Ghrelin directly interacts with neuropeptide-Y-containing neurons in the rat arcuate nucleus: Ca2+ signaling via protein kinase A and N-type channel-dependent mechanisms and cross-talk with leptin and orexin

CaMKK2: bridging the gap between Ca2+ signaling and energy-sensing

Calcium (Ca2+) ions are ubiquitous and indispensable signaling messengers that regulate virtually every cell function. The unique ability of Ca2+ to regulate so many different processes yet cause stimulus specific changes in cell function requires sensing and decoding of Ca2+ signals. Ca2+-sensing proteins, such as calmodulin, decode Ca2+ signals by binding and modifying the function of a diverse range of effector proteins. These effectors include the Ca2+-calmodulin dependent protein kinase kinase-2 (CaMKK2) enzyme, which is the core component of a signaling cascade that plays a key role in important physiological and pathophysiological processes, including brain function and cancer. In addition to its role as a Ca2+ signal decoder, CaMKK2 also serves as an important junction point that connects Ca2+ signaling with energy metabolism. By activating the metabolic regulator AMP-activated protein kinase (AMPK), CaMKK2 integrates Ca2+ signals with cellular energy status, enabling the synchronization of cellular activities regulated by Ca2+ with energy availability. Here, we review the structure, regulation, and function of CaMKK2 and discuss its potential as a treatment target for neurological disorders, metabolic disease, and cancer.

Effects of different winter paddock management of Thoroughbred weanlings and yearlings in the cold region of Japan on physiological function, endocrine function and growth

Effects of different winter paddock management of Thoroughbred weanlings and yearlings in Hokkaido, Japan, which is extremely cold in winter, on physiological function, endocrine function and growth were investigated. They were divided into two groups; those kept outdoors for 22 hr in the paddock (22hr group) and those kept outdoors for 7 hr in daytime with walking exercise for 1 hr using the horse-walker (7hr+W group), and the changes in daily distance travelled, body temperature (BT), heart rate (HR), HR variability (HRV), endocrine function and growth parameters were compared between the two groups from November at the year of birth to January at 1 year of age. The 7hr+W group could travel almost the same distance as the 22hr group by using the horse-walker. The 22hr group had a lower rate of increase in body weight than the 7hr+W group in January. In addition, lower in BT and HR were observed, and HRV analysis showed an increase in high frequency power spectral density, indicating that parasympathetic nervous activity was dominant. And also, changes in circulating cortisol and thyroxine were not observed despite cold environment. On the other hand, the 7hr+W group had higher prolactin and insulin like growth factor than the 22hr group in January, and cortisol and thyroxine were also increased. Physiological and endocrinological findings from the present study indicate that the management of the 7hr+W group is effective in promoting growth and maintaining metabolism during the winter season.

Leptin and ghrelin dynamics: unraveling their influence on food intake, energy balance, and the pathophysiology of type 2 diabetes mellitus

Purpose

Type 2 diabetes mellitus (T2DM) is a chronic metabolic disorder characterized by insulin resistance and impaired glucose homeostasis. In recent years, there has been growing interest in the role of hunger and satiety hormones such as ghrelin and leptin in the development and progression of T2DM. In this context, the present literature review aims to provide a comprehensive overview of the current understanding of how ghrelin and leptin influences food intake and maintain energy balance and its implications in the pathophysiology of T2DM.

Methods

A thorough literature search was performed using PubMed and Google Scholar to choose the studies that associated leptin and ghrelin with T2DM. Original articles and reviews were included, letters to editors and case reports were excluded.

Results

This narrative review article provides a comprehensive summary on mechanism of action of leptin and ghrelin, its association with obesity and T2DM, how they regulate energy and glucose homeostasis and potential therapeutic implications of leptin and ghrelin in managing T2DM.

Conclusion

Ghrelin, known for its appetite-stimulating effects, and leptin, a hormone involved in the regulation of energy balance, have been implicated in insulin resistance and glucose metabolism. Understanding the complexities of ghrelin and leptin interactions in the context of T2DM may offer insights into novel therapeutic strategies for this prevalent metabolic disorder. Further research is warranted to elucidate the molecular mechanisms underlying these hormone actions and to explore their clinical implications for T2DM prevention and management.

Octanoic acid-rich enteral nutrition attenuated hypercatabolism through the acylated ghrelin-POMC pathway in endotoxemic rats

OBJECTIVES

Metabolic disorders and no response to intravenous nutrition because of sepsis have been urgent problems for clinical nutrition support. Enteral nutrition (EN) has been an important clinical therapeutic measure in septic patients; however, simple EN has not demonstrated good performance. This study aimed to investigate the effects of different concentrations of octanoic acid (OA)-rich EN on hypercatabolism in endotoxemic rats and test whether OA-rich EN could attenuate hypercatabolism through the acylated ghrelin-proopiomelanocortin (POMC) pathway.

METHODS

Rats were randomly divided into six groups: sham, lipopolysaccharide (LPS), LPS + EN and LPS + EN + OA (0.25, 0.5, and 1 g/kg, respectively) groups to investigate the effects of different concentrations of OA-rich EN on hypercatabolism in endotoxemic rats. The rats were then randomly divided into four groups: sham, LPS, LPS + OA, and LPS + OA + Go-CoA-Tat, to test whether OA-rich EN attenuated hypercatabolism through the acylated ghrelin-POMC pathway. Rats received nutrition support via a gastric tube for 3 d (100 kcal/kg daily). Insulin resistance, muscle protein synthesis and atrophy, inflammatory cytokines, ghrelin in circulation and hypothalamus, ghrelin O-acyltransferase (GOAT), and the adenosine 5'-monophosphate-activated protein kinase (AMPK)-autophagy-POMC pathway were measured.

RESULTS

Compared with simple EN, OA-rich EN promoted the acylation of ghrelin in a dose-dependent manner and attenuated POMC-mediated hypercatabolism in endotoxemic rats. Inhibition of GOAT activity decreased the level of acylated ghrelin and aggravated POMC-mediated hypercatabolism conferred by OA-rich EN.

CONCLUSIONS

OA-rich EN could increase the level of acylated ghrelin and attenuate hypercatabolism through the acylated ghrelin-POMC pathway compared with simple EN in endotoxemic rats.

Central Mechanisms of Thermoregulation and Fever in Mammals

Thermoregulation is a fundamental homeostatic function in mammals mediated by the central nervous system. The framework of the central circuitry for thermoregulation lies in the hypothalamus and brainstem. The preoptic area (POA) of the hypothalamus integrates cutaneous and central thermosensory information into efferent control signals that regulate excitatory descending pathways through the dorsomedial hypothalamus (DMH) and rostral medullary raphe region (rMR). The cutaneous thermosensory feedforward signals are delivered to the POA by afferent pathways through the lateral parabrachial nucleus, while the central monitoring of body core temperature is primarily mediated by warm-sensitive neurons in the POA for negative feedback regulation. Prostaglandin E2, a pyrogenic mediator produced in response to infection, acts on the POA to trigger fever. Recent studies have revealed that this circuitry also functions for physiological responses to psychological stress and starvation. Master psychological stress signaling from the medial prefrontal cortex to the DMH has been discovered to drive a variety of physiological responses for stress coping, including hyperthermia. During starvation, hunger signaling from the hypothalamus was found to activate medullary reticular neurons, which then suppress thermogenic sympathetic outflows from the rMR for energy saving. This thermoregulatory circuit represents a fundamental mechanism of the central regulation for homeostasis.

Arcuate Nucleus of the Hypothalamus: Anatomy, Physiology, and Diseases

The hypothalamus is part of the diencephalon and has several nuclei, one of which is the arcuate nucleus. The arcuate nucleus of hypothalamus (ARH) consists of neuroendocrine neurons and centrally-projecting neurons. The ARH is the center where the homeostasis of nutrition/metabolism and reproduction are maintained. As such, dysfunction of the ARH can lead to disorders of nutrition/metabolism and reproduction. Here, we review various types of neurons in the ARH and several genetic disorders caused by mutations in the ARH.

Ghrelin's orexigenic action in the lateral hypothalamic area involves indirect recruitment of orexin neurons and arcuate nucleus activation

OBJECTIVE

Ghrelin is a potent orexigenic hormone, and the lateral hypothalamic area (LHA) has been suggested as a putative target mediating ghrelin's effects on food intake. Here, we aimed to investigate the presence of neurons expressing ghrelin receptor (a.k.a. growth hormone secretagogue receptor, GHSR) in the mouse LHA (LHAGHSR neurons), its physiological implications and the neuronal circuit recruited by local ghrelin action.

METHODS

We investigated the distribution of LHAGHSR neurons using different histologic strategies, including the use of a reporter mice expressing enhanced green fluorescent protein under the control of the GHSR promoter. Also, we investigated the physiological implications of local injections of ghrelin within the LHA, and the extent to which the orexigenic effect of intra-LHA-injected ghrelin involves the arcuate nucleus (ARH) and orexin neurons of the LHA (LHAorexin neurons) RESULTS: We found that: 1) LHAGHSR neurons are homogeneously distributed throughout the entire LHA; 2) intra-LHA injections of ghrelin transiently increase food intake and locomotor activity; 3) ghrelin's orexigenic effect in the LHA involves the indirect recruitment of LHAorexin neurons and the activation of ARH neurons; and 4) LHAGHSR neurons are not targeted by plasma ghrelin.

CONCLUSIONS

We provide a compelling neuroanatomical and functional characterization of LHAGHSR neurons in male mice that indicates that LHAGHSR cells are part of a hypothalamic neuronal circuit that potently induces food intake.

CaMK1D signalling in AgRP neurons promotes ghrelin-mediated food intake

Hypothalamic AgRP/NPY neurons are key players in the control of feeding behaviour. Ghrelin, a major orexigenic hormone, activates AgRP/NPY neurons to stimulate food intake and adiposity. However, cell-autonomous ghrelin-dependent signalling mechanisms in AgRP/NPY neurons remain poorly defined. Here we show that calcium/calmodulin-dependent protein kinase ID (CaMK1D), a genetic hot spot in type 2 diabetes, is activated upon ghrelin stimulation and acts in AgRP/NPY neurons to mediate ghrelin-dependent food intake. Global Camk1d-knockout male mice are resistant to ghrelin, gain less body weight and are protected against high-fat-diet-induced obesity. Deletion of Camk1d in AgRP/NPY, but not in POMC, neurons is sufficient to recapitulate above phenotypes. In response to ghrelin, lack of CaMK1D attenuates phosphorylation of CREB and CREB-dependent expression of the orexigenic neuropeptides AgRP/NPY in fibre projections to the paraventricular nucleus (PVN). Hence, CaMK1D links ghrelin action to transcriptional control of orexigenic neuropeptide availability in AgRP neurons.

Glucose-dependent insulinotropic polypeptide counteracts diet-induced obesity along with reduced feeding, elevated plasma leptin and activation of leptin-responsive and proopiomelanocortin neurons in the arcuate nucleus

AIM

To clarify the effects of glucose-dependent insulinotropic polypeptide (GIP) receptor agonists (GIPRAs) on feeding and body weight.

MATERIALS AND METHODS

Acute and subchronic effects of subcutaneous GIPFA-085, a long-acting GIPRA, on blood glucose, food intake, body weight, respiratory exchange ratio and plasma leptin levels were measured in diet-induced obese (DIO) mice and/or functional leptin-deficient ob/ob mice. The effects of GIPFA-085 on the hypothalamic arcuate nucleus (ARC) neurons from lean and DIO mice were studied by measuring cytosolic Ca²⁺ concentration ([Ca²⁺ ]_i ).

RESULTS

Single bolus GIPFA-085 (30, 300 nmol/kg) dose-dependently reduced blood glucose in glucose tolerance tests, elevated plasma leptin levels at 0.5-6 hours and inhibited food intake at 2-24 hours after injection in DIO mice. Daily GIPFA-085 (300 nmol/kg) inhibited food intake and increased fat utilization on day 1, and reduced body weight gain on days 3-12 of treatment in DIO, but not ob/ob, mice. GIPFA-085 increased [Ca²⁺ ]_i in the ARC leptin-responsive and proopiomelanocortin (POMC) neurons. GIPFA-085 and leptin cooperated to increase [Ca²⁺ ]_i in ARC neurons and inhibit food intake.

CONCLUSIONS

GIPFA-085 acutely inhibits feeding and increases lipid utilization, and sustainedly lowers body weight in DIO mice via mechanisms involving rises in leptin and activation of ARC leptin-responsive and POMC neurons. This study highlights the therapeutic potential of GIPRAs for treating obesity and diabetes.

Molecular and Cellular Crosstalk between Bone and Brain: Accessing Bidirectional Neural and Musculoskeletal Signaling during Aging and Disease

Molecular omics technologies, including proteomics, have enabled the elucidation of key signaling pathways that mediate bidirectional communication between the brain and bone tissues. Here we provide a brief summary of the clinical and molecular evidence of the need to study the bone-brain axis of cross-tissue cellular communication. Clear clinical and molecular evidence suggests biological interactions and similarities between bone and brain cells. Here we review the current mass spectrometric techniques for studying brain and bone diseases with an emphasis on neurodegenerative diseases and osteoarthritis/osteoporosis, respectively. Further study of the bone-brain axis on a molecular level and evaluation of the role of proteins, neuropeptides, osteokines, and hormones in molecular pathways linked to bone and brain diseases is critically needed. The use of mass spectrometry and other omics technologies to analyze these cross-tissue signaling events and interactions will help us better understand disease progression and comorbidities and potentially identify new pathways and targets for therapeutic interventions. Proteomic measurements are particularly favorable for investigating the role of signaling and secreted and circulating analytes and identifying molecular and metabolic pathways implicated in age-related diseases.

The Interplay between Ghrelin and Microglia in Neuroinflammation: Implications for Obesity and Neurodegenerative Diseases

Numerous studies have shown that microglia are capable of producing a wide range of chemokines to promote inflammatory processes within the central nervous system (CNS). These cells share many phenotypical and functional characteristics with macrophages, suggesting that microglia participate in innate immune responses in the brain. Neuroinflammation induces neurometabolic alterations and increases in energy consumption. Microglia may constitute an important therapeutic target in neuroinflammation. Recent research has attempted to clarify the role of Ghre signaling in microglia on the regulation of energy balance, obesity, neuroinflammation and the occurrence of neurodegenerative diseases. These studies strongly suggest that Ghre modulates microglia activity and thus affects the pathophysiology of neurodegenerative diseases. This review aims to summarize what is known from the current literature on the way in which Ghre modulates microglial activity during neuroinflammation and their impact on neurometabolic alterations in neurodegenerative diseases. Understanding the role of Ghre in microglial activation/inhibition regulation could provide promising strategies for downregulating neuroinflammation and consequently for diminishing negative neurological outcomes.

Molecular Mechanisms and Health Benefits of Ghrelin: A Narrative Review

Ghrelin, an endogenous brain-gut peptide, is secreted in large quantities, mainly from the stomach, in humans and rodents. It can perform the biological function of activating the growth hormone secretagogue receptor (GHSR). Since its discovery in 1999, ample research has focused on promoting its effects on the human appetite and pleasure-reward eating. Extensive, in-depth studies have shown that ghrelin is widely secreted and distributed in tissues. Its role in neurohumoral regulation, such as metabolic homeostasis, inflammation, cardiovascular regulation, anxiety and depression, and advanced cancer cachexia, has attracted increasing attention. However, the effects and regulatory mechanisms of ghrelin on obesity, gastrointestinal (GI) inflammation, cardiovascular disease, stress regulation, cachexia treatment, and the prognosis of advanced cancer have not been fully summarized. This review summarizes ghrelin's numerous effects in participating in a variety of biochemical pathways and the clinical significance of ghrelin in the regulation of the homeostasis of organisms. In addition, potential mechanisms are also introduced.

Role of brain-gut-muscle axis in human health and energy homeostasis

The interrelationship between brain, gut and skeletal muscle plays a key role in energy homeostasis of the body, and is becoming a hot topic of research. Intestinal microbial metabolites, such as short-chain fatty acids (SCFAs), bile acids (BAs) and tryptophan metabolites, communicate with the central nervous system (CNS) by binding to their receptors. In fact, there is a cross-talk between the CNS and the gut. The CNS, under the stimulation of pressure, will also affect the stability of the intestinal system, including the local intestinal transport, secretion and permeability of the intestinal system. After the gastrointestinal tract collects information about food absorption, it sends signals to the central system through vagus nerve and other channels to stimulate the secretion of brain-gut peptide and produce feeding behavior, which is also an important part of maintaining energy homeostasis. Skeletal muscle has receptors for SCFAs and BAs. Therefore, intestinal microbiota can participate in skeletal muscle energy metabolism and muscle fiber conversion through their metabolites. Skeletal muscles can also communicate with the gut system during exercise. Under the stimulation of exercise, myokines secreted by skeletal muscle causes the secretion of intestinal hormones, and these hormones can act on the central system and affect food intake. The idea of the brain-gut-muscle axis is gradually being confirmed, and at present it is important for regulating energy homeostasis, which also seems to be relevant to human health. This article focuses on the interaction of intestinal microbiota, central nervous, skeletal muscle energy metabolism, and feeding behavior regulation, which will provide new insight into the diagnostic and treatment strategies for obesity, diabetes, and other metabolic diseases.

A subpopulation of agouti-related peptide neurons exciting corticotropin-releasing hormone axon terminals in median eminence led to hypothalamic-pituitary-adrenal axis activation in response to food restriction

The excitatory action of gamma-aminobutyric-acid (GABA) in the median-eminence (ME) led to the steady-state release of corticotropin-releasing hormone (CRH) from CRH axon terminals, which modulates the hypothalamic-pituitary-adrenal (HPA) axis. However, in ME, the source of excitatory GABAergic input is unknown. We examined agouti-related peptide (AgRP) expressing neurons in the arcuate nucleus as a possible source for excitatory GABAergic input. Here, we show that a subpopulation of activated AgRP neurons directly project to the CRH axon terminals in ME elevates serum corticosterone levels in 60% food-restricted mice. This increase in serum corticosterone is not dependent on activation of CRH neuronal soma in the paraventricular nucleus. Furthermore, conditional deletion of Na⁺-K⁺-2Cl^– cotransporter-1 (NKCC1), which promotes depolarizing GABA action, from the CRH axon terminals results in significantly lower corticosterone levels in response to food restriction. These findings highlight the important role of a subset of AgRP neurons in HPA axis modulation via NKCC1-dependent GABAergic excitation in ME.

G protein-coupled receptor interactions and modification of signalling involving the ghrelin receptor, GHSR1a

The growth hormone secretagogue receptor 1a (GHSR1a) is intriguing because of its potential as a therapeutic target and its diverse molecular interactions. Initial studies of the receptor focused on the potential therapeutic ability for growth hormone (GH) release to reduce wasting in aging individuals, as well as food intake regulation for treatment of cachexia. Known roles of GHSR1a now extend to regulation of neurogenesis, learning and memory, gastrointestinal motility, glucose/lipid metabolism, the cardiovascular system, neuronal protection, motivational salience, and hedonic feeding. Ghrelin, the endogenous agonist of GHSR1a, is primarily located in the stomach and is absent from the central nervous system (CNS), including the spinal cord. However, ghrelin in the circulation does have access to a small number of CNS sites, including the arcuate nucleus, which is important in feeding control. At some sites, such as at somatotrophs, GHSR1a has high constitutive activity. Typically, ghrelin-dependent and constitutive GHSR1a activation occurs via Gα_q/11 pathways. In vitro and in vivo data suggest that GHSR1a heterodimerises with multiple G protein-coupled receptors (GPCRs), including dopamine D1 and D2, serotonin 2C, orexin, oxytocin and melanocortin 3 receptors (MCR3), as well as the MCR3 accessory protein, MRAP2, providing possible mechanisms for its many physiological effects. In all cases, the receptor interaction changes downstream signalling and the responses to receptor agonists. This review discusses the signalling mechanisms of GHSR1a alone and in combination with other GPCRs, and explores the physiological consequences of GHSR1a coupling with other GPCRs.

d-Allulose Inhibits Ghrelin-Responsive, Glucose-Sensitive and Neuropeptide Y Neurons in the Arcuate Nucleus and Central Injection Suppresses Appetite-Associated Food Intake in Mice

d-allulose, a rare sugar, has sweetness with few calories. d-allulose regulates feeding and glycemia, and ameliorates hyperphagia, obesity and diabetes. All these functions involve the central nervous system. However, central mechanisms underlying these effects of d-allulose remain unknown. We recently reported that d-allulose activates the anorexigenic neurons in the hypothalamic arcuate nucleus (ARC), the neurons that respond to glucagon-like peptide-1 and that express proopiomelanocortin. However, its action on the orexigenic neurons remains unknown. This study investigated the effects of d-allulose on the ARC neurons implicated in hunger, by measuring cytosolic Ca²⁺ concentration ([Ca²⁺]_i) in single neurons. d-allulose depressed the increases in [Ca²⁺]_i induced by ghrelin and by low glucose in ARC neurons and inhibited spontaneous oscillatory [Ca²⁺]_i increases in neuropeptide Y (NPY) neurons. d-allulose inhibited 10 of 35 (28%) ghrelin-responsive, 18 of 60 (30%) glucose-sensitive and 3 of 8 (37.5%) NPY neurons in ARC. Intracerebroventricular injection of d-allulose inhibited food intake at 20:00 and 22:00, the early dark phase when hunger is promoted. These results indicate that d-allulose suppresses hunger-associated feeding and inhibits hunger-promoting neurons in ARC. These central actions of d-allulose represent the potential of d-allulose to inhibit the hyperphagia with excessive appetite, thereby counteracting obesity and diabetes.

D-Allulose cooperates with glucagon-like peptide-1 and activates proopiomelanocortin neurons in the arcuate nucleus and central injection inhibits feeding in mice

A rare sugar D-Allulose has sweetness without calorie. Previous studies have shown that D-Allulose improves glucose and energy metabolism and ameliorates obesity. However, underlying mechanisms remain elusive. This study explored the effect of central injection of D-Allulose on feeding behavior in mice. We also examined direct effects of D-Allulose on the neurons in the hypothalamic arcuate nucleus (ARC) that regulate feeding, including the anorexigenic glucagon-like peptide-1 (GLP-1)-responsive neurons and proopiomelanocortin (POMC) neurons. Single neurons were isolated from ARC and cytosolic Ca²⁺ concentration ([Ca²⁺]_i) was measured by fura-2 microfluorometry. Administration of D-Allulose at 5.6, 16.7 and 56 mM concentration-dependently increased [Ca²⁺]_i in ARC neurons. The [Ca²⁺]_i increases took place similarly when the osmolarity of superfusion solution was kept constant. The majority (40%) of the D-Allulose-responsive neurons also responded to GLP-1 with [Ca²⁺]_i increases. D-Allulose increased [Ca²⁺]_i in 33% of POMC neurons in ARC. D-Allulose potentiated the GLP-1 action to increase [Ca²⁺]_i in ARC neurons including POMC neurons. Intracerebroventricular injection of D-Allulose significantly decreased food intake at 1 and 2 h after injection. These results demonstrate that D-Allulose cooperates with glucagon-like peptide-1 and activates the ARC neurons including POMC neurons. Furthermore, central injection of D-Allulose inhibits feeding. These central actions of D-Allulose may underlie the ability of D-Allulose to counteract obesity and diabetes.

Systemic infusion of exogenous ghrelin in male broiler chickens (Gallus gallus domesticus). The effect of pulse frequency, doses, and ghrelin forms on feed intake, average daily gain, corticosterone, and growth hormone concentrations

There is limited information on the effect of exogenous ghrelin infusion on feed intake (FI) in chickens. Therefore, male broilers were used in 3 factorial experiments to determine the relationships between doses (0, 1, or 4 nM; Dose), frequency (once every two h; 2 h), once every 4th h (4 h) or continuous infusion, and ghrelin forms including acylated-ghrelin (AG) and desacylated-ghrelin (DAG) on FI, ADG, and concentrations of corticosterone and Growth Hormone (GH). Treatments were delivered via a jugular cannula, using programmable pumps for 11 consecutive days. FI and ADG were recorded, and plasma was collected. Data were analyzed using a factorial design. In Experiment 1 the effect of AG pulse frequency and doses were evaluated. There was a linear decrease in FI (P = 0.002) and a linear increase in corticosterone (P = 0.033) and GH (P = 0.011) concentrations when AG was infused. However, ADG decreased with doses (P = 0.011) only when AG was given at 2 h. In Experiment 2 the effect of ghrelin forms and doses given at 2 h was evaluated. There was a linear decrease in FI when AG was infused and a linear increase in FI when DAG was infused (P < 0.05). Birds infused with DAG gained more weight than those infused with AG. There was a linear increase in corticosterone and GH concentrations only when AG was infused (P < 0.01). In Experiment 3 the effect of continuous infusion of 2 doses (0 and 1 nM) of AG and DAG were evaluated. There was a linear decrease in FI and ADG when AG (P < 0.001) was infused and a linear increase in FI and ADG when DAG was infused (P < 0.05). There was an increase in corticosterone concentrations only when AG was infused (P = 0.022). However, GH concentrations were not affected by treatments. We concluded that AG and DAG pulse frequency and doses had a differential effect on FI, ADG, corticosterone, and GH concentrations in broiler chickens.

Energetic demands of lactation produce an increase in the expression of growth hormone secretagogue receptor in the hypothalamus and ventral tegmental area of the rat despite a reduction in circulating ghrelin

Lactating rats show changes in the secretion of hormones and brain signals that promote hyperphagia and facilitate the production of milk. Little is known, however, about the role of ghrelin in the mechanisms sustaining lactational hyperphagia. Here, we used Wistar female rats that underwent surgery to sever the galactophores to prevent milk delivery (GC rats) and decrease the energetic drain of milk delivery. We compared plasma acyl-ghrelin concentrations and growth hormone secretagogue receptor (GHSR) mRNA expression in different brain regions of GC rats with those of sham operated lactating and nonlactating rats. Additional lactating and nonlactating rats were implanted with cannulae aimed at the lateral ventricles and were used to compare feeding responses to central ghrelin or GHSR antagonist infusions to those of nonlactating rats receiving similar infusions on day 14-16 postpartum (pp). Results show lower plasma acyl-ghrelin concentrations on day 15 pp sham operated lactating rats compared to GC or nonlactating rats. These changes occur in association with increased GHSR mRNA expression in the hypothalamic arcuate nucleus (ARC) and ventral tegmental area (VTA) of sham operated lactating rats. Despite lactational hyperphagia, infusions of ghrelin (0.25 or 1 μg) resulted in similar increases in food intake in lactating and nonlactating rats. In addition, infusions of the GHSR antagonist JMV3002 (4 μg in 1 μl of vehicle) produced greater suppression of food intake in lactating rats than in nonlactating rats. These data suggest that, despite lower plasma ghrelin, the energetic drain of lactation increases sensitivity to the orexigenic effects of ghrelin in brain regions important for food intake and energy balance, and these events are associated with lactational hyperphagia.

New Aspects of Corpus Luteum Regulation in Physiological and Pathological Conditions: Involvement of Adipokines and Neuropeptides

The corpus luteum is a small gland of great importance because its proper functioning determines not only the appropriate course of the estrous/menstrual cycle and embryo implantation, but also the subsequent maintenance of pregnancy. Among the well-known regulators of luteal tissue functions, increasing attention is focused on the role of neuropeptides and adipose tissue hormones-adipokines. Growing evidence points to the expression of these factors in the corpus luteum of women and different animal species, and their involvement in corpus luteum formation, endocrine function, angiogenesis, cells proliferation, apoptosis, and finally, regression. In the present review, we summarize the current knowledge about the expression and role of adipokines, such as adiponectin, leptin, apelin, vaspin, visfatin, chemerin, and neuropeptides like ghrelin, orexins, kisspeptin, and phoenixin in the physiological regulation of the corpus luteum function, as well as their potential involvement in pathologies affecting the luteal cells that disrupt the estrous cycle.

Neuropeptide Y interaction with dopaminergic and serotonergic pathways: interlinked neurocircuits modulating hedonic eating behaviours

Independent from homeostatic needs, the consumption of foods originating from hyperpalatable diets is defined as hedonic eating. Hedonic eating can be observed in many forms of eating phenotypes, such as compulsive eating and stress-eating, heightening the risk of obesity development. For instance, stress can trigger the consumption of palatable foods as a type of coping strategy, which can become compulsive, particularly when developed as a habit. Although eating for pleasure is observed in multiple maladaptive eating behaviours, the current understanding of the neurobiology underlying hedonic eating remains deficient. Intriguingly, the combined orexigenic, anxiolytic and reward-seeking properties of Neuropeptide Y (NPY) ignited great interest and has positioned NPY as one of the core neuromodulators operating hedonic eating behaviours. While extensive literature exists exploring the homeostatic orexigenic and anxiolytic properties of NPY, the rewarding effects of NPY continue to be investigated. As deduced from a series of behavioural and molecular-based studies, NPY appears to motivate the consumption and enhancement of food-rewards. As a possible mechanism, NPY may modulate reward-associated monoaminergic pathways, such as the dopaminergic and serotoninergic neural networks, to modulate hedonic eating behaviours. Furthermore, potential direct and indirect NPYergic neurocircuitries connecting classical homeostatic and hedonic neuropathways may also exist involving the anti-reward centre the lateral habenula. Therefore, this review investigates the participation of NPY in orchestrating hedonic eating behaviours through the modulation of monoaminergic pathways.

Neuronal GHS-R Differentially Modulates Feeding Patterns under Normal and Obesogenic Conditions

The orexigenic hormone ghrelin increases food intake and promotes obesity through its receptor, growth hormone secretagogue receptor (GHS-R). We previously reported two neuron-specific GHS-R knockout mouse lines, namely pan-neuronal deletion by Syn1-cre and hypothalamic deletion by AgRP-cre, exhibiting differential diet-dependent effects on body weight. GHS-R deficiency in neurons elicited less pronounced metabolic effects under regular diet (RD) than high fat diet (HFD). While there was no difference in total food intake of HFD in either mouse line, Syn1-cre; Ghsrf/f mice showed much greater anti-obesity effect than that of AgRP-cre; Ghsrf/f mice. Meal feeding pattern is known to have a major impact on energy homeostasis and obesity development. Here, we investigated the feeding behaviors of these two neuron-specific GHS-R knockout mice under RD and HFD feeding, by assessing meal number, meal size, meal duration, and feeding frequency. Under the normal diet, RD-fed Syn1-cre; Ghsrf/f mice showed a decreased meal size in dark phase, while RD-fed AgRP-cre; Ghsrf/f mice showed an increased meal duration in dark phase. Under the obesogenic diet, HFD-fed Syn1-cre; Ghsrf/f mice displayed reduced meal numbers in light phase and increased feeding in both light and dark phases, whereas HFD-fed AgRP-cre; Ghsrf/f mice showed a decreased meal duration in the light phase only. Consistently, the expression of neuropeptides (Neuropeptide Y and Orexin) was increased in the hypothalamus of RD-fed Syn1-cre; Ghsrf/f mice, whereas the expression of cannabinoid receptor type 1 (CB1) was increased in the hypothalamus of HFD fed Syn1-cre; Ghsrf/f mice. Overall, feeding pattern changes were more pronounced in Syn1-cre; Ghsrf/f mice than that in AgRP-cre; Ghsrf/f mice, and HFD elicited greater alteration than RD. While AgRP-cre; Ghsrf/f mice consumed HFD meals faster during the day (showing shorter meal duration), Syn1-cre; Ghsrf/f mice ate few HFD meals during the light phase and ate slowly throughout the day (showing longer meal duration in both phases). Our findings reveal that neuronal GHS-R regulates energy homeostasis by altering feeding patterns, and differentially modulates feeding patterns in a site- and diet-dependent manner. The distinctive data in these two mouse lines also suggest that eating slowly during the optimal feeding period (dark phase for mice) may be beneficial in combating obesity.

AgRP/NPY and POMC neurons in the arcuate nucleus and their potential role in treatment of obesity

Obesity is a major health crisis affecting over a third of the global population. This multifactorial disease is regulated via interoceptive neural circuits in the brain, whose alteration results in excessive body weight. Certain central neuronal populations in the brain are recognised as crucial nodes in energy homeostasis; in particular, the hypothalamic arcuate nucleus (ARC) region contains two peptide microcircuits that control energy balance with antagonistic functions: agouti-related peptide/neuropeptide-Y (AgRP/NPY) signals hunger and stimulates food intake; and pro-opiomelanocortin (POMC) signals satiety and reduces food intake. These neuronal peptides levels react to energy status and integrate signals from peripheral ghrelin, leptin, and insulin to regulate feeding and energy expenditure. To manage obesity comprehensively, it is crucial to understand cellular and molecular mechanisms of information processing in ARC neurons, since these regulate energy homeostasis. Importantly, a specific strategy focusing on ARC circuits needs to be devised to assist in treating obese patients and maintaining weight loss with minimal or no side effects. The aim of this review is to elucidate the recent developments in the study of AgRP-, NPY- and POMC-producing neurons, specific to their role in controlling metabolism. The impact of ghrelin, leptin, and insulin signalling via action of these neurons is also surveyed, since they also impact energy balance through this route. Lastly, we present key proteins, targeted genes, compounds, drugs, and therapies that actively work via these neurons and could potentially be used as therapeutic targets for treating obesity conditions.

Targeting the Gut in Obesity: Signals from the Inner Surface

Obesity is caused by prolonged energy surplus. Current anti-obesity medications are mostly centralized around the energy input part of the energy balance equation by increasing satiety and reducing appetite. Our gastrointestinal tract is a key organ for regulation of food intake and supplies a tremendous number of circulating signals that modulate the activity of appetite-regulating areas of the brain by either direct interaction or through the vagus nerve. Intestinally derived messengers are manifold and include absorbed nutrients, microbial metabolites, gut hormones and other enterokines, collectively comprising a fine-tuned signalling system to the brain. After a meal, nutrients directly interact with appetite-inhibiting areas of the brain and induce satiety. However, overall feeding behaviour also depends on secretion of gut hormones produced by highly specialized and sensitive enteroendocrine cells. Moreover, circulating microbial metabolites and their interactions with enteroendocrine cells further contribute to the regulation of feeding patterns. Current therapies exploiting the appetite-regulating properties of the gut are based on chemically modified versions of the gut hormone, glucagon-like peptide-1 (GLP-1) or on inhibitors of the primary GLP-1 inactivating enzyme, dipeptidyl peptidase-4 (DPP-4). The effectiveness of these approaches shows that that the gut is a promising target for therapeutic interventions to achieve significant weigh loss. We believe that increasing understanding of the functionality of the intestinal epithelium and new delivery systems will help develop selective and safe gut-based therapeutic strategies for improved obesity treatment in the future. Here, we provide an overview of the major homeostatic appetite-regulating signals generated by the intestinal epithelial cells and how these signals may be harnessed to treat obesity by pharmacological means.

The PACAP/PAC1 Receptor System and Feeding

Pituitary adenylyl cyclase activating polypeptide (PACAP) belongs to the vasoactive intestinal polypeptide (VIP)/secretin/glucagon superfamily. PACAP is present in two forms (PACAP-38 and PACAP-27) and binds to three guanine-regulatory (G) protein-coupled receptors (PAC1, VPAC1, and VPAC2). PACAP is expressed in the central and peripheral nervous systems, with high PACAP levels found in the hypothalamus, a brain region involved in feeding and energy homeostasis. PAC1 receptors are high-affinity and PACAP-selective receptors, while VPAC1 and VPAC2 receptors show a comparable affinity to PACAP and VIP. PACAP and its receptors are expressed in the central and peripheral nervous systems with moderate to high expression in the hypothalamus, amygdala, and other limbic structures. Consistent with their expression, PACAP is involved in several physiological responses and pathological states. A growing body of literature suggests that PACAP regulates food intake in laboratory animals. However, there is no comprehensive review of the literature on this topic. Thus, the purpose of this article is to review the literature regarding the role of PACAP and its receptors in food intake regulation and to synthesize how PACAP exerts its anorexic effects in different brain regions. To achieve this goal, we searched PubMed and reviewed 68 articles regarding the regulatory action of PACAP on food intake. Here, we present the literature regarding the effect of exogenous PACAP on feeding and the role of endogenous PACAP in this process. We also provide evidence regarding the effect of PACAP on the homeostatic and hedonic aspects of food intake, the neuroanatomical sites where PACAP exerts its regulatory action, which PACAP receptors may be involved, and the role of various signaling pathways and neurotransmitters in hypophagic effects of PACAP.

The Brain's Reward System in Health and Disease

Rhythmic gene expression is found throughout the central nervous system. This harmonized regulation can be dependent on- and independent of- the master regulator of biological clocks, the suprachiasmatic nucleus (SCN). Substantial oscillatory activity in the brain's reward system is regulated by dopamine. While light serves as a primary time-giver (zeitgeber) of physiological clocks and synchronizes biological rhythms in 24-h cycles, nonphotic stimuli have a profound influence over circadian biology. Indeed, reward-related activities (e.g., feeding, exercise, sex, substance use, and social interactions), which lead to an elevated level of dopamine, alters rhythms in the SCN and the brain's reward system. In this chapter, we will discuss the influence of the dopaminergic reward pathways on circadian system and the implication of this interplay on human health.

A hypothalamomedullary network for physiological responses to environmental stresses

Various environmental stressors, such as extreme temperatures (hot and cold), pathogens, predators and insufficient food, can threaten life. Remarkable progress has recently been made in understanding the central circuit mechanisms of physiological responses to such stressors. A hypothalamomedullary neural pathway from the dorsomedial hypothalamus (DMH) to the rostral medullary raphe region (rMR) regulates sympathetic outflows to effector organs for homeostasis. Thermal and infection stress inputs to the preoptic area dynamically alter the DMH → rMR transmission to elicit thermoregulatory, febrile and cardiovascular responses. Psychological stress signalling from a ventromedial prefrontal cortical area to the DMH drives sympathetic and behavioural responses for stress coping, representing a psychosomatic connection from the corticolimbic emotion circuit to the autonomic and somatic motor systems. Under starvation stress, medullary reticular neurons activated by hunger signalling from the hypothalamus suppress thermogenic drive from the rMR for energy saving and prime mastication to promote food intake. This Perspective presents a combined neural network for environmental stress responses, providing insights into the central circuit mechanism for the integrative regulation of systemic organs.

Cancer as a homeostatic challenge: the role of the hypothalamus

The initiation, progression, and metastatic spread of cancer elicits diverse changes in systemic physiology. In this way, cancer represents a novel homeostatic challenge to the host system. Here, we discuss how the hypothalamus, a critical brain region involved in homeostasis senses, integrates and responds to cancer-induced changes in physiology. Through this lens, cancer-associated changes in behavior (e.g., sleep disruption) and physiology (e.g., glucocorticoid dysregulation) can be viewed as the result of an inability to re-establish homeostasis. We provide examples at each level (receptor sensing, integration of systemic signals, and efferent regulatory pathways) of how homeostatic organization becomes disrupted across different cancers. Finally, we lay out predictions of this hypothesis and highlight outstanding questions that aim to guide further work in this area.

Deficiency of ER Ca2+ sensor STIM1 in AgRP neurons confers protection against dietary obesity

Store-operated calcium entry (SOCE) is pivotal in maintaining intracellular Ca2+ level and cell function; however, its role in obesity development remains largely unknown. Here, we show that the stromal interaction molecule 1 (Stim1), an endoplasmic reticulum (ER) Ca2+ sensor for SOCE, is critically involved in obesity development. Pharmacological blockade of SOCE in the brain, or disruption of Stim1 in hypothalamic agouti-related peptide (AgRP)-producing neurons (ASKO), significantly ameliorates dietary obesity and its associated metabolic disorders. Conversely, constitutive activation of Stim1 in AgRP neurons leads to an obesity-like phenotype. We show that the blockade of SOCE suppresses general translation in neuronal cells via the 2',5'-oligoadenylate synthetase 3 (Oas3)-RNase L signaling. While Oas3 overexpression in AgRP neurons protects mice against dietary obesity, deactivation of RNase L in these neurons significantly abolishes the effect of ASKO. These findings highlight an important role of Stim1 and SOCE in the development of obesity.

Onion component, isoalliin, stimulates feeding and activates the arcuate nucleus neuropeptide Y, ghrelin- and Ninjin'yoeito-responsive neurons

Appetite loss or anorexia substantially decreases the quality of life in patients with cancer, depression and gastrointestinal disorders, and can lead to sarcopenia and frailty. Foods that restore appetite have been sought-for but are not currently available. Historically, onion intake was adopted to treat a variety of diseases with reduced appetite including cancer and gastrointestinal disturbances. While isoalliin is a core component of onion, the effects of isoalliin on feeding behavior and feeding centers remain unknown. Neuropeptide Y (NPY) and ghrelin are the most potent central and peripheral inducers of appetite. A Japanese kampo medicine Ninjin'yoeito activates ghrelin-responsive NPY neurons in the hypothalamic arcuate nucleus (ARC) and counteracts anorexia induced by an anti-cancer drug cisplatin. This study explored the effects of isoalliin on feeding behavior and activities of ARC neurons in mice. Isoalliin, injected intraperitoneally, dose-dependently increased food intake during dark phase (DP) and daily without altering light phase (LP) food intake. We measured cytosolic Ca²⁺ concentration ([Ca²⁺]_i) in single ARC neurons including NPY neurons identified by GFP fluorescence. Isoalliin increased [Ca²⁺]_i in 10 of 18 (55.6%) NPY neurons, a majority of which also responded to ghrelin with [Ca²⁺]_i increases, indicating that the ARC ghrelin-responsive NPY neuron is the major target of isoalliin. Isoalliin also increased [Ca²⁺]_i in the ARC neurons that responded to Ninjin'yoeito. These results indicate that isoalliin enhances feeding at the active period and activates ARC ghrelin-responsive NPY neurons and Ninjin'yoeito-responsive neurons. These abilities of isoalliin to stimulate DP feeding and activate ARC orexigenic neurons provide scientific evidence for the health beneficial effects of onion experienced historically and globally.

Ghrelin treatment induces rapid and delayed increments of food intake: a heuristic model to explain ghrelin's orexigenic effects

Ghrelin is a stomach-derived peptide hormone with salient roles in the regulation of energy balance and metabolism. Notably, ghrelin is recognized as the most powerful known circulating orexigenic hormone. Here, we systematically investigated the effects of ghrelin on energy homeostasis and found that ghrelin primarily induces a biphasic effect on food intake that has indirect consequences on energy expenditure and nutrient partitioning. We also found that ghrelin-induced biphasic effect on food intake requires the integrity of Agouti-related peptide/neuropeptide Y-producing neurons of the hypothalamic arcuate nucleus, which seem to display a long-lasting activation after a single systemic injection of ghrelin. Finally, we found that different autonomic, hormonal and metabolic satiation signals transiently counteract ghrelin-induced food intake. Based on our observations, we propose a heuristic model to describe how the orexigenic effect of ghrelin and the anorectic food intake-induced rebound sculpt a timely constrain feeding response to ghrelin.

Contribution of Ghrelin to the Pathogenesis of Growth Hormone Deficiency

In this review we described the interactions between ghrelin and the growth hormone (GH)-insulin-like growth factor 1 (IGF-1) axis in children and adults with growth hormone deficiency (GHD). A possible involvement of these interactions in the pathogenesis of unexplained cases of GHD was suggested. Current research provides more and more details to the knowledge on the circadian rhythm of ghrelin. We gathered reports on the decreasing effect of Helicobacter pylori-related chronic gastritis on the number of ghrelin immunopositive cells and the consequent decrease in ghrelin serum concentration. The gastrointestinal tract microflora modification of the ghrelin action, by the mechanism of molecular mimicry, was also stressed. Moreover, the mutual relationships between ghrelin and the TSH-FT4/FT3 axis in growth and metabolic processes are described. It is to be recalled that FT4 and FT3 exert a permissive impact on IGF-1 action and, in turn, GH, in reaction mediated by IGF-1, enhances the monodeiodination of FT4 to FT3. Finally, we discussed the latest attempts to use the GH secretagogue receptor (GHS-R) analogues for possible diagnostic and therapeutic purposes.

The deletion of glucagon-like peptide-1 receptors expressing neurons in the dorsomedial hypothalamic nucleus disrupts the diurnal feeding pattern and induces hyperphagia and obesity

BACKGROUND

Feeding rhythm disruption contributes to the development of obesity. The receptors of glucagon-like peptide-1 (GLP-1) are distributed in the wide regions of the brain. Among these regions, GLP-1 receptors (GLP-1R) are expressed in the dorsomedial hypothalamic nucleus (DMH) which are known to be associated with thermogenesis and circadian rhythm development. However, the physiological roles of GLP-1R expressing neurons in the DMH remain elusive.

METHODS

To examine the physiological role of GLP-1R expressing neurons in the DMH, saporin-conjugated exenatide4 was injected into rat brain DMH to delete GLP-1R-positive neurons. Subsequently, locomotor activity, diurnal feeding pattern, amount of food intake and body weight were measured.

RESULTS

This deletion of GLP-1R-positive neurons in the DMH induced hyperphagia, the disruption of diurnal feeding pattern, and obesity. The deletion of GLP-1R expressing neurons also reduced glutamic acid decarboxylase 67 and cholecystokinin A receptor mRNA levels in the DMH. Also, it reduced the c-fos expression after refeeding in the suprachiasmatic nucleus (SCN). Thirty percent of DMH neurons projecting to the SCN expressed GLP-1R. Functionally, refeeding after fasting induced c-fos expression in the SCN projecting neurons in the DMH. As for the projection to the DMH, neurons in the nucleus tractus solitarius (NTS) were found to be projecting to the DMH, with 33% of those neurons being GLP-1-positive. Refeeding induced c-fos expression in the DMH projecting neurons in the NTS.

CONCLUSION

These findings suggest that GLP-1R expressing neurons in the DMH may mediate feeding termination. In addition, this meal signal may be transmitted to SCN neurons and change the neural activities.

The regulation of food intake by insulin in the central nervous system

Food intake and energy expenditure are regulated by peripheral signals providing feedback on nutrient status and adiposity to the central nervous system. One of these signals is the pancreatic hormone, insulin. Unlike peripheral administration of insulin, which often causes weight gain, central administration of insulin leads to a reduction in food intake and body weight when administered long-term. This is a result of feedback processes in regions of the brain that regulate food intake. Within the hypothalamus, the arcuate nucleus (ARC) contains subpopulations of neurones that produce orexinergic neuropeptides agouti-related peptide (AgRP)/neuropeptide Y (NPY) and anorexigenic neuropeptides, pro-opiomelanocortin (POMC)/cocaine- and amphetamine-regulated transcript (CART). Intracerebroventricular infusion of insulin down-regulates the expression of AgRP/NPY at the same time as up-regulating expression of POMC/CART. Recent evidence suggests that insulin activity within the amygdala may play an important role in regulating energy balance. Insulin infusion into the central nucleus of the amygdala (CeA) can decrease food intake, possibly by modulating activity of NPY and other neurone subpopulations. Insulin signalling within the CeA can also influence stress-induced obesity. Overall, it is evident that the CeA is a critical target for insulin signalling and the regulation of energy balance.

Ghrelin-Mediated Regeneration and Plasticity After Nervous System Injury

The nervous system is highly vulnerable to different factors which may cause injury followed by an acute or chronic neurodegeneration. Injury involves a loss of extracellular matrix integrity, neuronal circuitry disintegration, and impairment of synaptic activity and plasticity. Application of pleiotropic molecules initiating extracellular matrix reorganization and stimulating neuronal plasticity could prevent propagation of the degeneration into the tissue surrounding the injury. To find an omnipotent therapeutic molecule, however, seems to be a fairly ambitious task, given the complex demands of the regenerating nervous system that need to be fulfilled. Among the vast number of candidates examined so far, the neuropeptide and hormone ghrelin holds within a very promising therapeutic potential with its ability to cross the blood-brain barrier, to balance metabolic processes, and to stimulate neurorepair and neuroactivity. Compared with its well-established systemic effects in treatment of metabolism-related disorders, the therapeutic potential of ghrelin on neuroregeneration upon injury has received lesser appreciation though. Here, we discuss emerging concepts of ghrelin as an omnipotent player unleashing developmentally related molecular cues and morphogenic cascades, which could attenuate and/or counteract acute and chronic neurodegeneration.

Cortical Transcriptomic Alterations in Association With Appetitive Neuropeptides and Body Mass Index in Posttraumatic Stress Disorder

BACKGROUND

The molecular pathology underlying posttraumatic stress disorder (PTSD) remains unclear mainly due to a lack of human PTSD postmortem brain tissue. The orexigenic neuropeptides ghrelin, neuropeptide Y, and hypocretin were recently implicated in modulating negative affect. Drawing from the largest functional genomics study of human PTSD postmortem tissue, we investigated whether there were molecular changes of these and other appetitive molecules. Further, we explored the interaction between PTSD and body mass index (BMI) on gene expression.

METHODS

We analyzed previously reported transcriptomic data from 4 prefrontal cortex regions from 52 individuals with PTSD and 46 matched neurotypical controls. We employed gene co-expression network analysis across the transcriptomes of these regions to uncover PTSD-specific networks containing orexigenic genes. We utilized Ingenuity Pathway Analysis software for pathway annotation. We identified differentially expressed genes (DEGs) among individuals with and without PTSD, stratified by sex and BMI.

RESULTS

Three PTSD-associated networks (P < .01) contained genes in signaling families of appetitive molecules: 2 in females and 1 in all subjects. We uncovered DEGs (P < .05) between PTSD and control subjects stratified by sex and BMI with especially robust changes in males with PTSD with elevated vs normal BMI. Further, we identified putative upstream regulators (P < .05) driving these changes, many of which were enriched for involvement in inflammation.

CONCLUSIONS

PTSD-associated cortical transcriptomic modules contain transcripts of appetitive genes, and BMI further interacts with PTSD to impact expression. DEGs and inferred upstream regulators of these modules could represent targets for future pharmacotherapies for obesity in PTSD.

The ups and downs of growth hormone secretagogue receptor signaling

The growth hormone secretagogue receptor (GHSR) has emerged as one of the most fascinating molecules from the perspective of neuroendocrine control. GHSR is mainly expressed in the pituitary and the brain, and plays key roles regulating not only growth hormone secretion but also food intake, adiposity, body weight, glucose homeostasis and other complex functions. Quite atypically, GHSR signaling displays a basal constitutive activity that can be up- or downregulated by two digestive system-derived hormones: the octanoylated-peptide ghrelin and the liver-expressed antimicrobial peptide 2 (LEAP2), which was recently recognized as an endogenous GHSR ligand. The existence of two ligands with contrary actions indicates that GHSR activity can be tightly regulated and that the receptor displays the capability to integrate such opposing inputs in order to provide a balanced intracellular signal. This article provides a summary of the current understanding of the biology of ghrelin, LEAP2 and GHSR and discusses the reconceptualization of the cellular and physiological implications of the ligand-regulated GHSR signaling, based on the latest findings.

LEAP-2: An Emerging Endogenous Ghrelin Receptor Antagonist in the Pathophysiology of Obesity

Liver-expressed antimicrobial peptide 2 (LEAP-2), originally described as an antimicrobial peptide, has recently been recognized as an endogenous blocker of growth hormone secretagogue receptor 1a (GHS-R1a). GHS-R1a, also known as ghrelin receptor, is a G protein-coupled receptor (GPCR) widely distributed on the hypothalamus and pituitary gland where it exerts its major functions of regulating appetite and growth hormone (GH) secretion. The activity of GHS-R1a is controlled by two counter-regulatory endogenous ligands: Ghrelin (activation) and LEAP-2 (inhibition). Ghrelin activates GHS-R1a on the neuropeptide Y/Agouti-related protein (NPY/AgRP) neurons at the arcuate nucleus (ARC) to promote appetite, and on the pituitary somatotrophs to stimulate GH release. On the flip side, LEAP-2, acts both as an endogenous competitive antagonist of ghrelin and an inverse agonist of constitutive GHS-R1a activity. Such a biological property of LEAP-2 vigorously blocks ghrelin's effects on food intake and hormonal secretion. In circulation, LEAP-2 displays an inverse pattern as to ghrelin; it increases with food intake and obesity (positive energy balance), whereas decreases upon fasting and weight loss (negative energy balance). Thus, the LEAP-2/ghrelin molar ratio fluctuates in response to energy status and modulation of this ratio conversely influences energy intake. Inhibiting ghrelin's activity has shown beneficial effects on obesity in preclinical experiments, which sheds light on LEAP-2's anti-obesity potential. In this review, we will analyze LEAP-2's effects from a metabolic point of view with a focus on metabolic hormones (e.g., ghrelin, GH, and insulin), and discuss LEAP-2's potential as a promising therapeutic target for obesity.

Acylated Ghrelin as a Multi-Targeted Therapy for Alzheimer's and Parkinson's Disease

Much thought has been given to the impact of Amyloid Beta, Tau and Alpha-Synuclein in the development of Alzheimer's disease (AD) and Parkinson's disease (PD), yet the clinical failures of the recent decades indicate that there are further pathological mechanisms at work. Indeed, besides amyloids, AD and PD are characterized by the culminative interplay of oxidative stress, mitochondrial dysfunction and hyperfission, defective autophagy and mitophagy, systemic inflammation, BBB and vascular damage, demyelination, cerebral insulin resistance, the loss of dopamine production in PD, impaired neurogenesis and, of course, widespread axonal, synaptic and neuronal degeneration that leads to cognitive and motor impediments. Interestingly, the acylated form of the hormone ghrelin has shown the potential to ameliorate the latter pathologic changes, although some studies indicate a few complications that need to be considered in the long-term administration of the hormone. As such, this review will illustrate the wide-ranging neuroprotective properties of acylated ghrelin and critically evaluate the hormone's therapeutic benefits for the treatment of AD and PD.

The timing of fasting leads to different levels of food consumption and PYY3-36 in nocturnal mice

PURPOSE

The daily circadian cycle is known to modulate both feeding behavior and metabolism. As such, the timing of food consumption can play a role in regulating overall health. The purpose of this study is to determine whether fasting at different times of the day alters subsequent food consumption and levels of PYY_3-36, a hormone secreted after a meal which inhibits appetite.

METHODS

Separate groups of mice were fasted at different times of the day: (1) start of the day, (2) middle of the day, (3) start of the night, and (4) middle of the night, and either injected with vehicle or PYY_3-36 to assess their subsequent food consumption patterns, PYY_3-36 levels, and glucose and insulin levels. We also investigated whether light exposure during the night would alter food consumption and PYY_3-36 levels after fasting.

RESULTS

Mice fasted during the start of the daytime exhibited increased food consumption post-fast compared to mice fasted during the night. Injections of PYY_3-36 during the night were more effective in reducing food consumption compared to PYY_3-36 administration during the day. Constant light exposure suppressed food consumption after fasting and increased fasting PYY_3-36 levels.

CONCLUSIONS

These results indicate that mice exhibit distinct food consumption patterns after being presented with a fast at different times of the day. Light exposure also modulates both food consumption after a fast and levels of PYY_3-36.

The Potential Roles of Ghrelin in Metabolic Syndrome and Secondary Symptoms of Alzheimer's Disease

Although the major causative factors of Alzheimer's disease (AD) are the accumulation of amyloid β and hyperphosphorylated tau, AD can also be caused by metabolic dysfunction. The major clinical symptom of AD is cognitive dysfunction. However, AD is also accompanied by various secondary symptoms such as depression, sleep-wake disturbances, and abnormal eating behaviors. Interestingly, the orexigenic hormone ghrelin has been suggested to have beneficial effects on AD-related metabolic syndrome and secondary symptoms. Ghrelin improves lipid distribution and alters insulin sensitivity, effects that are hypothesized to delay the progression of AD. Furthermore, ghrelin can relieve depression by enhancing the secretion of hormones such as serotonin, noradrenaline, and orexin. Moreover, ghrelin can upregulate the expression of neurotrophic factors such as brain-derived neurotrophic factor and modulate the release of proinflammatory cytokines such as tumor necrosis factor α and interleukin 1β. Ghrelin alleviates sleep-wake disturbances by increasing the levels of melatonin, melanin-concentrating hormone. Ghrelin reduces the risk of abnormal eating behaviors by increasing neuropeptide Y and γ-aminobutyric acid. In addition, ghrelin increases food intake by inhibiting fatty acid biosynthesis. However, despite the numerous studies on the role of ghrelin in the AD-related pathology and metabolic disorders, there are only a few studies that investigate the effects of ghrelin on secondary symptoms associated with AD. In this mini review, our purpose is to provide the insights of future study by organizing the previous studies for the role of ghrelin in AD-related pathology and metabolic disorders.

Intracellular interplay between cholecystokinin and leptin signalling for satiety control in rats

Cholecystokinin (CCK) and leptin are satiety-controlling peptides, yet their interactive roles remain unclear. Here, we addressed this issue using in vitro and in vivo models. In rat C6 glioma cells, leptin pre-treatment enhanced Ca²⁺ mobilization by a CCK agonist (CCK-8s). This leptin action was reduced by Janus kinase inhibitor (AG490) or PI3-kinase inhibitor (LY294002). Meanwhile, leptin stimulation alone failed to mobilize Ca²⁺ even in cells overexpressing leptin receptors (C6-ObRb). Leptin increased nuclear immunoreactivity against phosphorylated STAT3 (pSTAT3) whereas CCK-8s reduced leptin-induced nuclear pSTAT3 accumulation in these cells. In the rat ventromedial hypothalamus (VMH), leptin-induced action potential firing was enhanced, whereas nuclear pSTAT3 was reduced by co-stimulation with CCK-8s. To further analyse in vivo signalling interplay, a CCK-1 antagonist (lorglumide) was intraperitoneally injected in rats following 1-h restricted feeding. Food access was increased 3-h after lorglumide injection. At this timepoint, nuclear pSTAT3 was increased whereas c-Fos was decreased in the VMH. Taken together, these results suggest that leptin and CCK receptors may both contribute to short-term satiety, and leptin could positively modulate CCK signalling. Notably, nuclear pSTAT3 levels in this experimental paradigm were negatively correlated with satiety levels, contrary to the generally described transcriptional regulation for long-term satiety via leptin receptors.

Ninjin'yoeito Targets Distinct Ca2+ Channels to Activate Ghrelin-Responsive vs. Unresponsive NPY Neurons in the Arcuate Nucleus

Appetite loss or anorexia substantially deteriorates quality of life in various diseases, and stand upstream of frailty. Neuropeptide Y (NPY) in the hypothalamic arcuate nucleus (ARC) and ghrelin released from stomach are potent inducers of appetite. We previously reported that Ninjin'yoeito, a Japanese kampo medicine comprising twelve herbs, restores food intake, and body weight in cisplatin-treated anorectic mice. Furthermore, Ninjin'yoeito increased cytosolic Ca²⁺ concentration ([Ca²⁺]_i) in not only ghrelin-responsive but ghrelin-unresponsive NPY neurons in ARC. The cellular lineage/differentiation of ghrelin-unresponsive neuron is less defined but might alter along with aging and diet. This study examined the occupancy of ghrelin-unresponsive neurons among ARC NPY neurons in adult mice fed normal chow, and explored the mechanisms underlying Ninjin'yoeito-induced [Ca²⁺]_i increases in ghrelin-unresponsive vs. ghrelin-responsive NPY neurons. Single ARC neurons were subjected to [Ca²⁺]_i measurement and subsequent immunostaining for NPY. Ghrelin failed to increase [Ca²⁺]_i in 42% of ARC NPY neurons. Ninjin'yoeito (10 μg/ml)-induced increases in [Ca²⁺]_i were abolished in Ca²⁺ free condition in ghrelin-responsive and ghrelin-unresponsive ARC NPY neurons. Ninjin'yoeito-induced [Ca²⁺]_i increases were inhibited by N-type Ca²⁺ channel blocker ω-conotoxin in the majority (17 of 20), while by L-type Ca²⁺ channel blocker nitrendipine in the minority (2 of 23), of ghrelin-responsive neurons. In contrast, Ninjin'yoeito-induced [Ca²⁺]_i increases were inhibited by nitrendipine in the majority (14 of 17), while by ω-conotoxin in the minority (8 of 24), of ghrelin-unresponsive neurons. These results indicate that ghrelin-unresponsive neurons occur substantially among NPY neurons of ARC in adult mice fed normal chow. Ninjin'yoeito preferentially target N-type and L-type Ca²⁺ channels in the majority of ghrelin-responsive and ghrelin-unresponsive neurons, respectively, to increase [Ca²⁺]_i. We suggest ARC N- and L-type Ca²⁺ channels as potential targets for activating, respectively, ghrelin-responsive, and unresponsive NPY neurons to treat anorexia.

Variation analysis of Ghrelin gene in Chinese patients with obesity, having polycystic ovarian syndrome

Association of single-nucleotide polymorphisms (SNPs) of the ghrelin gene with polycystic ovary syndrome (PCOS)is unclear. However, their correlation with PCOS-related obesity has been observed. The objective of this study was to evaluate the effects of ghrelin gene SNPs on PCOS-related obesity in Chinese women. The full-length sequence of the ghrelin gene was determined to explore the relationship of the SNPs with PCOS-related obesity in Chinese women. The gene was sequenced, including all exons, introns and exon-intron boundaries in 230 Han Chinese women with PCOS and 162 normal women. Significant genotypic and allelic differences were observed between the obese PCOS group and obese control group at rs35681 locus (p = .013 and .017). The genotypic analysis of obese and non-obese people in the PCOS group showed that the proportion of A allele in the obese PCOS group (10.9%) was higher than that of the G allele (3.6%). This study revealed that ghrelin rs35681 might be related to the occurrence of obesity associated with PCOS, and allele A was found to increase the risk of obesity in PCOS.

Effects of metabolic state on the regulation of melanocortin circuits

Dysfunction in neurophysiological systems that regulate food intake and metabolism are at least partly responsible for obesity and related comorbidities. An important component of this process is the hypothalamic melanocortin system, where an imbalance can result in severe obesity and deficits in glucose metabolism. Exercise offers many health benefits related to cardiovascular improvements, hunger control, and blood glucose homeostasis. However, the molecular mechanism underlying the exercise-induced improvements to the melanocortin system remain undefined. Here, we review the role of the melanocortin system to sense hormonal, nutrient, and neuronal signals of energy status. This information is then relayed onto secondary neurons in order to regulate physiological parameters, which promote proper energy and glucose balance. We also provide an overview on the effects of physical exercise to induce biophysical changes in the melanocortin circuit which may regulate food intake, glucose metabolism and improve overall metabolic health.

Effects of neuropeptide Y on the microvasculature of human skeletal muscle

BACKGROUND

Neuropeptide Y acts directly on the vasculature as a cotransmitter with norepinephrine for an augmented contraction. Little, however, is known about the effects of neuropeptide Y on the microvasculature of human skeletal muscle. Neuropeptide Y signaling has not been studied in the setting of cardiac surgery and cardiopulmonary bypass. We investigated the role of neuropeptide Y signaling on vasomotor tone in the microvessels of human skeletal muscle, as well as the effect of cardiopulmonary bypass on neuropeptide Y-induced responsiveness.

METHODS

Specimens taken from intercostal muscles were collected from patients, pre- and post-cardiopulmonary bypass, undergoing coronary artery bypass grafting or cardiac valve surgery (n = 8/group). Microvessels (157 ± 47 microns) were isolated in vitro in a no-flow state. Arterial microvascular responses to a neuropeptide Y agonist, a Y1 receptor antagonist, phenylephrine, and the coadministration of neuropeptide Y and phenylephrine were examined. The abundance and localization of the Y1 receptor were measured using Western blot and immunofluorescence, respectively.

RESULTS

Arterial microvessels showed responsiveness to the neuropeptide Y agonist (10^-9 to 4 × 10^-7 mol/L) both before and after cardiopulmonary bypass, reaching a 12.5% vasoconstriction from the baseline luminal diameter. With administration of the Y1 receptor antagonist after neuropeptide Y, the contractile response was eliminated (n = 3/group, P = .04). No difference in vasoconstriction was observed between pre- and post-cardiopulmonary bypass groups (P = .73). The coadministration of neuropeptide Y and phenylephrine (10^-9 to 10^-4 mol/L) elicited no difference in vasoconstriction (n = 7/group, P = .06 both pre- and post-cardiopulmonary bypass) when compared with phenylephrine alone (10^-9 to 10^-4 mol/L). No change in the protein expression or localization of the Y1 receptor was detected by Western blotting (n = 6/group, P = .44) or immunofluorescence (n = 6/group, P = .13).

CONCLUSION

Neuropeptide Y induced vasoconstriction, suggesting that neuropeptide Y may play an important role in the regulation of the peripheral microvasculature. There was no change in microvascular responsiveness to neuropeptide Y after cardiopulmonary bypass nor were there any synergistic effects of neuropeptide Y on phenylephrine-induced vasoconstriction in the skeletal muscle microvasculature.

Sirtuin-1 regulates organismal growth by altering feeding behavior and intestinal morphology in planarians

Nutrient availability upon feeding leads to an increase in body size in the planarian Schmidtea mediterranea However, it remains unclear how food consumption integrates with cell division at the organismal level. Here, we show that the NAD-dependent protein deacetylases sirtuins are evolutionarily conserved in planarians, and specifically demonstrate that the homolog of human sirtuin-1 (SIRT1) (encoded by Smed-Sirt-1), regulates organismal growth by impairing both feeding behavior and intestinal morphology. Disruption of Smed-Sirt-1 with RNAi or pharmacological inhibition of Sirtuin-1 leads to reduced animal growth. Conversely, enhancement of Sirtuin-1 activity with resveratrol accelerates growth. Differences in growth rates were associated with changes in the amount of time taken to locate food and overall food consumption. Furthermore, Smed-Sirt-1(RNAi) animals displayed reduced cell death and increased stem cell proliferation accompanied by impaired expression of intestinal lineage progenitors and reduced branching of the gut. Taken together, our findings indicate that Sirtuin-1 is a crucial metabolic hub capable of controlling animal behavior, tissue renewal and morphogenesis of the adult intestine.

17β-Estradiol Increases Arcuate KNDy Neuronal Sensitivity to Ghrelin Inhibition of the M-Current in Female Mice

Obesity and anorexia result in dysregulation of the hypothalamic-pituitary-gonadal axis, negatively impacting reproduction. Ghrelin, secreted from the stomach, potentially mediates negative energy states and neuroendocrine control of reproduction by acting through the growth hormone secretagogue receptor (GHSR). GHSR is expressed in hypothalamic arcuate (ARC) Kisspeptin/Neurokinin B (Tac2)/Dynorphin (KNDy) neurons. Ghrelin is known to inhibit the M-current produced by KCNQ channels in other ARC neurons. In addition, we have shown 17β-estradiol (E2) increases Ghsr expression in KNDy neurons 6-fold and increases the M-current in NPY neurons. We hypothesize that E2 increases GHSR expression in KNDy neurons to increase ghrelin sensitivity during negative energy states. Furthermore, we suspect ghrelin targets the M-current in KNDy neurons to control reproduction and energy homeostasis. We utilized ovariectomized Tac2-EGFP adult female mice, pretreated with estradiol benzoate (EB) or oil vehicle and performed whole-cell-patch-clamp recordings to elicit the M-current in KNDy neurons using standard activation protocols in voltage-clamp. Using the selective KCNQ channel blocker XE-991 (40 µM) to target the M-current, oil- and EB-treated mice showed a decrease in the maximum peak current by 75.7 ± 13.8 pA (n = 10) and 68.0 ± 14.7 pA (n = 11), respectively. To determine the actions of ghrelin on the M-current, ghrelin was perfused (100 nM) in oil- and EB-treated mice resulting in the suppression of the maximum peak current by 58.5 ± 15.8 pA (n = 9) and 59.2 ± 11.9 pA (n = 9), respectively. KNDy neurons appeared more sensitive to ghrelin when pretreated with EB, revealing that ARC KNDy neurons are more sensitive to ghrelin during states of high E2.

Ghrelin-Induced Sodium Reabsorption Is Mediated by PKA and Microtubule-Dependent αENaC Translocation in Female Rats

Intrarenal ghrelin infusion activates ghrelin receptors in the kidney collecting duct (CD) to increase α epithelial sodium (Na⁺) channel (αE_NaC)-dependent Na⁺ reabsorption in vivo, but the underlying mechanisms are unknown. Seventy-two hours following uninephrectomy, 12-week-old female Sprague-Dawley rats received the following renal interstitial (RI) infusions for 1 hour after a 1-hour control: vehicle (n = 10), ghrelin (3 μg/minute; n = 8), ghrelin + phosphatidylinositol 3-kinase (PI3K) inhibitor LY-294002 (0.1 μg/kg/minute; n = 7), ghrelin + protein kinase A (PKA) inhibitor adenosine 3'5'-cyclic monophosphorothioate, Rp-isomer (10 μg/kg/minute; n = 8), ghrelin + microtubule polymerization inhibitor nocodazole (0.3 μg/kg/minute; n = 7), or ghrelin + actin polymerization inhibitor cytochalasin D (0.3 μg/kg/minute; n = 6). Compared with vehicle infusion, RI ghrelin induced a significant anti-natriuresis (urine Na⁺ excretion was reduced by 53.7% ± 6.8%; P < 0.001). This effect was abolished during concomitant PKA or microtubule inhibition (106.4% ± 9.4% and 109.7% ± 10.6% of vehicle infusion, respectively; P < 0.01 from ghrelin) but not during concomitant PI3K or actin inhibition (reduced by 48.6% ± 3.9% and 52.8% ± 12.7%, respectively; P < 0.001 and P < 0.01 from vehicle, respectively; P = not significant from ghrelin). Infusions had no effect on mean arterial pressure. Western blot analysis demonstrated that CD membrane but not total αE_NaC expression increased in response to ghrelin infusion compared with vehicle, (0.39 ± 0.05 vs 0.12 ± 0.02 arbitrary units; P < 0.01). This effect was abolished during PKA or microtubule inhibition but persisted during PI3K or actin inhibition. Neural precursor cell expressed, developmentally down-regulated 4 isoform 2 (Nedd4-2) dependent internalization of αE_NaC was not affected by ghrelin, indicating that microtubule-dependent forward trafficking of αE_NaC is necessary for anti-natriuretic responses to ghrelin. Taken together, these studies highlight the importance of PKA and microtubule polymerization in ghrelin-induced αE_NaC-mediated Na⁺ reabsorption.

Amyloid-Beta Modulates Low-Threshold Activated Voltage-Gated L-Type Calcium Channels of Arcuate Neuropeptide Y Neurons Leading to Calcium Dysregulation and Hypothalamic Dysfunction

Weight loss is an early manifestation of Alzheimer's disease that can precede the cognitive decline, raising the possibility that amyloid-β (Aβ) disrupts hypothalamic neurons critical for the regulation of body weight. We previously reported that, in young transgenic mice overexpressing mutated amyloid precursor protein (Tg2576), Aβ causes dysfunction in neuropeptide Y (NPY)-expressing hypothalamic arcuate neurons before plaque formation. In this study, we examined whether Aβ causes arcuate NPY neuronal dysfunction by disrupting intracellular Ca²⁺ homeostasis. Here, we found that the L-type Ca²⁺ channel blocker nimodipine could hyperpolarize the membrane potential, decrease the spontaneous activity, and reduce the intracellular Ca²⁺ levels in arcuate NPY neurons from Tg2576 brain slices. In these neurons, there was a shift from high to low voltage-threshold activated L-type Ca²⁺ currents, resulting in increased Ca²⁺ influx closer to the resting membrane potential, an effect recapitulated by Aβ_1-42 and reversed by nimodipine. These low voltage-threshold activated L-type Ca²⁺ currents were dependent in part on calcium/calmodulin-dependent protein kinase II and IP₃ pathways. Furthermore, the effects on intracellular Ca²⁺ signaling by both a positive (ghrelin) and negative (leptin) modulator were blunted in these neurons. Nimodipine pretreatment restored the response to ghrelin-mediated feeding in young (3-5 months), but not older (10 months), female Tg2576 mice, suggesting that intracellular Ca²⁺ dysregulation is only reversible early in Aβ pathology. Collectively, these findings provide evidence for a key role for low-threshold activated voltage gated L-type Ca²⁺ channels in Aβ-mediated neuronal dysfunction and in the regulation of body weight.SIGNIFICANCE STATEMENT Weight loss is one of the earliest manifestations of Alzheimer's disease (AD), but the underlying cellular mechanisms remain unknown. Disruption of intracellular Ca²⁺ homeostasis by amyloid-β is hypothesized to be critical for the early neuronal dysfunction driving AD pathogenesis. Here, we demonstrate that amyloid-β causes a shift from high to low voltage-threshold activated L-type Ca²⁺ currents in arcuate neuropeptide Y neurons. This leads to increased Ca²⁺ influx closer to the resting membrane potential, resulting in intracellular Ca²⁺ dyshomeostasis and neuronal dysfunction, an effect reversible by the L-type Ca²⁺ channel blocker nimodipine early in amyloid-β pathology. These findings highlight a novel mechanism of amyloid-β-mediated neuronal dysfunction through L-type Ca²⁺ channels and the importance of these channels in the regulation of body weight.