Ethanol intake increases galanin mRNA in the hypothalamus and withdrawal decreases it

Altered c-Fos expression following alcohol intake in discrete brain regions of galanin 3 receptor knockout mice

The aim of this study was to investigate the brain regions involved in the role of galanin (GAL) and specifically GAL3-receptors (GAL3) in alcohol intake. GAL3-KO mice displayed an alcohol-preferring phenotype in a two-bottle, free choice paradigm. In contrast, no genotype differences in ethanol intake were observed in a Drinking In the Dark (DID) model, highlighting the differential involvement of brain GAL activity depending on the experimental model of alcohol consumption. Blood ethanol concentrations were approximately 10 % lower in GAL3-KO mice compared to wildtype (WT) following DID. WT mice drinking ethanol had significantly increased numbers of c-Fos immunoreactive (ir) neurons in the rostral prelimbic (PrL) and infralimbic (IL) regions of the prefrontal cortex (PFC) and decreased numbers of ir neurons in the CA1 region of the dorsal hippocampus (dHIP) compared to water drinking WT littermates, but these effects of ethanol were absent in GAL3-KO mice. Water drinking GAL3-KO mice furthermore had significantly increased numbers of c-Fos ir neurons compared to water drinking WT mice in the rostral PrL as well as the CA3 region of the dHIP. In the core and shell subregions of the nucleus accumbens (NAc), or in the paraventricular nucleus of the hypothalamus (PVN) or basolateral amygdala, there were no changes in the number of c-Fos ir cells or any involvement of GAL3 genotype. These findings support a role of GAL3-receptors in the effects of alcohol and implicate discrete brain regions involved in this interaction.

Sensitivity of Hypocretin System to Chronic Alcohol Exposure: A Human and Animal Study

Human heroin addicts and mice administered morphine for a 2 week period show a greatly increased number of hypothalamic hypocretin (Hcrt or orexin) producing neurons with a concomitant reduction in Hcrt cell size. Male rats addicted to cocaine similarly show an increased number of detectable Hcrt neurons. These findings led us to hypothesize that humans with alcohol use disorder (AUD) would show similar changes. We now report that humans with AUD have a decreased number and size of detectable Hcrt neurons. In addition, the intermingled melanin concentrating hormone (MCH) neurons are reduced in size. We saw no change in the size and number of tuberomammillary histamine neurons in AUD. Within the Hcrt/MCH neuronal field we found that microglia cell size was increased in AUD brains. In contrast, male rats with 2 week alcohol exposure, sufficient to elicit withdrawal symptoms, show no change in the number or size of Hcrt, MCH and histamine neurons, and no change in the size of microglia. The present study indicates major differences between the response of Hcrt neurons to opioids and that to alcohol in human subjects with a history of substance abuse.

OBEZİTENİN DOLAŞIMDAKİ GALANİN VE VASPİN DÜZEYLERİ İLE İLİŞKİSİ

Objective: Our aim was to compare vaspin and galanin in obese and normal weight individuals, to reveal whether these parameters are related to obesity and other related parameters. Material and Methods: Forty patients with obesity and 40 control subjects were included in the study. Biochemical parameters were recorded from patient’s files. Galanin and vaspin levels were studied by ELISA method, obtained as a result of centrifugation of these blood samples. Results: The groups were similar to each other in terms of gender and age (p>0.05). Galanine levels were higher in the group with obesity compared to the control group (p0.05). Glucose, insulin, triglyceride and LDL-C levels were statistically significantly higher in the patient group than in the control group (p0.05). A statistically significant positive correlation was found with galanin and glucose, insulin, and BMI, respectively (p

Acute ethanol induces behavioral changes and alters c-fos expression in specific brain regions, including the mammillary body, in zebrafish

Ethanol is one of the most commonly abused substances in the world, and ethanol abuse and dependence disorders represent major societal problems. However, appropriate treatment is lacking as we still do not fully understand the molecular bases of these disorders. The zebrafish is one of the model organisms utilized for studying such mechanisms. In this study, we examined the effects of acute ethanol administration on the behavior of zebrafish, and we also analyzed correlated gene expression changes using whole-mount in situ hybridization focusing on a number of genes associated with different neurotransmitter systems, stress response, and neuronal activity. We found ethanol treatment to result in hyperactivity and reduced shoal cohesion compared to control. Analysis of c-fos expression demonstrated altered activity patterns in certain brain regions, including intense activation of the mammillary body in zebrafish with acute ethanol treatment. We also found reduced level of gad1b expression in the cerebellum of ethanol treated fish compared to control. However, we could not detect significant changes in the expression level of other genes, including vglut2b, th, crh, hdc, avp, pomc, and galn in ethanol treated fish compared controls. Our results suggest that zebrafish is a promising animal model for the study of mechanisms underlying alcohol induced behavioral changes and alcohol related human disorders.

Adolescent alcohol exposure increases orexin-A/hypocretin-1 in the anterior hypothalamus

Adolescence is a time of marked changes in sleep, neuromaturation, and alcohol use. While there is substantial evidence that alcohol disrupts sleep and that disrupted sleep may play a role in the development of alcohol use disorders (AUD), there is very little known about the brain mechanisms underlying this phenomenon. The orexin (also known as hypocretin) system is fundamental for a number of homeostatic mechanisms, including the initiation and maintenance of wakefulness that may be impacted by adolescent alcohol exposure. The current study investigated the impact of adolescent ethanol exposure on adult orexin-A/hypocretin-1 immunoreactive (orexin-A + IR) cells in hypothalamic nuclei in two models of adolescent intermittent ethanol (AIE) exposure. Both models assess adult hypothalamic orexin following either an AIE vapor exposure paradigm, or an AIE intragastric gavage paradigm during adolescence. Both AIE exposure models found that binge levels of ethanol intoxication during adolescence significantly increased adult orexin-A + IR expression in the anterior hypothalamic nucleus (AHN). Further, both AIE models found no change in orexin-A + IR in the posterior hypothalamic area (PH), perifornical nucleus (PeF), dorsomedial hypothalamic nucleus dorsal part (DMD) or lateral hypothalamic area (LH). However, AIE vapor exposure reduced orexin-A + IR in the paraventricular nucleus (PVN), but AIE gavage exposure did not. These findings suggest that the AHN orexinergic system is increased in adults following binge-like patterns of intoxication during adolescence. Altered adult AHN orexin could contribute to long-lasting changes in sleep.

GAL3 receptor knockout mice exhibit an alcohol-preferring phenotype

Galanin is a neuropeptide which mediates its effects via three G-protein coupled receptors (GAL_1-3 ). Administration of a GAL₃ antagonist reduces alcohol self-administration in animal models while allelic variation in the GAL₃ gene has been associated with an increased risk of alcohol use disorders in diverse human populations. Based on the association of GAL₃ with alcoholism, we sought to characterize drug-seeking behavior in GAL₃ -deficient mice for the first time. In the two-bottle free choice paradigm, GAL₃ -KO mice consistently showed a significantly increased preference for ethanol over water when compared to wildtype littermates. Furthermore, male GAL₃ -KO mice displayed significantly increased responding for ethanol under operant conditions. These differences in alcohol seeking behavior in GAL₃ -KO mice did not result from altered ethanol metabolism. In contrast to ethanol, GAL₃ -KO mice exhibited similar preference for saccharin and sucrose over water, and a similar preference for a high fat diet over a low fat diet as wildtype littermates. No differences in cognitive and locomotor behaviors were observed in GAL₃ -KO mice to account for increased alcohol seeking behavior. Overall, these findings suggest genetic ablation of GAL₃ in mice increases alcohol consumption.

Central administration of galanin N-terminal fragment 1-15 decreases the voluntary alcohol intake in rats

Alcohol consumption is considered a major risk factor for disease and mortality worldwide. In the absence of effective treatments in alcohol use disorders, it is important to find new biological targets that could modulate alcohol consumption. We tested the role of the N-terminal galanin fragment (1-15) [GAL(1-15)] in voluntary ethanol consumption in rats using the two-bottle choice paradigm as well as compare the effects of GAL(1-15) with the whole molecule of GAL. We describe for the first time that GAL(1-15), via central mechanisms, induces a strong reduction in preference and ethanol consumption in rats. These effects were significantly different than GAL. GAL receptor (GALR) 2 was involved in these effects, because the specific GALR2 antagonist M871 blocked GAL(1-15) mediated actions in preference and ethanol intake. Importantly, the mechanism of this action involves changes in GALR expression and also in immediate-early gene C-Fos and receptors-internalization-related gene Rab5 in the striatum. The relevance of the striatum as a target for GAL(1-15) was supported by the effect of GAL(1-15) on the locomotor activity of rats after ethanol administration. These results may give the basis for the development of novel therapeutics strategies using GAL(1-15) analogues for the treatment of alcohol use disorders in humans.

Pharmacological interventions for obesity: current and future targets

PURPOSE OF REVIEW

Obesity in the United States has been on a constant rise since the Center for Disease Control and Prevention (CDC) began tracking it over 50 years ago. Despite focused attention on this epidemic, pharmacological treatments aimed at obesity are lacking. Here, we briefly give perspective on the central and peripheral mechanisms underlying feeding behaviors and describe the existing pharmacological treatments for obesity. With this lens, I suggest future targets for the treatment of obesity.

RECENT FINDINGS

Given the development of genetic and molecular tools, understanding of how energy expenditure is modulated is becoming more nuanced. There is growing evidence for a link between obesity and addiction, which should be utilized in the development of new pharmacological treatments.

SUMMARY

More focus is needed on identifying targets for anti-obesity pharmacology. In doing so, research should include intensive investigation of the brain's reward circuitry.

Hypothalamic neuropeptide signaling in alcohol addiction

The hypothalamus is now known to regulate alcohol intake in addition to its established role in food intake, in part through neuromodulatory neurochemicals termed neuropeptides. Certain orexigenic neuropeptides act in the hypothalamus to promote alcohol drinking, although they affect different aspects of the drinking response. These neuropeptides, which include galanin, the endogenous opioid enkephalin, and orexin/hypocretin, appear to stimulate alcohol intake not only through mechanisms that promote food intake but also by enhancing reward and reinforcement from alcohol. Moreover, these neuropeptides participate in a positive feedback relationship with alcohol, whereby they are upregulated by alcohol intake to promote even further consumption. They contrast with other orexigenic neuropeptides, such as melanin-concentrating hormone and neuropeptide Y, which promote alcohol intake under limited circumstances, are not consistently stimulated by alcohol, and do not enhance reward. They also contrast with neuropeptides that can be anorexigenic, including the endogenous opioid dynorphin, corticotropin-releasing factor, and melanocortins, which act in the hypothalamus to inhibit alcohol drinking as well as reward and therefore counter the ingestive drive promoted by orexigenic neuropeptides. Thus, while multiple hypothalamic neuropeptides may work together to regulate different aspects of the alcohol drinking response, excessive signaling from orexigenic neuropeptides or inadequate signaling from anorexigenic neuropeptides can therefore allow alcohol drinking to become dysregulated.

Alcohol consumption increases locomotion in an open field and induces Fos-immunoreactivity in reward and approach/withdrawal-related neurocircuitries

Drug addiction is a chronically relapsing disorder characterized by compulsion to seek and take the drug, loss of control in limiting intake and, eventually, the emergence of a negative emotional state when access to the drug is prevented. Both dopamine and corticotropin-releasing factor (CRF)-mediated systems seem to play important roles in the modulation of alcohol abuse and dependence. The present study investigated the effects of alcohol consumption on anxiety and locomotor parameters and on the activation of dopamine and CRF-innervated brain regions. Male Wistar rats were given a choice of two bottles for 31 days, one containing water and the other a solution of saccharin + alcohol. Control animals only received water and a solution of 0.2% saccharin. On the 31st day, animals were tested in the elevated plus-maze and open field, and euthanized immediately after the behavioral tests. An independent group of animals was treated with ethanol and used to measure blood ethanol concentration. Results showed that alcohol intake did not alter behavioral measurements in the plus-maze, but increased the number of crossings in the open field, an index of locomotor activity. Additionally, alcohol intake increased Fos-immunoreactivity (Fos-ir) in the prefrontal cortex, in the shell region of the nucleus accumbens, in the medial and central amygdala, in the bed nucleus of the stria terminalis, in the septal region, and in the paraventricular and dorsomedial hypothalamus, structures that have been linked to reward and to approach/withdrawal behavior. These observations might be relevant to a better understanding of the behavioral and physiological alterations that follow alcohol consumption.

Effects of embryonic ethanol exposure at low doses on neuronal development, voluntary ethanol consumption and related behaviors in larval and adult zebrafish: Role of hypothalamic orexigenic peptides

Embryonic exposure to ethanol is known to affect neurochemical systems in rodents and increase alcohol drinking and related behaviors in humans and rodents. With zebrafish emerging as a powerful tool for uncovering neural mechanisms of numerous diseases and exhibiting similarities to rodents, the present report building on our rat studies examined in zebrafish the effects of embryonic ethanol exposure on hypothalamic neurogenesis, expression of orexigenic neuropeptides, and voluntary ethanol consumption and locomotor behaviors in larval and adult zebrafish, and also effects of central neuropeptide injections on these behaviors affected by ethanol. At 24h post-fertilization, zebrafish embryos were exposed for 2h to ethanol, at low concentrations of 0.25% and 0.5%, in the tank water. Embryonic ethanol compared to control dose-dependently increased hypothalamic neurogenesis and the proliferation and expression of the orexigenic peptides, galanin (GAL) and orexin (OX), in the anterior hypothalamus. These changes in hypothalamic peptide neurons were accompanied by an increase in voluntary consumption of 10% ethanol-gelatin and in novelty-induced locomotor and exploratory behavior in adult zebrafish and locomotor activity in larvae. After intracerebroventricular injection, these peptides compared to vehicle had specific effects on these behaviors altered by ethanol, with GAL stimulating consumption of 10% ethanol-gelatin more than plain gelatin food and OX stimulating novelty-induced locomotor behavior while increasing intake of food and ethanol equally. These results, similar to those obtained in rats, suggest that the ethanol-induced increase in genesis and expression of these hypothalamic peptide neurons contribute to the behavioral changes induced by embryonic exposure to ethanol.

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.

Evaluating the role of a galanin enhancer genotype on a range of metabolic, depressive and addictive phenotypes

There is a large body of pre-clinical and some clinical data to link the neuropeptide galanin to a range of physiological and pathological functions that include metabolism, depression, and addiction. An enhancer region upstream of the human GAL transcriptional start site has previously been characterised. In-vitro transfection studies in rat hypothalamic neurons demonstrated that the CA allele was 40% less active than the GG allele in driving galanin expression. Our hypothesis was to investigate the effect of this galanin enhancer genotype on a range of variables that relate to the known functions of the galaninergic system in the Avon Longitudinal Study of Parents and Children (ALSPAC) cohort of young adults (N = 169-6,078). Initial findings showed a positive relationship of cannabis usage (OR = 2.070, P = 0.007, N = 406 (individuals who had used cannabis at least once within the last 12 months, total sample size 2731) with the GG haplotype, consistent with the previous published data linking galanin with an increased release of dopamine. As our sample size was relatively small we replicated the analysis in a larger cohort of 2,224 African Americans and 1,840 European Americans, but no discernible trend across genotypes was observed for the relationship with cannabis usage. Further, we found no association of the galanin enhancer genotype with any of the other pathophysiological parameters measured. These findings emphasise that preclinical data does not always predict clinical outcomes in cohort studies, noting that association studies are subject to multiple confounders.

Model of voluntary ethanol intake in zebrafish: effect on behavior and hypothalamic orexigenic peptides

Recent studies in zebrafish have shown that exposure to ethanol in tank water affects various behaviors, including locomotion, anxiety and aggression, and produces changes in brain neurotransmitters, such as serotonin and dopamine. Building on these investigations, the present study had two goals: first, to develop a method for inducing voluntary ethanol intake in individual zebrafish, which can be used as a model in future studies to examine how this behavior is affected by various manipulations, and second, to characterize the effects of this ethanol intake on different behaviors and the expression of hypothalamic orexigenic peptides, galanin (GAL) and orexin (OX), which are known in rodents to stimulate consumption of ethanol and alter behaviors associated with alcohol abuse. Thus, we first developed a new model of voluntary intake of ethanol in fish by presenting this ethanol mixed with gelatin, which they readily consume. Using this model, we found that individual zebrafish can be trained in a short period to consume stable levels of 10% or 20% ethanol (v/v) mixed with gelatin and that their intake of this ethanol-gelatin mixture leads to pharmacologically relevant blood ethanol concentrations which are strongly, positively correlated with the amount ingested. Intake of this ethanol-gelatin mixture increased locomotion, reduced anxiety, and stimulated aggressive behavior, while increasing expression of GAL and OX in specific hypothalamic areas. These findings, confirming results in rats, provide a method in zebrafish for investigating with forward genetics and pharmacological techniques the role of different brain mechanisms in controlling ethanol intake.

A high-fat diet or galanin in the PVN decreases phosphorylation of CREB in the nucleus accumbens

A high-fat diet (HFD) can increase hypothalamic galanin (GAL). GAL has recently been shown to inhibit opiate reward, which in turn, decreases cAMP response element-binding protein (CREB) in the nucleus accumbens (NAc). We hypothesized that injection of GAL into the paraventricular nucleus (PVN), or consumption of a HFD, would be associated with a decrease in NAc CREB. In Exp. 1, GAL in the PVN of naïve rats decreased phosphorylated-CREB (pCREB) which is the activated form of CREB, in the NAc compared to saline-injected controls. In Exp. 2, rats fed ad libitum HFD for 4 weeks had reduced NAc pCREB levels compared to rats with sporadic tastes of the HFD. Body weight, serum triglyceride and leptin levels were also raised in the chronic HFD-fed rats. These data suggest that PVN GAL or chronic intake of a HFD can decrease NAc pCREB. The implications of these findings may help to explain the lack of opiate-like withdrawal that has been reported in response to overeating a HFD, thereby providing a potential mechanism underlying behavioral differences seen with addiction-like overconsumption of different types of palatable foods.

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

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

Regulation of drug and palatable food overconsumption by similar peptide systems

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

Neurobiology of consummatory behavior: mechanisms underlying overeating and drug use

Consummatory behavior is driven by both caloric and emotional need, and a wide variety of animal models have been useful in research on the systems that drive consumption of food and drugs. Models have included selective breeding for a specific trait, manipulation of gene expression, forced or voluntary exposure to a substance, and identification of biomarkers that predict which animals are prone to overconsuming specific substances. This research has elucidated numerous brain areas and neurochemicals that drive consummatory behavior. Although energy homeostasis is primarily mediated by the hypothalamus, reinforcement is more strongly mediated by nuclei outside the hypothalamus, in mesocorticolimbic regions. Orexigenic neurochemicals that control food intake can provide a general signal for promoting caloric intake or a more specific signal for stimulating consumption of a particular macronutrient, fat, carbohydrate, or protein. The neurochemicals involved in controlling fat ingestion--galanin, enkephalin, orexin, melanin-concentrating hormone, and the endocannabinoids--show positive feedback with this macronutrient, as these peptides both increase fat intake and are further stimulated by its intake. This positive association offers some explanation for why foods high in fat are so often overconsumed. Consumption of ethanol, a drug of abuse that also contains calories, is similarly driven by the neurochemical systems involved in fat intake, according to evidence that closely relates fat and ethanol consumption. Further understanding of the systems involved in consummatory behavior will enable the development of effective therapies for the treatment of both overeating and drug abuse.

Differential activity by polymorphic variants of a remote enhancer that supports galanin expression in the hypothalamus and amygdala: implications for obesity, depression and alcoholism

The expression of the galanin gene (GAL) in the paraventricular nucleus (PVN) and in the amygdala of higher vertebrates suggests the requirement for highly conserved, but unidentified, regulatory sequences that are critical to allow the galanin gene to control alcohol and fat intake and modulate mood. We used comparative genomics to identify a highly conserved sequence that lay 42 kb 5' of the human GAL transcriptional start site that we called GAL5.1. GAL5.1 activated promoter activity in neurones of the PVN, arcuate nucleus and amygdala that also expressed the galanin peptide. Analysis in neuroblastoma cells demonstrated that GAL5.1 acted as an enhancer of promoter activity after PKC activation. GAL5.1 contained two polymorphisms; rs2513280(C/G) and rs2513281(A/G), that occurred in two allelic combinations (GG or CA) where the dominant GG alelle occurred in 70-83 % of the human population. Intriguingly, both SNPs were found to be in LD (R(2) of 0.687) with another SNP (rs2156464) previously associated with major depressive disorder (MDD). Recreation of these alleles in reporter constructs and subsequent magnetofection into primary rat hypothalamic neurones showed that the CA allele was 40 % less active than the GG allele. This is consistent with the hypothesis that the weaker allele may affect food and alcohol preference. The linkage of the SNPs analysed in this study with a SNP previously associated with MDD together with the functioning of GAL5.1 as a PVN and amygdala specific enhancer represent a significant advance in our ability to understand alcoholism, obesity and major depressive disorder.

Galanin and the orexin 2 receptor as possible regulators of enkephalin in the paraventricular nucleus of the hypothalamus: relation to dietary fat

Recent studies show that the non-opioid peptides, galanin (GAL) and orexin (OX), are similar to the opioid enkephalin (ENK) in being stimulated by dietary fat and also in enhancing the consumption of a high-fat diet (HFD). This suggests that, when an HFD is provided, these non-opioids may stimulate the opioid system to promote excess consumption of this diet. Using single- and double-labeling immunohistochemistry, the present study sought to identify possible neuroanatomical substrates for this close relationship. Focusing on the hypothalamic paraventricular nucleus (PVN), and particularly its anterior (aPVN), middle (mPVN) and posterior (pPVN) parts, the experiments examined whether GAL itself or the receptors for GAL and OX are stimulated by an HFD in the same areas and possibly the same neurons as ENK. Compared to animals fed a standard chow diet, rats consuming an HFD exhibited an increased density of medial parvocellular neurons immunoreactive (IR) for GAL in the mPVN and aPVN and for ENK in the mPVN and pPVN, distinguishing the mPVN as an area where both peptides were affected. While showing little evidence for GAL and ENK colocalization with a chow diet, double-labeling studies in HFD-fed rats revealed significant colocalization specifically in medial parvocellular neurons of the mPVN. Immediately posterior to this site, further analyses revealed a similar relationship between the OX 2 receptor (OX(2)R) and ENK in HFD-treated animals. While increasing the density of neurons immunoreactive for OX(2)R as well as for the GAL 1 receptor but not OX 1 receptor, HFD consumption increased the colocalization only of OX(2)R and ENK, specifically in the medial parvocellular neurons of the pPVN. These changes in HFD-fed rats, showing GAL and OX(2)R to colocalize with ENK exclusively in neurons of the medial parvocellular mPVN and pPVN, respectively, suggest possible neural substrates through which the non-opioid peptides may functionally interact with ENK when exposed to an HFD.

Similarities in hypothalamic and mesocorticolimbic circuits regulating the overconsumption of food and alcohol

Historically, studies of food intake regulation started with the hypothalamus and gradually expanded to mesocorticolimbic regions, while studies of drug use began with mesocorticolimbic regions and now include the hypothalamus. As research on ingestive behavior has progressed, it has uncovered more and more similarities between the regulation of palatable food and drug intake. It has also identified specific neurochemicals involved in palatable food and drug intake. Hypothalamic orexigenic neurochemicals specifically involved in controlling fat ingestion, including galanin, enkephalin, orexin and melanin-concentrating hormone, show positive feedback with this macronutrient, with these peptides both increasing fat intake and being further stimulated by its intake. This positive relationship offers some explanation for why foods high in fat are so often overconsumed. Research in Bart Hoebel's laboratory in conjunction with our own has shown that consumption of ethanol, a drug of abuse that also contains calories, is similarly driven by these neurochemical systems involved in fat intake, consistent with evidence closely relating fat and ethanol consumption. Both fat and ethanol intake are also regulated by dopamine and acetylcholine acting in mesocorticolimbic nuclei. This close relationship of fat and ethanol is likely driven in part by circulating lipids, which are increased by fat and ethanol intake, known to increase expression and levels of the neurochemicals, and found to promote further intake of fat and ethanol. Compellingly, recent studies suggest that these systems may already be dysregulated in animals prone to consuming excess fat or ethanol, even before they have ever been exposed to these substances. Further understanding of these systems involved in consummatory behavior will allow researchers to develop effective therapies for the treatment of overeating as well as drug abuse.

Alcohol and nutrient intake: mechanisms of reinforcement and dependence

Alcohol is not only a drug of abuse but is also a food. This combination has a significant impact on the development and consequences of alcohol abuse and dependence. Understanding the neurobiological and behavioral processes that mediate them is perhaps best approached from the perspective of ingestive behavior. Research from the Hoebel laboratory has provided innovation and leadership in understanding that feeding neuropeptides plays a significant role in alcohol intake. The research reviewed here shows that galanin and other feeding peptides increase intake and also motivate abuse and the development of dependence. In addition, the consequences of long term alcohol abuse and dependence alter nutritional systems and drinking behavior. A major challenge is understanding the role of alcohol's dual properties and feeding neuropeptide in the motivation to drink.

Decreased galanin serum levels are associated with alcohol-craving during withdrawal

BACKGROUND

The hypothalamic galanin expression has been associated with increased intake of carbohydrates and fats in preclinical studies. The appetite stimulating effect of galanin is thought to underlie the positive association between alcohol consumption and hypothalamic galanin expression observed in preclinical studies.

METHODS

In this pilot study we investigated alterations in galanin serum levels (33 male patients) in alcohol-dependent patients during alcohol withdrawal (days 1, 7 and 14) in comparison to healthy controls (19 male controls). In order to assess the putative association between appetite regulation, galanin serum levels and alcohol consumption we additionally investigated the serum levels of insulin, glucose and triglycerides.

RESULTS

The galanin serum levels on day 1 of alcohol withdrawal were significantly reduced in the alcohol-dependent patients (T=-3.302, p=0.002) and increased significantly from day 1 to day 14 of alcohol withdrawal (F=6.437, p=0.002). We found a significant negative association between the galanin serum levels and alcohol craving measured by the Obsessive Compulsive Drinking Scale (OCDS) (r=-0.449, p=0.009) and the obsessive subscale of the OCDS (r=-0.521, p=0.002) on day 1 of alcohol withdrawal. There was no association between the galanin serum levels and the parameters of energy homeostasis (triglycerides, cholesterol, insulin, and glucose) investigated.

CONCLUSIONS

Acute alcohol withdrawal was associated with decreased galanin serum levels in this pilot study. There was no association between the galanin serum levels and the parameters of energy homeostasis. Further research of galanin serum levels in active drinkers will be necessary to clarify the putative association between galanin serum levels, appetite regulation and alcohol consumption.

Role of melanin-concentrating hormone in the control of ethanol consumption: Region-specific effects revealed by expression and injection studies

The peptide melanin-concentrating hormone (MCH), produced mainly by cells in the lateral hypothalamus (LH), perifornical area (PF) and zona incerta (ZI), is suggested to have a role in the consumption of rewarding substances, such as ethanol, sucrose and palatable food. However, there is limited information on the specific brain sites where MCH acts to stimulate intake of these rewarding substances and on the feedback effects that their consumption has on the expression of endogenous MCH. The current study investigated MCH in relation to ethanol consumption, in Sprague-Dawley rats. In Experiment 1, chronic consumption of ethanol (from 0.70 to 2.7 g/kg/day) dose-dependently reduced MCH gene expression in the LH. In Experiments 2-4, the opposite effect was observed with acute oral ethanol, which stimulated MCH expression specifically in the LH but not the ZI. In Experiment 5, the effect of MCH injection in brain-cannulated rats on ethanol consumption was examined. Compared to saline, MCH injected in the paraventricular nucleus (PVN) and nucleus accumbens (NAc) selectively stimulated ethanol consumption without affecting food or water intake. In contrast, it reduced ethanol intake when administered into the LH, while having no effect in the ZI. These results demonstrate that voluntary, chronic consumption of ethanol leads to local negative feedback control of MCH expression in the LH. However, with a brief exposure, ethanol stimulates MCH-expressing neurons in this region, which through projections to the feeding-related PVN and reward-related NAc can promote further drinking behavior.

The galanin-3 receptor antagonist, SNAP 37889, reduces operant responding for ethanol in alcohol-preferring rats

BACKGROUND/OBJECTIVE

The galanin-3 receptor (GALR3) subtype has been identified as having a role in both feeding behaviour and the regulation of emotional states including anxiety. Despite the evidence for an association between galanin and alcohol, the current study is the first to explore the direct role of GALR3 in this context. The present study investigated the potential of the novel selective GALR3 antagonist, SNAP 37889, to reduce anxiety-like behaviour and voluntary ethanol consumption in the iP (alcohol-preferring) rat. This was achieved through a number of behavioural paradigms testing for anxiety, along with the operant self-administration model.

RESULTS

Overall, male iP rats treated with SNAP 37889 at a dose of 30 mg/kg (i.p.) did not show altered locomotor activity or changes in anxiety-like behaviour in the elevated plus maze or light-dark paradigms. Treatment with SNAP 37889 (30 mg/kg, i.p.) reduced operant responding for solutions containing ethanol, sucrose and saccharin. Collectively, results from the current study showed that SNAP 37889 (30 mg/kg, i.p.) is effective in reducing operant responding for ethanol, independent of a sedative effect.

CONCLUSIONS

These findings provide evidence that GALR3 antagonism reduces alcohol consumption and further suggest that GALR3 may be implicated in the rewarding effects of natural and drug reinforcers.

Predictors of ethanol consumption in adult Sprague-Dawley rats: relation to hypothalamic peptides that stimulate ethanol intake

To investigate mechanisms in outbred animals that increase the propensity to consume ethanol, it is important to identify and characterize these animals before or at early stages in their exposure to ethanol. In the present study, different measures were examined in adult Sprague-Dawley rats to determine whether they can predict long-term propensity to overconsume ethanol. Before consuming 9% ethanol with a two-bottle choice paradigm, rats were examined with the commonly used behavioral measures of novelty-induced locomotor activity and anxiety, as assessed during 15 min in an open-field activity chamber. Two additional measures, intake of a low 2% ethanol concentration or circulating triglyceride (TG) levels after a meal, were also examined with respect to their ability to predict chronic 9% ethanol consumption. The results revealed significant positive correlations across individual rats between the amount of 9% ethanol ultimately consumed and three of these different measures, with high scores for activity, 2% ethanol intake, and TGs identifying rats that consume 150% more ethanol than rats with low scores. Measurements of hypothalamic peptides that stimulate ethanol intake suggest that they contribute early to the greater ethanol consumption predicted by these high scores. Rats with high 2% ethanol intake or high TGs, two measures found to be closely related, had significantly elevated expression of enkephalin (ENK) and galanin (GAL) in the hypothalamic paraventricular nucleus (PVN) but no change in neuropeptide Y (NPY) in the arcuate nucleus (ARC). This is in contrast to rats with high activity scores, which in addition to elevated PVN ENK expression showed enhanced NPY in the ARC but no change in GAL. Elevated ENK is a common characteristic related to all three predictors of chronic ethanol intake, whereas the other peptides differentiate these predictors, with GAL enhanced with high 2% ethanol intake and TG measures but NPY related to activity.

Differential effects of acute and chronic ethanol exposure on orexin expression in the perifornical lateral hypothalamus

BACKGROUND

Recent reports support the involvement of hypothalamic orexigenic peptides in stimulating ethanol intake. Our previous studies have examined the effects of ethanol on hypothalamic peptide systems of the paraventricular nucleus (PVN) and identified a positive feedback loop in which PVN peptides, such as enkephalin and galanin, stimulate ethanol intake and ethanol, in turn, stimulates the expression of these peptides. Recently, orexin (OX), a peptide produced mainly by cells in the perifornical lateral hypothalamus (PFLH), has been shown to play an important role in mediating the rewarding aspects of ethanol intake. However, there is little evidence showing the effects that ethanol itself may have on the OX peptide system. In order to understand the feedback relationship between ethanol and the OX system, the current investigation was designed to measure OX gene expression in the PFLH following acute as well as chronic ethanol intake.

METHODS

In the first experiment, Sprague-Dawley rats were trained to voluntarily consume a 2 or 9% concentration of ethanol, and the expression of OX mRNA in the PFLH was measured using quantitative real-time polymerase chain reaction (qRT-PCR). The second set of experiments tested the impact of acute oral gavage of 0.75 and 2.5 g/kg ethanol solution on OX expression in the PFLH using qRT-PCR, as well as radiolabeled in situ hybridization. Further tests using digoxigenin-labeled in situ hybridization and immunofluorescence histochemistry allowed us to more clearly distinguish the effects of acute ethanol on OX cells in the lateral hypothalamic (LH) versus perifornical (PF) regions.

RESULTS

The results showed chronic consumption of ethanol versus water to dose-dependently reduce OX mRNA in the PFLH, with a larger effect observed in rats consuming 2.5 g/kg/d (-70%) or 1.0 g/kg/d (-50%) compared to animals consuming 0.75 g/kg/d (-40%). In contrast to chronic intake, acute oral ethanol compared to water significantly enhanced OX expression in the PFLH, and this effect occurred at the lower (0.75 g/kg) but not higher (2.5 g/kg) dose of ethanol. Additional analyses of the OX cells in the LH versus PF regions identified the former as the primary site of ethanol's stimulatory effect on the OX system. In the LH but not the PF, acute ethanol increased the density of OX-expressing and OX-immunoreactive neurons. The increase in gene expression was detected only at the lower dose of ethanol (0.75 g/kg), whereas the increase in OX peptide was seen only at the higher dose of ethanol (2.5 g/kg).

CONCLUSION

These results lead us to propose that OX neurons, while responsive to negative feedback signals from chronic ethanol consumption, are stimulated by acute ethanol administration, most potently in the LH where OX may trigger central reward mechanisms that promote further ethanol consumption.

Galanin and consummatory behavior: special relationship with dietary fat, alcohol and circulating lipids

Galanin (GAL) plays an integral role in consummatory behavior. In particular, hypothalamic GAL has a positive, reciprocal relationship with dietary fat and alcohol. In this relationship, GAL increases the consumption of fat or alcohol which, in turn, stimulates the expression of GAL, ultimately leading to overconsumption. Through actions in the amygdala, this relationship may become especially important in stress-induced food or drug intake. These effects of GAL in promoting overconsumption may involve various neurotransmitters, with GAL facilitating intake by stimulating norepinephrine and dopamine and reducing satiety by decreasing serotonin and acetylcholine. In addition, GAL in the hypothalamus stimulates the opioid, enkephalin, throughout the brain, which also promotes overconsumption. The relationship between GAL, fat, and alcohol may involve triglycerides, circulating lipids that are released by fat or alcohol and that correlate positively with hypothalamic GAL expression. In females, levels of endogenous GAL also fluctuate across the reproductive cycle, driven by a rise in the ovarian steroids, estrogen, and progesterone. They peak during the proestrous phase and also at puberty, simultaneous to a sharp increase in preference for fat to meet energy demands. Prenatal exposure to a high-fat diet also enhances hypothalamic expression of GAL into adulthood because of an increase in neurogenesis and proliferation of GAL-expressing neurons in this region. This organizational change may reflect the role of GAL in neuronal development, including neurite growth in adulthood, cell survival in aging, and cell stability in the disease state. By responding positively to fat and alcohol and guiding further neuronal development, GAL potentiates a long-term propensity to overconsume fat and alcohol.

Galanin and addiction

There has been increasing interest in the ability of neuropeptides involved in feeding to modulate circuits important for responses to drugs of abuse. A number of peptides with effects on hypothalamic function also modulate the mesolimbic dopamine system (ventral tegmental area and nucleus accumbens). Similarly, common stress-related pathways can modulate food intake, drug reward and symptoms of drug withdrawal. Galanin promotes food intake and the analgesic properties of opiates, thus it initially seemed possible that galanin might potentiate opiate reinforcement. Instead, galanin agonists decrease opiate reward, measured by conditioned place preference, and opiate withdrawal signs, whereas opiate reward and withdrawal are increased in knockout mice lacking galanin. This is consistent with studies showing that galanin decreases activity-evoked dopamine release in striatal slices and decreases the firing rate of noradrenergic neurons in locus coeruleus, areas involved in drug reward and withdrawal, respectively. These data suggest that polymorphisms in genes encoding galanin or galanin receptors might be associated with susceptibility to opiate abuse. Further, galanin receptors might be potential targets for development of novel treatments for addiction.

Pharmacological effects of ethanol on ingestive behavior of the preweanling rat

The present study was designed to test the hypothesis that sensitivity of ingestive behavior of infant rat to the pharmacological effects of ethanol changes between postnatal (P) days 9 and 12. The intake of 0.1% saccharin and water, general motor activity, and myoclonic twitching activity were assessed following administration of three doses of ethanol (0, 0.25, and 0.5 g/kg) while fluids were free available to the animals. The 0.5 g/kg dose of ethanol attenuated saccharin intake in P9 pups and enhanced saccharin intake in P12 rats. On P12 some sex-related differences emerged at 0.5 g/kg of ethanol, with saccharin intake being higher in females than in their male counterparts. Taste reactivity probe revealed that 0.5 g/kg of ethanol increased taste responsiveness to saccharin on P12 but only to infusions presented at a high rate. The results of the present study indicate that ontogenetic changes in sensitivity to the effects of ethanol on ingestive behavior occur during the second postnatal week, with P9 animals being more sensitive to the inhibitory (sedative) effects on saccharin intake and P12 rats being more sensitive to the stimulatory effects of ethanol. We suggest that acute ethanol enhanced saccharin intake via sensitization of oral response to appetitive taste stimulation.

Increased intake of ethanol and dietary fat in galanin overexpressing mice

Evidence suggests that the orexigenic peptide, galanin (GAL), in the hypothalamic paraventricular nucleus (PVN) has a role in stimulating the consumption of ethanol, in addition to a high-fat diet. This possibility was further examined in mutant mice that overexpress the GAL gene. Two sets of GAL-overexpressors (GALOE) compared with wild-type (WT) controls, maintained on laboratory chow and water, were trained to voluntarily drink increasing concentrations of ethanol, from 3 to 15%. In the GALOE versus WT mice, the results revealed the following: (1) a 35-40% increase in ethanol intake and ethanol preference, which was evident only at the highest (15%) ethanol concentration, in male but not female mice, and was seen with comparisons to littermate and nonlittermate WT controls, (2) a significantly larger, 60-75% increase in ethanol intake and ethanol preference after a day of food deprivation, again only in male GALOE mice, (3) no change in consumption of sucrose or quinine solutions in preference tests, and (4) a 55% increase in consumption of a fat-rich diet during a 2-h test period, in both male and female GALOE mice. These results obtained with overexpression of the GAL gene provide strong support for a physiological role of this peptide in stimulating the consumption of ethanol and a fat-rich diet. They reveal gender differences in the behavioral phenotype, which may reflect GAL's functional relationship to reproductive hormones in the stimulation of consummatory behavior.

Opioids in the hypothalamic paraventricular nucleus stimulate ethanol intake

BACKGROUND

Specialized hypothalamic systems that increase food intake might also increase ethanol intake. To test this possibility, morphine and receptor-specific opioid agonists were microinjected in the paraventricular nucleus (PVN) of rats that had learned to drink ethanol. To cross-validate the results, naloxone methiodide (m-naloxone), an opioid antagonist, was microinjected with the expectation that it would have the opposite effect of morphine and the specific opioid agonists.

METHODS

Sprague-Dawley rats were trained, without sugar, to drink 4 or 7% ethanol and were then implanted with chronic brain cannulas aimed at the PVN. After recovery, those drinking 7% ethanol, with food and water available, were injected with 2 doses each of morphine or m-naloxone. To test for receptor specificity, 2 doses each of the mu-receptor agonist [D-Ala(2),N-Me-Phe(4),Gly(5)-ol]-Enkephalin (DAMGO), delta-receptor agonist D-Ala-Gly-Phe-Met-NH2 (DALA), or kappa-receptor agonist U-50,488H were injected. DAMGO was also tested in rats drinking 4% ethanol without food or water available. As an anatomical control for drug reflux, injections were made 2 mm dorsal to the PVN.

RESULTS

A main result was a significant increase in ethanol intake induced by PVN injection of morphine. The opposite effect was produced by m-naloxone. The effects of morphine and m-naloxone were exclusively on intake of ethanol, even though food and water were freely available. In the analysis with specific receptor agonists, PVN injection of the delta-agonist DALA significantly increased 7% ethanol intake without affecting food or water intake. This is in contrast to the kappa-agonist U-50,488H, which decreased ethanol intake, and the mu-agonist DAMGO, which had no effect on ethanol intake in the presence or absence of food and water. In the anatomical control location 2 mm dorsal to the PVN, no drug caused any significant changes in ethanol, food, or water intake, providing evidence that the active site was close to the cannula tip.

CONCLUSIONS

The delta-opioid receptor agonist in the PVN increased ethanol intake in strong preference over food and water, while the kappa-opioid agonist suppressed ethanol intake. Prior studies show that learning to drink ethanol stimulates PVN expression and production of the peptides enkephalin and dynorphin, which are endogenous agonists for the delta- and kappa-receptors, respectively. These results suggest that enkephalin via the delta-opioid system can function locally within a positive feedback circuit to cause ethanol intake to escalate and ultimately contribute to the abuse of ethanol. This is in contrast to dynorphin via the kappa-opioid system, which may act to counter this escalation. Naltrexone therapy for alcoholism may act, in part, by blocking the enkephalin-triggered positive feedback cycle.

Galanin knockout mice show disturbances in ethanol consumption and expression of hypothalamic peptides that stimulate ethanol intake

BACKGROUND

There is growing evidence suggesting that hypothalamic galanin (GAL), which is known to stimulate intake of a fat-rich diet, has a role in promoting the consumption of ethanol. The present study further examined this possibility in GAL knockout (GALKO) mice.

METHODS

Two groups of female and male GALKO mice, compared to wild-type (WT) controls, were trained to voluntarily drink increasing concentrations of ethanol, while maintained on lab chow and water. They were examined in terms of their daily ethanol intake and preference, acute consumption of a high-fat diet, preference for flavored solutions, and expression of different peptides shown to stimulate ethanol intake.

RESULTS

In the GALKO mice compared to WT, the results revealed: (i) a 35 to 45% decrease in ethanol intake and preference, which was evident only at the highest (15%) ethanol concentration, was stronger in female than in male mice, and was seen with comparisons to littermate as well as nonlittermate WT mice; (ii) a 48% decrease in acute intake of a fat-rich diet, again stronger in female than male mice; (iii) no difference in consumption of sucrose or quinine solutions in preference tests; (iv) a total loss of GAL mRNA in the hypothalamic paraventricular nucleus (PVN) of female and male mice; and (v) a gender-specific change in mRNA levels of peptides in the perifornical lateral hypothalamus (PFLH), orexin and melanin-concentrating hormone, which are known to stimulate ethanol and food intake and were markedly decreased in females while increased in males.

CONCLUSIONS

These results provide strong support for a physiological role of PVN GAL in stimulating the consumption of ethanol, as well as a fat-rich diet. Ablation of the GAL gene produced a behavioral phenotype, particularly in females, which may reflect the functional relationship of galanin to ovarian steroids. It also altered the peptides in the PFLH, with their reduced expression contributing to the larger behavioral effects observed in females and their increased expression attenuating these effects in males.

Effects of galanin on monoaminergic systems and HPA axis: Potential mechanisms underlying the effects of galanin on addiction- and stress-related behaviors

Like a number of neuropeptides, galanin can alter neural activity in brain areas that are important for both stress-related behaviors and responses to drugs of abuse. Accordingly, drugs that target galanin receptors can alter behavioral responses to drugs of abuse and can modulate stress-related behaviors. Stress and drug-related behaviors are interrelated: stress can promote drug-seeking, and drug exposure and withdrawal can increase activity in brain circuits involved in the stress response. We review here what is known about the ability of galanin and galanin receptors to alter neuronal activity, and we discuss potential mechanisms that may underlie the effects of galanin on behaviors involved in responses to stress and addictive drugs. Understanding the mechanisms underlying galanin's effects on neuronal function in brain regions related to stress and addiction may be useful in developing novel therapeutics for the treatment of stress- and addiction-related disorders.

Galanin: a potential role in mesolimbic dopamine-mediated instrumental behavior

The involvement of the neuropeptide galanin in the consumption of the primary "commodities" of food and water is well established. However, the present review describes anatomical and behavioral evidence that suggests that galanin may also modulate ascending mesolimbic dopamine function and thereby play an inhibitory role in the systems by which instrumental behavior is energized toward acquiring primary commodities. General anatomical frameworks for this interaction are presented and future studies that could evaluate it are discussed.

Orexigenic peptides and alcohol intake: differential effects of orexin, galanin, and ghrelin

BACKGROUND

The question is which hypothalamic systems for food intake might play a role in ethanol intake and contribute to alcohol abuse. The peptide orexin was found to exhibit similar properties to galanin in its relation to dietary fat and may therefore be similar to galanin in having a stimulatory effect on alcohol intake.

METHODS

Rats were trained to drink 10% ethanol, implanted with brain cannulas, and then injected in the paraventricular nucleus (PVN), lateral hypothalamus (LH), or nucleus accumbens (NAc) with galanin, orexin-A, and for comparison, ghrelin. Ethanol, food, and water intake were measured at 1, 2, and 4 hours postinjection.

RESULTS

In the PVN, both orexin and galanin significantly increased ethanol intake, whereas ghrelin increased food intake. In the LH, orexin again induced ethanol intake, while ghrelin increased eating. In the NAc, orexin failed to influence ethanol intake but did stimulate food intake.

CONCLUSIONS

In ethanol-drinking rats, injection of orexin or galanin into the appropriate locus in the hypothalamus induced significant ethanol intake instead of food intake. Ghrelin, as a positive control, failed to influence ethanol intake at the same hypothalamic sites. In the NAc, as an anatomical control, orexin augmented eating but not ethanol intake. Thus orexin and galanin in the hypothalamus selectively stimulated ethanol intake at sites where other studies have shown that both ethanol and fat increase expression of the endogenous peptides. Thus, a neural circuit that evolved with the capability to augment food intake is apparently co-opted by ethanol and may serve as a potential positive feedback circuit for alcohol abuse.

Neurobiology of addiction. An integrative review

Evidence that psychoactive substance use disorders, bulimia nervosa, pathological gambling, and sexual addiction share an underlying biopsychological process is summarized. Definitions are offered for addiction and addictive process, the latter being the proposed designation for the underlying biopsychological process that addictive disorders are hypothesized to share. The addictive process is introduced as an interaction of impairments in three functional systems: motivation-reward, affect regulation, and behavioral inhibition. An integrative review of the literature that addresses the neurobiology of addiction is then presented, organized according to the three functional systems that constitute the addictive process. The review is directed toward identifying candidate neurochemical substrates for the impairments in motivation-reward, affect regulation, and behavioral inhibition that could contribute to an addictive process.

Alcoholism is associated withGALR3but not two other galanin receptor genes

The neuropeptide galanin is widely expressed in the periphery and the central nervous system and mediates diverse physiological processes and behaviors including alcohol abuse, depression and anxiety. Four genes encoding galanin and its receptors have been identified (GAL, GALR1, GALR2 and GALR3). Recently we found that GAL haplotypes were associated with alcoholism, raising the possibility that genetic variation in GALR1, GALR2 and GALR3 might also alter alcoholism risk. Tag single nucleotide polymorphisms (SNPs) were identified by genotyping SNP panels in controls from five populations. For the association study with alcoholism, six GALR1, four GALR2 and four GALR3 SNPs were genotyped in a large cohort of Finnish alcoholics and non-alcoholics. GALR3 showed a significant association with alcoholism that was driven by one SNP (rs3,091,367). Moreover, the combination of the GALR3 rs3,091,367 risk allele and GAL risk haplotypes led to a modestly increased odds ratio (OR) for alcoholism (2.4) as compared with the effect of either GAL (1.9) or GALR3 alone (1.4). Likewise, the combination of the GALR3 and GAL risk diplotypes led to an increased OR for alcoholism (4.6) as compared with the effect of either GAL (2.0) or GALR3 alone (1.6). There was no effect of GALR1 or GALR2 on alcoholism risk. This evidence suggests that GALR3 mediates the alcoholism-related actions of galanin.

Overconsumption of dietary fat and alcohol: mechanisms involving lipids and hypothalamic peptides

The studies described in this report provide interesting animal models for exploring some of the metabolic and neural antecedents to the over-consumption of fat and alcohol. The results provide strong support for the existence of positive feedback loops that involve a close relation between circulating lipids and orexigenic peptides in dorsal regions of the hypothalamus. The peptides involved in these circuits include galanin, enkephalin, dynorphin and orexin. These peptides are expressed in the paraventricular nucleus and perifornical lateral hypothalamus, and they have very different functions from peptides expressed in the arcuate nucleus. Through mechanisms involving circulating lipids that rise on energy-dense diets, these peptides in the dorsal hypothalamus are each increased by the consumption of fat and ethanol; these nutrients, in turn, stimulate further production of these same peptides that promote overeating and excess drinking. These mechanisms involving non-homeostatic, positive feedback circuits may be required under conditions when food supplies are scarce and periods of gorging are essential to survival. However, they have pathological and sometimes life-threatening consequences in modern society, where fat-rich foods and alcoholic drinks are abundantly available and are contributing to the marked rise over the past 25 years in obesity and diabetes in both children and adults.

Effect of ethanol on hypothalamic opioid peptides, enkephalin, and dynorphin: relationship with circulating triglycerides

BACKGROUND

Recent evidence has demonstrated that ethanol intake can stimulate the expression and production of the feeding-stimulatory peptide, galanin (GAL), in the hypothalamic paraventricular nucleus (PVN), and that PVN injection of this peptide, in turn, can increase the consumption of ethanol. To test the hypothesis that other feeding-related systems are involved in ethanol intake, this study examined the effect of ethanol on the hypothalamic opioid peptides, enkephalin (ENK), and dynorphin (DYN).

METHOD

Adult, male Sprague-Dawley rats were trained to voluntarily drink increasing concentrations of ethanol, up to 9% v/v, on a 12-hour access schedule or were given a single injection of ethanol (10% v/v) versus saline vehicle. The effect of ethanol on GAL, ENK, and DYN mRNA was measured using real-time quantitative polymerase chain reaction and radiolabeled in situ hybridization, while radioimmunoassay was used to measure peptide levels. In addition to blood alcohol, circulating levels of triglycerides (TG), leptin, and insulin were also measured.

RESULTS

The data demonstrated that: (1) rats voluntarily drinking 9% v/v ethanol (approximately 2.0 g/kg/d) show a significant increase in GAL, ENK, and DYN mRNA in the PVN compared with water-drinking rats; (2) voluntary consumption of ethanol also increases peptide levels of ENK and DYN in the PVN; (3) acute injection of 10% ethanol (1.0 g/kg of 10% v/v) similarly increases the expression of GAL, ENK, and DYN in the PVN; and (4) ethanol consumption and injection, while having little effect on leptin and insulin, consistently increase circulating levels of TG as well as alcohol, both of which are strongly, positively correlated with peptide expression in the PVN.

CONCLUSIONS

These findings, together with published studies, suggest a possible role for hypothalamic opioid peptides in the drinking of ethanol. Based on evidence that dietary fat and lipid injections stimulate the PVN peptides and injection of the opiates and GAL increase ethanol intake, it is proposed that both TG and alcohol in the circulation, which are elevated by the ingestion or injection of ethanol, are involved in stimulating these peptides in the PVN, which in turn promote further consumption of ethanol.

Effect of ethanol on 24-h hormonal changes in prolactin release mechanisms in growing male rats

This study analyzes the effect of chronic ethanol feeding on 24-h variation of hypothalamic-pituitary mechanisms involved in prolactin regulation in growing male Wistar rats. Animals were maintained under a 12:12 h light/dark photoperiod (lights off at 2000 h), and they received a liquid diet for 4 wk, starting on d 35 of life. The ethanol-fed group received a similar diet to controls except that maltose was isocalorically replaced by ethanol. Ethanol replacement provided 36% of the total caloric content of the diet. Rats were killed at six time intervals every 4 h, beginning at 0900 h. Mean concentration of serum prolactin in ethanol-fed rats was 58.7% higher than in controls. Peak circulating prolactin levels occurred at the early phase of the activity span in both groups of rats, whereas a second peak was found late in the resting phase in ethanol-fed rats only. In control rats, median eminence dopamine (DA), serotonin (5-HT), gamma-aminobutyric acid (GABA), and taurine levels exhibited two maxima, the major one preceding prolactin release and a second one during the first part of the resting phase. Median eminence DA and 5-HT turnover (as measured by 3,4-dihydroxyphenylacetic acid, DOPAC/DA, and 5-hydroxyindoleacetic acid, 5-HIAA/5-HT ratio) showed a single maximum preceding prolactin, at 0100 h. Ethanol treatment did not affect median eminence DA or 5-HT levels but it decreased significantly their turnover rate. The midday peak in DA and 5-HT levels (at 1300 h) was abolished and the night peak (at 0100 h) became spread and blunted in the ethanol-fed rats. This was accompanied with the disappearance of the 0100 h peak in DA and 5-HT turnover and the occurrence of a peak in 5-HT turnover at 1700 h. Ethanol intake suppressed the night peak in median eminence GABA and taurine (at 0100 h) as well as the midday peak of GABA. Ethanol augmented pituitary levels of DOPAC and 5-HIAA. The results indicate that chronic ethanol administration affects the mechanisms that modulate the circadian variation of prolactin release in growing male rats.

GEDA: new knowledge base of gene expression in drug addiction

Abuse of drugs can elicit compulsive drug seeking behaviors upon repeated administration, and ultimately leads to the phenomenon of addiction. We developed a procedure for the standardization of microarray gene expression data of rat brain in drug addiction and stored them in a single integrated database system, focusing on more effective data processing and interpretation. Another characteristic of the present database is that it has a systematic flexibility for statistical analysis and linking with other databases. Basically, we adopt an intelligent SQL querying system, as the foundation of our DB, in order to set up an interactive module which can automatically read the raw gene expression data in the standardized format. We maximize the usability of this DB, helping users study significant gene expression and identify biological function of the genes through integrated up-to-date gene information such as GO annotation and metabolic pathway. For collecting the latest information of selected gene from the database, we also set up the local BLAST search engine and nonredundant sequence database updated by NCBI server on a daily basis. We find that the present database is a useful query interface and data-mining tool, specifically for finding out the genes related to drug addiction. We apply this system to the identification and characterization of methamphetamine-induced genes' behavior in rat brain.

Association of galanin haplotypes with alcoholism and anxiety in two ethnically distinct populations

The neuropeptide galanin (GAL) is widely expressed in the central nervous system. Animal studies have implicated GAL in alcohol abuse and anxiety: chronic ethanol intake increases hypothalamic GAL mRNA; high levels of stress increase GAL release in the central amygdala. The coding sequence of the galanin gene, GAL, is highly conserved and a functional polymorphism has not yet been found. The aim of our study was, for the first time, to identify GAL haplotypes and investigate associations with alcoholism and anxiety. Seven single-nucleotide polymorphisms (SNPs) spanning GAL were genotyped in 65 controls from five populations: US and Finnish Caucasians, African Americans, Plains and Southwestern Indians. A single haplotype block with little evidence of historical recombination was observed for each population. Four tag SNPs were then genotyped in DSM-III-R lifetime alcoholics and nonalcoholics from two population isolates: 514 Finnish Caucasian men and 331 Plains Indian men and women. Tridimensional Personality Questionnaire harm avoidance (HA) scores, a dimensional measure of anxiety, were obtained. There was a haplotype association with alcoholism in both the Finnish (P=0.001) and Plains Indian (P=0.004) men. The SNPs were also significantly associated. Alcoholics were divided into high and low HA groups (>or= and Collapse

Key Words

• single-nucleotide polymorphism
• linkage disequilibrium
• haplotype
• galanin
• alcoholism
• anxiety

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MESH Headings

• Alcoholism/genetics
• Anxiety/genetics
• Base Sequence
• Black People/genetics
• DNA Primers
• Ethnicity/genetics
• Female
• Finland
• Galanin/genetics
• Genotype
• Harm Reduction
• Humans
• Indians, North American/genetics
• Male
• Surveys and Questionnaires
• United States
• White People/genetics
• Black or African American

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Grants

• Z99 AA999999 Intramural NIH HHS

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Affiliation(s)

I Belfer Pain and Neurosensory Mechanisms Branch, National Institute of Dental and Craniofacial Research, Bethesda, MD 20892, USA.
H Hipp
C McKnight
C Evans
B Buzas
A Bollettino
B Albaugh
M Virkkunen
Q Yuan
M B Max
D Goldman
M A Enoch

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Collaborators Collapse

Regulation and effects of hypothalamic galanin: relation to dietary fat, alcohol ingestion, circulating lipids and energy homeostasis

Galanin (GAL) is known to stimulate feeding behavior. This peptide has different properties and functions from other feeding stimulants, e.g., neuropeptide Y and agouti-related protein. Hypothalamic GAL is relatively unresponsive to food deprivation and to changes in corticosterone, glucose utilization, dietary carbohydrate and leptin. This indicates that this peptide is not essential under conditions when food is scarce or low-energy, high-carbohydrate diets are being consumed. In contrast, recent evidence suggests that GAL in the paraventricular nucleus (PVN) functions in close relation to dietary fat and alcohol. In particular, it mediates functions that allow animals to adapt to conditions of positive energy balance involving excess consumption of these nutrients. This peptide in the PVN is stimulated by a high-fat diet and also by alcohol. It is stimulated by an increase in circulating lipids caused by a fat-rich meal or alcohol consumption, and it rises during the middle of the active feeding cycle, when fat consumption and triglycerides naturally rise. When centrally injected, GAL in the PVN increases the consumption of food and alcohol. Moreover, it produces a significantly stronger feeding response in rats maintained on a fat-rich diet, which also promotes alcohol intake. This evidence supports the existence of non-homeostatic, positive feedback circuits between GAL and both dietary fat and alcohol. These circuits are believed to contribute to the large meal size, over-consumption of alcohol, and obesity which are generally associated with fat-rich foods.

Galanin and alcohol dependence: neurobehavioral research

It is known that microinjection of galanin (GAL) intraventricularly or in specific hypothalamic sites increases food consumption and, conversely, the intake of food increases the expression of GAL in hypothalamic sites. Ethanol (EtOH) is a calorie-rich food as well as a drug of abuse. The research reviewed here shows that GAL may play a similar role in alcohol intake. First, experiments in which GAL was microinjected into the third ventricle or the paraventricular nucleus (PVN) showed increases in EtOH consumption. The increase in EtOH consumption occurred during both the light and dark cycles after GAL injection in the third ventricle in rats with limited EtOH access. Injection of GAL did not increase food intake in rats that had been chronically drinking alcohol. GAL receptor blockade reversed these increases. Microinjection of GAL directly into the PVN also increased ad libitum EtOH intake and blockade of these receptors in the PVN inhibited ad libitum EtOH consumption. Secondly, rats administered EtOH showed increases in GAL in the PVN and related hypothalamic sites. EtOH injection and voluntary intake, both ad libitum and limited access, increased GAL gene and peptide expression in the PVN consistently across administration procedures. These experiments show that GAL injection increases alcohol intake and that the intake of alcohol increases GAL, suggesting a positive feedback relationship between alcohol intake and specific hypothalamic GAL systems. Such a relationship may contribute to the motivation to consume excessive alcoholic beverages and the development of alcohol dependence.

Effects of melanocortin receptor activation and blockade on ethanol intake: a possible role for the melanocortin-4 receptor

BACKGROUND

The melanocortin (MC) system is composed of peptides that are cleaved from the polypeptide precursor pro-opiomelanocortin. A growing body of literature suggests that the MC system modulates neurobiological responses to drugs of abuse. Because ethanol has direct effects on central pro-opiomelanocortin activity, it is possible that MC neuropeptides participate in the control of voluntary ethanol consumption. Here we assessed the possibility that MC receptor (MCR) agonists modulate ethanol intake via the MC3 receptor (MC3R) and/or the MC4 receptor (MC4R) and whether the MCR antagonist AgRP-(83-132) controls ethanol consumption.

METHODS

Mc3r-deficient (Mc3r) and wild-type (Mc3r) littermate mice were given intraperitoneal (10 mg/kg) and intracerebroventricular (1.0 microg ICV) doses of melanotan II (MTII), a nonselective MCR agonist. To assess the role of MC4R, C57BL/6J mice were given an ICV infusion of the highly selective MC4R agonist cyclo(NH-CH2-CH2-CO-His-d-Phe-Arg-Trp-Glu)-NH2 (1.0 or 3.0 microg). Finally, naïve C57BL/6J mice were given an ICV infusion of AgRP-(83-132) (0.05 and 1.0 microg).

RESULTS

MTII was similarly effective at reducing ethanol drinking in Mc3r-deficient (Mc3r) and wild-type (Mc3r) littermate mice. Furthermore, ICV infusion of the MC4R agonist significantly reduced ethanol drinking, whereas ICV infusion of AgRP-(83-132) significantly increased ethanol drinking in C57BL/6J mice. Neither MTII nor AgRP-(83-132) altered blood ethanol levels at doses that modulated ethanol drinking.

CONCLUSIONS

The present results suggest that MC4R, and not MC3R, modulates MCR agonist-induced reduction of ethanol consumption and that ethanol intake is increased by the antagonistic actions of AgRP-(83-132). These findings strengthen the argument that MCR signaling controls ethanol consumption and that compounds directed at MCR may represent promising targets for treating alcohol abuse disorders in addition to obesity.

Galanin Microinjection in the Third Ventricle Increases Voluntary Ethanol Intake

BACKGROUND

The neuropeptide galanin increases food intake. Chronic ethanol (EtOH) increases the expression of galanin in the hypothalamus. The research presented here examines the effects of microinjection of galanin in the third ventricle on voluntary alcohol intake.

METHODS

Male Sprague Dawley rats with a cannula in the third ventricle were given access to increasing concentrations of EtOH for 12 hr/day until all acquired a preference for 7% EtOH over water in a two-bottle choice. Rats then received a microinjection of galanin (0, 1, and 3 nmol) alone or in combination with the galanin antagonist M40 (1 nmol) and with M40 alone to determine the effects on EtOH and water intake. Tests were conducted during both the light and dark periods of a 12:12-hr light-dark cycle with food available ad libitum. As a control for galanin-induced calorie intake, both EtOH and food were measured in a subset of rats during the dark.

RESULTS

Microinjections of galanin (1.0 and 3.0 nmol) increased EtOH consumption during both periods of the light-dark cycle. Galanin's effect on ethanol intake during the light was large relative to the very low intake of food and water during this period. Rats increased their intake of EtOH but not food. Receptor specificity for galanin (3 nmol) was shown by the galanin antagonist M40, which blocked the increase in EtOH intake. M40 alone decreased EtOH intake slightly.

CONCLUSIONS

These data show that galanin injected in the third ventricle increases EtOH consumption and that the effect can occur during both the light and the dark periods of the diurnal cycle in the presence of food and water. This suggests that galanin may play a role in augmenting voluntary alcohol intake and perhaps the development of alcohol dependence.

A high-fat meal or injection of lipids stimulates ethanol intake

Findings of earlier studies support the idea of a possible relation between dietary fat and ethanol intake, but it is unclear whether acute exposure to fat can increase ethanol consumption directly. In the current series of experiments, we examined whether daily overeating of fat, a single high-fat meal, or the injection of fat can increase ethanol intake. In Experiment 1, adult Sprague-Dawley rats were maintained on a high-fat diet (50% fat) for 7 days and switched subsequently to a laboratory chow diet while being trained to drink 9% ethanol. Rats that had eaten the greatest amount of the high-fat diet subsequently drank the most ethanol. In Experiment 2, a 1-h meal of the high-fat diet (50% fat) produced a significant increase in 7% ethanol consumption in comparison with what occurred after consumption of an equicaloric, low-fat (10% fat) meal. In Experiment 3, the orosensory effect of fat was eliminated with an intraperitoneal injection of a fat emulsion, Intralipid (20% fat, 5.0 ml). The injection of Intralipid, in comparison with saline, increased the ingestion of 9% ethanol. This finding is in contrast to what occurred with injection of an equicaloric, 50% glucose solution, which suppressed ethanol intake. These findings provide new evidence to support a positive relation between dietary fat and the consumption of ethanol.