Lactate activates hypothalamic POMC neurons by intercellular signaling.

Previous studies indicate that the activity of hypothalamic POMC neurons can be regulated by glucose via intracellular mechanisms, but its regulation by lactate is poorly understood. In addition to its energetic role, lactate acts as a signaling molecule. In this study, we evaluated the function and location of the lactate receptor, hydroxycarboxylic acid receptor 1 (HCAR1). We used a conditional genetic approach to label POMC neurons and evaluated their sensitivity to lactate using patch-clamp recordings. L-Lactate and 3-chloro-5-hydroxybenzoic acid (3Cl-HBA), HCAR1 specific agonist depolarized POMC neurons and the increase in excitability was abolished by pertussis toxin (PTX), indicating the involvement of Gαi/o-protein-coupled receptors. In addition, the depolarization of a subset of POMC neurons was sensitive to α-cyano-4-hydroxycinnamate (4-CIN), a lactate transporter blocker, suggesting that the depolarization induced by L-lactate can also occur by direct intracellular action. Surprisingly, HCAR1 was not detected in POMC neurons, but instead localized in astrocytes. These results suggest a new lactate-mediated mechanism for astrocyte-neuron intercellular communication.

PERK in POMC neurons connects celastrol with metabolism.

ER stress and activation of the unfolded protein response in the periphery as well as the central nervous system have been linked to various metabolic abnormalities. Chemically lowering protein kinase R-like ER kinase (PERK) activity within the hypothalamus leads to decreased food intake and body weight. However, the cell populations required in this response remain undefined. In the current study, we investigated the effects of proopiomelanocortin-specific (POMC-specific) PERK deficiency on energy balance and glucose metabolism. Male mice deficient for PERK in POMC neurons exhibited improvements in energy balance on a high-fat diet, showing decreased food intake and body weight, independent of changes in glucose and insulin tolerances. The plant-based inhibitor of PERK, celastrol, increases leptin sensitivity, resulting in decreased food intake and body weight in a murine model of diet-induced obesity (DIO). Our data extend these observations by demonstrating that celastrol-induced improvements in leptin sensitivity and energy balance were attenuated in mice with PERK deficiency in POMC neurons. Altogether, these data suggest that POMC-specific PERK deficiency in male mice confers protection against DIO, possibly providing a new therapeutic target for the treatment of diabetes and metabolic syndrome.

Obesity, POMC, and POMC-processing Enzymes: Surprising Results From Animal Models.

Peptides derived from proopiomelanocortin (POMC) are well-established neuropeptides and peptide hormones that perform multiple functions, including regulation of body weight. In humans and some animals, these peptides include α- and ß-melanocyte-stimulating hormone (MSH). In certain rodent species, no ß-MSH is produced from POMC because of a change in the cleavage site. Enzymes that convert POMC into MSH include prohormone convertases (PCs), carboxypeptidases (CPs), and peptidyl-α-amidating monooxygenase (PAM). Humans and mice with inactivating mutations in either PC1/3 or carboxypeptidase E (CPE) are obese, which was assumed to result from defective processing of POMC into MSH. However, recent studies have shown that selective loss of either PC1/3 or CPE in POMC-expressing cells does not cause obesity. These findings suggest that defects in POMC processing cannot alone account for the obesity observed in global PC1/3 or CPE mutants. We propose that obesity in animals lacking PC1/3 or CPE activity depends, at least in part, on deficient processing of peptides in non-POMC-expressing cells either in the brain and/or the periphery. Genetic background may also contribute to the manifestation of obesity.

The Mesencephalic Trigeminal Nucleus Controls Food Intake and Body Weight via Hindbrain POMC Projections.

The mesencephalic trigeminal nucleus (Mes5) processes oral sensory-motor information, but its role in the control of energy balance remains unexplored. Here, using fluorescent in situ hybridization, we show that the Mes5 expresses the melanocortin-4 receptor. Consistent with MC4R activation in other areas of the brain, we found that Mes5 microinjection of the MC4R agonist melanotan-II (MTII) suppresses food intake and body weight in the mouse. Furthermore, NTS POMC-projecting neurons to the Mes5 can be chemogenetically activated to drive a suppression in food intake. Taken together, these findings highlight the Mes5 as a novel target of melanocortinergic control of food intake and body weight regulation, although elucidating the endogenous role of this circuit requires future study. While we observed the sufficiency of Mes5 MC4Rs for food intake and body weight suppression, these receptors do not appear to be necessary for food intake or body weight control. Collectively, the data presented here support the functional relevance of the NTS POMC to Mes5 projection pathway as a novel circuit that can be targeted to modulate food intake and body weight.

Cardiac Phenotype and Tissue Sodium Content in Adolescents With Defects in the Melanocortin System.

CONTEXT: Pro-opiomelanocortin (POMC) and the melanocortin-4 receptor (MC4R) play a pivotal role in the leptin-melanocortin pathway. Mutations in these genes lead to monogenic types of obesity due to severe hyperphagia. In addition to dietary-induced obesity, a cardiac phenotype without hypertrophy has been identified in MC4R knockout mice. OBJECTIVE: We aimed to characterize cardiac morphology and function as well as tissue Na+ content in humans with mutations in POMC and MC4R genes. METHODS: A cohort of 42 patients (5 patients with bi-allelic POMC mutations, 6 heterozygous MC4R mutation carriers, 19 obese controls without known monogenic cause, and 12 normal weight controls) underwent cardiac magnetic resonance (CMR) imaging and 23Na-MRI. RESULTS: Monogenic obese patients with POMC or MC4R mutation respectively had a significantly lower left ventricular mass/body surface area (BSA) than nonmonogenic obese patients. Left ventricular end-diastolic volume/BSA was significantly lower in POMC- and MC4R-deficient patients than in nonmonogenic obese patients. Subcutaneous fat and skin Na+ content was significantly higher in POMC- and MC4R-deficient patients than in nonmonogenic obese patients. In these compartments, the water content was significantly higher in patients with POMC and MC4R mutation than in control groups. CONCLUSION: Patients with POMC or MC4R mutations carriers had a lack of transition to hypertrophy, significantly lower cardiac muscle mass/BSA, and stored more Na+ within the subcutaneous fat tissue than nonmonogenic obese patients. The results point towards the role of the melanocortin pathway for cardiac function and tissue Na+ storage and the importance of including cardiologic assessments into the diagnostic work-up of these patients.

PGC-1ß-expressing POMC neurons mediate the effect of leptin on thermoregulation in the mouse.

The arcuate nucleus (ARC) of the hypothalamus is a key regulator of food intake, brown adipose tissue (BAT) thermogenesis, and locomotor activity. Whole-body deficiency of the transcriptional coactivator peroxisome proliferator-activated receptor γ (PPARγ) coactivator-1ß (PGC-1ß) disrupts mouse circadian locomotor activity and BAT-regulated thermogenesis, in association with altered gene expression at the central level. We examined whether PGC-1ß expression in the ARC is required for proper energy balance and locomotor behavior by generating mice lacking the PGC-1ß gene specifically in pro-opiomelanocortin (POMC) neurons. POMC neuron-specific deletion of PGC-1ß did not impact locomotor behavior, food intake, body composition, energy fuel utilization and metabolic rate in fed, 24-h fasted and 24-h refed conditions. In contrast, in the fed state, deletion of PGC-1ß in POMC cells elevated core body temperature during the nighttime period. Importantly, this higher body temperature is not associated with changes in BAT function and gene expression. Conversely, we provide evidence that mice lacking PGC-1ß in POMC neurons are more sensitive to the effect of leptin on heat dissipation. Our data indicate that PGC-1ß-expressing POMC neurons are part of a circuit controlling body temperature homeostasis and that PGC-1ß function in these neurons is involved in the thermoregulatory effect of leptin.

Pro-opiomelanocortin (POMC) neuron translatome signatures underlying obesogenic gestational malprogramming in mice.

OBJECTIVE: Maternal unbalanced nutritional habits during embryonic development and perinatal stages perturb hypothalamic neuronal programming of the offspring, thus increasing obesity-associated diabetes risk. However, the underlying molecular mechanisms remain largely unknown. In this study we sought to determine the translatomic signatures associated with pro-opiomelanocortin (POMC) neuron malprogramming in maternal obesogenic conditions. METHODS: We used the RiboTag mouse model to specifically profile the translatome of POMC neurons during neonatal (P0) and perinatal (P21) life and its neuroanatomical, functional, and physiological consequences. RESULTS: Maternal high-fat diet (HFD) exposure did not interfere with offspring's hypothalamic POMC neuron specification, but significantly impaired their spatial distribution and axonal extension to target areas. Importantly, we established POMC neuron-specific translatome signatures accounting for aberrant neuronal development and axonal growth. These anatomical and molecular alterations caused metabolic dysfunction in early life and adulthood. CONCLUSIONS: Our study provides fundamental insights on the molecular mechanisms underlying POMC neuron malprogramming in obesogenic contexts.

LGR4 is essential for R-spondin1-mediated suppression of food intake via pro-opiomelanocortin.

Leucine-rich repeat-containing G-protein coupled receptor 4 (LGR4) suppresses food intake after its activation by binding of its ligands, R-spondins. We investigated the mechanism of food intake suppression by R-spondin1 in a region-specific Lgr4 gene knockout (LGR4 cKO) mouse model, generated by deletion of the Lgr4 gene in arcuate nucleus (ARC) using Lgr4fx/fx mice combined with infection of an AAV-Cre vector. After R-spondin1 administration, LGR4 cKO mice didn't exhibit a suppressed appetite, compared to that in control mice, which received a vehicle. In ARC of LGR4 cKO mice, Pomc mRNA expression was reduced, leading to suppressed food intake. On the other hand, neurons-specific LGR4 KO mice exhibited no differences in Pomc expression, and no structural differences were observed in the ARC of mutant mice. These results suggest that LGR4 is an essential part of the mechanism, inducing Pomc gene expression with R-spondin1 in ARC neurons in mice, thereby regulating feeding behavior. Abbreviations: LGR4: Leucine-rich repeat-containing G-protein coupled receptor 4; RSPOs: roof plate-specific spondins; ARC: arcuate nucleus; AAV: adeno associated virus; POMC: pro-opiomelanocortin; CART: cocaine and amphetamine-regulated transcript; NPY: neuropeptide Y; AgRP: agouti-related peptide; Axin2: axis inhibition protein 2; Lef1: lymphoid enhancer binding factor 1; ccnd1: cyclin D1.

Nociceptin/orphanin FQ modulates energy homeostasis through inhibition of neurotransmission at VMN SF-1/ARC POMC synapses in a sex- and diet-dependent manner.

BACKGROUND: Orphanin FQ (aka nociceptin; N/OFQ) binds to its nociceptin opioid peptide (NOP) receptor expressed in proopiomelanocortin (POMC) neurons within the arcuate nucleus (ARC), a critical anorexigenic component of the hypothalamic energy balance circuitry. It inhibits POMC neurons by modifying neuronal excitability both pre- and postsynaptically. We tested the hypothesis that N/OFQ inhibits neurotransmission at synapses involving steroidogenic factor (SF)-1 neurons in the ventromedial nucleus (VMN) and ARC POMC neurons in a sex- and diet-dependent fashion. METHODS: Electrophysiological recordings were done in intact male and in cycling and ovariectomized female NR5A1-Cre and eGFP-POMC mice. Energy homeostasis was assessed in wildtype animals following intra-ARC injections of N/OFQ or its saline vehicle. RESULTS: N/OFQ (1 µM) decreased light-evoked excitatory postsynaptic current (leEPSC) amplitude more so in males than in diestrus or proestrus females, which was further accentuated in high-fat diet (HFD)-fed males. N/OFQ elicited a more robust outward current and increase in conductance in males than in diestrus, proestrus, and estrus females. These pleiotropic actions of N/OFQ were abrogated by the NOP receptor antagonist BAN ORL-24 (10 µM). In ovariectomized female eGFP-POMC mice, 17ß-estradiol (E2; 100 nM) attenuated the N/OFQ-induced postsynaptic response. SF-1 neurons from NR5A1-Cre mice also displayed a robust N/OFQ-induced outward current and increase in conductance that was sexually differentiated and suppressed by E2. Finally, intra-ARC injections of N/OFQ increased energy intake and decreased energy expenditure, which was further potentiated by exposure to HFD and diminished by estradiol benzoate (20 µg/kg; s.c.). CONCLUSION: These findings show that males are more responsive to the pleiotropic actions of N/OFQ at anorexigenic VMN SF-1/ARC POMC synapses, and this responsiveness can be further enhanced under conditions of diet-induced obesity/insulin resistance.

Role of SOCS3 in POMC neurons in metabolic and cardiovascular regulation.

Suppressor of cytokine signaling 3 (SOCS3) is a negative regulator of leptin signaling. We previously showed that the chronic effects of leptin on blood pressure (BP) and glucose regulation are mediated by stimulation of proopiomelanocortin (POMC) neurons. In this study we examined the importance of endogenous SOCS3 in POMC neurons in control of metabolic and cardiovascular function and potential sex differences. Male and female SOCS3flox/flox/POMC-Cre mice in which SOCS3 was selectively deleted in POMC neurons and control SOCS3flox/flox mice were studied during a control diet (CD) or a high-fat diet (HFD) and during chronic leptin infusion. Body weight was lower in male and female SOCS3flox/flox/POMC-Cre than control mice fed the CD, despite similar food intake. Male SOCS3flox/flox/POMC-Cre mice exhibited increased energy expenditure. BP and heart rate were similar in male and female SOCS3flox/flox/POMC-Cre and control mice fed the CD. HFD-fed male and female SOCS3flox/flox/POMC-Cre mice showed attenuated weight gain. HFD-induced elevations in baseline BP and BP responses to an air-jet stress test were greater in female SOCS3flox/flox/POMC-Cre than control mice. Chronic leptin infusion produced similar responses for food intake, body weight, oxygen consumption, blood glucose, BP, and heart rate in all groups. Thus SOCS3 deficiency in POMC neurons influences body weight regulation in the setting of CD and HFD and differentially affects BP and energy balance in a sex-specific manner but does not amplify the dietary, glycemic, or cardiovascular effects of leptin.

POMC Neurons: Feeding, Energy Metabolism, and Beyond.

The central melanocortin system is a well-established neuronal pathway involved in regulating energy metabolism. Pro-opiomelanocortin (POMC) neurons, agouti gene-related protein (AgRP) neurons, and their downstream cells expressing the melanocortin-3 (MC3R) and melanocortin-4 receptors (MC4R) are three key components of the central melanocortin pathway. This chapter focuses on the Pomc gene and the POMC neural system. First, I summarize the established role of this system in inhibiting food intake. Second, in light of new cutting-edge techniques, our understanding of how POMC neurons function to regulate energy homeostasis has been refined during the last few years. I describe some recent advances and discuss bidirectional effects of POMC neurons on feeding. Finally, the physiological significance beyond energy metabolism, in particular for reward and sex, is also discussed.

Electrophysiological Mechanism of Peripheral Hormones and Nutrients Regulating Energy Homeostasis.

In organism, energy homeostasis is a biological process that involves the coordinated homeostatic regulation of energy intake (food intake) and energy expenditure. The human brain, particularly the hypothalamic proopiomelanocortin (POMC)- and agouti-related protein/neuropeptide Y (AgRP/NPY)-expressing neurons in the arcuate nucleus, plays an essential role in regulating energy homeostasis. The regulation process is mainly dependent upon peripheral hormones such as leptin and insulin, as well as nutrients such as glucose, amino acids, and fatty acids. Although many studies have attempted to illustrate the exact mechanisms of glucose and hormones action on these neurons, we still cannot clearly see the full picture of this regulation action. Therefore, in this review we will mainly discuss those established theories and recent progresses in this area, demonstrating the possible physiological mechanism by which glucose, leptin, and insulin affect neuronal excitability of POMC and AgRP neurons. In addition, we will also focus on some important ion channels which are expressed by POMC and AgRP neurons, such as KATP channels and TRPC channels, and explain how these channels are regulated by peripheral hormones and nutrients and thus regulate energy homeostasis.

Blockade of analgesic effects following systemic administration of N-methyl-kyotorphin, NMYR and arginine in mice deficient of preproenkephalin or proopiomelanocortin gene.

Kyotorphin is a unique biologically active neuropeptide (l-tyrosine-l-arginine), which is reported to have opioid-like analgesic actions through a release of Met-enkephalin from the brain slices. N-methyl-l-tyrosine-l-arginine (NMYR), an enzymatically stable mimetic of kyotorphin, successfully caused potent analgesic effects in thermal and mechanical nociception tests in mice when it was given through systemic routes. NMYR analgesia was abolished in µ-opioid receptor-deficient (MOP-KO) mice, and by intracerebroventricular (i.c.v.) injection of naloxone and of N-methyl l-leucine-l-arginine (NMLR), a kyotorphin receptor antagonist. In the Ca2+-mobilization assay using CHO cells expressing Gαqi5 and hMOPr or hDOPr, however, the addition of kyotorphin neither activated MOPr-mechanisms, nor affected the concentration-dependent activation of DAMGO- or Met-Enkephalin-induced MOPr activation, and Met-enkephalin-induced DOPr activation. NMYR-analgesia was significantly attenuated in preproenkephalin (PENK)- or proopioimelanocortin (POMC)-KO mice. The systemic administration of arginine, which is reported to elevate the level of endogenous kyotorphin selectively in midbrain and medulla oblongata, pain-related brain regions, caused significant analgesia, and the analgesia was reversed by i.c.v. injection of NMLR or naloxone. In addition, PENK- and POMC-KO mice also attenuated the arginine-induced analgesia. All these findings suggest that NMYR and arginine activate brain kyotorphin receptor in direct and indirect manner, respectively and both compounds indirectly cause the opioid-like analgesia through the action of endogenous opioid peptides.

Motivational valence is determined by striatal melanocortin 4 receptors.

It is critical for survival to assign positive or negative valence to salient stimuli in a correct manner. Accordingly, harmful stimuli and internal states characterized by perturbed homeostasis are accompanied by discomfort, unease, and aversion. Aversive signaling causes extensive suffering during chronic diseases, including inflammatory conditions, cancer, and depression. Here, we investigated the role of melanocortin 4 receptors (MC4Rs) in aversive processing using genetically modified mice and a behavioral test in which mice avoid an environment that they have learned to associate with aversive stimuli. In normal mice, robust aversions were induced by systemic inflammation, nausea, pain, and κ opioid receptor-induced dysphoria. In sharp contrast, mice lacking MC4Rs displayed preference or indifference toward the aversive stimuli. The unusual flip from aversion to reward in mice lacking MC4Rs was dopamine dependent and associated with a change from decreased to increased activity of the dopamine system. The responses to aversive stimuli were normalized when MC4Rs were reexpressed on dopamine D1 receptor-expressing cells or in the striatum of mice otherwise lacking MC4Rs. Furthermore, activation of arcuate nucleus proopiomelanocortin neurons projecting to the ventral striatum increased the activity of striatal neurons in an MC4R-dependent manner and elicited aversion. Our findings demonstrate that melanocortin signaling through striatal MC4Rs is critical for assigning negative motivational valence to harmful stimuli.

GTRAP3-18 regulates food intake and body weight by interacting with pro-opiomelanocortin.

Pro-opiomelanocortin (POMC)-expressing neurons provide α-melanocyte-stimulating hormone (α-MSH), which stimulates melanocortin 4 receptor to induce hypophagia by AMPK inhibition in the hypothalamus. α-MSH is produced by POMC cleavage in secretory granules and released. However, it is not known yet whether any posttranscriptional regulatory mechanism of POMC signaling exists upstream of the secretory granules in neurons. Here we show that glutamate transporter-associated protein 3-18 (GTRAP3-18), an anchor protein that retains interacting proteins in the endoplasmic reticulum, is a critical regulator of food intake and body weight by interacting with POMC. GTRAP3-18-deficient mice showed hypophagia, lean bodies, and lower blood glucose, insulin, and leptin levels with increased serum and brain α-MSH levels, leading to AMPK inhibition. Intraperitoneal glucose tolerance tests revealed significantly decreased blood glucose levels and areas under the curve in GTRAP3-18-deficient mice compared to wild-type mice. An intracerebroventricular infusion of a selective melanocortin 4 receptor antagonist to GTRAP3-18-deficient mice significantly increased their food intake and body weight. A fluorescence resonance energy transfer study showed an interaction between GTRAP3-18 and POMC in vitro These findings suggest that activation of the melanocortin pathway by modulating GTRAP3-18/POMC interaction could be an alternative strategy for obesity and/or type 2 diabetes.-Aoyama, K., Bhadhprasit, W., Watabe, M., Wang, F., Matsumura, N., Nakaki, T. GTRAP3-18 regulates food intake and body weight by interacting with pro-opiomelanocortin.

The physiological and neuroendocrine correlates of hunger in the Red Junglefowl (Gallus gallus).

The ability to regulate food intake is critical to survival. The hypothalamus is central to this regulation, integrating peripheral signals of energy availability. Although our understanding of hunger in rodents is advanced, an equivalent understanding in birds is lacking. In particular, the relationship between peripheral energy indices and hypothalamic 'hunger' peptides, agouti-related protein (AgRP), pro-opiomelanocortin (POMC) and neuropeptide Y (NPY) is poorly understood. Here, we compare AgRP, POMC and NPY RNA levels in the hypothalamus of Red Junglefowl chicks raised under ad libitum, chronic restriction and intermittent feeding regimens. Hypothalamic gene expression differed between chronically and intermittently restricted birds, confirming that different restriction regimens elicit different patterns of hunger. By assessing the relationship between hypothalamic gene expression and carcass traits, we show for the first time in birds that AgRP and POMC are responsive to fat-related measures and therefore represent long-term energy status. Chronically restricted birds, having lower indices of fat, show elevated hunger according to AgRP and POMC. NPY was elevated in intermittently fasted birds during fasting, suggesting a role as a short-term index of hunger. The different physiological and neuroendocrine responses to quantitative versus temporal feed restriction provide novel insights into the divergent roles of avian hunger neuropeptides.

Neuronal Control of Bone Remodeling.

Although the brain is well established as a master regulator of homeostasis in peripheral tissues, central regulation of bone mass represents a novel and rapidly expanding field of study. This review examines the current understanding of central regulation of the skeleton, exploring several of the key pathways connecting brain to bone and their implications both in mice and the clinical setting. Our understanding of central bone regulation has largely progressed through examination of skeletal responses downstream of nutrient regulatory pathways in the hypothalamus. Mutations and modulation of these pathways, in cases such as leptin deficiency, induce marked bone phenotypes, which have provided vital insights into central bone regulation. These studies have identified several central neuropeptide pathways that stimulate well-defined changes in bone cell activity in response to changes in energy homeostasis. In addition, this work has highlighted the endocrine nature of the skeleton, revealing a complex cross talk that directly regulates other organ systems. Our laboratory has studied bone-active neuropeptide pathways and defined osteoblast-based actions that recapitulate central pathways linking bone, fat, and glucose homeostasis. Studies of neural control of bone have produced paradigm-shifting changes in our understanding of the skeleton and its relationship with the wider array of organ systems.

Hypothalamic effects of neonatal diet: reversible and only partially leptin dependent.

Early life diet influences metabolic programming, increasing the risk for long-lasting metabolic ill health. Neonatally overfed rats have an early increase in leptin that is maintained long term and is associated with a corresponding elevation in body weight. However, the immediate and long-term effects of neonatal overfeeding on hypothalamic anorexigenic pro-opiomelanocortin (POMC) and orexigenic agouti-related peptide (AgRP)/neuropeptide Y (NPY) circuitry, and if these are directly mediated by leptin, have not yet been examined. Here, we examined the effects of neonatal overfeeding on leptin-mediated development of hypothalamic POMC and AgRP/NPY neurons and whether these effects can be normalised by neonatal leptin antagonism in male Wistar rats. Neonatal overfeeding led to an acute (neonatal) resistance of hypothalamic neurons to exogenous leptin, but this leptin resistance was resolved by adulthood. While there were no effects of neonatal overfeeding on POMC immunoreactivity in neonates or adults, the neonatal overfeeding-induced early increase in arcuate nucleus (ARC) AgRP/NPY fibres was reversed by adulthood so that neonatally overfed adults had reduced NPY immunoreactivity in the ARC compared with controls, with no further differences in AgRP immunoreactivity. Short-term neonatal leptin antagonism did not reverse the excess body weight or hyperleptinaemia in the neonatally overfed, suggesting factors other than leptin may also contribute to the phenotype. Our findings show that changes in the availability of leptin during early life period influence the development of hypothalamic connectivity short term, but this is partly resolved by adulthood indicating an adaptation to the metabolic mal-programming effects of neonatal overfeeding.

Angiotensin AT1A receptors on leptin receptor-expressing cells control resting metabolism.

Leptin contributes to the control of resting metabolic rate (RMR) and blood pressure (BP) through its actions in the arcuate nucleus (ARC). The renin-angiotensin system (RAS) and angiotensin AT1 receptors within the brain are also involved in the control of RMR and BP, but whether this regulation overlaps with leptin's actions is unclear. Here, we have demonstrated the selective requirement of the AT1A receptor in leptin-mediated control of RMR. We observed that AT1A receptors colocalized with leptin receptors (LEPRs) in the ARC. Cellular coexpression of AT1A and LEPR was almost exclusive to the ARC and occurred primarily within neurons expressing agouti-related peptide (AgRP). Mice lacking the AT1A receptor specifically in LEPR-expressing cells failed to show an increase in RMR in response to a high-fat diet and deoxycorticosterone acetate-salt (DOCA-salt) treatments, but BP control remained intact. Accordingly, loss of RMR control was recapitulated in mice lacking AT1A in AgRP-expressing cells. We conclude that angiotensin activates divergent mechanisms to control BP and RMR and that the brain RAS functions as a major integrator for RMR control through its actions at leptin-sensitive AgRP cells of the ARC.

The melanocortin system regulates body pigmentation and social behaviour in a colour polymorphic cichlid fish.

The melanocortin system is a neuroendocrine system that regulates a range of physiological and behavioural processes. We examined the extent to which the melanocortin system simultaneously regulates colour and behaviour in the cichlid fish Astatotilapia burtoni We found that yellow males are more aggressive than blue males, in line with previous studies. We then found that exogenous α-melanocyte-stimulating hormone (α-MSH) increases yellowness of the body and dispersal of xanthophore pigments in both morphs. However, α-MSH had a morph-specific effect on aggression, with only blue males showing an increase in the rate of aggression. Exogenous agouti signalling peptide (ASIP), a melanocortin antagonist, did not affect coloration but reduced the rate of aggression in both colour morphs. Blue males had higher cortisol levels than yellow males. Neural gene expression of melanocortin receptors (mcr) and ligands was not differentially regulated between colour morphs. In the skin, however, mc1r and pro-opiomelanocortin (pomc) ß were upregulated in blue males, while asip 1 was upregulated in yellow males. The effects of α-MSH on behaviour and body coloration, combined with morph-specific regulation of the stress response and the melanocortin system, suggest that the melanocortin system contributes to the polymorphism in behaviour and coloration in A. burtoni.