertheless, seizures also occur in conditions where the hippocampus shows a hypoexcitable phenotype. Since TLE seizures most often originate in the hippocampus, it could therefore be assumed that both hippocampal hypoexcitability and hyperexcitability are undesirable states that make the epileptic hippocampal network less stable and may, under certain conditions, trigger seizures.

Anxiety, Depression, and the Microbiome: A Role for Gut Peptides

The complex bidirectional communication between the gut and the brain is finely orchestrated by different systems, including the endocrine, immune, autonomic, and enteric nervous systems. Moreover, increasing evidence supports the role of the microbiome and microbiota-derived molecules in regulating such interactions; however, the mechanisms underpinning such effects are only beginning to be resolved. Microbiota-gut peptide interactions are poised to be of great significance in the regulation of gut-brain signaling. Given the emerging role of the gut-brain axis in a variety of brain disorders, such as anxiety and depression, it is important to understand the contribution of bidirectional interactions between peptide hormones released from the gut and intestinal bacteria in the context of this axis. Indeed, the gastrointestinal tract is the largest endocrine organ in mammals, secreting dozens of different signaling molecules, including peptides. Gut peptides in the systemic circulation can bind cognate receptors on immune cells and vagus nerve terminals thereby enabling indirect gut-brain communication. Gut peptide concentrations are not only modulated by enteric microbiota signals, but also vary according to the composition of the intestinal microbiota. In this review, we will discuss the gut microbiota as a regulator of anxiety and depression, and explore the role of gut-derived peptides as signaling molecules in microbiome-gut-brain communication. Here, we summarize the potential interactions of the microbiota with gut hormones and endocrine peptides, including neuropeptide Y, peptide YY, pancreatic polypeptide, cholecystokinin, glucagon-like peptide, corticotropin-releasing factor, oxytocin, and ghrelin in microbiome-to-brain signaling. Together, gut peptides are important regulators of microbiota-gut-brain signaling in health and stress-related psychiatric illnesses.

The Role of Neuropeptide Y (NPY) in Alcohol and Drug Abuse Disorders

Neuropeptide Y (NPY) is a neuromodulator that is widely expressed throughout the central nervous system (CNS) and which is cosecreted with classic neurotransmitters including GABA and glutamate. There is a long history of research implicating a role for NPY in modulating neurobiological responses to alcohol (ethanol) as well as other drugs of abuse. Both ethanol exposure and withdrawal from chronic ethanol have been shown to produce changes in NPY and NPY receptor protein levels and mRNA expression in the CNS. Importantly, manipulations of NPY Y1 and Y2 receptor signaling have been shown to alter ethanol consumption and self-administration in a brain region-specific manner, with Y1 receptor activation and Y2 receptor blockade in regions of the extended amygdala promoting robust reductions of ethanol intake. Similar observations have been made in studies examining neurobiological responses to nicotine, psychostimulants, and opioids. When taken together with observations of potential genetic linkage between the NPY system and the human alcohol abuse disorders, NPY represents a promising target for treating problematic alcohol and drug use, and in protecting individuals from relapse during abstinence.

Effective G-protein coupling of Y2 receptors along axonal fiber tracts and its relevance for epilepsy

Neuropeptide Y (NPY)-Y2 receptors are G-protein coupled receptors and, upon activation, induce opening of potassium channels or closing of calcium channels. They are generally presynaptically located. Depending on the neuron in which they are expressed they mediate inhibition of release of NPY and of the neuron's classical transmitter GABA, glutamate or noradrenaline, respectively. Here we provide evidence that Y2 receptor binding is inhibited dose-dependently by GTPγS along Schaffer collaterals, the stria terminalis and the fimbria indicating that Y2 receptors are functionally coupled to G-proteins along these fiber tracts. Double immune fluorescence revealed coexistence of Y2-immunoreactivity with β-tubulin, a marker for axons in the stria terminalis, but not with synaptophysin labeling presynaptic terminals, supporting the localization of Y2 receptors along axonal tracts. After kainic acid-induced seizures in rats, GTPγS-induced inhibition of Y2 receptor binding is facilitated in the Schaffer collaterals but not in the stria terminalis. Our data indicate that Y2 receptors are not only located at nerve terminals but also along fiber tracts and are there functionally coupled to G-proteins.

Antidepressant-like activity of the neuropeptide Y Y5 receptor antagonist Lu AA33810: behavioral, molecular, and immunohistochemical evidence

RATIONALE

It has recently been found that chronic treatment with the highly selective, brain-penetrating Y5 receptor antagonist, Lu AA33810 [N-[[trans-4-[(4,5-dihydro [1] benzothiepino[5,4-d] thiazol-2-yl) amino] cyclohexyl]methyl]-methanesulfonamide], produces antidepressant-like effects in the rat chronic mild stress model.

OBJECTIVE

In the present study, we investigated the possible antidepressant-like activity of Lu AA33810 in rats subjected to glial ablation in the prefrontal cortex (PFC) by the gliotoxin L-AAA, which is an astroglial degeneration model of depression.

RESULTS

We observed that Lu AA33810 administered intraperitoneally at a single dose of 10 mg/kg both reversed depressive-like behavioral changes in the forced swim test (FST) and prevented degeneration of astrocytes in the mPFC. The mechanism of antidepressant and glioprotective effects of Lu AA33810 has not been studied, so far. We demonstrated the contribution of the noradrenergic rather than the serotonergic pathway to the antidepressant-like action of Lu AA33810 in the FST. Moreover, we found that antidepressant-like effect of Lu AA33810 was connected with the influence on brain-derived neurotrophic factor (BDNF) protein expression. We also demonstrated the antidepressant-like effect of Lu AA33810 in the FST in rats which did not receive the gliotoxin. We found that intracerebroventricular injection of the selective MAPK/ERK inhibitor U0126 (5 μg/2 μl) and the selective PI3K inhibitor LY294002 (10 nmol/2 μl) significantly inhibited the anti-immobility effect of Lu AA33810 in the FST in rats, suggesting that MAPK/ERK and PI3K signaling pathways could be involved in the antidepressant-like effect of Lu AA33810.

CONCLUSION

Our results indicate that Lu AA33810 exerts an antidepressant-like effect and suggest the Y5 receptors as a promising target for antidepressant therapy.

Neuropeptide Y Y2 and Y5 receptors as promising targets for neuroprotection in primary neurons exposed to oxygen-glucose deprivation and in transient focal cerebral ischemia in rats

It was postulated that neuropeptide Y (NPY)-ergic system could be involved in the ischemic pathophysiology, however, the role of particular subtypes of NPY receptors (YRs) in neuroprotection against ischemia is still not well known. Therefore, we investigated the effect of NPY and YR ligands using in vitro and in vivo experimental ischemic stroke models. Our in vitro findings showed that NPY (0.5-1μM) and specific agonists of Y2R (0.1-1μM) and Y5R (0.5-1μM) but not that of Y1R produced neuroprotective effects against oxygen-glucose deprivation (OGD)-induced neuronal cell death, being also effective when given 30min after the end of OGD. The neuroprotective effects of Y2R and Y5R agonists were reversed by appropriate antagonists. Neuroprotection mediated by NPY, Y2R and Y5R agonists was accompanied by the inhibition of both OGD-induced calpain activation and glutamate release. Data from in vivo studies demonstrated that Y2R agonist (10μg/6μl; i.c.v.) not only diminished the infarct volume in rats subjected to transient middle cerebral artery occlusion (MCAO) but also improved selected gait parameters in CatWalk behavioral test, being also effective after delayed treatment. Moreover, we found that a Y5R agonist (10μg/6μl; i.c.v.) did not reduce MCAO-evoked brain damage but improved stride length, when it was given 30min after starting the occlusion. In conclusion, our studies indicate that Y5 and especially Y2 receptors may be promising targets for neuroprotection against ischemic damage.

Neuropeptide Y in Alcohol Addiction and Affective Disorders

Neuropeptide Y (NPY), a neuropeptide highly conserved throughout evolution, is present at high levels in the central nervous system (CNS), as well as in peripheral tissues such as the gut and cardiovascular system. The peptide exerts its effects via multiple receptor subtypes, all belonging to the G-protein-coupled receptor superfamily. Of these subtypes, the Y1 and the Y2 are the most thoroughly characterized, followed by the Y5 subtype. NPY and its receptors have been shown to be of importance in central regulation of events underlying, for example, affective disorders, drug/alcohol use disorders, and energy homeostasis. Furthermore, within the CNS, NPY also affects sleep regulation and circadian rhythm, memory function, tissue growth, and plasticity. The potential roles of NPY in the etiology and pathophysiology of mood and anxiety disorders, as well as alcohol use disorders, have been extensively studied. This focus was prompted by early indications for an involvement of NPY in acute responses to stress, and, later, also data pointing to a role in alterations within the CNS during chronic, or repeated, exposure to adverse events. These functions of NPY, in addition to the peptide's regulation of disease states, suggest that modulation of the activity of the NPY system via receptor agonists/antagonists may be a putative treatment mechanism in affective disorders as well as alcohol use disorders. In this review, we present an overview of findings with regard to the NPY system in relation to anxiety and stress, acute as well as chronic; furthermore we discuss post-traumatic stress disorder and, in part depression. In addition, we summarize findings on alcohol use disorders and related behaviors. Finally, we briefly touch upon genetic as well as epigenetic mechanisms that may be of importance for NPY function and regulation. In conclusion, we suggest that modulation of NPY-ergic activity within the CNS, via ligands aimed at different receptor subtypes, may be attractive targets for treatment development for affective disorders, as well as for alcohol use disorders.

The role of NPY in learning and memory

High levels of NPY expression in brain regions important for learning and memory together with its neuromodulatory and neurotrophic effects suggest a regulatory role for NPY in memory processes. Therefore it is not surprising that an increasing number of studies have provided evidence for NPY acting as a modulator of neuroplasticity, neurotransmission, and memory. Here these results are presented in relation to the types of memory affected by NPY and its receptors. NPY can exert both inhibitory and stimulatory effects on memory, depending on memory type and phase, dose applied, brain region, and NPY receptor subtypes. Thus NPY act as a resilience factor by impairing associative implicit memory after stressful and aversive events, as evident in models of fear conditioning, presumably via Y1 receptors in the amygdala and prefrontal cortex. In addition, NPY impairs acquisition but enhances consolidation and retention in models depending on spatial and discriminative types of associative explicit memory, presumably involving Y2 receptor-mediated regulations of hippocampal excitatory transmission. Moreover, spatial memory training leads to increased hippocampal NPY gene expression that together with Y1 receptor-mediated neurogenesis could constitute necessary steps in consolidation and long-term retention of spatial memory. Altogether, NPY-induced effects on learning and memory seem to be biphasic, anatomically and temporally differential, and in support of a modulatory role of NPY at keeping the system in balance. Obtaining further insight into memory-related effects of NPY could inspire the engineering of new therapeutics targeting diseases where impaired learning and memory are central elements.

Variations of glutamate concentration within synaptic cleft in the presence of electromagnetic fields: an artificial neural networks study

Glutamate is an excitatory neurotransmitter that is released by the majority of central nervous system synapses and is involved in developmental processes, cognitive functions, learning and memory. Excessive elevated concentrations of Glu in synaptic cleft results in neural cell apoptosis which is called excitotoxicity causing neurodegenerative diseases. Hence, we investigated the possibility of extremely low frequency electromagnetic fields (ELF-EMF) as a risk factor which is able to change Glu concentration in synaptic clef. Synaptosomes as a model of nervous terminal were exposed to ELF-EMF for 15-55 min in flux intensity range from 0.1 to 2 mT and frequency range from 50 to 230 Hz. Finally, all raw data by INForm v4.02 software as an artificial neural network program was analyzed to predict the effect of whole mentioned range spectra. The results showed the tolerance of all effects between the ranges from -35 to +40 % compared to normal state when glutamatergic systems exposed to ELF-EMF. It indicates that glutamatergic system attempts to compensate environmental changes though release or reuptake in order to keep the system safe. Regarding to the wide range of ELF-EMF acquired in this study, the obtained outcomes have potential for developing treatments based on ELF-EMF for some neurological diseases; however, in vivo experiments on the cross linking responses between glutamatergic and cholinergic systems in the presence of ELF-EMF would be needed.

Gut-brain peptides in corticostriatal-limbic circuitry and alcohol use disorders

Peptides synthesized in endocrine cells in the gastrointestinal tract and neurons are traditionally considered regulators of metabolism, energy intake, and appetite. However, recent work has demonstrated that many of these peptides act on corticostriatal-limbic circuitry and, in turn, regulate addictive behaviors. Given that alcohol is a source of energy and an addictive substance, it is not surprising that increasing evidence supports a role for gut-brain peptides specifically in alcohol use disorders (AUD). In this review, we discuss the effects of several gut-brain peptides on alcohol-related behaviors and the potential mechanisms by which these gut-brain peptides may interfere with alcohol-induced changes in corticostriatal-limbic circuitry. This review provides a summary of current knowledge on gut-brain peptides focusing on five peptides: neurotensin, glucagon-like peptide 1, ghrelin, substance P, and neuropeptide Y. Our review will be helpful to develop novel therapeutic targets for AUD.

Neuropeptide Y protects cerebral cortical neurons by regulating microglial immune function

Neuropeptide Y has been shown to inhibit the immunological activity of reactive microglia in the rat cerebral cortex, to reduce N-methyl-D-aspartate current (I_NMDA) in cortical neurons, and protect neurons. In this study, after primary cultured microglia from the cerebral cortex of rats were treated with lipopolysaccharide, interleukin-1β and tumor necrosis factor-α levels in the cell culture medium increased, and mRNA expression of these cytokines also increased. After primary cultured cortical neurons were incubated with the lipopolysaccharide-treated microglial conditioned medium, peak I_NMDA in neurons increased. These effects of lipopolysaccharide were suppressed by neuropeptide Y. After addition of the neuropeptide Y Y1 receptor antagonist BIBP3226, the effects of neuropeptide Y completely disappeared. These results suggest that neuropeptide Y prevents excessive production of interleukin-1β and tumor necrosis factor-α by inhibiting microglial reactivity. This reduces I_NMDA in rat cortical neurons, preventing excitotoxicity, thereby protecting neurons.

Neuropeptide YY(2)R blockade in the central amygdala reduces anxiety-like behavior but not alcohol drinking in alcohol-dependent rats

Electrophysiological data suggest a dual role of Y2 receptors (Y2 Rs) as autoreceptors regulating neuropeptide Y release and heteroceptors regulating gamma-aminobutyric acid release in the central amygdala (CeA). Here, we report that neither systemic (JNJ-31020028) nor intra-CeA (BIIE0246) Y2 R antagonism altered operant alcohol responding by alcohol-dependent or non-dependent rats. Conversely, BIIE0246 in the CeA reduced anxiety-like behavior in alcohol-dependent and alcohol-naïve rats. The finding that Y2 R antagonism reduces anxiety-like behavior but not alcohol drinking suggests that these two effects may occur via different functions of the Y2 R (e.g. autoreceptor versus heteroceptor function).

The effect of neuropeptide Y on cell survival and neurotrophin expression in in-vitro models of Alzheimer's disease

Alzheimer's disease (AD) is a disorder characterized by the accumulation of abnormally folded protein fragments in neurons, i.e., β-amyloid (Aβ) and tau protein, leading to cell death. Several neuropeptides present in the central nervous system (CNS) are believed to be involved in the pathophysiology of AD. Among them, neuropeptide Y (NPY), a small peptide widely distributed throughout the brain, has generated interest because of its role in neuroprotection against excitotoxicity in animal models of AD. In addition, it has been shown that NPY modulates neurogenesis. Interestingly, these latter effects are similar to those elicited by neurotrophins, which are critical molecules for the function and survival of neurons that degenerate during the course of AD. In this review we summarize the evidence for the involvement of NPY and neurotrophins in AD pathogenesis, and the similarity between them in CNS neurons. Finally, we recapitulate our recent in-vitro evidence for the involvement of neurotrophin nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF) in the neuroprotective effect elicited by NPY in AD neuron-like models (neuroblastoma cells or primary cultures exposed to toxic concentrations of Aβ's pathogenic fragment 25-35), and propose a putative mechanism based on NPY-induced inhibition of voltage-dependent Ca(2+) influx in pre- and post-synaptic neurons.

Altered expression of neuropeptide Y, Y1 and Y2 receptors, but not Y5 receptor, within hippocampus and temporal lobe cortex of tremor rats

As an endogenous inhibitor of glutamate-mediated synaptic transmission in mammalian central nervous system, neuropeptide Y (NPY) plays a crucial role in regulating homeostasis of neuron excitability. Loss of balance between excitatory and inhibitory neurotransmission is thought to be a chief mechanism of epileptogenesis. The abnormal expression of NPY and its receptors observed following seizures have been demonstrated to be related to the production of epilepsy. The tremor rat (TRM) is a hereditary epileptic animal model. So far, there is no report concerning whether NPY and its receptors may be involved in TRM pathogenesis. In this study, we focused on the expression of NPY and its three receptor subtypes: Y1R, Y2R and Y5R in the TRM brain. We first found the expression of NPY in TRM hippocampus and temporal lobe cortex was increased compared with control (Wistar) rats. The mRNA and protein expression of Y1R was down-regulated in hippocampus but up-regulated in temporal lobe cortex, whereas Y2R expression was significantly increased in both areas. There was no significant change of Y5R expression in either area. The immunohistochemistry data showed that Y1R, Y2R, Y5R were present throughout CA1, CA3, dentate gyrus (DG) and the entorhinal cortex which is included in the temporal lobe cortex of TRM. In conclusion, our results showed the altered expression of NPY, Y1R and Y2R but not Y5R in hippocampus and temporal lobe cortex of TRM brain. This abnormal expression may be associated with the generation of epileptiform activity and provide a candidate target for treatment of genetic epilepsy.

Effect of Acetaldehyde Intoxication and Withdrawal on NPY Expression: Focus on Endocannabinoidergic System Involvement

Acetaldehyde (ACD), the first alcohol metabolite, plays a pivotal role in the rewarding, motivational, and addictive properties of the parental compound. Many studies have investigated the role of ACD in mediating neurochemical and behavioral effects induced by alcohol administration, but very little is known about the modulation of neuropeptide systems following ACD intoxication and withdrawal. Indeed, the neuropeptide Y (NPY) system is altered during alcohol withdrawal in key regions for cerebrocortical excitability and neuroplasticity. The primary goal of this research was to investigate the effects of ACD intoxication and withdrawal by recording rat behavior and by measuring NPY immunoreactivity in hippocampus and NAcc, two brain regions mainly involved in processes which encompass neuroplasticity in alcohol dependence. Furthermore, on the basis of the involvement of endocannabinoidergic system in alcohol and ACD reinforcing effects, the role of the selective CB1 receptor antagonist AM281 in modulating NPY expression during withdrawal was assessed. Our results indicate that (i) ACD intoxication induced a reduction in NPY expression in hippocampus and NAcc; (ii) symptoms of physical dependence, similar to alcohol's, were scored at 12 h from the last administration of ACD; and (iii) NPY levels increased in early and prolonged acute withdrawal in both brain regions examined. The administration of AM281 was able to blunt signs of ACD-induced physical dependence, to modulate NPY levels, and to further increase NPY expression during ACD withdrawal both in hippocampus and NAcc. In conclusion, the present study shows that complex plastic changes take place in NPY system during ACD intoxication and subsequent withdrawal in rat hippocampal formation and NAcc. The pharmacological inhibition of CB1 signaling could counteract the neurochemical imbalance associated with ACD, and alcohol withdrawal, likely boosting the setting up of homeostatic functional recovery.

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.

Neuropeptides in epilepsy

Neuropeptides play an important role in modulating seizures and epilepsy. Unlike neurotransmitters which operate on a millisecond time-scale, neuropeptides have longer half lives; this leads to modulation of neuronal and network activity over prolonged periods, so contributing to setting the seizure threshold. Most neuropeptides are stored in large dense vesicles and co-localize with inhibitory interneurons. They are released upon high frequency stimulation making them attractive targets for modulation of seizures, during which high frequency discharges occur. Numerous neuropeptides have been implicated in epilepsy; one, ACTH, is already used in clinical practice to suppress seizures. Here, we concentrate on neuropeptides that have a direct effect on seizures, and for which therapeutic interventions are being developed. We have thus reviewed the abundant reports that support a role for neuropeptide Y (NPY), galanin, ghrelin, somatostatin and dynorphin in suppressing seizures and epileptogenesis, and for tachykinins having pro-epileptic effects. Most in vitro and in vivo studies are performed in hippocampal tissue in which receptor expression is usually high, making translation to other brain areas less clear. We highlight recent therapeutic strategies to treat epilepsy with neuropeptides, which are based on viral vector technology, and outline how such interventions need to be refined in order to address human disease.

Emerging novel roles of neuropeptide Y in the retina: from neuromodulation to neuroprotection

Neuropeptide Y (NPY) and NPY receptors are widely expressed in the central nervous system, including the retina. Retinal cells, in particular neurons, astrocytes, and Müller, microglial and endothelial cells express this peptide and its receptors (Y1, Y2, Y4 and/or Y5). Several studies have shown that NPY is expressed in the retina of various mammalian and non-mammalian species. However, studies analyzing the distribution of NPY receptors in the retina are still scarce. Although the physiological roles of NPY in the retina have not been completely elucidated, its early expression strongly suggests that NPY may be involved in the development of retinal circuitry. NPY inhibits the increase in [Ca(2+)]i triggered by elevated KCl in retinal neurons, protects retinal neural cells against toxic insults and induces the proliferation of retinal progenitor cells. In this review, we will focus on the roles of NPY in the retina, specifically proliferation, neuromodulation and neuroprotection. Alterations in the NPY system in the retina might contribute to the pathogenesis of retinal degenerative diseases, such as diabetic retinopathy and glaucoma, and NPY and its receptors might be viewed as potentially novel therapeutic targets.

Lateral septal infusions of the neuropeptide Y Y2 receptor agonist, NPY(13-36) differentially affect different defensive behaviors in male, Long Evans rats

The lateral septum has been extensively implicated in regulating anxiety-related defensive behaviors in the rat. Neuropeptide Y (NPY) contributes to anxiety, likely through activity at the NPY Y1 and/or Y2 receptor binding sites. Although the lateral septum contains the highest density of Y2 receptors in brain, the involvement of this receptor in anxiety-related defensive behaviors is not clear. Thus, the purpose of the current study was to characterize lateral septal Y2 receptor contributions to rats' defensive responses to threat and/or potentially threatening environments. We investigated this by infusing the NPY Y2 agonist NPY13-36 into the lateral septum and testing rats across a battery of animal models of anxiety (Experiment 1). To verify the role of Y2 in mediating the observed effects, rats were pre-infused with the potent and highly selective Y2 antagonist BIIE 0246 prior to infusion with NPY13-36 (Experiment 2). Infusions of NPY13-36 into the lateral septum increased rats' open-arm exploration in the elevated plus-maze test (p<0.01) and decreased the proportion of rats' that buried (p<0.05) as well as their latency to initiate burying in the shock-probe burying test (p<0.01). By contrast, NPY13-36 did not affect either anxiety- or appetite-related responses in the novelty-induced suppression of feeding test (all ps>0.3; Experiment 1). Pre-treatment with the Y2 antagonist BIIE 0246 prevented the anxiolytic-like actions of NPY13-36 in the plus-maze but not in the shock-probe test (Experiment 2). Thus, it appears that the anxiolytic-like actions of lateral septal NPY13-36 are mediated by the Y2 receptor in a test-specific manner.

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.

Neuropeptide Y (NPY) in the extended amygdala is recruited during the transition to alcohol dependence

Neuropeptide Y (NPY) is abundant in the extended amygdala, a conceptual macrostructure in the basal forebrain important for regulation of negative affective states. NPY has been attributed a central role in anxiety-like behavior, fear, nociception, and reward in rodents. Deletion of the NPY gene in mice produces a high-anxiety high-alcohol-drinking phenotype. NPY infused into the brains of rats selectively bred to consume high quantities of alcohol suppresses alcohol drinking by those animals, an effect that is mediated by central amygdala (CeA). Likewise, alcohol-preferring rats exhibit basal NPY deficits in CeA. NPY infused into the brains of alcohol-dependent rats blocks excessive alcohol drinking by those animals, an effect that also has been localized to the CeA. NPY in CeA may rescue dependence-induced increases in anxiety and alcohol drinking via inhibition of downstream effector regions that receive GABAergic inputs from CeA. It is hypothesized here that NPY modulates anxiety-like behavior via Y2R regulation of NPY release, whereas NPY modulation of alcohol-drinking behavior in alcohol-dependent animals occurs via Y2R regulation of GABA release.

Multifaces of neuropeptide Y in the brain--neuroprotection, neurogenesis and neuroinflammation

Neuropeptide Y (NPY) has been implicated in the modulation of important features of neuronal physiology, including calcium homeostasis, neurotransmitter release and excitability. Moreover, NPY has been involved as an important modulator of hippocampal and thalamic circuits, receiving particular attention as an endogenous antiepileptic peptide and as a potential master regulator of feeding behavior. NPY not only inhibits excessive glutamate release (decreasing circuitry hyperexcitability) but also protects neurons from excitotoxic cell death. Furthermore, NPY has been involved in the modulation of the dynamics of dentate gyrus and subventricular zone neural stem cell niches. In both regions, NPY is part of the chemical resource of the neurogenic niche and acts through NPY Y1 receptors to promote neuronal differentiation. Interestingly, NPY is also considered a neuroimmune messenger. In this review, we highlight recent evidences concerning paracrine/autocrine actions of NPY involved in neuroprotection, neurogenesis and neuroinflammation. In summary, the three faces of NPY, discussed in the present review, may contribute to better understand the dynamics and cell fate decision in the brain parenchyma and in restricted areas of neurogenic niches, in health and disease.

The central amygdala and alcohol: role of γ-aminobutyric acid, glutamate, and neuropeptides

Alcohol dependence is a chronically relapsing disorder characterized by compulsive drug seeking and drug taking, loss of control in limiting intake, and the emergence of a withdrawal syndrome in the absence of the drug. Accumulating evidence suggests an important role for synaptic transmission in the central amygdala (CeA) in mediating alcohol-related behaviors and neuroadaptative mechanisms associated with alcohol dependence. Acute alcohol facilitates γ-aminobutyric acid-ergic (GABAergic) transmission in CeA via both pre- and postsynaptic mechanisms, and chronic alcohol increases baseline GABAergic transmission. Acute alcohol inhibits glutamatergic transmission via effects at N-methyl-d-aspartate (NMDA) and AMPA receptors in CeA, whereas chronic alcohol up-regulates N-methyl-d-aspartate receptor (NMDAR)-mediated transmission. Pro- (e.g., corticotropin-releasing factor [CRF]) and anti-stress (e.g., NPY, nociceptin) neuropeptides affect alcohol- and anxiety-related behaviors, and also alter the alcohol-induced effects on CeA neurotransmission. Alcohol dependence produces plasticity in these neuropeptide systems, reflecting a recruitment of those systems during the transition to alcohol dependence.

Corticotropin-releasing factor (CRF) and neuropeptide Y (NPY): effects on inhibitory transmission in central amygdala, and anxiety- & alcohol-related behaviors

The central amygdala (CeA) is uniquely situated to function as an interface between stress- and addiction-related processes. This brain region has long been attributed an important role in aversive (e.g., fear) conditioning, as well as the negative emotional states that define alcohol dependence and withdrawal. The CeA is the major output region of the amygdala and receives complex inputs from other amygdaloid nuclei as well as regions that integrate sensory information from the external environment (e.g., thalamus, cortex). The CeA is functionally and anatomically divided into lateral and medial subdivisions that themselves are interconnected and populated by inhibitory interneurons and projections neurons. Neuropeptides are highly expressed in the CeA, particularly in the lateral subdivision, and the role of many of these peptides in regulating anxiety- and alcohol-related behaviors has been localized to the CeA. This review focuses on two of these peptides, corticotropin-releasing factor (CRF) and neuropeptide Y (NPY), that exhibit a high degree of neuroanatomical overlap (e.g., in CeA) and largely opposite behavioral profiles (e.g., in regulating anxiety- and alcohol-related behavior). CRF and NPY systems in the CeA appear to be recruited and/or up-regulated during the transition to alcohol dependence. These and other neuropeptides may converge on GABA synapses in CeA to control projection neurons and downstream effector regions, thereby translating negative affective states into anxiety-like behavior and excessive alcohol consumption.

Somatostatin and neuropeptide Y neurons undergo different plasticity in parahippocampal regions in kainic acid-induced epilepsy

Parahippocampal brain areas including the subiculum, presubiculum and parasubiculum, and entorhinal cortex give rise to major input and output neurons of the hippocampus and exert increased excitability in animal models and human temporal lobe epilepsy. Using immunohistochemistry and in situ hybridization for somatostatin and neuropeptide Y, we investigated plastic morphologic and neurochemical changes in parahippocampal neurons in the kainic acid (KA) model of temporal lobe epilepsy. Although constitutively contained in similar subclasses of γ-aminobutyric acid (GABA)-ergic neurons, both neuropeptide systems undergo distinctly different changes in their expression. Somatostatin messenger RNA (mRNA) is rapidly but transiently expressed de novo in pyramidal neurons of the subiculum and entorhinal cortex 24 hours after KA. Surviving somatostatin interneurons display increased mRNA levels at late intervals (3 months) after KA and increased labeling of their terminals in the outer molecular layer of the subiculum; the labeling correlates with the number of spontaneous seizures, suggesting that the seizures may trigger somatostatin expression. In contrast, neuropeptide Y mRNA is consistently expressed in principal neurons of the proximal subiculum and the lateral entorhinal cortex and labeling for the peptide persistently increased in virtually all major excitatory pathways of the hippocampal formation. The pronounced plastic changes differentially involving both neuropeptide systems indicate marked rearrangement of parahippocampal areas, presumably aiming at endogenous seizure protection. Their receptors may be targets for anticonvulsive drug therapy.

Long-term neuropeptide Y administration in the periphery induces abnormal baroreflex sensitivity and obesity in rats

Neuropeptide Y (NPY) is an important neuronal element involved in cardiovascular regulation. Since elevated plasma levels of NPY have been observed in numerous pathological situations, this study aimed to determine whether long-term elevated plasma concentrations of NPY could result in aberrant baroreflex sensitivity. Mini-osmotic pump containing NPY (85 μg per 30 days) was subcutaneously implanted between scapulae in male rats for 4 months. The rats treated with NPY showed the following characters compared with control group: (1) attenuated heart rate responding to the increases in mean arterial blood pressure (MABP) induced by phenylephrine, but enhanced heart rate responding to the decreases in MABP induced by sodium nitroprusside; (2) decreased protein levels of substance P (SP) and GluR2, while increased the expression of γ-aminobutyric acid A receptor (GABA(A)R) in brainstem; (3) abdominal obesity indicated by increased body weight and accumulated fat mass in peritoneal cavity; (4) significant increases in total cholesterol, triglycerides, and low density lipoprotein levels in the periphery. These findings indicate that long-term NPY administration in the periphery leads to abnormal baroreflex sensitivity due, at least in part, to the down-regulated expression of SP/GluR2 and elevated expression of GABA(A)R in both protein and RNA levels, which indicate the alternations in glutamate function and GABA action in the nucleus tractus solitarii in NPY-treated rats. Furthermore, long-term NPY administration results in abdominal obesity and dyslipidemia.

Central functions of neuropeptide Y in mood and anxiety disorders

INTRODUCTION

Neuropeptide Y (NPY) is a highly conserved neuropeptide belonging to the pancreatic polypeptide family. Its potential role in the etiology and pathophysiology of mood and anxiety disorders has been extensively studied. NPY also has effects on feeding behavior, ethanol intake, sleep regulation, tissue growth and remodeling. Findings from animal studies have delineated the physiological and behavioral effects mediated by specific NPY receptor subtypes, of which Y1 and Y2 are the best understood.

AREAS COVERED

Physiological roles and alterations of the NPYergic system in anxiety disorders, depression, posttraumatic stress disorder (PTSD), alcohol dependence and epilepsy. For each disorder, studies in animal models and human investigations are outlined and discussed, focusing on behavior, neurophysiology, genetics and potential for novel treatment targets.

EXPERT OPINION

The wide implications of NPY in psychiatric disorders such as depression and PTSD make the NPYergic system a promising target for the development of novel therapeutic interventions. These include intranasal NPY administration, currently under study, and the development of agonists and antagonists targeting NPY receptors. Therefore, we are proposing that via this mode of administration, NPY might exert CNS therapeutic actions without untoward systemic effects. Future work will show if this is a feasible approach.

Neuropeptide modulation of central amygdala neuroplasticity is a key mediator of alcohol dependence

Alcohol use disorders are characterized by compulsive drug-seeking and drug-taking, loss of control in limiting intake, and withdrawal syndrome in the absence of drug. The central amygdala (CeA) and neighboring regions (extended amygdala) mediate alcohol-related behaviors and chronic alcohol-induced plasticity. Acute alcohol suppresses excitatory (glutamatergic) transmission whereas chronic alcohol enhances glutamatergic transmission in CeA. Acute alcohol facilitates inhibitory (GABAergic) transmission in CeA, and chronic alcohol increases GABAergic transmission. Electrophysiology techniques are used to explore the effects of neuropeptides/neuromodulators (CRF, NPY, nociceptin, dynorphin, endocannabinoids, galanin) on inhibitory transmission in CeA. In general, pro-anxiety peptides increase, and anti-anxiety peptides decrease CeA GABAergic transmission. These neuropeptides facilitate or block the action of acute alcohol in CeA, and chronic alcohol produces plasticity in neuropeptide systems, possibly reflecting recruitment of negative reinforcement mechanisms during the transition to alcohol dependence. A disinhibition model of CeA output is discussed in the context of alcohol dependence- and anxiety-related behaviors.