Distribution of neuropeptide Y-like immunoreactivity in the rat central nervous system--I. Radioimmunoassay and chromatographic characterisation

Role of differential food treatment on hypothalamic NPY expression and migratory phenology of redheaded bunting (Emberiza bruniceps)

The present study explores the effect of differential food treatment on the migratory phenology of redheaded bunting (Emberiza bruniceps). Birds were divided into four groups (N = 10 each) on the basis of the food provided. Group I was fed with seeds of Setaria italica (kakuni), while group II was provided with protein-rich diet (combination of; 3 parts egg white and 1 part kakuni seeds). Likewise, group III birds received fat-rich food (i.e. 3 parts sesame seeds and 1 part kakuni seeds). Birds in group IV were provided with all three food items mentioned above separately. The experiment continued until the appearance of 7 cycles of zugunruhe. The results reveal a significant impact of food on locomotor activity and food intake behavior of birds, although the physiological response as demonstrated by a gain in body mass, fat score, and gonadal recrudescence was mainly influenced by the LHS. Besides the behavioral and physiological responses, the hypothalamic expression of neuropeptide Y (NPY) in infundibular complex (INc) was significantly high for group IV, highlighting the importance of "variety" in food intake. Thus, the present study suggests a significant role of food in influencing seasonal responses via hypothalamic NPY stimulation.

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

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

The Periaqueductal Gray and Its Extended Participation in Drug Addiction Phenomena

The periaqueductal gray (PAG) is a complex mesencephalic structure involved in the integration and execution of active and passive self-protective behaviors against imminent threats, such as immobility or flight from a predator. PAG activity is also associated with the integration of responses against physical discomfort (e.g., anxiety, fear, pain, and disgust) which occurs prior an imminent attack, but also during withdrawal from drugs such as morphine and cocaine. The PAG sends and receives projections to and from other well-documented nuclei linked to the phenomenon of drug addiction including: (i) the ventral tegmental area; (ii) extended amygdala; (iii) medial prefrontal cortex; (iv) pontine nucleus; (v) bed nucleus of the stria terminalis; and (vi) hypothalamus. Preclinical models have suggested that the PAG contributes to the modulation of anxiety, fear, and nociception (all of which may produce physical discomfort) linked with chronic exposure to drugs of abuse. Withdrawal produced by the major pharmacological classes of drugs of abuse is mediated through actions that include participation of the PAG. In support of this, there is evidence of functional, pharmacological, molecular. And/or genetic alterations in the PAG during the impulsive/compulsive intake or withdrawal from a drug. Due to its small size, it is difficult to assess the anatomical participation of the PAG when using classical neuroimaging techniques, so its physiopathology in drug addiction has been underestimated and poorly documented. In this theoretical review, we discuss the involvement of the PAG in drug addiction mainly via its role as an integrator of responses to the physical discomfort associated with drug withdrawal.

The Role of Neuropeptide Y in the Nucleus Accumbens

Neuropeptide Y (NPY), an abundant peptide in the central nervous system, is expressed in neurons of various regions throughout the brain. The physiological and behavioral effects of NPY are mainly mediated through Y1, Y2, and Y5 receptor subtypes, which are expressed in regions regulating food intake, fear and anxiety, learning and memory, depression, and posttraumatic stress. In particular, the nucleus accumbens (NAc) has one of the highest NPY concentrations in the brain. In this review, we summarize the role of NPY in the NAc. NPY is expressed principally in medium-sized aspiny neurons, and numerous NPY immunoreactive fibers are observed in the NAc. Alterations in NPY expression under certain conditions through intra-NAc injections of NPY or receptor agonists/antagonists revealed NPY to be involved in the characteristic functions of the NAc, such as alcohol intake and drug addiction. In addition, control of mesolimbic dopaminergic release via NPY receptors may take part in these functions. NPY in the NAc also participates in fat intake and emotional behavior. Accumbal NPY neurons and fibers may exert physiological and pathophysiological actions partly through neuroendocrine mechanisms and the autonomic nervous system.

Current views on neuropeptides in atopic dermatitis

Atopic dermatitis (AD) is a chronic inflammatory skin disease involving skin barrier dysfunction and immune imbalance. However, the mechanism of AD is not clear completely and may be related to heredity and environment. Neuropeptides are a class of peptides secreted by nerve endings, they may play roles in promoting vasodilation, plasma extravasation, chemotaxis of inflammatory cells and mediating pruritus. Since itching and immune cell infiltration are the main manifestations of atopic dermatitis, to further investigate the impact of neuropeptides on AD, our review summarized the mechanisms of several common neuropeptides in AD and hypothesized that neuropeptides may be the novel potential targets in AD treatment.

The Emerging Role of Neuropeptides in Parkinson's Disease

Parkinson’s disease (PD), the second most common age-related neurodegenerative disease, results from the loss of dopamine neurons in the substantia nigra. This disease is characterized by cardinal non-motor and motor symptoms. Several studies have demonstrated that neuropeptides, such as ghrelin, neuropeptide Y, pituitary adenylate cyclase-activating polypeptide, substance P, and neurotensin, are related to the onset of PD. This review mainly describes the changes in these neuropeptides and their receptors in the substantia nigra-striatum system as well as the other PD-related brain regions. Based on several in vitro and in vivo studies, most neuropeptides play a significant neuroprotective role in PD by preventing caspase-3 activation, decreasing mitochondrial-related oxidative stress, increasing mitochondrial biogenesis, inhibiting microglial activation, and anti-autophagic activity. Thus, neuropeptides may provide a new strategy for PD therapy.

Shifting motivational states: The effects of nucleus accumbens dopamine and opioid receptor activation on a modified effort-based choice task

The nucleus accumbens (NAc) is critical for regulating the appetitive and consummatory phases of motivated behavior. These experiments examined the effects of dopamine and opioid receptor manipulations within the NAc during an effort-based choice task that allowed for simultaneous assessment of both phases of motivation. Male Sprague-Dawley rats received bilateral guide cannulas targeting the NAc core and were tested in 1-hr sessions with free access to rat chow and the choice to work for sugar pellets on a progressive ratio 2 (PR2) reinforcement schedule. Individual groups of rats were tested following stimulation or blockade of NAc D1-like or D2-like receptors, stimulation of μ-, δ-, or κ-opioid receptors, or antagonism of opioid receptors. Behavior was examined under ad libitum conditions and following 23-h food restriction. NAc blockade of the D1-like receptors or stimulation of the D2 receptor reduced break point for earning sugar pellets; D2 receptor stimulation also modestly lowered chow intake. NAc μ-opioid receptor stimulation increased intake of the freely-available chow while simultaneously reducing break point for the sugar pellets. In non-restricted conditions, δ-opioid receptor stimulation increased both food intake and breakpoint. There were no effects of stimulating NAc D1 or κ receptors, nor did blocking D2 or opioid receptors affect task behavior. These data support prior literature linking dopamine to appetitive motivational processes, and suggest that μ- and δ-opioid receptors affect food-directed motivation differentially. Specifically, μ-opioid receptors shifted behavior towards consumption, and δ-opioid receptor enhanced both sugar-seeking and consumption of the pabulum chow when animals were not food restricted.

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

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

Spatial and temporal immunoreactivity in the rat brain using an affinity purified polyclonal antibody to DNSP-11

DNSP-11 antibody signal was investigated in perfusion fixated Fischer 344 rat brains by immunohistochemistry with a custom, affinity purified polyclonal antibody. The DNSP-11-antibody signal was differentially localized from the mature GDNF protein both spatially and temporally. In the mesencephalon of post-natal day 10 animals, when GDNF is maximally expressed, DNSP-11 and GDNF antibody immunoreactivities co-localize extensively but not exclusively. In adult 3-month-old animals, GDNF expression is markedly reduced while the DNSP-11 signal remains intense. DNSP-11-antibody signal was present in the 3-month-old rat brain with signal in the substantia nigra, ventral tegmental area, dentate gyrus of the hippocampus, with the strongest signal observed in the locus ceruleus where GDNF is not expressed. While amino acid sequence homologues such as NPY and Tfg do exist, binding patterns reported in the literature of do not recapitulate the immunoreactive patterns observed for the DNSP-11-antibody signal.

Afferent neuropeptide Y projections to the ventral tegmental area in normal-weight male Wistar rats

The hypothalamic neuropeptide Y (NPY) circuitry is a key regulator of feeding behavior. NPY also acts in the mesolimbic dopaminergic circuitry, where it can increase motivational aspects of feeding behavior through effects on dopamine output in the nucleus accumbens (NAc) and on neurotransmission in the ventral tegmental area (VTA). Endogenous NPY in the NAc originates from local interneurons and afferent projections from the hypothalamic arcuate nucleus (Arc). However, the origin of endogenous NPY in the VTA is unknown. We determined, in normal‐weight male Wistar rats, if the source of VTA NPY is local, and/or whether it is derived from VTA‐projecting neurons. Immunocytochemistry, in situ hybridization and RT‐qPCR were utilized, when appropriate in combination with colchicine treatment or 24 hr fasting, to assess NPY/Npy expression locally in the VTA. Retrograde tracing using cholera toxin beta (CTB) in the VTA, fluorescent immunocytochemistry and confocal microscopy were used to determine NPY‐immunoreactive afferents to the VTA. NPY in the VTA was observed in fibers, but not following colchicine pretreatment. No NPY‐ or Npy‐expressing cell bodies were observed in the VTA. Fasting for 24 hr, which increased Npy expression in the Arc, failed to induce Npy expression in the VTA. Double‐labeling with CTB and NPY was observed in the Arc and in the ventrolateral medulla. Thus, VTA NPY originates from the hypothalamic Arc and the ventrolateral medulla of the brainstem in normal‐weight male Wistar rats. These afferent connections link hypothalamic and brainstem processing of physiologic state to VTA‐driven motivational behavior.

Neuropeptide systems and new treatments for nicotine addiction

RATIONALE

The mildly euphoric and cognitive enhancing effects of nicotine play a role in the initiation of smoking, while dysphoria and anxiety associated with smoking cessation contribute to relapse. After the acute withdrawal phase, smoking cues, a few cigarettes (i.e., lapse), and stressors can cause relapse. Human and animal studies have shown that neuropeptides play a critical role in nicotine addiction.

OBJECTIVES

The goal of this paper is to describe the role of neuropeptide systems in the initiation of nicotine intake, nicotine withdrawal, and the reinstatement of extinguished nicotine seeking.

RESULTS

The reviewed studies indicate that several drugs that target neuropeptide systems diminish the rewarding effects of nicotine by preventing the activation of dopaminergic systems. Other peptide-based drugs diminish the hyperactivity of brain stress systems and diminish withdrawal-associated symptom severity. Blockade of hypocretin-1 and nociceptin receptors and stimulation of galanin and neurotensin receptors diminishes the rewarding effects of nicotine. Both corticotropin-releasing factor type 1 and kappa-opioid receptor antagonists diminish dysphoria and anxiety-like behavior associated with nicotine withdrawal and inhibit stress-induced reinstatement of nicotine seeking. Furthermore, blockade of vasopressin 1b receptors diminishes dysphoria during nicotine withdrawal, and melanocortin 4 receptor blockade prevents stress-induced reinstatement of nicotine seeking. The role of neuropeptide systems in nicotine-primed and cue-induced reinstatement is largely unexplored, but there is evidence for a role of hypocretin-1 receptors in cue-induced reinstatement of nicotine seeking.

CONCLUSION

Drugs that target neuropeptide systems might decrease the euphoric effects of smoking and improve relapse rates by diminishing withdrawal symptoms and improving stress resilience.

Neuropeptide Y Y5 receptor localization in mouse central nervous system

Neuropeptide Y (NPY) and its receptors affect blood pressure, feeding behavior, and neurogenesis. In this study, the distribution of neurons expressing NPY Y₅ receptor (Y₅) was examined in adult mouse central nervous system by immunohistochemistry. Y₅ protein localization was investigated using polyclonal anti-Y₅ antibody, which was successfully preabsorbed with Y₅ knockout brain tissues. The preabsorbed anti-Y₅ antibody did not react with Y₅ knockout brain tissues, thus meeting the "hard specificity criterion," which is the absence of staining in tissues genetically deficient for the antigen (Pradidarcheep et al., 2008). Y₅-positive neurons were found in most brain areas. Most Y₅ immunoreactivities were observed as dot-like structures adjacent to the plasma membrane, as expected for a cell membrane receptor. In situ hybridization showed that the Y₅ mRNA expression was correlated with the Y₅ protein level in each case and that it was probably controlled by the transcriptional regulation of the Y₅ gene. In the nuclei where Y₅ was expressed, Y₅ immunoreactivities were found mainly in the somatic and dendritic areas. The distribution patterns of the Y₅-positive cells that were broader than previously expected suggest important biological activities of the Y₅ in many brain areas.

Neuropeptide Y (NPY) as a therapeutic target for neurodegenerative diseases

Neuropeptide Y (NPY) and NPY receptors are widely expressed in the mammalian central nervous system. Studies in both humans and rodent models revealed that brain NPY levels are altered in some neurodegenerative disorders, such as Alzheimer's disease, Parkinson's disease, Huntington's disease and Machado-Joseph disease. In this review, we will focus on the roles of NPY in the pathological mechanisms of these disorders, highlighting NPY as a neuroprotective agent, as a neural stem cell proliferative agent, as an agent that increases trophic support, as a stimulator of autophagy and as an inhibitor of excitotoxicity and neuroinflammation. Moreover, the effect of NPY in some clinical manifestations commonly observed in Alzheimer's disease, Parkinson's disease, Huntington's disease and Machado-Joseph disease, such as depressive symptoms and body weight loss, are also discussed. In conclusion, this review highlights NPY system as a potential therapeutic target in neurodegenerative diseases.

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

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

The role of NPY in learning and memory

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

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.

Aging and long-term caloric restriction regulate neuropeptide Y receptor subtype densities in the rat brain

The effects of aging and long-term caloric restriction (LTCR), on the regulation of neuropeptide Y (NPY) Y1, Y2 and Y5 receptors subtypes, was studied in 20-month-old male rats fed ad libitum (AL) or submitted to a 40% caloric restriction for 12 months. [(125)I]GR231118, a Y1 antagonist was used as Y1 receptor radioligand. [(125)I][Leu(31), Pro(34)]PYY, a high affinity agonist of Y1 and Y5 subtypes was used in the absence or presence of 100 nM BIBO3304 (a highly selective Y1 receptor antagonist) to assess the apparent levels of [(125)I][Leu(31), Pro(34)]PYY/BIBO3304 insensitive sites (Y5-like) from [(125)I][Leu(31), Pro(34)]PYY/BIBO3304 sensitive sites (Y1). [(125)I]PYY(3-36) was used to label the Y2 receptor. In the brain of 3-month-old AL rats, the distribution and densities of Y1, Y2 and Y5 receptors were in agreement with previous reports. In the brain of 20AL rats, a decrease of NPY receptor subtype densities in regions having important physiological functions such as the cingulate cortex, hippocampus and dentate gyrus, thalamus and hypothalamus was observed. In contrast, LTCR had multiple effects. It induced specific decreases of Y1-receptor densities in the dentate gyrus, thalamic and hypothalamic nuclei and lateral hypothalamic area and Y2-receptor densities in the suprachiasmatic nucleus of hypothalamus. Moreover, it prevented the age-induced increase in Y1-receptor densities in the ventromedial hypothalamic nucleus and decrease in the mediodorsal thalamic nucleus, and increased Y2-receptor densities in the CA2 subfield of the hippocampus. These results indicate that LTCR not only counteracts some of the deleterious effects of aging on NPY receptor subtype densities but exerts specific effects of its own. The overall impact of the regulation of NPY receptor subtypes in the brain of old calorie-restricted rats may protect the neural circuits involved in pain, emotions, feeding and memory functions.

Neuropeptide Y modulation of interleukin-1{beta} (IL-1{beta})-induced nitric oxide production in microglia

Given the modulatory role of neuropeptide Y (NPY) in the immune system, we investigated the effect of NPY on the production of NO and IL-1β in microglia. Upon LPS stimulation, NPY treatment inhibited NO production as well as the expression of inducible nitric-oxide synthase (iNOS). Pharmacological studies with a selective Y(1) receptor agonist and selective antagonists for Y(1), Y(2), and Y(5) receptors demonstrated that inhibition of NO production and iNOS expression was mediated exclusively through Y(1) receptor activation. Microglial cells stimulated with LPS and ATP responded with a massive release of IL-1β, as measured by ELISA. NPY inhibited this effect, suggesting that it can strongly impair the release of IL-1β. Furthermore, we observed that IL-1β stimulation induced NO production and that the use of a selective IL-1 receptor antagonist prevented NO production upon LPS stimulation. Moreover, NPY acting through Y(1) receptor inhibited LPS-stimulated release of IL-1β, inhibiting NO synthesis. IL-1β activation of NF-κB was inhibited by NPY treatment, as observed by confocal microscopy and Western blotting analysis of nuclear translocation of NF-κB p65 subunit, leading to the decrease of NO synthesis. Our results showed that upon LPS challenge, microglial cells release IL-1β, promoting the production of NO through a NF-κB-dependent pathway. Also, NPY was able to strongly inhibit NO synthesis through Y(1) receptor activation, which prevents IL-1β release and thus inhibits nuclear translocation of NF-κB. The role of NPY in key inflammatory events may contribute to unravel novel gateways to modulate inflammation associated with brain pathology.

Involvement of neuropeptide Y in the acute, chronic and withdrawal responses of morphine in nociception in neuropathic rats: behavioral and neuroanatomical correlates

Although morphine is a potent antinociceptive agent, its chronic use developed tolerance in neuropathic pain (NP). Furthermore, opioid antagonist naloxone attenuated the antinociceptive effect of neuropeptide Y (NPY). The present study investigated the role of NPY and NPY Y1/Y5 receptors in acute and chronic actions of morphine in neuropathic rats using thermal paw withdrawal test and immunocytochemistry. In acute study, intracerebroventricular (icv) administration of morphine, NPY or NPY Y1/Y5 receptors agonist [Leu(31),Pro(34)]-NPY produced antinociception, whereas selective NPY Y1 receptors antagonist BIBP3226 caused hyperalgesia. While NPY or [Leu(31),Pro(34)]-NPY potentiated, BIBP3226 attenuated morphine induced antinociception. Chronic icv infusion of morphine via osmotic minipumps developed tolerance to its antinociceptive effect, and produced hyperalgesia following withdrawal. However, co-administration of NPY or [Leu(31),Pro(34)]-NPY prevented the development of tolerance and withdrawal hyperalgesia. Sciatic nerve ligation resulted in significant increase in the NPY-immunoreactive (NPY-ir) fibers in ventrolateral periaqueductal gray (VLPAG) and locus coeruleus (LC); fibers in the dorsal part of dorsal raphe nucleus (DRD) did not respond. While chronic morphine treatment significantly reduced NPY-ir fibers in VLPAG and DRD, morphine withdrawal triggered significant augmentation in NPY-immunoreactivity in the VLPAG. NPY-immunoreactivity profile of LC remained unchanged in all the morphine treatment conditions. Furthermore, removal of sciatic nerve ligation reversed the effects of NP, increased pain threshold and restored NPY-ir fiber population in VLPAG. NPY, perhaps acting via Y1/Y5 receptors, might profoundly influence the processing of NP information and interact with the endogenous opioid system primarily within the framework of the VLPAG.

Neuropeptide Y modulates the antidepressant activity of imipramine in olfactory bulbectomized rats: involvement of NPY Y1 receptors

Since long-term treatment with imipramine increases the neuropeptide Y (NPY) levels in the frontal cortex and hypothalamus, the possibility exists that the antidepressant action of imipramine may be mediated via the NPY Y1 receptors. Bilateral olfactory bulbectomy (OBX) resulted in hyperactivity (increased number of ambulation, rearing and grooming episodes) in open field test (OFT) suggesting a depression-like condition. Chronic (14 days) administration of NPY, NPY Y1/Y5 receptor agonist [Leu(31), Pro(34)]-NPY (intracerebroventricular, i.c.v.) or tricyclic antidepressant imipramine (intraperitoneal) to OBX rats dose-dependently resulted in decreased hyperactivity in OFT, while selective NPY Y1 receptor antagonist BIBP3226 (i.c.v.) produced opposite effects. The antidepressant actions of imipramine were enhanced by co-administration of NPY or [Leu(31), Pro(34)]-NPY, and antagonized by BIBP3226 given at sub-effective doses. The data suggest that NPY, acting via NPY Y1 receptors, may be involved in antidepressant action of imipramine in OBX rats.

Regulation of maternal food intake and mother-pup interactions by the Y5 receptor

Neuropeptide Y (NPY) is increased in the hypothalamus during lactation. To investigate the role of the NPY Y5 receptor during lactation, an antisense oligodeoxynucleotide (ODN) targeted to the NPY Y5 receptor, an equivalent scrambled ODN or vehicle, was chronically infused into the 3rd ventricle of lactating rats from day 8 postpartum. Y5 antisense ODN treatment reduced Y5 positive cell number in the paraventricular nucleus and resulted in significant reductions in food intake and litter growth. Litters from pair-fed vehicle treated dams gained significantly more weight than the litters of Y5 antisense ODN treated dams suggesting that decreased maternal food intake is not the only mechanism involved in suppressing litter weight gain. When mother-litter interaction was examined on day 13 pp, Y5 antisense ODN treated dams spent significantly less time on the nest and had significantly shorter nest bouts. These results suggest that in addition to regulating feeding behaviour, the Y5 receptor subtype may have previously unrecognised roles in the control of nesting behaviour during lactation with subsequent effects on litter growth rates.

The neuropeptide Y Y1 receptor subtype is necessary for the anxiolytic-like effects of neuropeptide Y, but not the antidepressant-like effects of fluoxetine, in mice

RATIONALE

Neuropeptide Y (NPY) is implicated in the pathophysiology of affective illness. Multiple receptor subtypes (Y1R, Y2R, and Y5R) have been suggested to contribute to NPY's effects on rodent anxiety and depression-related behaviors.

OBJECTIVES

To further elucidate the role of Y1R in (1) NPY's anxiolytic-like effects and (2) fluoxetine's antidepressant-like and neurogenesis-inducing effects.

METHODS

Mice lacking Y1R were assessed for spontaneous anxiety-like behavior (open field, elevated plus-maze, and light/dark exploration test) and Pavlovian fear conditioning, and for the anxiolytic-like effects of intracerebroventricularly (icv)-administrated NPY (elevated plus-maze). Next, Y1R -/- were assessed for the antidepressant-like effects of acute fluoxetine in the forced swim test and chronic fluoxetine in the novelty-induced hypophagia test, as well as for chronic fluoxetine-induced hippocampal neurogenesis.

RESULTS

Y1R -/- exhibited largely normal baseline behavior as compared to +/+ littermate controls. Intraventricular administration of NPY in Y1R -/- mice failed to produce the normal anxiolytic-like effect in the elevated plus-maze test seen in +/+ mice. Y1R mutant mice showed higher immobility in the forced swim test and longer latencies in the novelty-induced hypophagia test. In addition, Y1R -/- mice responded normally to the acute and chronic effects of fluoxetine treatment in the forced swim test and the novelty-induced hypophagia test, respectively, as well as increased neuronal precursor cell proliferation in the hippocampus.

CONCLUSIONS

These data demonstrate that Y1R is necessary for the anxiolytic-like effects of icv NPY, but not for the antidepressant-like or neurogenesis-inducing effects of fluoxetine. The present study supports targeting Y1R as a novel therapeutic target for anxiety disorders.

Morphological characterization of electrophysiologically and immunohistochemically identified basal forebrain cholinergic and neuropeptide Y-containing neurons

The basal forebrain (BF) contains cholinergic as well as different types of non-cholinergic corticopetal neurons and interneurons, including neuropeptide Y (NPY) containing cells. BF corticopetal neurons constitute an extrathalamic route to the cortex and their activity is associated with an increase in cortical release of the neurotransmitter acetylcholine, concomitant with low voltage fast cortical EEG activity. It has been shown in previous studies (Duque et al. in J Neurophysiol 84:1627-1635, 2000) that in anesthetized rats BF cholinergic neurons fire mostly during low voltage fast cortical EEG epochs, while increased NPY neuronal firing is accompanied by cortical slow waves. In this paper, electrophysiologically and neurochemically characterized cholinergic and NPY-containing neurons were 3D reconstructed from serial sections and morphometrically analyzed. Cholinergic and NPY-containing neurons, although having roughly the same dendritic surface areas and lengths, were found to differ in dendritic thickness and branching structure. They also have distinct patterns of dendritic endings. The subtle differences in dendritic arborization pattern may have an impact on how synaptic integration takes place in these functionally distinct neuronal populations. Cholinergic neurons exhibited cortically projecting axons and extensive local axon collaterals. Elaborate local axonal arbors confined to the BF also originated from NPY-containing neurons. The presence of local axon collaterals in both cholinergic and NPY neurons indicates that the BF is not a mere conduit for various brainstem inputs to the cortex, but a site where substantial local processing must take place.

Characterization of neuropeptide Y2 receptor protein expression in the mouse brain. I. Distribution in cell bodies and nerve terminals

Neuropeptide Y (NPY), a 36-amino-acid peptide, mediates biological effects by activating Y1, Y2, Y5, and y6 receptors. NPY neurons innervate many brain regions, including the hypothalamus, where NPY is involved in regulation of a broad range of homeostatic functions. We examined, by immunohistochemistry with tyramide signal amplification, the expression of the NPY Y2 receptor (Y2R) in the mouse brain with a newly developed rabbit polyclonal antibody. Y2R immunoreactivity was specific with its absence in Y2R knockout (KO) mice and in adjacent sections following preadsorption with the immunogenic peptide (10(-5) M). Y2R-positive processes were located in many brain regions, including the olfactory bulb, some cortical areas, septum, basal forebrain, nucleus accumbens, amygdala, hippocampus, hypothalamus, substantia nigra compacta, locus coeruleus, and solitary tract nucleus. However, colchicine treatment was needed to detect Y2R-like immunoreactivity in cell bodies in many, but not all, areas. The densest distributions of cell bodies were located in the septum basal forebrain, including the bed nucleus, and amygdala, with lower density in the anterior olfactory nucleus, nucleus accumbens, caudal striatum, CA1, CA2, and CA3 hippocampal fields, preoptic nuclei lateral hypothalamus, and A13 DA cells. The widespread distribution of Y2R-positive cell bodies and fibers suggests that NPY signaling through the Y2R is common in the mouse brain. Localization of the Y2R suggests that it is mostly presynaptic, a view supported by its frequent absence in cell bodies in the normal mouse and its dramatic increase in cell bodies of colchicine-treated mice.

BODIPY-conjugated neuropeptide Y ligands: new fluorescent tools to tag Y1, Y2, Y4 and Y5 receptor subtypes

N-terminal labelled fluorescent BODIPY-NPY peptide analogues were tested in Y1, Y2, Y4 and Y5 receptor-binding assays performed in rat brain membrane preparations and HEK293 cells expressing the rat Y1, Y2, Y4 and Y5 receptors. BODIPY TMR/FL-[Leu31, Pro34]NPY/PYY were able to compete for specific [125][Leu31, Pro34]PYY-binding sites with an affinity similar to that observed for the native peptide at the Y1 (Ki=1-6 nM), Y2 (Ki>1000 nM), Y4 (Ki=10 nM) and Y5 (Ki=1-4 nM) receptor subtypes. BODIPY FL-PYY(3-36) was able to compete for specific Y2 (Ki=10 nM) and Y5 (Ki=30 nM) binding sites, but had almost no affinity in Y1 and Y4 assays. BODIPY FL-hPP was able to compete with high affinity (Ki; 1 and 15 nM) only in Y4 and Y5 receptor-binding assays. BODIPY TMR-[cPP(1-7), NPY(19-23), Ala31, Aib32, Gln34]hPP and BODIPY TMR-[hPP(1-17), Ala31, Aib32]NPY were potent competitors only on specific Y5-binding sites (Ki=0.1-0.6 nM). As expected, these fluorescent peptides inhibited forskolin-induced cAMP accumulation, demonstrating that they retained their agonist properties. When tested in confocal microscopy imaging, fluorescent Y1 and Y5 agonists internalized in a time-dependent manner in Y1 and Y5 transfected cells, respectively. These results demonstrate that BODIPY-conjugated NPY analogues retain their selectivity, affinity and agonist properties for the Y1, Y2, Y4 and Y5 receptor subtypes, respectively. Thus, they represent novel tools to study and visualize NPY receptors in living cells.

Alterations in striatal neuropeptide Y system activity of rats with haloperidol-induced behavioral supersensitivity

The study was conducted to determine whether the expression of behavioral supersensitivity induced by haloperidol (HAL) administered once daily (2 mg/kg i.p.) for 14 days is associated with the alterations in activity of neuropeptide Y (NPY) system in the striatum (caudate-putamen) and nucleus accumbens. Dopamine supersensitivity was tested by measurement of locomotor activity and stereotyped behavior after administration of the dopamine D2/D3 receptor agonist quinpirole (1 mg/kg i.p.) on day 1, 3 and 7 after HAL withdrawal. Neuropeptide Y-like immunoreactivity (NPY-LI) was determined in the striatum and nucleus accumbens isolated 6 h after quinpirole injection on day 1, 3 and 7 after the end of HAL treatment. NPY mRNA was quantified in these structures on day 7 after HAL withdrawal. HAL increased spontaneous locomotor activity and prevalence of rearing, grooming and head-down sniffing. At the same time, striatal NPY-LI increased progressively from the reduced level found on day 1 of haloperidol withdrawal. NPY mRNA remained unchanged. In saline-treated rats, quinpirole enhanced locomotion, rearing, and induced intense head-down sniffing and oral activity. These behavioral effects were accompanied by a decrease in striatal NPY-LI. NPY mRNA was slightly increased. HAL treatment altered response to quinpirole, namely it increased locomotion, intensified oral activity and reduced rearing and head-down sniffing. The second and the third quinpirole injection decreased NPY-LI levels. NPY mRNA was unchanged. In the nucleus accumbens, apart from a decrease in NPY-LI on day 1 after the last haloperidol dose, the level of NPY-LI and NPY mRNA in any experimental group did not differ from the control value. The presented results suggest that the alterations in the activity of the striatal but not nucleus accumbens NPY system contribute to adaptive changes induced by long-term haloperidol treatment and may be of significance to the motor hyperactivity induced by intermittent stimulation of postsynaptic dopamine D2 receptors.

Role of serotonin (5-HT) in the antidepressant-like properties of neuropeptide Y (NPY) in the mouse forced swim test

Neuropeptide Y (NPY) is thought to be implicated in depressive disorders. The mouse forced swim test (FST) is an animal model widely used as a predictor of the efficacy of antidepressant drugs. The present study was undertaken to explore the possible contribution of endogenous serotonin (5-HT) systems in the behavioral effects elicited by NPY in this model. The selective serotonin re-uptake inhibitor (SSRI), fluoxetine, was also tested for comparison. 5-HT was depleted prior to testing by the administration of the tryptophan hydroxylase inhibitor p-chlorophenylalanine (PCPA; 300 mg/kg, i.p., each day for 3 days; control mice received saline-vehicle over the same period). On the fourth day, mice received NPY (3 nmol, I.C.V.), fluoxetine (16 mg/kg, i.p.) or saline injections before testing in the FST. Both NPY and fluoxetine significantly reduced immobility time in saline-treated control animals. Pre-treatment with PCPA significantly blocked the effects of fluoxetine in the FST, confirming the role of endogenous 5-HT. Similarly, pre-treatment with PCPA also significantly attenuated the anti-immobility effects of NPY, thus suggesting a role for 5-HT in the effects of NPY in the FST. Quantitative receptor autoradiography revealed increases in specific [125I][Leu31, Pro34]PYY sites that were sensitive to BIBP3226 (Y1-like sites) in various brain regions. Specific [125I]GR231118 and [125I]PYY(3-36) binding levels were not changed following PCPA treatment, suggesting that depletion of endogenous 5-HT resulted in an apparent increase in the level of Y1 sites in their high-affinity state. Taken together, these results suggest a role for 5-HT-related systems in the antidepressant-like properties of NPY.

Estrogen induces a rapid increase in galanin levels in female rat hippocampal formation − possibly a nongenomic/indirect effect

Administration of 17beta-estradiol to ovariectomized rats increased the concentrations of galanin-like immunoreactivity (LI) in the hippocampal formation by 215% (P < 0.001) within 1 h. An increase of 125% (P < 0.05) was observed in the same brain region in the proestrous phase of a normal estrous cycle. Tamoxifen did not block the 17beta-estradiol-induced increase in the concentration of galanin-LI but resulted in a 62% decrease in the hypothalamus within 1 h. In vivo microdialysis in the dorsal hippocampal formation showed a decrease of extracellular galanin-LI (P < 0.001) 1-2 h after treatment with 17beta-estradiol, indicating a decreased release of galanin. For comparison, we studied the concentrations of neuropeptide Y, which were not influenced significantly in any of the regions studied. Taken together our results suggest that 17beta-estradiol inhibits galanin release, presumably from noradrenergic nerve terminals, and primarily via a nongenomic/indirect action, not necessarily involving the classical nuclear receptors ER-alpha or ER-beta. These rapid estrogen-induced changes in galanin release could influence transmitter signalling and plasticity in the hippocampal formation.

Anxiolytic-like actions of centrally-administered neuropeptide Y, but not galanin, in C57BL/6J mice

Neuropeptide Y (NPY) and galanin (GAL) are densely localized in brain regions subserving stress, fear and anxiety. While previous research supports a role for both neuropeptides in the mediation of rodent emotional behaviors, there is currently a lack of information on the effects of central administration of NPY and GAL on fear- and anxiety-related behaviors in mice. In the present study, the effects of intracerebroventricularly administered NPY and GAL were assessed in C57BL/6J mice on a battery of tests for fear- and anxiety-related behavior. NPY (0.5, 1.0 nmol) produced clear anxiolytic-like effects in the elevated plus-maze and light<-->dark exploration test, whereas GAL (0.5, 1.0 nmol) was without effect. NPY (0.5 nmol) also increased locomotor activity in the open field test. In the fear conditioning paradigm, NPY administered prior to training reduced freezing to context (0.5, 1.0 nmol) and auditory cue (1.0 nmol). Pre-training GAL (0.5 nmol) treatment reduced freezing to context. Taken together, results demonstrate robust effects of centrally-administered NPY, but not GAL, on anxiety-like behaviors and fear conditioning in mice. These findings provide a basis for future studies of mice with targeted gene mutations, directed at delineating the anatomical regions and receptor subtypes mediating the effects of NPY and GAL on emotion.

Continuous exposure to brain-derived neurotrophic factor is required for persistent activation of TrkB receptor, the ERK signaling pathway, and the induction of neuropeptide Y production in cortical cultures

We have previously demonstrated that brain-derived neurotrophic factor (BDNF) induces persistent neuropeptide Y (NPY) production in cortical cultures in an ERK1/2-dependent manner. In some studies, it was shown that BDNF leads to the downregulation of TrkB receptor and some of its downstream responses, whereas in others it does not. We examined whether the BDNF requirement for induction of persistent NPY production correlates with that for induction of phosphorylation of TrkB and ERK1/2. Continuous 24-h exposure to BDNF led to a 2- to 3-fold increase in NPY production (maximal level). While 1 h of BDNF exposure induced NPY production at a half maximal level, 8 h was required for induction of a maximal level. BDNF-induced NPY production was completely inhibited by co-exposure to TrkB-Fc fusion protein (TrkB extracellular domain fused to Fc) and partially inhibited by TrkB-Fc added 1 h after BDNF; TrkC-Fc did not do so. Activation of TrkB receptor was analyzed at two potential tyrosine phosphorylated sites, the activation loop and the Shc binding. BDNF led to coordinated phosphorylation of the two sites that persisted for 6-8 h, and this was not associated with changes in the content of TrkB protein. The presence of BDNF throughout the 6- to 8-h period was required for the persistent phosphorylation of TrkB and ERK1/2. Thus, continuous BDNF activation of TrkB is required for persistent activation of the ERK1/2 pathway and induction of NPY production. We propose that, within the time frame analyzed in this study, BDNF does not lead to the downregulation of TrkB receptor or of the biological responses leading to NPY production.

Effect of a graded single constriction of the rat sciatic nerve on pain behavior and expression of immunoreactive NPY and NPY Y1 receptor in DRG neurons and spinal cord

In the present study, the rat sciatic nerve was constricted to varying degrees using only one ligature with a very thin polyethylene sheath placed between nerve and ligature thread. Complete nerve transection was studied for comparison. With a 40-80% constriction of the nerve we observed allodynia to a similar extent as in the so-called Bennett model based on four loose ligatures. We also monitored changes in the expression of neuropeptide Y (NPY) and the NPY Y1 receptor (Y1R) in the lumbar 4-5 dorsal root ganglia (DRG) and dorsal horn and found upregulation of NPY and downregulation of the Y1R in DRG neurons after injury. These results indicate that similar peptide and receptor changes occur in this model as after axotomy and in other nerve injury models, although the immunohistochemical and behavioral changes seem to be dependent on the degree of constriction of the nerve. Thus, it seems relevant to monitor the degree of constriction when evaluating pain and other post-injury events. The possibility that some of the changes in NPY-ergic neurotransmission are related to the generation of allodynia is discussed; as well as the possibility to use this mononeuropathic model based on a single ligature nerve constriction (SLNC) as a complementary approach to other widely used pain models.

Neuropeptide Y, ubiquitous and elusive

This paper reviews aspects of NPY research that were emerging in 1985, shortly after the isolation and characterization of the peptide. NPY had become known for its widespread distribution especially in the central and peripheral nervous systems, but also in the gastro-intestinal and respiratory tracts and in fibers innervating smooth muscle around blood vessels. Consistent with its distribution, it was determined that NPY is a potent vasoconstrictor, affects neuroendocrine systems and is involved in appetite regulation--areas of research still relevant today. Through advances in technology knowledge about NPY's role in these and newly discovered physiological functions has deepened considerably. Successful cloning of a series of NPY receptors has opened up new and complex research vistas. Lately, the creation of mice genetically modified for NPY as well as for several receptor subtypes has brought many puzzling observations--followed by questions yet to be answered.

Receptor autoradiography as mean to explore the possible functional relevance of neuropeptides: focus on new agonists and antagonists to study natriuretic peptides, neuropeptide Y and calcitonin gene-related peptides

Over the past 20 years, receptor autoradiography has proven most useful to provide clues as to the role of various families of peptides expressed in the brain. Early on, we used this method to investigate the possible roles of various brain peptides. Natriuretic peptide (NP), neuropeptide Y (NPY) and calcitonin (CT) peptide families are widely distributed in the peripheral and central nervous system and induced multiple biological effects by activating plasma membrane receptor proteins. The NP family includes atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP) and C-type natriuretic peptide (CNP). The NPY family is composed of at least three peptides NPY, peptide YY (PYY) and the pancreatic polypeptides (PPs). The CT family includes CT, calcitonin gene-related peptide (CGRP), amylin (AMY), adrenomedullin (AM) and two newly isolated peptides, intermedin and calcitonin receptor-stimulating peptide (CRSP). Using quantitative receptor autoradiography as well as selective agonists and antagonists for each peptide family, in vivo and in vitro assays revealed complex pharmacological responses and radioligand binding profile. The existence of heterogeneous populations of NP, NPY and CT/CGRP receptors has been confirmed by cloning. Three NP receptors have been cloned. One is a single-transmembrane clearance receptor (NPR-C) while the other two known as CG-A (or NPR-A) and CG-B (or NPR-B) are coupled to guanylate cyclase. Five NPY receptors have been cloned designated as Y(1), Y(2), Y(4), Y(5) and y(6). All NPY receptors belong to the seven-transmembrane G-protein coupled receptors family (GPCRs; subfamily type I). CGRP, AMY and AM receptors are complexes which include a GPCR (the CT receptor or CTR and calcitonin receptor-like receptor or CRLR) and a single-transmembrane domain protein known as receptor-activity-modifying-proteins (RAMPs) as well as an intracellular protein named receptor-component-protein (RCP). We review here tools that are currently available in order to target each NP, NPY and CT/CGRP receptor subtype and establish their respective pathophysiological relevance.

Extraction and radioimmunoassay quantitation of neuropeptide Y (NPY) and vasoactive intestinal polypeptide (VIP) from human dental pulp tissue

The measurement of neuropeptides in complex biological tissue samples requires efficient and appropriate extraction methods so that immunoreactivity is retained for subsequent radioimmunoassay detection. Since neuropeptides differ in their molecular mass, charge and hydrophobicity, no single method will suffice for the optimal extraction of various neuropeptides. In this study, dental pulp tissue was obtained from 30 human non-carious teeth. Of the three different neuropeptide extraction methods employed, boiling in acetic acid in the presence of protease inhibitors yielded the highest levels of neuropeptide Y (NPY) and vasoactive intestinal polypeptide (VIP). High pressure liquid chromatography (HPLC) analysis of dental pulp tissue verified the authenticity of the neuropeptides extracted.

Neuroendocrine pharmacology of stress

Exposure to hostile conditions initiates responses organized to enhance the probability of survival. These coordinated responses, known as stress responses, are composed of alterations in behavior, autonomic function and the secretion of multiple hormones. The activation of the renin-angiotensin system and the hypothalamic-pituitary-adrenocortical axis plays a pivotal role in the stress response. Neuroendocrine components activated by stressors include the increased secretion of epinephrine and norepinephrine from the sympathetic nervous system and adrenal medulla, the release of corticotropin-releasing factor (CRF) and vasopressin from parvicellular neurons into the portal circulation, and seconds later, the secretion of pituitary adrenocorticotropin (ACTH), leading to secretion of glucocorticoids by the adrenal gland. Corticotropin-releasing factor coordinates the endocrine, autonomic, behavioral and immune responses to stress and also acts as a neurotransmitter or neuromodulator in the amygdala, dorsal raphe nucleus, hippocampus and locus coeruleus, to integrate brain multi-system responses to stress. This review discussed the role of classical mediators of the stress response, such as corticotropin-releasing factor, vasopressin, serotonin (5-hydroxytryptamine or 5-HT) and catecholamines. Also discussed are the roles of other neuropeptides/neuromodulators involved in the stress response that have previously received little attention, such as substance P, vasoactive intestinal polypeptide, neuropeptide Y and cholecystokinin. Anxiolytic drugs of the benzodiazepine class and other drugs that affect catecholamine, GABA(A), histamine and serotonin receptors have been used to attenuate the neuroendocrine response to stressors. The neuroendocrine information for these drugs is still incomplete; however, they are a new class of potential antidepressant and anxiolytic drugs that offer new therapeutic approaches to treating anxiety disorders. The studies described in this review suggest that multiple brain mechanisms are responsible for the regulation of each hormone and that not all hormones are regulated by the same neural circuits. In particular, the renin-angiotensin system seems to be regulated by different brain mechanisms than the hypothalamic-pituitary-adrenal system. This could be an important survival mechanism to ensure that dysfunction of one neurotransmitter system will not endanger the appropriate secretion of hormones during exposure to adverse conditions. The measurement of several hormones to examine the mechanisms underlying the stress response and the effects of drugs and lesions on these responses can provide insight into the nature and location of brain circuits and neurotransmitter receptors involved in anxiety and stress.

Effects of haloperidol and clozapine on neuropeptide Y-like immunoreactivity in the nucleus accumbens and striatum of rats pretreated with psychostimulants

It has been shown that the synthesis, release and levels of neuropeptide Y (NPY), a peptide linked to the dopamine system, are altered by stimulants with psychotomimetic properties and by antipsychotic drugs. This study was designed to evaluate the effect of 3-day haloperidol (HAL) (2 mg/kg i.p.) or clozapine (CLOZ) (25 mg/kg i.p.) treatment on neuropeptide Y-like immunoreactivity (NPY-LI) in nucleus accumbens and striatum (caudate-putamen) in rats pretreated with d-amphetamine or phencyclidine. D-amphetamine (5 mg/kg s.c. twice daily for 6 days and once on day 7) and phencyclidine (10 mg/kg i.p. once daily for 2 days and 15 mg/kg once on day 3) induced marked stereotypy with different symptomatology. Stereotypy is thought to resemble psychosis-related behavior. The first dose of either HAL or CLOZ was given 3 or 2h after the final d-amphetamine or phencyclidine injection, respectively. The control groups were injected with either saline alone, saline instead of psychostimulants, which was followed by antipsychotics, or psychostimulants followed by saline. Rats were sacrificed 24h after antipsychotics or 72 h after the last psychostimulant dose. Both psychostimulants similarly reduced nucleus accumbens and striatal NPY-LI. In saline-pretreated rats, HAL and CLOZ decreased nucleus accumbens NPY-LI, but only HAL decreased striatal NPY-LI. In both the structures examined the effects of HAL and d-amphetamine on NPY-LI were additive. HAL slightly enhanced but CLOZ reversed the phencyclidine-induced decrease in accumbens NPY-LI. The present study has shown that HAL and CLOZ produce different effects on nucleus accumbens and striatal NPY-LI in d-amphetamine or phencyclidine pretreated rats, and it suggests that these effects are related particularly to the dopaminergic and glutamatergic systems whose activities were altered by psychostimulants.

Expression of the neuropeptide Y Y1 receptor in the CNS of rat and of wild-type and Y1 receptor knock-out mice. Focus on immunohistochemical localization

The distribution of neuropeptide Y (NPY) Y1 receptor-like immunoreactivity (Y1R-LI) has been studied in detail in the CNS of rat using a rabbit polyclonal antibody against the C-terminal 13 amino acids of the rat receptor protein. The indirect immunofluorescence technique with tyramide signal amplification has been employed. For specificity and comparative reasons Y1 knock-out mice and wild-type controls were analyzed. The distribution of Y1R mRNA was also studied using in situ hybridization. A limited comparison between Y1R-LI and NPY-LI was carried out.A widespread and abundant distribution of Y1R-LI, predominantly in processes but also in cell bodies, was observed. In fact, Y1R-LI was found in most regions of the CNS with a similar distribution pattern between rat and wild-type mouse. This staining was specific in the sense that it was absent in adjacent sections following preadsorption of the antibody with 10(-5) M of the antigenic peptide, and that it could not be observed in sections of the Y1 KO mouse. In contrast, the staining obtained with an N-terminally directed Y1R antiserum did not disappear, strongly suggesting unspecificity. In brief, very high levels of Y1R-LI were seen in the islands of Calleja, the anterior olfactory nucleus, the molecular layer of the dentate gyrus, parts of the habenula, the interpeduncular nucleus, the mammillary body, the spinal nucleus of the trigeminal, caudal part, the paratrigeminal nucleus, and superficial layers of the dorsal horn. High levels were found in most cortical areas, many thalamic nuclei, some subnuclei of the amygdaloid complex, the hypothalamus and the nucleus of the stria terminalis, the nucleus of the solitary tract, the parabrachial nucleus, and the inferior olive. Moderate levels of Y1R-LI were detected in the cornu Ammonis and the subicular complex, many septal, some thalamic and many brainstem regions. Y1R staining of processes, often fiber and/or dot-like, and occasional cell bodies was also seen in tracts, such as the lateral lemniscus, the rubrospinal tract and the spinal tract of the trigeminal. There was in general a good overlap between Y1R-LI and NPY-LI, but some exceptions were found. Thus, some areas had NPY innervation but apparently lacked Y1Rs, whereas in other regions Y1R-LI, but no or only few NPY-positive nerve endings could be detected. Our results demonstrate that NPY signalling through the Y1R is common in the rat (and mouse) CNS. Mostly the Y1R is postsynaptic but there are also presynaptic Y1Rs. Mostly there is a good match between NPY-releasing nerve endings and Y1Rs, but 'volume transmission' may be 'needed' in some regions. Finally, the importance of using proper control experiments for immunohistochemical studies on seven-transmembrane receptors is stressed.

Striatal NPY-Containing Neurons Receive GABAergic Afferents and may also Contain GABA: An Electron Microscopic Study in the Rat

Dual labelling methods were applied to localize simultaneously neuropeptide Y (NPY) and glutamate decarboxylase (GAD) immunoreactivities on ultrathin sections of the rat caudate-putamen (CP). By means of a double peroxidase-anti-peroxidase technique, using 3,3'-diaminobenzidine and benzidine dihydrochloride as chromogens in animals with no colchicine pretreatment, GAD immunoreactivity was found to be present in terminals only whereas NPY immunoreactivity was detected in neurons displaying the features of aspiny type cells and processes. With this approach, we observed numerous synaptic associations of the symmetrical type between GAD-immunoreactive (-Ir) axonal boutons and NPY-Ir cell bodies and dendrites. By combining immunoperoxidase and radioimmunocytochemical labelling in animals pretreated with colchicine, NPY was again detected in a single population of aspiny type neurons whereas GAD immunoreactivity was observed in neurons which could be classified as aspiny and spiny on the basis of their ultrastructural characteristics. All the cells of the aspiny type displaying clear-cut NPY immunoreactivity were also found to be GAD-positive. Some other neurons of both the aspiny and the spiny type were found to be immunoreactive to GAD alone. GAD/NPY dually labelled terminals were also observed and some axo-axonic appositions between GAD- and NPY-Ir terminals were also detected. All in all, these data show that NPY aspiny type neurons of the rat CP receive GABAergic afferents and provide morphological support for two hypotheses: that NPY is co-localized with GABA in some cell bodies, dendrites and axons, and that presynaptic interactions may occur between NPY and GABAergic neuronal systems.

The neurocircuitry and receptor subtypes mediating anxiolytic-like effects of neuropeptide Y

This review aims to give a brief overview of NPY receptor distribution and physiology in the brain and summarizes series of studies, test by test and region by region, aimed at identification receptor subtypes and neuronal circuitry mediating anxiolytic-like effects of NPY. We conclude that from four known NPY receptor subtypes in the rat (Y(1), Y(2), Y(4), Y(5)), only the NPY Y(1) receptor can be linked to anxiety-regulation with certainty in the forebrain, and that NPY Y(2) receptor may have a role in the pons. Microinjection studies with NPY and NPY receptor antagonists support the hypothesis that the amygdala, the dorsal periaqueductal gray matter, dorsocaudal lateral septum and locus coeruleus form a neuroanatomical substrate that mediates anxiolytic-like effects of NPY. The release of NPY in these areas is likely phasic, as NPY receptor antagonists are silent on their own. However, constant NPY-ergic tone seems to exist in the dorsal periaqueductal gray, the only brain region where NPY Y(1) receptor antagonists had anxiogenic-like effects. We conclude that endogenous NPY has an important role in reducing anxiety and serves as a physiological stabilizer of neural activity in circuits involved in the regulation of arousal and anxiety.

Localization and characterization of NPY/PYY receptors in rat frontoparietal cortex during development

Neuropeptide Y (NPY) is present in most cerebrocortical areas during fetal and postnatal development. In the rat frontal cortex, a dense radial fiber network containing NPY immunoreactivity is observed transiently as early as embryonic day 17 (E17) and disappears at the end of the first postnatal week. We have investigated the distribution of NPY receptors in the frontoparietal cortex at 13 stages of development, from E15 fetuses to adults, by in vitro autoradiography, using (125)I-pPYY as a radioligand. Quantitative receptor density was measured through all cortical layers at each developmental stage. Pharmacological identification of (125)I-pPPY binding sites was made by competition experiments using pNPY or [Leu(31),Pro(34)]pNPY and pNPY(13-36), as selective competitors for Y1 and Y2 receptors, respectively. NPY receptors were first detected in the cerebral cortex at low densities at E19 in a thin layer of tissue corresponding to the inner half of the intermediate zone (IZ) and the upper ventricular zone (VZ). The neuroepithelium did not contain binding sites. High densities of sites were observed by E21 onward to P10 in the deep cortical layers corresponding to the IZ and layers V-VI. A decreasing gradient of receptor density was observed from layer VI to the marginal zone (layer I). The distribution of NPY receptors does not match with the perikarya of transient NPY-immunoreactive neurons located in the cortical plate but does coincide with their axonal extension. The receptor density decreased abruptly between P10 and P12 in deep layers, whereas a moderate expression of binding sites is detected from P10 to P12 in layers I-III. By P14, the binding level was the lowest observed in the postnatal period. From P21 onward, receptors were observed in superficial layers I-III, and their density rose by two- to threefold up to adulthood. Competition studies indicated that the NPY receptors located in the deep cortical layers of the E21 or P1 rat cortex exhibit Y2 receptor type characteristics. The binding sites detected in the superficial layers from P10 to P12 rats also show Y2 receptors characteristics, unlike the NPY receptors in layers II-III of the adult, which behave like Y1 receptors. These data show that different NPY receptor types are successively expressed in specific layers during late gestation and early postnatal life in the rat frontoparietal cortex.

Induction of functional and morphological expression of neuropeptide Y (NPY) in cortical cultures by brain-derived neurotrophic factor (BDNF): evidence for a requirement for extracellular-regulated kinase (ERK)-dependent and ERK-independent mechanisms

Previous studies have demonstrated that brain-derived neurotrophic factor (BDNF) induces expression of neuropeptide Y (NPY) neurons in aggregate cultures derived from the fetal rat cortex. Using BDNF induction of NPY production and neurite extension of NPY neurons as functional and morphological criteria, respectively, we addressed the question: Does BDNF activate the extracellular-regulated kinase (ERK) pathway and if so, is activated (phosphorylated, P)-ERK required for the induction of both the functional and morphological expression of NPY? BDNF led to a rapid (30 min) and sustained (6 h) phosphorylation of ERK. PD98059 (PD, a specific inhibitor of the ERK kinase MEK), drastically inhibited, LY294002 (LY, a specific inhibitor of phosphatidylinositol-3-kinase, PI-3K) partially inhibited, and GF 109203X (GF, a specific inhibitor of protein kinase C) did not inhibit phosphorylation of ERK. A 24-h exposure to BDNF led to approximately 2-fold increase in the total culture content of NPY ( approximately 60% of which was secreted and approximately 40% remained in the aggregates) and to an abundance of neurite-bearing NPY neurons. BDNF-induced NPY produced and secreted into the medium was inhibited 73% by PD, 52% by LY and not at all by GF. In contrast, BDNF-induced NPY produced and sequestered in the aggregates was not inhibited by any of these inhibitors, suggesting a role for the ERK pathway in induced secretion of NPY. PD or LY did not inhibit BDNF-induced abundance of neurite-bearing NPY neurons. K252a (an inhibitor of TrkB-tyrosine kinase) abolished all the effects of BDNF assessed in our cultures. In summary, we demonstrate that TrkB-mediated activation of the ERK pathway is preferentially required for BDNF induction of NPY produced and secreted but not for the induction of the expression of neurite-bearing NPY neurons. Thus, BDNF induction of the functional and morphological expression of NPY is brought about by ERK-dependent and ERK-independent mechanisms.

The hypothalamus and hypertension

Most forms of hypertension are associated with a wide variety of functional changes in the hypothalamus. Alterations in the following substances are discussed: catecholamines, acetylcholine, angiotensin II, natriuretic peptides, vasopressin, nitric oxide, serotonin, GABA, ouabain, neuropeptide Y, opioids, bradykinin, thyrotropin-releasing factor, vasoactive intestinal polypeptide, tachykinins, histamine, and corticotropin-releasing factor. Functional changes in these substances occur throughout the hypothalamus but are particularly prominent rostrally; most lead to an increase in sympathetic nervous activity which is responsible for the rise in arterial pressure. A few appear to be depressor compensatory changes. The majority of the hypothalamic changes begin as the pressure rises and are particularly prominent in the young rat; subsequently they tend to fluctuate and overall to diminish with age. It is proposed that, with the possible exception of the Dahl salt-sensitive rat, the hypothalamic changes associated with hypertension are caused by renal and intrathoracic cardiopulmonary afferent stimulation. Renal afferent stimulation occurs as a result of renal ischemia and trauma as in the reduced renal mass rat. It is suggested that afferents from the chest arise, at least in part, from the observed increase in left auricular pressure which, it is submitted, is due to the associated documented impaired ability to excrete sodium. It is proposed, therefore, that the hypothalamic changes in hypertension are a link in an integrated compensatory natriuretic response to the kidney's impaired ability to excrete sodium.

Interleukin-1beta induces expression of neuropeptide Y in primary astrocyte cultures in a cytokine-specific manner: induction in human but not rat astrocytes

Previous studies have demonstrated that astrocyte cultures express neuropeptide Y (NPY) in a regulated manner, namely, phorbol ester leads to an increase in proNPY-mRNA and NPY production. In this respect, the behavior of astrocytes derived from the human fetal or rat neonatal brain is similar (Regul. Pept. 75 (1998) 293). Since astrocytes can be exposed to high levels of IL-1beta, we addressed the question: Does IL-1beta regulate NPY expression by the astrocytes? Primary astrocytes derived from the human fetal or rat neonatal cortex were cultured in serum-free medium. IL-1beta, but not IL-6 or TNF-alpha, led to an increase in NPY production dose-dependently. IL-1beta action manifested in the human but not in the rat astrocytes and it was completely abolished by IL-1 receptor antagonist. The responsiveness to IL-1beta did not diminish upon sub-culture of the astrocytes (five passages). In addition, IL-1beta led to an increase in the abundance of proNPY-mRNA, which was preceded by a rapid and transient increase in cFos-mRNA and a rapid and sustained increase in JunB-mRNA. In contrast to cFos/JunB, IL-1beta did not alter the abundance of cJun-mRNA. In summary, we demonstrate that IL-1beta induction of NPY expression in astrocytes is species- and cytokine-specific and that IL-1 receptor is involved. Moreover, induction of NPY expression is preceded by a rapid increase in the expression of two transcription factors (cFos, JunB) that have been previously (Oncogene 9 (1994) 2369; J. Neurochem. 70 (1998) 1887) implicated in transcriptional regulation of the human NPY gene.