Centrally administered galanin-like peptide modifies food intake in the rat: a comparison with galanin

Transcriptomic (DNA Microarray) and Metabolome (LC-TOF-MS) Analyses of the Liver in High-Fat Diet Mice after Intranasal Administration of GALP (Galanin-like Peptide)

The aim of this research was to test the efficacy and potential clinical application of intranasal administration of galanin-like peptide (GALP) as an anti-obesity treatment under the hypothesis that GALP prevents obesity in mice fed a high-fat diet (HFD). Focusing on the mechanism of regulation of lipid metabolism in peripheral tissues via the autonomic nervous system, we confirmed that, compared with a control (saline), intranasally administered GALP prevented further body weight gain in diet-induced obesity (DIO) mice with continued access to an HFD. Using an omics-based approach, we identified several genes and metabolites in the liver tissue of DIO mice that were altered by the administration of intranasal GALP. We used whole-genome DNA microarray and metabolomics analyses to determine the anti-obesity effects of intranasal GALP in DIO mice fed an HFD. Transcriptomic profiling revealed the upregulation of flavin-containing dimethylaniline monooxygenase 3 (Fmo3), metallothionein 1 and 2 (Mt1 and Mt2, respectively), and the Aldh1a3, Defa3, and Defa20 genes. Analysis using the DAVID tool showed that intranasal GALP enhanced gene expression related to fatty acid elongation and unsaturated fatty acid synthesis and downregulated gene expression related to lipid and cholesterol synthesis, fat absorption, bile uptake, and excretion. Metabolite analysis revealed increased levels of coenzyme Q10 and oleoylethanolamide in the liver tissue, increased levels of deoxycholic acid (DCA) and taurocholic acid (TCA) in the bile acids, increased levels of taurochenodeoxycholic acid (TCDCA), and decreased levels of ursodeoxycholic acid (UDCA). In conclusion, intranasal GALP administration alleviated weight gain in obese mice fed an HFD via mechanisms involving antioxidant, anti-inflammatory, and fatty acid metabolism effects and genetic alterations. The gene expression data are publicly available at NCBI GSE243376.

Exogenous galanin alleviates hepatic steatosis by promoting autophagy via the AMPK-mTOR pathway

Defective autophagy-induced intracellular lipid degradation is causally associated with non-alcoholic fatty liver disease (NAFLD) development. Therefore, agents that can restore autophagy may have potential clinical application prospects on this public health issue. Galanin (GAL) is a pleiotropic peptide that regulates autophagy and is a potential drug for the treatment of NAFLD. In this study, we used an MCD-induced NAFLD mouse model in vivo and an FFA-induced HepG2 hepatocyte model in vitro to evaluate the anti-NAFLD effect of GAL. Exogenous GAL supplementation significantly attenuated lipid droplet accumulation and suppressed hepatocyte TG levels in mice and cell models. Mechanistically, Galanin-mediated reduction of lipid accumulation was positively correlated with upregulated p-AMPK, as evidenced by upregulated protein expressions of fatty acid oxidation-related gene markers (PPAR-α and CPT1A), upregulated expressions of the autophagy-related marker (LC3B), and downregulated autophagic substrate p62 levels. In FFA-treated HepG2 cells, activation of fatty acid oxidation and autophagy-related proteins by galanin was reversed by autophagy inhibitors, chloroquine, and the AMPK inhibitor. Galanin ameliorates hepatic fat accumulation by inducing autophagy and fatty acid oxidation via the AMPK/mTOR pathway.

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.

Functions of galanin, spexin and kisspeptin in metabolism, mood and behaviour

The bioactive peptides galanin, spexin and kisspeptin have a common ancestral origin and their pathophysiological roles are increasingly the subject of investigation. Evidence suggests that these bioactive peptides play a role in the regulation of metabolism, pancreatic β-cell function, energy homeostasis, mood and behaviour in several species, including zebrafish, rodents and humans. Galanin signalling suppresses insulin secretion in animal models (but not in humans), is potently obesogenic and plays putative roles governing certain evolutionary behaviours and mood modulation. Spexin decreases insulin secretion and has potent anorectic, analgesic, anxiolytic and antidepressive-like effects in animal models. Kisspeptin modulates glucose-stimulated insulin secretion, food intake and/or energy expenditure in animal models and humans. Furthermore, kisspeptin is implicated in the control of reproductive behaviour in animals, modulation of human sexual and emotional brain processing, and has antidepressive and fear-suppressing effects. In addition, galanin-like peptide is a further member of the galaninergic family that plays emerging key roles in metabolism and behaviour. Therapeutic interventions targeting galanin, spexin and/or kisspeptin signalling pathways could therefore contribute to the treatment of conditions ranging from obesity to mood disorders. However, many gaps and controversies exist, which must be addressed before the therapeutic potential of these bioactive peptides can be established.

ASSESSMENT OF SERUM ALARIN LEVELS IN PATIENTS WITH TYPE 2 DIABETES MELLITUS

OBJECTIVE

We aimed to investigate the potential relationship between plasma alarin levels and type 2 diabetes mellitus (T2DM).

PATIENTS AND METHOD

We included 154 participants, divided into four groups in a cross-sectional study design. The first group includes patients with T2DM without complications (n=30), the second group patients with T2DM with microvascular complications (T2DM-noC n=32), the third group patients with T2DM with macrovascular complications, T2DM-MV (n=32) and the last group is the healthy control group (n=60).

RESULTS

In our study 94 patients were diabetic; 47 females and 47 males. The control group consists of 60 people, 30 women and 30 men. It was found that these had a significant (p>0.05) variation in serum alarin levels among the T2DM (T2DM-noC=3.1±0.7 ng/mL T2DM-mV=2.8±0.4 ng/mL, T2DM-MV= 3.6±0.4 ng/mL) versus control group (15.6±2.6).We failed to find a significant variation of serum alarin levels (p>0.05) between T2DM subgroups. Serum alarin levels were significantly higher among control patients (p<0.05). There was no difference between diabetic sub-groups.

CONCLUSION

We concluded that serum alarin levels in patients with T2DM are lower than in normal people. Further studies are needed to investigate the possible prognostic value of alarin in clinical practice in T2DM.

Spexin-Based Galanin Receptor Type 2 Agonist for Comorbid Mood Disorders and Abnormal Body Weight

Despite the established comorbidity between mood disorders and abnormal eating behaviors, the underlying molecular mechanism and therapeutics remain to be resolved. Here, we show that a spexin-based galanin receptor type 2 agonist (SG2A) simultaneously normalized mood behaviors and body weight in corticosterone pellet-implanted (CORTI) mice, which are underweight and exhibit signs of anhedonia, increased anxiety, and depression. Administration of SG2A into the lateral ventricle produced antidepressive and anxiolytic effects in CORTI mice. Additionally, SG2A led to a recovery of body weight in CORTI mice while it induced significant weight loss in normal mice. In Pavlovian fear-conditioned mice, SG2A decreased contextual and auditory fear memory consolidation but accelerated the extinction of acquired fear memory without altering innate fear and recognition memory. The main action sites of SG2A in the brain may include serotonergic neurons in the dorsal raphe nucleus for mood control, and proopiomelanocortin/corticotropin-releasing hormone neurons in the hypothalamus for appetite and body weight control. Furthermore, intranasal administration of SG2A exerted the same anxiolytic and antidepressant-like effects and decreased food intake and body weight in a dose-dependent manner. Altogether, these results indicate that SG2A holds promise as a clinical treatment for patients with comorbid mood disorders and abnormal appetite/body weight.

Acute central effects of alarin on the regulation on energy homeostasis

Hypothalamic neuropeptides influence the main components of energy balance: metabolic rate, food intake, body weight as well as body temperature, by exerting either an overall anabolic or catabolic effect. The contribution of alarin, the most recently discovered member of the galanin peptide family to the regulation of energy metabolism has been suggested. Our aim was to analyze the complex thermoregulatory and food intake-related effects of alarin in rats. Adult male Wistar rats received different doses of alarin (0.3; 1; 3 and 15μg corresponding approximately to 0.1, 0.33, 1, and 5 nmol, respectively) intracerebroventricularly. Regarding thermoregulatory analysis, oxygen consumption (indicating metabolic rate), core temperature and heat loss (assessed by tail skin temperature) were recorded in an Oxymax indirect calorimeter system complemented with thermocouples and Benchtop thermometer. In order to investigate potential prostaglandin-mediated mechanisms of the hyperthermic effect of alarin, effects of intraperitoneally applied non-selective (indomethacin, 2mg/kg) or selective cyclooxygenase inhibitor (COX-2 inhibitor meloxicam, 1; 2mg/kg) were tested. Effects of alarin on daytime and nighttime spontaneous food intake, as well as, 24-h fasting-induced re-feeding were recorded in an automated FeedScale system. Alarin increased oxygen consumption with simultaneous suppression of heat loss leading to a slow coordinated rise in core temperature. Both applied COX-inhibitors suppressed this action. Alarin failed to induce daytime food intake, but suppressed spontaneous nighttime and also fasting-induced re-feeding food intake. Alarin appears to elicit a slow anorexigenic and prostaglandin-mediated, fever-like hyperthermic response in rats. Such a combination would characterize a catabolic mediator. The potential involvement of alarin in sickness behavior may be assumed.

Injections of Galanin-Like Peptide directly into the nucleus of the tractus solitarius (NTS) reduces food intake and body weight but increases metabolic rate and plasma leptin

Galanin-Like Peptide (GALP) is a hypothalamic neuromediator of metabolism and reproduction. GALP is known to stimulate reproduction and alter food intake and body weight in multiple species. The regulation of body weight involves control of both energy intake and energy expenditure. Since GALP is known to alter food intake - possibly via the autonomic nervous system - we first hypothesized that GALP would increase metabolic rate. First, male Sprague-Dawley rats were implanted with intracerebroventricular (ICV) cannulae and abdominal radiotelemetry temperature transmitters. Following ICV injection with either 5nmol GALP or vehicle, the oxygen consumption of each rat was monitored for 8h. Food intake, core temperature, and general motor activity were monitored for 24h. GALP significantly increased oxygen consumption, an indirect estimator of metabolic rate, without having any significant effect on motor activity. Compared to controls, GALP increased core body temperature during the photophase and reduced food intake over the 24h period following injection. ICV GALP also increased plasma levels of luteinizing hormone (LH). A second group of male Sprague-Dawley rats were implanted with abdominal transmitters and given injections of GALP directly into the nucleus of the tractus solitarius (NTS). These injections resulted in a significant reduction in food intake, and a significant increase in both oxygen consumption and core body temperature compared to vehicle injections. Direct injections of GALP into the NTS compared to vehicle also resulted in a significant increase in plasma leptin levels, but not LH levels. GALP appears to increase energy expenditure in addition to decreasing energy input by actions within the NTS and thus may play an important role in the hypothalamic regulation of body weight.

Brain and intestinal expression of galanin-like peptide (GALP), galanin receptor R1 and galanin receptor R2, and GALP regulation of food intake in goldfish (Carassius auratus)

Galanin-like peptide (GALP) is a 60 amino acid neuropeptide originally discovered from porcine hypothalamus, and is involved in the regulation of food intake in mammals. Since its discovery, GALP and its receptors (GALR1 and GALR2) have been characterized in mammals, but no publications are available on GALP in fish and other non-mammals. The present study aimed to characterize brain and intestinal GALP and its receptors using immunohistochemistry in a teleost, the goldfish (Carassius auratus), and to study its effects on feeding behavior. Immunostaining of brain sections shows the presence of GALP- and GALR1- and GALR2-like immunoreactive cells in different encephalic areas, including the telencephalon, some hypothalamic nuclei, the optic tectum, the torus longitudinalis and the cerebellum. Signal for GALP was also observed in the fasciculus retroflexus. In the gut, GALP-and GALR1 and GALR2 immunoreactive cells were detected in the mucosa. Results from the feeding study demonstrate that intracerebroventricular administration of GALP (1ng/g bodyweight) increases goldfish food intake at 1h post-injection. These observations form the first report on the presence of GALP in the fish brain and gut, and also on its modulatory role on fish feeding behavior. GALP, as in mammals, appears to be a functional neuropeptide in goldfish.

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.

Chronic venlafaxine treatment fails to alter the levels of galanin system transcripts in normal rats

It is widely accepted that efficacy and speed of current antidepressants' therapeutic effect are far from optimal. Thus, there is a need for the development of antidepressants with new mechanisms of action. The neuropeptide galanin and its receptors (GalR1, GalR2 and GalR3) are among the promising targets. However, it is not clear whether or not the galanin system is involved in the antidepressant effect exerted by the currently much used inhibitors of the reuptake of serotonin and/or noradrenaline. To answer this question we administered the selective serotonin and noradrenaline reuptake inhibitor (SNRI) venlafaxine (40mg/kg/day via osmotic minipumps) to normal rats and examined the levels of the transcripts for galanin and GalR1-3 after a 3-week venlafaxine treatment in the dorsal raphe, hippocampus and frontal cortex. These areas are known to be involved in the effects of antidepressants and in depression itself. Venlafaxine failed to alter the expression of any of the galanin system genes in these areas. Our results show that one of the most efficient, currently used SNRIs does not alter transcript levels of galanin or its three receptors in normal rats. These findings suggest that the pro- and antidepressive-like effects of galanin reported in animal experiments may employ a novel mechanism(s).

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.

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.

Intranasal Delivery of Proteins and Peptides in the Treatment of Neurodegenerative Diseases

The blood-brain barrier (BBB) is a major impediment to the therapeutic delivery of peptides and proteins to the brain. Intranasal delivery often provides a non-invasive means to bypass the BBB. Advantages of using intranasal delivery include minimizing exposure to peripheral organs and tissues, thus reducing systemic side effects. It also allows substances that typically have rapid degradation in the blood time to exert their effect. Intranasal delivery provides the ability to target proteins and peptides to specific regions of the brain when administered with substrates like cyclodextrins. In this review, we examined the use of intranasal delivery of various proteins and peptides that have implications in the treatment of neurodegenerative diseases, focusing especially on albumin, exendin/GLP-1, GALP, insulin, leptin, and PACAP. We have described their rationale for use, distribution in the brain after intranasal injection, how intranasal administration differed from other modes of delivery, and their use in clinical trials, if applicable. Intranasal delivery of drugs, peptides, and other proteins could be very useful in the future for the prevention or treatment of brain related diseases.

Central administration of chicken growth hormone-releasing hormone decreases food intake in chicks

Growth hormone-releasing hormone (GHRH) is well known as a stimulator of growth hormone (GH) secretion. GHRH not only stimulates GH release but also modifies feeding behavior and energy homeostasis in rodents. In chickens (Gallus gallus domesticus), on the other hand, two types of GHRH, namely, chicken GHRH (cGHRH) and cGHRH-like peptide (cGHRH-LP), have been identified. The purpose of the present study was to investigate the effect of central injection of cGHRH and cGHRH-LP on feeding behavior in chicks. Intracerebroventricular (ICV) injection of both cGHRH and cGHRH-LP (0.04 to 1 nmol) significantly decreased food intake without any abnormal behavior in chicks. Furthermore, the feeding-inhibitory effect was not abolished by co-injection of the antagonist for pituitary adenylate cyclase-activating polypeptide (PACAP) or corticotropin-releasing hormone (CRH) receptors, suggesting that the anorexigenic effect of cGHRH and cGHRH-LP might not be related to the PACAP and CRH systems in the brain of chicks. Finally, 24-h food deprivation increased mRNA expression of cGHRH but not cGHRH-LP in the diencephalon. These results suggest that central cGHRH is related to inhibiting feeding behavior and energy homeostasis in chicks.

Can neuropeptides treat obesity? A review of neuropeptides and their potential role in the treatment of obesity

Obesity is a major worldwide public health issue. The physiological systems that regulate body weight are thus of great interest as targets for anti-obesity agents. Peptidergic systems are critical to the regulation of energy homeostasis by key regions in the hypothalamus and brainstem. A number of neuropeptide systems have therefore been investigated as potential treatments for obesity. Blocking orexigenic peptide signals such as neuropeptide Y, melanin-concentrating hormone, orexins, relaxin-3 and galanin-like peptide or stimulating anorectic signalling pathways used by peptides such as the melanocortins, ciliary neurotrophic factor and brain-derived neurotrophic factor, are approaches that have shown some promise, but which have also highlighted possible concerns. Manipulation of central peptidergic systems poses a number of therapeutic problems, including brain access and side effects. Given that the homeostatic defence of body weight may limit the effectiveness of any single-target therapy developed, a combination therapy approach may offer the best hope for the effective prevention and treatment of obesity.

LINKED ARTICLES

This article is part of a themed section on Neuropeptides. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2013.170.issue-7.

Thermoregulatory effect of alarin, a new member of the galanin peptide family

In the background of obesity, among other factors, regulatory alterations in energy balance affecting peptide systems may also be assumed. Regulation of energy balance does not only involve maintenance of body weight but also that of metabolic rate and core temperature. The contribution of alarin, a new member of the potentially orexigenic galanin peptide family, to the regulation of energy metabolism has been recently suggested. Our aim was to analyze the thermoregulatory effects of alarin in rats.

 

Adult male Wistar rats received full-length alarin (alarin 1–25), its truncated form (alarin 6–25Cys) or scrambled alarin in various doses intracerebroventricularly at different ambient temperatures. Oxygen consumption, heat loss (assessed by tail skin temperature) and core temperature of rats were recorded in an indirect calorimeter system.

Upon alarin injection at 25 °C, an increase in oxygen consumption and continuous tail skin vasoconstriction induced a slow rise in core temperature that reached 0.5 °C by 120 and 1.0 °C by 180 min. At cooler or slightly warmer temperatures similar responses were seen. Neither the truncated nor the scrambled alarin elicited any significant thermoregulatory response, however, the truncated form antagonized the hyperthermic actions of the full-length peptide.

Alarin appears to elicit a slow hypermetabolic, hyperthermic response in rats. Such a thermoregulatory response would characterize a catabolic (anorexic and hypermetabolic) mediator. Further investigations are needed to clarify the complex role of alarin in energy homeostasis.

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-like peptide (GALP) facilitates thermogenesis via synthesis of prostaglandin E2 by astrocytes in the periventricular zone of the third ventricle

Administration of galanin-like peptide (GALP) leads to a decrease in both total food intake and body weight 24 h after injection, compared to controls. Moreover, GALP induces an increase in core body temperature. To elucidate the mechanism by which GALP exerts its effect on energy homeostasis, urethane-anesthetized rats were intracerebroventricularly injected with GALP or saline, after which oxygen consumption, heart rate, and body temperature were monitored for 4 h. In some cases, animals were also pretreated with the cyclooxygenase (COX) inhibitor, diclofenac, via intracerebroventricular (i.c.v.) or intravenous (i.v.) injection. c-Fos expression in the brain was also examined after injection of GALP, and the levels of COX and prostaglandin E(2) synthetase (PGES) mRNA in primary cultured astrocytes treated with GALP were analyzed by using qPCR. The i.c.v. injection of GALP caused biphasic thermogenesis, an effect which could be blocked by pretreatment with centrally (i.c.v.), but not peripherally (i.v.) administered diclofenac. c-Fos immunoreactivity was observed in astrocytes in the periventricular zone of the third ventricle. GALP treatment also increased COX-2 and cytosolic PGES, but not COX-1, microsomal PGES-1, or microsomal PGES-2 mRNA levels in cultured astrocytes. We, therefore, suggest that GALP elicits thermogenesis via a prostaglandin E(2)-mediated pathway in astrocytes of the central nervous system.

Neuronal circuits involving neuropeptide Y in hypothalamic arcuate nucleus-mediated feeding regulation

Neuropeptide Y (NPY) is a 36-amino-acid neuropeptide that was first discovered in porcine brain extracts and later in the porcine intestine. It is widely distributed in both the central and peripheral nervous systems and exerts a powerful orexigenic effect. NPY-producing neuronal cell bodies are abundantly localized in the medial arcuate nucleus of the hypothalamus, this being a brain center that integrates signals for energy homeostasis. Accumulated evidence shows that hypothalamic neuropeptides such as ghrelin, orexin, melanin-concentrating hormone (MCH), galanin-like peptide (GALP) and proopiomelanocortin (POMC) are involved in the regulation of feeding behavior and energy homeostasis via neuronal circuits in the hypothalamus. NPY also forms part of the feeding-regulating neuronal circuitry in conjunction with other feeding-regulating peptide-containing neurons within the hypothalamus. We summarize here current knowledge of the neuronal interactions between NPY and the different types of feeding-regulating peptide-containing neurons in the hypothalamus based on evidence at the immunohistochemicl level and with calcium imaging techniques.

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'.

The role of NPY in hypothalamic mediated food intake

Neuropeptide Y (NPY) is a highly conserved neuropeptide with orexigenic actions in discrete hypothalamic nuclei that plays a role in regulating energy homeostasis. NPY signals via a family of high affinity receptors that mediate the widespread actions of NPY in all hypothalamic nuclei. These actions are also subject to tight, intricate regulation by numerous peripheral and central energy balance signals. The NPY system is embedded within a densely-redundant network designed to ensure stable energy homeostasis. This redundancy may underlie compensation for the loss of NPY or its receptors in germline knockouts, explaining why conventional knockouts of NPY or its receptors rarely yield a marked phenotypic change. We discuss insights into the hypothalamic role of NPY from studies of its physiological actions, responses to genetic manipulations and interactions with other energy balance signals. We conclude that numerous approaches must be employed to effectively study different aspects of NPY action.

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-like peptide: a key player in the homeostatic regulation of feeding and energy metabolism?

The hypothalamus has a critical role in the regulation of feeding behavior, energy metabolism and reproduction. Galanin-like peptide (GALP), a novel 60 amino-acid peptide with a nonamidated C-terminus, was first discovered in porcine hypothalamus. GALP is mainly produced in the hypothalamic arcuate nucleus and is involved in the regulation of feeding behavior and energy metabolism, with GALP-containing neurons forming networks with several feeding-regulating peptide-containing neurons. The effects of GALP on food intake and body weight are complex. In rats, the central effect of GALP is to first stimulate and then reduce food intake, whereas in mice, GALP has an anorectic function. Furthermore, GALP regulates plasma luteinizing hormone levels through activation of gonadotropin-releasing hormone-producing neurons, suggesting that it is also involved in the reproductive system. This review summarizes the research on these topics and discusses current evidence regarding the function of GALP, particularly in relation to feeding and energy metabolism. We also discuss the effects of GALP activity on food intake, body weight and locomotor activity after intranasal infusion, a clinically viable mode of delivery.

Central injection of the stable somatostatin analog ODT8-SST induces a somatostatin2 receptor-mediated orexigenic effect: role of neuropeptide Y and opioid signaling pathways in rats

Somatostatin and octreotide injected into the brain have been reported to modulate food intake. However, little is known regarding the underlying mechanisms. The stable oligosomatostatin analog, des-AA(1,2,4,5,12,13)-[DTrp(8)]-somatostatin (ODT8-SST), like somatostatin, binds to all five somatostatin receptors (sst(1-5)). We characterized the effects of ODT8-SST injected intracerebroventricularly (i.c.v.) on food consumption and related mechanisms of action in freely fed rats. ODT8-SST (0.3 and 1 microg per rat, i.c.v.) injected during the light or dark phase induced an early onset (within 1 h) and long-lasting (4 h) increase in food intake in nonfasted rats. By contrast, i.p. injection (0.3-3 mg/kg) or i.c.v. injection of selective sst(1) or sst(4) agonists (1 microg per rat) had no effect. The 2 h food intake response during the light phase was blocked by i.c.v. injection of a sst(2) antagonist, the neuropeptide Y (NPY) Y(1) receptor antagonist, BIBP-3226, and ip injection of the mu-opioid receptor antagonist, naloxone, and not associated with changes in plasma ghrelin levels. ODT8-SST (1 microg per rat, i.c.v.) stimulated gastric emptying of a solid meal which was also blocked by naloxone. The increased food intake was accompanied by a sustained increase in respiratory quotient, energy expenditure, and drinking as well as mu-opioid receptor-independent grooming behavior and hyperthermia, while ambulatory movements were not altered after ODT8-SST (1 microg per rat, i.c.v.). These data show that ODT8-SST acts primarily through brain sst(2) receptors to induce a long-lasting orexigenic effect that involves the activation of Y(1) and opiate-receptors, accompanied by enhanced gastric transit and energy expenditure suggesting a modulation of NPYergic and opioidergic orexigenic systems by brain sst(2) receptors.

Alarin stimulates food intake in male rats and LH secretion in castrated male rats

Alarin is a newly identified member of the galanin family of neuropeptides that includes galanin-like peptide (GALP) and galanin. Alarin was discovered as an alternate transcript of the GALP gene in neuroblastoma cells, and subsequently alarin mRNA was detected in the brain of rodents. GALP and galanin are important central regulators of both feeding and reproductive behavior. We hypothesized, that, as a member of the galanin family of peptides, alarin would also have central effects on feeding and reproduction. To test this hypothesis, we treated male rats with alarin intracerebroventricularly (i.c.v.) and measured its effects on food intake and energy homeostasis as well as sexual behavior and luteinizing hormone (LH) secretion. We observed that i.c.v. injection of 1.0 nmol alarin significantly increased food intake (p<0.01) and body weight (p<0.05). Alarin did not affect sexual behavior in male rats; however, alarin did significantly (p<0.01) increase LH levels in castrated, but not intact, male rats. Alarin immunoreactive cell bodies were detected within the locus coeruleus and locus subcoeruleus of the midbrain, which is a brainstem nucleus involved in coordinating many physiological activities, including food intake and reproduction. Lastly, alarin stimulated Fos induction in hypothalamic nuclei, such as the paraventricular nucleus and the nucleus of the tractus solitarious. Our studies demonstrate that alarin, like other members of the galanin family, is a neuromediator of food intake and body weight.

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.

Blood-brain barrier and feeding: regulatory roles of saturable transport systems for ingestive peptides

The two main ways for peptides in the peripheral body to enter the brain are by either saturable transport or passive diffusion across the blood-brain barrier (BBB). Saturable transport systems have the advantage of being responsive to physiological and pathological stimuli. Since saturable systems can regulate peptide entry into the brain, they have the potential to play controlling roles in feeding behavior. For therapeutic applications, however, saturable systems have the disadvantage of functioning as a threshold to limit access of large amounts of peptides into the brain. This pharmacological problem presumably would not be encountered for peptides crossing the BBB by passive diffusion, a process dependent on physicochemical properties. Thus, the gatekeeper function of the BBB can be expanded to a primary governing role, especially for entry of ingestive peptides subject to their respective saturable transport systems.

The relative impact of chronic food restriction and acute food deprivation on plasma hormone levels and hypothalamic neuropeptide expression

Our understanding of the central regulation of food intake and body weight has increased tremendously through implication of a high number of neuropeptides. However, lack of all-embracing studies have made comparison difficult in the past. The objective of this study was to demonstrate the relative importance of the different neuropeptides in terms of involvement in appetite regulatory mechanisms. We quantified expression levels of 21 hypothalamic neuropeptides and circulating levels of leptin, insulin, corticosterone, adrenocorticotropic hormone, ghrelin and adiponectin in rats after acute food deprivation and chronic food restriction using validated quantitative real-time PCR and hormone measurements. Body weight, insulin and leptin were reduced whereas corticosterone was increased by both acute food deprivation and chronic food restriction. Our results confirmed the relative importance in body weight homeostasis of neuropeptide Y and proopiomelanocortin, which were increased and decreased as predicted. The expression of other neuropeptides previously attributed central roles in body weight homeostasis, e.g. melanin-concentrating hormone and orexin, appeared to be less affected by the treatments. Moreover, the expression of dynorphin, galanin-like peptide and neuropeptide B was dramatically reduced after both treatments. This suggests that the latter neuropeptides--although previously known to be involved in body weight homeostasis--may be of unexpected importance in states of negative energy balance.

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.

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

Galanin-like peptide (GALP) is a neuropeptide that is thought to act on the galanin receptors GALR1, GALR2 and GALR3. In rats, i.c.v. injection of GALP has dichotomous actions on energy balance, stimulating feeding over the first hour, but reducing food intake and body weight at 24 h, as well as causing an increase in core body temperature. In mice, GALP only induces an anorexic action, and its effects on core body temperature are unknown. One aim of the present study was to determine the effects of GALP on core body temperature in mice. Intracerebroventricular injection of GALP into conscious mice had no effect on feeding over 1 h, but caused a significant reduction in food intake and body weight at 24 h. It also caused an immediate drop in core body temperature, which was followed by an increase in body temperature. To understand these different effects of GALP on energy balance in mice compared to rats, and to determine the involvement of GALR2 and GALR3, immunohistochemistry was performed to localise c-Fos, a marker of cell activation. Intracerebroventricular injection of GALP induced c-Fos expression in the parenchyma surrounding the ventricles, the ventricular ependymal cells and the meninges in mice and rats. GALP also induced c-Fos expression in the supraoptic nucleus, dorsomedial hypothalamic nucleus, lateral hypothalamus and nucleus tractus solitarius in rats but not in mice. Central administration of a GALR2/3 agonist in rats did not induce c-Fos in any of the brain regions that expressed this protein after GALP injection, and had no effect on food intake, body weight and body temperature in rats or mice. These data suggest that GALP induces differential effects on energy balance and brain activity in mice compared to rats, which are unlikely to be due to activation of the GALR2 or GALR3 receptor.

Postnatal development of galanin-like peptide mRNA expression in rat hypothalamus

We examined the developmental change of GALP mRNA in male and female rat hypothalamus during postnatal day 1 to 60, using in situ hybridization histochemistry. Neuropeptide Y (NPY) and proopiomelanocortin (POMC) mRNA in the hypothalamus were also examined because they are important in the regulation of food intake. GALP mRNA was first detected in the arcuate nucleus (ARC) on day 8. GALP mRNA was gradually increased between day 8 and 14 and markedly increased between day 14 and 40, which is the weaning and pubertal period in rats. After day 40, there were no significant differences in GALP mRNA. In contrast to GALP, NPY and POMC mRNAs were detected in the ARC from day 1 and lasted to day 60. There was no sexual dimorphism in GALP, NPY and POMC mRNAs during postnatal development. Next, we examined the effect of the milk deprivation for 24 h on GALP, NPY and POMC mRNA in pups. GALP mRNA did not change by milk deprivation on day 9 and 15, while milk deprivation had a significant effect on NPY and POMC mRNA on day 15. These results suggest that the development of GALP may be associated with developmental changes such as weaning, feeding and maturation of reproductive functions. The regulatory mechanism of GALP mRNA is different from that of the NPY and POMC genes during postnatal development.

Morphological interaction between galanin-like peptide- and dopamine-containing neurons in the rat arcuate nucleus

Galanin-like peptide (GALP) is a 60-amino acid neuropeptide that plays an important role in the neuronal regulation of feeding, energy balance and reproduction. GALP is produced in the hypothalamic arcuate nucleus, an area containing, amongst other neuron types, two populations of neurons in which we were interested: a population of GALP-containing neurons which regulate energy balance and reproduction, and a second population consisting of tuberoinfundibular dopaminergic neurons which suppress prolactin secretion from the adenohypophysis. To characterize morphologically the relationship between GALP and dopamine-containing neurons in the arcuate nucleus, a double immunofluorescence study was performed on cryosections from rat brain. Immunohistochemical double labeling studies revealed that GALP-immunoreactive nerve fibers made direct contact on tyrosine hydroxylase (TH)-containing neuronal cell bodies in the arcuate nucleus. These results suggest that GALP-containing neurons innervate tuberoinfundibular dopaminergic neurons.

Induction of the galanin-like peptide gene expression in the posterior pituitary gland after acute osmotic stimulus in rats

Galanin-like peptide (GALP) is a 60 amino-acid peptide, and the GALP mRNA is restricted to pituicytes in the posterior pituitary gland (PP) and neurons in the hypothalamic arcuate nucleus (Arc). We examined whether the GALP gene expression in the PP and Arc would be induced after intraperitoneal (i.p.) administration of hypertonic saline, that is, acute osmotic stimulus, in rats. The dose-response (2.8, 4.5, 6.0 and 9.0% NaCl) and time-course (6.0% NaCl, 1, 3, 6, 12 and 24h) effects of acute osmotic stimulus on GALP mRNA levels in the PP and Arc were examined in rats by using in situ hybridization histochemistry. Plasma osmolality and plasma sodium concentration increased significantly at 1h, and returned to control level at 6h after i.p. administration of hypertonic saline (6.0% NaCl). The GALP mRNA level in the PP increased significantly 3 and 6h after i.p. administration of hypertonic saline (6.0% NaCl), but the level in the Arc did not change. These results showed that acute osmotic stimulus-induced GALP gene expression in the pituicyte of the PP, but not in the neurons in the Arc, and the gene expression in the pituicyte might be regulated by plasma osmolality and/or plasma sodium concentration.

Prenatal exposure to undernutrition and programming of responses to high-fat feeding in the rat

Fetal undernutrition programmes risk of later metabolic disorders. Postnatal factors modify the programmed phenotype. This study aimed to assess the effects of a postnatal high-fat (HF) challenge on body weight gain, adiposity and gene expression following prenatal undernutrition. Pregnant rats were fed either a control diet or a low-protein (LP) diet, targeted at days 0-7 (LPE), days 8-14 (LPM), or days 15-22 (LPL) gestation. At 12 weeks of age offspring were either fed standard laboratory chow diet (4.13 % fat), or a 39.5 % fat diet, for 10 weeks. LP exposure had no effect on weight gain or abdominal fat in males. Females exposed to LP diet in utero exhibited a similar weight gain on HF diet as on the chow diet. Programming of fat deposition was noted in LPE females and males of the LPM and LPL groups (P = 0.019). Hypothalamic expression of galanin mRNA was similar in all groups, but expression of the galanin-2 receptor was modified by LP exposure in female offspring. Hepatic expression of sterol response element binding protein (SREBP-1c) was decreased by LP at both the mRNA (P = 0.008) and protein (P < 0.001) level. HF feeding increased expression of SREBP-1c mRNA three-fold in controls, with little response noted in the LP groups. Interactions of factors such as postnatal diet, age and sex act together with prenatal factors to determine metabolic function and responsiveness at any stage of postnatal life. This study further establishes a role for prenatal nutrition in programming the genes involved in lipid metabolism and appetite regulation.

Exposure to undernutrition in fetal life determines fat distribution, locomotor activity and food intake in ageing rats

OBJECTIVE

To assess the long-term impact of undernutrition during specific periods of fetal life, upon central adiposity, control of feeding behaviour and locomotor activity.

DESIGN

Pregnant rats were fed a control or low-protein (LP) diet, targeted to early (LPE), mid (LPM) or late (LPL) pregnancy or throughout gestation (LPA). The offspring were studied at 9 and 18 months of age.

MEASUREMENTS

Adiposity was assessed by measuring weight of abdominal fat depots relative to body weight. Locomotor activity was assessed using an infrared sensor array system in both light and dark conditions. Hypothalamic expression of mRNA for galanin and the galanin 2 receptor (Gal2R) was determined using real-time PCR.

RESULTS

At 9 months, male rats exposed to LP in utero had less fat in the gonadal depot, but were of similar body weight to controls. By 18 months, the males of groups LPA and LPM had more abdominal and less subcutaneous fat. Females deposited more fat centrally than males between 9 and 18 months of age, and this was more marked in groups LPA and LPL. Food intake was greater in LPM males. Among females hypophagia was noted in groups LPA and LPL. Expression of galanin and Gal2R were unaffected by maternal diet. Total locomotor activity was reduced in LPE males and all LP females in the light but not in the dark.

CONCLUSION

Locomotor activity and feeding behaviour in aged rats are subject to prenatal programming influences. Fetal undernutrition does not programme obesity in rats without postnatal dietary challenge.

Neural interaction between galanin-like peptide (GALP)- and luteinizing hormone-releasing hormone (LHRH)-containing neurons

Galanin-like peptide (GALP), commonly known as an appetite-regulating peptide, has been shown to increase plasma luteinizing hormone (LH) through luteinizing hormone-releasing hormone (LHRH). This led us to investigate, using both light and electron microscopy, whether GALP-containing neurons in the rat brain make direct inputs to LHRH-containing neurons. As LHRH-containing neurons are very difficult to demonstrate immunohistochemically with LHRH antiserum without colchicine treatment, we used a transgenic rat in which LHRH tagged with enhanced green fluorescence protein facilitated the precise detection of LHRH-producing neuronal cell bodies and processes. This is the first study to report on synaptic inputs to LHRH-containing neurons at the ultrastructural level using this transgenic model. We also used immunohistochemistry to investigate the neuronal interaction between GALP- and LHRH-containing neurons. The experiments revealed that GALP-containing nerve terminals lie in close apposition with LHRH-containing cell bodies and processes in the medial preoptic area and the bed nucleus of the stria terminalis. At the ultrastructural level, the GALP-positive nerve terminals were found to make axo-somatic and axo-dendritic synaptic contacts with the EGFP-positive neurons in these areas. These results strongly suggest that GALP-containing neurons provide direct input to LHRH-containing neurons and that GALP plays a crucial role in the regulation of LH secretion via LHRH.

Galanin-like peptide stimulates food intake via activation of neuropeptide Y neurons in the hypothalamic dorsomedial nucleus of the rat

Galanin-like peptide (GALP), a 29-amino-acid neuropeptide, is located in the hypothalamic arcuate nucleus (ARC), binds to galanin receptor subtype 2, and induces food intake upon intracerebroventricular (icv) injection in rats. However, neural mechanisms underlying its orexigenic action remain unclear. We aimed to identify the nuclei and neuron species that mediate the food intake in response to icv GALP injection. Intracerebroventricular injection of GALP, as powerfully as that of neuropeptide Y (NYP), increased food intake for the initial 2 h. GALP injected focally into the dorsomedial nucleus (DMN), but not the ARC, lateral hypothalamus, or paraventricular nucleus (PVN), stimulated food intake for 2 h after injection. In contrast, galanin injected into the DMN had no effect. DMN-lesion rats that received icv GALP injection showed attenuated feeding compared with control rats. Intracerebroventricular GALP injection increased c-Fos expression in NPY-containing neurons in the DMN, but not the ARC. GALP increased the cytosolic calcium concentration ([Ca(2+)](i)) in NPY-immunoreactive neurons isolated from the DMN, but not the ARC. Furthermore, both anti-NPY IgG and NPY antagonists, when preinjected, counteracted the feeding induced by GALP injection. These data show that icv GALP injection induces a potent short-term stimulation of food intake mainly via activation of NPY-containing neurons in the DMN.

Galanin and galanin-like peptide differentially modulate neuronal activities in rat arcuate nucleus neurons

Neuropeptides galanin and galanin-like peptide (GALP) share similar amino acid sequence and presumably interact with the same group of receptors, but they differentially regulate a variety of physiological and pathophysiological processes including metabolism and reproduction. Here we explored the neurophysiological basis of the in vivo differential effect between galanin and GALP by examining galanin and GALP modulation of neuronal activities of neurons in the arcuate nucleus (Arc), a brain region critically involved in energy homeostasis and reproductive function. We demonstrated that galanin and GALP inhibited excitatory and inhibitory postsynaptic currents in a similar way. In contrast, galanin and GALP differentially affected the intrinsic membrane property. In most recorded Arc neurons, galanin perfusion induced significant hyperpolarization of the resting membrane potential, which was not affected by GALP perfusion. In addition, galanin perfusion substantially suppressed the spontaneous spike firing in most Arc neurons, whereas in response to GALP perfusion, about half of the Arc neurons exhibited mild reduction in spontaneous spike firing and the other half showed enhancement. Furthermore, the Arc neurons that had been previously responsive to galanin perfusion no longer responded to galanin if co-applied with GALP, indicating that GALP can physiologically antagonize galanin effect. This differential effect appears to be mediated by G protein within the recorded cell, as the galanin effect on firing rate was abolished when the recorded cell was loaded with GDP-betaS, an agent that blocks G protein activity. Taken together, these differential effects of galanin and GALP may provide a neurophysiological mechanism through which galanin and GALP differentially regulate energy balance, reproductive function, and other physiological processes.

Galanin-like peptide promotes feeding behaviour via activation of orexinergic neurones in the rat lateral hypothalamus

Galanin-like peptide (GALP) is produced in neurones in the hypothalamic arcuate nucleus and is implicated in the neural control of feeding behaviour. Previously, we have reported that GALP immunoreactive fibres were in direct contact with orexin/hypocretin immunoreactive neurones in the rat lateral hypothalamus using double-immunofluorescence. Centrally administered GALP is known to stimulate feeding behaviour. However, the target neurones of this action have not been clarified. The present study aimed to determine features of the GALP-mediated neuronal feeding pathway in rat. Accordingly, at the ultrastructural level, GALP-immunoreactive axon terminals were found to make synapses on orexin/hypocretin immunoreactive cell bodies and dendritic processes in the lateral hypothalamus. c-Fos immunoreactivity was expressed in orexin/hypocretin-immunoreactive neurones but not in melanin concentrating hormone-immunoreactive neurones in the lateral hypothalamus at 90 min after the application of GALP by i.c.v. infusion. Furthermore, to determine whether GALP regulates feeding behaviour via orexin/hypocretin neurones, the feeding behaviour of rats was studied following GALP i.c.v. injection with or without anti-orexin A and B immunoglobulin (IgG) pretreatment. The anti-orexin IgGs markedly inhibited GALP-induced hyperphagia. These results suggest that orexin/hypocretin-containing neurones in the lateral hypothalamus are targeted by GALP, and that GALP-induced hyperphagia is mediated via orexin/hypocretin neurones in the rat hypothalamus.

PVN galanin increases fat storage and promotes obesity by causing muscle to utilize carbohydrate more than fat

To understand the function of the feeding-stimulatory peptide, galanin (GAL), in eating and body weight regulation, the present experiments tested the effects of both acute and chronic injections of this peptide into the paraventricular nucleus (PVN) of rats. With food absent during the test, acute injection of GAL (300 pmol/0.3 microl) significantly increased phosphofructokinase activity in muscle, suggesting enhanced capacity to metabolize carbohydrate, and reduced circulating glucose levels. It also decreased beta-hydroxyacyl-CoA dehydrogenase activity in muscle, indicating reduced fat oxidation, while increasing circulating non-esterified fatty acids (NEFA) and lipoprotein lipase activity in adipose tissue (aLPL). Chronic PVN injections of GAL (300 pmol/0.3 microl/injection) versus saline over 7-10 days significantly stimulated daily caloric intake and increased the weight of four dissected fat depots by 30-40%. These effects, accompanied by elevated levels of leptin, triglycerides, NEFA and aLPL activity, were evident only in rats on a diet with at least 35% fat. Thus, by favoring carbohydrate over fat metabolism in muscle and reversing hyperglycemia, PVN GAL may have a function in counteracting the metabolic disturbances induced by a high-fat diet. As a consequence of these actions, GAL can promote the partitioning of lipids away from oxidation in muscle towards storage in adipose tissue.