Phenotypic analysis of GalR2 knockout mice in anxiety- and depression-related behavioral tests

Enhanced neuronal survival and BDNF elevation via long-term co-activation of galanin 2 (GALR2) and neuropeptide Y1 receptors (NPY1R): potential therapeutic targets for major depressive disorder

BACKGROUND

Major Depressive Disorder (MDD) is a prevalent and debilitating condition, necessitating novel therapeutic strategies due to the limited efficacy and adverse effects of current treatments. We explored how galanin receptor 2 (GALR2) and Neuropeptide Y1 Receptor (NPYY1R) agonists, working together, can boost brain cell growth and increase antidepressant-like effects in rats. This suggests new ways to treat Major Depressive Disorder (MDD).

RESEARCH DESIGN AND METHODS

In a controlled laboratory setting, adult naive Sprague-Dawley rats were administered directly into the brain's ventricles, a method known as intracerebroventricular (ICV) administration, with GALR2 agonist (M1145), NPYY1R agonist, both, or in combination with a GALR2 antagonist (M871). Main outcome measures included long-term neuronal survival, differentiation, and behavioral.

RESULTS

Co-administration of M1145 and NPYY1R agonist significantly enhanced neuronal survival and maturation in the ventral dentate gyrus, with a notable increase in Brain-Derived Neurotrophic Factor (BDNF) expression. This neurogenic effect was associated with an antidepressant-like effect, an outcome partially reversed by M871.

CONCLUSIONS

GALR2 and NPYY1R agonists jointly promote hippocampal neurogenesis and exert antidepressant-like effects in rats without adverse outcomes, highlighting their therapeutic potential for MDD. The study's reliance on an animal model and intracerebroventricular delivery warrants further clinical exploration to confirm these promising results.

Investigating the potential of GalR2 as a drug target for neuropathic pain

Neuropathic pain is a chronic and debilitating condition characterised by episodes of hyperalgesia and allodynia. It occurs following nerve damage from disease, inflammation or injury and currently impacts up to 17% of the UK population. Existing therapies lack efficacy and have deleterious side effects that can be severely limiting. Galanin receptor 2 (GalR2) is a G-protein coupled receptor (GPCR) implicated in the control and processing of painful stimuli. Within the nervous system it is expressed in key tissues involved in these actions such as dorsal root ganglia (DRG) and the dorsal horn of the spinal cord. Stimulation of GalR2 is widely reported to have a role in the attenuation of inflammatory and neuropathic pain. Several studies have indicated GalR2 as a possible drug target, highlighting the potential of specific GalR2 agonists to both provide efficacy and to address the side-effect profiles of current pain therapies in clinical use. A strong biological target for drug discovery will be well validated with regards to its role in the relevant disease pathology. Ideally there will be good translational models, sensitive probes, selective and appropriate molecular tools, translational biomarkers, a clearly defined patient population and strong opportunities for commercialisation. Before GalR2 can be considered as a drug target suitable for investment, key questions need to be asked regarding its expression profile, receptor signalling and ligand interactions. This article aims to critically review the available literature and determine the current strength of hypothesis of GalR2 as a target for the treatment of neuropathic pain.

GALR2 and Y1R agonists intranasal infusion enhanced adult ventral hippocampal neurogenesis and antidepressant-like effects involving BDNF actions

Dysregulation of adult hippocampal neurogenesis is linked to major depressive disorder (MDD), with more than 300 million people diagnosed and worsened by the COVID-19 pandemic. Accumulating evidence for neuropeptide Y (NPY) and galanin (GAL) interaction was shown in various limbic system regions at molecular-, cellular-, and behavioral-specific levels. The purpose of the current work was to evaluate the proliferating role of GAL2 receptor (GALR2) and Y1R agonists interaction upon intranasal infusion in the ventral hippocampus. We studied their hippocampal proliferating actions using the proliferating cell nuclear antigen (PCNA) on neuroblasts or stem cells and the expression of the brain-derived neurothrophic factor (BDNF). Moreover, we studied the formation of Y1R-GALR2 heteroreceptor complexes and analyzed morphological changes in hippocampal neuronal cells. Finally, the functional outcome of the NPY and GAL interaction on the ventral hippocampus was evaluated in the forced swimming test. We demonstrated that the intranasal infusion of GALR2 and the Y1R agonists promotes neuroblasts proliferation in the dentate gyrus of the ventral hippocampus and the induction of the neurotrophic factor BDNF. These effects were mediated by the increased formation of Y1R-GALR2 heteroreceptor complexes, which may mediate the neurites outgrowth observed on neuronal hippocampal cells. Importantly, BDNF action was found necessary for the antidepressant-like effects after GALR2 and the Y1R agonists intranasal administration. Our data may suggest the translational development of new heterobivalent agonist pharmacophores acting on Y1R-GALR2 heterocomplexes in the ventral hippocampus for the novel therapy of MDD or depressive-affecting diseases.

Running from Stress: Neurobiological Mechanisms of Exercise-Induced Stress Resilience

Chronic stress, even stress of a moderate intensity related to daily life, is widely acknowledged to be a predisposing or precipitating factor in neuropsychiatric diseases. There is a clear relationship between disturbances induced by stressful stimuli, especially long-lasting stimuli, and cognitive deficits in rodent models of affective disorders. Regular physical activity has a positive effect on the central nervous system (CNS) functions, contributes to an improvement in mood and of cognitive abilities (including memory and learning), and is correlated with an increase in the expression of the neurotrophic factors and markers of synaptic plasticity as well as a reduction in the inflammatory factors. Studies published so far show that the energy challenge caused by physical exercise can affect the CNS by improving cellular bioenergetics, stimulating the processes responsible for the removal of damaged organelles and molecules, and attenuating inflammation processes. Regular physical activity brings another important benefit: increased stress robustness. The evidence from animal studies is that a sedentary lifestyle is associated with stress vulnerability, whereas a physically active lifestyle is associated with stress resilience. Here, we have performed a comprehensive PubMed Search Strategy for accomplishing an exhaustive literature review. In this review, we discuss the findings from experimental studies on the molecular and neurobiological mechanisms underlying the impact of exercise on brain resilience. A thorough understanding of the mechanisms underlying the neuroprotective potential of preconditioning exercise and of the role of exercise in stress resilience, among other things, may open further options for prevention and therapy in the treatment of CNS diseases.

Structure of the human galanin receptor 2 bound to galanin and Gq reveals the basis of ligand specificity and how binding affects the G-protein interface

Galanin is a neuropeptide expressed in the central and peripheral nervous systems, where it regulates various processes including neuroendocrine release, cognition, and nerve regeneration. Three G-protein coupled receptors (GPCRs) for galanin have been discovered, which is the focus of efforts to treat diseases including Alzheimer’s disease, anxiety, and addiction. To understand the basis of the ligand preferences of the receptors and to assist structure-based drug design, we used cryo-electron microscopy (cryo-EM) to solve the molecular structure of GALR2 bound to galanin and a cognate heterotrimeric G-protein, providing a molecular view of the neuropeptide binding site. Mutant proteins were assayed to help reveal the basis of ligand specificity, and structural comparison between the activated GALR2 and inactive hβ2AR was used to relate galanin binding to the movements of transmembrane (TM) helices and the G-protein interface.

Anxiety and Depression: What Do We Know of Neuropeptides?

In modern society, there has been a rising trend of depression and anxiety. This trend heavily impacts the population’s mental health and thus contributes significantly to morbidity and, in the worst case, to suicides. Modern medicine, with many antidepressants and anxiolytics at hand, is still unable to achieve remission in many patients. The pathophysiology of depression and anxiety is still only marginally understood, which encouraged researchers to focus on neuropeptides, as they are a vast group of signaling molecules in the nervous system. Neuropeptides are involved in the regulation of many physiological functions. Some act as neuromodulators and are often co-released with neurotransmitters that allow for reciprocal communication between the brain and the body. Most studied in the past were the antidepressant and anxiolytic effects of oxytocin, vasopressin or neuropeptide Y and S, or Substance P. However, in recent years, more and more novel neuropeptides have been added to the list, with implications for the research and development of new targets, diagnostic elements, and even therapies to treat anxiety and depressive disorders. In this review, we take a close look at all currently studied neuropeptides, their related pathways, their roles in stress adaptation, and the etiology of anxiety and depression in humans and animal models. We will focus on the latest research and information regarding these associated neuropeptides and thus picture their potential uses in the future.

Galanin Regulates Myocardial Mitochondrial ROS Homeostasis and Hypertrophic Remodeling Through GalR2

The regulatory peptide galanin is broadly distributed in the central nervous systems and peripheral tissues where it modulates numerous physiological and pathological processes through binding to its three G-protein-coupled receptors, GalR1-3. However, the function and identity of the galaninergic system in the heart remain unclear. Therefore, we investigated the expression of the galanin receptors in cardiac cells and tissues and found that GalR2 is the dominant receptor subtype in adult mouse hearts, cardiomyocytes and H9C2 cardiomyoblasts. In vivo, genetic suppression of GalR2 promotes cardiac hypertrophy, fibrosis and mitochondrial oxidative stress in the heart. In vitro, GalR2 silencing by siRNA abolished the beneficial effects of galanin on cell hypertrophy and mitochondrial reactive oxygen species (ROS) production. These findings unravel new insights into the role of galaninergic system in the heart and suggest novel therapeutic strategies in heart disease.

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.

Neuropeptides as regulators of the hypothalamus-pituitary-gonadal (HPG) axis activity and their putative roles in stress-induced fertility disorders

Neuropeptides being regulators of the hypothalamus-pituitary-adrenal (HPA) axis activity, also affect the function of the hypothalamus-pituitary-gonadal (HPG) axis by regulating gonadotrophin-releasing hormone (GnRH) secretion from hypothalamic neurons. Here, we review the available data on how neuropeptides affect HPG axis activity directly or indirectly via their influence on the HPA axis. The putative role of neuropeptides in stress-induced infertility, such as polycystic ovary syndrome, is also described. This review discusses both well-known neuropeptides (i.e., kisspeptin, Kp; oxytocin, OT; arginine-vasopressin, AVP) and more recently discovered peptides (i.e., relaxin-3, RLN-3; nesfatin-1, NEFA; phoenixin, PNX; spexin, SPX). For the first time, we present an up-to-date review of all published data regarding interactions between the aforementioned neuropeptide systems. The reviewed literature suggest new pathophysiological mechanisms leading to fertility disturbances that are induced by stress.

Functions of habenula in reproduction and socio-reproductive behaviours

Habenula is an evolutionarily conserved structure in the brain of vertebrates. Recent reports have drawn attention to the habenula as a processing centre for emotional decision-making and its role in psychiatric disorders. Emotional decision-making process is also known to be closely associated with reproductive conditions. The habenula receives innervations from reproductive centres within the brain and signals from key reproductive neuroendocrine regulators such as gonadal sex steroids, gonadotropin-releasing hormone (GnRH), and kisspeptin. In this review, based on morphological, biochemical, physiological, and pharmacological evidence we discuss an emerging role of the habenula in reproduction. Further, we discuss the modulatory role of reproductive endocrine factors in the habenula and their association with socio-reproductive behaviours such as mating, anxiety and aggression.

Update on GPCR-based targets for the development of novel antidepressants

Traditional antidepressants largely interfere with monoaminergic transport or degradation systems, taking several weeks to have their therapeutic actions. Moreover, a large proportion of depressed patients are resistant to these therapies. Several atypical antidepressants have been developed which interact with G protein coupled receptors (GPCRs) instead, as direct targeting of receptors may achieve more efficacious and faster antidepressant actions. The focus of this review is to provide an update on how distinct GPCRs mediate antidepressant actions and discuss recent insights into how GPCRs regulate the pathophysiology of Major Depressive Disorder (MDD). We also discuss the therapeutic potential of novel GPCR targets, which are appealing due to their ligand selectivity, expression pattern, or pharmacological profiles. Finally, we highlight recent advances in understanding GPCR pharmacology and structure, and how they may provide new avenues for drug development.

Prophylactic treatment of curcumin in a rat model of depression by attenuating hippocampal synaptic loss

Curcumin is a polyphenol substance considered to be effective in the treatment of a number of neurodegenerative diseases. However, details regarding the exact mechanisms for the protective effects of curcumin in neuropsychiatric disorders, like depression, remain unknown. In the pathogenesis of major depressive disorder (MDD) it appears that dysregulation of oxidative stress and immune systems, particularly within the hippocampal region, may play a critical role. Here, we show that pre-treatment with curcumin (40 mg kg^-1) alleviates depression-like behaviors in a LPS-induced rat model of depression, effects which were accompanied with suppression of oxidative stress and inflammation and an inhibition of neuronal apoptosis in the hippocampal CA1 region, and results from ultramicrostructure electrophysiological experiments revealed that the curcumin pre-treatment significantly prevented excessive synaptic loss and enhanced synaptic functioning in this LPS-induced rat model. In addition, curcumin attenuated the increases in levels of miR-146a-5p and decreases in the expression of p-ERK signaling that would normally occur within CA1 regions of these depressed rats. Taken together, these results demonstrated that curcumin exerts neuroprotective and antidepressant activities by suppressing oxidative stress, neural inflammation and their related effects upon synaptic dysregulation. One of the mechanisms for these beneficial effects of curcumin appears to involve the miR-146a-5p/ERK signaling pathway within the hippocampal CA1 region. These findings not only elucidated some of the mechanisms underlying the neuroprotective/antidepressant effects of curcumin, but also suggested a role of curcumin as a potential therapeutic strategy for depression.

Galanin and neuropeptide Y interactions elicit antidepressant activity linked to neuronal precursor cells of the dentate gyrus in the ventral hippocampus

A need for new antidepressants is necessary since traditional antidepressants have several flaws. Neuropeptide Y(NPY) Y1 receptor (NPYY1R) and galanin (GAL) receptor 2 (GALR2) interact in several regions of the limbic system, including the hippocampus. The current study assesses the antidepressant effects induced by GALR2 and NPYY1R coactivation, together with the evaluation of cell proliferation through 5-Bromo-2'-deoxyuridine expression within the dentate gyrus of the ventral hippocampus (vDG). We employed in situ proximity ligation assay to manifest GALR2/NPYY1R heteroreceptor complexes. Additionally, the expression pattern of GALR2 and the activation of the extracellular-regulated kinases (ERK) pathway after GALR2 and NPYY1R costimulation in cell cultures were examined. GALR2 and NPYY1R coactivation resulted in sustained antidepressant behaviors in the FST after 24 h, linked to increased cell proliferation in the vDG. Moreover, an increased density of GALR2/NPYY1R heteroreceptor complexes was observed in vDG, on doublecortin-expressing neuroblasts. Recruitment of the GALR2 expression to the plasma membrane was observed upon the coactivation of GALR2 and NPYY1R in cell cultures, presumably associated to the enhanced effects on the activation of ERK pathway. GALR2 may promote the GALR2/NPYY1R heteroreceptor complexes formation in the ventral hippocampus. It may induce a transformation of cell proliferation toward a neuronal lineage by enhancement of ERK pathway. Thus, it may give the mechanism for the antidepressant behavior observed. These results may provide the basis for the development of heterobivalent agonist pharmacophores, targeting GALR2/NPYY1R heteromers, especially in the neuronal precursor cells of the dentate gyrus in the ventral hippocampus for the novel treatment of depression.

Nutrient regulation of somatic growth in teleost fish. The interaction between somatic growth, feeding and metabolism

This review covers the current knowledge on the regulation of the somatic growth axis and its interaction with metabolism and feeding regulation. The main endocrine and neuroendocrine factors regulating both the growth axis and feeding behavior will be briefly summarized. Recently discovered neuropeptides and peptide hormones will be mentioned in relation to feeding control as well as growth hormone regulation. In addition, the influence of nutrient and nutrient sensing mechanisms on growth axis will be highlighted. We expect that in this process gaps of knowledge will be exposed, stimulating future research in those areas.

Beneficial effects of galanin system on diabetic peripheral neuropathic pain and its complications

Diabetic peripheral neuropathic pain (DPNP) is a distal spontaneous pain, caused by lesion of sensory neurons and accompanied by depression and anxiety frequently, which reduce life quality of patients and increase society expenditure. To date, antidepressants, serotonin-noradrenaline reuptake inhibitors and anticonvulsants are addressed as first-line therapy to DPNP, alone or jointly. It is urgently necessary to develop novel agents to treat DPNP and its complications. Evidences indicate that neuropeptide galanin can regulate multiple physiologic and pathophysiological processes. Pain, depression and anxiety may upregulate galanin expression. In return, galanin can modulate depression, anxiety, pain threshold and pain behaviors. This article provides a new insight into regulative effects of galanin and its subtype receptors on antidepressant, antianxiety and against DPNP. Through activating GALR1, galanin reinforces depression-like and anxiogenic-like behaviors, but exerts antinociceptive roles. While via activating GALR2, galanin is referred to as anti-depressive and anti-anxiotropic compounds, and at low and high concentration facilitates and inhibits nociceptor activity, respectively. The mechanism of the galanin roles is relative to increase in K⁺ currents and decrease in Ca²⁺ currents, as well as neurotrophic and neuroprotective roles. These data are helpful to develop novel drugs to treat DPNP and its complications.

No evidence that Spexin impacts LH release and seasonal breeding in the ewe

Spexin (SPX) is a recently identified peptide hormone of 14 amino acids. Interestingly, Spx and Kiss1 genes share a common ancestor gene. Considering that KISS1 peptides are key controllers of breeding in mammals and circumstantial evidence that SPX regulates gonadotropins in some fish species, we hypothesized that SPX may play a KISS1-related role in sheep. Here, we cloned the ovine Spx cDNA, performed in vivo injection and infusion of SPX (i.c.v. route, with or without concomittant KISS1 presence) and assessed a potential regulation of Spx expression by season, thyroid hormone and estradiol in the medio-basal hypothalamus of the ewe. Our data do not provide support for a role of SPX in the control of the gonadotropic axis in the ewe.

Overexpression of Spexin 1 in the Dorsal Habenula Reduces Anxiety in Zebrafish

Spexin (SPX) is an evolutionarily conserved neuropeptide that is expressed in the mammalian brain and peripheral tissue. Two orthologs are present in the teleost, SPX1 and SPX2. SPX1 is involved in reproduction and food intake. Recently, SPX1 neurons have been found to be located in the specific nuclei of dorsal habenula (dHb) and to project into the interpeduncular nucleus (IPN), in which galanin receptor 2a/2b (GALR2a/2b) expression was also observed. This indicates that habenula SPX1 neurons may interact with GALR2a/2b in the IPN; however, the function of SPX1 in the dHb-IPN neuronal circuit remains unknown. To determine the role of SPX1 in the dHb-IPN neural circuit, we generated transgenic zebrafish overexpressing SPX1 specifically in the dHb. We found that transgenic zebrafish overexpressing SPX1 in the dHb had anxiolytic behaviors compared with their wildtype siblings. Furthermore, quantitative PCR revealed that mRNA expression of galr2a and galr2b in the IPN and serotonin-related genes in the raphe was upregulated in the brains of transgenic zebrafish. Taken together, our data suggest that SPX1 function in the dHb-IPN neural circuits is implicated in the regulation of anxiety behaviors via modulation of the serotoninergic system in zebrafish.

Implication of NMDA-NO pathway in the antidepressant-like effect of ellagic acid in male mice

Depression is one the common psychiatric disorders through the world. Nitric oxide (NO) and N-methyl-d-aspartate receptor (NMDA-R) are involved in the pathophysiology of depression. Previous studies have been reported various pharmacological properties for ellagic acid (EA). We aimed to evaluate possible involvement of NMDA-NO pathway in the antidepressant-like effect of EA. To do this, we used relevant behavioral tests to evaluate depressive-like behavior. In order to find effective and sub-effective doses of agents, mice treated with EA (6.25, 12.5, 25, 50 and 100 mg/kg), L-NAME (5 and 10 mg/kg), L-arg (25 and 50 mg/kg), NMDA (75 and 150 mg/kg) and ketamine (0.25 and 0.5 mg/kg). Furthermore, mice were treated with combination of sub-effective dose of EA plus sub-effective doses of L-NAME and/or ketamine as well as treated with effective dose of EA in combination of effective doses of L-arg and/or NMDA. Level of NO and gene expression of NR2A and NR2B subunits of NMDA-R were assessed in the hippocampus. Results showed that EA dose dependently provoked antidepressant-like effects and also decreased the hippocampal NO level as well as expression of NMDA-Rs. Co-administration of sub-effective doses of L-NAME or ketamine with sub-effective dose of EA potentiated the effect of EA on behaviors, NO level as well as NMDA-Rs gene expression in the hippocampus. However, co-treatment of effective dose of EA with effective doses of L-arg or NMDA mitigated effects of EA. In conclusion, our data suggested that NMDA-NO, partially at least, are involved in the antidepressant-like effect of EA.

Virus-Mediated Overexpression of ETS-1 in the Ventral Hippocampus Counteracts Depression-Like Behaviors in Rats

ETS-1 is a transcription factor that is a member of the E26 transformation-specific (ETS) family. Galanin receptor 2 (GalR2), a subtype of receptors of the neuropeptide galanin, has been shown to have an antidepressant-like effect after activation in rodents. Our previous study has shown that overexpression of ETS-1 increases the expression of GalR2 in PC12 phaeochromocytoma cells. However, whether ETS-1 has an antidepressant-like effect is still unclear. In this study, we found that chronic mild stress (CMS) decreased the expression of both ETS-1 and GalR2 in the ventral hippocampus of rats. Meanwhile, we demonstrated that overexpression of ETS-1 increased the expression of GalR2 in primary hippocampal neurons. Importantly, we showed that overexpression of ETS-1 in the ventral hippocampus counteracted the depression-like behaviors of CMS rats. Furthermore, we found that overexpression of ETS-1 increased the level of downstream phosphorylated extracellular signal-regulated protein kinases 1 and 2 (p-ERK1/2) of GalR2 in the ventral hippocampus of CMS rats. Taken together, our findings suggest that ETS-1 has an antidepressant-like effect in rats, which might be mediated by increasing the level of GalR2 and its downstream p-ERK1/2 in the ventral hippocampus.

Distribution and neuronal circuit of spexin 1/2 neurons in the zebrafish CNS

Spexin (SPX) is a highly conserved neuropeptide that is widely expressed in mammalian brain and peripheral tissue. In teleost, SPX1 is mainly expressed in the brain and ovary, and is involved in reproduction and food intake. A second form of SPX, SPX2, was recently identified in chick, Xenopus, and zebrafish. The expression pattern and roles of SPX2 are unknown. SPX (spx1) is highly expressed in the vertebrate brain, but its distribution, circuits, and interactions with its putative receptor are unknown. Here, we observed expression of spx1 in the midbrain and hindbrain, and spx2 in the hypothalamic preoptic area using in situ RNA hybridization in zebrafish. Analysis of transgenic reporter zebrafish revealed that hindbrain SPX1 neurons are PAX2⁺ inhibitory interneurons and project to the spinal cord, where they interact with galanin receptor 2b (GALR2b) neurons, suggesting that hindbrain SPX1 neurons are reticulospinal neurons. spx1 mRNA and SPX1 reporter expression were observed in dorsal habenula (dHb). SPX1 neurons in the dHb project to the interpeduncular nucleus (IPN), where GALR2a and GALR2b expression was also observed, suggesting that habenula SPX1 neurons may interact with GALR2a/2b in the IPN.

Neuropeptide and Small Transmitter Coexistence: Fundamental Studies and Relevance to Mental Illness

Neuropeptides are auxiliary messenger molecules that always co-exist in nerve cells with one or more small molecule (classic) neurotransmitters. Neuropeptides act both as transmitters and trophic factors, and play a role particularly when the nervous system is challenged, as by injury, pain or stress. Here neuropeptides and coexistence in mammals are reviewed, but with special focus on the 29/30 amino acid galanin and its three receptors GalR1, -R2 and -R3. In particular, galanin's role as a co-transmitter in both rodent and human noradrenergic locus coeruleus (LC) neurons is addressed. Extensive experimental animal data strongly suggest a role for the galanin system in depression-like behavior. The translational potential of these results was tested by studying the galanin system in postmortem human brains, first in normal brains, and then in a comparison of five regions of brains obtained from depressed people who committed suicide, and from matched controls. The distribution of galanin and the four galanin system transcripts in the normal human brain was determined, and selective and parallel changes in levels of transcripts and DNA methylation for galanin and its three receptors were assessed in depressed patients who committed suicide: upregulation of transcripts, e.g., for galanin and GalR3 in LC, paralleled by a decrease in DNA methylation, suggesting involvement of epigenetic mechanisms. It is hypothesized that, when exposed to severe stress, the noradrenergic LC neurons fire in bursts and release galanin from their soma/dendrites. Galanin then acts on somato-dendritic, inhibitory galanin autoreceptors, opening potassium channels and inhibiting firing. The purpose of these autoreceptors is to act as a 'brake' to prevent overexcitation, a brake that is also part of resilience to stress that protects against depression. Depression then arises when the inhibition is too strong and long lasting - a maladaption, allostatic load, leading to depletion of NA levels in the forebrain. It is suggested that disinhibition by a galanin antagonist may have antidepressant activity by restoring forebrain NA levels. A role of galanin in depression is also supported by a recent candidate gene study, showing that variants in genes for galanin and its three receptors confer increased risk of depression and anxiety in people who experienced childhood adversity or recent negative life events. In summary, galanin, a neuropeptide coexisting in LC neurons, may participate in the mechanism underlying resilience against a serious and common disorder, MDD. Existing and further results may lead to an increased understanding of how this illness develops, which in turn could provide a basis for its treatment.

Gabrb2-knockout mice displayed schizophrenia-like and comorbid phenotypes with interneuron-astrocyte-microglia dysregulation

Intronic polymorphisms of the GABA_A receptor β₂ subunit gene (GABRB2) under adaptive evolution were associated with schizophrenia and reduced expression, especially of the long isoform which differs in electrophysiological properties from the short isoform. The present study was directed to examining the gene dosage effects of Gabrb2 in knockout mice of both heterozygous (HT) and homozygous (KO) genotypes with respect to possible schizophrenia-like and comorbid phenotypes. The KO mice, and HT mice to a lesser extent, were found to display prepulse inhibition (PPI) deficit, locomotor hyperactivity, stereotypy, sociability impairments, spatial-working and spatial-reference memory deficits, reduced depression and anxiety, and accelerated pentylenetetrazol (PTZ)-induced seizure. In addition, the KO mice were highly susceptible to audiogenic epilepsy. Some of the behavioral phenotypes showed evidence of imprinting, gender effect and amelioration by the antipsychotic risperidone, and the audiogenic epilepsy was inhibited by the antiepileptic diazepam. GABAergic parvalbumin (PV)-positive interneuron dystrophy, astrocyte dystrophy, and extensive microglia activation were observed in the frontotemporal corticolimbic regions, and reduction of newborn neurons was observed in the hippocampus by immunohistochemical staining. The neuroinflammation indicated by microglial activation was accompanied by elevated brain levels of oxidative stress marker malondialdehyde (MDA) and the pro-inflammatory cytokines tumor necrosis factor-alpha (TNF-α) and interleukin-6 (IL-6). These extensive schizophrenia-like and comorbid phenotypes brought about by Gabrb2 knockout, in conjunction with our previous findings on GABRB2 association with schizophrenia, support a pivotal role of GABRB2 in schizophrenia etiology.

Effect of long-term treatment with classical neuroleptics on NPQ/spexin, kisspeptin and POMC mRNA expression in the male rat amygdala

Neuroleptics modulate the expression level of some regulatory neuropeptides in the brain. However, if these therapeutics influence the peptidergic circuits in the amygdala remains unclear. This study specifies the impact profile of the classical antipsychotic drugs on mRNA expression of the spexin/NPQ, kisspeptin-1 and POMC in the rat amygdala. Animals were treated with haloperidol and chlorpromazine for 28 days prior to transcript quantification via qPCR. Haloperidol and chlorpromazine induced a change in the expression of all neuropeptides analyzed. Both drugs led to the decrease of Kiss-1 expression, whereas in POMC and spexin/NPQ their up-regulation in the amygdala was detected. These modulating effects on may represent alternative, so far unknown mechanisms, of classical antipsychotic drugs triggering pharmacological responses.

Understanding the Role of GPCR Heteroreceptor Complexes in Modulating the Brain Networks in Health and Disease

The introduction of allosteric receptor-receptor interactions in G protein-coupled receptor (GPCR) heteroreceptor complexes of the central nervous system (CNS) gave a new dimension to brain integration and neuropsychopharmacology. The molecular basis of learning and memory was proposed to be based on the reorganization of the homo- and heteroreceptor complexes in the postjunctional membrane of synapses. Long-term memory may be created by the transformation of parts of the heteroreceptor complexes into unique transcription factors which can lead to the formation of specific adapter proteins. The observation of the GPCR heterodimer network (GPCR-HetNet) indicated that the allosteric receptor-receptor interactions dramatically increase GPCR diversity and biased recognition and signaling leading to enhanced specificity in signaling. Dysfunction of the GPCR heteroreceptor complexes can lead to brain disease. The findings of serotonin (5-HT) hetero and isoreceptor complexes in the brain over the last decade give new targets for drug development in major depression. Neuromodulation of neuronal networks in depression via 5-HT, galanin peptides and zinc involve a number of GPCR heteroreceptor complexes in the raphe-hippocampal system: GalR1-5-HT1A, GalR1-5-HT1A-GPR39, GalR1-GalR2, and putative GalR1-GalR2-5-HT1A heteroreceptor complexes. The 5-HT1A receptor protomer remains a receptor enhancing antidepressant actions through its participation in hetero- and homoreceptor complexes listed above in balance with each other. In depression, neuromodulation of neuronal networks in the raphe-hippocampal system and the cortical regions via 5-HT and fibroblast growth factor 2 involves either FGFR1-5-HT1A heteroreceptor complexes or the 5-HT isoreceptor complexes such as 5-HT1A-5-HT7 and 5-HT1A-5-HT2A. Neuromodulation of neuronal networks in cocaine use disorder via dopamine (DA) and adenosine signals involve A2AR-D2R and A2AR-D2R-Sigma1R heteroreceptor complexes in the dorsal and ventral striatum. The excitatory modulation by A2AR agonists of the ventral striato-pallidal GABA anti-reward system via targeting the A2AR-D2R and A2AR-D2R-Sigma1R heteroreceptor complex holds high promise as a new way to treat cocaine use disorders. Neuromodulation of neuronal networks in schizophrenia via DA, adenosine, glutamate, 5-HT and neurotensin peptides and oxytocin, involving A2AR-D2R, D2R-NMDAR, A2AR-D2R-mGluR5, D2R-5-HT2A and D2R-oxytocinR heteroreceptor complexes opens up a new world of D2R protomer targets in the listed heterocomplexes for treatment of positive, negative and cognitive symptoms of schizophrenia.

Effect of glycation inhibitors on aging and age-related diseases

Vast evidence supports the view that glycation of proteins is one of the main factors contributing to aging and is an important element of etiopathology of age-related diseases, especially type 2 diabetes mellitus, cataract and neurodegenerative diseases. Counteracting glycation can therefore be a means of increasing both the lifespan and healthspan. In this review, accumulation of glycation products during aging is presented, pathophysiological effects of glycation are discussed and ways of attenuation of the effects of glycation are described, concentrating on prevention of glycation. The effects of glycation and glycation inhibitors on the course of selected age-related diseases, such as Alzheimer's disease, Parkinson's disease and cataract are also reviewed.

Characterization of the Rat GAL2R Promoter: Positive Role of ETS-1 in Regulation of the Rat GAL2R Gene in PC12 Cells

Galanin receptor 2 (GAL2R) is a G protein-coupled receptor for the neuropeptide galanin that regulates many important physiological functions and pathological processes. To investigate the molecular mechanism governing GAL2R gene transcription, the rat GAL2R promoter was isolated and analyzed. We found that the region from -320 to -300 of the GAL2R promoter contains two putative ETS-1 elements and plays an important role in regulating GAL2R promoter activity. We also showed that transcription factor ETS-1 bound to this region in vitro and in vivo. Overexpression of ETS-1 significantly increased GAL2R promoter activity and transcription of the GAL2R gene, whereas knockdown of ETS-1 produced the opposite effects. In addition, we showed that ETS-1 recruited co-activator p300 to the GAL2R promoter. These data indicate a role for ETS-1 in the control of the GAL2R gene expression and provide a basis for understanding the transcriptional regulation of the GAL2R gene.

Expression of galanin and its receptors are perturbed in a rodent model of mild, blast-induced traumatic brain injury

The symptomatology, mood and cognitive disturbances seen in post-traumatic stress disorder (PTSD) and mild blast-induced traumatic brain injury (mbTBI) overlap considerably. However the pathological mechanisms underlying the two conditions are currently unknown. The neuropeptide galanin has been suggested to play a role in the development of stress and mood disorders. Here we applied bio- and histochemical methods with the aim to elucidate the nature of any changes in the expression of galanin and its receptors in a rodent model of mbTBI. In situ hybridization and quantitative polymerase chain reaction studies revealed significant, injury-induced changes, in some cases lasting at least for one week, in the mRNA levels of galanin and/or its three receptors, galanin receptor 1-3 (GalR1-3). Such changes were seen in several forebrain regions, and the locus coeruleus. In the ventral periaqueductal gray GalR1 mRNA levels were increased, while GalR2 were decreased. Analysis of galanin peptide levels using radioimmunoassay demonstrated an increase in several brain regions including the locus coeruleus, dorsal hippocampal formation and amygdala. These findings suggest a role for the galanin system in the endogenous response to mbTBI, and that pharmacological studies of the effects of activation or inhibition of different galanin receptors in combination with functional assays of behavioral recovery may reveal promising targets for new therapeutic strategies in mbTBI.

Development of Spexin-based Human Galanin Receptor Type II-Specific Agonists with Increased Stability in Serum and Anxiolytic Effect in Mice

The novel neuropeptide spexin (SPX) was discovered to activate galanin receptor 2 (GALR2) and 3 (GALR3) but not galanin receptor 1 (GALR1). Although GALR2 is known to display a function, particularly in anxiety, depression, and appetite regulation, the further determination of its function would benefit from a more stable and selective agonist that acts only at GALR2. In the present study, we developed a GALR2-specific agonist with increased stability in serum. As galanin (GAL) showed a low affinity to GALR3, the residues in SPX were replaced with those in GAL, revealing that particular mutations such as Gln5 → Asn, Met7 → Ala, Lys11 → Phe, and Ala13 → Pro significantly decreased potencies toward GALR3 but not toward GALR2. Quadruple (Qu) mutation of these residues still retained potency to GALR2 but totally abolished the potency to both GALR3 and GALR1. The first amino acid modifications or D-Asn1 substitution significantly increased the stability when they are incubated in 100% fetal bovine serum. Intracerebroventricular administration of the mutant peptide with D-Asn1 and quadruple substitution (dN1-Qu) exhibited an anxiolytic effect in mice. Taken together, the GALR2-specific agonist with increased stability can greatly help delineation of GALR2-mediated functions and be very useful for treatments of anxiety disorder.

Galanin microinjection into the dorsal periaqueductal gray matter produces paradigm-dependent anxiolytic effects

Galanin is a peptide that is present in the central nervous system in mammals, including rodents and humans. The actions of galanin are mediated by three types of metabotropic receptors: GAL1, GAL2, and GAL3. GAL1 and GAL3 increase K(+) efflux, and GAL2 increases intracellular Ca(2+) levels. The distribution of galanin and its receptors suggests its involvement in fear and/or anxiety. The periaqueductal gray matter (PAG) is a key mediator of defensive behaviors that is both targeted by galaninergic projections and supplied with GAL1 receptors and, less markedly, GAL2 receptors. We examined the effects of galanin microinjections in the dorsal PAG (dPAG) on the performance of rats in different models of anxiety. Male Wistar rats (n=7-12) were implanted with guide cannulae in the dPAG. They received microinjections of either galanin (0.3, 1.0, and 3.0 nmol) or vehicle and were tested in the Vogel conflict test (VCT), elevated plus maze (EPM), and elevated T-maze (ETM). Rats that were tested in the ETM were further evaluated for exploratory activity in the open field test (OFT). Galanin microinjections had no effects on anxiety-like behavior in the EPM or VCT or exploratory activity in the EPM or OFT. In the ETM, however, microinjections of 3 nmol galanin impaired learned anxiety (i.e., avoidance of the open arms) without changing unconditioned fear (i.e., escape from the open arms). The present data suggest that galanin transmission in the dPAG inhibits the acquisition of anxiety-like responses in the ETM.

Regulation of neurological and neuropsychiatric phenotypes by locus coeruleus-derived galanin

Decades of research confirm that noradrenergic locus coeruleus (LC) neurons are essential for arousal, attention, motivation, and stress responses. While most studies on LC transmission focused unsurprisingly on norepinephrine (NE), adrenergic signaling cannot account for all the consequences of LC activation. Galanin coexists with NE in the vast majority of LC neurons, yet the precise function of this neuropeptide has proved to be surprisingly elusive given our solid understanding of the LC system. To elucidate the contribution of galanin to LC physiology, here we briefly summarize the nature of stimuli that drive LC activity from a neuroanatomical perspective. We go on to describe the LC pathways in which galanin most likely exerts its effects on behavior, with a focus on addiction, depression, epilepsy, stress, and Alzheimer׳s disease. We propose a model in which LC-derived galanin has two distinct functions: as a neuromodulator, primarily acting via the galanin 1 receptor (GAL1), and as a trophic factor, primarily acting via galanin receptor 2 (GAL2). Finally, we discuss how the recent advances in neuropeptide detection, optogenetics and chemical genetics, and galanin receptor pharmacology can be harnessed to identify the roles of LC-derived galanin definitively. This article is part of a Special Issue entitled SI: Noradrenergic System.

The generation of knock-in mice expressing fluorescently tagged galanin receptors 1 and 2

The neuropeptide galanin has diverse roles in the central and peripheral nervous systems, by activating the G protein-coupled receptors Gal1, Gal2 and the less studied Gal3 (GalR1-3 gene products). There is a wealth of data on expression of Gal1-3 at the mRNA level, but not at the protein level due to the lack of specificity of currently available antibodies. Here we report the generation of knock-in mice expressing Gal1 or Gal2 receptor fluorescently tagged at the C-terminus with, respectively, mCherry or hrGFP (humanized Renilla green fluorescent protein). In dorsal root ganglia (DRG) neurons expressing the highest levels of Gal1-mCherry, localization to the somatic cell membrane was detected by live-cell fluorescence and immunohistochemistry, and that fluorescence decreased upon addition of galanin. In spinal cord, abundant Gal1-mCherry immunoreactive processes were detected in the superficial layers of the dorsal horn, and highly expressing intrinsic neurons of the lamina III/IV border showed both somatic cell membrane localization and outward transport of receptor from the cell body, detected as puncta within cell processes. In brain, high levels of Gal1-mCherry immunofluorescence were detected within thalamus, hypothalamus and amygdala, with a high density of nerve endings in the external zone of the median eminence, and regions with lesser immunoreactivity included the dorsal raphe nucleus. Gal2-hrGFP mRNA was detected in DRG, but live-cell fluorescence was at the limits of detection, drawing attention to both the much lower mRNA expression than to Gal1 in mice and the previously unrecognized potential for translational control by upstream open reading frames (uORFs).

Galanin receptors as a potential target for neurological disease

INTRODUCTION

Galanin is a 29/30 amino acid long neuropeptide that is widely expressed in the brains of many mammals. Galanin exerts its biological activities through three different G protein-coupled receptors, GalR1, GalR2 and GalR3. The widespread distribution of galanin and its receptors in the CNS and the various physiological and pharmacological effects of galanin make the galanin receptors attractive drug targets.

AREAS COVERED

This review provides an overview of the role of galanin and its receptors in the CNS, the involvement of the galaninergic system in various neurological diseases and the development of new galanin receptor-specific ligands.

EXPERT OPINION

Recent advances and novel approaches in migrating the directions of subtype-selective ligand development and chemical modifications of the peptide backbone highlight the importance of the galanin neurochemical system as a potential target for drug development.

Physiology, signaling, and pharmacology of galanin peptides and receptors: three decades of emerging diversity

Galanin was first identified 30 years ago as a "classic neuropeptide," with actions primarily as a modulator of neurotransmission in the brain and peripheral nervous system. Other structurally-related peptides-galanin-like peptide and alarin-with diverse biologic actions in brain and other tissues have since been identified, although, unlike galanin, their cognate receptors are currently unknown. Over the last two decades, in addition to many neuronal actions, a number of nonneuronal actions of galanin and other galanin family peptides have been described. These include actions associated with neural stem cells, nonneuronal cells in the brain such as glia, endocrine functions, effects on metabolism, energy homeostasis, and paracrine effects in bone. Substantial new data also indicate an emerging role for galanin in innate immunity, inflammation, and cancer. Galanin has been shown to regulate its numerous physiologic and pathophysiological processes through interactions with three G protein-coupled receptors, GAL1, GAL2, and GAL3, and signaling via multiple transduction pathways, including inhibition of cAMP/PKA (GAL1, GAL3) and stimulation of phospholipase C (GAL2). In this review, we emphasize the importance of novel galanin receptor-specific agonists and antagonists. Also, other approaches, including new transgenic mouse lines (such as a recently characterized GAL3 knockout mouse) represent, in combination with viral-based techniques, critical tools required to better evaluate galanin system physiology. These in turn will help identify potential targets of the galanin/galanin-receptor systems in a diverse range of human diseases, including pain, mood disorders, epilepsy, neurodegenerative conditions, diabetes, and cancer.

In silico Analysis and Experimental Validation of Lignan Extracts from Kadsura longipedunculata for Potential 5-HT1AR Agonists

Objectives

Kadsura longipedunculata (KL) has been widely used for the treatment of insomnia in traditional Chinese medicine. The aim of this study was to explore the mechanism of the sedative and hypnotic effects of KL.

Materials and Methods

The content of KL was evaluated by HPLC-TOF-MS, and a potential target was found and used to construct its 3D structure to screen for potential ligands among the compounds in KL by using bioinformatics analysis, including similarity ensemble approach (SEA) docking, homology modeling, molecular docking and ligand-based pharmacophore. The PCPA-induced insomnia rat model was then applied to confirm the potential targets related to the sedative effects of KL by performing the forced swimming test (FST), the tail suspension test (TST) and the measurement of target-related proteins using western blotting and immunofluorescence.

Results

Bioinformatics analysis showed that most of lignan compounds in KL were optimal ligands for the 5-HT1A receptor (5-HT1AR), and they were found to be potential targets related to sedative effects; the main lignan content of KL extracts was characterized by HPLC-TOF-MS, with 7 proposed lignans detected. Administration of KL could significantly reduce FST and TST immobility time in the PCPA-induced 5HT-depleted insomnia rat model. The expressions of proteins related to the 5-HT1AR pathway were regulated by extracts of KL in a concentration-dependent manner, indicating that extracts of KL had 5-HT1AR agonist-like effects.

Conclusion

In silico analysis and experimental validation together demonstrated that lignan extracts from KL can target 5-HT1AR in insomniac rats, which could shed light on its use as a potential 5-HT1AR agonist drug.

A role for galanin N-terminal fragment (1-15) in anxiety- and depression-related behaviors in rats

BACKGROUND

Galanin (GAL) plays a role in mood regulation. In this study we analyzed the action of the active N-terminal fragment [GAL(1-15)] in anxiety- and depression-related behavioral tests in rats.

METHODS

The effect of GAL(1-15) was analyzed in the forced swimming test, tail suspension test, open field test, and light/dark test. The proximity of GAL1 and GAL2 receptors was examined with the proximity ligation assay (PLA). We tested the GAL receptors involved in GAL(1-15) effects with the GAL2 receptor antagonist M871 and with an in vivo model of siRNA GAL2 receptor knockdown or siRNA GAL1 receptor knockdown rats. The effects of GAL(1-15) were also studied in the cell line RN33B.

RESULTS

GAL(1-15) induced strong depression-like and anxiogenic-like effects in all the tests. These effects were stronger than the ones induced by GAL. The involvement of the GAL2 receptor was demonstrated with M871 and with the siRNA GAL2 receptor knockdown rats. The PLA indicated the possible existence of GAL1 and GAL2 heteroreceptor complexes in the dorsal hippocampus and especially in the dorsal raphe nucleus. In the siRNA GAL1 receptor knockdown rats the behavioral actions of GAL(1-15) disappeared, and in the siRNA GAL2 receptor knockdown rats the reductions of the behavioral actions of GAL(1-15) was linked to a disappearance of PLA. In the cell line RN33B, GAL(1-15) decreased 5-HT immunoreactivity more strongly than GAL.

CONCLUSIONS

Our results indicate that GAL(1-15) exerts strong depression-related and anxiogenic-like effects and may give the basis for the development of drugs targeting GAL1 and GAL2 heteroreceptor complexes in the raphe-limbic system for the treatment of depression and anxiety.

Gender differences in genetic mouse models evaluated for depressive-like and antidepressant behavior

Depression is a mental disease that affects complex cognitive and emotional functions. It is believed that depression is twice as prevalent in women as in men. This phenomenon may influence the response to various antidepressant therapies, and these differences are still underestimated in clinical treatment. Nevertheless, most of the current findings are based on studies on male animal models, and relatively few of these studies take possible gender differences into consideration. Advancements in genetic engineering over the last two decades have introduced many transgenic lines that have been screened to study the pathomechanisms of depression. In this mini-review, we provide a compendious list of genetically altered mice that underwent tests for depressive-like or antidepressant behavior and determine if and how the gender factor was analyzed in their evaluation. Furthermore, we compile the gender differences in response to antidepressant treatment. On the basis of these analyses, we conclude that in many cases, gender variability is neglected or not taken into consideration in the presented results. We note the necessity of discussing this issue in the phenotypic characterization of transgenic mice, which seems to be particularly important while modeling mental diseases.

GAL3 receptor KO mice exhibit an anxiety-like phenotype

The neuropeptide galanin (GAL) is widely distributed in the central and peripheral nervous systems. It is a modulator of various physiological and pathological processes, and it mediates its effects via three G protein-coupled receptors (GAL1-3 receptors). A role for GAL as a modulator of mood and anxiety was suggested, because GAL and its receptors are highly expressed in limbic brain structures of rodents. In recent years, numerous studies of animal models have suggested an involvement of GAL and GAL1 and GAL2 receptors in anxiety- and depression-related behavior. However, to date, there is sparse literature implicating GAL3 receptors in behavioral functions. Therefore, we studied the behavior of GAL3 receptor-deficient (GAL3-KO) mice to elucidate whether GAL3 receptors are involved in mediating behavior-associated actions of GAL. The GAL3-KO mouse line exhibited normal breeding and physical development. In addition to behavioral tests, phenotypic characterization included analysis of hematology, amino acid profiles, metabolism, and sudomotor function. In contrast to WT littermates, male GAL3-KO mice exhibited an anxiety-like phenotype in the elevated plus maze, open field, and light/dark box tests, and they were less socially affiliated than WT animals to a stranger mouse in a social interaction test. In conclusion, our data suggest involvement of GAL3 receptors in GAL-mediated effects on mood, anxiety, and behavior, making it a possible target for alternative treatment strategies for mood disorders.

Trophic Mechanisms for Exercise-Induced Stress Resilience: Potential Role of Interactions between BDNF and Galanin

Current concepts of the neurobiology of stress-related disorders, such as anxiety and depression emphasize disruptions in neural plasticity and neurotrophins. The potent trophic actions of exercise, therefore, represent not only an effective means for prevention and treatment of these disorders, they also afford the opportunity to employ exercise paradigms as a basic research tool to uncover the neurobiological mechanisms underlying these disorders. Novel approaches to studying stress-related disorders focus increasingly on trophic factor signaling in corticolimbic circuits that both mediate and regulate cognitive, behavioral, and physiological responses to deleterious stress. Recent evidence demonstrates that the neural plasticity supported by these trophic mechanisms is vital for establishing and maintaining resilience to stress. Therapeutic interventions that promote these mechanisms, be they pharmacological, behavioral, or environmental, may therefore prevent or reverse stress-related mental illness by enhancing resilience. The present paper will provide an overview of trophic mechanisms responsible for the enhancement of resilience by voluntary exercise with an emphasis on brain-derived neurotrophic factor, galanin, and interactions between these two trophic factors.

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

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

Antidepressant and anticonvulsant effects of exercise in a rat model of epilepsy and depression comorbidity

The bidirectional comorbidity between epilepsy and depression is associated with severe challenges for treatment efficacy and safety, often resulting in poor prognosis and outcome for the patient. We showed previously that rats selectively bred for depression-like behaviors (SwLo rats) also have increased limbic seizure susceptibility compared with their depression-resistant counterparts (SwHi rats). In this study, we examined the therapeutic efficacy of voluntary exercise in our animal model of epilepsy and depression comorbidity. We found that chronic wheel running significantly increased both struggling duration in the forced swim test and latency to pilocarpine-induced limbic motor seizure in SwLo rats but not in SwHi rats. The antidepressant and anticonvulsant effects of exercise were associated with an increase in galanin mRNA specifically in the locus coeruleus of SwLo rats. These results demonstrate the beneficial effects of exercise in a rodent model of epilepsy and depression comorbidity and suggest a potential role for galanin.

Receptor subtype-dependent galanin actions on gamma-aminobutyric acidergic neurotransmission and ethanol responses in the central amygdala

The neuropeptide galanin and its three receptor subtypes (GalR1-3) are expressed in the central amygdala (CeA), a brain region involved in stress- and anxiety-related behaviors, as well as alcohol dependence. Galanin also has been suggested to play a role in alcohol intake and alcohol dependence. We examined the effects of galanin in CeA slices from wild-type and knockout (KO) mice deficient of GalR2 and both GalR1 and GalR2 receptors. Galanin had dual effects on gamma-aminobutyric acid (GABA)-ergic transmission, decreasing the amplitudes of pharmacologically isolated GABAergic inhibitory postsynaptic potentials (IPSPs) in over half of CeA neurons but augmenting IPSPs in the others. The increase in IPSP size was absent after superfusion of the GalR3 antagonist SNAP 37889, whereas the IPSP depression was absent in CeA neurons of GalR1 × GalR2 double KO and GalR2 KO mice. Paired-pulse facilitation studies showed weak or infrequent effects of galanin on GABA release. Thus, galanin may act postsynaptically through GalR3 to augment GABAergic transmission in some CeA neurons, whereas GalR2 receptors likely are involved in the depression of IPSPs. Co-superfusion of ethanol, which augments IPSPs presynaptically, together with galanin caused summated effects of ethanol and galanin in those CeA neurons showing galanin-augmented IPSPs, suggesting the two agents act via different mechanisms in this population. However, in neurons showing IPSP-diminishing galanin effects, galanin blunted the ethanol effects, suggesting a preemptive effect of galanin. These findings may increase understanding of the complex cellular mechanisms that underlie the anxiety-related behavioral effects of galanin and ethanol in CeA.

Regulation of drug and palatable food overconsumption by similar peptide systems

This review is aimed at understanding some of the common neurochemical, behavioral and physiological determinants of drug and food overconsumption. Much current work has been devoted to determining the similarities between the brain circuits controlling excessive use of addictive drugs and the overconsumption of palatable foods. The brain systems involved likely include peptides of both mesolimbic and hypothalamic origin. Evidence gathered from expression and injection studies suggests that the consumption of drugs, such as ethanol and nicotine, and also of palatable foods rich in fat is stimulated by different orexigenic peptides, such as enkephalin, galanin, orexin, and melaninconcentrating hormone, acting within the hypothalamus or various limbic structures, while another peptide, neuropeptide Y, is closely related to carbohydrate consumption and shows an inverse relationship with ethanol and nicotine consumption. Moreover, studies in animal models suggest that a propensity to overconsume these reinforcing substances may result from preexisting disturbances in these same peptide systems. These neurochemical disturbances, in turn, may also be closely linked to specific behaviors associated with excessive consummatory behavior, such as hyperactivity or novelty-seeking, palatable food preference, and also fluctuations in circulating lipid levels. Clear understanding of the relationship between these various determinants of consummatory behavior will allow researchers to effectively predict and examine at early stages of exposure animals that are prone to drug and food overconsumption. This work may ultimately aid in the identification of inherent traits that increase the risk for drug abuse and palatable food overconsumption.

Regulation of the galanin system by repeated electroconvulsive seizures in mice

Even though induction of seizures by electroconvulsive stimulation (ECS) is a treatment widely used for major depression in humans, the working mechanism of ECS remains uncertain. The antiepileptic effect of ECS has been suggested to be involved in mediating the therapeutic effect of ECS. The neuropeptide galanin exerts antiepileptic and antidepressant-like effects and has also been implicated in the pathophysiology of depression. To explore a potential role of galanin in working mechanisms of ECS, the present study examined effects of repeated ECS on the galanin system using QRT-PCR, in situ hybridization, and [(125) I]galanin receptor binding. ECS was administered to adult mice daily for 14 days, and this paradigm was confirmed to exert antidepressant-like effect in the tail suspension test. Prominent increases in galanin gene expression were found in several brain regions involved in regulation of epileptic activity and depression, including the piriform cortex, hippocampal dentate gyrus, and amygdala. Likewise, GalR2 gene expression was up-regulated in both the central and the medial amygdala, whereas GalR1 gene expression showed a modest down-regulation in the medial amygdala. [(125) I]galanin receptor binding in the piriform cortex, hippocampus, and amygdala was found to be significantly down-regulated. These data show that the galanin system is regulated by repeated ECS in a number of brain regions implicated in seizure regulation and depression. These changes may play a role in the therapeutic effect of ECS.

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.