CCK-8S activates c-Fos in a dose-dependent manner in nesfatin-1 immunoreactive neurons in the paraventricular nucleus of the hypothalamus and in the nucleus of the solitary tract of the brainstem

Neonatal overnutrition, but not neonatal undernutrition, disrupts CCK-induced hypophagia and neuron activation of the nucleus of the solitary tract and paraventricular nucleus of hypothalamus of male Wistar rats

Metabolic programming may be induced by reduction or enhancement of litter size, which lead to neonatal over or undernutrition, respectively. Changes in neonatal nutrition can challenge some regulatory processes in adulthood, such as the hypophagic effect of cholecystokinin (CCK). In order to investigate the effects of nutritional programming on the anorexigenic function of CCK in adulthood, pups were raised in small (SL, 3 pups per dam), normal (NL, 10 pups per dam), or large litters (LL, 16 pups per dam), and on postnatal day 60, male rats were treated with vehicle or CCK (10 µg/Kg) for the evaluation of food intake and c-Fos expression in the area postrema (AP), nucleus of solitary tract (NTS), and paraventricular (PVN), arcuate (ARC), ventromedial (VMH), and dorsomedial (DMH) nuclei of the hypothalamus. Overnourished rats showed increased body weight gain that was inversely correlated with neuronal activation of PaPo, VMH, and DMH neurons, whereas undernourished rats had lower body weight gain, inversely correlated with increased neuronal activation of PaPo only. SL rats showed no anorexigenic response and lower neuron activation in the NTS and PVN induced by CCK. LL exhibited preserved hypophagia and neuron activation in the AP, NTS, and PVN in response to CCK. CCK showed no effect in c-Fos immunoreactivity in the ARC, VMH, and DMH in any litter. These results indicate that anorexigenic actions, associated with neuron activation in the NTS and PVN, induced by CCK were impaired by neonatal overnutrition. However, these responses were not disrupted by neonatal undernutrition. Thus, data suggest that an excess or poor supply of nutrients during lactation display divergent effects on programming CCK satiation signaling in male adult rats.

The Actions of Centrally Administered Nesfatin-1 on Emesis, Feeding, and Locomotor Activity in Suncus murinus (House Musk Shrew)

Nesfatin-1 is an anorectic peptide expressed in both peripheral tissues and brain areas involved in the regulation of feeding, emotion and emesis. The aim of the present study is to characterize the distribution of NUCB2/nesfatin-1 in Suncus murinus and to investigate the actions of nesfatin-1 to affect gastrointestinal contractility, emesis, food and water intake, and locomotor activity. The deduced amino acid sequence of S. murinus nesfatin-1 using in silico cloning showed high homology with humans and rodents. NUCB2 mRNA was detected throughout the entire brain and in the gastrointestinal tract, including the stomach and gut. Western blot analysis and immunohistochemistry confirmed the expression of nesfatin-1 protein in these regions. The NUCB2 mRNA levels in the hypothalamus, hippocampus and brainstem were significantly decreased, whereas that in the striatum were increased after 24 h starvation compared to ad libitum-fed animals (p < 0.05). In in vitro studies, nesfatin-1 (0.3–1,000 pM) failed to contract or relax the isolated gastric antrum and intestinal segments. In conscious, freely moving animals, intracerebroventricular administration of nesfatin-1 (1–50 pmol) induced emesis (p < 0.05) and suppressed 6-h cumulative food intake (p < 0.05), without affecting the latency to feeding. Nesfatin-1 (25 pmol, i.c.v.) decreased 24-h cumulative food and water intake by 28.3 and 35.4%, respectively (p < 0.01). No significant differences in locomotor activity were observed. In conclusion, NUCB2/nesfatin-1 might be a potent regulator of feeding and emesis in S. murinus. Further studies are required to elucidate the mechanism of actions of this peptide as a mediator linking the brainstem NUCB2/nesfatin-1 to forebrain system.

"Sibling" battle or harmony: crosstalk between nesfatin-1 and ghrelin

Ghrelin was first identified as an endogenous ligand of the growth hormone secretagogue receptor (GHSR) in 1999, with the function of stimulating the release of growth hormone (GH), while nesfatin-1 was identified in 2006. Both peptides are secreted by the same kind of endocrine cells, X/A-like cells in the stomach. Compared with ghrelin, nesfatin-1 exerts opposite effects on energy metabolism, glucose metabolism, gastrointestinal functions and regulation of blood pressure, but exerts similar effects on anti-inflammation and neuroprotection. Up to now, nesfatin-1 remains as an orphan ligand because its receptor has not been identified. Several studies have shown the effects of nesfatin-1 are dependent on the receptor of ghrelin. We herein compare the effects of nesfatin-1 and ghrelin in several aspects and explore the possibility of their interactions.

A comparative account of nesfatin-1 in vertebrates

Nesfatin-1 was discovered as an anorexigenic peptide derived from proteolytic cleavage of the prepropeptide, nucleobindin 2 (NUCB2). It is widely expressed in central as well as peripheral tissues and is known to have pleiotropic effects such as regulation of feeding, reproduction, cardiovascular functions and maintenance of glucose homeostasis. In order to execute its multifaceted role, nesfatin-1 employs diverse signaling pathways though its receptor has not been identified till date. Further, nesfatin-1 is reported to be under the regulatory effect of feeding state, nutritional status as well as several metabolic and reproductive hormones. This peptide has also been associated with variety of human diseases, especially metabolic, reproductive, cardiovascular and mental disorders. The current review is aimed to present a consolidated picture and highlight lacunae for further investigation in order to develop a deeper comprehensive understanding on physiological significance of nesfatin-1 in vertebrates.

Impact of Gut and Metabolic Hormones on Feeding Reward

Ingestion of food activates a cascade of endocrine responses (thereby reflecting a contemporaneous feeding status) that include the release of hormones from the gastrointestinal (GI) tract, such as cholecystokinin (CCK), glucagonlike peptide YY (PYY), peptide PP, and oleoylethanolamide, as well as suppression of ghrelin secretion. The pancreas and adipose tissue, on the other hand, release hormones that serve as a measure of the current metabolic state or the long-term energy stores, that is, insulin, leptin, and adiponectin. It is well known and intuitively understandable that these hormones target either directly (by crossing the blood-brain barrier) or indirectly (e.g., via vagal input) the "homeostatic" brainstem-hypothalamic pathways involved in the regulation of appetite. The current article focuses on yet another target of the metabolic and GI hormones that is critical in inducing changes in food intake, namely, the reward system. We discuss the physiological basis of this functional interaction, its importance in the control of appetite, and the impact that disruption of this crosstalk has on energy intake in select physiological and pathophysiological states. We conclude that metabolic and GI hormones have a capacity to strengthen or weaken a response of the reward system to a given food, and thus, they are fundamental in ensuring that feeding reward is plastic and dependent on the energy status of the organism. © 2021 American Physiological Society. Compr Physiol 11:1425-1447, 2021.

Neurochemical Characterization of Brainstem Pro-Opiomelanocortin Cells

Genetic research has revealed pro-opiomelanocortin (POMC) to be a fundamental regulator of energy balance and body weight in mammals. Within the brain, POMC is primarily expressed in the arcuate nucleus of the hypothalamus (ARC), while a smaller population exists in the brainstem nucleus of the solitary tract (POMCNTS). We performed a neurochemical characterization of this understudied population of POMC cells using transgenic mice expressing green fluorescent protein (eGFP) under the control of a POMC promoter/enhancer (PomceGFP). Expression of endogenous Pomc mRNA in the nucleus of the solitary tract (NTS) PomceGFP cells was confirmed using fluorescence-activating cell sorting (FACS) followed by quantitative PCR. In situ hybridization histochemistry of endogenous Pomc mRNA and immunohistochemical analysis of eGFP revealed that POMC is primarily localized within the caudal NTS. Neurochemical analysis indicated that POMCNTS is not co-expressed with tyrosine hydroxylase (TH), glucagon-like peptide 1 (GLP-1), cholecystokinin (CCK), brain-derived neurotrophic factor (BDNF), nesfatin, nitric oxide synthase 1 (nNOS), seipin, or choline acetyltransferase (ChAT) cells, whereas 100% of POMCNTS is co-expressed with transcription factor paired-like homeobox2b (Phox2b). We observed that 20% of POMCNTS cells express receptors for adipocyte hormone leptin (LepRbs) using a PomceGFP:LepRbCre:tdTOM double-reporter line. Elevations in endogenous or exogenous leptin levels increased the in vivo activity (c-FOS) of a small subset of POMCNTS cells. Using ex vivo slice electrophysiology, we observed that this effect of leptin on POMCNTS cell activity is postsynaptic. These findings reveal that a subset of POMCNTS cells are responsive to both changes in energy status and the adipocyte hormone leptin, findings of relevance to the neurobiology of obesity.

Effects of age on feeding response: Focus on the rostral C1 neuron and its glucoregulatory proteins

BACKGROUND

Older people are likely to develop anorexia of aging. Rostral C1 (rC1) catecholaminergic neurons in rostral ventrolateral medulla (RVLM) are recently discovered its role in food intake control. It is well established that these neurons regulate cardiovascular function.

OBJECTIVE

This study aims to determine the effect of age on the function of rostral C1 (rC1) neurons in mediating feeding response.

METHOD

Male Sprague Dawley rats at 3-months (n = 22) and 24-months (n = 22) old were used and further divided into two subgroups; 1) treatment group with 2-deoxy-d-glucose (2DG) and 2) vehicle group. Feeding hormones such as cholecystokinin (CCK), ghrelin and leptin were analysed using enzyme-linked immunosorbent assay (ELISA). Rat brain was carefully dissected to obtain the brainstem RVLM region. Further analysis was carried out to determine the level of proteins and genes in RVLM that were associated with feeding pathway. Protein expression of tyrosine hydroxylase (TH), phosphorylated TH at Serine40 (pSer40TH), AMP-activated protein kinase (AMPK), phosphorylated AMPK (phospho AMPK) and neuropeptide Y Y5 receptor (NPY5R) were determined by western blot. Expression of TH, AMPK and NPY genes were determined by real-time PCR.

RESULTS

This study showed that blood glucose level was elevated in young and old rats following 2DG administration. Plasma CCK-8 concentration was higher in the aged rats at basal and increased with 2DG administration in young rats, but the leptin and ghrelin showed no changes. Old rats showed higher TH and lower AMPK mRNA levels. Glucoprivation decreased AMPK mRNA level in young rats and decreased TH mRNA in old rats. Aged rC1 neurons showed higher NPY5R protein level. Following glucoprivation, rC1 neurons produced distinct molecular changes across age in which, in young rats, AMPK phosphorylation level was increased and in old rats, TH phosphorylation level was increased.

CONCLUSION

These findings suggest that glucose-counterregulatory responses by rC1 neurons at least, contribute to the ability of young and old rats in coping glucoprivation. Age-induced molecular changes within rC1 neurons may attenuate the glucoprivic responses. This situation may explain the impairment of feeding response in the elderly.

[Nutrient Sensing and Anorexia via Neuropeptides]

 Various neuropeptides play an essential role in the nutrient sensing mechanism and related homeostasis. Nesfatin-1 is a newly identified neuropeptide having anorectic activity, and nesfatin-1-containing neurons are widely distributed in the brain, including the hypothalamus and brain stem. Our previous study showed that dehydration-induced anorectic effects are mediated via the central nesfatin-1 pathway in rats. Our recent studies have also shown that peripheral anorectic peptides (cholecystokinin-8, glucagon-like peptide-1, and leptin) and an antineoplastic agent (cisplatin) caused inhibition of feeding via the central nesfatin-1 pathway in rats. Nesfatin-1-containing neurons in the central nervous system, in particular the hypothalamus and the brain stem, may mediate peripheral nutrient signals and regulate feeding behavior.

Hypothalamic Integration of the Endocrine Signaling Related to Food Intake

Hypothalamic integration of gastrointestinal and adipose tissue-derived hormones serves as a key element of neuroendocrine control of food intake. Leptin, adiponectin, oleoylethanolamide, cholecystokinin, and ghrelin, to name a few, are in a constant "cross talk" with the feeding-related brain circuits that encompass hypothalamic populations synthesizing anorexigens (melanocortins, CART, oxytocin) and orexigens (Agouti-related protein, neuropeptide Y, orexins). While this integrated neuroendocrine circuit successfully ensures that enough energy is acquired, it does not seem to be equally efficient in preventing excessive energy intake, especially in the obesogenic environment in which highly caloric and palatable food is constantly available. The current review presents an overview of intricate mechanisms underlying hypothalamic integration of energy balance-related peripheral endocrine input. We discuss vulnerabilities and maladaptive neuroregulatory processes, including changes in hypothalamic neuronal plasticity that propel overeating despite negative consequences.

Nesfatin-1: functions and physiology of a novel regulatory peptide

Nesfatin-1 was identified in 2006 as a potent anorexigenic peptide involved in the regulation of homeostatic feeding. It is processed from the precursor-peptide NEFA/nucleobindin 2 (NUCB2), which is expressed both in the central nervous system as well as in the periphery, from where it can access the brain via non-saturable transmembrane diffusion. In hypothalamus and brainstem, nesfatin-1 recruits the oxytocin, the melancortin and other systems to relay its anorexigenic properties. NUCB2/nesfatin-1 peptide expression in reward-related areas suggests that nesfatin-1 might also be involved in hedonic feeding. Besides its initially discovered anorexigenic properties, over the last years, other important functions of nesfatin-1 have been discovered, many of them related to energy homeostasis, e.g. energy expenditure and glucose homeostasis. Nesfatin-1 is not only affecting these physiological processes but also the alterations of the metabolic state (e.g. fat mass, glycemic state) have an impact on the synthesis and release of NUCB2 and/or nesfatin-1. Furthermore, nesfatin-1 exerts pleiotropic actions at the level of cardiovascular and digestive systems, as well as plays a role in stress response, behavior, sleep and reproduction. Despite the recent advances in nesfatin-1 research, a putative receptor has not been identified and furthermore potentially distinct functions of nesfatin-1 and its precursor NUCB2 have not been dissected yet. To tackle these open questions will be the major objectives of future research to broaden our knowledge on NUCB2/nesfatin-1.

Activation of Nesfatin-1-Containing Neurones in the Hypothalamus and Brainstem by Peripheral Administration of Anorectic Hormones and Suppression of Feeding via Central Nesfatin-1 in Rats

Peripheral anorectic hormones, such as glucagon-like peptide (GLP)-1, cholecystokinin (CCK)-8 and leptin, suppress food intake. The newly-identified anorectic neuropeptide, nesfatin-1, is synthesised in both peripheral tissues and the central nervous system, particularly by various nuclei in the hypothalamus and brainstem. In the present study, we examined the effects of i.p. administration of GLP-1 and CCK-8 and co-administrations of GLP-1 and leptin at subthreshold doses as confirmed by measurement of food intake, on nesfatin-1-immunoreactive (-IR) neurones in the hypothalamus and brainstem of rats by Fos immunohistochemistry. Intraperitoneal administration of GLP-1 (100 μg/kg) caused significant increases in the number of nesfatin-1-IR neurones expressing Fos-immunoreactivity in the supraoptic nucleus (SON), the area postrema (AP) and the nucleus tractus solitarii (NTS) but not in the paraventricular nucleus (PVN), the arcuate nucleus (ARC) or the lateral hypothalamic area (LHA). On the other hand, i.p. administration of CCK-8 (50 μg/kg) resulted in marked increases in the number of nesfatin-1-IR neurones expressing Fos-immunoreactivity in the SON, PVN, AP and NTS but not in the ARC or LHA. No differences in the percentage of nesfatin-1-IR neurones expressing Fos-immunoreactivity in the nuclei of the hypothalamus and brainstem were observed between rats treated with saline, GLP-1 (33 μg/kg) or leptin. However, co-administration of GLP-1 (33 μg/kg) and leptin resulted in significant increases in the number of nesfatin-1-IR neurones expressing Fos-immunoreactivity in the AP and the NTS. Furthermore, decreased food intake induced by GLP-1, CCK-8 and leptin was attenuated significantly by pretreatment with i.c.v. administration of antisense nesfatin-1. These results indicate that nesfatin-1-expressing neurones in the brainstem may play an important role in sensing peripheral levels of GLP-1 and leptin in addition to CCK-8, and also suppress food intake in rats.

Peripheral injection of bombesin induces c-Fos in NUCB2/nesfatin-1 neurons

As anorexigenic hormones bombesin and nucleobindin2 (NUCB2)/nesfatin-1 decrease food intake in rodents. Both hormones have been described in brain nuclei that play a role in the modulation of hunger and satiety, like the paraventricular nucleus of the hypothalamus (PVN) and the nucleus of the solitary tract (NTS). However, the direct interaction of the two hormones is unknown so far. The aim of study was to elucidate whether bombesin directly interacts with NUCB2/nesfatin-1 neurons in the PVN and NTS. Therefore, we injected bombesin intraperitoneally (ip) at two doses (26 and 32nmol/kg body weight) and assessed c-Fos activation in the PVN, arcuate nucleus (ARC) and NTS compared to vehicle treated rats (0.15M NaCl). We also performed co-localization studies with oxytocin or tyrosine hydroxylase. Bombesin at both doses increased the number of c-Fos positive neurons in the PVN (p<0.05) and NTS (p<0.05) compared to vehicle, while in the ARC no modulation was observed (p>0.05). In the PVN and NTS the number of c-Fos positive neurons colocalized with NUCB2/nesfatin-1 increased after bombesin injection compared to vehicle treatment (p<0.05). Moreover, an increase of activated NUCB2/nesfatin-1 immunoreactive neurons that co-expressed oxytocin in the PVN (p<0.05) or tyrosine hydroxylase in the NTS (p<0.05) was observed compared to vehicle. Our results show that peripherally injected bombesin activates NUCB2/nesfatin-1 neurons in the PVN and NTS giving rise to a possible interaction between bombesin and NUCB2/nesfatin-1 in the modulation of food intake.

Mechanistic relationship between the vagal afferent pathway, central nervous system and peripheral organs in appetite regulation

The hypothalamus is a center of food intake and energy metabolism regulation. Information signals from peripheral organs are mediated through the circulation or the vagal afferent pathway and input into the hypothalamus, where signals are integrated to determine various behaviors, such as eating. Numerous appetite-regulating peptides are expressed in the central nervous system and the peripheral organs, and interact in a complex manner. Of such peptides, gut peptides are known to bind to receptors at the vagal afferent pathway terminal that extend into the mucosal layer of the digestive tract, modulate the electrical activity of the vagus nerve, and subsequently send signals to the solitary nucleus and furthermore to the hypothalamus. All peripheral peptides other than ghrelin suppress appetite, and they synergistically suppress appetite through the vagus nerve. In contrast, the appetite-enhancing peptide, ghrelin, antagonizes the actions of appetite-suppressing peptides through the vagus nerve, and appetite-suppressing peptides have attenuated effects in obesity as a result of inflammation in the vagus nerve. With greater understanding of the mechanism for food intake and energy metabolism regulation, medications that apply the effects of appetite-regulating peptides or implantable devices that electrically stimulate the vagus nerve are being investigated as novel treatments for obesity in basic and clinical studies.

Nesfatin-1 - More than a food intake regulatory peptide

Nesfatin-1 was discovered a decade ago and despite the fact that it represents just one of a multitude of food intake-inhibiting factors it received increasing attention. This led to a detailed characterization of NUCB2/nesfatin-1's physiological property to reduce food intake and also gave rise to an involvement in the long term regulation of body weight, especially under conditions of obesity. In addition, studies indicated the involvement of NUCB2/nesfatin-1 in other homeostatic functions as well: glucose homeostasis, water intake, gastrointestinal functions, temperature regulation, cardiovascular functions, puberty onset and sleep. These pleiotropic actions underline the physiological relevance of this peptide. Recently, the involvement of NUCB2/nesfatin-1 in psychiatric disorders such as anxiety has been investigated giving rise to the speculation that NUCB2/nesfatin-1 represents a peptidergic link between eating and anxiety/depression disorders.

Regulation of NUCB2/nesfatin-1 production in rat's stomach and adipose tissue is dependent on age, testosterone levels and lactating status

Nesfatin-1, which is derived from the NEFA/nucleobindin 2 (NUCB2) precursor, was recently identified as an anorexigenic peptide that is produced in several tissues including the hypothalamus. Currently, no data exist regarding the regulation of NUCB2/nesfatin-1 production in peripheral tissues, such as gastric mucosa and adipose tissue, through different periods of development. The aim of the present work was to study the variations on circulating levels, mRNA expression and tissue content in gastric mucosa and adipose tissue of NUCB2/nesfatin-1 with age and specially in two clue periods of maturation, weaning and puberty. The weaning period affected NUCB2/nesfatin-1 production in gastric tissue. The testosterone changes associated with the initiation of puberty regulated NUCB2/nesfatin-1 production via adipose tissue and gastric NUCB2/nesfatin-1 production. In conclusion, the production of NUCB2/nesfatin-1 by the stomach and adipose tissue fluctuates with age to regulate energy homeostasis during different states of development.

A novel Peptide-binding motifs inference approach to understand deoxynivalenol molecular toxicity

Deoxynivalenol (DON) is a type B trichothecene mycotoxin that is commonly detected in cereals and grains world-wide. The low-tolerated levels of this mycotoxin, especially in mono-gastric animals, reflect its bio-potency. The toxicity of DON is conventionally attributed to its ability to inhibit ribosomal protein biosynthesis, but recent advances in molecular tools have elucidated novel mechanisms that further explain DON’s toxicological profile, complementing the diverse symptoms associated with its exposure. This article summarizes the recent findings related to novel mechanisms of DON toxicity as well as how structural modifications to DON alter its potency. In addition, it explores feasible ways of expanding our understating of DON-cellular targets and their roles in DON toxicity, clearance, and detoxification through the utilization of computational biology approaches.

Regulation of the hypothalamic-pituitary-adrenal axis by neuropeptides

The major endocrine response to stress occurs via activation of the hypothalamic-pituitary-adrenal (HPA) axis, leading ultimately to increases in circulating glucocorticoids, which are essential for the metabolic adaptation to stress. The major players in the HPA axis are the hypothalamic neuropeptide, corticotropin releasing hormone (CRH), the pituitary hormone adrenocorticotropic hormone, and the negative feedback effects of adrenal glucocorticoids. In addition, a number of other neuropeptides, including vasopressin (VP), angiotensin II, oxytocin, pituitary adenylate cyclase activating peptide, orexin and cholecystokinin, and nesfatin can affect HPA axis activity by influencing the expression and secretion of CRH, and also by modulating pituitary corticotroph function or adrenal steroidogenesis. Of these peptides, VP co-secreted with CRH from axonal terminals in the external zone of the median eminence plays a prominent role by potentiating the stimulatory effect of CRH and by increasing the number of pituitary corticotrophs during chronic challenge. Although the precise role and significance of many of these neuropeptides in regulating HPA axis activity requires further investigation, it is likely that they are part of a multifactorial system mediating the fine tuning of HPA axis activity during adaptation to a variety of physiological and stressful conditions.

Dysregulation of energy balance by trichothecene mycotoxins: Mechanisms and prospects

Trichothecenes are toxic metabolites produced by fungi that constitute a worldwide hazard for agricultural production and both animal and human health. More than 40 countries have introduced regulations or guidelines for food and feed contamination levels of the most prevalent trichothecene, deoxynivalenol (DON), on the basis of its ability to cause growth suppression. With the development of analytical tools, evaluation of food contamination and exposure revealed that a significant proportion of the human population is chronically exposed to DON doses exceeding the provisional maximum tolerable daily dose. Accordingly, a better understanding of trichothecene impact on health is needed. Upon exposure to low or moderate doses, DON and other trichothecenes induce anorexia, vomiting and reduced weight gain. Several recent studies have addressed the mechanisms by which trichothecenes induce these symptoms and revealed a multifaceted action targeting gut, liver and brain and causing dysregulation in neuroendocrine signaling, immune responses, growth hormone axis, and central neurocircuitries involved in energy homeostasis. Newly identified trichothecene toxicosis biomarkers are just beginning to be exploited and already open up new questions on the potential harmful effects of chronic exposure to DON at apparently asymptomatic very low levels. This review summarizes our current understanding of the effects of DON and other trichothecenes on food intake and weight growth.

Acute oral metformin enhances satiation and activates brainstem nesfatinergic neurons

OBJECTIVE

The study was designed to determine metformin effects on meal pattern, gastric emptying, energy expenditure, and to identify metformin-sensitive neurons and their phenotype.

METHODS

This study was performed on C57BL/6J and obese/diabetic (db/db) mice. Metformin (300 mg/kg) was administered by oral gavage. Food intake, meal pattern, oxygen consumption (VO2 ), and carbon dioxide production (VCO2 ) were obtained using an Oxylet Physiocage System. Gastric emptying assay and real-time RT-PCR from dorsal vagal complex extracts were also performed. C-Fos expression was used as a marker of neuronal activation. Phenotypic characterization of activated neurons was performed using either proopiomelanocortin (POMC)-Tau-Topaz GFP transgenic mice or NUCB2/nesfatin-1 and tyrosine hydroxylase (TH) labeling.

RESULTS

Acute per os metformin treatment slowed down gastric emptying, reduced meal size, but not meal number in a leptin-independent manner, and transiently decreased energy expenditure in a leptin-dependent manner. Metformin specifically activated central circuitry within the brainstem, independently of vagal afferents. Finally, while POMC neurons seemed sparsely activated, we report that a high proportion of the c-Fos positive cells were nesfatinergic neurons, some of which coexpressing TH.

CONCLUSIONS

Altogether, these results show that metformin modifies satiation by activating brainstem circuitry and suggest that NUCB2/nesfatin-1 could be involved in this metformin effect.

Peripheral injected cholecystokinin-8S modulates the concentration of serotonin in nerve fibers of the rat brainstem

Serotonin and cholecystokinin (CCK) play a role in the short-term inhibition of food intake. It is known that peripheral injection of CCK increases c-Fos-immunoreactivity (Fos-IR) in the nucleus of the solitary tract (NTS) in rats, and injection of the serotonin antagonist ondansetron decreases the number of c-Fos-IR cells in the NTS. This supports the idea of serotonin contributing to the effects of CCK. The aim of the present study was to elucidate whether peripherally injected CCK-8S modulates the concentration of serotonin in brain feeding-regulatory nuclei. Ad libitum fed male Sprague-Dawley rats received 5.2 and 8.7 nmol/kg CCK-8S (n=3/group) or 0.15M NaCl (n=3-5/group) injected intraperitoneally (ip). The number of c-Fos-IR neurons, and the fluorescence intensity of serotonin in nerve fibers were assessed in the paraventricular nucleus (PVN), arcuate nucleus (ARC), NTS and dorsal motor nucleus of the vagus (DMV). CCK-8S increased the number of c-Fos-ir neurons in the NTS (mean±SEM: 72±4, and 112±5 neurons/section, respectively) compared to vehicle-treated rats (7±2 neurons/section, P<0.05), but did not modulate c-Fos expression in the DMV or ARC. Additionally, CCK-8S dose-dependently increased the number of c-Fos-positive neurons in the PVN (218±15 and 128±14, respectively vs. 19±5, P<0.05). In the NTS and DMV we observed a decrease of serotonin-immunoreactivity 90 min after injection of CCK-8S (46±2 and 49±8 pixel/section, respectively) compared to vehicle (81±8 pixel/section, P<0.05). No changes of serotonin-immunoreactivity were observed in the PVN and ARC. Our results suggest that serotonin is involved in the mediation of CCK-8's effects in the brainstem.

The central question of type 2 diabetes

Type 2 diabetes (T2D) represents a significant global epidemic with more than 285 million people affected worldwide. Regulating glycemia in T2D patients can be partially achieved with currently available treatment, but intensive research during the last decades have led to the discovery of modified compounds or new targets that could represent great hope for safe and effective treatment in the future. Among them, targets in the CNS that are known to control feeding and body weight have been also shown to exert glucoregulatory actions, and could be a key in the development of a new generation of drugs in the field of T2D. Such drugs would be of great interest since they can be used both in the treatment of diabetes and obesity. This patent review aims to establish an overview of recent patents disclosing new therapeutic opportunities targeting peripheral, as well as central targets for the treatment of T2D.

Nesfatin-1 influences the excitability of glucosensing neurons in the dorsal vagal complex and inhibits food intake

Nesfatin-1 is a recently discovered metabolic peptide hormone that decreases food intake after lateral, third, or fourth brain ventricle; cisterna magna; or paraventricular nucleus (PVN) injection in ad libitum fed rats. Additional micro-injection studies will improve the understanding of how nesfatin-1 acts on the brain and define specific nuclei responsive to nesfatin-1, which will provide insight on its effects on food intake. We evaluated how nesfatin-1 injection into the dorsal vagal complex (DVC) modulates food intake response in rats during the dark phase. Consistent with previous observations, nesfatin-1-injected rats significantly reduced cumulative food intake over a 5-h period in rats. Chronic administration of nesfatin-1 into the DVC reduced body weight gain over a 10-day period. Because glucosensing neurons in the DVC are involved in glucoprivic feeding and homeostatic control of blood glucose, we examined the effect of nesfatin-1 on the excitability of DVC glucosensing neurons. Nesfatin-1 inhibited most of the glucose-inhibitory (GI) neurons and excited most of the glucose-excitatory (GE) neurons in the DVC. Current-clamp electrophysiology recordings from DVC glucosensing neurons in slice preparation showed that bath applied nesfatin-1(10 nM) increased the firing frequency of GE neurons and inhibited the firing rate of GI-neurons. Nesfatin-1 inhibited 88.9% (16/18) of gastric distension inhibitory (GD-INH) neurons and excited 76.2% (32/42) of gastric distension excitatory (GD-EXC) neurons. Thus, nesfatin-1 may control food intake by modulating the excitability of glucosensing neurons in the DVC.

Intraperitoneal CCK and fourth-intraventricular Apo AIV require both peripheral and NTS CCK1R to reduce food intake in male rats

Apolipoprotein AIV (Apo AIV) and cholecystokinin (CCK) are secreted in response to fat consumption, and both cause satiation via CCK 1 receptor (CCK-1R)-containing vagal afferent nerves to the nucleus of the solitary tract (NTS), where Apo AIV is also synthesized. Fasted male Long-Evans rats received ip CCK-8 or fourth-ventricular (i4vt) Apo AIV alone or in combination. Food intake and c-Fos proteins (a product of the c-Fos immediate-early gene) were assessed. i4vt Apo AIV and/or ip CCK at effective doses reduced food intake and activated c-Fos proteins in the NTS and hypothalamic arcuate nucleus and paraventricular nucleus. Blockade of the CCK-1R by i4vt lorglumide adjacent to the NTS attenuated the satiating and c-Fos-stimulating effects of CCK and Apo AIV, alone or in combination. Maintenance on a high-fat diet (HFD) for 10 weeks resulted in weight gain and attenuation of both the behavioral and c-Fos responses to a greater extent than occurred in low-fat diet-fed and pair-fed HFD animals. These observations suggest that NTS Apo AIV or/and peripheral CCK requires vagal CCK-1R signaling to elicit satiation and that maintenance on a HFD reduces the satiating capacity of these 2 signals.

The subfornical organ: a novel site of action of cholecystokinin

The subfornical organ (SFO) is an important sensory circumventricular organ implicated in the regulation of fluid homeostasis and energy balance. We investigated whether the SFO is activated by the hormone cholecystokinin (CCK). CCK₁ and CCK₂ receptors were identified in the SFO by RT-PCR. Dissociated SFO neurons that responded to CCK (40/77), were mostly depolarized (9.2 ± 0.9 mV, 30/77), but some were hyperpolarized (-7.3 ± 1.1 mV, 10/77). We next examined the responses of SFO neurons in vivo to CCK (16 μg/kg ip), in the presence and absence of CCK₁ or CCK₂ receptor antagonists (devazepide; 600 μg/kg and L-365,260; 100 μg/kg, respectively), using the functional activation markers c-Fos and phosphorylated extracellular signal-related kinase (p-ERK). The nucleus of the solitary tract (NTS) served as a control for CCK-induced activity. There was a significant increase in c-Fos expression in the NTS (259.2 ± 20.8 neurons) compared with vehicle (47.5 ± 2.5). Similarly, in the SFO, c-Fos was expressed in 40.5 ± 10.6 neurons in CCK-treated compared with 6.6 ± 2.7 in vehicle-treated rats (P < 0.01). Devazepide significantly reduced the effects of CCK in the NTS but not in SFO. L-365,260 blocked the effects of CCK in both brain regions. CCK increased the number of p-ERK neurons in NTS (27.0 ± 4.0) as well as SFO (18.0 ± 4.0), compared with vehicle (8.0 ± 2.6 and 4.3 ± 0.6, respectively; P < 0.05). Both devazepide and L-365,260 reduced CCK-induced p-ERK in NTS, but only L-365,260 reduced it in the SFO. In conclusion, the SFO represents a novel brain region at which circulating CCK may act via CCK₂ receptors to influence central autonomic control.

The role of nesfatin-1 in the regulation of food intake and body weight: recent developments and future endeavors

Nesfatin-1 was discovered in 2006 and introduced as a potential novel anorexigenic modulator of food intake and body weight. The past years have witnessed increasing evidence establishing nesfatin-1 as a potent physiological inhibitor of food intake and body weight and unravelled nesfatin-1's interaction with other brain transmitters to exert its food consumption inhibitory effect. As observed for other anorexigenic brain neuropeptides, nesfatin-1 is also likely to exert additional, if not pleiotropic, actions in the brain and periphery. Recent studies established the prominent expression of the nesfatin-1 precursor, nucleobindin2 (NUCB2), in the stomach and pancreas, where nesfatin-1 influences endocrine secretion. This review will highlight the current experimental state-of-knowledge on the effects of NUCB2/nesfatin-1 on food intake, body weight and glucose homeostasis. Potential implications in human obesity will be discussed in relation to the evidence of changes in circulating levels of NUCB2/nesfatin-1 in disease states, the occurrence of genetic NUCB2 polymorphisms and--in contrast to several other hormones--the independence of leptin signalling known to be blunted under conditions of chronically increased body weight.

Gastric distension activates NUCB2/nesfatin-1-expressing neurons in the nucleus of the solitary tract

Brainstem structures such as the nucleus of the solitary tract (NTS) and the dorsal motor nucleus of the vagus nerve (DMNX) are essential for the digestive function of the stomach. A large number of neurotransmitters including glutamate and gamma-aminobutyric acid (GABA) are involved in the central control of gastric functions. However, the neuropeptidergic systems implicated in this process remain undetermined. Nesfatin-1 was recently identified as a neuropeptide cleaved from the N-terminal part of NEFA/nucleobindin 2 precursor (NUCB2). Central administration of this neuropeptide inhibits food consumption and gastroduodenal motility in rodents. Interestingly, the NTS and the DMNX contain a dense population of NUCB2/nesfatin-1 cell bodies. These observations led us to investigate the possible involvement of NUCB2/nesfatin-1 neurons in the brainstem neuronal pathways that modulate gastric functions. We observed an activation of NTS NUCB2/nesfatinergic neurons after gastric distention in rats. In addition, we found that several NTS NUCB2/nesfatinergic neurons were GABAergic. Finally, when fluorogold was injected at the stomach level, many retrogradely labeled neurons were observed in the DMNX which were also positive for NUCB2/nesfatin-1. Taken together, these observations suggest for the first time that NUCB2/nesfatin-1 neurons of the NTS are sensitive to gastric distension and then may contribute to the satiety signal.

Multi-functional peptide hormone NUCB2/nesfatin-1

The recently discovered nesfatin-1 is regulated by hunger and satiety. The precursor protein NUCB2 is proteolytically cleaved into three resulting fragments: nesfatin-1, nesfatin-2, and nesfatin-3. The middle segment of nesfatin-1 (M30) is responsible for limiting food intake, while the exact physiological role of nesfatin-2 and nesfatin-3 are not currently known yet. This hormone plays role/roles on diabetic hyperphagia, epilepsy, mood, stress, sleeping, anxiety, hyperpolarization, depolarization, and reproductive functions. This review will address nesfatin, focusing on its discovery and designation, biochemical structure, scientific evidence of its anorexigenic character, the results of the human and animal studies until the present day, its main biochemical and physiological effects, and its possible clinical applications.

Insulin Activates Vagal Afferent Neurons Including those Innervating Pancreas via Insulin Cascade and Ca(2+) Influx: Its Dysfunction in IRS2-KO Mice with Hyperphagic Obesity

Some of insulin’s functions, including glucose/lipid metabolism, satiety and neuroprotection, involve the alteration of brain activities. Insulin could signal to the brain via penetrating through the blood-brain barrier and acting on the vagal afferents, while the latter remains unproved. This study aimed to clarify whether insulin directly regulates the nodose ganglion neurons (NGNs) of vagal afferents in mice. NGs expressed insulin receptor (IR) and insulin receptor substrate-2 (IRS2) mRNA, and some of NGNs were immunoreactive to IR. In patch-clamp and fura-2 microfluorometric studies, insulin (10⁻¹²∼10⁻⁶ M) depolarized and increased cytosolic Ca²⁺ concentration ([Ca²⁺]_i) in single NGNs. The insulin-induced [Ca²⁺]_i increases were attenuated by L- and N-type Ca²⁺ channel blockers, by phosphatidylinositol 3 kinase (PI3K) inhibitor, and in NGNs from IRS2 knockout mice. Half of the insulin-responsive NGNs contained cocaine- and amphetamine-regulated transcript. Neuronal fibers expressing IRs were distributed in/around pancreatic islets. The NGNs innervating the pancreas, identified by injecting retrograde tracer into the pancreas, responded to insulin with much greater incidence than unlabeled NGNs. Insulin concentrations measured in pancreatic vein was 64-fold higher than that in circulation. Elevation of insulin to 10⁻⁷ M recruited a remarkably greater population of NGNs to [Ca²⁺]_i increases. Systemic injection of glibenclamide rapidly released insulin and phosphorylated AKT in NGs. Furthermore, in IRS2 knockout mice, insulin action to suppress [Ca²⁺]_i in orexigenic ghrelin-responsive neurons in hypothalamic arcuate nucleus was intact while insulin action on NGN was markedly attenuated, suggesting a possible link between impaired insulin sensing by NGNs and hyperphagic obese phenotype in IRS2 knockout mice These data demonstrate that insulin directly activates NGNs via IR-IRS2-PI3K-AKT-cascade and depolarization-gated Ca²⁺ influx. Pancreas-innervating NGNs may effectively sense dynamic changes of insulin released in response to nutritional states. These interactions could serve to convey the changes in pancreatic and systemic insulin to the brain.

Involvement of prolactin-releasing peptide in the activation of oxytocin neurones in response to food intake

Food intake activates neurones expressing prolactin-releasing peptide (PrRP) in the medulla oblongata and oxytocin neurones in the hypothalamus. Both PrRP and oxytocin have been shown to have an anorexic action. In the present study, we investigated whether the activation of oxytocin neurones following food intake is mediated by PrRP. We first examined the expression of PrRP receptors (also known as GPR10) in rats. Immunoreactivity of PrRP receptors was observed in oxytocin neurones and in vasopressin neurones in the paraventricular and supraoptic nuclei of the hypothalamus and in the bed nucleus of the stria terminalis. Application of PrRP to isolated supraoptic nuclei facilitated the release of oxytocin and vasopressin. In mice, re-feeding increased the expression of Fos protein in oxytocin neurones of the hypothalamus and bed nucleus of the stria terminalis. The increased expression of Fos protein in oxytocin neurones following re-feeding or i.p. administration of cholecystokinin octapeptide (CCK), a peripheral satiety factor, was impaired in PrRP-deficient mice. CCK-induced oxytocin increase in plasma was also impaired in PrRP-deficient mice. Furthermore, oxytocin receptor-deficient mice showed an increased meal size, as reported in PrRP-deficient mice and in CCKA receptor-deficient mice. These findings suggest that PrRP mediates, at least in part, the activation of oxytocin neurones in response to food intake, and that the CCK-PrRP-oxytocin pathway plays an important role in the control of the termination of each meal.

Overnight food deprivation markedly attenuates hindbrain noradrenergic, glucagon-like peptide-1, and hypothalamic neural responses to exogenous cholecystokinin in male rats

Systemic administration of sulfated cholecystokinin-8 (CCK) activates neurons within the hindbrain nucleus of the solitary tract (NTS) that project directly to the paraventricular nucleus of the hypothalamus (PVN), and these projections underlie the ability of exogenous CCK to activate the hypothalamic-pituitary-adrenal (HPA) stress axis. CCK inhibits food intake, increases NTS neuronal cFos expression, and activates the HPA axis in a dose-dependent manner. While the hypophagic effects of exogenous CCK are attenuated in food-deprived rats, CCK dose-response relationships for NTS and hypothalamic activation in fed and fasted rats are unknown. Within the NTS, noradrenergic A2 and glucagon-like peptide-1 (GLP-1) neurons express cFos after high doses of CCK, and both neuronal populations project directly to the medial parvocellular (mp)PVN. We hypothesized that increasing and correlated proportions of A2, GLP-1, and mpPVN neurons would express cFos in rats after increasing doses of CCK, and that food deprivation would attenuate both hindbrain and hypothalamic neural activation. To test these hypotheses, ad libitum-fed (ad lib) and overnight food-deprived (DEP) rats were anesthetized and perfused with fixative 90min after i.p. injection of 1.0ml saline vehicle containing CCK at doses of 0, 3, or 10μg/kg BW. Additional ad lib and DEP rats served as non-handled (NH) controls. Brain tissue sections were processed for dual immunocytochemical localization of cFos and dopamine-β-hydroxylase to identify A2 neurons, or cFos and GLP-1. Compared to negligible A2 cFos activation in NH control rats, i.p. vehicle and CCK dose-dependently increased A2 activation, and this was significantly attenuated by DEP. DEP also attenuated mpPVN cFos expression across all treatment groups, and A2 activation was strongly correlated with mpPVN activation in both ad lib and DEP rats. In ad lib rats, large and similar numbers of GLP-1 neurons expressed cFos across all i.p. treatment groups, regardless of CCK dose. Surprisingly, DEP nearly abolished baseline GLP-1 cFos expression in NH controls, and also in rats after i.p. injection of vehicle or CCK. We conclude that CCK-induced hypothalamic cFos activation is strongly associated with A2 activation, whereas the relationship between mpPVN and GLP-1 activation is less clear. Furthermore, activation of A2, GLP-1, and mpPVN neurons is significantly modulated by feeding status, suggesting a mechanism through which food intake and metabolic state might impact hypothalamic neuroendocrine responses to homeostatic challenge.

Central NUCB2/Nesfatin-1-expressing neurones belong to the hypothalamic-brainstem circuitry activated by hypoglycaemia

Nesfatin-1 is a recently identified 82 amino acid peptide shown to have an anorexigenic effect on rodents when administrered centrally and peripherally. Nesfatin-1 is expressed not only in neurones of various brain areas, including the hypothalamic and brainstem nuclei, but also in peripheral organs, such as the stomach and the pancreas. Nesfatinergic neurones were reported to participate in the regulation of satiety signals and in the responses to other stimuli, including restraint stress, abdominal surgery, and lipopolysaccharide-induced inflammation. The present study aimed to investigate whether NUCB2/nesfatin-1 expressing neurones also take part in the central signalling activated in response to hypoglycaemia and therefore are involved in central glucose sensing. Using immunolabelling methods based on the detection of the neuronal activation marker c-Fos and of nesfatin-1, we showed that peripheral injection of insulin induced a strong activation of nesfatin-1-expressing neurones in the brain vagal-regulatory nuclei, including the arcuate nucleus, paraventricular nucleus, lateral hypothalamic area, dorsal motor nucleus of the vagus (DMNX) and nucleus of the tractus solitarius. In response to intracellular glucopaenia induced by i.p. or i.c.v. 2-deoxyglucose injection, the c-Fos/nesfatin-1 colocalisations observed at the hypothalamic and brainstem levels were similar to those observed after insulin-induced hypoglycaemia. Moreover, using Fluorogold as a retrograde tracer, we showed that nesfatinergic preganglionic DMNX neurones activated by hypoglycaemia target the stomach and the pancreas. Taken together, these results suggest that a subpopulation of nesfatinergic neurones belongs to the central network activated by hypoglycaemia, and that nesfatin-1 participates in the triggering of physiological and hormonal counter-regulations observed in response to hypoglycaemia.

c-Fos immunoreactivity in the pig brain following deoxynivalenol intoxication: focus on NUCB2/nesfatin-1 expressing neurons

Deoxynivalenol (DON), produced by the cereal-contaminating Fusarium fungi, is a major trichothecene responsible for mycotoxicoses in farm animals, including swine. The main effect of DON-intoxication is food intake reduction and the consequent body weight loss. The present study aimed to identify brain structures activated during DON intoxication in pigs. To this goal, we used c-Fos staining which constitutes a useful approach to identify activated neurons. We showed that per os administration of Fusarium graminearum extracts (containing the equivalent of 1mg DON per kg of body weight) induced an increase in c-Fos immunoreactivity in several central structures, including the ventrolateral medulla (VLM), dorsal vagal complex (DVC), paraventricular nucleus of the hypothalamus (PVN), arcuate nucleus (Arc), supraoptic nucleus (SON) and amygdala (CeA). Moreover, we coupled c-Fos staining with phenotypic markers detection in order to specify the neuronal populations activated during DON intoxication. This phenotypic characterization revealed the activation of catecholaminergic but not of serotoninergic neurons in response to the toxin. In this context, we also paid a particular attention to NUCB2/nesfatin-1 positive cells, since nesfatin-1 is known to exert a satiety effect. We report here, for the first time in the pig brain, the presence of NUCB2/nesfatin-1 neurons in the VLM, DVC, PVN, Arc and SON, and their activation during DON intoxication. Taken together, these data show that DON stimulates the main structures involved in food intake in pigs and suggest that catecholaminergic and NUCB2/nesfatin-1 neurons could contribute in the anorexigenic effects of the mycotoxin.

Advances in deoxynivalenol toxicity mechanisms: the brain as a target

Deoxynivalenol (DON), mainly produced by Fusarium fungi, and also commonly called vomitoxin, is a trichothecene mycotoxin. It is one of the most abundant trichothecenes which contaminate cereals consumed by farm animals and humans. The extent of cereal contamination is strongly associated with rainfall and moisture at the time of flowering and with grain storage conditions. DON consumption may result in intoxication, the severity of which is dose-dependent and may lead to different symptoms including anorexia, vomiting, reduced weight gain, neuroendocrine changes, immunological effects, diarrhea, leukocytosis, hemorrhage or circulatory shock. During the last two decades, many studies have described DON toxicity using diverse animal species as a model. While the action of the toxin on peripheral organs and tissues is well documented, data illustrating its effect on the brain are significantly less abundant. Yet, DON is known to affect the central nervous system. Recent studies have provided new evidence and detail regarding the action of the toxin on the brain. The purpose of the present review is to summarize critical studies illustrating this central action of the toxin and to suggest research perspectives in this field.

Nesfatin-1, a unique regulatory neuropeptide of the brain

Nesfatin-1, a newly discovered NUCB2-derived satiety neuropeptide is expressed in several neurons of forebrain, hindbrain, brainstem and spinal cord. This novel anorexigenic substance seems to play an important role in hypothalamic pathways regulating food intake and energy homeostasis. Nesfatin-1 immunoreactive cells are detectable in arcuate (ARC), paraventricular (PVN) and supraoptic nuclei (SON), where the peptide is colocalized with POMC/CART, NPY, oxytocin and vasopressin. The nesfatin-1 molecule interacts with a G-protein coupled receptor and its cytophysiological effect depends on inhibitory hyperpolarization of NPY/AgRP neurons in ARC and melanocortin signaling in PVN. Administration of nesfatin-1 significantly inhibits consumatory behavior and decreases weight gain in experimental animals. These recent findings suggest the evidence for nesfatin-1 involvement in other important brain functions such as reproduction, sleep, cognition and anxiety- or stress-related responses. The neuroprotective and antiapoptotic properties of nesfatin-1 were also reported. From the clinical viewpoint it should be noteworthy, that the serum concentration of nesfatin-1 may be a sensitive marker of epileptic seizures. However, the details of nesfatin-1 physiology ought to be clarified, and it may be considered suitable in the future, as a potential drug in the pharmacotherapy of obesity, especially in patients treated with antipsychotics and antidepressants. On the other hand, some putative nesfatin-1 antagonists may improve eating disorders.

Cellular distribution, regulated expression, and functional role of the anorexigenic peptide, NUCB2/nesfatin-1, in the testis

Nesfatin-1, product of the precursor NEFA/nucleobindin2 (NUCB2), was initially identified as anorectic hypothalamic neuropeptide, acting in a leptin-independent manner. In addition to its central role in the control of energy homeostasis, evidence has mounted recently that nesfatin-1 is also produced in peripheral metabolic tissues, such as pancreas, adipose, and gut. Moreover, nesfatin-1 has been shown to participate in the control of body functions gated by whole-body energy homeostasis, including puberty onset. Yet, whether, as is the case for other metabolic neuropeptides, NUCB2/nesfatin-1 participates in the direct control of gonadal function remains unexplored. We document here for the first time the expression of NUCB2 mRNA in rat, mouse, and human testes, where NUCB2/nesfatin-1 protein was identified in interstitial mature Leydig cells. Yet in rats, NUCB2/nesfatin-1 became expressed in Sertoli cells upon Leydig cell elimination and was also detected in Leydig cell progenitors. Although NUCB2 mRNA levels did not overtly change in rat testis during pubertal maturation and after short-term fasting, NUCB2/nesfatin-1 content significantly increased along the puberty-to-adult transition and was markedly suppressed after fasting. In addition, testicular NUCB2/nesfatin-1 expression was up-regulated by pituitary LH, because hypophysectomy decreased, whereas human choriogonadotropin (super-agonist of LH receptors) replacement enhanced, NUCB2/nesfatin-1 mRNA and peptide levels. Finally, nesfatin-1 increased human choriogonadotropin-stimulated testosterone secretion by rat testicular explants ex vivo. Our data are the first to disclose the presence and functional role of NUCB2/nesfatin-1 in the testis, where its expression is regulated by developmental, metabolic, and hormonal cues as well as by Leydig cell-derived factors. Our observations expand the reproductive dimension of nesfatin-1, which may operate directly at the testicular level to link energy homeostasis, puberty onset, and gonadal function.

The molecular physiology of CRH neurons

Corticotropin releasing hormone (CRH) is essential for stress adaptation by mediating hypothalamic-pituitary-adrenal (HPA) axis, behavioral and autonomic responses to stress. Activation of CRH neurons depends on neural afferents from the brain stem and limbic system, leading to sequential CRH release and synthesis. CRH transcription is required to restore mRNA and peptide levels, but termination of the response is essential to prevent pathology associated with chronic elevations of CRH and HPA axis activity. Inhibitory feedback mediated by glucocorticoids and intracellular production of the repressor, Inducible Cyclic AMP Early Repressor (ICER), limit the magnitude and duration of CRH neuronal activation. Induction of CRH transcription is mediated by the cyclic AMP/protein kinase A/cyclic AMP responsive element binding protein (CREB)-dependent pathways, and requires cyclic AMP-dependent nuclear translocation of the CREB co-activator, Transducer of Regulated CREB activity (TORC). This article reviews current knowledge on the mechanisms regulating CRH neuron activity.

Minireview: nesfatin-1--an emerging new player in the brain-gut, endocrine, and metabolic axis

Nesfatin-1 is a recently identified 82-amino-acid peptide derived from the precursor protein, nucleobindin2 (NUCB2). The brain distribution of NUCB2/nesfatin-1 at the mRNA and protein level along with functional studies in rodents support a role for NUCB2/nesfatin-1 as a novel satiety molecule acting through leptin-independent mechanisms. In addition, nesfatin-1 induces a wide spectrum of central actions to stimulate the pituitary-adrenal axis and sympathetic nervous system and influences visceral functions and emotion. These central actions combined with the activation of NUCB2/nesfatin-1 neurons in the brain by various stressors are indicative of a role in the adaptive response under stressful conditions. In the periphery, evidence is mounting that nesfatin-1 exerts a direct glucose-dependent insulinotropic action on β-cells of the pancreatic islets. However, the cellular mechanisms of nesfatin-1's action remain poorly understood, partly because the receptor through which nesfatin-1 exerts its pleiotropic actions is yet to be identified.

Melanocortin control of energy balance: evidence from rodent models

Regulation of energy balance is extremely complex, and involves multiple systems of hormones, neurotransmitters, receptors, and intracellular signals. As data have accumulated over the last two decades, the CNS melanocortin system is now identified as a prominent integrative network of energy balance controls in the mammalian brain. Here, we will review findings from rat and mouse models, which have provided an important framework in which to study melanocortin function. Perhaps most importantly, this review attempts for the first time to summarize recent advances in our understanding of the intracellular signaling pathways thought to mediate the action of melanocortin neurons and peptides in control of longterm energy balance. Special attention will be paid to the roles of MC4R/MC3R, as well as downstream neurotransmitters within forebrain and hindbrain structures that illustrate the distributed control of melanocortin signaling in energy balance. In addition, distinctions and controversy between rodent species will be discussed.

Interaction between gastric and upper small intestinal hormones in the regulation of hunger and satiety: ghrelin and cholecystokinin take the central stage

Several peptides are produced and released from endocrine cells scattered within the gastric oxyntic and the small intestinal mucosa. These peptide hormones are crucially involved in the regulation of gastrointestinal functions and food intake by conveying their information to central regulatory sites located in the brainstem as well as in the forebrain, such as hypothalamic nuclei. So far, ghrelin is the only known hormone that is peripherally produced in gastric X/A-like cells and centrally acting to stimulate food intake, whereas the suppression of feeding seems to be much more redundantly controlled by a number of gut peptides. Cholecystokinin produced in the duodenum is a well established anorexigenic hormone that interacts with ghrelin to modulate food intake indicating a regulatory network located at the first site of contact with nutrients in the stomach and upper small intestine. In addition, a number of peptides including leptin, urocortin 2, amylin and glucagon-like peptide 1 interact synergistically with CCK to potentiate its satiety signaling effect. New developments have led to the identification of additional peptides in X/A-like cells either derived from the pro-ghrelin gene by alternative splicing and posttranslational processing (obestatin) or a distinct gene (nucleobindin2/nesfatin-1) which have been investigated for their influence on food intake.

Nesfatin-1: a novel inhibitory regulator of food intake and body weight

The protein nucleobindin 2 (NUCB2) or NEFA (DNA binding/EF-hand/acidic amino acid rich region) was identified over a decade ago and implicated in intracellular processes. New developments came with the report that post-translational processing of hypothalamic NUCB2 may result in nesfatin-1, nesfatin-2 and nesfatin-3 and convergent studies showing that nesfatin-1 and full length NUCB2 injected in the brain potently inhibit the dark phase food intake in rodents including leptin receptor deficient Zucker rats. Nesfatin-1 also reduces body weight gain, suggesting a role as a new anorexigenic factor and modulator of energy balance. In light of the obesity epidemic and its associated diseases, underlying new mechanisms regulating food intake may be promising targets in the drug treatment of obese patients particularly as the vast majority of them display reduced leptin sensitivity or leptin resistance while nesfatin-1's mechanism of action is leptin independent. Although much progress on the localization of NUCB2/nesfatin-1 in the brain and periphery as well as on the understanding of nesfatin-1's anorexic effect have been achieved during the past three years, several important mechanisms have yet to be unraveled such as the identification of the nesfatin-1 receptor and the regulation of NUCB2 processing and nesfatin-1 release.

Sulfated cholecystokinin-8 activates phospho-mTOR immunoreactive neurons of the paraventricular nucleus in rats

The serin/threonin-kinase, mammalian target of rapamycin (mTOR) was detected in the arcuate nucleus (ARC) and paraventricular nucleus of the hypothalamus (PVN) and suggested to play a role in the integration of satiety signals. Since cholecystokinin (CCK) plays a role in the short-term inhibition of food intake and induces c-Fos in PVN neurons, the aim was to determine whether intraperitoneally injected CCK-8S affects the neuronal activity in cells immunoreactive for phospho-mTOR in the PVN. Ad libitum fed male Sprague-Dawley rats received 6 or 10 μg/kg CCK-8S or 0.15M NaCl ip (n=4/group). The number of c-Fos-immunoreactive (ir) neurons was assessed in the PVN, ARC and in the nucleus of the solitary tract (NTS). CCK-8S increased the number of c-Fos-ir neurons in the PVN (6 μg: 103 ± 13 vs. 10 μg: 165 ± 14 neurons/section; p<0.05) compared to vehicle treated rats (4 ± 1, p<0.05), but not in the ARC. CCK-8S also dose-dependently increased the number of c-Fos neurons in the NTS. Staining for phospho-mTOR and c-Fos in the PVN showed a dose-dependent increase of activated phospho-mTOR neurons (17 ± 3 vs. 38 ± 2 neurons/section; p<0.05), while no activated phospho-mTOR neurons were observed in the vehicle group. Triple staining in the PVN showed activation of phospho-mTOR neurons co-localized with oxytocin, corresponding to 9.8 ± 3.6% and 19.5 ± 3.3% of oxytocin neurons respectively. Our observations indicate that peripheral CCK-8S activates phospho-mTOR neurons in the PVN and suggest that phospho-mTOR plays a role in the mediation of CCK-8S's anorexigenic effects.

Peripherally injected CCK-8S activates CART positive neurons of the paraventricular nucleus in rats

Cholecystokinin (CCK) plays a role in the short-term inhibition of food intake. Cocaine- and amphetamine-regulated transcript (CART) peptide has been observed in neurons of the paraventricular nucleus (PVN). It has been reported that intracerebroventricular injection of CART peptide inhibits food intake in rodents. The aim of the study was to determine whether intraperitoneally (ip) injected CCK-8S affects neuronal activity of PVN-CART neurons. Ad libitum fed male Sprague-Dawley rats received 6 or 10 microg/kg CCK-8S or 0.15M NaCl ip (n=4/group). The number of c-Fos-immunoreactive neurons was determined in the PVN, arcuate nucleus (ARC), and the nucleus of the solitary tract (NTS). CCK-8S dose-dependently increased the number of c-Fos-immunoreactive neurons in the PVN (mean+/-SEM: 102+/-6 vs. 150+/-5 neurons/section, p<0.05) and compared to vehicle treated rats (18+/-7, p<0.05 vs. 6 and 10 microg/kg CCK-8S). CCK-8S at both doses induced an increase in the number of c-Fos-immunoreactive neurons in the NTS (65+/-13, p<0.05, and 182+/-16, p<0.05). No effect on the number of c-Fos neurons was observed in the ARC. Immunostaining for CART and c-Fos revealed a dose-dependent increase of activated CART neurons (19+/-3 vs. 29+/-7; p<0.05), only few activated CART neuron were observed in the vehicle group (1+/-0). The present observation shows that CCK-8S injected ip induces an increase in neuronal activity in PVN-CART neurons and suggests that CART neurons in the PVN may play a role in the mediation of peripheral CCK-8S's anorexigenic effects.

Nesfatin-1--role as possible new potent regulator of food intake

Nesfatin-1 is an 82 amino acid peptide recently discovered in the brain which is derived from nucleobindin2 (NUCB2), a protein that is highly conserved across mammalian species. Nesfatin-1 has received much attention over the past two years due to its reproducible food intake-reducing effect that is linked with recruitment of other hypothalamic peptides regulating feeding behavior. A growing amount of evidence also supports that various stressors activate fore- and hindbrain NUCB2/nesfatin-1 circuitries. In this review, we outline the central nervous system distribution of NUCB2/nesfatin-1, and recent developments on the peripheral expression of NUCB2/nesfatin-1, in particular its co-localization with ghrelin in gastric X/A-like cells and insulin in ss-cells of the endocrine pancreas. Functional studies related to the characteristics of nesfatin-1's inhibitory effects on dark phase food intake are detailed as well as the central activation of NUCB2/nesfatin-1 immunopositive neurons in the response to psychological, immune and visceral stressors. Lastly, potential clinical implications of targeting NUCB2/nesfatin-1 signaling and existing gaps in knowledge to ascertain the role and mechanisms of action of nesfatin-1 are presented.

Effects of cholecystokinin in the supraoptic nucleus and paraventricular nucleus are negatively modulated by leptin in 24-h fasted lean male rats

Cholecystokinin (CCK) and leptin are two important satiety factors that are considered to act in synergy to reduce meal size. Peripheral injection of CCK activates neurones in several hypothalamic nuclei, including the supraoptic (SON) and paraventricular (PVN) nuclei and neurones in the brainstem of fed rats. We investigated whether peripheral leptin would modulate the effects of CCK on neuronal activity in the hypothalamus and brainstem of fasted rats by investigating Fos expression in the PVN, SON, arcuate nucleus, ventromedial hypothalamus (VMH), dorsomedial hypothalamus (DMH), area postrema (AP) and the nucleus tractus solitarii (NTS). Male rats, fasted for 24 h, received either one i.p. injection of vehicle, leptin or CCK-8 alone, or received one injection of vehicle or leptin before an i.p. injection of CCK-8. We found that CCK increased Fos expression in the PVN and SON as well as in the NTS and AP, but had no effect on Fos expression in the arcuate nucleus, VMH or DMH compared to vehicle. Leptin injected alone significantly increased Fos expression in the arcuate nucleus but had no effect on Fos expression in the VMH, DMH, SON, PVN, AP or NTS compared to vehicle. Fos expression was significantly increased in the AP in rats injected with both leptin and CCK compared to rats injected with vehicle and CCK. Unexpectedly, there was significantly less Fos expression in the PVN and SON of fasted rats injected with leptin and CCK than in rats injected with vehicle and CCK, suggesting that leptin attenuated CCK-induced Fos expression in the SON and PVN. However, Fos expression in the NTS was similar in fasted rats injected with vehicle and CCK or with leptin and CCK. Taken together, these results suggest that leptin dampens the effects of CCK on Fos expression in the SON and PVN, independently from NTS pathways, and this may reflect a direct action on magnocellular neurones.

Nesfatin-1 evokes Ca2+ signaling in isolated vagal afferent neurons via Ca2+ influx through N-type channels

Nesfatin-1, processed from nucleobindin 2, is an anorexigenic peptide expressed in the brain and several peripheral tissues including the stomach and pancreas. Peripheral, as well as intracerebroventricular, administration of nesfatin-1 suppresses feeding behavior, though underlying mechanisms are unknown. In this study, we examined effects of nesfatin-1 on cytosolic Ca(2+) concentration ([Ca(2+)](i)) in the neurons isolated from the vagal afferent nodose ganglion of mice. Nesfatin-1 at 10(-10)-10(-8)M increased [Ca(2+)](i) in the isolated neurons in a concentration-dependent manner, and at 10(-8)M it increased [Ca(2+)](i) in 33 out of 263 (12.5%) neurons. These responses were inhibited under Ca(2+)-free conditions and by N-type Ca(2+) channel blocker, omega-conotoxin GVIA. All the nesfatin-1-responsive neurons also exhibited [Ca(2+)](i) responses to capsaicin and cholecystokinin-8. These results provide direct evidence that nesfatin-1 activates vagal afferent neurons by stimulating Ca(2+) influx through N-type channels, demonstrating the machinery through which peripheral nesfatin-1 can convey signals to the brain.

Central nesfatin-1-expressing neurons are sensitive to peripheral inflammatory stimulus

Recently, a novel factor with anorexigenic properties was identified and called nesfatin-1. This protein (82 aac) is not only expressed in peripheral organs but it is also found in neurons located in specific structures including the hypothalamus and the brainstem, two sites strongly involved in food intake regulation. Here, we studied whether some of the neurons that become activated following an injection of an anorectic dose of lipopolysaccharides (LPS) exhibit a nesfatin-1 phenotype. To this end, we used double immunohistochemistry to target the expression of the immediate-early gene c-fos and of nesfatin-1 on coronal frozen sections of the rat brain. The number of c-Fos+/nesfatin-1+ neurons was evaluated in the immunosensitive structures reported to contain nesfatin-1 neurons; i.e. paraventricular hypothalamic nucleus (PVN), supraoptic nucleus (SON), arcuate nucleus (ARC) and nucleus of the solitary tract (NTS). LPS strongly increased the number of c-Fos+/nesfatin-1+ neurons in the PVN, SON and NTS, and to a lesser extent in the ARC. Triple labeling showed that a portion of the nesfatin-1 neurons activated in response to LPS within the NTS are catecholaminergic since they co-express tyrosine hydroxylase (TH). Our data therefore indicate that a portion of nesfatin-1 neurons of both the hypothalamus and brainstem are sensitive to peripheral inflammatory signals, and provide the first clues suggesting that centrally released nesfatin-1 may contribute to the neural mechanisms leading to endotoxaemic anorexia.