Neurobiology of consummatory behavior: mechanisms underlying overeating and drug use

Neuro-immune-metabolism: The tripod system of homeostasis

Homeostatic regulation of cellular and molecular processes is essential for the efficient physiological functioning of body organs. It requires an intricate balance of several networks throughout the body, most notable being the nervous, immune and metabolic systems. Several studies have reported the interactions between neuro-immune, immune-metabolic and neuro-metabolic pathways. Current review aims to integrate the information and show that neuro, immune and metabolic systems form the triumvirate of homeostasis. It focuses on the cellular and molecular interactions occurring in the extremities and intestine, which are innervated by the peripheral nervous system and for the intestine in particular the enteric nervous system. While the interdependence of neuro-immune-metabolic pathways provides a fallback mechanism in case of disruption of homeostasis, in chronic pathologies of continued disequilibrium, the collapse of one system spreads to the other interacting networks as well. Current review illustrates this domino-effect using diabetes as the main example. Together, this review attempts to provide a holistic picture of the integrated network of neuro-immune-metabolism and attempts to broaden the outlook when devising a scientific study or a treatment strategy.

Ketogenic Diet Decreases Alcohol Intake in Adult Male Mice

The classic ketogenic diet is a diet high in fat, low in carbohydrates, and well-adjusted proteins. The reduction in glucose levels induces changes in the body’s metabolism, since the main energy source happens to be ketone bodies. Recent studies have suggested that nutritional interventions may modulate drug addiction. The present work aimed to study the potential effects of a classic ketogenic diet in modulating alcohol consumption and its rewarding effects. Two groups of adult male mice were employed in this study, one exposed to a standard diet (SD, n = 15) and the other to a ketogenic diet (KD, n = 16). When a ketotic state was stable for 7 days, animals were exposed to the oral self-administration paradigm to evaluate the reinforcing and motivating effects of ethanol. Rt-PCR analyses were performed evaluating dopamine, adenosine, CB1, and Oprm gene expression. Our results showed that animals in a ketotic state displayed an overall decrease in ethanol consumption without changes in their motivation to drink. Gene expression analyses point to several alterations in the dopamine, adenosine, and cannabinoid systems. Our results suggest that nutritional interventions may be a useful complementary tool in treating alcohol-use disorders.

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

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

CB1/5-HT/GABA interactions and food intake regulation

Despite historically the serotonergic, GABAergic, and cannabinoid systems have been shown to play a crucial role in the central regulation of eating behavior, interest in the study of the interactions of these neurotransmission systems has only now been investigated. Current evidence suggests that serotonin may influence normal and pathological eating behavior in significantly more complex ways than was initially thought. This knowledge has opened the possibility of exploring the potential clinical utility of new therapeutic strategies more effective and safer than the current approaches to treat pathological eating behavior. Furthermore, the nature and complexity of the interactions between these neurotransmitter systems have provided a better understanding of the pathophysiological mechanisms not only of eating behavior and eating disorders but also of some of the comorbidities associated with modulation of cortical circuits, which are involved in high order cognitive processes. Accordingly, in the present chapter, the clinical and experimental findings of the interactions between serotonin, GABA, and cannabinoids are synthesized, emphasizing the pharmacological, neurophysiological, and neuroanatomical aspects that could potentially improve the current therapeutic approaches against pathological eating behavior.

The anxiety and ethanol intake controlling GAL5.1 enhancer is epigenetically modulated by, and controls preference for, high-fat diet

Excess maternal fat intake and obesity increase offspring susceptibility to conditions such as chronic anxiety and substance abuse. We hypothesised that environmentally modulated DNA methylation changes (5mC/5hmC) in regulatory regions of the genome that modulate mood and consumptive behaviours could contribute to susceptibility to these conditions. We explored the effects of environmental factors on 5mC/5hmC levels within the GAL5.1 enhancer that controls anxiety-related behaviours and alcohol intake. We first observed that 5mC/5hmC levels within the GAL5.1 enhancer differed significantly in different parts of the brain. Moreover, we noted that early life stress had no significant effect of 5mC/5hmC levels within GAL5.1. In contrast, we identified that allowing access of pregnant mothers to high-fat diet (> 60% calories from fat) had a significant effect on 5mC/5hmC levels within GAL5.1 in hypothalamus and amygdala of resulting male offspring. Cell transfection-based studies using GAL5.1 reporter plasmids showed that 5mC has a significant repressive effect on GAL5.1 activity and its response to known stimuli, such as EGR1 transcription factor expression and PKC agonism. Intriguingly, CRISPR-driven disruption of GAL5.1 from the mouse genome, although having negligible effects on metabolism or general appetite, significantly decreased intake of high-fat diet suggesting that GAL5.1, in addition to being epigenetically modulated by high-fat diet, also actively contributes to the consumption of high-fat diet suggesting its involvement in an environmentally influenced regulatory loop. Furthermore, considering that GAL5.1 also controls alcohol preference and anxiety these studies may provide a first glimpse into an epigenetically controlled mechanism that links maternal high-fat diet with transgenerational susceptibility to alcohol abuse and anxiety.

Brain and kidney GHS-R1a underexpression is associated with changes in renal function and hemodynamics during neurogenic hypertension

Ghrelin is a peptide hormone whose effects are mediated by the growth hormone secretagogue receptor subtype 1a (GHS-R1a), mainly expressed in the brain but also in kidneys. The hypothesis herein raised is that GHS-R1a would be player in the renal contribution to the neurogenic hypertension pathophysiology. To investigate GHS-R1a role on renal function and hemodynamics, we used Wistar (WT) and spontaneously hypertensive rats (SHR). First, we assessed the effect of systemically injected vehicle, ghrelin, GHS-R1a antagonist PF04628935, ghrelin plus PF04628935 or GHS-R1a synthetic agonist MK-677 in WT and SHR rats housed in metabolic cages (24 h). Blood and urine samples were also analyzed. Then, we assessed the GHS-R1a contribution to the control of renal vasomotion and hemodynamics in WT and SHR. Finally, we assessed the GHS-R1a levels in brain areas, aorta, renal artery, renal cortex and medulla of WT and SHR rats using western blot. We found that ghrelin and MK-677 changed osmolarity parameters of SHR, in a GHS-R1a-dependent manner. GHS-R1a antagonism reduced the urinary Na⁺ and K⁺ and creatinine clearance in WT but not in SHR. Ghrelin reduced arterial pressure and increased renal artery conductance in SHR. GHS-R1a protein levels were decreased in the kidney and brain areas of SHR when compared to WT. Therefore, GHS-R1a role in the control of renal function and hemodynamics during neurogenic hypertension seem to be different, and this may be related to brain and kidney GHS-R1a downregulation.

Access schedules mediate the impact of high fat diet on ethanol intake and insulin and glucose function in mice

Alcoholism and high fat diet (HFD)-induced obesity individually promote insulin resistance and glucose intolerance in clinical populations, increasing risk for metabolic diseases. HFD can also stimulate alcohol intake in short-term clinical studies. Unfortunately, there is currently a disconnect between animal models and the clinical findings, as animal studies typically show that HFD decreases ethanol intake while ethanol intake mitigates HFD-induced effects on insulin and glucose dysfunction. However, most previous animal studies utilized forced or continuous HFD and/or ethanol. In three experiments we sought to determine whether HFD (HFD = 60% calories from fat) vs. control diet (chow = 16% fat) alters voluntary two-bottle choice ethanol intake in male C57Bl/6J mice given differing access schedules for 6-7 weeks, and we assessed the resultant impact on metabolic function via insulin and glucose tolerance tests. Experiment 1: Unlimited Access Ethanol + HFD (UAE + HFD; n = 15; 10% ethanol v/v, ad libitum diet and ethanol) or UAE + Chow (n = 15). Experiment 2: Limited Access Ethanol + HFD (LAE + HFD; n = 15; ethanol = 4 h/day; 3 days/week, ad libitum diet) or LAE + Chow (n = 15) with increasing ethanol concentrations (10%, 15%, 20%). Experiment 3: Intermittent HFD with limited access to ethanol (iHFD-E; HFD = single 24-h session/week; ethanol = 4 h/day; 4 days/week) (n = 10). UAE + HFD mice consumed significantly less ethanol and were insulin-resistant and hyperglycemic compared with UAE + Chow mice. LAE + HFD mice consumed ethanol similarly to LAE + Chow mice, but exhibited hyperglycemia, insulin resistance, and glucose intolerance. iHFD-E mice displayed binge eating-like behaviors and consumed significantly more ethanol than mice given ad libitum chow or HFD. iHFD-E mice did not have significantly altered body composition, but developed insulin insensitivity and glucose intolerance. These findings suggest that access schedules influence HFD effects on ethanol consumption and resultant metabolic dysfunction, ethanol intake does not improve HFD-induced metabolic dysfunction, and binge eating-like behaviors can transfer to binge drinking behaviors.

Effects of ethanol on plasma ghrelin levels in the rat during early and late adolescence

Ghrelin is an appetite-regulating peptide that is primarily secreted by endocrine cells in the stomach and is implicated in regulation of alcohol consumption and alcohol-reinforced behaviors. In the present study, adolescent Sprague-Dawley rats received intermittent ethanol (AIE) exposure by intragastric intubation (5 g/kg) or vapor inhalation, manipulations conducted between postnatal days (PD) 28-43. On the first and last day of AIE exposure, the level of intoxication was examined 1 h after ethanol gavage or upon removal from the vapor chamber. This was immediately followed by a blood draw for determination of the blood ethanol concentration (BEC) and plasma levels of acylated ghrelin (acyl-ghrelin; active). On PD29, plasma levels of acyl-ghrelin were significantly elevated in male (but not female) rats in response to acute ethanol exposure by both gastric gavage and vapor inhalation. Importantly, assessment of plasma acyl-ghrelin in response to repeated ethanol exposure revealed a complex interaction of both sex and method of AIE exposure. On PD43, vapor inhalation increased plasma acyl-ghrelin in both males and females compared to their air-control counterparts, whereas there was no change in plasma levels of acyl-ghrelin in either male or female rats in response to exposure by intragastric gavage. Assessment of plasma acyl-ghrelin following a 30-day ethanol-free period revealed AIE exposure did not produce a change in basal levels. In addition, an acute ethanol challenge in adult rats of 5 g/kg via gastric gavage had no effect on plasma ghrelin levels when assessed 1 h after initiation of exposure. Collectively, these observations suggest that acyl-ghrelin, a primary gut-brain signaling hormone, is elevated by ethanol during early adolescence independent of administration route, and in gender-dependent fashion.

Fish as models for understanding the vertebrate endocrine regulation of feeding and weight

The frequencies of eating disorders and obesity have increased worldwide in recent years. Their pathophysiologies are still unclear, but recent evidence suggests that they might be related to changes in endocrine and neural factors that regulate feeding and energy homeostasis. In order to develop efficient therapeutic drugs, a more thorough knowledge of the neuronal circuits and mechanisms involved is needed. Although to date, rodents have mostly been used models in the area of neuroscience and neuroendocrinology, an increasing number of studies use non-mammalian vertebrates, in particular fish, as model systems. Fish present several advantages over mammalian models and they share genetic and physiological homology to mammals with close similarities in the mechanisms involved in the neural and endocrine regulation of appetite. This review briefly describes the regulation of feeding in two model species, goldfish and zebrafish, how this regulation compares to that in mammals, and how these fish could be used for studies on endocrine regulation of eating and weight and its dysregulations.

Expression of neural markers of gustatory signaling are differentially altered by continuous and intermittent feeding patterns

Food intake patterns are regulated by signals from the gustatory neural circuit, a complex neural network that begins at the tongue and continues to homeostatic and hedonic brain regions involved in eating behavior. The goal of the current study was to investigate the short-term effects of continuous access to a high fat diet (HFD) versus limited access to dietary fat on the gustatory neural circuit. Male Sprague-Dawley rats were fed a chow diet, a HFD (56% kcal from fat), or provided limited, daily (2 h/day) or limited, intermittent (2 h/day, 3 times/week) access to vegetable shortening for 2 weeks. Real time PCR was used to determine mRNA expression of markers of fat sensing/signaling (e.g. CD36) on the circumvallate papillae, markers of homeostatic eating in the mediobasal hypothalamus (MBH) and markers of hedonic eating in the nucleus accumbens (NAc). Continuous HFD increased mRNA levels of lingual CD36 and serotonin signaling, altered markers of homeostatic and hedonic eating. Limited, intermittent access to dietary fat selectively altered the expression of genes associated with the regulation of dopamine signaling. Overall, these data suggest that short-term, continuous access to HFD leads to altered fat taste and decreased expression of markers of homeostatic and hedonic eating. Limited, intermittent access, or binge-like, consumption of dietary fat led to an overall increase in markers of hedonic eating, without altering expression of lingual fat sensors or homeostatic eating. These data suggest that there are differential effects of meal patterns on gustatory neurocircuitry which may regulate the overconsumption of fat and lead to obesity.

Mu opioid receptors in GABAergic neurons of the forebrain promote alcohol reward and drinking

Mu opioid receptors (MORs) are widely distributed throughout brain reward circuits and their role in drug and social reward is well established. Substantial evidence has implicated MOR and the endogenous opioid system in alcohol reward, but circuit mechanisms of MOR-mediated alcohol reward and intake behavior remain elusive, and have not been investigated by genetic approaches. We recently created conditional knockout (KO) mice targeting the Oprm1 gene in GABAergic forebrain neurons. These mice (Dlx-MOR KO) show a major MOR deletion in the striatum, whereas receptors in midbrain (including the Ventral Tegmental Area or VTA) and hindbrain are intact. Here, we compared alcohol-drinking behavior and rewarding effects in total (MOR KO) and conditional KO mice. Concordant with our previous work, MOR KO mice drank less alcohol in continuous and intermittent two-bottle choice protocols. Remarkably, Dlx-MOR KO mice showed reduced drinking similar to MOR KO mice, demonstrating that MOR in the forebrain is responsible for the observed phenotype. Further, alcohol-induced conditioned place preference was detected in control but not MOR KO mice, indicating that MOR is essential for alcohol reward and again, Dlx-MOR KO recapitulated the MOR KO phenotype. Taste preference and blood alcohol levels were otherwise unchanged in mutant lines. Together, our data demonstrate that MOR expressed in forebrain GABAergic neurons is essential for alcohol reward-driven behaviors, including drinking and place conditioning. Challenging the prevailing VTA-centric hypothesis, this study reveals another mechanism of MOR-mediated alcohol reward and consumption, which does not necessarily require local VTA MORs but rather engages striatal MOR-dependent mechanisms.

Incubation of feeding behavior is regulated by neuromedin U receptor 2 in the paraventricular nucleus of the hypothalamus

A diet of energy-dense food, characterized mainly as a high-fat diet, leads to a persistent excessive consumption defined as overeating. According to the National Institute of Health, more than 2 in 3 adults in the United States are overweight or obese, straining our healthcare system with epidemic proportions. Diets that include abstaining from high-fat foods, ironically, result in an increase in motivation and craving for said high-fat foods, defined as an incubation effect because the behavior aids in developing overeating. Previously, we have shown that modulation of neuromedin U receptor 2 (NMUR2) in the paraventricular nucleus of the hypothalamus (PVN) results in increased food intake and motivation for energy-dense foods. Here, we continue our focus on NMUR2 in the PVN, but in relation to the incubation effect on craving for high-fat food. We employed a model for incubation of craving by having rats abstain from high-fat foods for 30 days before undergoing intake of fatty food on fixed ratio and progressive ratio schedules of reinforcement, and then assess their response to reactivity to cues. Using this model, we compared the feeding behaviors of rats that underwent an mRNA knockdown of the NMUR2 in the PVN to controls after both underwent a 30-day abstinence from high-fat foods. Our results show knockdown of NMUR2 in the PVN blocks the incubation of feeding behavior for food-related cues and high-fat foods.

The Melanin-Concentrating Hormone as an Integrative Peptide Driving Motivated Behaviors

The melanin-concentrating hormone (MCH) is an important peptide implicated in the control of motivated behaviors. History, however, made this peptide first known for its participation in the control of skin pigmentation, from which its name derives. In addition to this peripheral role, MCH is strongly implicated in motivated behaviors, such as feeding, drinking, mating and, more recently, maternal behavior. It is suggested that MCH acts as an integrative peptide, converging sensory information and contributing to a general arousal of the organism. In this review, we will discuss the various aspects of energy homeostasis to which MCH has been associated to, focusing on the different inputs that feed the MCH peptidergic system with information regarding the homeostatic status of the organism and the exogenous sensory information that drives this system, as well as the outputs that allow MCH to act over a wide range of homeostatic and behavioral controls, highlighting the available morphological and hodological aspects that underlie these integrative actions. Besides the well-described role of MCH in feeding behavior, a prime example of hypothalamic-mediated integration, we will also examine those functions in which the participation of MCH has not yet been extensively characterized, including sexual, maternal, and defensive behaviors. We also evaluated the available data on the distribution of MCH and its function in the context of animals in their natural environment. Finally, we briefly comment on the evidence for MCH acting as a coordinator between different modalities of motivated behaviors, highlighting the most pressing open questions that are open for investigations and that could provide us with important insights about hypothalamic-dependent homeostatic integration.

Regulation of motivation for food by neuromedin U in the paraventricular nucleus and the dorsal raphe nucleus

BACKGROUND

Motivation for high-fat food is thought to contribute to excess caloric intake in obese individuals. A novel regulator of motivation for food may be neuromedin U (NMU), a highly-conserved neuropeptide that influences food intake. Although these effects of NMU have primarily been attributed to signaling in the paraventricular nucleus of the hypothalamus (PVN), NMU has also been found in other brain regions involved in both feeding behavior and motivation. We investigate the effects of NMU on motivation for food and food intake, and identify the brain regions mediating these effects.

METHODS

The motivational state for a particular reinforcer (e.g., high-fat food) can be assessed using a progressive-ratio schedule of reinforcement under which an increasing number of lever presses are required to obtain subsequent reinforcers. Here, we have used a progressive-ratio operant responding paradigm in combination with an assessment of cumulative food intake to evaluate the effects of NMU administration in rats, and identify the brain regions mediating these effects.

RESULTS

We found that peripheral administration of NMU decreases operant responding for high-fat food in rats. Evaluation of Fos-like immunoreactivity in response to peripheral NMU indicated the PVN and dorsal raphe nucleus (DRN) as sites of action for NMU. NMU infusion into either region mimics the effects of peripheral NMU on food intake and operant responding for food. NMU-containing projections from the lateral hypothalamus (LH) to the PVN and DRN were identified as an endogenous source of NMU.

CONCLUSIONS

These results identify the DRN as a site of action for NMU, demonstrate that the LH provides endogenous NMU to the PVN and DRN and implicate NMU signaling in the PVN and DRN as a novel regulator of motivation for high-fat foods.

Common genes regulate food and ethanol intake in Drosophila

The abuse liability of alcohol (ethanol) is believed to result in part from its actions on neurobiological substrates that underlie the motivation toward food and other natural reinforcers, and a growing body of evidence indicates that these substrates are broadly conserved among animal phyla. Understanding the extent to which the substrates regulating ethanol and food intake overlap is an important step toward developing therapeutics that selectively reduce ethanol intake. In the current experiments, we measured food and ethanol intake in Recombinant Inbred (RI) lines of Drosophila melanogaster using several assays, and then calculated genetic correlations to estimate the degree to which common genes might underlie behavior in these assays. We found that food intake and ethanol intake as measured in the capillary assay are genetically correlated traits in D. melanogaster, as well as in a panel of 11 Drosophila species that we tested subsequently. RI line differences in food intake in a dyed food assay were genetically unrelated to ethanol intake in the capillary assay or to ethanol preference measured using an olfactory trap apparatus. Using publicly available gene expression data, we found that expression profiles across the RI lines of a number of genes (including the D2-like dopamine receptor, DOPA decarboxylase, and fruitless) correlated with the RI line differences in food and ethanol intake we measured, while the expression profiles of other genes, including NPF, and the NPF and 5-HT2 receptors, correlated only with ethanol intake or preference. Our results suggest that food and ethanol intake are regulated by some common genes in Drosophila, but that other genes regulate ethanol intake independently of food intake. These results have implications toward the development of therapeutics that preferentially reduce ethanol intake.

Prenatal fat exposure and hypothalamic PPAR β/δ: Possible relationship to increased neurogenesis of orexigenic peptide neurons

Gestational exposure to a fat-rich diet, while elevating maternal circulating fatty acids, increases in the offspring's hypothalamus and amygdala the proliferation and density of neurons that express neuropeptides known to stimulate consummatory behavior. To understand the relationship between these phenomena, this study examined in the brain of postnatal offspring (day 15) the effect of prenatal fat exposure on the transcription factor, peroxisome proliferator-activated receptor (PPAR) β/δ, which is sensitive to fatty acids, and the relationship of PPAR β/δ to the orexigenic neuropeptides, orexin, melanin-concentrating hormone, and enkephalin. Prenatal exposure to a fat-rich diet compared to low-fat chow increased the density of cells immunoreactive for PPAR β/δ in the hypothalamic paraventricular nucleus (PVN), perifornical lateral hypothalamus (PFLH), and central nucleus of the amygdala (CeA), but not the hypothalamic arcuate nucleus or basolateral amygdaloid nucleus. It also increased co-labeling of PPAR β/δ with the cell proliferation marker, BrdU, or neuronal marker, NeuN, and the triple labeling of PPAR β/δ with BrdU plus NeuN, indicating an increase in proliferation and density of new PPAR β/δ neurons. Prenatal fat exposure stimulated the double-labeling of PPAR β/δ with orexin or melanin-concentrating hormone in the PFLH and enkephalin in the PVN and CeA and also triple-labeling of PPAR β/δ with BrdU and these neuropeptides, indicating that dietary fat increases the genesis of PPAR β/δ neurons that produce these peptides. These findings demonstrate a close anatomical relationship between PPAR β/δ and the increased proliferation and density of peptide-expressing neurons in the hypothalamus and amygdala of fat-exposed offspring.

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.

Prenatal exposure to ethanol stimulates hypothalamic CCR2 chemokine receptor system: Possible relation to increased density of orexigenic peptide neurons and ethanol drinking in adolescent offspring

Clinical and animal studies indicate that maternal consumption of ethanol during pregnancy increases alcohol drinking in the offspring. Possible underlying mechanisms may involve orexigenic peptides, which are stimulated by prenatal ethanol exposure and themselves promote drinking. Building on evidence that ethanol stimulates neuroimmune factors such as the chemokine CCL2 that in adult rats is shown to colocalize with the orexigenic peptide, melanin-concentrating hormone (MCH) in the lateral hypothalamus (LH), the present study sought to investigate the possibility that CCL2 or its receptor CCR2 in LH is stimulated by prenatal ethanol exposure, perhaps specifically within MCH neurons. Our paradigm of intraoral administration of ethanol to pregnant rats, at low-to-moderate doses (1 or 3g/kg/day) during peak hypothalamic neurogenesis, caused in adolescent male offspring twofold increase in drinking of and preference for ethanol and reinstatement of ethanol drinking in a two-bottle choice paradigm under an intermittent access schedule. This effect of prenatal ethanol exposure was associated with an increased expression of MCH and density of MCH(+) neurons in LH of preadolescent offspring. Whereas CCL2(+) cells at this age were low in density and unaffected by ethanol, CCR2(+) cells were dense in LH and increased by prenatal ethanol, with a large percentage (83-87%) identified as neurons and found to colocalize MCH. Prenatal ethanol also stimulated the genesis of CCR2(+) and MCH(+) neurons in the embryo, which co-labeled the proliferation marker, BrdU. Ethanol also increased the genesis and density of neurons that co-expressed CCR2 and MCH in LH, with triple-labeled CCR2(+)/MCH(+)/BrdU(+) neurons that were absent in control rats accounting for 35% of newly generated neurons in ethanol-exposed rats. With both the chemokine and MCH systems believed to promote ethanol consumption, this greater density of CCR2(+)/MCH(+) neurons in the LH of preadolescent rats suggests that these systems function together in promoting alcohol drinking during adolescence.

Nicotine and ethanol co-use in Long-Evans rats: Stimulatory effects of perinatal exposure to a fat-rich diet

Clinical studies demonstrate frequent co-existence of nicotine and alcohol abuse and suggest that this may result, in part, from the ready access to and intake of fat-rich diets. Whereas animal studies show that high-fat diet intake in adults can enhance the consumption of either nicotine or ethanol and that maternal consumption of a fat-rich diet during pregnancy increases operant responding for nicotine in offspring, little is known about the impact of dietary fat on the co-abuse of these two drugs. The goal of this study was to test in Long-Evans rats the effects of perinatal exposure to fat on the co-use of nicotine and ethanol, using a novel paradigm that involves simultaneous intravenous (IV) self-administration of these two drugs. Fat- vs. chow-exposed offspring were characterized and compared, first in terms of their nicotine self-administration behavior, then in terms of their nicotine/ethanol self-administration behavior, and lastly in terms of their self-administration of ethanol in the absence of nicotine. The results demonstrate that maternal consumption of fat compared to low-fat chow during gestation and lactation significantly stimulates nicotine self-administration during fixed-ratio testing. It also increases nicotine/ethanol self-administration during fixed-ratio and dose-response testing, with BEC elevated to 120 mg/dL, and causes an increase in breakpoint during progressive ratio testing. Of particular note is the finding that rats perinatally exposed to fat self-administer significantly more of the nicotine/ethanol mixture as compared to nicotine alone, an effect not evident in the chow-control rats. After removal of nicotine from the nicotine/ethanol mixture, this difference between the fat- and chow-exposed rats was lost, with both groups failing to acquire the self-administration of ethanol alone. Together, these findings suggest that perinatal exposure to a fat-rich diet, in addition to stimulating self-administration of nicotine, causes an even greater vulnerability to the excessive co-use of nicotine and ethanol.

Neural responses to macronutrients: hedonic and homeostatic mechanisms

The brain responds to macronutrients via intricate mechanisms. We review how the brain's neural systems implicated in homeostatic control of feeding and hedonic responses are influenced by the ingestion of specific types of food. We discuss how these neural systems are dysregulated in preclinical models of obesity. Findings from these studies can increase our understanding of overeating and, perhaps in some cases, the development of obesity. In addition, a greater understanding of the neural circuits affected by the consumption of specific macronutrients, and by obesity, might lead to new treatments and strategies for preventing unhealthy weight gain.

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.

Hypothalamic QRFP: regulation of food intake and fat selection

QRFP, a member of the RFamide-related peptide family, is a strongly conserved hypothalamic neuropeptide that has been characterized in various species. Prepro-QRFP mRNA expression is localized to select regions of the hypothalamus, which are involved in the regulation of feeding behavior. The localization of the peptide precursor has led to the assessment of QRFP on feeding behaviors and the orexigenic effects of QRFP have been detected in mice, rats, and birds. QRFP acts in a macronutrient specific manner in satiated rats to increase the intake of a high fat diet, but not the intake of a low fat diet, and increases the intake of chow in food-restricted rats. Studies suggest that QRFP's effects on food intake are mediated by the adiposity signal, leptin, and hypothalamic neuropeptides. Additionally, QRFP regulates the expression and release of hypothalamic Neuropeptide Y and proopiomelanocortin/α-Melanocyte-Stimulating Hormone. QRFP binds to receptors throughout the brain, including regions associated with food intake and reward. Taken together, these data suggest that QRFP is a mediator of motivated behaviors, particularly the drive to ingest high fat food. The present review discusses the role of QRFP in the regulation of feeding behavior, with emphasis on the intake of dietary fat.