Hypothalamic CART and serum leptin levels are reduced in the anorectic (anx/anx) mouse

The emerging role of the endocannabinoidome-gut microbiome axis in eating disorders

Among the sources of chemical signals regulating food intake, energy metabolism and body weight, few have attracted recently as much attention as the expanded endocannabinoid system, or endocannabinoidome (eCBome), and the gut microbiome, the two systems on which this review article is focussed. Therefore, it is legitimate to expect that these two systems also play a major role in the etiopathology of eating disorders (EDs), in particular of anorexia nervosa, bulimia nervosa and binge-eating disorder. The major mechanisms through which, also via interactions with other endogenous signaling systems, the eCBome, with its several lipid mediators and receptors, and the gut microbiome, via its variety of microbial kingdoms, phyla and species, and armamentarium of metabolites, intervene in these disorders, are described here, based on several published studies in either experimental models or patients. Additionally, in view of the emerging multi-faceted cross-talk mechanisms between these two complex systems, we discuss the possibility that the eCBome-gut microbiome axis is also involved in EDs.

The Head-to-Toe Hormone: Leptin as an Extensive Modulator of Physiologic Systems

Leptin is a well-known hunger-sensing peptide hormone. The role of leptin in weight gain and metabolic homeostasis has been explored for the past two decades. In this review, we have tried to shed light upon the impact of leptin signaling on health and diseases. At low or moderate levels, this peptide hormone supports physiological roles, but at chronically higher doses exhibits detrimental effects on various systems. The untoward effects we observe with chronically higher levels of leptin are due to their receptor-mediated effect or due to leptin resistance and are not well studied. This review will help us in understanding the non-anorexic roles of leptin, including their contribution to the metabolism of various systems and inflammation. We will be able to get an alternative perspective regarding the physiological and pathological roles of this mysterious peptide hormone.

Pioglitazone rescues high-fat diet-induced depression-like phenotypes and hippocampal astrocytic deficits in mice

The prevalence of diabetes is rapidly increasing worldwide and is highly associated with the incidence of depression. Pioglitazone, a Peroxisome proliferator-activated receptor gamma (PPAR-γ) agonist, is widely used for treating patients with type 2 diabetes. However, whether pioglitazone alleviates metabolic disorder-related depression and astrocytic deficits remains unclear. Here we showed that 12 weeks of high-fat diet (HFD) feeding (from 8- to 20-week-old) induced not only obesity and insulin resistance, but also depression-like behaviors in mice. Astrocytic activation, a sign closely associated with depression, was also evident in the ventral hippocampus. Four weeks of pioglitazone (10 or 20 mg/kg, daily, from 20- to 24-week-old) treatment alleviated the HFD-induced glucose-metabolic dysfunctions, upregulation of ventral hippocampal GFAP, reduction of the total process lengths and the number of branch points of the ventral hippocampal CA1 GFAP-immunoreactive astrocytes and depressive phenotypes but had no effect on anxiety-like behaviors or hippocampus-related learning and memory in mice. These findings suggest that pioglitazone could be a potential therapeutic agent for metabolic disorders and associated depression.

Animal Models for Anorexia Nervosa-A Systematic Review

Anorexia nervosa is an eating disorder characterized by intense fear of gaining weight and a distorted body image which usually leads to low caloric intake and hyperactivity. The underlying mechanism and pathogenesis of anorexia nervosa is still poorly understood. In order to learn more about the underlying pathophysiology of anorexia nervosa and to find further possible treatment options, several animal models mimicking anorexia nervosa have been developed. The aim of this review is to systematically search different databases and provide an overview of existing animal models and to discuss the current knowledge gained from animal models of anorexia nervosa. For the systematic data search, the Pubmed—Medline database, Embase database, and Web of Science database were searched. After removal of duplicates and the systematic process of selection, 108 original research papers were included in this systematic review. One hundred and six studies were performed with rodents and 2 on monkeys. Eighteen different animal models for anorexia nervosa were used in these studies. Parameters assessed in many studies were body weight, food intake, physical activity, cessation of the estrous cycle in female animals, behavioral changes, metabolic and hormonal alterations. The most commonly used animal model (75 of the studies) is the activity-based anorexia model in which typically young rodents are exposed to time-reduced access to food (a certain number of hours a day) with unrestricted access to a running wheel. Of the genetic animal models, one that is of particular interest is the anx/anx mice model. Animal models have so far contributed many findings to the understanding of mechanisms of hunger and satiety, physical activity and cognition in an underweight state and other mechanisms relevant for anorexia nervosa in humans.

Is there a hypothalamic basis for anorexia nervosa?

The hypothalamus has long been known to control food intake and energy metabolism through a complex network of primary and secondary neurons and glial cells. Anorexia nervosa being a complex disorder characterized by abnormal feeding behavior and food aversion, it is thus quite surprising that not much is known concerning potential hypothalamic modifications in this disorder. In this chapter, we review the recent advances in the fields of genetics, epigenetics, structural and functional imaging, and brain connectivity, as well as neuroendocrine findings and emerging animal models, which have begun to unravel the importance of hypothalamic adaptive processes to our understanding of the pathology of eating disorders.

Induced Pluripotent Stem Cells; New Tools for Investigating Molecular Mechanisms in Anorexia Nervosa

Anorexia nervosa (AN) is a dramatic psychiatric disorder characterized by dysregulations in food intake and reward processing, involving molecular and cellular changes in several peripheral cell types and central neuronal networks. Genomic and epigenomic analyses have allowed the identification of multiple genetic and epigenetic modifications highlighting the complex pathophysiology of AN. Behavioral and genetic rodent models have been used to recapitulate and investigate, with some limitations, the cellular and molecular changes that potentially underlie eating disorders. In the last 5 years, the use of induced pluripotent stem cells (IPSCs), combined with CRISPR-Cas9 technology, has led to the generation of specific neuronal cell subtypes engineered from human somatic samples, representing a powerful tool to complement observations made in human samples and data collected from animal models. Systems biology using IPSCs has indeed proved to be a valuable approach for the study of metabolic disorders, in addition to neurodevelopmental and psychiatric disorders. The manuscript, while reviewing the main findings related to the genetic, epigenetic, and cellular bases of AN, will present how new studies published, or to be performed, in the field of IPSC-derived cells should improve our current understanding of the pathophysiology of AN and provide potential therapeutic strategies addressing specific endophenotypes.

The anx/anx Mouse - A Valuable Resource in Anorexia Nervosa Research

Animal models are invaluable resources in research concerning the neurobiology of anorexia nervosa (AN), to a large extent since valid clinical samples are rare. None of the existing models can capture all aspects of AN but they are able to mirror the core features of the disorder e.g., elective starvation, emaciation and premature death. The anorectic anx/anx mouse is of particular value for the understanding of the abnormal response to negative energy balance seen in AN. These mice appear normal at birth but gradually develops starvation and emaciation despite full access to food, and die prematurely around three weeks of age. Several changes in hypothalamic neuropeptidergic and -transmitter systems involved in regulating food intake and metabolism have been documented in the anx/anx mouse. These changes are accompanied by signs of inflammation and degeneration in the same hypothalamic regions; including activation of microglia cells and expression of major histocompatibility complex I by microglia and selective neuronal populations. These aberrances are likely related to the dysfunction of complex I (CI) in the oxidative phosphorylation system of the mitochondria, and subsequent increased oxidative stress, which also has been revealed in the hypothalamus of these mice. Interestingly, a similar CI dysfunction has been shown in leukocytes from patients with AN. In addition, a higher expression of the Neurotrophic Receptor Tyrosine Kinase 3 gene has been shown in the anx/anx hypothalamus. This agrees with AN being associated with specific variants of the genes for brain derived neurotrophic factor and Neurotrophic Receptor Tyrosine Kinase 2. The anx/anx mouse is also glucose intolerant and display pancreatic dysfunction related to increased levels of circulating free fatty acids (FFA) and pancreatic inflammation. An increased incidence of eating disorders has been reported for young diabetic women, and as well has increased levels of circulating FFAs in AN. Also similar to individuals with AN, the anx/anx mouse has reduced leptin and increased cholesterol levels in serum. Thus, the anx/anx mouse shares several characteristics with patients with AN, including emaciation, starvation, premature death, diabetic features, increased FFA and low leptin, and is therefore a unique resource in research on the (neuro)biology of AN.

Animal Models of Eating Disorders

Eating disorders (EDs) include a range of chronic and disabling pathologies characterized by persistent maladaptive eating habits and/or behaviors aimed at controlling body shape and size, with important consequences on physical health. Different animal models of EDs have been developed to investigate pharmacological, environmental, and genetic determinants that contribute to the development and maintenance of these disorders as well as for the identification of potential therapeutic targets. In this chapter, we will provide an overview of the most useful animal models of EDs, focusing mainly on those used to study anorexia nervosa and binge eating disorder.

Metabolic and neuroendocrine adaptations to undernutrition in anorexia nervosa: from a clinical to a basic research point of view

The exact mechanisms linking metabolic and neuroendocrine adaptations to undernutrition and the pathophysiology of anorexia nervosa (AN) are not fully understood. AN is a psychiatric disorder of complex etiology characterized by extreme starvation while the disease is progressing into a chronic state. Metabolic and endocrine alterations associated to this disorder are part of a powerful response to maintain whole body energy homeostasis. But these modifications may also contribute to associated neuropsychiatric symptoms (reward abnormalities, anxiety, depression) and thus participate to sustain the disease. The current review presents data with both a clinical and basic research point of view on the role of nutritional and energy sensors with neuroendocrine actions in the pathophysiology of the disease, as they modulate metabolic responses, reproductive functions, stress responses as well as physical activity. While clinical data present a full description of changes occurring in AN, animal models that integrate either spontaneous genetic mutations or experimentally-induced food restriction with hyperactivity and/or social stress recapitulate the main metabolic and endocrine alterations of AN and provide mechanistic information between undernutrition state and symptoms of the disease. Further progress on the central and peripheral mechanism involved in the pathophysiology of eating disorders partly relies on the development and/or refinement of existing animal models to include recently identified genetic traits and better mimic the complex and multifactorial dimensions of the disease.

Reduced metabolism in the hypothalamus of the anorectic anx/anx mouse

The anorectic anx/anx mouse exhibits a mitochondrial complex I dysfunction that is related to aberrant expression of hypothalamic neuropeptides and transmitters regulating food intake. Hypothalamic activity, i.e. neuronal firing and transmitter release, is dependent on glucose utilization and energy metabolism. To better understand the role of hypothalamic activity in anorexia, we assessed carbohydrate and high-energy phosphate metabolism, in vivo and in vitro, in the anx/anx hypothalamus. In the fasted state, hypothalamic glucose uptake in the anx/anx mouse was reduced by ~50% of that seen in wild-type (wt) mice (P < 0.05). Under basal conditions, anx/anx hypothalamus ATP and glucose 6-P contents were similar to those in wt hypothalamus, whereas phosphocreatine was elevated (~2-fold; P < 0.001) and lactate was reduced (~35%; P < 0.001). The anx/anx hypothalamus had elevated total AMPK (~25%; P < 0.05) and GLUT4 (~60%; P < 0.01) protein contents, whereas GLUT1 and GLUT3 were similar to that of wt hypothalamus. Interestingly, the activation state of AMPK (ratio of phosphorylated AMPK/total AMPK) was significantly decreased in hypothalamus of the anx/anx mouse (~60% of that in wt; P < 0.05). Finally, during metabolic stress (ischemia), accumulation of lactate (measure of glycolysis) and IMP and AMP (breakdown products of ATP) were ~50% lower in anx/anx vs wt hypothalamus. These data demonstrate that carbohydrate and high-energy phosphate utilization in the anx/anx hypothalamus are diminished under basal and stress conditions. The decrease in hypothalamic metabolism may contribute to the anorectic behavior of the anx/anx mouse, i.e. its inability to regulate food intake in accordance with energy status.

Glucose intolerance and pancreatic β-cell dysfunction in the anorectic anx/anx mouse

Inflammation and impaired mitochondrial oxidative phosphorylation are considered key players in the development of several metabolic disorders, including diabetes. We have previously shown inflammation and mitochondrial dysfunction in the hypothalamus of an animal model for anorexia, the anx/anx mouse. Moreover, increased incidence of eating disorders, e.g., anorexia nervosa, has been observed in diabetic individuals. In the present investigation we evaluated whether impaired mitochondrial phosphorylation and inflammation also occur in endocrine pancreas of anorectic mice, and if glucose homeostasis is disturbed. We show that anx/anx mice exhibit marked glucose intolerance associated with reduced insulin release following an intraperitoneal injection of glucose. In contrast, insulin release from isolated anx/anx islets is increased after stimulation with glucose or KCl. In isolated anx/anx islets there is a strong downregulation of the mitochondrial complex I (CI) assembly factor, NADH dehydrogenase (ubiquinone) 1α subcomplex, assembly factor 1 (Ndufaf1), and a reduced CI activity. In addition, we show elevated concentrations of free fatty acids (FFAs) in anx/anx serum and increased macrophage infiltration (indicative of inflammation) in anx/anx islets. However, isolated islets from anx/anx mice cultured in the absence of FFAs do not exhibit increased inflammation. We conclude that the phenotype of the endocrine pancreas of the anx/anx mouse is characterized by increased levels of circulating FFAs, as well as inflammation, which can inhibit insulin secretion in vivo. The anx/anx mouse may represent a useful tool for studying molecular mechanisms underlying the association between diabetes and eating disorders.

The use of animal models to decipher physiological and neurobiological alterations of anorexia nervosa patients

Extensive studies were performed to decipher the mechanisms regulating feeding due to the worldwide obesity pandemy and its complications. The data obtained might be adapted to another disorder related to alteration of food intake, the restrictive anorexia nervosa. This multifactorial disease with a complex and unknown etiology is considered as an awful eating disorder since the chronic refusal to eat leads to severe, and sometimes, irreversible complications for the whole organism, until death. There is an urgent need to better understand the different aspects of the disease to develop novel approaches complementary to the usual psychological therapies. For this purpose, the use of pertinent animal models becomes a necessity. We present here the various rodent models described in the literature that might be used to dissect central and peripheral mechanisms involved in the adaptation to deficient energy supplies and/or the maintenance of physiological alterations on the long term. Data obtained from the spontaneous or engineered genetic models permit to better apprehend the implication of one signaling system (hormone, neuropeptide, neurotransmitter) in the development of several symptoms observed in anorexia nervosa. As example, mutations in the ghrelin, serotonin, dopamine pathways lead to alterations that mimic the phenotype, but compensatory mechanisms often occur rendering necessary the use of more selective gene strategies. Until now, environmental animal models based on one or several inducing factors like diet restriction, stress, or physical activity mimicked more extensively central and peripheral alterations decribed in anorexia nervosa. They bring significant data on feeding behavior, energy expenditure, and central circuit alterations. Animal models are described and criticized on the basis of the criteria of validity for anorexia nervosa.

CART in the regulation of appetite and energy homeostasis

The cocaine- and amphetamine-regulated transcript (CART) has been the subject of significant interest for over a decade. Work to decipher the detailed mechanism of CART function has been hampered by the lack of specific pharmacological tools like antagonists and the absence of a specific CART receptor(s). However, extensive research has been devoted to elucidate the role of the CART peptide and it is now evident that CART is a key neurotransmitter and hormone involved in the regulation of diverse biological processes, including food intake, maintenance of body weight, reward and addiction, stress response, psychostimulant effects and endocrine functions (Rogge et al., 2008; Subhedar et al., 2014). In this review, we focus on knowledge gained on CART's role in controlling appetite and energy homeostasis, and also address certain species differences between rodents and humans.

CART in the brain of vertebrates: circuits, functions and evolution

Cocaine- and amphetamine-regulated transcript peptide (CART) with its wide distribution in the brain of mammals has been the focus of considerable research in recent years. Last two decades have witnessed a steady rise in the information on the genes that encode this neuropeptide and regulation of its transcription and translation. CART is highly enriched in the hypothalamic nuclei and its relevance to energy homeostasis and neuroendocrine control has been understood in great details. However, the occurrence of this peptide in a range of diverse circuitries for sensory, motor, vegetative, limbic and higher cortical areas has been confounding. Evidence that CART peptide may have role in addiction, pain, reward, learning and memory, cognition, sleep, reproduction and development, modulation of behavior and regulation of autonomic nervous system are accumulating, but an integration has been missing. A steady stream of papers has been pointing at the therapeutic potentials of CART. The current review is an attempt at piecing together the fragments of available information, and seeks meaning out of the CART elements in their anatomical niche. We try to put together the CART containing neuronal circuitries that have been conclusively demonstrated as well as those which have been proposed, but need confirmation. With a view to finding out the evolutionary antecedents, we visit the CART systems in sub-mammalian vertebrates and seek the answer why the system is shaped the way it is. We enquire into the conservation of the CART system and appreciate its functional diversity across the phyla.

Animal models of eating disorders

Feeding is a fundamental process for basic survival and is influenced by genetics and environmental stressors. Recent advances in our understanding of behavioral genetics have provided a profound insight on several components regulating eating patterns. However, our understanding of eating disorders, such as anorexia nervosa, bulimia nervosa, and binge eating, is still poor. The animal model is an essential tool in the investigation of eating behaviors and their pathological forms, yet development of an appropriate animal model for eating disorders still remains challenging due to our limited knowledge and some of the more ambiguous clinical diagnostic measures. Therefore, this review will serve to focus on the basic clinical features of eating disorders and the current advances in animal models of eating disorders.

The role of leptin in antipsychotic-induced weight gain: genetic and non-genetic factors

Schizophrenia is a chronic and disabling mental illness affecting millions of people worldwide. A greater proportion of people with schizophrenia tends to be overweight. Antipsychotic medications have been considered the primary risk factor for obesity in schizophrenia, although the mechanisms by which they increase weight and produce metabolic disturbances are unclear. Several lines of research indicate that leptin could be a good candidate involved in pathways linking antipsychotic treatment and weight gain. Leptin is a circulating hormone released by adipocytes in response to increased fat deposition to regulate body weight, acting through receptors in the hypothalamus. In this work, we reviewed preclinical, clinical, and genetic data in order to infer the potential role played by leptin in antipsychotic-induced weight gain considering two main hypotheses: (1) leptin is an epiphenomenon of weight gain; (2) leptin is a consequence of antipsychotic-induced "leptin-resistance status," causing weight gain.

Hypothalamic mitochondrial dysfunction associated with anorexia in the anx/anx mouse

The anorectic anx/anx mouse exhibits disturbed feeding behavior and aberrances, including neurodegeneration, in peptidergic neurons in the appetite regulating hypothalamic arcuate nucleus. Poor feeding in infants, as well as neurodegeneration, are common phenotypes in human disorders caused by dysfunction of the mitochondrial oxidative phosphorylation system (OXPHOS). We therefore hypothesized that the anorexia and degenerative phenotypes in the anx/anx mouse could be related to defects in the OXPHOS. In this study, we found reduced efficiency of hypothalamic OXPHOS complex I assembly and activity in the anx/anx mouse. We also recorded signs of increased oxidative stress in anx/anx hypothalamus, possibly as an effect of the decreased hypothalamic levels of fully assembled complex I, that were demonstrated by native Western blots. Furthermore, the Ndufaf1 gene, encoding a complex I assembly factor, was genetically mapped to the anx interval and found to be down-regulated in anx/anx mice. These results suggest that the anorexia and hypothalamic neurodegeneration of the anx/anx mouse are associated with dysfunction of mitochondrial complex I.

The cocaine- and amphetamine-regulated transcript (CART) immunoreactivity in the amygdala of the pig

The distribution and morphology of neurons containing cocaine- and amphetamine-regulated transcript (CART) was investigated in the pig amygdala. CART- immunoreactive (CART-IR) cell bodies were rarely observed in the pig amygdala and most often they were present in the posterior (small-celled) parts of the basolateral and basomedial nuclei. In all other subdivisions only a small number of randomly scattered pericarya were present. In every region studied the CART-IR neurons formed a heterogeneous population consisting mostly of small, rounded or slightly elongated cell bodies, with a few poorly branched, smooth dendrites. In general, the morphological features of these cells clearly resembled non-pyramidal Golgi type II interneurons. Some randomly scattered CART-IR cell bodies were significantly larger and they demonstrated features of pyramidal-like Golgi type I projecting neurons. The highest densities of CART-IR fibres were evident within the central and medial nuclei. Moderate to high expression was found within the large-celled part of the basolateral nucleus and moderate to low levels in the lateral, basomedial and cortical nuclei. The routine double-labelling studies with antisera directed against CART and somatostatin (SOM), or neuropeptide Y (NPY), or cholecystokinin (CCK), or vasoactive intestinal peptide (VIP), or substance P (SP) demonstrated that, in general, these peptides do not co-exist in the CART-IR neurons. However, small subpopulations of the CART-IR fibres contained SOM, CCK, VIP or SP together.

Regulation of cocaine- and amphetamine-regulated transcript mRNA expression by calcium-mediated signaling in GH3 cells

Cocaine- and amphetamine-regulated-transcript (CART) peptides are associated with multiple physiological processes, including, feeding, body weight, and the response to drugs of abuse. CART mRNA and peptide levels and the expression of the CART gene appears to be under the control of a number of extra- and intra-cellular factors including the transcription factor, cAMP response element binding protein (CREB). Similar to the effects of CART, Ca(2+) signaling leads to the phosphorylation of CREB and has been associated with both feeding and the actions of psychostimulants; therefore, we hypothesized that Ca(2+) may play a role in CART gene regulation. We used real-time PCR (rtPCR) and GH3 cells to examine the effect of ionomycin, which increases intracellular Ca(2+), on CART mRNA levels. Ionomycin increased CART mRNA in a dose- and time-dependent manner. The effect of ionomycin appeared transient as CART mRNA had returned to control levels 3 h following treatment. Calmidazolium and KN93, inhibitors of calmodulin and Ca(2+)-modulated protein (CaM) kinases respectively, attenuated the effect of ionomycin (10 microM) on CART mRNA levels suggesting a calmodulin-dependent mechanism. Western immunoblotting indicated that ionomycin increased phosphorylated cAMP response element binding protein (pCREB) levels and electrophoretic mobility shift assay/supershift assay using antibodies against pCREB demonstrated increased levels of a CART oligo/pCREB protein complex. Finally, we showed that injection of ionomycin into the rat nucleus accumbens increases CART mRNA levels. To our knowledge, this is the first study providing evidence that the CART gene is, in part, regulated by Ca(2+)/CaM/CREB-dependent cell signaling.

NPY and its involvement in axon guidance, neurogenesis, and feeding

OBJECTIVES

The role of neuropeptides in nervous system function is still in many cases undefined. In the present study we examined a possible role of the 36-amino acid neuropeptide Y (NPY) with regard to three functions: axon guidance and attraction/repulsion, adult neurogenesis, and control of food intake.

METHODS

Growth cones from embryonic dorsal root ganglion neurons were studied in culture during asymmetrical gradient application of NPY. Growth cones were monitored over a 60-min period, and final turning angle and growth rate were recorded. In the second part the NPY Y(1) and Y(2) receptors were studied in the subventricular zone, the rostral migratory stream, and the olfactory bulb in normal mice and mice with genetically deleted NPY Y(1) or Y(2) receptors. In the third part an anorectic mouse was analyzed with immunohistochemistry.

RESULTS

1) NPY elicited an attractive turning response and an increase in growth rate, effects exerted via the NPY Y(1) receptor. 2) The NPY Y(1) receptor was expressed in neuroblasts in the anterior rostral migratory stream. Mice deficient in the Y(1) or Y(2) receptor had fewer proliferating precursor cells and neuroblasts in the subventricular zone and rostral migratory stream and fewer neurons in the olfactory bulb expressing calbindin, calretinin or tyrosine hydroxylase. 3) In the anorectic mouse markers for microglia were strongly upregulated in the arcuate nucleus and in projection areas of the NPY/agouti gene-related protein arcuate system.

CONCLUSION

NPY participates in several mechanisms involved in the development of the nervous system and is of importance in the control of food intake.

Hypothalamus transcriptome profile suggests an anorexia-cachexia syndrome in the anx/anx mouse model

The anx/anx mouse displays poor appetite and lean appearance and is considered a good model for the study of anorexia nervosa. To identify new genes involved in feeding behavior and body weight regulation we performed an expression profiling in the hypothalamus of the anx/anx mice. Using commercial microarrays we detected 156 differentially expressed genes and validated 92 of those using TaqMan low-density arrays. The expression of a set of 87 candidate genes selected based on literature evidences was also quantified by TaqMan low-density arrays. Our results showed enrichment in deregulated genes involved in cell death, cell morphology, and cancer, as well as an alteration of several signaling circuits involved in energy balance including neuropeptide Y and melanocortin signaling. The expression profile along with the phenotype led us to conclude that anx/anx mice resemble the anorexia-cachexia syndrome typically observed in cancer, infection with human immunodeficiency virus or chronic diseases, rather than starvation, and that anx/anx mice could be considered a good model for the treatment and investigation of this condition.

Aberrant agouti-related protein system in the hypothalamus of the anx/anx mouse is associated with activation of microglia

Agouti-related protein (AgRP) is a key orexigenic neuropeptide expressed in the hypothalamic arcuate nucleus and a marker for neurons conveying hormonal signals of hunger to the brain. Mice homozygous for the anorexia (anx) mutation are characterized by decreased food intake, starvation, and death by 3-5 weeks of age. At this stage immunoreactivity for AgRP is increased in cell bodies but decreased in the nerve terminals. We studied when during early postnatal development the aberrant phenotype of the AgRP system becomes apparent in anx/anx mice and possible underlying mechanisms. AgRP and ionized calcium binding adapter molecule (Iba1), a marker for activated microglia, as well as Toll-like receptor 2 (TLR-2), were studied by immunohistochemistry at postnatal days P1, P5, P10, P12, P15 and P21 in anx/anx and wild-type mice. We found that the AgRP system in the anx/anx mouse develops similarly to the wild type until P12, when AgRP fibers in anx/anx mice cease to increase in density in the main projection areas. At P21, AgRP fiber density in anx/anx mice was significantly reduced vs. P15, in certain regions. At P21, many strongly AgRP-positive cell bodies were observed in the anx/anx arcuate nucleus vs. only few and weakly fluorescent ones in the wild type. The decrease in AgRP fiber density in anx/anx mice overlapped with an increase in Iba1 and TLR-2 immunoreactivities. Thus, the aberrant appearance of the AgRP system in the anx/anx mouse in the early postnatal development could involve a microglia-associated process and the innate immune system.

Evidence for hypothalamic dysregulation in mouse models of anorexia as well as in humans

Eating disorders constitute major medical health problems in the western world. Even though little is known about the molecular mechanisms behind abnormal eating behavior, it has become clear that the central nervous system (CNS), particularly the hypothalamus, plays a significant role. The anorexic anx/anx mouse is a unique model for studying food intake and energy expenditure. The anx mutation is linked to marked alterations in hypothalamic distributions of signal substances known to have potent regulatory roles in the control of food intake. Another mouse model that displays an anorectic phenotype similar to the anx/anx mouse is the Contactin KO mouse. This model displays very similar hypothalamic alterations as seen in the anx/anx mouse, arguing for a role of these specific hypothalamic changes in an anorectic phenotype. In human eating disorders, hypothalamic systems corresponding to those defective in mouse models could be compromised since autoantibodies against melanocortin peptides have been detected in anorectic and bulimic patients. These findings represent research avenues that may lead to a better understanding of eating disorders and development of targeted therapeutic approaches.

Processing of cocaine- and amphetamine-regulated transcript (CART) precursor proteins by prohormone convertases (PCs) and its implications

Cocaine- and amphetamine-regulated transcript (CART) peptides are expressed in several neuroendocrine tissues, including hypothalamus, pituitary, gut, adrenal and pancreas, and are involved in regulating important biological processes including feeding/appetite, drug reward and stress. CART is synthesized as larger, inactive peptide precursors (pro-CART) that require endoproteolytic processing to generate smaller, active forms. Prohormone/proprotein convertases (PCs), a family of calcium-dependent, serine endoproteases, have been shown to cleave many protein precursors in the regulated/constitutive secretory pathway to generate smaller fragments. In our previous studies, we have demonstrated the important roles of the two neuroendocrine-specific PCs, PC2 and PC1/3, in processing the two pro-CART isoforms, long (102aa) and short (89aa), to generate the bioactive CART peptides, I (55-102/42-89) and II (62-102/49-89) as well as the intermediate fragments, 10-89 and 33-102. Our subsequent studies have revealed the participation of another PC family member, PC5/6A (the soluble isoform of a widely expressed PC, PC5/6), in cleaving both precursor isoforms. We conclude that PC5/6A contributes to the normal efficient processing of pro-CART and is functionally more redundant with PC2 than PC1/3 in generating both CART I and II.

CART peptide diurnal variations in blood and brain

The central role of CART peptide in feeding, drug abuse and stress has been widely researched however, CART's role in the peripheral system are less explored. CART peptide is present in a variety of peripheral tissues including sympathetic ganglion neurons, adrenal glands, gut, pancreas and blood. Studies that examined circulating CART demonstrated that the active fragment with a molecular weight of CART55-102 is present in the blood of rats and rhesus macaques. Interestingly, CART expression in these species exhibits a distinctive diurnal rhythm which correlates with the respective daily rhythms of corticosterone and feeding. In the rat, adrenalectomy significantly reduces blood CART levels and abolishes its daily rhythm while corticosterone replacement reinstates CART expression to control levels. In addition, direct administration of corticosterone significantly increases CART blood levels while administration of corticosterone synthesis blocker metyrapone, inhibits CART blood levels. These data suggest that the adrenal gland could be a source of blood CART and that glucocorticoids may play a role in the generation of CART's diurnal rhythm. Moreover, fuel availability may be important in the control of CART levels and its daily rhythm, since 24 h food restriction alters CART levels and abolishes its rhythm. In addition to blood, both CART peptide and mRNA exhibit food-dependent diurnal rhythm in discrete rat brain areas including the nucleus accumbens, amygdala and hypothalamus. Altogether, these findings suggest that CART is influenced by hypothalamic-pituitary-adrenal interactions and that it may play a role in multiple physiological processes possibly involving feeding, stress, reward and motivation.

The CART (Cocaine- and Amphetamine-Regulated Transcript) System in Appetite and Drug Addiction

CART (cocaine- and amphetamine-regulated transcript) peptides are neuromodulators that are involved in feeding, drug reward, stress, cardiovascular function, and bone remodeling. CART peptides are abundant but discretely distributed in the brain, pituitary and adrenal glands, pancreas, and gut. High expression of CART in discrete hypothalamic nuclei associated with feeding has led to behavioral and pharmacological studies that strongly support an anorectic action of CART in feeding. Subsequent studies on humans and transgenic animals provide additional evidence that CART is important in the regulation of appetite as mutations in the CART gene are linked to eating disorders, including obesity and anorexia. The expression of CART in the mesolimbic dopamine circuit has lead to functional studies demonstrating CART's psychostimulant-like effects on locomotor activity and conditioned place preference in rats. These and other findings demonstrated that CART modulates mesolimbic dopamine systems and affects psychostimulant-induced reward and reinforcing behaviors. The link between CART and psychostimulants was substantiated by demonstrating alterations of the CART system in human cocaine addicts. CART seems to regulate the mesolimbic dopamine system, which serves as a common mechanism of action for both feeding and addiction. Indeed, recent studies that demonstrated CART projections from specific hypothalamic areas associated with feeding to specific mesolimbic areas linked to reward/motivation behaviors provide evidence that CART may be an important connection between food- and drug-related rewards. Given the enormous public health burden of both obesity and drug addiction, future studies exploring the pharmacotherapies targeting CART peptide represent an exciting and challenging research area.

Effect of starvation on Fos and neuropeptide immunoreactivities in the brain and pituitary gland of Xenopus laevis

In mammals complex interactions between various brain structures and neuropeptides such as corticotropin-releasing factor (CRF) and urocortin 1 (Ucn1) underlay the control of feeding by the brain. Recently, in the amphibian Xenopus laevis, CRF- and Ucn1-immunoreactivities were shown in the hypothalamic magnocellular nucleus (Mg) and evidence was obtained for their involvement in food intake. To gain a better understanding of the brain structures controlling feeding in X. laevis, the effects of 16 weeks starvation on neurones immunoreactive (ir) to Fos and neuropeptides in various brain structures were quantified. In the Mg, compared to controls, starved animals showed fewer neurones immunopositive for Fos (-55.9%), Ucn1 (-44.0%), cocaine and amphetamine-regulated transcript (CART) (-94.3%) and metenkephalin (ENK) (-65.0%), whereas CRF-ir neurones were 2.1 times more numerous. These differences were mainly apparent in the ventral part of the Mg, followed by the medial and dorsal part of the nucleus. In the neural lobe of the pituitary gland a 22.5% lower optical density of CART-ir was observed. In the four other brain structures investigated, starvation had different effects. The dorsomedial part of the suprachiasmatic nucleus showed 5.9 times more NPY-ir cells and in the ventromedial thalamic area a lower number of NPY-ir cells (-33.6%) was found, whereas the Edinger-Westphal nucleus contained fewer CART-ir cells (-42.2%); no effect of starvation was seen in the ventral hypothalamic nucleus. Our results support the hypothesis that in X. laevis, the Mg plays a pivotal role in feeding-related processes and, moreover, that starvation also has neuropeptide- and brain structure-specific effects in other parts of the brain and in the pituitary gland, suggesting particular roles of these structures and their neuropeptides in physiological adaptation to starvation.

Alterations of arcuate nucleus neuropeptidergic development in contactin-deficient mice: comparison with anorexia and food-deprived mice

A mutation in the Contactin-1 gene results in an ataxic and anorectic phenotype that is apparent by postnatal day 10 and lethal by postnatal day 19 [Berglund et al. (1999) Neuron 24, 739-750]. The resemblance of this phenotype with the anorexia (anx/anx) mouse mutation prompted us to investigate the hypothalamic neurochemistry of Contactin knock-out (KO) mice. Contactin was expressed in the hypothalamic neuropil of wild-type (WT) but not Contactin KO mice. In the KO condition, neuropeptide Y (NPY) and agouti-related protein (AgRP) immunoreactivity (IR) accumulated in the somata of arcuate nucleus neurons, whereas IR for these neuropeptides as well as for alpha-melanocyte-stimulating hormone (alpha-MSH) decreased in the corresponding axon projections. These changes in the pattern of neuropeptide expression in the Contactin-deficient hypothalamus were similar but more pronounced than those found in anx/anx mice. Increased levels of NPY and AgRP and decreased concentrations of pro-opiomelanocortin mRNA in arcuate neurons accompanied these changes. In relating these alterations a 24-h food deprivation period, we observed in 3-week-old WT mice an elevation of NPY- and AgRP-IR in the perikarya of arcuate neurons without notable reduction of NPY- or AgRP-IR in nerve fibers, suggesting that the decrease of arcuate projections can be associated with postnatal anorectic phenotype. Our data implicate Contactin in the postnatal development of the NPY/AgRP and alpha-MSH arcuate neurons and suggest that similar to anx/anx mutant mice, compromised orexigenic signaling via NPY/AgRP neurons may contribute to reduced food intake by the Contactin-mutant animals.

Gene expression profiling reveals an inflammatory process in the anx/anx mutant mice

Anorexia (anx) is a recessive mutation that causes lethal starvation in homozygous mice. Studies of anx/anx mice hypothalamus have shown abnormalities in the orexigenic (NPY/AGRP neurons) and the anorexigenic (POMC/CART neurons) pathways. By gene expression profiling using cDNA and oligonucleotide microarrays, we have shown that a surexpression of genes involved in inflammatory process occurred in anx mice hypothalamus. This inflammatory process could be the cause of the anorexia phenotype observed in these mice.

CART in feeding and obesity

CART (cocaine- and amphetamine-regulated transcript) peptides are neurotransmitters that have received much attention as mediators of feeding behavior and body-weight regulation in mammals. CART peptides and their mRNAs are found in many brain regions and in peripheral tissues that are involved in feeding, and many animal studies implicate CART as an inhibitor of feeding. Animal studies also demonstrate that CART expression is regulated by both leptin and glucocorticoids, two hormones known to be associated with the regulation of body weight. A recent study also links a mutation in the CART gene to obesity in humans. These peptides might become targets for drug development in the area of obesity.

Effects of cocaine–amphetamine regulated transcript (CART) on hormone release

OBJECTIVE

Cocaine- and amphetamine-regulated transcript (CART) is a recently described neuropeptide widely expressed in the rat brain. CART is abundant in hypothalamus nuclei controlling anterior pituitary function. In the paraventricular nucleus CART mRNA is colocalized with vasopressin and corticotrophin-releasing factor containing neurons. The data may suggest that CART plays a role in hypothalamic regulation of neuroenocrine functions.

MATERIAL AND METHODS

Male Wistar-Kyoto rats were investigated. Experiment I: CART was administered intracerebroventricularly (i.c.v.) in a dose of 0.5 microg dissolved in 5 microl vehicle. At 60, 120 min after the infusion of CART or vehicle animals were decapitated and trunk blood was collected until hormonal estimations. Experiment II: CART in a dose of 10 microg was injected intravenously (i.v.). At 60, 120, 240 min the rats were decapitated and the trunk blood was collected. Serum rLH, rFSH, rPRL, rTSH, rGH and plasma leptin, NPY concentrations were measured by RIA methods.

RESULTS

CART administered centrally (i.c.v.) simulated significantly GH release after 60 min (p<0.05) and after 120 min (p<0.01). CART increased also PRL after 60 min (p<0.05). A marked increase of corticosterone level was observed at 60 and 120 min (p<0.01, p<0.01). We did not observe significant changes in LH, FSH and TSH. We found an increase of serum leptin concentrations at 60 min after CART administration (p<0.01). However, serum NPY levels did not change. After intravenous injection (i.v.) of CART an increase of GH was observed at 120, 240 min (p<0.01, p<0.01, respectively). A rise in serum PRL was found at 240 min (p<0.05). Corticosterone concentrations were enhanced at 60, 120, 240 min (p<0.01, p<0.01, p<0.01, respectively). We did not observe significant changes in LH, FSH and TSH.

CONCLUSIONS

CART may play a modulating role in the mechanism of pituitary hormone release.

The premammillary hypothalamic area of the ewe: anatomical characterization of a melatonin target area mediating seasonal reproduction

Recent evidence suggests that the ovine premammillary hypothalamic area (PMH) is an important target for the pineal hormone, melatonin, and its role in seasonal reproduction. In rodents, the PMH is a complex region consisting of several cell groups with differing neurochemical content and anatomical connections. Therefore, to obtain a better understanding of the potential neural targets for melatonin in this area of the sheep brain, we have undertaken a detailed anatomical characterization of the PMH, including its nuclear divisions and the location of neuropeptide/neurotransmitter cells within them. By combining immunocytochemistry for NeuN, a neuronal marker, with Nissl staining in anestrous, ovariectomized, estradiol-treated ewes, we identified three nuclei within the PMH: a caudal continuation of the hypothalamic arcuate nucleus (cARC), the ventral division of the premammillary nucleus (PMv), and the ventral tuberomammillary nucleus (TMv). The cARC contained neurons that were immunoreactive for tyrosine hydroxylase, dynorphin, estrogen receptor alpha, cocaine- and amphetamine-regulated transcript peptide (CART), and nitric oxide synthase (NOS). The PMv was also characterized by the presence of cells that contained NOS and CART, although the size of these cells was larger than that of their corresponding phenotype in the cARC. By contrast, in the TMv, of the markers examined in the present study, only fibers immunoreactive for orexin were seen. Thus, the ovine PMH is a heterogeneous region comprised of three subdivisions, each with distinct morphological and neurochemical characteristics. This anatomical map of the PMH provides a basis for future studies to determine the functional contribution of each component to the influence of melatonin on seasonal reproduction.

Systemic 5-hydroxy-L-tryptophan down-regulates the arcuate CART mRNA level in rats

This study was conducted to determine if serotonin (5-hydroxytryptamine; 5-HT) system correlates with the hypothalamic expression of cocaine-amphetamine-regulated transcript (CART) gene. Rats received intraperitoneal 5-hydroxy-L-tryptophan (5-HTP; a single or three daily injections at a dose of 100 mg/kg/10 ml), and CART mRNA level in the hypothalamus was examined by in situ hybridization at different time points. The 5-HT contents of the hypothalamus as well as the brainstem was increased persistently by 5-HTP injections, and food intake and body weight gain reduced. CART mRNA level decreased significantly in the hypothalamic arcuate nucleus by three daily 5-HTP, but not by a single injection. The pair-fed group of the chronic 5-HTP did not show a decrease in the arcuate CART mRNA level. The plasma leptin level markedly decreased in the chronic 5-HTP group, compared to the saline group, however, still higher than the pair-fed group with a statistical significance. These results suggest that 5-HT may suppress CART mRNA expression in the arcuate nucleus, not only by leptin signaling via its anorectic effect on the control of food intake, but also by some non-leptin mediated pathway.

Animal models in the investigation of anorexia

Anorexia nervosa (AN) is an eating disorder of unknown origin that most commonly occurs in women and usually has its onset in adolescence. Patients with AN invariably have a disturbed body image and an intense fear of weight gain. There is currently no definitive treatment for this disease, which carries a 20% mortality over 20 years. Development of an appropriate animal model of AN has been difficult, as the etiology of this eating disorder likely involves a complex interaction between genetic, environmental, social, and cultural factors. In this review, we focus on several possible rodent models of AN. In our laboratory, we have developed and studied three different mouse models of AN based on clinical profiles of the disease; separation stress, activity, and diet restriction (DR). In addition, we discuss the spontaneous mouse mutation anx/anx and several mouse gene knockout models, which have resulted in an anorexic phenotype. We highlight what has been learned from each of these models and possibilities for future models. It is hoped that a combination of the study of such models, together with genetic and clinical studies in patients, will lead to more rational and successful prevention/treatment of this tragic, and often fatal, disease.

Hyperleptinemia in A(y)/a mice upregulates arcuate cocaine- and amphetamine-regulated transcript expression

The effects of leptin on cocaine- and amphetamine-regulated transcript (CART) and agouti-related protein (AGRP) expression in the hypothalamic arcuate nucleus of obese A(y)/a mice were investigated. CART mRNA expression was upregulated by 41% and AGRP mRNA downregulated by 78% in hyperleptinemic A(y)/a mice relative to levels in lean a/a mice. The mRNA expression of these neuropeptides in either young nonobese A(y)/a mice or rats treated with SHU-9119, a synthetic melanocortin-4 receptor (MC4R) antagonist, did not differ significantly from that in the corresponding controls. After a 72-h fast, which decreased the concentration of serum leptin, CART and AGRP mRNA expression decreased and increased, respectively, in A(y)/a mice. The expression levels of these neuropeptides in leptin-deficient A(y)/a ob/ob double mutants were comparable to those in a/a ob/ob mice. Leptin thus modulates both CART and AGRP mRNA expression in obese A(y)/a mice, whereas leptin signals are blocked at the MCR4R level. Taken together, the present findings indicate that differential expression of these neuropeptides in A(y)/a and ob/ob mice results in dissimilar progression toward obesity.

Characterization of two forms of cocaine- and amphetamine-regulated transcript (CART) peptide precursors in goldfish: molecular cloning and distribution, modulation of expression by nutritional status, and interactions with leptin

Complementary DNAs encoding two forms of cocaine- and amphetamine-regulated transcript (CART) peptide precursors were identified from goldfish brain and named CART I and CART II. Each cDNA contains a signal peptide sequence, the putative CART-like peptide, and a carboxy-terminal extension peptide. Form I encodes a 117-amino acid pro-CART, whereas form II encodes a 120-amino acid pro-CART. Both forms resemble mammalian CART peptides. Each goldfish CART precursor is encoded by three exons interrupted by two introns within genomic DNA. RT-PCR, slot blot, and Northern blot analysis showed that the mRNAs for form I and II precursors have a widespread distribution. Form I and II are present in the brain, pituitary, eye, gonads, and kidney. Form I is also present in the gill. In the brain, form I is predominant in the olfactory bulb and hypothalamus, and form II is predominant in the optic tectum. Food deprivation for 96 h induced a decrease in form I mRNA levels in the telencephalon-preoptic region, hypothalamus, and olfactory bulb and in form II mRNA expression in the olfactory bulb. An increase in mRNA levels was observed 2 h following a meal in the olfactory bulbs and hypothalamus for form I whereas no postprandial changes in form II mRNA levels were observed. Intracerebroventricular injections of human CART alone induced a significant decrease in food intake. Injections of leptin reinforced the inhibition of feeding behavior and food intake seen in CART-treated fish. Central injection of leptin induced an increase in CART I mRNA in the optic tectum, hypothalamus, and olfactory bulbs but had no effect on CART II mRNA expression in the brain. These results suggest that CART peptides act as leptin-regulated satiety factors in goldfish and that they might have other physiological roles besides feeding, possibly in sensory information processing.

Hypothalamic and vagal neuropeptide circuitries regulating food intake

It has been recognized for some time that a number of different neuropeptides exert powerful effects on food intake. During the last few years, the neurocircuitry within which these peptides operate has also begun to be elucidated. Peptidergic feeding-regulatory neurones are found both in the hypothalamus and the brainstem, where they act as input stations for hormonal and gastrointestinal information, respectively. These cell populations both project to several other brain regions and interconnect extensively. The present review summarizes the neuroanatomy and connectivity of some prominent peptides involved in food intake control, including neuropeptide Y, melanocortin peptides, agouti gene-related protein, cocaine- and amphetamine-regulated transcript, orexin/hypocretin, melanin-concentrating hormone and cholecystokinin. Disturbances in the hypothalamic neuropeptide systems have been implicated in the phenotype of a genetic model of fatal hypophagia, the mouse anorexia (anx) mutation, which is also discussed.