The effects of galanin-like peptide on energy balance, body temperature and brain activity in the mouse and rat are independent of the GALR2/3 receptor

Effect of Intracerebroventricular Administration of Galanin-Like Peptide on Hepatokines in C57BL/6 J Mice

Galanin-like peptide (GALP) is a neuropeptide that was first isolated and identified from the porcine hypothalamus. Studies have described an anti-obesity effect of GALP. We previously found that intracerebroventricular administration of GALP in mice resulted in an increase in respiratory exchange rate 12 to 16 h later. GALP may also affect glucose metabolism, but the detailed mechanism has not been elucidated. In this study, we investigated the effects of GALP on glucose and lipid metabolism in the liver. Nine-week-old male C57BL / 6 J mice were administered a single intracerebroventricular dose of saline or GALP and dissected 16 h later. There were no significant between-group differences in body weight and blood glucose levels. With regard to gene and protein expression, G6Pase associated with hepatic gluconeogenesis was significantly reduced in the GALP group. In addition, the hepatokines selenoprotein P and fetuin-A, which induce insulin resistance in the liver, were significantly decreased in the GALP group. These results suggest that intracerebroventricular administration of GALP decreases the expression of key hepatokines, thereby enhancing glucose metabolism.

Natural product P57 induces hypothermia through targeting pyridoxal kinase

Induction of hypothermia during hibernation/torpor enables certain mammals to survive under extreme environmental conditions. However, pharmacological induction of hypothermia in most mammals remains a huge challenge. Here we show that a natural product P57 promptly induces hypothermia and decreases energy expenditure in mice. Mechanistically, P57 inhibits the kinase activity of pyridoxal kinase (PDXK), a key metabolic enzyme of vitamin B6 catalyzing phosphorylation of pyridoxal (PL), resulting in the accumulation of PL in hypothalamus to cause hypothermia. The hypothermia induced by P57 is significantly blunted in the mice with knockout of PDXK in the preoptic area (POA) of hypothalamus. We further found that P57 and PL have consistent effects on gene expression regulation in hypothalamus, and they may activate medial preoptic area (MPA) neurons in POA to induce hypothermia. Taken together, our findings demonstrate that P57 has a potential application in therapeutic hypothermia through regulation of vitamin B6 metabolism and PDXK serves as a previously unknown target of P57 in thermoregulation. In addition, P57 may serve as a chemical probe for exploring the neuron circuitry related to hypothermia state in mice.

The evolving roles of alarin in physiological and disease conditions, and its future potential clinical implications

Alarin is a member of the galanin family of neuropeptides that is widely expressed in the central nervous system and peripheral tissues in humans and rodents. It was initially isolated fifteen years ago in ganglionic cells of human neuroblastoma. Subsequently, it was demonstrated to be broadly distributed in the blood vessels, skin, eyes, peripheral and central nervous systems, thymus, gastrointestinal tract, and endocrine organs of different species. Alarin is a 25 amino acid neuropeptide derived from the alternative splicing of the GALP gene, missing exon 3. It is found to be involved in several physiological functions that include feeding behavior, energy homeostasis, glucose homeostasis, body temperature, and reproduction. It has also vasoactive, anti-inflammatory, anti-edema, and antimicrobial activities. However, the physiological effects of alarin have not been fully elucidated and the receptors that mediate these effects are not currently known. Unearthing the novel biological effects of alarin and its unidentified receptors will therefore be a task in future biomedical research. In addition, alarin is involved in various disease conditions, such as metabolic syndrome, obesity, insulin resistance, type 2 diabetes, diabetic retinopathy, hypertension, cardiac fibrosis, polycystic ovarian syndrome, and depression. Thus, alarin may serve as a promising tool for future pharmacological treatment and diagnosis. But further research is awaited to confirm whether alarin has a protective or pathological role in these diseases. This article provides a comprehensive review on the evolving implications of alarin in a variety of physiological and disease conditions, and its future perspectives.

Inhibitory effect of desflurane on degranulation of mast cells induced by lateral ventricular injection of stimulator-C48/80 in C57BL/6 male mice

Inhalation of anesthetic agents have been observed to confer neuroprotection for decades. The present study was intended to determine whether desflurane (DES) prohibits mast cells (MCs) from degranulation induced by lateral ventricular injection (LVC) with Compound 48/80 (C48/80) in C57BL/6. Total 100 mice were recruited to this study, but only 88 male mice (20–24 weeks) were survived from the procedure, and randomized and allocated into four groups: (A) the saline group; (B) the C48/80 group; (C) the sodium cromoglycate (CRO + C48/80) group; (D) 7.5% DES preconditioning for 2 h + C48/80 lateral ventricular injection (DES + C48/80) group. The slices of mice brain thalamus were performed for toluidine blue staining (MCs) and immunochemistry (fluorescence of Iba1 and GFAP, respectively), and brain tissues were extracted to probe IL-6, TNF-α, NF-κB (p65), and TLR4 against GAPDH by western blotting. Our results demonstrated that administration of C48/80 provoked degranulation of mast cells at thalamus, increasing the fluorescence intensities of Iba1 and GFAP, and over-expressing IL-6, TNF-α, NF-κB(p65), and TLR4. However, pre-conditioning inhalation of DES prohibited MCs from degranulation, diminishing the fluorescent intensities of Iba1 and GFAP, decreasing expressed levels of IL-6, TNF-α, NF-κB(p65), as well as TLR4. It suggests inhalation DES could inhibit the neuroinflammation and deactivate glial and astrocytes via direct prohibiting degranulation of MCs at thalamus in the central nervous system (CNS).

Neuropeptidergic Control of Feeding: Focus on the Galanin Family of Peptides

Obesity/overweight are important health problems due to metabolic complications. Dysregulation of peptides exerting orexigenic/anorexigenic effects must be investigated in-depth to understand the mechanisms involved in feeding behaviour. One of the most important and studied orexigenic peptides is galanin (GAL). The aim of this review is to update the mechanisms of action and physiological roles played by the GAL family of peptides (GAL, GAL-like peptide, GAL message-associated peptide, alarin) in the control of food intake and to review the involvement of these peptides in metabolic diseases and food intake disorders in experimental animal models and humans. The interaction between GAL and NPY in feeding and energy metabolism, the relationships between GAL and other substances involved in food intake mechanisms, the potential pharmacological strategies to treat food intake disorders and obesity and the possible clinical applications will be mentioned and discussed. Some research lines are suggested to be developed in the future, such as studies focused on GAL receptor/neuropeptide Y Y₁ receptor interactions in hypothalamic and extra-hypothalamic nuclei and sexual differences regarding the expression of GAL in feeding behaviour. It is also important to study the possible GAL resistance in obese individuals to better understand the molecular mechanisms by which GAL regulates insulin/glucose metabolism. GAL does not exert a pivotal role in weight regulation and food intake, but this role is crucial in fat intake and also exerts an important action by regulating the activity of other key compounds under conditions of stress/altered diet.

Activation of central galanin receptor 2 mitigated insulin resistance in adipocytes of diabetic rats

PURPOSE

Our and other's studies showed that administration of neuropeptide galanin may mitigate insulin resistance via promoting glucose transporter 4 (GLUT4) expression and translocation in rats. The objective of this study is to investigate whether galanin receptor 2 (GAL2-R) in brain mediates the ameliorative effect of galanin on insulin resistance in adipose tissues of type 2 diabetic rats.

METHODS

In this study galanin, GAL2-R agonist M1145 and GAL2-R antagonist M871 were respectively or cooperatively injected into intracerebroventricles of type 2 diabetic rats once a day for successive fifteen days. Then the plasma and fat tissues of rats were used to estimate the alterations of insulin resistance indexes.

RESULTS

The central administration of galanin enhanced 2-deoxy-[³H]-D-glucose, peroxisome proliferator-activated receptor γ and adiponectin levels, food intake and body weight, GLUT4 mRNA expression and GLUT4 concentration in plasma membranes, as well as homeostasis model assessment-insulin resistance index. Those effects of galanin may be blocked by M817, and imitated by M1145 except for food intake and body weight.

CONCLUSION

Those results suggest that central GAL2-R mediates the beneficial effects of galanin on insulin sensitivity in type 2 diabetic rats. GAL2-R agonist may be taken as a potential antidiabetic agent to treat insulin resistance and type 2 diabetes.

Epigenetic upregulation of galanin-like peptide mediates deoxynivalenol induced-growth inhibition in pituitary cells

Deoxynivalenol (DON) is an unavoidable contaminant in human food, animal feeds, and agricultural products. Growth retardation in children caused by extensive DON pollution has become a global problem that cannot be ignored. Previous studies have shown that DON causes stunting in children through intestinal dysfunction, insulin-like growth factor-1 (IGF-1) axis disorder and peptide YY (PYY). Galanin-like peptide (GALP) is an important growth regulator, but its role in DON-induced growth retardation is unclear. In this study, we report the important role of GALP during DON-induced growth inhibition in the rat pituitary tumour cell line GH3. DON was found to increase the expression of GALP through hypomethylationin the promoter region of the GALP gene and upregulate the expression of proinflammatory factors, while downregulate the expression of growth hormone (GH). Furthermore, GALP overexpression promoted proinflammatory cytokines, including TNF-α, IL-1β, IL-11 and IL-6, and further reduced cell viability and cell proliferation, while the inhibitory effect of GALP was the opposite. The expression of GALP and insulin like growth factor binding protein acid labile subunit (IGFALS) showed the opposite trend, which was the potential reason for the regulation of cell proliferation by GALP. In addition, GALP has anti-apoptotic effects, which could not eliminate the inflammatory damage of cells, thus aggravating cell growth inhibition. The present findings provide new mechanistic insights into the toxicity of DON-induced growth retardation and suggest a therapeutic potential of GALP in DON-related diseases.

Galanin peptide family regulation of glucose metabolism

Recent preclinical and clinical studies have indicated that the galanin peptide family may regulate glucose metabolism and alleviate insulin resistance, which diminishes the probability of type 2 diabetes mellitus. The galanin was discovered in 1983 as a gut-derived peptide hormone. Subsequently, galanin peptide family was found to exert a series of metabolic effects, including the regulation of gut motility, body weight and glucose metabolism. The galanin peptide family in modulating glucose metabolism received recently increasing recognition because pharmacological activiation of galanin signaling might be of therapeutic value to improve insuin resistance and type 2 diabetes mellitus. To date, however, few papers have summarized the role of the galanin peptide family in modulating glucose metabolism and insulin resistance. In this review we summarize the metabolic effect of galanin peptide family and highlight its glucoregulatory action and discuss the pharmacological value of galanin pathway activiation for the treatment of glucose intolerance and type 2 diabetes mellitus.

Activiated galanin receptor 2 attenuates insulin resistance in skeletal muscle of obese mice

The results of our and other's studies showed that activation of galanin receptor 1 could mitigate insulin resistance via promoting glucose transporter 4 (GLUT4) expression and translocation in the skeletal muscle of rats. But no literature are available regarding the effect of galanin receptor 2 (GALR2) on insulin resistance in skeletal muscle of type 2 diabetes. Herein, in this study we intended to survey the effect of GALR2 and its signal mechanisms in the mice with high fat diet-induced obese. The mice were intraperitoneally injected with vehicle, GALR2 agonist M1145 and antagonist M871 respectively once a day for continuous 21 days. The skeletal muscles were processed for determination of glucose uptake, and GLUT4 mRNA and protein expression levels. The PGC-1α, AKT, p38MAPK, AS160, pAKT, pP38MAPK and pAS160 expression levels were quantitatively assessed too. We found that pharmacological activation of GALR2 enhanced energy expenditure, and increased GLUT4 expression and translocation in skeletal muscle of mice during high-fat diet regimens. Activation of GALR2 alleviated insulin resistance through P38MAPK/PGC-1α/GLUT4 and AKT/AS160/GLUT4 pathway in the skeletal muscle of mice. Overall, these results identify that GALR2 is a regulator of insulin resistance and activation of GALR2 represents a promising strategy against obesity-induced insulin resistance.

Anti-obesity effect of intranasal administration of galanin-like peptide (GALP) in obese mice

Galanin-like peptide (GALP) has an anti-obesity effect in rats and mice. It has been reported that the uptake of GALP by the brain is higher after intranasal administration than with intravenous injection. This study therefore aimed to clarify the effect of intranasal administration of GALP on the feeding behavior of lean and obese mice. Autoradiography revealed the presence of (125)I-GALP in the olfactory bulb and the brain microcirculation. The body weights of ob/ob mice gradually increased during vehicle treatment, but remained unchanged in response to repeated intranasal administration of GALP, with both ob/ob and diet-induced obese mice displaying significantly decreased food intake, water intake and locomotor activity when treated with GALP. These results suggest that intranasal administration is an effective route whereby GALP can exert its effect as an anti-obesity drug.

Autonomic nervous system-mediated effects of galanin-like peptide on lipid metabolism in liver and adipose tissue

Galanin-like peptide (GALP) is a neuropeptide involved in the regulation of feeding behavior and energy metabolism in mammals. While a weight loss effect of GALP has been reported, its effects on lipid metabolism have not been investigated. The aim of this study was to determine if GALP regulates lipid metabolism in liver and adipose tissue via an action on the sympathetic nervous system. The respiratory exchange ratio of mice administered GALP intracerebroventricularly was lower than that of saline-treated animals, and fatty acid oxidation-related gene mRNA levels were increased in the liver. Even though the respiratory exchange ratio was reduced by GALP, this change was not significant when mice were treated with the sympatholytic drug, guanethidine. Lipolysis-related gene mRNA levels were increased in the adipose tissue of GALP-treated mice compared with saline-treated animals. These results show that GALP stimulates fatty acid β-oxidation in liver and lipolysis in adipose tissue, and suggest that the anti-obesity effect of GALP may be due to anorexigenic actions and improvement of lipid metabolism in peripheral tissues via the sympathetic nervous system.

Type 2 diabetes mellitus as a disorder of galanin resistance

The increasing prevalence of type 2 diabetes mellitus with its high morbidity and mortality becomes an important health problem. The multifactorial etiology of type 2 diabetes mellitus is relative to many gene and molecule alterations, and increased insulin resistance. Besides these, however, there are still other predisposing and risk factors accounting for type 2 diabetes mellitus not to be identified and recognized. Emerging evidence indicated that defects in galanin function played a crucial role in development of type 2 diabetes mellitus. Galanin homeostasis is tightly relative to insulin resistance and is regulated by blood glucose. Hyperglycemia, hyperinsulinism, enhanced plasma galanin levels and decreased galanin receptor activities are some of the characters of type 2 diabetes mellitus. The discrepancy between high insulin level and low glucose handling is named as insulin resistance. Similarly, the discrepancy between high galanin level and low glucose handling may be denominated as galanin resistance too. In this review, the characteristic milestones of type 2 diabetes mellitus were condensed as two analogical conceptual models, obesity-hyper-insulin-insulin resistance-type 2 diabetes mellitus and obesity-hyper-galanin-galanin resistance-type 2 diabetes mellitus. Both galanin resistance and insulin resistance are correlative with each other. Conceptualizing the etiology of type 2 diabetes mellitus as a disorder of galanin resistance may inspire a new concept to deepen our knowledge about pathogenesis of type 2 diabetes mellitus, eventually leading to novel preventive and therapeutic interventions for type 2 diabetes mellitus.

The regulative effect of galanin family members on link of energy metabolism and reproduction

It is essential for the species survival that an efficient coordination between energy storage and reproduction through endocrine regulation. The neuropeptide galanin, one of the endocrine hormones, can potently coordinate energy metabolism and the activities of hypothalamic-pituitary-gonadal reproductive axis to adjust synthesis and release of metabolic and reproductive hormones in animals and humans. However, few papers have summarized the regulative effect of the galanin family members on the link of energy storage and reproduction as yet. To address this issue, this review attempts to summarize the current information available about the regulative effect of galanin, galanin-like peptide and alarin on the metabolic and reproductive events, with special emphasis on the interactions between galanin and hypothalamic gonadotropin-releasing hormone, pituitary luteinizing hormone and ovarian hormones. This research line will further deepen our understanding of the physiological roles of the galanin family in regulating the link of energy metabolism and reproduction.

Galanin and galanin-like peptide modulate vasopressin and oxytocin release in vitro: the role of galanin receptors

Galanin (Gal) and galanin-like peptide (GALP) may be involved in the mechanisms of the hypothalamo-neurohypophysial system. The aim of the present in vitro study was to compare the influence of Gal and GALP on vasopressin (AVP) and oxytocin (OT) release from isolated rat neurohypophysis (NH) or hypothalamo-neurohypophysial explants (Hth-NH). The effect of Gal/GALP on AVP/OT secretion was also studied in the presence of galantide, the non-selective galanin receptors antagonist. Gal at concentrations of 10(-10 )M and 10(-8 )M distinctly inhibited basal and K(+)-stimulated AVP release from the NH and Hth-NH explants, whereas Gal exerted a similar action on OT release only during basal incubation. Gal added to the incubation medium in the presence of galantide did not exert any action on the secretion of either neurohormone from NH and Hth-NH explants. GALP (10(-10 )M and 10(-9 )M) induced intensified basal AVP release from the NH and Hth-NH complex as well as the release of potassium-evoked AVP from the Hth-NH. The same effect of GALP has been observed in the presence of galantide. GALP added to basal incubation medium was the reason for stimulated OT release from the NH as well as from the Hth-NH explants. However, under potassium-stimulated conditions, OT release from the NH and Hth-NH complexes has been observed to be distinctly impaired. Galantide did not block this inhibitory effect of GALP on OT secretion. It may be concluded that: (i) Gal as well as GALP modulate AVP and OT release at every level of the hypothalamo-neurohypophysial system; (ii) Gal acts in the rat central nervous system as the inhibitory neuromodulator for AVP and OT release via its galanin receptors; (iii) the stimulatory effect of GALP on AVP and OT release is likely to be mediated via an unidentified specific GALP receptor(s).

Interactive effect of galanin-like peptide (GALP) and spontaneous exercise on energy metabolism

Galanin-like peptide (GALP) is a neuropeptide involved in energy metabolism. The interactive effect of GALP and exercise on energy metabolism has not been investigated. The aim of this study was to determine if energy metabolism in spontaneously exercising mice could be promoted by intracerebroventricular (ICV) GALP administration. Changes in respiratory exchange ratio in response to GALP ICV administration indicated that lipids were primarily consumed followed by a continuous consumption of glucose throughout the dark period in non-exercising mice. In mice permitted to spontaneously exercise on a running-wheel, GALP ICV administration increased the consumed oxygen volume and heat production level from 5 to 11h after administration. These effects occurred independently from the total running distance. The interaction between GALP ICV administration and spontaneous exercise decreased body weight within 24h (F(1,16)=5.772, p<0.05), with no significant interaction observed regarding food and water intake or total distance. Energy metabolism-related enzymes were assessed in liver and skeletal muscle samples, with a significant interaction on mRNA expression between GALP ICV administration and spontaneous exercise observed in phosphoenolpyruvate carboxykinase (F(1,16)=18.602, p<0.001) that regulates gluconeogenesis and glucose transporter-4 (F(1,16)=21.092, p<0.001). GALP significantly decreased the mRNA expression of sterol regulatory element-binding protein-1c (p<0.05) that regulates fatty acid synthesis regardless of spontaneous exercise with no changes to acetyl-CoA carboxylase a and fatty acid synthetase. These results indicate the GALP ICV administration can further promote energy metabolism when administered to spontaneously exercising mice.

Alarin 6-25Cys antagonizes alarin-specific effects on food intake and luteinizing hormone secretion

Previous data from our labs and from others have demonstrated that intracerebroventricular (ICV) injection of alarin has orexigenic activity and significantly increases plasma luteinizing hormone (LH) secretion in a gonadotropin-releasing hormone (GnRH) dependent manner. The purpose of the current experiments was to determine if the amino acids at the amino-terminal end of the alarin peptide are critical for alarin's effects on reproductive and feeding systems. First, we injected male mice ICV with full-length alarin (Ala1-25) or peptide fragments missing residues at the amino-terminal end (Ala3-25 or Ala6-25 Cys). Neither peptide fragment alone, significantly increased food intake in male mice compared to controls. Second, ICV injection of Ala1-25, but not Ala3-25, significantly (p < 0.01) increased GnRH-mediated LH secretion. Surprisingly, Ala6-25 Cys significantly (p < 0.05) inhibited plasma LH secretion and inhibited Ala1-25 actions. In conclusion, elimination of the first five amino acids of alarin not only abolishes the biological activity of alarin, but becomes an antagonist to alarin-specific effects. Furthermore, Ala6-25 Cys seems to act as a specific antagonist to putative alarin receptors and therefore may be an important tool in identifying alarin-specific receptors.

Galanin peptide family as a modulating target for contribution to metabolic syndrome

Metabolic syndrome (MetS) is defined as abdominal central obesity, atherogenic dyslipidemia, insulin resistance, glucose intolerance and hypertension. The rapid increasing prevalence of MetS and the consequent diseases, such as type 2 diabetes mellitus and cardiovascular disorder, are becoming a global epidemic health problem. Despite considerable research into the etiology of this complex disease, the precise mechanism underlying MetS and the association of this complex disease with the development of type 2 diabetes mellitus and increased cardiovascular disease remains elusive. Therefore, researchers continue to actively search for new MetS treatments. Recent animal studies have indicated that the galanin peptide family of peptides may increase food intake, glucose intolerance, fat preference and the risk for obesity and dyslipidemia while decreasing insulin resistance and blood pressure, which diminishes the probability of type 2 diabetes mellitus and hypertension. To date, however, few papers have summarized the role of the galanin peptide family in modulating MetS. Through a summary of available papers and our recent studies, this study reviews the updated evidences of the effect that the galanin peptide family has on the clustering of MetS components, including obesity, dyslipidemia, insulin resistance and hypertension. This line of research will further deepen our understanding of the relationship between the galanin peptide family and the mechanisms underlying MetS, which will help develop new therapeutic strategies for this complex disease.

Galanin and its receptors: a novel strategy for appetite control and obesity therapy

The rapid increase in the prevalence of overweight and obesity is becoming an important health problem. Overweight and obesity may cause several metabolic complications, including type 2 diabetes mellitus, hyperlipidemia, high cholesterol, coronary artery disease as well as hypertension. Prevention and treatment of obesity will benefit the treatment of these related diseases. Current strategies for treatment of obesity are not adequately effective and are frequently companied with many side effects. Thus, new ways to treat obesity are urgently needed. Galanin is undoubtedly involved in the regulation of food intake and body weight. The aim of this review is to provide up-to-date knowledge concerning the roles of central and peripheral galanin as well as its receptors in the regulation of metabolism, obesity and appetite. We also highlight the mechanisms of galanin and its receptors in experimental obesity, trying to establish a novel anti-obesity strategy.

Sudomotor function and sweat gland innervation in galanin knockout mice

The presence of galanin and galanin binding sites in sweat gland has been demonstrated previously. In order to investigate whether galanin can influence sweat gland function, we compared sweating induced in footpads of wild type and galanin knockout mice by cholinergic and thermal stimulation using the silicone impression technique. Pilocarpine injections resulted in a similar number of reactive sweat glands and non-significant difference in the amount of sweat secretion in wild type and galanin knockout mice. However, thermal stimulation led to a significant increase in the number of secreting sweat glands in galanin knockout mice. To further evaluate possible differences in the innervation of sweat glands that could explain differences in their secretory activity, immunohistochemical labeling of cutaneous and sudomotor innervations against protein gene product 9.5, vasoactive intestinal polypeptide and choline acetyltransferase in plantar pads was performed. Immunohistochemical analysis revealed no significant differences in the distribution and intensity of the innervations between wild type mice and galanin knockout mice. Although our results indicate normal cholinergic responses and innervation of the sweat glands in galanin knockout mice, they also demonstrate that galanin plays a role in regulating the sudomotor activity in response to thermal stimulation.

Effects of alarin on food intake, body weight and luteinizing hormone secretion in male mice

Alarin is a member of the galanin family of neuropeptides that includes galanin and galanin-like peptide (GALP). Alarin is an alternate transcript of the GALP gene and is expressed in the brain and periphery. Recently, it was shown in male rats that alarin is an orexigenic peptide that also regulates reproductive hormone secretion. We hypothesized that alarin would also have similar central effects on feeding and luteinizing hormone (LH) secretion in mice as observed in rats. To test this hypothesis, we treated male mice with alarin intracerebroventricularly (i.c.v.) and measured its effects on food intake, body weight, body temperature, LH secretion, and Fos induction. We observed that i.c.v. injection of 1.0 nmol alarin significantly increased immediate food intake (p<0.01) from 30 to 120 min post-injection and relative body weight (p<0.05) after 24 h. Alarin had no effect on body temperature compared to controls. Alarin increased LH levels in male mice, an effect that was dependent on gonadotropin-Releasing-Hormone (GnRH) signaling. Furthermore, alarin-stimulated Fos immunoreactivity was observed in diencephalic nuclei, including the hypothalamic dorsomedial nucleus and the bed nucleus of the stria terminalis. Our studies demonstrated that alarin, like other members of the galanin peptide family, is a neuromediator of food intake and reproductive hormone secretion in male mice.

Hypothalamic neuropeptides and the regulation of appetite

Neuropeptides released by hypothalamic neurons play a major role in the regulation of feeding, acting both within the hypothalamus, and at other appetite regulating centres throughout the brain. Where classical neurotransmitters signal only within synapses, neuropeptides diffuse over greater distances affecting both nearby and distant neurons expressing the relevant receptors, which are often extrasynaptic. As well as triggering a behavioural output, neuropeptides also act as neuromodulators: altering the response of neurons to both neurotransmitters and circulating signals of nutrient status. The mechanisms of action of hypothalamic neuropeptides with established roles in feeding, including melanin-concentrating hormone (MCH), the orexins, α-melanocyte stimulating hormone (α-MSH), agouti-gene related protein (AgRP), neuropeptide Y, and oxytocin, are reviewed in this article, with emphasis laid on both their effects on appetite regulating centres throughout the brain, and on examining the evidence for their physiological roles. In addition, evidence for the involvement of several putative appetite regulating hypothalamic neuropeptides is assessed including, ghrelin, cocaine and amphetamine-regulated transcript (CART), neuropeptide W and the galanin-like peptides. This article is part of a Special Issue entitled 'Central control of Food Intake'.

Galanin receptors and ligands

The neuropeptide galanin was first discovered 30 years ago. Today, the galanin family consists of galanin, galanin-like peptide (GALP), galanin-message associated peptide (GMAP), and alarin and this family has been shown to be involved in a wide variety of biological and pathological functions. The effect is mediated through three GPCR subtypes, GalR1-3. The limited number of specific ligands to the galanin receptor subtypes has hindered the understanding of the individual effects of each receptor subtype. This review aims to summarize the current data of the importance of the galanin receptor subtypes and receptor subtype specific agonists and antagonists and their involvement in different biological and pathological functions.

Galanin-like peptide and the regulation of feeding behavior and energy metabolism

The hypothalamic neuropeptides modulate physiological activity via G protein-coupled receptors (GPCRs). Galanin-like peptide (GALP) is a 60 amino acid neuropeptide that was originally isolated from porcine hypothalamus using a binding assay for galanin receptors, which belong to the GPCR family. GALP is mainly produced in neurons in the hypothalamic arcuate nucleus. GALP-containing neurons form neuronal networks with several other types of peptide-containing neurons and then regulate feeding behavior and energy metabolism. In rats, the central injection of GALP produces a dichotomous action that involves transient hyperphasia followed by hypophasia and a reduction in body weight, whereas, in mice, it has only one action that reduces both food intake and body weight. In the present minireview, we discuss current evidence regarding the function of GALP, particularly in relation to feeding and energy metabolism. We also examine the effects of GALP activity on food intake, body weight and locomotor activity after intranasal infusion, a clinically viable mode of delivery. We conclude that GALP may be of therapeutic value for obesity and life-style-related diseases in the near future.

Galanin-like peptide (GALP) is a hypothalamic regulator of energy homeostasis and reproduction

Galanin-like peptide (GALP) was discovered in 1999 in the porcine hypothalamus and was found to be a 60 amino acid neuropeptide. GALP shares sequence homology to galanin (1-13) in position 9-21 and can bind to, as well as activate, the three galanin receptor subtypes (GalR1-3). GALP-expressing cells are limited, and are mainly found in the arcuate nucleus of the hypothalamus (ARC) and the posterior pituitary. GALP-positive neurons in the ARC project to several brain regions where they appear to make contact with multiple neuromodulators. These neuromodulators are involved in the regulation of energy homeostasis and reproduction, anatomical evidence that suggests a role for GALP in these physiological functions. In support of this idea, GALP gene expression is regulated by several factors that reflect metabolic state including the metabolic hormones leptin and insulin, thyroid hormones, and blood glucose. Considerable evidence now exists to support the hypothesis that GALP has a role in the regulation of energy homeostasis and reproduction; and, that GALP's role may be independent of the known galanin receptors. In this review, we (1) provide an overview of the distribution of GALP, and discuss the potential relationship between GALP and other neuromodulators of energy homeostasis and reproduction, (2) discuss the metabolic factors that regulate GALP expression, (3) review the evidence for the role of GALP in energy homeostasis and reproduction, (4) discuss the potential downstream mediators and mechanisms underlying GALP's effects, and (5) discuss the possibility that GALP may mediate its effects via an as yet unidentified GALP-specific receptor.

Galanin family of peptides in skin function

The skin, the largest organ of the body, functions as a barrier between the body proper and the external environment, as it is constantly exposed to noxious stressors. During the last few years, the concept of an interactive network involving cutaneous nerves, the neuroendocrine axis, and the immune system has emerged. The neuroendocrine system of the skin is composed of locally produced neuroendocrine mediators that interact with specific receptors. Among these mediators are neuropeptides, including members of the galanin peptide family--galanin, galanin-message associated peptide, galanin-like peptide, and alarin--which are produced in neuronal as well as nonneuronal cells in the skin. Here, we review the expression of the galanin peptides and their receptors in the skin, and the known functions of galanin peptides in different compartments of the skin. We discuss these data in light of the role of the galanin peptide family in inflammation and cell proliferation.

Interleukin-1 mediates the anorexic and febrile actions of galanin-like Peptide

Galanin-like peptide (GALP) is a neuropeptide that has complex actions on energy balance, producing orexigenic effects in the short term in rats but anorexigenic and febrile effects over the longer term in rats and mice. GALP is thought to promote feeding via neuropeptide Y and orexin neurons, but the mediators of the anorexia are unknown. However, the anorexic and febrile actions of GALP are similar in magnitude and profile to those seen after central injections of the cytokine IL-1. Thus, the aim of this study was to test the hypothesis that IL-1 mediates the effects of GALP on energy balance. Intracerebroventricular injection of GALP (1.5 nmol) in male Sprague-Dawley rats stimulated production of IL-1alpha and IL-1beta protein in macrophages and/or microglia in selected brain areas, including the meninges, and periventricular brain regions. Intracerebroventricular injection of GALP in rats stimulated food intake over 1 h but decreased feeding and body weight at 24 h and caused a rise in core body temperature over 8 h. Coinfusion of the IL-1 receptor antagonist had no effect on the GALP-induced orexigenic response but significantly reduced the longer-term actions of GALP observed at 24 h and its effect on body temperature. Furthermore, the actions of GALP on feeding, body weight, and body temperature were significantly reduced in IL-1alpha/beta-, IL-1beta-, or IL-1 type I receptor (IL-1RI)-deficient mice. These data suggest that GALP induces expression of IL-1 in the brain, and its anorexic and febrile actions are mediated by this cytokine acting via IL-1 type I receptor.

Altered response to metabolic challenges in mice with genetically targeted deletions of galanin-like peptide

Galanin-like peptide (GALP) is expressed in the arcuate nucleus and is implicated in the neuroendocrine regulation of metabolism and reproduction. To investigate the physiological significance of GALP, we generated and characterized a strain of mice with a genetically targeted deletion in the GALP gene [GALP knockout (KO) mice]. We report that GALP KO mice have a subtle, but notable, metabolic phenotype that becomes apparent during adaptation to changes in nutrition. GALP KO mice are indistinguishable from wild-type (WT) controls in virtually all aspects of growth, sexual development, body weight, food and water consumption, and motor behaviors, when they are allowed unlimited access to standard rodent chow. However, GALP KO mice have an altered response to changes in diet. 1) Male GALP KO mice consumed less food during refeeding after a fast than WT controls (P < 0.01). 2) GALP KO mice of both sexes gained less weight on a high-fat diet than WT controls (P < 0.01), despite both genotypes having consumed equal amounts of food. We conclude that although GALP signaling may not be essential for the maintenance of energy homeostasis under steady-state nutritional conditions, GALP may play a role in readjusting energy balance under changing nutritional circumstances.

Galanin-like peptide: a role in the homeostatic regulation of energy balance?

Galanin-like peptide (GALP) is a neuropeptide that has been proposed to play a role in the regulation of food intake behaviour and body weight. However, the actions of GALP on energy balance are complex. In rats, it appears to impel both appetite stimulating and suppressing effects, whereas in mice, the only effect is a reduction in food intake. Thus, it is currently unclear whether GALP is important in the homeostatic regulation of energy balance, or if it produces effects on appetite and body weight by non-specific actions. This review discusses current evidence of the role of GALP with respect to energy balance, and the mechanisms involved in its regulation. We describe recent evidence that suggests that GALP may elicit differential effects in different rodent species. Furthermore, we provide an insight into a potential novel role for GALP in inflammation, and discuss how this may relate to the non-homeostatic regulation of energy balance.