Neuropeptide Y (NPY) Y2 receptors mediate behaviour in two animal models of anxiety: evidence from Y2 receptor knockout mice

Neurocircuitry underlying the actions of glucagon-like peptide 1 and peptide YY3-36 in the suppression of food, drug-seeking, and anxiogenesis

Obesity is a critical health condition worldwide that increases the risks of comorbid chronic diseases, but it can be managed with weight loss. However, conventional interventions relying on diet and exercise are inadequate for achieving and maintaining weight loss, thus there is significant market interest for pharmaceutical anti-obesity agents. For decades, receptor agonists for the gut peptide glucagon-like peptide 1 (GLP-1) featured prominently in anti-obesity medications by suppressing appetite and food reward to elicit rapid weight loss. As the neurocircuitry underlying food motivation overlaps with that for drugs of abuse, GLP-1 receptor agonism has also been shown to decrease substance use and relapse, thus its therapeutic potential may extend beyond weight management to treat addictions. However, as prolonged use of anti-obesity drugs may increase the risk of mood-related disorders like anxiety and depression, and individuals taking GLP-1-based medication commonly report feeling demotivated, the long-term safety of such drugs is an ongoing concern. Interestingly, current research now focuses on dual agonist approaches that include GLP-1 receptor agonism to enable synergistic effects on weight loss or associated functions. GLP-1 is secreted from the same intestinal cells as the anorectic gut peptide, Peptide YY3-36 (PYY3-36), thus this review assessed the therapeutic potential and underlying neural circuits targeted by PYY3-36 when administered independently or in combination with GLP-1 to curb the appetite for food or drugs of abuse like opiates, alcohol, and nicotine. Additionally, we also reviewed animal and human studies to assess the impact, if any, for GLP-1 and/or PYY3-36 on mood-related behaviors in relation to anxiety and depression. As dual agonists targeting GLP-1 and PYY3-36 may produce synergistic effects, they can be effective at lower doses and offer an alternative approach for therapeutic benefits while mitigating undesirable side effects.

Epistasis in neurotransmitter receptors linked to posttraumatic stress disorder and major depressive disorder comorbidity in traumatized Chinese

Background

Posttraumatic stress disorder (PTSD) and major depressive disorder (MDD) comorbidity occurs through exposure to trauma with genetic susceptibility. Neuropeptide-Y (NPY) and dopamine are neurotransmitters associated with anxiety and stress-related psychiatry through receptors. We attempted to explore the genetic association between two neurotransmitter receptor systems and the PTSD-MDD comorbidity.

Methods

Four groups were identified using latent profile analysis (LPA) to examine the patterns of PTSD and MDD comorbidity among survivors exposed to earthquake-related trauma: low symptoms, predominantly depression, predominantly PTSD, and PTSD-MDD comorbidity. NPY2R (rs4425326), NPY5R (rs11724320), DRD2 (rs1079597), and DRD3 (rs6280) were genotyped from 1,140 Chinese participants exposed to earthquake-related trauma. Main, gene-environment interaction (G × E), and gene-gene interaction (G × G) effects for low symptoms, predominantly depression, and predominantly PTSD were tested using a multinomial logistic model with PTSD-MDD comorbidity as a reference.

Results

The results demonstrated that compared to PTSD-MDD comorbidity, epistasis (G × G) NPY2R-DRD2 (rs4425326 × rs1079597) affects low symptoms (β = -0.66, OR = 0.52 [95% CI: 0.32-0.84], p = 0.008, pperm = 0.008) and predominantly PTSD (β = -0.56, OR = 0.57 [95% CI: 0.34-0.97], p = 0.037, pperm = 0.039), while NPY2R-DRD3 (rs4425326 × rs6280) impacts low symptoms (β = 0.82, OR = 2.27 [95% CI: 1.26-4.10], p = 0.006, pperm = 0.005) and predominantly depression (β = 1.08, R = 2.95 [95% CI: 1.55-5.62], p = 0.001, pperm = 0.001). The two G × G effects are independent.

Conclusion

NPY and dopamine receptor genes are related to the genetic etiology of PTSD-MDD comorbidity, whose specific mechanisms can be studied at multiple levels.

Cross talk about the role of Neuropeptide Y in CNS disorders and diseases

A peptide composed of a 36 amino acid called Neuropeptide Y (NPY) is employed in a variety of physiological processes to manage and treat conditions affecting the endocrine, circulatory, respiratory, digestive, and neurological systems. NPY naturally binds to G-protein coupled receptors, activating the Y-receptors (Y1-Y5 and y6). The findings on numerous therapeutic applications of NPY for CNS disease are presented in this review by the authors. New targets for treating diseases will be revealed by medication combinations that target NPY and its receptors. This review is mainly focused on disorders such as anxiety, Alzheimer's disease, Parkinson's disease, Huntington's disease, Machado Joseph disease, multiple sclerosis, schizophrenia, depression, migraine, alcohol use disorder, and substance use disorder. The findings from the preclinical studies and clinical studies covered in this article may help create efficient therapeutic plans to treat neurological conditions on the one hand and psychiatric disorders on the other. They may also open the door to the creation of novel NPY receptor ligands as medications to treat these conditions.

Neuropeptide Y interaction with dopaminergic and serotonergic pathways: interlinked neurocircuits modulating hedonic eating behaviours

Independent from homeostatic needs, the consumption of foods originating from hyperpalatable diets is defined as hedonic eating. Hedonic eating can be observed in many forms of eating phenotypes, such as compulsive eating and stress-eating, heightening the risk of obesity development. For instance, stress can trigger the consumption of palatable foods as a type of coping strategy, which can become compulsive, particularly when developed as a habit. Although eating for pleasure is observed in multiple maladaptive eating behaviours, the current understanding of the neurobiology underlying hedonic eating remains deficient. Intriguingly, the combined orexigenic, anxiolytic and reward-seeking properties of Neuropeptide Y (NPY) ignited great interest and has positioned NPY as one of the core neuromodulators operating hedonic eating behaviours. While extensive literature exists exploring the homeostatic orexigenic and anxiolytic properties of NPY, the rewarding effects of NPY continue to be investigated. As deduced from a series of behavioural and molecular-based studies, NPY appears to motivate the consumption and enhancement of food-rewards. As a possible mechanism, NPY may modulate reward-associated monoaminergic pathways, such as the dopaminergic and serotoninergic neural networks, to modulate hedonic eating behaviours. Furthermore, potential direct and indirect NPYergic neurocircuitries connecting classical homeostatic and hedonic neuropathways may also exist involving the anti-reward centre the lateral habenula. Therefore, this review investigates the participation of NPY in orchestrating hedonic eating behaviours through the modulation of monoaminergic pathways.

Restraint stress potentiates neuropeptide Y-mediated impairment on spatial memory in rats

Memory is the ability to store, retrieve and use information that requires a progressive time-dependent stabilization process known as consolidation to be established. The hippocampus is essential for processing all the information that forms memory, especially spatial memory. Neuropeptide Y (NPY) affects memory, so in this study we investigated the participation and recruitment of NPY receptors during spatial memory consolidation in rats. Using the water maze test, we show that NPY (1 pmol) injected into the dorsal hippocampus impaired memory consolidation and that previous restraint stress (30 min) potentiates NPY effects, i.e. further impaired memory consolidation. Using selective antagonists for NPY Y₁ and Y₂ receptors we demonstrate that both receptors play a key role on spatial memory consolidation. Our data suggest that NPY modulates aversive and adaptive memory formation by NPY receptors activation.

Effect of depression and suicidal behavior on neuropeptide Y (NPY) and its receptors in the adult human brain: A postmortem study

Neuropeptides are small proteinaceous molecules (3-100 amino acids) that are secreted by neurons and act on both neuronal and non-neuronal cells. Neuropeptide Y (NPY), a highly conserved and expressed neuropeptide in the central nervous system of mammals, plays a major role in stress response and resilience. Increasing evidence suggests that NPY and its receptors are altered in depression and suicide, pointing to their antidepressant-like nature. The objective of this study was to examine the role of NPY system in depression and suicidal behavior. Expression of NPY and its four receptors, NPY1R, NPY2R, NPY4R, and NPY5R was studied at the transcriptional and translational levels in the prefrontal cortex (PFC) and hippocampus regions of the postmortem brain of normal control (NC) (n = 24) and depressed suicide (DS) (n = 24) subjects. We observed a significant decrease in NPY mRNA and upregulation in NPY1R and NPY2R mRNA in both brain regions of DS subjects compared with NC subjects. We also observed a significant decrease in NPY protein expression in the PFC of subjects with DS. This study provides the first detailed evidence of alterations in the NPY system and the associated stress response in depression and suicidal behavior in humans. The outcomes of this study could be applied in the development of novel NPY system-targeted approaches for the treatment of depression.

Neuropeptide Y and glutamatergic mechanisms in the amygdala and ventral hippocampus differentially mediate impaired social behavior in diabetic mice

Though patients with diabetes mellitus are reported to show deficits in social interaction, the mechanisms of these impairments are unclear. The present study investigated the role of AMPA and neuropeptide Y (NPY) receptors in the ventral hippocampus (vHC) and basolateral amygdala (BLA) in the social behavior of diabetic mice. In the three-chamber test, streptozotocin (STZ)-induced diabetic mice showed impairment in social novelty preference, but not in sociability. Injection of the AMPA receptor antagonist NBQX into vHC or BLA each restored social novelty preference in STZ-induced diabetic mice. NPY content in amygdala, but not in vHC, of STZ-induced diabetic mice was increased relative to non-diabetic mice. In STZ-induced diabetic mice, injection of the NPY Y₂ receptor antagonist BIIE 0246 into BLA restored social novelty preference, whereas injection of BIIE 0246 into vHC was without effect. Finally, in non-diabetic mice social novelty preference was impaired by the NPY Y₂ receptor agonist NPY 13-36 injected into BLA and restored by co-injection of NBQX. These results indicate that in diabetic mice glutamatergic function is enhanced in both vHC and BLA, which impairs social novelty preference through AMPA receptors. In addition, they indicate that NPYergic function in BLA, but not vHC, is enhanced in diabetic mice, which impairs social novelty preference through NPY Y₂ receptors.

Activation of NPY receptor subtype 1 by [D-His26]NPY is sufficient to prevent development of anxiety and depressive like effects in the single prolonged stress rodent model of PTSD

The neuropeptide Y (NPY) system plays an important role in mediating resilience to the harmful effect of stress in post-traumatic stress disorder (PTSD). It can mediate its effects via several G-protein coupled receptors: Y1R, Y2R, Y4R and Y5R. To investigate the role of individual NPY receptors in the resilience effects of NPY to traumatic stress, intranasal infusion of either Y1R agonists [D-His²⁶]NPY, [Leu³¹Pro³⁴]NPY, Y2R agonist NPY (3-36) or NPY were administered to male Sprague-Dawley rats immediately following the last stressor of the single prolonged stress (SPS) protocol, a widely used PTSD animal model. After 7 or 14 days, effects of the treatments were measured on the elevated plus maze (EPM) for anxiety, in forced swim test (FST) for development of depressive-like or re-experiencing behavior, in social interaction (SI) test for impaired social behavior, and acoustic startle response (ASR) for hyperarousal. [D-His²⁶]NPY, but not [Leu³¹Pro³⁴]NPY nor NPY (3-36) Y2R, was effective in preventing the SPS-elicited development of anxiety. Y1R, but not Y2R agonists prevented development of depressive- feature on FST, with [D-His²⁶]NPY superior to NPY. The results demonstrate that [D-His²⁶]NPY was sufficient to prevent development of anxiety, social impairment and depressive symptoms, and has promise as an early intervention therapy following traumatic stress.

Usefulness of a Kampo Medicine on Stress-Induced Delayed Gastric Emptying in Mice

Anxiety and depression often occur with gastrointestinal symptoms. Although the Japanese traditional medicine (Kampo medicine) bukuryoingohangekobokuto (BGH) is approved for treating anxiety, neurotic gastritis, and heartburn, its effect on gastrointestinal motility remains poorly known. This study aimed to examine the effect of BGH on delayed gastric emptying in stress model mice and clarified its action mechanism. Seven-week-old C57BL/6 male mice were acclimated for a week and fasted overnight. Stress hormone, corticotropin-releasing factor (CRF), was intracerebroventricularly injected to mice, and solid nutrient meal (ground chow and distilled water) was orally administered 1 hour after. Gastric contents were collected to evaluate gastric emptying rates by measuring its dry weight. Injection of CRF (0.3 or 1.0 μg/mouse) significantly delayed the 2-hour gastric emptying in mice. BGH (1.0 g/kg), which was administered 30 minutes before the CRF injection, significantly ameliorated the delayed gastric emptying induced by CRF (0.3 μg/mouse). BGH (0.5, 1.0 g/kg) significantly enhanced the 1-hour gastric emptying and slightly increased the 2-hour gastric emptying in mice without CRF injection. In vitro functional assays showed that components of BGH antagonized or inhibited CRF type-2, dopamine D2/D3, neuropeptide Y Y2 receptors, or acetylcholinesterase. In conclusion, the components of BGH may exert synergistic effects on improving gastric emptying via various targets. BGH is considered to be potentially useful for treating gastrointestinal dysmotility with psychological symptoms.

Characterization of the Brain Penetrant Neuropeptide Y Y2 Receptor Antagonist SF-11

This paper discusses the biological and three-dimensional molecular structure of the novel, nonpeptide Y2R antagonist, SF-11 [N-(4-ethoxyphenyl)-4-(hydroxydiphenylmethyl)-1-piperidinecarbothioamide]. Pharmacokinetic studies in a rat model indicated that, following intraperitoneal dosing, SF-11 crossed the blood-brain barrier and was able to penetrate the brain, making it a suitable tool for behavioral studies. We showed for the first time that SF-11 decreased the immobility time in the forced swim test (FST) after acute peripheral administration (10 and 20 mg/kg), indicating that it has antidepressant potential. Inhibitors of the mitogen-activated protein kinase/extracellular signal regulated kinase (MAPK/ERK) and phosphatidylinositol 3-kinase (PI3K) signaling pathways blocked the anti-immobility effect of SF-11, suggesting that these pathways are involved in the antidepressant-like activity of SF-11 in the FST. The results of locomotor activity of rats indicate that the effects observed in the FST are specific and due to the antidepressant-like activity of SF-11. These findings provide further evidence for the antidepressant potential of Y2R antagonists. Also, the application of Fourier transform infrared absorption (FT-IR) and Raman spectroscopy (RS) methods combined with theoretical density functional theory (DFT) calculations allowed us to present the optimized spatial orientation of the investigated drug. Structural characterization of SF-11 based on vibrational spectroscopic data is of great importance and will aid in understanding its biological activity and pave the way for its development as a new antidepressant agent.

Preclinical findings on the potential of intranasal neuropeptide Y for treating hyperarousal features of PTSD

Acoustic startle response (ASR) assesses hyperarousal, a core symptom of posttraumatic stress disorder (PTSD). Intranasal neuropeptide Y (NPY) administration was shown to prevent hyperarousal in single prolonged stress (SPS) rodent PTSD model. However, it is unclear how ASR itself alters responses to stress. Rats (A-S-A) were exposed to acoustic startle (AS) 1 day before SPS (ASR1) and 2 weeks afterward (ASR2). Other groups were exposed in parallel to either AS (A-A) or SPS or neither. SPS enhanced ASR2. In relevant brain areas, mRNA levels were determined by qRT-PCR. In mediobasal hypothalamus, AS or SPS each increased CRH mRNA levels without an additive effect. Exposure to AS appeared to dampen some responses to SPS. The SPS-triggered reduction of GR and FKBP5 gene expression was not observed in A-S-A group. In locus coeruleus, SPS increased CRHR1 and reduced Y2R mRNAs, but not in A-S-A group. In both regions, AS altered NPY receptor gene expression, which may mediate dampening responses to SPS. In second experiment, intranasal NPY administered 2 weeks after SPS reversed hyperarousal symptoms for at least 7 days. This study reveals important effects of AS on the NPY system and demonstrates that intranasal NPY elicits long-lasting reversal of traumatic stress-triggered hyperarousal.

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.

Peptide YY Causes Apathy-Like Behavior via the Dopamine D2 Receptor in Repeated Water-Immersed Mice

Apathy is observed across several neurological and psychiatric conditions; however, its pathogenesis remains unclear. We clarified the involvement of brain–gut signaling in the disruption of goal-directed behavior. Male C57BL/6J mice were exposed to water immersion (WI) stress for 3 days. Food intake and nesting behavior were measured as indexes of motivation. Repeated WI caused decrease in food intake and nesting behavior. Plasma levels of peptide YY (PYY), IL-6, and ratio of dopamine metabolites in the striatum were significantly elevated after WI. PYY and IL-6 administration significantly decreased nesting behavior. The reductions in feeding and nesting behavior were blocked by PYY receptor (Y2R) antagonist or dopamine agonist. The ameliorative effect of the Y2R antagonist was diminished by the dopamine D2 receptor (D2R) antagonist. The reduction in goal-directed behavior is associated with dysfunction of D2R signaling via increased peripheral PYY, suggesting that PYY antagonism is a novel candidate for decline of motivation in several depressive diseases.

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.

Neuropeptide Y: An Anti-Aging Player?

Accumulating evidence suggests that neuropeptide Y (NPY) has a role in aging and lifespan determination. In this review, we critically discuss age-related changes in NPY levels in the brain, together with recent findings concerning the contribution of NPY to, and impact on, six hallmarks of aging, specifically: loss of proteostasis, stem cell exhaustion, altered intercellular communication, deregulated nutrient sensing, cellular senescence, and mitochondrial dysfunction. Understanding how NPY contributes to, and counteracts, these hallmarks of aging will open new avenues of research on limiting damage related to aging.

Neuropeptide Y input to the rat basolateral amygdala complex and modulation by conditioned fear

Within the basolateral amygdaloid complex (BLA), neuropeptide Y (NPY) buffers against protracted anxiety and fear. Although the importance of NPY's actions in the BLA is well documented, little is known about the source(s) of NPY fibers to this region. The current studies identified sources of NPY projections to the BLA by using a combination of anatomical and neurochemical approaches. NPY innervation of the BLA was assessed in rats by examining the degree of NPY coexpression within interneurons or catecholaminergic fibers with somatostatin and tyrosine hydroxylase (TH) or dopamine β-hydroxylase (DβH), respectively. Numerous NPY(+) /somatostatin(+) and NPY(+) /somatostatin(-) fibers were observed, suggesting at least two populations of NPY fibers within the BLA. No colocalization was noted between NPY and TH or DβH immunoreactivities. Additionally, Fluorogold (FG) retrograde tracing with immunohistochemistry was used to identify the precise origin of NPY projections to the BLA. FG(+) /NPY(+) cells were identified within the amygdalostriatal transition area (AStr) and stria terminalis and scattered throughout the bed nucleus of the stria terminalis. The subpopulation of NPY neurons in the AStr also coexpressed somatostatin. Subjecting animals to a conditioned fear paradigm increased NPY gene expression within the AStr, whereas no changes were observed within the BLA or stria terminalis. Overall, these studies identified limbic regions associated with stress circuits providing NPY input to the BLA and demonstrated that a unique NPY projection from the AStr may participate in the regulation of conditioned fear. J. Comp. Neurol. 524:2418-2439, 2016. © 2016 Wiley Periodicals, Inc.

The role of Neuropeptide Y in fear conditioning and extinction

While anxiety disorders are the brain disorders with the highest prevalence and constitute a major burden for society, a considerable number of affected people are still treated insufficiently. Thus, in an attempt to identify potential new anxiolytic drug targets, neuropeptides have gained considerable attention in recent years. Compared to classical neurotransmitters they often have a regionally restricted distribution and may bind to several distinct receptor subtypes. Neuropeptide Y (NPY) is a highly conserved neuropeptide that is specifically concentrated in limbic brain areas and signals via at least 5 different G-protein-coupled receptors. It is involved in a variety of physiological processes including the modulation of emotional-affective behaviors. An anxiolytic and stress-reducing property of NPY is supported by many preclinical studies. Whether NPY may also interact with processing of learned fear and fear extinction is comparatively unknown. However, this has considerable relevance since pathological, inappropriate and generalized fear expression and impaired fear extinction are hallmarks of human post-traumatic stress disorder and a major reason for its treatment-resistance. Recent evidence from different laboratories emphasizes a fear-reducing role of NPY, predominantly mediated by exogenous NPY acting on Y1 receptors. Since a reduction of fear expression was also observed in Y1 receptor knockout mice, other Y receptors may be equally important. By acting on Y2 receptors, NPY promotes fear extinction and generates a long-term suppression of fear, two important preconditions that could support cognitive behavioral therapies in human patients. A similar effect has been demonstrated for the closely related pancreatic polypeptide (PP) when acting on Y4 receptors. Preliminary evidence suggests that NPY modulates fear in particular by activation of Y1 and Y2 receptors in the basolateral and central amygdala, respectively. In the basolateral amygdala, NPY signaling activates inhibitory G protein-coupled inwardly-rectifying potassium channels or suppresses hyperpolarization-induced I(h) currents in a Y1 receptor-dependent fashion, favoring a general suppression of neuronal activity. A more complex situation has been described for the central extended amygdala, where NPY reduces the frequency of inhibitory and excitatory postsynaptic currents. In particular the inhibition of long-range central amygdala output neurons may result in a Y2 receptor-dependent suppression of fear. The role of NPY in processes of learned fear and fear extinction is, however, only beginning to emerge, and multiple questions regarding the relevance of endogenous NPY and different receptor subtypes remain elusive. Y2 receptors may be of particular interest for future studies, since they are the most prominent Y receptor subtype in the human brain and thus among the most promising therapeutic drug targets when translating preclinical evidence to potential new therapies for human anxiety disorders.

Structure and function of the amygdaloid NPY system: NPY Y2 receptors regulate excitatory and inhibitory synaptic transmission in the centromedial amygdala

The amygdala is essential for generating emotional-affective behaviors. It consists of several nuclei with highly selective, elaborate functions. In particular, the central extended amygdala, consisting of the central amygdala (CEA) and the bed nucleus of the stria terminalis (BNST) is an essential component actively controlling efferent connections to downstream effectors like hypothalamus and brain stem. Both, CEA and BNST contain high amounts of different neuropeptides that significantly contribute to synaptic transmission. Among these, neuropeptide Y (NPY) has emerged as an important anxiolytic and fear-reducing neuromodulator. Here, we characterized the expression, connectivity and electrophysiological function of NPY and Y2 receptors within the CEA. We identified several NPY-expressing neuronal populations, including somatostatin- and calretinin-expressing neurons. Furthermore, in the main intercalated nucleus, NPY is expressed primarily in dopamine D1 receptor-expressing neurons but also in interspersed somatostatin-expressing neurons. Interestingly, NPY neurons did not co-localize with the Y2 receptor. Retrograde tract tracing experiments revealed that NPY neurons reciprocally connect the CEA and BNST. Functionally, the Y2 receptor agonist PYY3-36, reduced both, inhibitory as well as excitatory synaptic transmission in the centromedial amygdala (CEm). However, we also provide evidence that lack of NPY or Y2 receptors results in increased GABA release specifically at inhibitory synapses in the CEm. Taken together, our findings suggest that NPY expressed by distinct populations of neurons can modulate afferent and efferent projections of the CEA via presynaptic Y2 receptors located at inhibitory and excitatory synapses.

NPY Y2 receptors in the central amygdala reduce cued but not contextual fear

The amygdala is fundamental for associative fear and extinction learning. Recently, also the central nucleus of the amygdala (CEA) has emerged as a site of plasticity actively controlling efferent connections to downstream effector brain areas. Although synaptic transmission is primarily mediated by glutamate and GABA, neuropeptides critically influence the overall response. While neuropeptide Y (NPY) acting via postsynaptic Y1 receptors exerts an important anxiolytic and fear-reducing action, the role of the predominantly presynaptic Y2 receptors is less defined. To investigate the role of Y2 receptors in the CEA we employed viral-vector mediated over-expression of the Y2 selective agonist NPY3-36 in fear conditioning and extinction experiments. NPY3-36 over-expression in the CEA resulted in reduced fear expression during fear acquisition and recall. Interestingly, this effect was blocked by intraperitoneal injection of a brain-penetrant Y2 receptor antagonist. Furthermore, over-expression of NPY3-36 in the CEA also reduced fear expression during fear extinction of CS-induced but not context-related fear. Again, fear extinction appeared delayed by peripheral injection of a Y2 receptor antagonist JNJ-31020028. Importantly, mice with over-expression of NPY3-36 in the CEA also displayed reduced spontaneous recovery and reinstatement, suggesting that Y2 receptor activation supports a permanent suppression of fear. Local deletion of Y2 receptors in the CEA, on the other hand, increased the expression of CS-induced freezing during fear recall and fear extinction. Thus, NPY inhibits fear learning and promotes cued extinction by reducing fear expression also via activation of presynaptic Y2 receptors on CEA neurons.

Schizophrenia and Depression Co-Morbidity: What We have Learned from Animal Models

Patients with schizophrenia are at an increased risk for the development of depression. Overlap in the symptoms and genetic risk factors between the two disorders suggests a common etiological mechanism may underlie the presentation of comorbid depression in schizophrenia. Understanding these shared mechanisms will be important in informing the development of new treatments. Rodent models are powerful tools for understanding gene function as it relates to behavior. Examining rodent models relevant to both schizophrenia and depression reveals a number of common mechanisms. Current models which demonstrate endophenotypes of both schizophrenia and depression are reviewed here, including models of CUB and SUSHI multiple domains 1, PDZ and LIM domain 5, glutamate Delta 1 receptor, diabetic db/db mice, neuropeptide Y, disrupted in schizophrenia 1, and its interacting partners, reelin, maternal immune activation, and social isolation. Neurotransmission, brain connectivity, the immune system, the environment, and metabolism emerge as potential common mechanisms linking these models and potentially explaining comorbid depression in schizophrenia.

Effects of sex and deletion of neuropeptide Y2 receptors from GABAergic neurons on affective and alcohol drinking behaviors in mice

A large literature has demonstrated that neuropeptide Y (NPY) regulates many emotional and reward-related behaviors via its primary receptors, Y1R and Y2R. Classically, NPY actions at postsynaptic Y1R decrease anxiety, depression, and alcohol drinking, while its actions at presynaptic Y2R produce the opposite behavioral phenotypes. However, emerging evidence suggests that activation of Y2R can also produce anxiolysis in a brain region and neurotransmitter system-dependent fashion. Further, numerous human and rodent studies have reported that females display higher levels of anxiety, depression, and alcohol drinking. In this study, we evaluated sex differences and the role of Y2R on GABAergic transmission in these behaviors using a novel transgenic mouse that lacks Y2R specifically in VGAT-expressing neurons (VGAT-Y2R knockout). First, we confirmed our genetic manipulation by demonstrating that Y2R protein expression was decreased and that a Y2R agonist could not alter GABAergic transmission in the extended amygdala, a limbic brain region critically implicated in the regulation of anxiety and alcohol drinking behaviors, using immunofluorescence and slice electrophysiology. Then, we tested male and female VGAT-Y2R knockout mice on a series of behavioral assays for anxiety, depression, fear, anhedonia, and alcohol drinking. We found that females displayed greater basal anxiety, higher levels of ethanol consumption, and faster fear conditioning than males, and that knockout mice exhibited enhanced depressive-like behavior in the forced swim test. Together, these results confirm previous studies that demonstrate higher expression of negative affective and alcohol drinking behaviors in females than males, and they highlight the importance of Y2R function in GABAergic systems in the expression of depressive-like behavior.

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.

Administration of the Y2 receptor agonist PYY3-36 in mice induces multiple behavioral changes relevant to schizophrenia

Functional changes in neuropeptide Y (NPY) signaling at the Y2 receptor subtype have been widely implicated in stress-related neuropsychiatric illnesses such as depression and anxiety disorders. Altered Y2 receptor signaling may also play a role in the precipitation of behavioral and cognitive symptoms associated with schizophrenia. To seek preclinical evidence for this possibility, we explored the functional consequences of treatment with the selective Y2 receptor agonist PYY(3-36) using translational tests for the assessment of schizophrenia-relevant behavioral and cognitive deficits in mice. We found that acute systemic administration of PYY(3-36) at a low dose (1 μg/100 g body weight) or high dose (20 μg/100 g body weight) profoundly impaired social interaction without affecting innate anxiety. PYY(3-36) treatment at the high dose further led to a disruption of sensorimotor gating in the form of prepulse inhibition deficiency. This effect was fully antagonized by acute treatment with the preferential dopamine D2 receptor antagonist haloperidol, but not with clozapine. In addition, both doses of PYY(3-36) impaired selective associative learning in the latent inhibition paradigm and spatial working memory in a matching-to-position water maze test. The wide range of abnormalities induced by PYY(3-36) suggests that signaling at the Y2 subtype of NPY receptors is critical for a number of behavioral and cognitive functions, some of which are highly relevant to schizophrenia and related psychotic disorders. At least some of the behavioral deficits induced by augmentation of Y2 receptor signaling may involve increased dopaminergic activity.

Neuropeptide Y and posttraumatic stress disorder

Resiliency to the adverse effects of extraordinary emotional trauma on the brain varies within the human population. Accordingly, some people cope better than others with traumatic stress. Neuropeptide Y (NPY) is a 36-amino-acid peptide transmitter abundantly expressed in forebrain limbic and brain stem areas that regulate stress and emotional behaviors. Studies largely in rodents demonstrate a role for NPY in promoting coping with stress. Moreover, accruing data from the genetic to the physiological implicate NPY as a potential 'resilience-to-stress' factor in humans. Here, we consolidate findings from preclinical and clinical studies of NPY that are of relevance to stress-associated syndromes, most prototypically posttraumatic stress disorder (PTSD). Collectively, these data suggest that reduced central nervous system (CNS) NPY concentrations or function may be associated with PTSD. We also link specific symptoms of human PTSD with extant findings in the NPY field to reveal potential physiological contributions of the neuropeptide to the disorder. In pursuit of understanding the physiological basis and treatment of PTSD, the NPY system is an attractive target.

Role of NPY Y1 receptor on acquisition, consolidation and extinction on contextual fear conditioning: dissociation between anxiety, locomotion and non-emotional memory behavior

Neuropeptide Y (NPY) is the most abundant peptide in the central nervous system (CNS) and is densely localized in the brain regions involved in stress, memory, fear and anxiety. Although previous research supports a role for NPY in the mediation of rodent and human emotional behavior, there is currently a lack of information on the effects of low doses of NPY that could have a potential therapeutic advantage, minimizing side-effects such as cognition impairment or sedation. Herein, we assessed the effects of intracerebroventricular (i.c.v.) administration of low doses of NPY, and of the Y1-agonist Leu31Pro34-NPY (LP-NPY) on contextual fear conditioning (CFC), as they have no effect on unconditioned anxiety-like, locomotor activity and non-emotional memory. NPY (3 pmol) and LP-NPY (1 pmol) inhibited freezing behavior when administered in the acquisition or consolidation stages, indicating a reduction of fear. When injected in the extinction phase, only NPY inhibited freezing behavior on CFC. Pre-treatment with the Y1-antagonist BIBO3304 before NPY and LP-NPY was able to prevent the inhibition of fear responses induced by both NPY agonists. Taken together, our results demonstrate robust fear-inhibiting effects of i.c.v. injection of NPY on contextual fear conditioning in rats, a response that is mediated, at least in part, by the Y1 receptor. Moreover, these treatments were unable to change locomotor activity or to show an anxiolytic-like effect, as evaluated in an open-field and an elevated plus-maze. This specific fear reduction effect may underlie resilience systems in the CNS and has potential therapeutic relevance in PTSD.

Mood and memory-associated behaviors in neuropeptide Y5 knockout mice

Recent data led to suggest that in addition to Y1 and Y2 subtypes, Y5 receptors may be involved in mood-related behaviors (Morales-Medina et al., 2010). In the present study, using a battery of behavioral tests to assess anxiety and depression-like paradigms, as well as memory function, we evaluated the potential behavioral changes induced in mice devoid of Y5 receptors. Those paradigms were assessed using the open field (OF), elevated plus maze (EPM), forced swim test (FST), social interaction test (SI), object recognition test (ORT) and Morris water maze (MWM) in Y5 knockout (KO) mice and wild type (WT) animals. In the tests associated to anxiety related behaviors (OF, EPM and SI), no difference for locomotion and time spent in the lateral area of open field were observed between Y5 KO and WT mice. Similar results were observed for time and number of entries in open arms in EPM. Additionally, in SI test, Y5 KO mice spent same amount of time and number of entries in the stranger chamber as compared to WT animals. In the FST, as compared to WT mice, Y5 KO mice had similar immobility time on day 1. No memory dysfunction was observed in the MWM and ORT in Y5 KO mice, as compared to WT. Altogether these data suggest that under basal conditions Y5 KO and WT mice display similar mood behaviors and memory functions. However, as compared to WT, Y5 KO mice display increased grooming and rearing in the OF, lower ratio entries in open arms in the EPM and increased immobility time on the second day of the FST.

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, peptide YY and pancreatic polypeptide in the gut-brain axis

The gut-brain axis refers to the bidirectional communication between the gut and the brain. Four information carriers (vagal and spinal afferent neurons, immune mediators such as cytokines, gut hormones and gut microbiota-derived signalling molecules) transmit information from the gut to the brain, while autonomic neurons and neuroendocrine factors carry outputs from the brain to the gut. The members of the neuropeptide Y (NPY) family of biologically active peptides, NPY, peptide YY (PYY) and pancreatic polypeptide (PP), are expressed by cell systems at distinct levels of the gut-brain axis. PYY and PP are exclusively expressed by endocrine cells of the digestive system, whereas NPY is found at all levels of the gut-brain and brain-gut axis. The major systems expressing NPY comprise enteric neurons, primary afferent neurons, several neuronal pathways throughout the brain and sympathetic neurons. In the digestive tract, NPY and PYY inhibit gastrointestinal motility and electrolyte secretion and in this way modify the input to the brain. PYY is also influenced by the intestinal microbiota, and NPY exerts, via stimulation of Y1 receptors, a proinflammatory action. Furthermore, the NPY system protects against distinct behavioural disturbances caused by peripheral immune challenge, ameliorating the acute sickness response and preventing long-term depression. At the level of the afferent system, NPY inhibits nociceptive input from the periphery to the spinal cord and brainstem. In the brain, NPY and its receptors (Y1, Y2, Y4, Y5) play important roles in regulating food intake, energy homeostasis, anxiety, mood and stress resilience. In addition, PP and PYY signal to the brain to attenuate food intake, anxiety and depression-related behaviour. These findings underscore the important role of the NPY-Y receptor system at several levels of the gut-brain axis in which NPY, PYY and PP operate both as neural and endocrine messengers.

NPY controls fear conditioning and fear extinction by combined action on Y₁ and Y₂ receptors

BACKGROUND AND PURPOSE

Neuropeptide Y (NPY) and its receptors have been implicated in the control of emotional-affective processing, but the mechanism is unclear. While it is increasingly evident that stimulation of Y₁ and inhibition of Y₂ receptors produce prominent anxiolytic and antidepressant effects, the contribution of the individual NPY receptor subtypes in the acquisition and extinction of learned fear are unknown.

EXPERIMENTAL APPROACH

Here we performed Pavlovian fear conditioning and extinction in NPY knockout (KO) and in NPY receptor KO mice.

KEY RESULTS

NPY KO mice display a dramatically accelerated acquisition of conditioned fear. Deletion of Y₁ receptors revealed only a moderately accelerated acquisition of conditioned fear, while lack of Y₂ receptors was without any effect on fear learning. However, the strong phenotype seen in NPY KO mice was reproduced in mice lacking both Y₁ and Y₂ receptors. In addition, NPY KO mice showed excessive recall of conditioned fear and impaired fear extinction. This behaviour was replicated only after deletion of both Y₁ and Y₂ receptors. In Y₁ receptor single KO mice, fear extinction was delayed and was unchanged in Y₂ receptor KO mice. Deletion of NPY and particularly Y₂ receptors resulted in a generalization of conditioned fear.

CONCLUSIONS AND IMPLICATIONS

Our data demonstrate that NPY delays the acquisition, reduces the expression of conditioned fear while promoting fear extinction. Although these effects appear to be primarily mediated by Y₁ receptors, the pronounced phenotype of Y₁Y₂ receptor double KO mice suggests a synergistic role of Y₂ receptors in fear acquisition and in fear extinction.

The selective neuropeptide Y Y5 agonist [cPP(1-7),NPY(19-23),Ala31,Aib32,Gln34]hPP differently modulates emotional processes and body weight in the rat

The neuropeptide Y (NPY) has been suggested to act as a major regulator of emotional processes and body weight. The full spectrum of biological effects of this peptide is mediated by at least four classes of receptors known as the Y(1), Y(2), Y(4), and Y(5) subtypes. However, the respective contribution of each of these receptor subtypes, especially the Y(5) subtype, in emotional processes is still mostly unknown. In the present study, we investigated the effect of long term administration of a selective Y(5) agonist [cPP(1-7),NPY(19-23),Ala(31),Aib(32),Gln(34)]hPP on emotional processes and body weight using two rat models of emotional dysfunctions, the corticosterone (CORT)-induced anxiety model as well as the olfactory bulbectomized (OBX) model of depression and anxiety in Wistar and Sprague-Dawley rats, respectively. The sub-chronic administration of the Y(5) agonist reversed the high levels of locomotion, rearing and grooming in the open field test and the impaired social activity induced by OBX, while increased the percentage of entries and time in the open arm of the elevated plus maze in CORT-treated rats. Furthermore, this Y(5) agonist increased body weight in both strains of control rats. These data further demonstrate that Y(5) receptors are not only involved in the control of body weight but also mediate emotional processing under challenged conditions. Thus, the pharmacotherapeutic administration of a Y(5) agonist could be considered as a potentially novel strategy to alleviate some forms of anxiety and depression in humans.

Y5 neuropeptide Y receptor overexpression in mice neither affects anxiety- and depression-like behaviours nor seizures but confers moderate hyperactivity

Neuropeptide Y (NPY) has been implicated in anxiolytic- and antidepressant-like behaviour as well as seizure-suppressant effects in rodents. Although these effects appear to be predominantly mediated via other NPY receptors (Y1 and/or Y2), several studies have also indicated a role for Y5 receptors. Gene therapy using recombinant viral vectors to induce overexpression of NPY, Y1 or Y2 receptors in the hippocampus or amygdala has previously been shown to modulate emotional behaviour and seizures in rodents. The present study explored the potential effects of gene therapy with the Y5 receptor, by testing effects of recombinant adeno-associated viral vector (rAAV) encoding Y5 (rAAV-Y5) in anxiety- and depression-like behaviour as well as in kainate-induced seizures in adult mice. The rAAV-Y5 vector injected into the hippocampus and amygdala induced a pronounced and sustained increase in Y5 receptor mRNA expression and functional Y5 receptor binding, but no significant effects were found with regard to anxiety- and depression-like behaviours or seizure susceptibility. Instead, rAAV-mediated Y5 receptor transgene overexpression resulted in moderate hyperactivity in the open field test. These results do not support a potential role for single transgene overexpression of Y5 receptors for modulating anxiety-/depression-like behaviours or seizures in adult mice. Whether the induction of hyperactivity by rAAV-Y5 could be relevant for other conditions remains to be studied.

'Idiopathic' intestinal failure--the importance of identifying and treating primary psychopathology

BACKGROUND

Gastrointestinal neuromuscular disorders (GINMD) are an important cause of intestinal failure (IF). We present six cases of IF in whom a diagnosis of GINMD was initially suspected, but in whom psychopathology was discovered to be the primary etiology.

METHODS

(i) Six consecutive cases referred to our unit with IF, initially presumed to be due to GINMD, were selected. Informed consent was obtained from all patients. Case notes were reviewed for salient clinical information. (ii) A literature search was performed to ascertain the epidemiology of psychopathology in IF and the current evidence for the management of severe functional GI disorders with a multidisciplinary psychiatric approach.

KEY RESULTS

(i)All six cases required multidisciplinary psychiatric management in a specialized psychiatric unit that included the use of antidepressants, antipsychotics, mood stabilizers, and Electroconvulsive therapy in addition to nutritional support via enteral or parenteral routes. (ii) The evidence base for the treatment of severe FGIDs is sparse.

CONCLUSIONS & INFERENCES

There is a need for additional reporting of such cases and further research. Our experience would suggest that a delay in the involvement of a specialist liaison psychiatrist has the potential to be life threatening in such cases. This may be more likely with greater severity, where the apparent predominance of 'physical' symptoms generates reluctance in both patient and physician to consider a psychiatric etiology and also appears to occur due to a lengthier investigative process than existed previously. We therefore propose that the provision of a specialist psychiatric assessment for all patients presenting with IF is indicated at the point of initial clinical contact, based upon the substantial clinical benefit it has the potential to confer upon a significant minority. This process need not delay investigation, which can continue as indicated in parallel, but can be life-saving.

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.

Effects of Cistanche deserticola on behavior and signs of cataract and retinopathy in senescence-accelerated OXYS rats

ETHNOPHARMACOLOGICAL RELEVANCE

Cistanche deserticola (СD) has been traditionally used in the Chinese medicine as a tonic, vasodilator and neuroprotective agent.

AIM OF THE STUDY

To investigate the effect of CD on the age-related behavior decline and cataract and retinopathy development in senescent accelerated OXYS rats.

MATERIALS AND METHODS

OXYS and Wistar (control) rats were supplemented with 15 mg CD on kg of body weight during 2 months from the age of 12 months. Behavioral responses of animals were assessed in the elevated plus-maze (EPM), open field (OF) and in a Morris water maze (MWM). Before and after CD treatment OXYS rats were examined by an ophthalmologist.

RESULTS

14-month-old OXYS rats had demonstrated considerably reduced activities in OF, increased anxiety in EPM, and manifestly impaired learning abilities in the MWM as compared to Wistar rats. Supplementation of CD had no effect on motor and exploratory activity of Wistar and OXYS rats in the OF, but it reduced their anxiety in the EPM compared to age-matched controls. CD significantly improved visual ability of the rats, reducing the severity of the developed signs of retinopathy and cataract while having no impact on OXYS rats' spatial memory in the MWM. CD-treated Wistar rats exhibited slower learning ability in the MWM task comparison to the control group. The effect of CD on the learning ability in OXYS and Wistar rats may be associated with differences in their redox homeostasis.

CONCLUSION

All in all, the findings suggest that CD improves the age-related behavioral decline, which makes it an attractive candidate for treatment of various neurodegenerative disorders. Primarily it demonstrated its ability to slow development and to reduce to some extent severity of pathological manifestations of cataract and retinopathy in OXYS rats, which makes it an attractive candidate for treatment of age-related eye diseases too.

Neuropeptide Y Y1 receptor hippocampal overexpression via viral vectors is associated with modest anxiolytic-like and proconvulsant effects in mice

Neuropeptide Y (NPY) exerts anxiolytic- and antidepressant-like effects in rodents that appear to be mediated via Y1 receptors. Gene therapy using recombinant viral vectors to induce overexpression of NPY in the hippocampus or amygdala has previously been shown to confer anxiolytic-like effect in rodents. The present study explored an alternative and more specific approach: overexpression of Y1 receptors. Using a recombinant adeno-associated viral vector (rAAV) encoding the Y1 gene (rAAV-Y1), we, for the first time, induced overexpression of functional transgene Y1 receptors in the hippocampus of adult mice and tested the animals in anxiety- and depression-like behavior. Hippocampal Y1 receptors have been suggested to mediate seizure-promoting effect, so the effects of rAAV-induced Y1 receptor overexpression were also tested in kainate-induced seizures. Y1 receptor transgene overexpression was found to be associated with modest anxiolytic-like effect in the open field and elevated plus maze tests, but no effect was seen on depression-like behavior using the tail suspension and forced swim tests. However, the rAAV-Y1 vector modestly aggravated kainate-induced seizures. These data indicate that rAAV-induced overexpression of Y1 receptors in the hippocampus could confer anxiolytic-like effect accompanied by a moderate proconvulsant adverse effect. Further studies are clearly needed to determine whether Y1 gene therapy might have a future role in the treatment of anxiety disorders.

The novel, selective, brain-penetrant neuropeptide Y Y2 receptor antagonist, JNJ-31020028, tested in animal models of alcohol consumption, relapse, and anxiety

Neuropeptide Y (NPY) signaling has been shown to modulate stress responses and to be involved in regulation of alcohol intake and dependence. The present study explores the possibility that blockade of NPY Y2 autoreceptors using a novel, blood-brain barrier penetrant NPY Y2 receptor antagonist, JNJ-31020028 (N-(4-{4-[2-(diethylamino)-2-oxo-1-phenylethyl]piperazin-1-yl}-3-fluorophenyl)-2-pyridin-3-ylbenzamide), may achieve a therapeutically useful activation of the NPY system in alcohol- and anxiety-related behavioral models. We examined JNJ-31020028 in operant alcohol self-administration, stress-induced reinstatement to alcohol seeking, and acute alcohol withdrawal (hangover)-induced anxiety. Furthermore, we tested its effects on voluntary alcohol consumption in a genetic animal model of alcohol preference, the alcohol-preferring (P) rat. Neither systemic (0, 15, 30, and 40 mg/kg, subcutaneously [s.c.]) nor intracerebroventricular (0.0, 0.3, and 1.0 nmol/rat) administration of JNJ-31020028 affected alcohol-reinforced lever pressing or relapse to alcohol seeking behavior following stress exposure. Also, when its effects were tested on unlimited access to alcohol in P rats, preference for alcohol solution was transiently suppressed but without affecting voluntary alcohol intake. JNJ-31020028 (15 mg/kg, s.c.) did reverse the anxiogenic effects of withdrawal from a single bolus dose of alcohol on the elevated plus-maze, confirming the anxiolytic-like properties of NPY Y2 antagonism. Our data do not support Y2 antagonism as a mechanism for reducing alcohol consumption or relapse-like behavior, but the observed effects on withdrawal-induced anxiety suggest that NPY Y2 receptor antagonists may be a putative treatment for the negative affective states following alcohol withdrawal.

The discovery and synthesis of JNJ 31020028, a small molecule antagonist of the Neuropeptide Y Y₂ receptor

A series of small molecules based on a chemotype identified from our compound collection were synthesized and tested for binding affinity (IC(50)) at the human Neuropeptide Y Y(2) receptor (NPY Y(2)). Six of the 23 analogs tested possessed an NPY Y(2) IC(50) ≤ 15 nM. One member of this series, JNJ 31020028, is a selective, high affinity, receptor antagonist existing as a racemic mixture. As such a synthetic route to the desired enantiomer was designed starting from commercially available (S)-(+)-mandelic acid.

Sex-dependent control of murine emotional-affective behaviour in health and colitis by peptide YY and neuropeptide Y

BACKGROUND AND PURPOSE

Peptide YY (PYY) and neuropeptide Y (NPY) are involved in regulating gut and brain function. Because gastrointestinal inflammation is known to enhance anxiety, we explored whether experimental colitis interacts with genetic deletion (knockout) of PYY and NPY to alter emotional-affective behaviour.

EXPERIMENTAL APPROACH

Male and female wild-type, NPY (NPY(-/-) ), PYY (PYY(-/-) ) and NPY(-/-) ; PYY(-/-) double knockout mice were studied in the absence and presence of mild colitis induced by ingestion of dextran sulphate sodium (2%) in drinking water. Anxiety-like behaviour was tested on the elevated plus maze and open field, and depression-like behaviour assessed by the forced swim test.

KEY RESULTS

In the absence of colitis, anxiety-like behaviour was increased by deletion of NPY but not PYY in a test- and sex-dependent manner, while depression-like behaviour was enhanced in NPY(-/-) and PYY(-/-) mice of either sex. The severity of DSS-induced colitis, assessed by colonic myeloperoxidase content, was attenuated in NPY(-/-) but not PYY(-/-) mice. Colitis modified anxiety- and depression-related behaviour in a sex-, genotype- and test-related manner, and knockout experiments indicated that NPY and PYY were involved in some of these behavioural effects of colitis.

CONCLUSIONS AND IMPLICATIONS

These data demonstrate sex-dependent roles of NPY and PYY in regulation of anxiety- and depression-like behaviour in the absence and presence of colitis. Like NPY, the gut hormone PYY has the potential to attenuate depression-like behaviour but does not share the ability of NPY to reduce anxiety-like behaviour.

Ghrelin, peptide YY and their hypothalamic targets differentially regulate spontaneous physical activity

Recent studies suggest that spontaneous physical activity (SPA) may be under the non-conscious control of neuroendocrine circuits that are known to control food intake. To further elucidate endocrine gut-brain communication as a component of such circuitry, we here analyzed long-term and acute effects of the gastrointestinal hormones ghrelin and PYY 3-36 as well as their hypothalamic neuropeptide targets NPY, AgRP and POMC (alpha-MSH), on locomotor activity and home cage behaviors in rats. For the analysis of SPA, we used an automated infrared beam break activity measuring system, combined with a novel automated video-based behavior analysis system (HomeCageScan (HCS)). Chronic (one-month) peripheral infusion of ghrelin potently increased body weight and fat mass in rats. Such positive energy balance was intriguingly not due to an overall increased caloric ingestion, but was predominantly associated with a decrease in SPA. Chronic intracerebroventricular infusion (7 days) of ghrelin corroborated the decrease in SPA and suggested a centrally mediated mechanism. Central administration of AgRP and NPY increased food intake as expected. AgRP administration led to a delayed decrease in SPA, while NPY acutely (but transiently) increased SPA. Behavioral dissection using HCS corroborated the observed acute and transient increases of food intake and SPA by central NPY infusion. Acute central administration of alpha-MSH rapidly decreased food intake but did not change SPA. Central administration of the NPY receptor agonist PYY 3-36 transiently increased SPA. Our data suggest that the control of spontaneous physical activity by gut hormones or their neuropeptide targets may represent an important mechanistic component of energy balance regulation.

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.

Evidence from knockout mice that neuropeptide-Y Y2 and Y4 receptor signalling prevents long-term depression-like behaviour caused by immune challenge

Neuropeptide Y participates in the acute behavioural responses to immune challenge, since Y2 receptor knockout (Y2⁻/⁻) mice are particularly sensitive to the short-term anxiogenic-like effect of bacterial lipopolysaccharide. The present exploratory study addressed the involvement of Y2 and Y4 receptors in the long-term behavioural responses to immune challenge. A single intraperitoneal injection of lipopolysaccharide (0.83 mg/kg) to control mice did not affect open field behaviour 3 h post-treatment but enhanced anxiety-like behaviour in Y2⁻/⁻ as well as Y4⁻/⁻ mice. Four weeks post-treatment this behavioural effect of lipopolysaccharide persisted in Y4⁻/⁻ mice but had gone in Y2⁻/⁻ mice. Depression-related behaviour in the forced swim test was enhanced 1 day post-lipopolysaccharide in control and Y2⁻/⁻ mice, but not in Y4⁻/⁻ mice. Four weeks post-treatment, the depressogenic-like effect of lipopolysaccharide had waned in control mice, persisted in Y2⁻/⁻ mice and was first observed in Y4⁻/⁻ mice. In summary, knockout of Y2 and/or Y4 receptors unmasks the ability of a single lipopolysaccharide injection to cause a delayed and prolonged increase in anxiety- and/or depression-like behaviour. These findings suggest that neuropeptide Y acting via Y2 and Y4 receptors prevents the development of long-term anxiety- and depression-like behaviour caused by acute immune challenge.

Cell and gene therapies for refractory epilepsy

Despite recent advances in the development of antiepileptic drugs, refractory epilepsy remains a major clinical problem affecting up to 35% of patients with partial epilepsy. Currently, there are few therapies that affect the underlying disease process. Therefore, novel therapeutic concepts are urgently needed. The recent development of experimental cell and gene therapies may offer several advantages compared to conventional systemic pharmacotherapy: (i) Specificity to underlying pathogenetic mechanisms by rational design; (ii) specificity to epileptogenic networks by focal delivery; and (iii) avoidance of side effects. A number of naturally occurring brain substances, such as GABA, adenosine, and the neuropeptides galanin and neuropeptide Y, may function as endogenous anticonvulsants and, in addition, may interact with the process of epileptogenesis. Unfortunately, the systemic application of these compounds is compromised by limited bioavailability, poor penetration of the blood-brain barrier, or the widespread systemic distribution of their respective receptors. Therefore, in recent years a new field of cell and gene-based neuropharmacology has emerged, aimed at either delivering endogenous anticonvulsant compounds by focal intracerebral transplantation of bioengineered cells (ex vivo gene therapy), or by inducing epileptogenic brain areas to produce these compounds in situ (in vivo gene therapy). In this review, recent efforts to develop GABA-, adenosine-, galanin-, and neuropeptide Y- based cell and gene therapies are discussed. The neurochemical rationales for using these compounds are discussed, the advantages of focal applications are highlighted and preclinical cell transplantation and gene therapy studies are critically evaluated. Although many promising data have been generated recently, potential problems, such as long-term therapeutic efficacy, long-term safety, and efficacy in clinically relevant animal models, need to be addressed before clinical applications can be contemplated.

The central and basolateral amygdala are critical sites of neuropeptide Y/Y2 receptor-mediated regulation of anxiety and depression

Anxiety is integrated in the amygdaloid nuclei and involves the interplay of the amygdala and various other areas of the brain. Neuropeptides play a critical role in regulating this process. Neuropeptide Y (NPY), a 36 aa peptide, is highly expressed in the amygdala. It exerts potent anxiolytic effects through cognate postsynaptic Y1 receptors, but augments anxiety through presynaptic Y2 receptors. To identify the precise anatomical site(s) of Y2-mediated anxiogenic action, we investigated the effect of site-specific deletion of the Y2 gene in amygdaloid nuclei on anxiety and depression-related behaviors in mice. Ablating the Y2 gene in the basolateral and central amygdala resulted in an anxiolytic phenotype, whereas deletion in the medial amygdala or in the bed nucleus of the stria terminalis had no obvious effect on emotion-related behavior. Deleting the Y2 receptor gene in the central amygdala, but not in any other amygdaloid nucleus, resulted in an added antidepressant-like effect. It was associated with a reduction of presumably presynaptic Y2 receptors in the stria terminalis/bed nucleus of the stria terminalis, the nucleus accumbens, and the locus ceruleus. Our results are evidence of the highly site-specific nature of the Y2-mediated function of NPY in the modulation of anxiety- and depression-related behavior. The activity of NPY is likely mediated by the presynaptic inhibition of GABA and/or NPY release from interneurons and/or efferent projection neurons of the basolateral and central amygdala.

Neurobiological constituents of active, passive, and variable coping strategies in rats: integration of regional brain neuropeptide Y levels and cardiovascular responses

Effective coping strategies build resilience against stress-induced pathology. In the current study, young male rats were categorized as active, passive, or variable copers by observing their responses to being gently restrained on their backs (i.e., the back-test). The rats were subsequently exposed to chronic unpredictable stress, which included several ethologically relevant stressors such as predator odors and calls, for approximately three weeks. During this time, the variable copers, defined as rats that demonstrated a variable as opposed to a rigid response to stress, exhibited more seemingly adaptive responsiveness in three successive forced swim tests than the more consistently responding passive and active copers. This behavioral flexibility was accompanied by increased neuropeptide Y-immunoreactivity in the bed nucleus of the stria terminalis (BNST) and the amygdala and increased fos-immunoreactivity in the BNST. Additionally, the alterations in fecal corticosteroid levels and cardiovascular measures (systolic blood pressure and tail blood volume) between baseline and stress conditions differed according to coping strategy. Factor analysis indicates that variable copers were characterized by a distinct cardiovascular and neural response to the stress exposure. These results suggest that this animal coping model may be useful in discerning the adaptive nature of particular response strategies in the face of environmental exigencies.

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

RATIONALE

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

OBJECTIVE

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

METHODS

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

RESULTS

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

CONCLUSION

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