Neuropeptide Y blocks anxiogenic-like behavioral action of corticotropin-releasing factor in an operant conflict test and elevated plus maze

Chronic Nicotine Consumption and Withdrawal Regulate Melanocortin Receptor, CRF, and CRF Receptor mRNA Levels in the Rat Brain

Alterations in the various neuropeptide systems in the mesocorticolimbic circuitry have been implicated in negative effects associated with drug withdrawal. The corticotropin-releasing factor (CRF) and α-melanocyte-stimulating hormone are two peptides that may be involved. This study investigated the regulatory effects of chronic nicotine exposure and withdrawal on the mRNA levels of melanocortin receptors (MC3R, MC4R), CRF, and CRF receptors (CRFR1 and CRFR2) expressed in the mesocorticolimbic system. Rats were given drinking water with nicotine or without nicotine (control group) for 12 weeks, after which they continued receiving nicotine (chronic exposure) or were withdrawn from nicotine for 24 or 48 h. The animals were decapitated following behavioral testing for withdrawal signs. Quantitative real-time PCR analysis demonstrated that nicotine exposure (with or without withdrawal) increased levels of CRF and CRFR1 mRNA in the amygdala, CRF mRNA in the medial prefrontal cortex, and CRFR1 mRNA in the septum. Nicotine withdrawal also enhanced MC3R and MC4R mRNA levels in different brain regions, while chronic nicotine exposure was associated with increased MC4R mRNA levels in the nucleus accumbens. These results suggest that chronic nicotine exposure and withdrawal regulate CRF and melanocortin signaling in the mesocorticolimbic system, possibly contributing to negative affective state and nicotine addiction.

Can Neuropeptide S Be an Indicator for Assessing Anxiety in Psychiatric Disorders?

Neuropeptide S (NPS) is a neuropeptide primarily produced within three brainstem regions including locus coeruleus, trigeminal nerve nucleus, and lateral parabrachial nucleus. NPS is involved in the central regulation of stress, fear, and cognitive integration. NPS is a mediator of behavior, seeking food, and the proliferation of new adipocytes in the setting of obesity. So far, current research of NPS is only limited to animal models; data regarding its functions in humans is still scarce. Animal studies showed that anxiety and appetite might be suppressed by the action of NPS. The discovery of this neuromodulator peptide is effective considering its strong anxiolytic action, which has the potential to be an interesting therapeutic option in treating neuropsychiatric disorders. In this article, we aimed to analyze the pharmaceutical properties of NPS as well as its influence on several neurophysiological aspects-modulation of behavior, association with obesity, as well as its potential application in rehabilitation and treatment of psychiatric disorders.

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.

Sex-Related Predisposition to Post-Traumatic Stress Disorder Development-The Role of Neuropeptides

Post-traumatic stress disorder (PTSD) is characterized by re-experiencing a traumatic event, avoidance, negative alterations in cognitions and mood, hyperarousal, and severe functional impairment. Women have a two times higher risk of developing PTSD than men. The neurobiological basis for the sex-specific predisposition to PTSD might be related to differences in the functions of stress-responsive systems due to the interaction between gonadal hormones and stress peptides such as corticotropin-releasing factor (CRF), orexin, oxytocin, and neuropeptide Y. Additionally, in phases where estrogens levels are low, the risk of developing or exacerbating PTSD is higher. Most studies have revealed several essential sex differences in CRF function. They include genetic factors, e.g., the CRF promoter contains estrogen response elements. Importantly, sex-related differences are responsible for different predispositions to PTSD and diverse treatment responses. Fear extinction (the process responsible for the effectiveness of behavioral therapy for PTSD) in women during periods of high endogenous estradiol levels (the primary form of estrogens) is reportedly more effective than in periods of low endogenous estradiol. In this review, we present the roles of selected neuropeptides in the sex-related predisposition to PTSD development.

Modulation of neuropeptide Y levels is impaired in crack withdrawal patients

Introduction The dysregulation of the hypothalamic-pituitary-adrenal (HPA) axis has a key role in drug addiction susceptibility. In addition to the well-known relationship between cortisol and the HPA axis, other molecules are involved with stress response and could modify the HPA activation, such as the neuropeptide Y (NPY), which has anxiolytic proprieties. There are few studies evaluating the effect of NPY levels on addiction, especially in crack cocaine dependence. Objective To evaluate NPY in crack users during early withdrawal to determine its relationship with drug use and cortisol levels. Methods We analyzed 25 male inpatient crack users. Serum NPY levels were measured at admission and discharge (mean of 24 days). Morning salivary cortisol was measured at admission. Results Serum NPY levels at admission and discharge were very similar. Lower NPY levels at discharge were associated with higher lifetime crack use. Also, a negative correlation was found between morning cortisol and delta NPY (NPY discharge - NPY admission). Conclusion These preliminary findings indicate that crack use influences the modulation of NPY levels and modifies stress response. The NPY pathway may play an important role in the pathophysiology of crack addiction, and the anxiolytic effect of NPY may be impaired in crack users. Future studies should consider NPY as a measurable indicator of the biological state in addiction.

Neuropeptide Y in PTSD, MDD, and chronic stress: A systematic review and meta-analysis

Previous studies have suggested that neuropeptide Y (NPY) levels may be altered in patients with major depressive disorder (MDD), post-traumatic stress disorder (PTSD) and chronic stress. We investigated, through systematic review and meta-analysis, whether the mean levels of NPY are significantly different in patients with MDD, PTSD or chronic stress, compared to controls. The main outcome was the pooled standardized mean difference (SMD) with 95% confidence intervals between cases and controls, using the random-effects model. Heterogeneity and publication bias were evaluated. Thirty-five studies met eligibility criteria. Meta-regression determined that medication and sex could explain 27% of the between-study variance. Females and participants currently prescribed psychotropic medications had significantly higher levels of NPY. NPY levels were significantly lower in plasma and cerebrospinal fluid (CSF) in PTSD patients versus controls. Patients with MDD had significantly lower levels of NPY in plasma compared to controls, but not in the CSF. The magnitudes of the decrease in plasma NPY levels were not significantly different between PTSD and MDD. However, chronic stress patients had significantly higher plasma NPY levels compared to controls, PTSD or MDD. Our findings may imply a shared role of NPY in trauma and depression: nevertheless, it is not clear that the association is specific to these disorders. Psychotropic medications may help restore NPY levels. Further controlled studies are needed to better delineate the contribution of confounding variables such as type of depression, body mass index, appetite or sleep architecture.

Intranasal Neuropeptide Y Blunts Lipopolysaccharide-Evoked Sickness Behavior but Not the Immune Response in Mice

Neuropeptide Y (NPY) has been demonstrated to exert stress buffering effects and promote resilience. Non-invasive intranasal (IN) application of NPY to rodents is able to mitigate traumatic stress-induced behavioral changes as well as dysfunction of the hypothalamic-pituitary-adrenal (HPA) axis. However, it is unknown whether IN NPY could prevent the behavioral, pro-inflammatory and neurochemical responses to peripheral immune activation by the Toll-like receptor 4 (TLR4) stimulant lipopolysaccharide (LPS). Therefore, we analyzed the effects of IN NPY (100 μg) on the behavioral sickness response (reduced locomotion and exploration) and the underlying molecular mechanisms, 3 h and 21 h after intraperitoneal injections of LPS (0.03 mg/kg) in male C57BL/6N mice. The acute behavioral sickness response was significantly dampened by pretreatment with IN NPY 3 h after LPS injection. This effect was accompanied by diminished weight loss and lowered plasma corticosterone (CORT) levels 21 h after LPS injection. In contrast, acute circulating cytokine levels and hypothalamic cytokine mRNA expression remained unaltered by IN NPY, which indicates that the peripheral and cerebral immune response to LPS was left undisturbed. Our findings are in agreement with the reported activity of NPY to dampen the response of the HPA axis to stress. We propose that IN NPY ablates sickness behavior at a site beyond the peripheral and cerebral cytokine response, an action that is associated with reduced activity of the HPA axis as determined by decreased plasma CORT.These results indicate that IN NPY administration may be relevant to the management of neuropsychiatric disorders arising from immune-induced neuroendocrine dysfunction.

Reduced Sensory-Evoked Locus Coeruleus-Norepinephrine Neural Activity in Female Rats With a History of Dietary-Induced Binge Eating

Noradrenergic pathways have been implicated in eating pathologies. These experiments sought to examine how dietary-induced binge eating influences the neuronal activity of the locus coeruleus (LC)-norepinephrine (NE) system. Young adult female Sprague Dawley rats (7-8 weeks old) were exposed to a repeated intermittent (twice weekly) cycle of 30-min access to a highly palatable sweetened fat (i.e., vegetable shortening with 10% sucrose) with or without intermittent (24 h) calorie restriction (Restrict Binge or Binge groups, respectively). Age- and weight-matched female control rats were exposed to standard chow feeding (Naive group) or intermittent chow feeding (Restrict group). The Binge and Restrict Binge groups demonstrated an escalation in sweet-fat food intake after 2.5 weeks. On week 3, in vivo single-unit LC electrophysiological activity was recorded under isoflurane anesthesia. Restrict Binge (20 cells from six rats) and Binge (27 cells from six rats) had significantly reduced (approximate 20% and 26%, respectively) evoked LC discharge rates compared with naive rats (22 cells, seven rats). Spontaneous and tonic discharge rates were not different among the groups. Signal-to-noise ratio was reduced in the groups with intermittent sweetened fat exposure. In order to investigate the neuropeptide alterations as a consequence of dietary binge eating, relative gene expression of neuropeptide Y (NPY), glucagon-like peptide 1 receptor (GLP-1r), prodynorphin, and related genes were measured in LC and hypothalamic arcuate (Arc) regions. Glp-1r, Npy2r, and Pdyn in LC region were reduced with repeated intermittent restriction. Npy1r was reduced by approximately 27% in ARC of Restrict compared with Naive group. Such data indicate that dietary-induced binge eating alters the neural response of LC neurons to sensory stimuli and dampens the neural stress response.

NPY Induces Stress Resilience via Downregulation of Ih in Principal Neurons of Rat Basolateral Amygdala

Neuropeptide Y (NPY) expression is tightly linked with the development of stress resilience in rodents and humans. Local NPY injections targeting the basolateral amygdala (BLA) produce long-term behavioral stress resilience in male rats via an unknown mechanism. Previously, we showed that activation of NPY Y1 receptors hyperpolarizes BLA principal neurons (PNs) through inhibition of the hyperpolarization-activated, depolarizing H-current, Ih The present studies tested whether NPY treatment induces stress resilience by modulating Ih NPY (10 pmol) was delivered daily for 5 d bilaterally into the BLA to induce resilience; thereafter, the electrophysiological properties of PNs and the expression of Ih in the BLA were characterized. As reported previously, increases in social interaction (SI) times persisted weeks after completion of NPY administration. In vitro intracellular recordings showed that repeated intra-BLA NPY injections resulted in hyperpolarization of BLA PNs at 2 weeks (2W) and 4 weeks (4W) after NPY treatment. At 2W, spontaneous IPSC frequencies were increased, whereas at 4W, resting Ih was markedly reduced and accompanied by decreased levels of HCN1 mRNA and protein expression in BLA. Knock-down of HCN1 channels in the BLA with targeted delivery of lentivirus containing HCN1-shRNA increased SI beginning 2W after injection and induced stress resilience. NPY treatment induced sequential, complementary changes in the inputs to BLA PNs and their postsynaptic properties that reduce excitability, a mechanism that contributes to less anxious behavior. Furthermore, HCN1 knock-down mimicked the increases in SI and stress resilience observed with NPY, indicating the importance of Ih in stress-related behavior.SIGNIFICANCE STATEMENT Resilience improves mental health outcomes in response to adverse situations. Neuropeptide Y (NPY) is associated with decreased stress responses and the expression of resilience in rodents and humans. Single or repeated injections of NPY into the basolateral amygdala (BLA) buffer negative behavioral effects of stress and induce resilience in rats, respectively. Here, we demonstrate that repeated administration of NPY into the BLA unfolds several cellular mechanisms that decrease the activity of pyramidal output neurons. One key mechanism is a reduction in levels of the excitatory ion channel HCN1. Moreover, shRNA knock-down of HCN1 expression in BLA recapitulates some of the actions of NPY and causes potent resilience to stress, indicating that this channel may be a possible target for therapy.

The Corticotropin Releasing Factor Receptor 1 in Alcohol Use Disorder: Still a Valid Drug Target?

Corticotropin releasing factor (CRF) is a neuropeptide that plays a key role in behavioral and physiological responses to stress. A large body of animal literature implicates CRF acting at type 1 CRF receptors (CRFR1) in consumption by alcohol-dependent subjects, stress-induced reinstatement of alcohol seeking, and possibly binge alcohol consumption. These studies have encouraged recent pilot studies of CRFR1 antagonists in humans with alcohol use disorder (AUD). It was a great disappointment to many in the field that these studies failed to show an effect of these compounds on stress-induced alcohol craving. Here, we examine these studies to explore potential limitations and discuss preclinical and human literature to ask whether CRFR1 is still a valid drug target to pursue for the treatment of AUD.

Posttraumatic stress disorder: A metabolic disorder in disguise?

Posttraumatic stress disorder (PTSD) is a heterogeneous psychiatric disorder that affects individuals exposed to trauma and is highly co-morbid with other adverse health outcomes, including cardiovascular disease and obesity. The unique pathophysiological feature of PTSD is the inability to inhibit fear responses, such that individuals suffering from PTSD re-experience traumatic memories and are unable to control psychophysiological responses to trauma-associated stimuli. However, underlying alterations in sympathetic nervous system activity, neuroendocrine systems, and metabolism associated with PTSD are similar to those present in traditional metabolic disorders, such as obesity and diabetes. The current review highlights existing clinical, translational, and preclinical data that support the notion that underneath the primary indication of impaired fear inhibition, PTSD is itself also a metabolic disorder and proposes altered function of inflammatory responses as a common underlying mechanism. The therapeutic implications of treating PTSD as a whole-body condition are significant, as targeting any underlying biological system whose activity is altered in both PTSD and metabolic disorders, (i.e. HPA axis, sympathetic nervous systems, inflammation) may elicit symptomatic relief in individuals suffering from these whole-body adverse outcomes.

Supersensitive Kappa Opioid Receptors Promotes Ethanol Withdrawal-Related Behaviors and Reduce Dopamine Signaling in the Nucleus Accumbens

BACKGROUND

Chronic ethanol exposure reduces dopamine transmission in the nucleus accumbens, which may contribute to the negative affective symptoms associated with ethanol withdrawal. Kappa opioid receptors have been implicated in withdrawal-induced excessive drinking and anxiety-like behaviors and are known to inhibit dopamine release in the nucleus accumbens. The effects of chronic ethanol exposure on kappa opioid receptor-mediated changes in dopamine transmission at the level of the dopamine terminal and withdrawal-related behaviors were examined.

METHODS

Five weeks of chronic intermittent ethanol exposure in male C57BL/6 mice were used to examine the role of kappa opioid receptors in chronic ethanol-induced increases in ethanol intake and marble burying, a measure of anxiety/compulsive-like behavior. Drinking and marble burying were evaluated before and after chronic intermittent ethanol exposure, with and without kappa opioid receptor blockade by nor-binaltorphimine (10mg/kg i.p.). Functional alterations in kappa opioid receptors were assessed using fast scan cyclic voltammetry in brain slices containing the nucleus accumbens.

RESULTS

Chronic intermittent ethanol-exposed mice showed increased ethanol drinking and marble burying compared with controls, which was attenuated with kappa opioid receptor blockade. Chronic intermittent ethanol-induced increases in behavior were replicated with kappa opioid receptor activation in naïve mice. Fast scan cyclic voltammetry revealed that chronic intermittent ethanol reduced accumbal dopamine release and increased uptake rates, promoting a hypodopaminergic state of this region. Kappa opioid receptor activation with U50,488H concentration-dependently decreased dopamine release in both groups; however, this effect was greater in chronic intermittent ethanol-treated mice, indicating kappa opioid receptor supersensitivity in this group.

CONCLUSIONS

These data suggest that the chronic intermittent ethanol-induced increase in ethanol intake and anxiety/compulsive-like behaviors may be driven by greater kappa opioid receptor sensitivity and a hypodopaminergic state of the nucleus accumbens.

Resilience to the effects of social stress: evidence from clinical and preclinical studies on the role of coping strategies

The most common form of stress encountered by people stems from one's social environment and is perceived as more intense than other types of stressors. One feature that may be related to differential resilience or vulnerability to stress is the type of strategy used to cope with the stressor, either active or passive coping. This review focuses on models of social stress in which individual differences in coping strategies produce resilience or vulnerability to the effects of stress. Neurobiological mechanisms underlying these individual differences are discussed. Overall, the literature suggests that there are multiple neural mechanisms that underlie individual differences in stress-induced resilience and vulnerability. How these mechanisms interact with one another to produce a resilient or vulnerable phenotype is not understood and such mechanisms have been poorly studied in females and in early developmental periods. Finally, we propose that resilience may be stress context specific and resilience phenotypes may need to be fine-tuned to suit a shifting environment.

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Resilience is considered positive adaptation in the face of adversity.

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Coping strategy impacts one's susceptibility to social stress-induced psychopathology.

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Neurobiological substrates such as CRF, NPY and DA may impact stress susceptibility.

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Individual differences within females and during adolescence are poorly understood.

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.

Cardiac autonomic imbalance by social stress in rodents: understanding putative biomarkers

Exposure to stress or traumatic events can lead to the development of depression and anxiety disorders. In addition to the debilitating consequences on mental health, patients with psychiatric disorders also suffer from autonomic imbalance, making them susceptible to a variety of medical disorders. Emerging evidence utilizing spectral analysis of heart rate variability (HRV), a reliable non-invasive measure of cardiovascular autonomic regulation, indicates that patients with depression and various anxiety disorders (i.e., panic, social, generalized anxiety disorders, and post traumatic stress disorder) are characterized by decreased HRV. Social stressors in rodents are ethologically relevant experimental stressors that recapitulate many of the dysfunctional behavioral and physiological changes that occur in psychological disorders. In this review, evidence from clinical studies and preclinical stress models identify putative biomarkers capable of precipitating the comorbidity between disorders of the mind and autonomic dysfunction. Specifically, the role of corticotropin releasing factor, neuropeptide Y and inflammation are investigated. The impetus for this review is to highlight stress-related biomarkers that may prove critical in the development of autonomic imbalance in stress -related psychiatric disorders.

Neuropeptide Y in the central nucleus of amygdala regulates the anxiolytic effect of agmatine in rats

In the present study, modulation of anxiolytic action of agmatine by neuropeptide Y (NPY) in the central nucleus of amygdala (CeA) is evaluated employing Vogel's conflict test (VCT) in rats. The intra-CeA administration of agmatine (0.6 and 1.2µmol/rat), NPY (10 and 20pmol/rat) or NPY Y1/Y5 receptors agonist [Leu(31), Pro(34)]-NPY (30 and 60pmol/rat) significantly increased the number of punished drinking licks following 15min of treatment. Combination treatment of subeffective dose of NPY (5pmol/rat) or [Leu(31), Pro(34)]-NPY (15pmol/rat) and agmatine (0.3µmol/rat) produced synergistic anxiolytic-like effect. However, intra-CeA administration of selective NPY Y1 receptor antagonist, BIBP3226 (0.25 and 0.5mmol/rat) produced anxiogenic effect. In separate set of experiment, pretreatment with BIBP3226 (0.12mmol/rat) reversed the anxiolytic effect of agmatine (0.6µmol/rat). Furthermore, we evaluated the effect of intraperitoneal injection of agmatine (40mg/kg) on NPY-immunoreactivity in the nucleus accumbens shell (AcbSh), lateral part of bed nucleus of stria terminalis (BNSTl) and CeA. While agmatine treatment significantly decreased the fibers density in BNSTl, increase was noticed in AcbSh. In addition, agmatine reduced NPY-immunoreactive cells in the AcbSh and CeA. Immunohistochemical data suggest the enhanced transmission of NPY from the AcbSh and CeA. Taken together, this study suggests that agmatine produced anxiolytic effect which might be regulated via modulation of NPYergic system particularly in the CeA.

Individual differences in the neurobiology of social stress: implications for depression-cardiovascular disease comorbidity

Stress initiates a cascade of complex neural and peripheral changes that promote healthy adaption to stress, but when unabated, leads to pathology. Fascinating individual differences arise in the ability to cope with a stressor, rendering an individual more or less likely to develop stress-induced pathologies such as depression, anxiety, and cardiovascular disease. In this review we evaluate recent findings that investigate the neural underpinnings of adopting a passive or active coping response during social defeat stress. Because passive coping is associated with vulnerability to stress-related pathologies and active coping confers resiliency, understanding neurobiological adaptations associated with these diverse coping strategies may reveal biomarkers or targets impacting stress susceptibility. The co-occurrence of stress-induced depression and cardiovascular disease is becoming increasingly clear. Therefore this review focuses on the central mechanisms capable of contributing to psychopathology and cardiovascular disease such as corticotropin releasing factor, neuropeptide Y, monoamines, cytokines and oxidative stress. The impetus for this review is to highlight neurobiological systems that warrant further evaluation for their contribution to the pathophysiology of depression-cardiovascular disease comorbidity.

Agmatine attenuates nicotine induced conditioned place preference in mice through modulation of neuropeptide Y system

The purpose of the present study was to examine the effect of agmatine on nicotine induced conditioned place preference (CPP) in male albino mice. Intra-peritoneal (ip) administration of nicotine (1mg/kg) significantly increased time spent in drug-paired compartment. Agmatine (20 and 40 mg/kg, ip) co-administered with nicotine during the 6 days conditioning sessions completely abolished the acquisition of nicotine-induced CPP in mice. Concomitant administration of neuropeptide Y (NPY) (1 pg/mouse, icv) or [Leu(31), Pro(34)]-NPY (0.1 pg/mouse, icv), selective NPY Y1 receptor agonist potentiated the inhibitory effect of agmatine (10 mg/kg, ip) on nicotine CPP. Conversely, pretreatment with NPY Y1 receptor antagonist, BIBP3226 (0.01 ng/mouse, icv) blocked the effect of agmatine (20 mg/kg, ip) on nicotine induced CPP. In immunohistochemical study, nicotine decreased NPY-immunoreactivity in nucleus accumbens shell (AcbSh), bed nucleus of stria terminalis, lateral part (BNSTl), arcuate nucleus (ARC) and paraventricular nucleus (PVN). Conversely, administration of agmatine prior to the nicotine significantly reversed the effect of nicotine on NPY-immunoreactivity in the above brain nuclei. This data indicate that agmatine attenuate nicotine induced CPP via modulation of NPYergic neurotransmission in brain.

Biological studies of post-traumatic stress disorder

Post-traumatic stress disorder (PTSD) is the only major mental disorder for which a cause is considered to be known: that is, an event that involves threat to the physical integrity of oneself or others and induces a response of intense fear, helplessness or horror. Although PTSD is still largely regarded as a psychological phenomenon, over the past three decades the growth of the biological PTSD literature has been explosive, and thousands of references now exist. Ultimately, the impact of an environmental event, such as a psychological trauma, must be understood at organic, cellular and molecular levels. This Review attempts to present the current state of this understanding on the basis of psychophysiological, structural and functional neuroimaging, and endocrinological, genetic and molecular biological studies in humans and in animal models.

The psychobiology of resilience and vulnerability to anxiety disorders: implications for prevention and treatment

Much of the research on the neurobiology of human anxiety disorders has focused on psychopaihological abnormalities in patients with anxiety disorders. While this line of research is obviously important, more investigation is needed to elucidate the psychobiology of resilience to extreme stress. Study of the psychobiology of resilience has the potential to identify neurochemical, neuropeptide, and hormonal mediators of vulnerability and resilience to severe stress. In addition, the relevance of neural mechanisms of reward and motivation, fear responsiveness, and social behavior to character traits associated with risk and resistance to anxiety disorders may be clarified. These areas of investigation should lead to improved methods of diagnosis, novel approaches to prevention, and new targets for antianxiety drug discovery.

Nicotine-induced anxiety-like behavior in a rat model of the novelty-seeking phenotype is associated with long-lasting neuropeptidergic and neuroplastic adaptations in the amygdala: effects of the cannabinoid receptor 1 antagonist AM251

A rat model of the novelty-seeking phenotype predicts vulnerability to the expression of behavioral sensitization to nicotine, where locomotor reactivity to novelty is used to screen experimentally-naïve rats for high (HR) versus low (LR) responders. The present study examines the long-term neuropeptidergic and neuroplastic adaptations associated with the expression of locomotor sensitization to a low dose nicotine challenge and social anxiety-like behavior following chronic intermittent nicotine exposure during adolescence in the LRHR phenotype. Our data show that the expression of behavioral sensitization to nicotine and abstinence-related anxiety are detected in nicotine pre-exposed HRs even across a long (3 wks) abstinence. Moreover, these behavioral effects of nicotine are accompanied by a persistent imbalance between neuropeptide Y and corticotrophin releasing factor systems, and a persistent increase in brain-derived neurotrophic factor (BDNF) and spinophilin mRNA levels in the amygdala. Furthermore, treatment with the cannabinoid receptor 1 antagonist, AM251 (5 mg/kg) during a short (1 wk) abstinence is ineffective in reversing nicotine-induced anxiety, fluctuations in BDNF and spinophilin mRNAs, and the neuropeptidergic dysregulations in the amygdala; although this treatment is effective in reversing the expression of locomotor sensitization to challenge nicotine even after a long abstinence. Interestingly, the identical AM251 treatment administered during the late phase of a long abstinence further augments anxiety and associated changes in BDNF and spinophilin mRNA in the basolateral nucleus of the amygdala in nicotine pre-exposed HRs. These findings implicate long-lasting neuropeptidergic and neuroplastic changes in the amygdala in vulnerability to the behavioral effects of nicotine in the novelty-seeking phenotype.

The neuropeptide Y (NPY)-ergic system is associated with behavioral resilience to stress exposure in an animal model of post-traumatic stress disorder

Converging evidence implicates the regulatory neuropeptide Y (NPY) in anxiety- and depression-related behaviors. The present study sought to assess whether there is an association between the magnitude of behavioral responses to stress and patterns of NPY in selected brain areas, and subsequently, whether pharmacological manipulations of NPY levels affect behavior in an animal model of PTSD. Animals were exposed to predator-scent stress for 15 min. Behaviors were assessed with the elevated plus maze and acoustic startle response tests 7 days later. Preset cutoff criteria classified exposed animals according to their individual behavioral responses. NPY protein levels were assessed in specific brain regions 8 days after the exposure. The behavioral effects of NPY agonist, NPY-Y1-receptor antagonist, or placebo administered centrally 1 h post-exposure were evaluated in the same manner. Immunohistochemical technique was used to detect the expression of the NPY, NPY-Y1 receptor, brain-derived neurotrophic factor, and GR 1 day after the behavioral tests. Animals whose behavior was extremely disrupted (EBR) selectively displayed significant downregulation of NPY in the hippocampus, periaqueductal gray, and amygdala, compared with animals whose behavior was minimally (MBR) or partially (PBR) disrupted, and with unexposed controls. One-hour post-exposure treatment with NPY significantly reduced prevalence rates of EBR and reduced trauma-cue freezing responses, compared with vehicle controls. The distinctive pattern of NPY downregulation that correlated with EBR as well as the resounding behavioral effects of pharmacological manipulation of NPY indicates an intimate association between NPY and behavioral responses to stress, and potentially between molecular and psychopathological processes, which underlie the observed changes in behavior. The protective qualities attributed to NPY are supported by the extreme reduction of its expression in animals severely affected by the stressor and imply a role in promoting resilience and/or recovery.

Differential Regulation of Neuropeptide Y in the Amygdala and Prefrontal Cortex during Recovery from Chronic Variable Stress

Accumulating evidence from clinical studies and pre-clinical animal models supports a role for neuropeptide Y (NPY) in adaptive emotional response following stress. The long-term impact of stress, particularly chronic stress, on availability, and function of resilience factors such as NPY may be critical to understanding the etiology of stress-related psychopathology. In these studies, we examined expression of NPY during recovery from a chronic variable stress (CVS) model of repetitive trauma in rats. Due to the importance of amygdala and prefrontal cortex in regulating emotional responses, we predicted chronic changes in NPY expression could contribute to persistent behavioral deficits seen in this model. Consistent with the hypothesis, ELISA for NPY peptide identified a significant reduction in NPY at the delayed (7 days) recovery time-point. Interestingly, a significant increase in prefrontal NPY was observed at the same recovery time-point. The mRNA expression for NPY was not changed in the amygdala or PFC, although there was a modest but not statistically significant increase in NPY mRNA at the delayed recovery time-point in the prefrontal cortex. The observed changes in NPY expression are consistent with maladaptive coping and enhanced emotionality, due to the nature of NPY signaling within these respective regions, and the nature of reciprocal connections between amygdala and prefrontal cortex.

Infusions of neuropeptide Y into the lateral septum reduce anxiety-related behaviors in the rat

Neuropeptide Y (NPY) is one of the most abundant peptides in mammalian brain and NPY-like-immunoreactivity is highly expressed in the lateral septum, an area extensively involved in anxiety regulation. NPY counteracts the neurochemical and behavioral responses to acute threat in animal models, and intracerebroventricular (i.c.v.) administration of NPY at low doses is anxiolytic. Less is known about the specific contributions of the lateral septum to NPY-mediated anxiety regulation. In Experiment 1, the effects of infusions of NPY (1.5 μg) into the lateral septum were investigated in three animal models of anxiety: the elevated plus-maze, novelty-induced suppression of feeding, and shock-probe burying tests. Experiment 2 examined the role of the NPY Y1 receptor in these models by co-infusing the Y1 antagonist BIBO 3304 (0.15 μg, 0.30 μg) with NPY into the lateral septum. In the elevated plus-maze, there were no changes in rats' open arm exploration, the index of anxiety reduction in this test. In the novelty-induced suppression of feeding test, rats infused with NPY showed decreases in the latency to consume a palatable snack in a novel (but not familiar) environment, suggesting a reduction in anxiety independent of increases in appetite. This anxiolysis was attenuated by co-infusion with BIBO 3304 (0.30 μg) in Experiment 2. Lastly, rats infused with NPY showed decreases in the duration of burying behavior in the shock-probe burying test, also indicative of anxiety reduction. However, unlike in the feeding test, BIBO 3304 did not attenuate the NPY-induced anxiolysis in the shock-probe test. It is concluded that NPY produces anxiolytic-like actions in the lateral septum in two animal models of anxiety: the novelty-induced suppression of feeding, and shock-probe burying tests, and that this anxiolysis is dependent on Y1 receptor activation in the feeding test.

Intraperitoneal injection of neuropeptide Y (NPY) alters neurotrophin rat hypothalamic levels: Implications for NPY potential role in stress-related disorders

Neuropeptide Y (NPY) is a 36-amino acid peptide which exerts several regulatory actions within peripheral and central nervous systems. Among NPY actions preclinical and clinical data have suggested that the anxiolytic and antidepressant actions of NPY may be related to its antagonist action on the hypothalamic-pituitary-adrenal (HPA) axis. The neurotrophins brain-derived neurotrophic factor (BDNF) and nerve growth factor (NGF) are proteins involved in the growth, survival and function of neurons. In addition to this, a possible role of neurotrophins, particularly BDNF, in HPA axis hyperactivation has been proposed. To characterize the effect of NPY on the production of neurotrophins in the hypothalamus we exposed young adult rats to NPY intraperitoneal administration for three consecutive days and then evaluated BDNF and NGF synthesis in this brain region. We found that NPY treatment decreased BDNF and increased NGF production in the hypothalamus. Given the role of neurotrophins in the hypothalamus, these findings, although preliminary, provide evidence for a role of NPY as inhibitor of HPA axis and support the idea that NPY might be involved in pathologies characterized by HPA axis dysfunctions.

Anxiety responses and neurochemical changes in a kaolin-induced rat model of hydrocephalus

OBJECT

Hydrocephalus is a pathological enlargement of the ventricles of the brain, which can result from various diseases of the central nervous system. Patients with hydrocephalus frequently show motor abnormalities, such as abnormal gait and posture, as well as intellectual and emotional impairment. The present study was designed to investigate anxiety responses in rats with kaolin-induced hydrocephalus.

METHODS

A total of 26 Sprague-Dawley rats were used for this study. Hydrocephalus was induced in 14 Sprague-Dawley rats by injecting 0.1 ml of 20% kaolin solution into the cisterna magna; 12 rats were administered the same volume of saline in the same fashion and served as controls. Seven of the rats that were injected with kaolin and 6 of the rats injected with saline were killed 3 days after injection (Group 1); the remaining rats were killed 4 weeks after injection (Group 2) to evaluate effects related to acute and chronic hydrocephalus. The rats were tested in an elevated plus maze after induction of hydrocephalus by kaolin injection. After the animals were killed, brain sections were immunostained for cholecystokinin and neuropeptide Y. In addition, tyrosine hydroxylase immunoreactivity in the ventral tegmental area was evaluated by immunohistological staining.

RESULTS

The rats with acute hydrocephalus showed decreased entry into and spent less time in the open arms of the elevated plus maze as compared with the control rats. The hydrocephalic rats had significantly more cholecystokinin-immunoreactive neurons and fewer neuropeptide Y-immunoreactive neurons in their brains. In addition, hydrocephalus progress in this model was positively correlated with the anxiety response. The numbers of tyrosine hydroxylase-immunoreactive neurons were decreased significantly in the hydrocephalic rats as compared with the control rats.

CONCLUSIONS

These results suggest that the rat model of hydrocephalus is characterized by increased anxiety response and is associated with the functional impairment of the central dopamine system.

Countervailing modulation of Ih by neuropeptide Y and corticotrophin-releasing factor in basolateral amygdala as a possible mechanism for their effects on stress-related behaviors

Stress and anxiety-related behaviors controlled by the basolateral amygdala (BLA) are regulated in vivo by neuropeptide Y (NPY) and corticotrophin-releasing factor (CRF): NPY produces anxiolytic effects, whereas CRF produces anxiogenic effects. These opposing actions are likely mediated via regulation of excitatory output from the BLA to afferent targets. In these studies, we examined mechanisms underlying the effects of NPY and CRF in the BLA using whole-cell patch-clamp electrophysiology in rat brain slices. NPY, even with tetrodotoxin present, caused a dose-dependent membrane hyperpolarization in BLA pyramidal neurons. The hyperpolarization resulted in the inhibition of pyramidal cells, despite arising from a reduction in a voltage-dependent membrane conductance. The Y(1) receptor agonist, F(7)P(34) NPY, produced a similar membrane hyperpolarization, whereas the Y(1) antagonist, BIBO3304 [(R)-N-[[4-(aminocarbonylaminomethyl)-phenyl]methyl]-N(2)-(diphenylacetyl)-argininamide trifluoroacetate], blocked the effect of NPY. The NPY-inhibited current was identified as I(h), which is active at and hyperpolarized to rest. Responses to NPY were occluded by either Cs(+) or ZD7288 (4-ethylphenylamino-1,2-dimethyl-6-methylaminopyrimidinium chloride), but unaffected by the G(IRK)-preferring blockers Ba(2+) and SCH23390 [(R)-(+)-7-chloro-8-hydroxy-3-methyl-l-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine hydrochloride]. Application of CRF, with or without TTX present, depolarized NPY-sensitive BLA pyramidal neurons, resulting from an increase in I(h). Electrophysiological and immunocytochemical data were consistent with a major role for the HCN1 subunit. Our results indicate that NPY, via Y(1) receptors, directly inhibits BLA pyramidal neurons by suppressing a postsynaptic I(h), whereas CRF enhances resting I(h), causing an increased excitability of BLA pyramidal neurons. The opposing actions of these two peptides on the excitability of BLA output cells are consistent with the observed behavioral actions of NPY and CRF in the BLA.

Adaptation to extreme stress: post-traumatic stress disorder, neuropeptide Y and metabolic syndrome

The prevalence rates of obesity and metabolic syndrome are on the rise in the United States. Epidemiological surveys suggest that the rates of these medical conditions are especially high among persons with psychiatric disorders, including post-traumatic stress disorder (PTSD). A variety of factors are thought to contribute to the risk for metabolic syndrome, including excessive caloric intake, decreased activity and energy expenditure, use of certain medications, stress and genetic influences. Recent research demonstrates that stress, acting through the neuropeptide Y (NPY) and glucocorticoid systems, potentiates the development of obesity and other aspects of metabolic syndrome in mice fed a high caloric, fat and sugar diet. Alterations in the NPY and glucocorticoid systems also impact behavioral adaptation to stress, as indicated by studies in animals and persons exposed to severe, life-threatening or traumatic stress. The following review examines the biology of the NPY and neuroactive steroid systems as physiological links between metabolic syndrome and PTSD, a paradigmatic neuropsychiatric stress disorder. Hopefully, understanding the function of these systems from both a translational and systems biology point of view in relation to stress will enable development of more effective methods for preventing and treating the negative physical and mental health consequences of stress.

Pathogenic involvement of neuropeptides in anxiety and depression

Anxiety and depression are highly prevalent disorders of mood posing significant challenges to individuals and society. Current evidence indicates no single neurobiological determinant underpins these conditions and an integrated approach in both research and treatment is expedient. Basic, behavioral, and clinical science indicates various stress-responsive neuropeptides in the neuroendocrine, autonomic, and behavioral pathophysiology of stress-related disorders including anxiety and depression. This review draws on recent research to capture the consensus and implications of neuropeptide research concerning the pathogenesis of anxiety and depression.

Behavioral effects of neuropeptides in rodent models of depression and anxiety

In recent years, studies have advocated neuropeptide systems as modulators for the behavioral states found in mood disorders such as depression and anxiety disorders. Neuropeptides have been tested in traditional animal models and screening procedures that have been validated by known antidepressants and anxiolytics. However, it has become clear that although these tests are very useful, neuropeptides have distinct behavioral effects and dose-dependent characteristics, and therefore, use of these tests with neuropeptides must be done with an understanding of their unique characteristics. This review will focus on the behavioral actions of neuropeptides and their synthetic analogs, particularly in studies utilizing various preclinical tests of depression and anxiety. Specifically, the following neuropeptide systems will be reviewed: corticotropin-releasing factor (CRF), urocortin (Ucn), teneurin C-terminal associated peptide (TCAP), neuropeptide Y (NPY), arginine vasopressin (AVP), oxytocin, the Tyr-MIF-1 family, cholecystokinin (CCK), galanin, and substance P. These neuropeptide systems each have a unique role in the regulation of stress-like behavior, and therefore provide intriguing therapeutic targets for mood disorder treatment.

Estradiol and neuropeptide Y (intra-lateral septal) reduce anxiety-like behavior in two animal models of anxiety

Anxiolytic-like effects of intra-lateral septal nuclei (LSN) infusions of the neuropeptide Y (NPY) alone or combined with estradiol benzoate were assessed in ovariectomized Wistar rats in two animal models of anxiety-like behavior. In a conflict test, immediately punished responses were assessed: 17-beta-estradiol (50.0microg/rat, P<0.05) plus vehicle (intra-LSN) or intra-LSN infusions of NPY (2.5microg/microl, P<0.05; 3.0microg/mul, P<0.05) plus vehicle (systemic route) or the combination of subthreshold doses of 17-beta-estradiol (25.0microg/kg) plus intra-LSN infusions of NPY (2.0microg/mul, P<0.05) increased the amount of immediately punished reinforcers. In the elevated plus-maze test several spatial-temporal variables were evaluated: 17-beta-estradiol (50.0microg/kg, P<0.05) plus vehicle (intra-LSN) or intra-LSN infusions of NPY (2.5microg/mul, P<0.05; 3.0microg/mul, P<0.05) plus vehicle (systemic route) or the combination of subthreshold doses of 17-beta-estradiol (25.0microg/kg) plus intra-LSN infusions of NPY (2.0microg/mul, P<0.05) produced anxiolytic-like actions without affecting locomotion. It is concluded that estradiol or NPY may produce anxiolytic-like actions and that subthreshold doses of estradiol and subthreshold doses of NPY when combined produced anxiolytic-like actions.

Neuroendocrine pathways in benzodiazepine dependence: new targets for research and therapy

Benzodiazepines are known to modulate the activity of the hypothalamo-pituitary-adrenocortical (HPA) axis by antagonizing the effects of corticotropin-releasing factor (CRH). Besides regulating the HPA axis CRH evolves properties of a neurotransmitter in the limbic system that is closely involved in the delivery of the emotional consequences of the stress response. At a superordinated level Neuropeptide Y (NPY) and Cholecystokinin (CCK) affect the release of CRH and modulate thereby the intensity of the physiological stress response. Benzodiazepine treatment interferes not only with the release of CRH but also with the release of NPY and CCK. Alterations in the intracortical ratio of NPY, CCK and CRH are correlated with behavioural changes like increased respectively decreased anxiety and subsequent alterations in the activity of the HPA axis. Recent research offers the possibility that the alterations of plasma levels of these neuropeptides are not only a secondary phenomenon due to drug intake, but that low levels of those neuropeptides that modulate anxiety and fear can possibly explain addiction to substances that counterbalance these deficits. Depending on the available results possible implications of NPY and CCK on benzodiazepine addiction and withdrawal symptoms are reviewed, thereby providing topics for further research.

Bidirectional changes in water-maze learning following recombinant adenovirus-associated viral vector (rAAV)-mediated brain-derived neurotrophic factor expression in the rat hippocampus

Alterations in hippocampal brain-derived neurotrophic factor (BDNF) expression have been implicated in the pathogenesis of emotional and cognitive dysfunction. Here, we induced BDNF overexpression in the rat hippocampus using recombinant adenovirus-associated viral (rAAV) vectors, and studied its long-term (2 months postinduction) effects on anxiety-related behaviour, exploration in the open field, and spatial learning in the water maze. Although the treatment successfully led to substantial elevation of hippocampal BDNF levels, its effect on spatial learning was bidirectional: a subset of rAAV-induced BDNF-overexpressing rats performed well above control level, whereas the rest were clearly impaired. This behavioural distinction corresponded to two markedly different levels of BDNF overexpression. The increase in dorsal hippocampal BDNF content achieved in the 'water-maze-impaired' subgroup was twice that attained in the 'water-maze-improved' rats. Although neither subgroup of rAAV-induced BDNF-overexpressing rats differed from controls in the open field, the 'water-maze-impaired' subgroup also showed a significant anxiolytic effect. Our results suggest that hippocampal BDNF elevation significantly affects cognitive and emotional behaviours, but the direction and magnitude of the effects critically depend on the precise levels of overexpression. This factor must be taken into account in future studies examining the functional consequences of hippocampal BDNF overexpression.

Resilience: research evidence and conceptual considerations for posttraumatic stress disorder

The growing recognition and occurrence of traumatic exposure in the general population has given increased salience to the need to understand the concept of resilience. More than just the "flip side" of a risk factor, the notion of resilience encompasses psychological and biological characteristics, intrinsic to an individual, that might be modifiable and that confer protection against the development of psychopathology in the face of stress. In this review, we provide some perspective on the concept of "resilience" by examining early use of the term in research on "children at risk" and discuss the relationship between risk and resilience factors. We then review psychological and biological factors that may confer resilience to the development of posttraumatic stress disorder (PTSD) following trauma, examine how resilience has been assessed and measured, and discuss issues to be addressed in furthering our understanding of this critical concept going forward.

Estrus variation in anxiolytic-like effects of intra-lateral septal infusions of the neuropeptide Y in Wistar rats in two animal models of anxiety-like behavior

Anxiolytic-like effects of intra-lateral septal infusions of the neuropeptide Y (NPY) were assessed during several estrus phases in Wistar rats tested in two animal models of anxiety-like behavior. In a conflict operant test, results showed that during late proestrus, intra-lateral septal nuclei infusions of NPY (1.0 microg/microl, P<0.05; 2.0 microg/microl, P<0.05; 2.5 microg/microl, P<0.05) increased the number of immediately punished responses. During metestrus-diestrus only the highest doses of NPY (2.5 microg/microl, P<0.05) increased the number of immediately punished reinforcers. In the elevated plus-maze test, results showed that during late proestrus, intra-lateral septal nuclei infusions of NPY (1.0 microg/microl, P<0.05; 2.0 microg/microl, P<0.05) produced anxiolytic-like actions. During metestrus-diestrus only the highest doses of NPY (2.0 microg/microl, P<0.05) produced anxiolytic-like actions. Neither NPY nor estrus phases significantly modified the number of closed arms entries in the elevated plus-maze test. It is concluded that anxiolytic-like effects of NPY vary within the estrus cycle in Wistar rats.

Physiology and gene regulation of the brain NPY Y1 receptor

Neuropeptide Y (NPY) is one of the most prominent and abundant neuropeptides in the mammalian brain where it interacts with a family of G-protein coupled receptors, including the Y(1) receptor subtype (Y(1)R). NPY-Y(1)R signalling plays a prominent role in the regulation of several behavioural and physiological functions including feeding behaviour and energy balance, sexual hormone secretion, stress response, emotional behaviour, neuronal excitability and ethanol drinking. Y(1)R expression is regulated by neuronal activity and peripheral hormones. The Y(1)R gene has been isolated from rodents and humans and it contains multiple regulatory elements that may participate in the regulation of its expression. Y(1)R expression in the hypothalamus is modulated by changes in energetic balance induced by a wide variety of conditions (fasting, pregnancy, hyperglycaemic challenge, hypophagia, diet induced obesity). Estrogens up-regulate responsiveness to NPY to stimulate preovulatory GnRH and gonadotropin surges by increasing Y(1)R gene expression both in the hypothalamus and the pituitary. Y(1)R expression is modulated by different kinds of brain insults, such as stress and seizure activity, and alteration in its expression may contribute to antidepressant action. Chronic modulation of GABA(A) receptor function by benzodiazepines or neuroactive steroids also affects Y(1)R expression in the amygdala, suggesting that a functional interaction between the GABA(A) receptor and Y(1)R mediated signalling may contribute to the regulation of emotional behaviour. In this paper, we review the state of the art concerning Y(1)R function and gene expression, including our personal contribution to many of the subjects mentioned above.

Neuropeptide Y administration into the amygdala alters high fat food intake

The orexigenic effects of neuropeptide Y (NPY) are mediated through the hypothalamus, while the anxiolytic effects of NPY appear to be mediated through the amygdala. We hypothesized that intra-amygdalar administration of NPY might alter food preference without changing total food intake. Neuropeptide Y was administered into the central nucleus of the amygdala in both satiated and overnight-fasted rats, and intake and preference for a high fat diet (56%)/low carbohydrate (20%) diet or a low fat (10%)/high carbohydrate (66%) diet were measured. Intra-amygdalar NPY administration in satiated rats did not change total caloric intake, but it did produce a dose-dependent decrease in intake of and preference for high fat diet relative to low fat diet over 24 h. In overnight-fasted rats, intra-amygdalar NPY also decreased the intake and preference for a high fat diet relative to low fat diet over 24 h, without altering total caloric intake. Intra-amygdalar NPY administration did not produce conditioned taste aversions to a novel saccharin solution. These results suggest that amygdalar NPY may have a role in macronutrient selection, without altering total caloric intake.

Multi-target strategies for the improved treatment of depressive states: Conceptual foundations and neuronal substrates, drug discovery and therapeutic application

Major depression is a debilitating and recurrent disorder with a substantial lifetime risk and a high social cost. Depressed patients generally display co-morbid symptoms, and depression frequently accompanies other serious disorders. Currently available drugs display limited efficacy and a pronounced delay to onset of action, and all provoke distressing side effects. Cloning of the human genome has fuelled expectations that symptomatic treatment may soon become more rapid and effective, and that depressive states may ultimately be "prevented" or "cured". In pursuing these objectives, in particular for genome-derived, non-monoaminergic targets, "specificity" of drug actions is often emphasized. That is, priority is afforded to agents that interact exclusively with a single site hypothesized as critically involved in the pathogenesis and/or control of depression. Certain highly selective drugs may prove effective, and they remain indispensable in the experimental (and clinical) evaluation of the significance of novel mechanisms. However, by analogy to other multifactorial disorders, "multi-target" agents may be better adapted to the improved treatment of depressive states. Support for this contention is garnered from a broad palette of observations, ranging from mechanisms of action of adjunctive drug combinations and electroconvulsive therapy to "network theory" analysis of the etiology and management of depressive states. The review also outlines opportunities to be exploited, and challenges to be addressed, in the discovery and characterization of drugs recognizing multiple targets. Finally, a diversity of multi-target strategies is proposed for the more efficacious and rapid control of core and co-morbid symptoms of depression, together with improved tolerance relative to currently available agents.

A Functional Continuum of Regulatory Anxiety-Enhancing Peptides. The Search for Complexes Providing the Optimal Basis for Developing Inhibitory Therapeutic Agents

Regulatory peptides are actively involved in controlling most physiological processes. One such function is regulation of the level of anxiety and panic states. We report here a meta-analysis of data published from 1960 to 2004 on the effects of anxiety-enhancing regulatory peptides. The resulting database was used to investigate the organization and functioning of the anxiogenic regulatory peptide system. Using vector representation of the effects of these peptides, the spectra of physiological effects which might be provoked by each anxiety- and fear-increasing regulatory peptide alone and in combination were evaluated. Complexes of regulatory peptides with anxiogenic profiles with the greatest potential for the further experimental development of inhibitory pharmacological agents were identified.

Neuropeptide Y activates urocortin 1 neurons in the nonpreganglionic Edinger-Westphal nucleus

Central regulatory pathways promoting stress adaptation utilize various neurotransmitters/neuropeptides, such as urocortin 1 (Ucn1) and neuropeptide Y (NPY). Ucn1 is abundantly expressed in the nonpreganglionic Edinger-Westphal nucleus (npEW), where it is codistributed with NPY-immunoreactive (ir) terminals. A special role for both neuropeptides has been postulated in stress adaptation. Using double-labeling immunohistochemistry, we observed close appositions between NPY-ir terminals and neurons immunoreactive for Ucn1 in the rat, as well as in the human npEW. Therefore, we hypothesized that NPY might control the activity of Ucn1-positive neurons in the npEW. To test this hypothesis, NPY was injected into the lateral cerebral ventricle of rats, resulting in a strong activation of npEW Ucn1 neurons as revealed by Fos immunohistochemistry. Ucn1 mRNA was also upregulated in the npEW 2 hours after the injection of NPY. In a search for the type of NPY receptor that mediates this NPY-induced recruitment of npEW-Ucn1 cells, we found that the great majority of Ucn1 cells exhibited NPY Y5 receptor immunoreactivity, and only a few of the Ucn1 cells coexpressed the Y1 receptor. We concluded that NPY, via NPY Y5 and to a lesser extent via the Y1 receptors, exerts a stimulatory action on Ucn1 cells in the npEW. Further studies are currently in progress to elucidate the significance of this NPY-Ucn1 interaction in the npEW.

Effects of altered amygdalar neuropeptide Y expression on anxiety-related behaviors

Neuropeptide Y (NPY) decreases anxiety-related behaviors in various animal models of anxiety. The purpose of the present study was to examine the role of the amygdalar NPY system in anxiety-related responses in the elevated plus maze. The first experiment determined if herpes virus-mediated alterations in amygdalar NPY levels would alter anxiety-related behaviors in the elevated plus maze. Viral vectors encoding NPY, NPY antisense, or LacZ (control virus) were bilaterally injected into the amygdala, and 4 days postinjection, rats were tested in the elevated plus maze test. NPY-like immunoreactivity (NPY-ir) was measured in the amygdala of these rats. In rats injected with the viral vector encoding NPY, reduced anxiety-related behaviors in the elevated plus maze accompanied by moderate increases in NPY-ir were detected compared to NPY-antisense viral vector-treated subjects. Elevated plus maze behavior did not differ compared to LacZ-treated controls. NPY overexpression at this time point was also suggested by enhanced NPY mRNA expression seen in the amygdala 4 days postinjection using real-time polymerase chain reaction analysis. Experiment 2 was conducted to provide further evidence for a role of amygdalar NPY in regulating anxiety-related behaviors in the elevated plus maze test. The nonpeptide NPY Y1 receptor antagonist, BIBP 3226 (1.5 microg/microl), was bilaterally injected into the amygdala and rats were tested in the elevated plus maze test. Rats receiving BIBP 3226 exhibited increased anxiety-related behaviors in this test. The results of these experiments provide further support for the role of amygdalar NPY in anxiety-related behaviors.

The therapeutic potential of CRF1 antagonists for anxiety

Preclinical studies suggest that the brain corticotropin-releasing factor (CRF) systems mediate anxiety-like behavioural and somatic responses through actions at the CRF1 receptor. CRF1 antagonists block the anxiogenic-like effects of CRF and stress in animal models. Cerebrospinal fluid levels of CRF are elevated in some anxiety disorders and normalise with effective treatment, further implicating CRF systems as a therapeutic target. Prototypical CRF1 antagonists are highly lipophilic, non-competitive antagonists of peptide ligands. Modification of the chemotype and the identification of novel pharmacophores are yielding more drug-like structures with increased hydrophilicity at physiological pHs. Newer compounds exhibit improved solubility, pharmacokinetic properties, potency and efficacy. Several clinical candidates have entered Phase I/II trials. However, unmet challenges await resolution during further discovery, clinical development and therapeutic application of CRF1 antagonists.

Effects of the traditional Japanese medicine Unkei-to on the corticotropin-releasing factor-induced increase in locomotor activity

The effect of Unkei-to, a traditional Japanese herbal medicine and strong in vitro releaser of cytokine-induced neutrophil chemoattractant (CINC), on the increase in locomotor activity induced by intracerebroventricular (icv) injection of corticotropin-releasing factor (CRF) in male rats in a familiar environment was investigated. Oral administration of Unkei-to (100 mg/kg) for 1 week significantly attenuated the CRF-induced increase in locomotor activity. Unkei-to also reduced the CRF-induced accumulation of hypothalamic CINC, which has a functional antagonistic action on the response to CRF; the reduction may reflect an increased release of CINC. These results suggest that Unkei-to has an alleviative effect on the action induced by brain CRF and the mechanism of this effect may partly involve CINC.

Effects of neuropeptide Y and corticotropin-releasing factor on ethanol intake in Wistar rats: interaction with chronic ethanol exposure

Neuropeptide Y (NPY) and corticotropin-releasing factor (CRF) have opposing effects on stress-associated and consummatory behaviors in rodents. Recent studies also suggest that both peptides influence ethanol intake. In the present study, the effects of administration of CRF and NPY into the lateral ventricle on ethanol intake in naive and ethanol-vapor-exposed Wistar rats were examined. A limited access paradigm was used to measure intake of a 10% (v/v) ethanol solution in Wistar rats trained to drink using a sucrose fading procedure. Ethanol vapor exposure for 8 weeks significantly elevated ethanol intake in this limited access paradigm relative to pre-exposure levels. The effects of icv administration of CRF (1 microg), NPY (10 microg) or NPY/CRF combined (10 and 1 microg, respectively) on ethanol intake were then assessed. In non-vapor-exposed subjects, icv infusion of NPY had no effect on ethanol intake, while a significant suppression of drinking was seen following icv administration of CRF. Administration of NPY in combination with CRF had no effect on ethanol intake in non-ethanol-vapor-exposed rats. In vapor-exposed subjects, both NPY and CRF reduced ethanol intake, but when given in combination, no difference from vehicle was detected. Locomotor activity was measured during drinking sessions and was unaffected by peptide administration. These studies underscore the importance of a history of exposure to chronic ethanol vapor in the regulation of ethanol intake by NPY. Furthermore, the results presented here suggest that a balance between the stress-related peptides NPY and CRF may be involved in the regulation of ethanol intake.

Neuropeptides in anxiety modulation

This review is focused on the involvement of neuropeptides in the modulation of physiological and pathological anxiety. Neuropeptides play a major role as endogenous modulators of complex behaviours, including anxiety-related behaviour and psychopathology, particularly due to their high number and diversity, the dynamics of release patterns in distinct brain areas and the multiple and variable modes of interneuronal communication they are involved in. Manipulations of central neuropeptidergic systems to reveal their role in anxiety (and often comorbid depression-like behaviour) include a broad spectrum of loss-of-function and gain-of-function approaches. This article concentrates on those neuropeptides for which an involvement as endogenous anxiolytic or anxiogenic modulators is well established by such complementary approaches. Particular attention is paid to corticotropin-releasing hormone (CRH) and vasopressin (AVP) which, closely linked to stress, neuroendocrine regulation, social behaviour and learning/memory, play critical roles in the regulation of anxiety-related behaviour of rodents. Provided that their neurobiology, neuroendocrinology and molecular-genetic background are well characterized, these and other neuropeptidergic systems may be promising targets for future anxiolytic strategies.