Systemic urocortin 2, but not urocortin 1 or stressin 1-A, suppresses feeding via CRF2 receptors without malaise and stress

Linking stress with urocortin in rats

The corticotropin-releasing factor neuropeptides (CRH and UCN-1,2,3), as well as spexin, contribute to the control of energy balance and limit food intake in mammals. However, the role of these neuropeptides in chronic variable stress remains unknown. The effect of chronic varied stress on circulating corticosterone levels and urocortin expression levels in the brains of experimental rats was studied in this study. Rats were subjected with 28 days long term stress protocol, end of stress protocol experimental and control animal organs isolated, brain urocorcortin-1,2,3 expression by RT-PCR and serum corticosterone by ELISA method. UCN levels in the brain were altered in rats subjected to prolonged varied stress. Furthermore, corticosterone levels were elevated as a result of the same urocortin expression pattern, indicating that urocortin expression is controlled by glucocorticoids via a glucocorticoid-responsive element (GRE). Thus, data shows that hypothalamus-pituitary-adrenal (HPA) axis, also known as the LHPA axis, and limbic system are both stimulated by stress, which is reflected in the form of elevated corticosterone levels, according to the genes UCN1, 2, and 3.

Aging Changes the Efficacy of Central Urocortin 2 to Induce Weight Loss in Rats

Middle-aged obesity and aging cachexia present healthcare challenges. Central responsiveness to body-weight-reducing mediators, e.g., to leptin, changes during aging in a way, which may promote middle-aged obesity and aging cachexia. Leptin is connected to urocortin 2 (Ucn2), an anorexigenic and hypermetabolic member of the corticotropin family. We aimed to study the role of Ucn2 in middle-aged obesity and aging cachexia. The food intake, body weight and hypermetabolic responses (oxygen consumption, core temperature) of male Wistar rats (3, 6, 12 and 18 months) were tested following intracerebroventricular injections of Ucn2. Following one central injection, Ucn2-induced anorexia lasted for 9 days in the 3-month, 14 days in the 6-month and 2 days in the 18-month group. Middle-aged 12-month rats failed to show anorexia or weight loss. Weight loss was transient (4 days) in the 3-month, 14 days in the 6-month and slight but long-lasting in the 18-month rats. Ucn2-induced hypermetabolism and hyperthermia increased with aging. The age-dependent changes in the mRNA expression of Ucn2 detected by RNAscope in the paraventricular nucleus correlated with the anorexigenic responsiveness. Our results show that age-dependent changes in Ucn2 may contribute to middle-aged obesity and aging cachexia. Ucn2 shows potential in the prevention of middle-aged obesity.

Corticotropin-releasing factor receptor agonists decrease interstitial cells of Cajal in murine colon

BACKGROUND

Peripheral corticotropin-releasing factor (CRF) has been reported to affect gastrointestinal motility through corticotropin-releasing factor receptor located in enteric nervous system (ENS), but less is known about of the relationship between peripheral CRF and interstitial cells of Cajal (ICC).

METHODS

Mice were intraperitoneally injected with CRF receptor agonists to determine their effects on colonic ICC. Chronic heterotypic stress (CHeS) was applied to mice to determine endogenous CRF-CRF receptor signaling on colonic ICC.

RESULTS

We found that stressin1, a selective CRF receptor 1 (CRF₁ ) agonist, significantly increased the expression of CRF₁ but had no effect on the expression of CRF₂ in the smooth muscles of murine colon. The protein expression of c-Kit, Anoctamin-1 (ANO1), and stem cell factor (SCF) in the colonic smooth muscles was significantly decreased in stressin1-treated mice. Accordingly, 2-(4-Chloro-2-methylphenoxy)-N'-(2-methoxybenzylidene) acetohydrazide (Ani 9), a selective ANO1 blocker, had a less significant inhibitory effect on CMMC in stressin1-treated mice compared to the saline-treated ones. Similarly, we also found that ICC and ANO1 were reduced in the colonic smooth muscles of mice by treatment with sauvagine (ip), a CRF₂ agonist. However, different with stressin1, sauvagine decreased the expression of CRF₂ besides increasing CRF₁ expression in the colonic smooth muscles. Similar results of CRF₁ and c-Kit expressions were also obtained from the colon of CHeS-treated mice.

CONCLUSION

All these results suggest that CRF may be involved in the abnormality of colonic motility through peripheral CRF₁ to decrease the number and function of ICC, which provides a potential target for treating stress-induced gastrointestinal motility disorder.

The Pituitary Adenylate Cyclase-Activating Polypeptide (PACAP) System of the Central Amygdala Mediates the Detrimental Effects of Chronic Social Defeat Stress in Rats

Many psychiatric diseases stem from an inability to cope with stressful events, as chronic stressors can precipitate or exacerbate psychopathologies. The neurobiological mechanisms underlying the response to chronic stress and the resulting anxiety states remain poorly understood. Stress neuropeptides in the extended amygdala circuitry mediate the behavioral response to stress, and hyperactivity of these systems has been hypothesized to be responsible for the emergence of persistent negative outcomes and for the pathogenesis of anxiety-related and trauma-related disorders. Pituitary adenylate cyclase-activating polypeptide (PACAP) and its receptor PAC1R are highly expressed within the central amygdala (CeA) and play a key role in stress regulation. Here, we used chronic social defeat stress (CSDS), a clinically relevant model of psychosocial stress that produces robust maladaptive behaviors in rodents. We found that 10 days of CSDS cause a significant increase in PACAP levels selectively in the CeA of rats, as well as an increase in PAC1R mRNA. Using a viral vector strategy, we found that PAC1R knock-down in the CeA attenuates the CSDS-induced body weight loss and prevents the CSDS-induced increase in anxiety-like behavior. Notably, CSDS animals display reduced basal corticosterone (CORT) levels and PAC1R knock-down in CeA further reduce them. Finally, the CeA PAC1R knock-down blocks the increase in corticotropin-releasing factor (CRF) immunoreactivity induced by CSDS in CeA. Our findings support the notion that the persistent activation of the PACAP-PAC1R system in the CeA mediates the behavioral outcomes of chronic psychosocial stress independently of the hypothalamic-pituitary-adrenal axis, perhaps via the recruitment of the CRF system.

Decreased excitability of leptin-sensitive anterior insula pyramidal neurons in a rat model of compulsive food demand

Compulsive eating is an overlapping construct with binge eating that shares many characteristics with substance use disorders. Compulsive eating may impact millions of Americans; presenting in some cases of binge eating disorders, overweight/obesity, and among individuals who have not yet been diagnosed with a recognized eating disorder. To study the behavioral and neurobiological underpinnings of compulsive eating, we employ a published rodent model using cyclic intermittent access to a palatable diet to develop a self-imposed binge-withdrawal cycle. Here, we further validated this model of compulsive eating in female Wistar rats, through the lens of behavioral economic analyses and observed heightened demand intensity, inelasticity and essential value as well as increased food-seeking during extinction. Using electrophysiological recordings in the anterior insular cortex, a region previously implicated in modulating compulsive-like eating in intermittent access models, we observed functional adaptations of pyramidal neurons. Within the same neurons, application of leptin led to further functional adaptations, suggesting a previously understudied, extrahypothalamic role of leptin in modulating feeding-related cortical circuits. Collectively, the findings suggest that leptin may modulate food-related motivation or decision-making via a plastic cortical circuit that is influenced by intermittent access to a preferred diet. These findings warrant further study of whether behavioral economics analysis of compulsive eating can impact disordered eating outcomes in humans and of the translational relevance of a leptin-sensitive anterior insular circuit implicated in these behaviors.

Characterization of a differential reinforcement of low rates of responding task in non-deprived male and female rats: Role of Sigma-1 receptors

Impulsive action can be defined as the inability to withhold a response and represents one of the dimensions of the broad construct impulsivity. Here, we characterized a modified differential reinforcement of low rates of responding (DRL) task developed in our laboratory, in which impulsive action is measured in ad libitum fed/watered subjects. Specifically, we first determined the effects of both sex and estrous cycle on impulsive action by systematically comparing male and estrous-synchronized female subjects. In addition, we evaluated the convergent validity of this modified DRL task by testing the effects of the D2R/5HT2AR antagonist, aripiprazole, and the noncompetitive NMDAR antagonist, MK-801. Finally, we tested the effects of the selective antagonist BD-1063 and agonist PRE-084 of Sigma-1 receptor (Sig-1R) on impulsive action using this modified DRL task. We found that female rats showed and increased inability to withhold a response when compared to males, and this effect was driven by the metestrus/diestrus phase of the estrous cycle. In addition, aripiprazole and MK-801 fully retained their capability to reduce and increase impulsive action, respectively. Finally, the selective Sig-1R antagonist, BD-1063 dose-dependently reduced the inability to withhold a response in both sexes, though more potently in female rats. In summary, we show that impulsive action, as measured in a modified DRL task which minimizes energy-homeostatic influences, is a function of both sex and estrous cycle. Furthermore, we validate the convergent validity of the task and provide evidence that Sig-1R antagonism may represent a novel pharmacological strategy to reduce impulsive action.

Gray areas: Neuropeptide circuits linking the Edinger-Westphal and Dorsal Raphe nuclei in addiction

The circuitry of addiction comprises several neural networks including the midbrain - an expansive region critically involved in the control of motivated behaviors. Midbrain nuclei like the Edinger-Westphal (EW) and dorsal raphe (DR) contain unique populations of neurons that synthesize many understudied neuroactive molecules and are encircled by the periaqueductal gray (PAG). Despite the proximity of these special neuron classes to the ventral midbrain complex and surrounding PAG, functions of the EW and DR remain substantially underinvestigated by comparison. Spanning approximately -3.0 to -5.2 mm posterior from bregma in the mouse, these various cell groups form a continuum of neurons that we refer to collectively as the subaqueductal paramedian zone. Defining how these pathways modulate affective behavioral states presents a difficult, yet conquerable challenge for today's technological advances in neuroscience. In this review, we cover the known contributions of different neuronal subtypes of the subaqueductal paramedian zone. We catalogue these cell types based on their spatial, molecular, connectivity, and functional properties and integrate this information with the existing data on the EW and DR in addiction. We next discuss evidence that links the EW and DR anatomically and functionally, highlighting the potential contributions of an EW-DR circuit to addiction-related behaviors. Overall, we aim to derive an integrated framework that emphasizes the contributions of EW and DR nuclei to addictive states and describes how these cell groups function in individuals suffering from substance use disorders. This article is part of the special Issue on 'Neurocircuitry Modulating Drug and Alcohol Abuse'.

The hypoxia response and nutritional peptides

Hypoxia controls metabolism at several levels, e.g., via mitochondrial ATP production, glucose uptake and glycolysis. Hence it is likely that hypoxia also affects the action and/or production of many peptide hormones linked to food intake and appetite control. Many of those are produced in the gastrointestinal tract, endocrine pancreas, adipose tissue, and selective areas in the brain which modulate and concert their actions. However, the complexity of the hypoxia response and the links to peptides/hormones involved in food intake and appetite control in the different organs are not well known. This review summarizes the role of the hypoxia response and its effects on major peptides linked to appetite regulation, nutrition and metabolism.

Insula to ventral striatal projections mediate compulsive eating produced by intermittent access to palatable food

Compulsive eating characterizes many binge-related eating disorders, yet its neurobiological basis is poorly understood. The insular cortex subserves visceral-emotional functions, including taste processing, and is implicated in drug craving and relapse. Here, via optoinhibition, we implicate projections from the anterior insular cortex to the nucleus accumbens as modulating highly compulsive-like food self-administration behaviors that result from intermittent access to a palatable, high-sucrose diet. We identified compulsive-like eating behavior in female rats through progressive ratio schedule self-administration and punishment-resistant responding, food reward tolerance and escalation of intake through 24-h energy intake and fixed-ratio operant self-administration sessions, and withdrawal-like irritability through the bottle brush test. We also identified an endocrine profile of heightened GLP-1 and PP but lower ghrelin that differentiated rats with the most compulsive-like eating behavior. Measures of compulsive eating severity also directly correlated to leptin, body weight and adiposity. Collectively, this novel model of compulsive-like eating symptoms demonstrates adaptations in insula-ventral striatal circuitry and metabolic regulatory hormones that warrant further study.

Progress in understanding the roles of Urocortin3 (UCN3) in the control of appetite from studies using animal models

Urocortin3 (UCN3), the newest member of corticotrophin releasing hormone (CRH) family polypeptides, is an anorexic factor discovered in 2001, which has a strong inhibitory effect on animal appetite regulation. UCN3 is widely distributed in various tissues of animals and has many biological functions. Based on the research progress of UCN3 on mammals and non-mammals, this paper summarized the discovery, tissue distribution, appetite regulation and mechanism of UCN3 in animals, in order to provide a reference for feeding regulation and growth in mammals and fish in further research and production.

UCN3 suppresses food intake in coordination with CCK and the CCK2R in Siberian sturgeon (Acipenser baerii)

Urocortin-3 (UCN3) as a brain-gut peptide inhibits food intake of animal, but the underlying mechanism is not clear. To explore the appetite mechanism about the action of UCN3 in fish, intraperitoneal injection of UCN3 with CCK8, Lorglumide (CCK1R antagonist) or LY225910 (CCK2R antagonist) were conducted. Siberian sturgeon administrated with UCN3 and CCK8 showed a drastic reduction in food intake. The anorectic effect of UCN3 was significantly blocked by LY225910, but not affected by Lorglumide. Furthermore, LY225910 could effectively reverse appetite factor mRNA expressions, including cck, pyy, cart, npy, ucn3, apelin and nucb2 in the whole brain, stomach and intestinum valvula, but Lorglumide could only partially reverse these effects, suggesting the anorectic effect of UCN3 may be primarily mediated CCK2R in Siberian sturgeon. This study indicates for the first time in fish that UCN3 may inhibit food intake in coordination with CCK and CCK2R.

Gut-Brain Neuroendocrine Signaling Under Conditions of Stress-Focus on Food Intake-Regulatory Mediators

The gut-brain axis represents a bidirectional communication route between the gut and the central nervous system comprised of neuronal as well as humoral signaling. This system plays an important role in the regulation of gastrointestinal as well as homeostatic functions such as hunger and satiety. Recent years also witnessed an increased knowledge on the modulation of this axis under conditions of exogenous or endogenous stressors. The present review will discuss the alterations of neuroendocrine gut-brain signaling under conditions of stress and the respective implications for the regulation of food intake.

The involvement of Rhopr-CRF/DH in feeding and reproduction in the blood-gorging insect Rhodnius prolixus

Rhodnius prolixus is a blood-gorging insect and a vector for human Chagas disease. The insect transmits the disease following feeding, when it excretes urine and feces contaminated with the Trypanosoma cruzi parasite. A corticotropin-releasing factor-like peptide acts as a diuretic hormone in R. prolixus (Rhopr-CRF/DH); however, its distribution throughout the insect's central nervous system (CNS) and the expression of its receptor in feeding-related tissue as well as the female reproductive system suggests a multifaceted role for the hormone beyond that of diuresis. Here we investigate the involvement of Rhopr-CRF/DH in feeding and reproduction in R. prolixus. Immunohistochemistry of the CNS showed diminished CRF-like staining in neurosecretory cells (NSCs) of the mesothoracic ganglionic mass (MTGM) immediately following feeding, and partial restocking of those same cells two hours later, indicating Rhopr-CRF/DH stores in this regions are involved in feeding. The results of the temporal qPCR analysis were consistent with the immunohistochemical findings, showing an increase in Rhopr-CRF/DH transcript expression in the MTGM immediately after feeding, presumably capturing the restocking of Rhopr-CRF/DH in the lateral NSCs following release of the peptide during feeding. Elevating haemolymph Rhopr-CRF/DH titres by injection of Rhopr-CRF/DH prior to feeding resulted in the intake of a significantly smaller blood meal in 5th instars and adults without an apparent effect on the rate of short-term diuresis. When adult females were injected with Rhopr-CRF/DH, they also produced and laid significantly fewer eggs. Finally, in vitro oviduct contraction assays illustrate that Rhopr-CRF/DH inhibits the amplitude of contractions of the lateral oviducts, highlighting a potential mechanism via which the hormone diminishes reproductive capacity. To conclude, the study of the Rhopr-CRF/DH pathway, its components and mechanisms of action, has implications for vector control by highlighting targets to alter feeding, diuresis, and reproduction of this disease vector.

Regulation of gonadotropins by urocortin 2 in gonadotropic tumor LβT2 cells

A close interaction has been shown between the hypothalamo-pituitary-gonadal axis and the hypothalamic-pituitary-adrenal axis. Urocortin 2 (Ucn2) has a very high affinity for the corticotropin-releasing factor (CRF) type 2 (CRF₂) receptor. Pituitary Ucn2 regulates expression and secretion of gonadotropins in response to stress. The CRF₂ receptor in the pituitary contributes to the modulation of gonadotropins. To explore the possible function of Ucn2 and the CRF₂ receptor in pituitary gonadotropic tumor cells, we examined the direct regulation of gonadotropins by Ucn2 in a representative pituitary gonadotropic tumor, mouse LβT2 cells. LβT2 cells were found to express CRF₁ receptor and CRF₂ receptor mRNA. Ucn2 decreased CRF₁ receptor mRNA levels, while it increased CRF₂ receptor mRNA levels. Ucn2 directly decreased the mRNA levels of both luteinizing hormone (LH) and follicle-stimulating hormone (FSH) in LβT2 cells. Ucn2 also decreased gonadotropin-releasing hormone receptor (GnRHR) mRNA levels. A selective CRF₂ receptor antagonist suppressed the Ucn2-induced decreases in LH, FSH, and GnRHR mRNA levels. Ucn2 acts on gonadotrophs expressing the CRF₂ receptor, and inhibits the production of gonadotropins in the pituitary gonadotropic tumor cells. (177 words).

Intraperitoneal injection urocortin-3 reduces the food intake of Siberian sturgeon (Acipenser baerii)

Urocortin-3 (UCN3), one of the corticotropin releasing factor (CRF) family peptides, which was discovered in 2001, has a variety of biological functions. However, the researches of UCN3 in fish were scarce. In order to understand whether UCN3 play a role in regulating food intake in fish, we first cloned the ucn3 cDNAs sequence of Siberian sturgeon (Acipenser baerii Brandt), and investigated the ucn3 mRNA levels in 11 tissues. The Siberian sturgeon ucn3 cDNA sequence was 1044bp, including an open reading frame (ORF) of 447bp that encoded 148 amino acids with a mature peptide of 40 amino acids, a 5'-terminal untranslated region (5'-UTR) of 162bp and a 3'-terminal untranslated region (3'-UTR) of 435bp. The result of tissue distribution showed that ucn3 widely distributed in 11 tissues with highest expression in brain. We also assessed the effects of periprandial (pre- and post-feeding), fasting and re-feeding on ucn3 mRNAs abundance in brain. The results showed the expression of ucn3 mRNA in brain was significantly elevated after feeding, decreased after fasting 17 days and increased after re-feeding. To further investigate the food intake role of UCN3 in Siberian sturgeon, we performed intraperitoneal (i.p.) injection of Siberian sturgeon UCN3 (SsUCN3) with three doses (60, 120 or 240ng/g) and recorded the food intake. Acute and chronic i.p. injection SsUCN3 reduced the food intake in a dose-dependent pattern. In conclusion, this study indicates that SsUCN3 acts as a satiety factor to inhibit the food intake of Siberian sturgeon.

Energetic stress: The reciprocal relationship between energy availability and the stress response

The worldwide epidemic of metabolic syndromes and the recognized burden of mental health disorders have driven increased research into the relationship between the two. A maladaptive stress response is implicated in both mental health disorders and metabolic disorders, implicating the hypothalamic-pituitary-adrenal (HPA) axis as a key mediator of this relationship. This review explores how an altered energetic state, such as hyper- or hypoglycemia, as may be manifested in obesity or diabetes, affects the stress response and the HPA axis in particular. We propose that changes in energetic state or energetic demands can result in "energetic stress" that can, if prolonged, lead to a dysfunctional stress response. In this review, we summarize the role of the hypothalamus in modulating energy homeostasis and then briefly discuss the relationship between metabolism and stress-induced activation of the HPA axis. Next, we examine seven mechanisms whereby energetic stress interacts with neuroendocrine stress response systems, including by glucocorticoid signaling both within and beyond the HPA axis; by nutrient-induced changes in glucocorticoid signaling; by impacting the sympathetic nervous system; through changes in other neuroendocrine factors; by inducing inflammatory changes; and by altering the gut-brain axis. Recognizing these effects of energetic stress can drive novel therapies and prevention strategies for mental health disorders, including dietary intervention, probiotics, and even fecal transplant.

Pituitary adenylate cyclase-activating polypeptide (PACAP) in the central nucleus of the amygdala induces anxiety via melanocortin receptors

RATIONALE

Anxiety disorders are the most common mental disorders in the USA. Characterized by feelings of uncontrollable apprehension, they are accompanied by physical, affective, and behavioral symptoms. The neuropeptide pituitary adenylate cyclase-activating polypeptide (PACAP) and its receptor PAC1 (PAC1R) are highly expressed in the central nucleus of the amygdala (CeA), and they have gained growing attention for their proposed role in mediating the body's response to stress.

OBJECTIVES

The aim of this study was to evaluate the anxiogenic effects of PACAP in the CeA and its effects on the hypothalamic-pituitary-adrenal (HPA) axis. Furthermore, the mechanism of action of PACAP in the CeA was investigated.

METHODS

PACAP was microinfused into the CeA of rats, and its effects in the elevated plus maze (EPM), the defensive withdrawal tests, and plasma corticosterone levels were evaluated. The ability of the melanocortin receptor antagonist SHU9119 to block PACAP effect in the EPM was assessed.

RESULTS

Intra-CeA PACAP exerted a dose-dependent anxiogenic effect and activated the HPA axis. In contrast, PACAP microinfused into the basolateral nucleus of the amygdala (BlA) had no effect. Finally, the anxiogenic effect of intra-CeA PACAP was prevented by SHU9119.

CONCLUSIONS

These data prove an anxiogenic role for the PACAP system of the CeA and reveal that the melanocortin receptor 4 (MC4R) system of CeA mediates these effects. Our data provide insights into this neuropeptide system as a mechanism for modulating the behavioral and endocrine response to stress and suggest that dysregulations of this system may contribute to the pathophysiology of anxiety-related disorders.

Urocortin 2 in cardiovascular health and disease

Urocortin (Ucn)-2 - corticotropin-releasing hormone receptor 2 signaling has favorable effects in the cardiovascular system, including coronary vasodilatation, with increased coronary blood flow and conductance and augmented cardiac contractility and output, as well as protection against ischemia/reperfusion injury. Indeed, several animal studies have confirmed the salutary therapeutic effects of Ucn-2 in chronic heart failure, with improvements in cardiac performance and animal survival. In addition, recent clinical trials have demonstrated the benefits of Ucn-2 in patients with stable chronic heart failure on optimal medical therapy.

Chronic and acute effects of stress on energy balance: are there appropriate animal models?

Stress activates multiple neural and endocrine systems to allow an animal to respond to and survive in a threatening environment. The corticotropin-releasing factor system is a primary initiator of this integrated response, which includes activation of the sympathetic nervous system and the hypothalamic-pituitary-adrenal (HPA) axis. The energetic response to acute stress is determined by the nature and severity of the stressor, but a typical response to an acute stressor is inhibition of food intake, increased heat production, and increased activity with sustained changes in body weight, behavior, and HPA reactivity. The effect of chronic psychological stress is more variable. In humans, chronic stress may cause weight gain in restrained eaters who show increased HPA reactivity to acute stress. This phenotype is difficult to replicate in rodent models where chronic psychological stress is more likely to cause weight loss than weight gain. An exception may be hamsters subjected to repeated bouts of social defeat or foot shock, but the data are limited. Recent reports on the food intake and body composition of subordinate members of group-housed female monkeys indicate that these animals have a similar phenotype to human stress-induced eaters, but there are a limited number of investigators with access to the model. Few stress experiments focus on energy balance, but more information on the phenotype of both humans and animal models during and after exposure to acute or chronic stress may provide novel insight into mechanisms that normally control body weight.

Capsaicin-induced transcriptional changes in hypothalamus and alterations in gut microbial count in high fat diet fed mice

Obesity is a global health problem and recently it has been seen as a growing concern for developing countries. Several bioactive dietary molecules have been associated with amelioration of obesity and associated complications and capsaicin is one among them. The present work is an attempt to understand and provide evidence for the novel mechanisms of anti-obesity activity of capsaicin in high fat diet (HFD)-fed mice. Swiss albino mice divided in three groups (n=8-10) i.e. control, HFD fed and capsaicin (2mg/kg, po)+HFD fed were administered respective treatment for 3months. After measuring phenotypic and serum related biochemical changes, effect of capsaicin on HFD-induced transcriptional changes in hypothalamus, white adipose tissue (WAT) (visceral and subcutaneous), brown adipose tissue (BAT) and gut microbial alterations was studied and quantified. Our results suggest that, in addition to its well-known effects, oral administration of capsaicin (a) modulates hypothalamic satiety associated genotype, (b) alters gut microbial composition, (c) induces "browning" genotype (BAT associated genes) in subcutaneous WAT and (d) increases expression of thermogenesis and mitochondrial biogenesis genes in BAT. The present study provides evidence for novel and interesting mechanisms to explain the anti-obesity effect of capsaicin.

CRF and urocortin peptides as modulators of energy balance and feeding behavior during stress

Early on, corticotropin-releasing factor (CRF), a hallmark brain peptide mediating many components of the stress response, was shown to affect food intake inducing a robust anorexigenic response when injected into the rodent brain. Subsequently, other members of the CRF signaling family have been identified, namely urocortin (Ucn) 1, Ucn 2, and Ucn 3 which were also shown to decrease food intake upon central or peripheral injection. However, the kinetics of feeding suppression was different with an early decrease following intracerebroventricular injection of CRF and a delayed action of Ucns contrasting with the early onset after systemic injection. CRF and Ucns bind to two distinct G-protein coupled membrane receptors, the CRF1 and CRF2. New pharmacological tools such as highly selective peptide CRF1 or CRF2 agonists or antagonists along with genetic knock-in or knock-out models have allowed delineating the primary role of CRF2 involved in the anorexic response to exogenous administration of CRF and Ucns. Several stressors trigger behavioral changes including suppression of feeding behavior which are mediated by brain CRF receptor activation. The present review will highlight the state-of-knowledge on the effects and mechanisms of action of CRF/Ucns-CRF1/2 signaling under basal conditions and the role in the alterations of food intake in response to stress.

Regulation of corticotropin-releasing factor and urocortin 2/3 mRNA by leptin in hypothalamic N39 cells

Corticotropin-releasing factor (CRF) activates the pituitary-adrenal axis during stress, and shows anorectic effects via CRF type 1 receptors in the hypothalamus. Both urocortin (Ucn) 2 and Ucn3 also act as anorectic neuropeptides via CRF type 2 receptors. Leptin, a product of the obesity gene secreted mainly from adipose tissue, reduces food intake and increases energy expenditure. A possible interaction between leptin and CRF/Ucns has been suggested, as leptin can regulate expression and activation of CRF and Ucns in the hypothalamus. This study aimed to explore the possible function of leptin in the hypothalamus, and its effects in regulating CRF and Ucns. The study identified mRNA expression of the leptin receptor (Ob-R) and its subtypes, CRF, and Ucn2/3 in mouse hypothalamic N39 cells. Leptin stimulated signal transducer and activators of transcription type 3 (STAT3) phosphorylation, directly increased the mRNA levels of both CRF and Ucn2/3 in hypothalamic cells, and increased Ob-Rb mRNA levels. A Janus kinase inhibitor inhibited the leptin-mediated increase in STAT3 phosphorylation, and then the increases in CRF and Ucn2/3 mRNA levels. Leptin may contribute to a stress response or anorectic effect via the regulation of CRF and Ucn2/3 in the hypothalamus.

Appetite-suppressing effects and interactions of centrally administered corticotropin-releasing factor, urotensin I and serotonin in rainbow trout (Oncorhynchus mykiss)

Corticotropin-releasing factor (CRF), urotensin I (UI) and serotonin (5-HT) are generally recognized as key regulators of the anorexigenic stress response in vertebrates, yet the proximal effects and potential interactions of these central messengers on food intake in salmonids are not known. Moreover, no study to date in fishes has compared the appetite-suppressing effects of CRF and UI using species-specific peptides. Therefore, the objectives of this study were to (1) assess the individual effects of synthesized rainbow trout CRF (rtCRF), rtUI as well as 5-HT on food intake in rainbow trout, and (2) determine whether the CRF and serotonergic systems interact in the regulation of food intake in this species. Intracerebroventricular (icv) injections of rtCRF and rtUI both suppressed food intake in a dose-related manner but rtUI [ED₅₀ = 17.4 ng/g body weight (BW)] was significantly more potent than rtCRF (ED₅₀ = 105.9 ng/g BW). Co-injection of either rtCRF or rtUI with the CRF receptor antagonist α-hCRF_(9–41) blocked the reduction in food intake induced by CRF-related peptides. Icv injections of 5-HT also inhibited feeding in a dose-related manner (ED₅₀ = 14.7 ng/g BW) and these effects were blocked by the serotonergic receptor antagonist methysergide. While the anorexigenic effects of 5-HT were reversed by α-hCRF_(9–41) co-injection, the appetite-suppressing effects of either rtCRF or rtUI were not affected by methysergide co-injection. These results identify CRF, UI and 5-HT as anorexigenic agents in rainbow trout, and suggest that 5-HT-induced anorexia may be at least partially mediated by CRF- and/or UI-secreting neurons.

CRF mediates the anxiogenic and anti-rewarding, but not the anorectic effects of PACAP

Anxiety disorders represent the most common mental disturbances in the world, and they are characterized by an abnormal response to stress. Pituitary adenylate cyclase-activating polypeptide (PACAP) and its receptor PAC1 have been proposed to have a key role in mediating the responses to stress as well as the regulation of food intake and body weight. Corticotropin-releasing factor (CRF), the major stress peptide in the brain, has been hypothesized to be involved in PACAP effects, but the reports are conflicting so far. The present study was aimed at further characterizing the behavioral effects of PACAP in rats and at determining the role of central CRF receptors. We found that intracerebroventricular PACAP treatment induced anxiety-like behavior in the elevated plus maze test and elevated intracranial self-stimulation thresholds; both of these effects were fully blocked by concurrent treatment with the CRF receptor antagonist D-Phe-CRF(12-41). Interestingly, the CRF antagonist had no effect on PACAP-induced increased plasma corticosterone, reduction of food intake, and body weight loss. Finally, we found that PACAP increased CRF levels in the paraventricular nucleus of the hypothalamus and, importantly, in the central nucleus of the amygdala, as measured by solid phase radioimmunoassay and quantitative real-time PCR. Our results strengthen the notion that PACAP is a strong mediator of the behavioral response to stress and prove for the first time that this neuropeptide has anti-rewarding (ie, pro-depressant) effects. In addition, we identified the mechanism by which PACAP exerts its anxiogenic and pro-depressant effects, via the recruitment of the central CRF system and independently from HPA axis activation.

The effects of extended intravenous nicotine administration on body weight and meal patterns in male Sprague-Dawley rats

RATIONALE

Increased appetite and weight gain after cessation is a deterrent for quitting smoking. Attempts to understand the mechanism for these effects using animals have been hampered by the difficulty or inconsistency of modeling the effects seen in humans.

OBJECTIVE

To examine the effects of extended daily access to intravenous nicotine, via programmed infusions, on body weight and meal patterns in rats.

METHODS

Intravenous (IV) nicotine infusions (0.06 mg/kg/inf) were administered noncontingently, every 30 min throughout the dark cycle and the last 3 h of the light cycle, to emulate self-administration. The effect of these infusions on food intake, meal patterns, and weight change were examined relative to a control group during treatment and in a post-nicotine phase.

RESULTS

Nicotine-treated rats gained half the weight that vehicle treated animals gained and ate approximately 20 % less food overall than vehicle-treated rats. Whereas a compensatory increase in meal frequency occurred during the dark period to account for smaller meals, no compensation was observed throughout the light period. In a post-nicotine phase, the nicotine group maintained a lower weight for 1 week and then gained weight back to control levels. The rate of weight gain post-cessation was faster in animals that had received nicotine compared to controls.

CONCLUSION

Compared to previous studies examining the effects of minipump or intraperitoneal injections of nicotine on food intake, the present study was able to detect previously unknown circadian differences in meal patterns which will be important in the development of smoking cessation and weight gain prevention drugs.

An intrinsic CRF signaling system within the optic tectum

Previous work indicates that CRF administration inhibits visually guided feeding in amphibians. We used the African clawed frog Xenopus laevis to examine the hypothesis that CRF acts as a neurotransmitter in the optic tectum, the major brain area integrating the visual and premotor pathways regulating visually guided feeding in anurans. Reverse transcriptase PCR revealed that cells in the optic tectum express mRNA for CRF and the CRF R1 receptor but not the CRF R2 receptor. Radioligand binding studies indicated that specific binding of [(125)I]-Tyr-oCRF to tectal cell membranes can be displaced by the CRF R1 antagonists antalarmin or NBI-27914. CRF increased the expression of mRNA encoding regulator of G-protein signaling 2 (rgs2) in tectal explants and this effect was blocked by antalarmin. CRF had no effect on basal glutamate or gamma-aminobutyric acid (GABA) secretion but inhibited secretion of norepinephrine from tectal explants, an effect that completely blocked by antalarmin. Using a homologous radioimmunoassay we determined that CRF release from tectal explants in vitro was potassium- and calcium-dependent. Basal and depolarization-induced CRF secretion was greater from optic tectum than hypothalamus/thalamus, telencephalon, or brainstem. We concluded that the optic tectum possesses a CRF signaling system that may be involved in modulating communication between sensory and motor pathways involved in food intake.

The cytokine ciliary neurotrophic factor (CNTF) activates hypothalamic urocortin-expressing neurons both in vitro and in vivo

Ciliary neurotrophic factor (CNTF) induces neurogenesis, reduces feeding, and induces weight loss. However, the central mechanisms by which CNTF acts are vague. We employed the mHypoE-20/2 line that endogenously expresses the CNTF receptor to examine the direct effects of CNTF on mRNA levels of urocortin-1, urocortin-2, agouti-related peptide, brain-derived neurotrophic factor, and neurotensin. We found that treatment of 10 ng/ml CNTF significantly increased only urocortin-1 mRNA by 1.84-fold at 48 h. We then performed intracerebroventricular injections of 0.5 mg/mL CNTF into mice, and examined its effects on urocortin-1 neurons post-exposure. Through double-label immunohistochemistry using specific antibodies against c-Fos and urocortin-1, we showed that central CNTF administration significantly activated urocortin-1 neurons in specific areas of the hypothalamus. Taken together, our studies point to a potential role for CNTF in regulating hypothalamic urocortin-1-expressing neurons to mediate its recognized effects on energy homeostasis, neuronal proliferaton/survival, and/or neurogenesis.

Posttranslational processing of human and mouse urocortin 2: characterization and bioactivity of gene products

Mouse (m) and human (h) urocortin 2 (Ucn 2) were identified by molecular cloning strategies and the primary sequence of their mature forms postulated by analogy to closely related members of the corticotropin-releasing factor (CRF) neuropeptide family. Because of the paucity of Ucn 2 proteins in native tissues, skin, muscle, and pancreatic cell lines were transduced with lentiviral constructs and secretion media were used to isolate and characterize Ucn 2 products and study processing. Primary structures were assigned using a combination of Edman degradation sequencing and mass spectrometry. For mUcn 2, transduced cells secreted a 39 amino acid peptide and the glycosylated prohormone lacking signal peptide; both forms were C-terminally amidated and highly potent to activate the type 2 CRF receptor. Chromatographic profiles of murine tissue extracts were consistent with cleavage of mUcn 2 prohormone to a peptidic form. By contrast to mUcn 2, mammalian cell lines transduced with hUcn 2 constructs secreted significant amounts of an 88 amino acid glycosylated hUcn 2 prohormone but were unable to further process this molecule. Similarly, WM-266-4 melanoma cells that express endogenous hUcn 2 secreted only the glycosylated prohormone lacking the signal peptide and unmodified at the C terminus. Although not amidated, hUcn 2 prohormone purified from overexpressing lines activated CRF receptor 2. Hypoxia and glycosylation, paradigms that might influence secretion or processing of gene products, did not significantly impact hUcn 2 prohormone cleavage. Our findings identify probable Ucn 2 processing products and should expedite the characterization of these proteins in mammalian tissues.

Regulation of gonadotropins by corticotropin-releasing factor and urocortin

While stress activates the hypothalamic-pituitary-adrenal (HPA) axis, it suppresses the hypothalamic-pituitary-gonadal (HPG) axis. Corticotropin-releasing factor (CRF) is a major regulatory peptide in the HPA axis during stress. Urocortin 1 (Ucn1), a member of the CRF family of peptides, has a variety of physiological functions and both CRF and Ucn1 contribute to the stress response via G protein-coupled seven transmembrane receptors. Ucn2 and Ucn3, which belong to a separate paralogous lineage from CRF, are highly selective for the CRF type 2 receptor (CRF(2) receptor). The HPA and HPG axes interact with each other, and gonadal function and reproduction are suppressed in response to various stressors. In this review, we focus on the regulation of gonadotropins by CRF and Ucn2 in pituitary gonadotrophs and of gonadotropin-releasing hormone (GnRH) via CRF receptors in the hypothalamus. In corticotrophs, stress-induced increases in CRF stimulate Ucn2 production, which leads to the inhibition of gonadotropin secretion via the CRF(2) receptor in the pituitary. GnRH in the hypothalamus is regulated by a variety of stress conditions. CRF is also involved in the suppression of the HPG axis, especially the GnRH pulse generator, via CRF receptors in the hypothalamus. Thus, complicated regulation of GnRH in the hypothalamus and gonadotropins in the pituitary via CRF receptors contributes to stress responses and adaptation of gonadal functions.

The link between stress and feeding behaviour

Exposure to stress is inevitable, and it may occur, to varying degrees, at different phases throughout the lifespan. The impact of stress experienced in later life has been well documented as many populations in modern society experience increasing socio-economic demands. The effects of stress early in life are less well known, partly as the impact of an early exposure may be difficult to quantify, however emerging evidence shows it can impact later in life. One of the major impacts of stress besides changes in psychosocial behaviour is altered feeding responses. The system that regulates stress responses, the hypothalamo-pituitary-adrenal axis, also regulates feeding responses because the neural circuits that regulate food intake converge on the paraventricular nucleus, which contains corticotrophin releasing hormone (CRH), and urocortin containing neurons. In other words the systems that control food intake and stress responses share the same anatomy and thus each system can influence each other in eliciting a response. Stress is known to alter feeding responses in a bidirectional pattern, with both increases and decreases in intake observed. Stress-induced bidirectional feeding responses underline the complex mechanisms and multiple contributing factors, including the levels of glucocorticoids (dependent on the severity of a stressor), the interaction between glucocorticoids and feeding related neuropeptides such as neuropeptide Y (NPY), alpha-melanocyte stimulating hormone (α-MSH), agouti-related protein (AgRP), melanocortins and their receptors, CRH, urocortin and peripheral signals (leptin, insulin and ghrelin). This review discusses the neuropeptides that regulate feeding behaviour and how their function can be altered through cross-talk with hormones and neuropeptides that also regulate the hypothalamo-pituitary-adrenal axis. In addition, long-term stress induced alterations in feeding behaviour, and changes in gene expression of neuropeptides regulating stress and food intake through epigenetic modifications will be discussed. This article is part of a Special Issue entitled 'SI: Central Control of Food Intake'.