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

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.

Neuroglobin deficiency increases seizure susceptibility but does not affect basal behavior in mice

Neuroglobin (Ngb) is found in the neurones of several different brain areas and is known to bind oxygen and other gaseous molecules and reactive oxygen species (ROS) in vitro, but it does not seem to act as a respiratory molecule for neurones. Using male and female Ngb‐knockout (KO) mice, we addressed the role of Ngb in neuronal brain activity using behavioral tests but found no differences in general behaviors, memory processes, and anxiety−/depression‐like behaviors. Oxidative stress and ROS play key roles in epileptogenesis, and oxidative injury produced by an excessive production of free radicals is involved in the initiation and progression of epilepsy. The ROS binding properties led us to hypothesize that lack of Ngb could affect central coping with excitatory stimuli. We consequently explored whether exposure to the excitatory molecule kainate (KA) would increase severity of seizures in mice lacking Ngb. We found that the duration and severity of seizures were increased, while the latency time to develop seizures was shortened in Ngb‐KO compared to wildtype adult female mice. Consistently, c‐fos expression after KA was significantly increased in Ngb‐KO mice in the amygdala and piriform cortex, regions rich in Ngb and known to be centrally involved in seizure generation. Moreover, the measured c‐fos expression levels were correlated with seizure susceptibility. With these new findings combined with previous studies we propose that Ngb could constitute an intrinsic defense mechanism against neuronal hyperexcitability and oxidative stress by buffering of ROS in amygdala and other Ngb‐containing brain regions.

Exploring the role of neuropeptides in depression and anxiety

Depression is one of the most prevalent forms of mental disorders and is the most common cause of disability in the Western world. Besides, the harmful effects of stress-related mood disorders on the patients themselves, they challenge the health care system with enormous social and economic impacts. Due to the high proportion of patients not responding to existing drugs, finding new treatment strategies has become an important topic in neurobiology, and there is much evidence that neuropeptides are not only involved in the physiology of stress but may also be clinically important. Based on preclinical trial data, new neuropharmaceutical candidates may target neuropeptides and their receptors and are expected to be essential and valuable tools in the treatment of psychiatric disorders. In the current article, we have summarized data obtained from animal models of depressive disorder and transgenic mouse models. We also focus on previously published research data of clinical studies on corticotropin-releasing hormone (CRH), galanin (GAL), neuropeptide Y (NPY), neuropeptide S (NPS), Oxytocin (OXT), vasopressin (VP), cholecystokinin (CCK), and melanin-concentrating hormone (MCH) stress research fields.

Pathological Targets for Treating Temporal Lobe Epilepsy: Discoveries From Microscale to Macroscale

Temporal lobe epilepsy (TLE) is one of the most common and severe types of epilepsy, characterized by intractable, recurrent, and pharmacoresistant seizures. Histopathology of TLE is mostly investigated through observing hippocampal sclerosis (HS) in adults, which provides a robust means to analyze the related histopathological lesions. However, most pathological processes underlying the formation of these lesions remain elusive, as they are difficult to detect and observe. In recent years, significant efforts have been put in elucidating the pathophysiological pathways contributing to TLE epileptogenesis. In this review, we aimed to address the new and unrecognized neuropathological discoveries within the last 5 years, focusing on gene expression (miRNA and DNA methylation), neuronal peptides (neuropeptide Y), cellular metabolism (mitochondria and ion transport), cellular structure (microtubule and extracellular matrix), and tissue-level abnormalities (enlarged amygdala). Herein, we describe a range of biochemical mechanisms and their implication for epileptogenesis. Furthermore, we discuss their potential role as a target for TLE prevention and treatment. This review article summarizes the latest neuropathological discoveries at the molecular, cellular, and tissue levels involving both animal and patient studies, aiming to explore epileptogenesis and highlight new potential targets in the diagnosis and treatment of TLE.

Chronic oral nicotine administration and withdrawal regulate the expression of neuropeptide Y and its receptors in the mesocorticolimbic system

Neuropeptide Y (NPY) and its receptors are involved in the regulation of mood, stress, and anxiety. In parallel, NPY signaling may play a vital role in the negative affective state induced by drug withdrawal. This study examined the changes in the transcript levels of NPY, Y1, Y2, and Y5 receptors in the mesocorticolimbic system during chronic nicotine exposure and withdrawal. Rats were administered with nicotine (initial dose: 25 μg/ml, maintenance dose: 50 μg/ml, free base) in drinking water for 12 weeks. Control group received only tap water. In the final week of the study, some of the nicotine-treated animals continued to receive nicotine (0-W), whereas some were withdrawn for either 24 (24-W) or 48 (48-W) h. All animals were decapitated after the evaluation of somatic signs (frequency of gasps, eye blinks, ptosis, shakes, teeth chatter) and the duration of locomotor activity and immobility. mRNA levels of NPY, Y1, Y2, and Y5 receptors in the mesocorticolimbic system were measured by quantitative real-time PCR (qRT-PCR). Results showed that nicotine withdrawal increased overall somatic signs. Moreover, chronic nicotine treatment increased the duration of locomotor activity, whereas withdrawal increased the duration of immobility. qRT-PCR analysis revealed that chronic nicotine treatment increased NPY mRNA levels in the hippocampus. On the other hand, 24- and 48-h withdrawals increased NPY mRNA levels in the amygdala and medial prefrontal cortex (mPFC), Y1 and Y2 mRNA levels in the nucleus accumbens and mPFC, and Y5 mRNA levels in the mPFC. These findings suggest that nicotine withdrawal enhances NPY signaling in the mesocorticolimbic system, which could be an important mechanism involved in regulating the negative affective state triggered during nicotine withdrawal.

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.

Long term effects of stress on hippocampal function: Emphasis on early life stress paradigms and potential involvement of neuropeptide Y

The brain is both central in orchestrating the response to stress, and, a very sensitive target when such response is not controlled. In fact, stress has long been associated with the onset and/or exacerbation of several neuropsychiatric disorders such as anxiety, depression, and drug addiction. The hippocampus is a key brain region involved in the response to stress, not only due to its anatomical connections with the hypothalamic-pituitary-adrenal axis but also as a major target of stress mediators. The hippocampal dentate gyrus (DG)-CA3 circuit, composed of DG granule cells axons (mossy fibers) synapsing onto CA3 pyramidal cells, plays an essential role in memory encoding and retrieval, functions that are vulnerable to stress. Although naturally excitatory, this circuit is under the inhibitory control of GABAergic interneurons that maintain the excitation/inhibition balance. One subgroup of such interneurons produces neuropeptide Y (NPY), which has emerged as a promising endogenous stress "resilience molecule" due to its anxiolytic and anti-epileptic properties. Here we examine existing evidence that reveals a potential role for hilar NPY+ interneurons in mediating stress-induced changes in hippocampal function. We will focus specifically on rodent models of early life stress (ELS), defined as adverse conditions during the early postnatal period that can have profound consequences for neurodevelopment. Collectively, these findings suggest that the long-lasting effects of ELS might stem from the loss of GABAergic NPY+ cells, which then can lead to reduced inhibition in the DG-CA3 pathway. Such change might then lead to hyperexcitability and concomitant hippocampal-dependent behavioral deficits.

Gene Therapy Vector Encoding Neuropeptide Y and Its Receptor Y2 for Future Treatment of Epilepsy: Preclinical Data in Rats

Gene therapy to treat pharmacoresistant temporal lobe epilepsy in humans is now being developed using an AAV vector (CG01) that encodes the combination of neuropeptide Y and its antiepileptic receptor Y2. With this in mind, the present study aimed to provide important preclinical data on the effects of CG01 on the duration of transgene expression, cellular tropism, and potential side effects on body weight and cognitive function. The CG01 vector was administered unilaterally into the dorsal and ventral hippocampus of adult male rats and expression of both transgenes was found to remain elevated without a sign of decline at 6 months post-injection. CG01 appeared to mediate expression selectively in hippocampal neurons, without expression in astrocytes or oligodendrocytes. No effects were seen on body weight as well as on short- or long-term memory as revealed by testing in the Y-maze or Morris water maze tests. Thus these data show that unilateral CG01 vector treatment as future gene therapy in pharmacoresistant temporal lobe epilepsy patients should result in stable and long-term expression predominantly in neurons and be well tolerated without side effects on body weight and cognitive function.

Protein kinase C mediates neuropeptide Y-induced reduction in inhibitory neurotransmission in the lateral habenula

Neuropeptide Y (NPY) is one of peptide neuromodulators, well known for orexigenic, anxiolytic and antidepressant effects. We previously reported that NPY decreases GABAergic transmission in the lateral habenula (LHb). In the current study, we aim to investigate the underlying signaling pathways that mediate inhibitory action of NPY in the LHb by employing whole-cell patch clamp recording with pharmacological interventions. Here, we revealed that Y1 receptors (Y1Rs) but not Y2Rs mediate NPY-induced decrease of GABAergic transmission in the LHb. Surprisingly, NPY-induced decrease of inhibitory transmission in the LHb was not dependent on adenylyl cyclase (AC)/protein kinase A (PKA)-dependent pathway as reported in other brain areas. Instead, pharmacological blockade of phospholipase C (PLC) or protein kinase C (PKC) activity abolished the decrease of GABAergic transmission by NPY in the LHb. Our findings suggest that Y1Rs in the LHb may trigger the activation of PLC/PKC-dependent pathway but not the classical AC/PKA-dependent pathway to decrease inhibitory transmission of the LHb.

Neuropeptide Y Is an Immunomodulatory Factor: Direct and Indirect

Neuropeptide Y (NPY), which is widely distributed in the nervous system, is involved in regulating a variety of biological processes, including food intake, energy metabolism, and emotional expression. However, emerging evidence points to NPY also as a critical transmitter between the nervous system and immune system, as well as a mediator produced and released by immune cells. In vivo and in vitro studies based on gene-editing techniques and specific NPY receptor agonists and antagonists have demonstrated that NPY is responsible for multifarious direct modulations on immune cells by acting on NPY receptors. Moreover, via the central or peripheral nervous system, NPY is closely connected to body temperature regulation, obesity development, glucose metabolism, and emotional expression, which are all immunomodulatory factors for the immune system. In this review, we focus on the direct role of NPY in immune cells and particularly discuss its indirect impact on the immune response.

Disease Modification by Combinatorial Single Vector Gene Therapy: A Preclinical Translational Study in Epilepsy

Gene therapy has been suggested as a plausible novel approach to achieve seizure control in patients with focal epilepsy that do not adequately respond to pharmacological treatment. We investigated the seizure-suppressant potential of combinatorial neuropeptide Y and Y2 receptor single vector gene therapy based on adeno-associated virus serotype 1 (AAV1) in rats. First, a dose-response study in the systemic kainate-induced acute seizure model was performed, whereby the 10¹² genomic particles (gp)/mL titer of the vector was selected as an optimal concentration. Second, an efficacy study was performed in the intrahippocampal kainate chronic model of spontaneous recurrent seizures (SRSs), designed to reflect a likely clinical scenario, with magnetic resonance image (MRI)-guided focal unilateral administration of the vector in the hippocampus during the chronic stage of the disease. The efficacy study demonstrated a favorable outcome of the gene therapy, with a 31% responder rate (more than 50% reduction in SRS frequency) and 13% seizure-freedom rate, whereas no such effects were observed in the control animals. The inter-SRS and SRS cluster intervals were also significantly prolonged in the treated group compared to controls. In addition, the SRS duration was significantly reduced in the treated group but not in the controls. This study establishes the SRS-suppressant ability of the single vector combinatorial neuropeptide Y/Y2 receptor gene therapy in a clinically relevant chronic model of epilepsy.

Sustained overexpression of neuropeptide S in the amygdala reduces anxiety-like behavior in rats

Neuropeptide S (NPS) has shown anxiolytic-like effects in rodents after acute administration, but its long-term effects remain unknown. Gene therapy enables the targeted delivery of DNA to cell nuclei, and recombinant adeno-associated viral (rAAV) vectors have been identified as suitable tools for stable overexpression. Thus, to explore the effects of long-term expression of NPS, the present study examined anxiety- and depressive-like effects after rAAV-mediated NPS overexpression in the rat amygdala. Compared to rats injected with an empty control vector (rAAV-Empty), rAAV-NPS treatment was associated with reduced anxiety-like behavior in the elevated plus maze and light-dark box, but did not affect depressive-like behavior in the forced swim test. Importantly, rAAV-NPS did not cause confounding effects on locomotion or bodyweight as opposed to currently used anxiolytic drugs. Immunohistochemical stainings revealed NPS-positive cells in the central and basolateral region of the amygdala in rAAV-NPS but not rAAV-Empty rats, indicating successful transduction. Our study provides novel evidence for sustained anxiolytic-like properties of NPS by transgenic overexpression. These data suggest that rAAV-NPS application deserves further attention as a potential treatment strategy for anxiety in humans.

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

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

Exploring the Behavioral and Metabolic Phenotype Generated by Re-Introduction of the Ghrelin Receptor in the Ventral Tegmental Area

Ghrelin receptor (Ghr-R) signaling in neurons of the ventral tegmental area (VTA) can modulate dopaminergic function and the reward-related effects of both palatable foods and drugs of abuse. In this study, we re-introduced the Ghr-R in VTA neurons in Ghr-R knockout mice (Ghr-R^VTA mice) to specifically study the importance of the constitutively active Ghr-R for VTA neuronal signaling. Our results showed that re-introduction of the Ghr-R in the VTA had no impact on body weight or food intake under basal conditions. However, during novel environment stress Ghr-R^VTA mice showed increased food intake and energy expenditure compared to Ghr-R knockout mice, demonstrating the significance of Ghr-R signaling in the response to stress. Ghr-R^VTA mice also showed increased cocaine-induced locomotor activity compared to Ghr-R knockout mice, highlighting the importance of ghrelin signaling for the reward-related effects of activation of VTA neurons. Overall, our data suggest that re-introduction of the Ghr-R in the mesolimbic reward system of Ghr-R knockout mice increases the level of activation induced by both cocaine and novelty stress.

Neuropeptide Y expression confers benzo[a]pyrene induced anxiolytic like behavioral response during early adolescence period of male Wistar rats

Environmental neurotoxicant like benzo[a]pyrene (B[a]P) is known to induce neurobehavioral changes. Our previous reports address the adverse effect of B[a]P on the neurobehavioral responses and neuromorphology of sensitive brain regions in adolescent rats. Present study was conducted on male Wistar rat neonates at postnatal day 5 (PND5) to ascertain B[a]P induced anxiolytic like behavioral response could be an outcome of neuropeptide Y (NPY) overexpression in brain. Single intracisternal administration of B[a]P was carried out at PND5 to elucidate the role of NPY on neurobehavioral responses at PND30. The behavioral studies showed anxiolytic like effect of B[a]P in both light and dark box and elevated plus maze tests. Antioxidant assay involving glutathione peroxidase activity was significantly decreased where as lipid peroxidation was significantly augmented in both hippocampus and hypothalamus of B[a]P treated group as compared to naive and control. The neurotransmitter estimation by HPLC-ECD showed significant increase in 5-HT level in both hippocampus and hypothalamus of B[a]P treated group. Significant elevation in NPY expression was observed in both hippocampus and hypothalamus of B[a]P group. Intracellular Ca²⁺ estimation using Fura-2AM by fluorometry showed that B[a]P induced increase in Ca²⁺ influx was associated with augmented NPY expression in brain. As NPY has orexigenic effect, our result revealed that there was a significant increase in body weight at PND30 following B[a]P administration to rat neonates at PND5. These findings suggested that NPY overexpression in brain regions might be associated with anxiolytic like behavioral response and orexigenic effect in rats following single intracisternal B[a]P administration. Future research directing towards understanding the signaling cascades of B[a]P induced biochemical and neuromorphological alteration might address the independent pathway which induce neurodegeneration despite NPY overexpression in brain regions of adolescent rats.

Neuropeptide Y, resilience, and PTSD therapeutics

Resilience to traumatic stress is a complex psychobiological process that protects individuals from developing posttraumatic stress disorder (PTSD) or other untoward consequences of exposure to extreme stress, including depression. Progress in translational research points toward the neuropeptide Y (NPY) system - among others - as a key mediator of stress response and as a potential therapeutic focus for PTSD. Substantial preclinical evidence supports the role of NPY in the modulation of stress response and in the regulation of anxiety in animal models. Clinical studies testing the safety and efficacy of modulating the NPY system in humans, however, have lagged behind. In the current article, we review the evidence base for targeting the NPY system as a therapeutic approach in PTSD, and consider impediments and potential solutions to therapeutic development.

Anxiolytic-Like Effects of Increased Ghrelin Receptor Signaling in the Amygdala

BACKGROUND

Besides the well-known effects of ghrelin on adiposity and food intake regulation, the ghrelin system has been shown to regulate aspects of behavior including anxiety and stress. However, the effect of virus-mediated overexpression of the ghrelin receptor in the amygdala has not previously been addressed directly.

METHODS

First, we examined the acute effect of peripheral ghrelin administration on anxiety- and depression-like behavior using the open field, elevated plus maze, forced swim, and tail suspension tests. Next, we examined the effect of peripheral ghrelin administration and ghrelin receptor deficiency on stress in a familiar and social environment using the Intellicage system. Importantly, we also used a novel approach to study ghrelin receptor signaling in the brain by overexpressing the ghrelin receptor in the amygdala. We examined the effect of ghrelin receptor overexpression on anxiety-related behavior before and after acute stress and measured the modulation of serotonin receptor expression.

RESULTS

We found that ghrelin caused an anxiolytic-like effect in both the open field and elevated plus maze tests. Additionally, it attenuated air-puff-induced stress in the social environment, while the opposite was shown in ghrelin receptor deficient mice. Finally, we found that overexpression of the ghrelin receptor in the basolateral division of the amygdala caused an anxiolytic-like effect and decreased the 5HT1a receptor expression.

CONCLUSIONS

Ghrelin administration and overexpression of the ghrelin receptor in the amygdala induces anxiolytic-like behavior. Since the ghrelin receptor has high constitutive activity, ligand-independent signaling in vivo may be important for the observed anxiolytic-like effects. The anxiolytic effects seem to be mediated independently from the HPA axis, potentially engaging the central serotonin system.

Neuroendocrinological and Epigenetic Mechanisms Subserving Autonomic Imbalance and HPA Dysfunction in the Metabolic Syndrome

Impact of environmental stress upon pathophysiology of the metabolic syndrome (MetS) has been substantiated by epidemiological, psychophysiological, and endocrinological studies. This review discusses recent advances in the understanding of causative roles of nutritional factors, sympathomedullo-adrenal (SMA) and hypothalamic-pituitary adrenocortical (HPA) axes, and adipose tissue chronic low-grade inflammation processes in MetS. Disturbances in the neuroendocrine systems for leptin, melanocortin, and neuropeptide Y (NPY)/agouti-related protein systems have been found resulting directly in MetS-like conditions. The review identifies candidate risk genes from factors shown critical for the functioning of each of these neuroendocrine signaling cascades. In its meta-analytic part, recent studies in epigenetic modification (histone methylation, acetylation, phosphorylation, ubiquitination) and posttranscriptional gene regulation by microRNAs are evaluated. Several studies suggest modification mechanisms of early life stress (ELS) and diet-induced obesity (DIO) programming in the hypothalamic regions with populations of POMC-expressing neurons. Epigenetic modifications were found in cortisol (here HSD11B1 expression), melanocortin, leptin, NPY, and adiponectin genes. With respect to adiposity genes, epigenetic modifications were documented for fat mass gene cluster APOA1/C3/A4/A5, and the lipolysis gene LIPE. With regard to inflammatory, immune and subcellular metabolism, PPARG, NKBF1, TNFA, TCF7C2, and those genes expressing cytochrome P450 family enzymes involved in steroidogenesis and in hepatic lipoproteins were documented for epigenetic modifications.

Neuropeptide Y: A stressful review

Stress is defined as an adverse condition that disturbs the homeostasis of the body and activates adaptation responses. Among the many pathways and mediators involved, neuropeptide Y (NPY) stands out due to its unique stress-relieving, anxiolytic and neuroprotective properties. Stress exposure alters the biosynthesis of NPY in distinct brain regions, the magnitude and direction of this effect varying with the duration and type of stress. NPY is expressed in particular neurons of the brainstem, hypothalamus and limbic system, which explains why NPY has an impact on stress-related changes in emotional-affective behaviour and feeding as well as on stress coping. The biological actions of NPY in mammals are mediated by the Y1, Y2, Y4 and Y5 receptors, Y1 receptor stimulation being anxiolytic whereas Y2 receptor activation is anxiogenic. Emerging evidence attributes NPY a role in stress resilience, the ability to cope with stress. Thus there is a negative correlation between stress-induced behavioural disruption and cerebral NPY expression in animal models of post-traumatic stress disorder. Exogenous NPY prevents the negative consequences of stress, and polymorphisms of the NPY gene are predictive of impaired stress processing and increased risk of neuropsychiatric diseases. Stress is also a factor contributing to, and resulting from, neurodegenerative diseases such as Alzheimer's, Parkinson's and Huntington's disease, in which NPY appears to play an important neuroprotective role. This review summarizes the evidence for an implication of NPY in stress-related and neurodegenerative pathologies and addresses the cerebral NPY system as a therapeutic target.

Translational approach for gene therapy in epilepsy: Model system and unilateral overexpression of neuropeptide Y and Y2 receptors

Although novel treatment strategies based on the gene therapy approach for epilepsy has been encouraging, there is still a gap in demonstrating a proof-of-concept in a clinically relevant animal model and study design. In the present study, a conceptually novel framework reflecting a plausible clinical trial for gene therapy of temporal lobe epilepsy was explored: We investigated (i) whether the post intrahippocampal kainate-induced status epilepticus (SE) model of chronic epilepsy in rats could be clinically relevant; and (ii) whether a translationally designed neuropeptide Y (NPY)/Y2 receptor-based gene therapy approach targeting only the seizure-generating focus unilaterally can decrease seizure frequency in this chronic model of epilepsy. Our data suggest that the intrahippocampal kainate model resembles the disease development of human chronic mesial temporal lobe epilepsy (mTLE): (i) spontaneous seizures originate in the sclerotic hippocampus; (ii) only a part of the animals develops chronic epilepsy; (iii) animals show largely variable seizure frequency that (iv) tends to progressively increase over time. Despite significant hippocampal degeneration caused by the kainate injection, the use of MRI allowed targeting the recombinant adeno-associated viral (rAAV) vectors encoding NPY and Y2 receptor genes to the remaining dorsal and ventral hippocampal areas ipsilateral to the kainate injection. Continuous video-EEG monitoring demonstrated not only prevention of the progressive increase in seizure frequency in rAAV-NPY/Y2 treated animals as compared to the controls, but even 45% decrease of seizure frequency in 80% of the epileptic animals. This translationally designed study in a clinically relevant model of epilepsy suggests that simultaneous overexpression of NPY and Y2 receptors unilaterally in the seizure focus is a relevant and promising approach that can be further validated in more extensive preclinical studies to develop a future treatment strategy for severe, often pharmacoresistant focal epilepsy cases that cannot be offered alternative therapeutic options.

Dextran sulfate sodium-induced colitis alters stress-associated behaviour and neuropeptide gene expression in the amygdala-hippocampus network of mice

Psychological stress causes disease exacerbation and relapses in inflammatory bowel disease (IBD) patients. Since studies on stress processing during visceral inflammation are lacking, we investigated the effects of experimental colitis as well as psychological stress on neurochemical and neuroendocrine changes as well as behaviour in mice. Dextran sulfate sodium (DSS)-induced colitis and water avoidance stress (WAS) were used as mouse models of colitis and mild psychological stress, respectively. We measured WAS-associated behaviour, gene expression and proinflammatory cytokine levels within the amygdala, hippocampus and hypothalamus as well as plasma levels of cytokines and corticosterone in male C57BL/6N mice. Animals with DSS-induced colitis presented with prolonged immobility during the WAS session, which was associated with brain region-dependent alterations of neuropeptide Y (NPY), NPY receptor Y1, corticotropin-releasing hormone (CRH), CRH receptor 1, brain-derived neurotrophic factor and glucocorticoid receptor gene expression. Furthermore, the combination of DSS and WAS increased interleukin-6 and growth regulated oncogene-α levels in the brain. Altered gut-brain signalling in the course of DSS-induced colitis is thought to cause the observed distinct gene expression changes in the limbic system and the aberrant molecular and behavioural stress responses. These findings provide new insights into the effects of stress during IBD.

Targeting the Neuropeptide Y System in Stress-related Psychiatric Disorders

Repeated, extreme, or traumatic stressors can elicit pathological effects leading to many negative physical and psychological outcomes. Stressors can precipitate the onset of psychiatric diseases, or exacerbate pre-existing disorders including various anxiety and mood disorders. As stressors can negatively impact human psychiatric health, it is essential to identify neurochemicals that may confer protection from the negative sequelae of repeated or extreme stress exposure. Elucidating the neurobiological underpinnings of stress resilience will enhance our ability to promote resilience to, or recovery from, stress-related psychiatric disease. Herein, we will review the evidence for neuropeptide Y as an endogenous mediator of resilience and its potential relevance for the treatment of stress-related psychiatric diseases.

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Overview of neuropeptide Y and receptor subtypes in the central nervous system.

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Alterations of neuropeptide Y in human stress-related psychiatric disorders.

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Evidence for neuropeptide Y in resilience to stress-related emotionality in rodent behavioral models.

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Pharmacotherapeutic implications for neuropeptide Y in the treatment of stress-related psychiatric disorders.

Anxiolytic-like effects after vector-mediated overexpression of neuropeptide Y in the amygdala and hippocampus of mice

Neuropeptide Y (NPY) causes anxiolytic- and antidepressant-like effects after central administration in rodents. These effects could theoretically be utilized in future gene therapy for anxiety and depression using viral vectors for induction of overexpression of NPY in specific brain regions. Using a recombinant adeno-associated viral (rAAV) vector, we addressed this idea by testing effects on anxiolytic- and depression-like behaviours in adult mice after overexpression of NPY transgene in the amygdala and/or hippocampus, two brain regions implicated in emotional behaviours. In the amygdala, injections of rAAV-NPY caused significant anxiolytic-like effect in the open field, elevated plus maze, and light-dark transition tests. In the hippocampus, rAAV-NPY treatment was associated with anxiolytic-like effect only in the elevated plus maze. No additive effect was observed after combined rAAV-NPY injection into both the amygdala and hippocampus where anxiolytic-like effect was found in the elevated plus maze and light-dark transition tests. Antidepressant-like effects were not detected in any of the rAAV-NPY injected groups. Immobility was even increased in the tail suspension and forced swim tests after intra-amygdaloid rAAV-NPY. Taken together, the present data show that rAAV-NPY treatment may confer non-additive anxiolytic-like effect after injection into the amygdala or hippocampus, being most pronounced in the amygdala.

Expression of neuropeptide Y1 receptors in the amygdala and hippocampus and anxiety-like behavior associated with Ammon's horn sclerosis following intrahippocampal kainate injection in C57BL/6J mice

Damage to the amygdala is often linked to Ammon's horn sclerosis (AHS) in surgical specimens of patients suffering from temporal lobe epilepsy (TLE). Moreover, amygdalar pathology is thought to contribute to the development of anxiety symptoms frequently found in TLE. The neuropeptide Y (NPY) Y1 receptor is critical in the regulation of anxiety-related behavior and epileptiform activity in TLE. Therefore, intrahippocampal kainate (KA) injection was performed to induce AHS-associated TLE and to investigate behavioral and cytoarchitectural changes that occur in the amygdala related to Y1 receptor expression. Status epilepticus was induced by intrahippocampal KA injection in C57BL/6J mice. Anxiety-like behavior was assessed using the elevated plus maze (EPM). Pathology of hippocampus and amygdala (volume loss and gliosis) was examined in KA-injected and saline-injected controls. Y1 receptor expression was measured using immunohistochemistry and ELISA. Animal injected with KA showed increased anxiety-like behaviors and reduced risk assessment in the EPM test compared with saline-injected controls. In the ipsilateral hippocampus of KA-injected animals, CA1 ablation, granule cell dispersion, and volume reduction were accompanied by astrogliosis indicating the development of AHS. In the amygdala, a significant decrease in the volume of nuclei and numbers of neurons was observed in the ipsilateral lateral, basolateral, and central amygdalar nuclei, which was accompanied by astrogliosis. In addition, a decrease in Y1 receptor-expressing cells in the ipsilateral CA1 and CA3 sectors of the hippocampus, ipsilateral and contralateral granule cell layer of the dentate gyrus, and ipsilateral central nucleus of the amygdala was found, consistent with a reduction in Y1 receptor protein levels. Our results suggest that plastic changes in hippocampal and/or amygdalar Y1 receptor expression may negatively impact anxiety levels. Moreover, intrahippocampal KA injection can induce amygdalar damage suggesting that AHS-associated amygdala damage may contribute to behavioral alterations seen in patients with TLE.

Neuropeptide Y-stimulated [(35) S]GTPγs functional binding is reduced in the hippocampus after kainate-induced seizures in mice

Kainate-induced seizures constitute a model of temporal lobe epilepsy where prominent changes are observed in the hippocampal neuropeptide Y (NPY) system. However, little is known about the functional state and signal transduction of the NPY receptor population resulting from kainate exposure. Thus, in this study, we explored functional NPY receptor activity in the mouse hippocampus and neocortex after kainate-induced seizures using NPY-stimulated [(35) S]GTPγS binding. Moreover, we also studied levels of [(125) I]-peptide YY (PYY) binding and NPY, Y1, Y2, and Y5 receptor mRNA in these kainate-treated mice. Functional NPY binding was unchanged up to 12 h post-kainate, but decreased significantly in all hippocampal regions after 24 h and 1 week. Similarly, a decrease in [(125) I]-PYY binding was found in the dentate gyrus (DG) 1 week post-kainate. However, at 2 h, 6 h, and 12 h, [(125) I]-PYY binding was increased in all regions, and in the CA1 also at 24 h post-kainate. NPY mRNA levels were prominently increased in hippocampal regions, reaching maximum at 12 and 24 h. Y1 and Y5 mRNA levels were lowered in the DG at 24 and 2 h, respectively, while Y2 mRNA levels were elevated at 24 h in the DG and CA3. This study confirms rat kainate studies by showing pronounced adaptive changes in the mouse hippocampus both with regard to NPY synthesis and NPY receptor synthesis and binding, which may contribute to regulating neuronal seizure susceptibility after kainate. However, the potential seizure-suppressant effects of increased NPY gene expression at late time points post-kainate could be attenuated by the novel finding of reduced NPY-receptor G-protein activation.

Role of neuropeptides in anxiety, stress, and depression: from animals to humans

Major depression, with its strikingly high prevalence, is the most common cause of disability in communities of Western type, according to data of the World Health Organization. Stress-related mood disorders, besides their deleterious effects on the patient itself, also challenge the healthcare systems with their great social and economic impact. Our knowledge on the neurobiology of these conditions is less than sufficient as exemplified by the high proportion of patients who do not respond to currently available medications targeting monoaminergic systems. The search for new therapeutical strategies became therefore a "hot topic" in neuroscience, and there is a large body of evidence suggesting that brain neuropeptides not only participate is stress physiology, but they may also have clinical relevance. Based on data obtained in animal studies, neuropeptides and their receptors might be targeted by new candidate neuropharmacons with the hope that they will become important and effective tools in the management of stress related mood disorders. In this review, we attempt to summarize the latest evidence obtained using animal models for mood disorders, genetically modified rodent models for anxiety and depression, and we will pay some attention to previously published clinical data on corticotropin releasing factor, urocortin 1, urocortin 2, urocortin 3, arginine-vasopressin, neuropeptide Y, pituitary adenylate-cyclase activating polypeptide, neuropeptide S, oxytocin, substance P and galanin fields of stress research.

Early phase of plasticity-related gene regulation and SRF dependent transcription in the hippocampus

Hippocampal organotypic cultures are a highly reliable in vitro model for studying neuroplasticity: in this paper, we analyze the early phase of the transcriptional response induced by a 20 µM gabazine treatment (GabT), a GABA-Ar antagonist, by using Affymetrix oligonucleotide microarray, RT-PCR based time-course and chromatin-immuno-precipitation. The transcriptome profiling revealed that the pool of genes up-regulated by GabT, besides being strongly related to the regulation of growth and synaptic transmission, is also endowed with neuro-protective and pro-survival properties. By using RT-PCR, we quantified a time-course of the transient expression for 33 of the highest up-regulated genes, with an average sampling rate of 10 minutes and covering the time interval [10∶90] minutes. The cluster analysis of the time-course disclosed the existence of three different dynamical patterns, one of which proved, in a statistical analysis based on results from previous works, to be significantly related with SRF-dependent regulation (p-value<0.05). The chromatin immunoprecipitation (chip) assay confirmed the rich presence of working CArG boxes in the genes belonging to the latter dynamical pattern and therefore validated the statistical analysis. Furthermore, an in silico analysis of the promoters revealed the presence of additional conserved CArG boxes upstream of the genes Nr4a1 and Rgs2. The chip assay confirmed a significant SRF signal in the Nr4a1 CArG box but not in the Rgs2 CArG box.

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

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

Neuropeptide Y Y5 receptor antagonism attenuates cocaine-induced effects in mice

RATIONALE

Several studies suggest a role for neuropeptide Y (NPY) in addiction to drugs of abuse, including cocaine. However, the NPY receptors mediating addiction-related effects remain to be determined.

OBJECTIVES

To explore the potential role of Y5 NPY receptors in cocaine-induced behavioural effects.

METHODS

The Y5 antagonist L-152,804 and Y5-knockout (Y5-KO) mice were tested in two models of cocaine addiction-related behaviour: acute self-administration and cocaine-induced hyperactivity. We also studied effects of Y5 receptor antagonism on cocaine-induced c-fos expression and extracellular dopamine with microdialysis as well as dopamine transporter-mediated uptake of dopamine in vitro. Immunocytochemistry was used to determine whether dopamine neurons express Y5-like immunoreactivity.

RESULTS

In self-administration, L-152,804 prominently decreased nose-poking for the peak dose of cocaine and shifted the dose-response curve for cocaine downward. Y5-KO mice also showed modestly attenuated self-administration. Cocaine-induced hyperactivity was attenuated by L-152,804 and in Y5-KO mice. Cocaine failed to increase c-fos expression in the nucleus accumbens and striatum of L-152,804-treated mice, indicating that the Y5 antagonist could act by influencing neural activity in these regions. Accordingly, the cocaine-induced increase in accumbal extracellular dopamine was attenuated by L-152,804 and in Y5-KO mice, suggesting that Y5 antagonism influences cocaine-induced behaviour by regulating dopamine. Consistent with this concept, dopamine neurons in the ventral tegmental area appeared to contain Y5 receptors. In contrast, neither L-152,804 nor NPY influenced dopamine transporter-mediated dopamine uptake.

CONCLUSIONS

The present data indicate that Y5 antagonism may attenuate cocaine-induced behavioural effects, suggesting that Y5 receptors could be a potential therapeutic target in cocaine addiction.

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.