Role of melanocortins in the central control of feeding

Immunohistochemical determination of the excitatory and inhibitory axonal endings contacting NUCB2/nesfatin-1 neurons

Nesfatin-1 is an anorexigenic peptide suppressing food intake and is synthesized and secreted by neurons located in the hypothalamus. Our study was aimed to demonstrate the effect of excitatory and inhibitory neurotransmitters on NUCB2/nesfatin-1 neurons. In this context, dual peroxidase immunohistochemistry staining was performed using NUCB2/nesfatin-1 primary antibody with each of the primary antibodies of vesicular transporter proteins applied as markers for neurons using glutamate, acetylcholine, and GABA as neurotransmitters. In double labeling applied on floating sections, the NUCB2/nesfatin-1 reaction was determined in brown color with diaminobenzidine, while vesicular carrier proteins were marked in black. Slides were analyzed to determine the ratio of nesfatin-1 neurons in the three hypothalamic nucleus in contact with a relevant vesicular carrier protein. The ratios of NUCB2/nesfatin-1 neurons with the innervation were compared among neurotransmitters. In addition, possible gender differences between males and females were examined. The difference in the number of VGLUT2-contacting NUCB2/nesfatin-1 neurons was significantly higher in males when compared to females. When both genders were compared in different nuclei, it was seen that there was no statistical significance in terms of the percentage of NUCB2/nesfatin-1 neuron apposition with VGLUT3. The statistical evaluation showed that number of NUCB2/nesfatin-1 neurons receiving GABAergic innervation is higher in males when compared to females (*p ≤ 0.05; p = 0.045). When the axonal contact of vesicular neurotransmitter transporter proteins was compared between the neurotransmitters, it was determined that the most prominent innervation is GABAergic. In the supraoptic region, no contacts of VAChT-containing axons were found on NUCB2/nesfatin-1 neurons in both female and male subjects. In conclusion, it is understood that both excitatory and inhibitory neurons can innervate the NUCB2/nesfatin-1 neurons and the glutamatergic system is effective in the excitatory innervation while the GABAergic system plays a role in the inhibitory mechanism.

Effects of different acute stressors on the regulation of appetite genes in the carp (Cyprinus carpio L.) brain

Our understanding of the timing of stress responses and specific roles of different regulatory pathways that drive stress responses is incomplete. In particular, the regulation of appetite genes as a consequence of exposure to different stressors has not been studied in sufficient detail in fish. Therefore, a stress trial was conducted with koi carp, aiming at identifying typical effects of stress on regulation of appetite genes. The stressors tank manipulation, air exposure and feed rewarding were chosen. The responses to these stressors were evaluated 10, 30 and 60 min after the stressors were applied. Orexigenic and anorexigenic genes were investigated in four different brain regions (telencephalon, hypothalamus, optic tectum and rhombencephalon). The results show that, apart from the typical appetite regulation in the hypothalamus, the different brain regions also display pronounced responses of appetite genes to the different stressors. In addition, several genes in the serotonergic, dopaminergic and gaba-related pathways were investigated. These genes revealed that rearing in pairs of two and opening of the tank lid affected anorexigenic genes, such as cart and cck, which were not changed by air exposure or feed rewarding. Moreover, distress and eustress led to limited, but distinguishable gene expression pattern changes in the investigated brain regions.

Effect of supplementation with different fatty acid profile to the dam in early gestation and to the offspring on the finishing diet on offspring growth and hypothalamus mRNA expression in sheep

Supplementation with omega-3 and omega-9 fatty acids (FA) during late gestation regulates offspring development; however, their effect in the first third of gestation is unknown in sheep. The objective of this experiment was to evaluate the effects of the maternal supplementation with an enriched source of monounsaturated FA (MUFA) or an enriched source of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) during the first third of gestation on productive performance on ewes and offspring, and hypothalamic neuropeptides on offspring. Seventy-nine post-weaning lambs, born of sheep supplemented in the first third of gestation with 1.61% Ca salts rich with MUFA or EPA+DHA (dam supplementation, DS), were distributed in a 2×2 factorial arrangement of treatments to finishing diets containing 1.48% of Ca salts of MUFA or EPA+DHA (lamb supplementation, LS). The finishing period of the offspring lasted for 56 d. During the finishing period dry matter intake (DMI, daily) and body weight (BW) were recorded. Plasma was collected for metabolites analysis. Twenty-four lambs were slaughtered, and hypothalamus was collected for mRNA expression of hormone receptors, neuropeptides, and lipid transport genes. The data were analyzed with a mixed model in SAS (9.4) using repeated measurements, when needed. There was a DS×LS interaction for BW (P = 0.10) where LS with EPA+DHA born from DS with MUFA were heavier than the other 3 treatments. Lambs born from DS with MUFA have a greater DMI (P < 0.01) than the offspring born from DS with EPA+DHA. Lambs born from MUFA supplemented dams had a greater (P ≤ 0.05) hypothalamus mRNA expression for cocaine and amphetamine regulated transcript, growth hormone receptor, metastasis suppressor 1, leptin receptor, pro-opiomelanocortin, and Neuropeptide Y. These results indicate that growth depends not on the type of FA during the finishing phase but the interaction of different sources of FA ad different stages. Also, supplementation with FA during early pregnancy changes productive performance and neuropeptides' mRNA expression of lambs independently of the finishing diet.

Combined Computational and Structural Approach into Understanding the Role of Peptide Binding and Activation of Melanocortin Receptor 4

Melanocortin receptor 4 (MC4R) is expressed predominantly in the central nervous system and regulates food intake and sexual function and is also thought to be responsible for effects on mood and cognition. It belongs to the melanocortin receptor subfamily of G protein-coupled receptors (GPCRs). Here, we have synthesized and structurally characterized three peptides that bind to MC4R, producing different signaling events. AgRP is a naturally occurring antagonist, HLWNRS is the minimal sequence of the N-terminal with partial agonist activity, and aMSH is a full agonistic peptide. By implementing molecular dynamics simulations on the different peptide-receptor complexes, we propose their molecular basis of binding to investigate their differential molecular properties regarding the activation states of the receptor. Our analysis shows that the agonist and partial agonist may induce rotation in transmembrane helix 3, which is known to be involved in the key events occurring during GPCR activation, and this movement is impacted by certain aromatic residues and their positioning in the orthosteric binding site of the receptor.

Hindbrain lactoprivic regulation of hypothalamic neuron transactivation and gluco-regulatory neurotransmitter expression: Impact of antecedent insulin-induced hypoglycemia

Hindbrain energy state shapes hypothalamic control of glucostasis. Dorsal vagal complex (DVC) L-lactate deficiency is a potent glucose-stimulatory signal that triggers neuronal transcriptional activation in key hypothalamic metabolic loci. The energy gauge AMPK is activated in DVC metabolic-sensory A2 noradrenergic neurons by hypoglycemia-associated lactoprivation, but sensor reactivity is diminished by antecedent hypoglycemia (AH). Current research addressed the premise that AH alters hindbrain lactoprivic regulation of hypothalamic metabolic transmitter function. AH did not modify reductions in A2 dopamine-beta-hydroxylase and monocarboxylate-2 (MCT2) protein expression elicited by caudal fourth ventricular delivery of the MCT inhibitor alpha-cyano-4-hydroxycinnamic acid (4CIN), but attenuated 4CIN activation of A2 AMPK. 4CIN constraint of hypothalamic norepinephrine (NE) activity was averted by AH in a site-specific manner. 4CIN induction of Fos immunolabeling in hypothalamic arcuate (ARH), ventromedial (VMN), dorsomedial (DMN) and paraventricular (PVN) nuclei and lateral hypothalamic area (LHA) was avoided by AH. AH affected reactivity of select hypothalamic metabolic neurotransmitter/enzyme marker proteins, e.g. ARH neuropeptide Y, VMN glutamate decarboxylase, DMN RFamide-related peptide-1 and -3, and LHA orexin-A profiles to 4CIN, but did not alleviate drug inhibition of ARH proopiomelanocortin. AH prevented 4CIN augmentation of circulating glucagon, but did not alter hyperglycemic or hypocorticosteronemic responses to that treatment. Results identify hindbrain lactate deficiency as a stimulus for glucagon secretion, and imply that habituation of this critical counter-regulatory hormone to recurring hypoglycemia may involve one or more hypothalamic neurotransmitters characterized here by acclimation to this critical sensory stimulus.

N/OFQ-NOP System in Food Intake

While lifestyle modifications should be the first-line actions in preventing and treating obesity and eating disorders, pharmacotherapy also provides a necessary tool for the management of these diseases.However, given the limitations of current anti-obesity drugs, innovative treatments that improve efficacy and safety are needed.Since the discovery that the activation of the Nociceptin/Orphanin (N/OFQ) FQ peptide (NOP) receptor by N/OFQ induces an increase of food intake in laboratory animals, and the finding that this effect can be blocked by NOP antagonists, many NOP agonists and antagonists have been synthesized and tested in vitro and in vivo for their potential regulation of feeding behavior. Promising results seem to suggest that the N/OFQergic system may be a potential therapeutic target for the neural control of feeding behavior and related pathologies, especially in binge-like eating behavior.

Lateral but not Medial Hypothalamic AMPK Activation Occurs at the Hypoglycemic Nadir in Insulin-injected Male Rats: Impact of Caudal Dorsomedial Hindbrain Catecholamine Signaling

The hypothalamic energy sensor adenosine 5'-monophosphate-activated protein kinase (AMPK), an important regulator of counter-regulatory responses to hypoglycemia, responds to pharmacological manipulation of hindbrain AMPK activity. Dorsomedial hindbrain A2 noradrenergic neurons express hypoglycemia-sensitive metabolo-sensory biomarkers, including AMPK. Here, adult male rats were pretreated by intra-caudal fourth ventricular administration of the selective neurotoxin 6-hydroxydopamine (6-OHDA) to determine if catecholamine signaling from the aforesaid site governs hypothalamic AMPK activation during insulin-induced hypoglycemia (IIH). Micropunched arcuate (ARH), ventromedial (VMH), paraventricular (PVH), dorsomedial (DMH) nuclei and lateral hypothalamic area (LHA) tissues were obtained at the neutral protamine Hagedorn insulin-induced hypoglycemic nadir, coincident with A2 AMPK activation, for Western blot analysis of AMPK, phospho-AMPK (pAMPK), and relevant metabolic neuropeptides. ARH, VMH, LHA, and DMH norepinephrine levels were altered according to insulin dose; 6-OHDA-mediated reversal of these responses was site-specific. IIH elevated LHA and reduced VMH pAMPK protein, profiles that were respectively unchanged or increased by 6-OHDA. PVH and ARH pAMPK was resistant to IIH, but augmented in ARH of neurotoxin- plus insulin-treated rats. ARH neuropeptide Y (NPY) and pro-opiomelanocortin (POMC) proteins were correspondingly increased or refractory to IIH; 6-OHDA pretreatment normalized NPY and elevated POMC expression after insulin injection. Results demonstrate site-specific bi-directional adjustments in hypothalamic AMPK reactivity to hypoglycemia. Intensification of ARH/VMH pAMPK by 6-OHDA implies dorsomedial hindbrain improvement of energy balance in those sites during IIH. Neurotoxin-mediated augmentation versus suppression of basal catabolic (ARH POMC/VMH steroidogenic factor-1) or IIH-associated anabolic (ARH NPY) neuropeptide profiles, respectively, may involve local AMPK-dependent against independent mechanisms.

Role of hindbrain adenosine 5'-monophosphate-activated protein kinase (AMPK) in hypothalamic AMPK and metabolic neuropeptide adaptation to recurring insulin-induced hypoglycemia in the male rat

Glucose counter-regulatory dysfunction correlates with impaired activation of the hypothalamic metabolic sensor adenosine 5'-monophosphate-activated protein kinase (AMPK). Hypothalamic AMPK is controlled by hindbrain energy status; we examined here whether hindbrain AMPK regulates hypothalamic AMPK and metabolic neurotransmitter maladaptation to recurring insulin-induced hypoglycemia (RIIH). Brain tissue was harvested after single versus serial insulin (I) dosing for Western blot analysis of AMPK, phospho-AMPK (pAMPK), and relevant biosynthetic enzyme/neuropeptide expression in micro-punch dissected arcuate (ARH), ventromedial (VMH), dorsomedial (DMH) nuclei and lateral hypothalamic area (LHA) tissue. The AMPK inhibitor compound c (Cc) or vehicle was administered to the caudal fourth ventricle ahead of antecedent I injections. RIIH caused site-specific elevation (ARH, VMH, LHA) or reduction (DMH) of total AMPK protein versus acute hypoglycemia; Cc respectively exacerbated or attenuated this response in the ARH and VMH. Hindbrain AMPK correspondingly inhibited or stimulated LHA and DMH pAMPK expression during RIIH. RIIH elicited Cc-reversible augmentation of VMH glutamate decarboxylase profiles, but stimulated (ARH pro-opiomelanocortin; LHA orexin-A) or decreased (VMH nitric oxide synthase) other metabolic neurotransmitters without hindbrain sensor involvement. Results demonstrate acclimated up-regulation of total AMPK protein expression in multiple hypothalamic loci during RIIH, and document hindbrain sensor contribution to amplification of this protein profile in the VMH. Concurrent lack of net change in ARH and VMH tissue pAMPK implies adaptive reductions in local sensor activity, which may/may not reflect positive gain in energy state. It remains unclear if 'glucose-excited' VMH GABAergic and/or ARH pro-opiomelanocortin neurons exhibit AMPK habituation to RIIH, and whether diminished sensor activation in these and other mediobasal hypothalamic neurotransmitter populations may contribute to HAAF.

Multiple beneficial effects of melanocortin MC4 receptor agonists in experimental neurodegenerative disorders: Therapeutic perspectives

Melanocortin peptides induce neuroprotection in acute and chronic experimental neurodegenerative conditions. Melanocortins likewise counteract systemic responses to brain injuries. Furthermore, they promote neurogenesis by activating critical signaling pathways. Melanocortin-induced long-lasting improvement in synaptic activity and neurological performance, including learning and memory, sensory-motor orientation and coordinated limb use, has been consistently observed in experimental models of acute and chronic neurodegeneration. Evidence indicates that the neuroprotective and neurogenic effects of melanocortins, as well as the protection against systemic responses to a brain injury, are mediated by brain melanocortin 4 (MC₄) receptors, through an involvement of the vagus nerve. Here we discuss the targets and mechanisms underlying the multiple beneficial effects recently observed in animal models of neurodegeneration. We comment on the potential clinical usefulness of melanocortin MC₄ receptor agonists as neuroprotective and neuroregenerative agents in ischemic stroke, subarachnoid hemorrhage, traumatic brain injury, spinal cord injury, and Alzheimer's disease.

Hindbrain estrogen receptor-beta antagonism normalizes reproductive and counter-regulatory hormone secretion in hypoglycemic steroid-primed ovariectomized female rats

Hindbrain dorsal vagal complex A2 noradrenergic signaling represses the pre-ovulatory luteinizing hormone (LH) surge in response to energy deficiency. Insulin-induced hypoglycemia augments A2 neuron adenosine 5'-monophosphate-activated protein kinase (AMPK) activity and estrogen receptor-beta (ERβ) expression, coincident with LH surge suppression. We hypothesized that ERβ is critical for hypoglycemia-associated patterns of LH secretion and norepinephrine (NE) activity in key reproduction-relevant forebrain structures. The neural mechanisms responsible for tight coupling of systemic energy balance and procreation remain unclear; here, we investigated whether ERβ-dependent hindbrain signals also control glucose counter-regulatory responses to hypoglycemia. Gonadal steroid-primed ovariectomized female rats were pretreated by caudal fourth ventricular administration of the ERβ antagonist 4-[2-phenyl-5,7-bis(trifluoromethyl)pyrazolo[1,5-a]pyrimidin-3-yl]phenol (PHTPP) or vehicle before insulin injection at LH surge onset. Western blot analysis of laser-microdissected A2 neurons revealed hypoglycemic intensification of AMPK activity and dopamine-β-hydroxylase protein expression; the latter response was attenuated by PHTPP pretreatment. PHTPP regularized LH release, but not preoptic GnRH-I precursor protein expression in insulin-injected rats, and reversed hypoglycemic stimulation of glucagon and corticosterone secretion. Hypoglycemia caused PHTPP-reversible changes in NE and prepro-kisspeptin protein content in the hypothalamic arcuate (ARH), but not anteroventral periventricular nucleus. Results provide novel evidence for ERβ-dependent caudal hindbrain regulation of LH and counter-regulatory hormone secretion during hypoglycemia. Observed inhibition of LH likely involves mechanisms at the axon terminal that impede GnRH neurotransmission. Data also show that caudal hindbrain ERβ exerts site-specific control of NE activity in forebrain projection sites during hypoglycemia, including the ARH where prepro-kisspeptin may be a target of that signaling.

The role of pancreatic polypeptide in the regulation of energy homeostasis

Imbalances in normal regulation of food intake can cause obesity and related disorders. Inadequate therapies for such disorders necessitate better understanding of mechanisms that regulate energy homeostasis. Pancreatic polypeptide (PP), a robust anorexigenic hormone, effectively modulates food intake and energy homeostasis, thus potentially aiding anti-obesity therapeutics. Intra-gastric and intra-intestinal infusion of nutrients stimulate PP secretion from the gastrointestinal tract, leading to vagal stimulation that mediates complex actions via the neuropeptide Y4 receptor in arcuate nucleus of the hypothalamus, subsequently activating key hypothalamic nuclei and dorsal vagal complex of the brainstem to influence energy homeostasis and body composition. Novel studies indicate affinity of PP for the relatively underexplored neuropeptide y6 receptor, mediating actions via the suprachiasmatic nucleus and pathways involving vasoactive intestinal polypeptide and insulin like growth factor 1. This review highlights detailed mechanisms by which PP mediates its actions on energy balance through various areas in the brain.

DRD2 and DRD4 genes related to cognitive deficits in HIV-infected adults who abuse alcohol

Background

HIV-infected individuals continue to experience neurocognitive deterioration despite virologically successful treatments. The causes of neurocognitive impairment are still unclear. However, several factors have been suggested including the role of genetics. There is evidence suggesting that neurocognitive impairment is heritable and individual differences in cognition are strongly driven by genetic variations. The contribution of genetic variants affecting the metabolism and activity of dopamine may influence these individual differences.

Methods

The present study explored the relationship between two candidate genes (DRD4 and DRD2) and neurocognitive performance in HIV-infected adults. A total of 267 HIV-infected adults were genotyped for polymorphisms, DRD4 48 bp-variable number tandem repeat (VNTR), DRD2 rs6277 and ANKK1 rs1800497. The Short Category (SCT), Color Trail (CTT) and Rey-Osterrieth Complex Figure Tests (ROCT) were used to measure executive function and memory.

Results

Results showed significant associations with the SNP rs6277 and impaired executive function (odds ratio = 3.3, 95 % CI 1.2–2.6; p = 0.004) and cognitive flexibility (odds ratio = 1.6, 95 % CI 2.0–5.7; p = 0.001). The results were further stratified by race and sex and significant results were seen in males (odds ratio = 3.5, 95 % CI 1.5–5.5; p = 0.008) and in African Americans (odds ratio = 3.1, 95 % CI 2.3–3.5; p = 0.01). Also, DRD4 VNTR 7-allele was significantly associated with executive dysfunction.

Conclusion

The study shows that genetically determined differences in the SNP rs6277 DRD2 gene and DRD4 48 bp VNTR may be risk factors for deficits in executive function and cognitive flexibility.

Melanocortins protect against brain damage and counteract cognitive decline in a transgenic mouse model of moderate Alzheimer׳s disease

We previously reported that melanocortins induce neuroprotection in experimental acute and chronic neurodegenerative conditions, including Alzheimer׳s disease (AD) of mild severity. Here we investigated whether melanocortins afford neuroprotection and counteract cognitive decline in AD with a medium level of severity by using 24 week-old (at the start of the study) APPSwe transgenic mice (Tg2576). Saline-treated (days 1-50) control Tg2576 mice showed an impairment in spatial learning and memory, associated (at day 50, end of the study) with hippocampus at low levels of the synaptic activity-dependent gene Zif268, relevant brain changes such as cerebral cortex/hippocampus increased level of β-amyloid (Aβ) deposit, and neuronal loss, in comparison with wild-type animals. Treatment of Tg2576 mice (once daily at days 1-50) with a nanomolar dose of the melanocortin analog [Nle4,D-Phe7]α-melanocyte-stimulating hormone (NDP-α-MSH) reduced cerebral cortex/hippocampus level of Aβ deposit, decreased neuronal loss, increased hippocampus Zif268 expression and improved cognitive functions, relative to saline-treated Tg2576 mice. Pharmacological blockade of melanocortin MC4 receptors with the MC4 receptor antagonist HS024 prevented all favorable effects of NDP-α-MSH. Our data indicate that MC4 receptor-stimulating melanocortins are able to counteract cognitive decline in experimental AD of medium severity through induction of neuroprotection and improvement of synaptic transmission. After further studies, these agents could gain a role as disease modifying therapeutics for AD.

Investigation of safety, tolerability, pharmacokinetics, and pharmacodynamics of single and multiple doses of a long-acting α-MSH analog in healthy overweight and obese subjects

MC4-NN2-0453 is a novel, long-acting, selective, melanocortin-4-receptor agonist developed for treatment of obesity. This first-human-dose, randomized, double-blind, placebo-controlled trial investigated the safety, tolerability, pharmacokinetics, and pharmacodynamics of single and multiple doses of MC4-NN2-0453 in overweight to obese but otherwise healthy subjects. The trial included a single-dose part of ascending subcutaneous 0.03-1.50 mg/kg doses in overweight to obese but otherwise healthy men, and a multiple-dose part of ascending subcutaneous 0.75-3.0 mg/day doses in obese but otherwise healthy men/women. The single-dose part included 7 cohorts of 8 subjects, randomized 6:2 to active drug/placebo; the multiple-dose part included 4 cohorts of 20 subjects, randomized 16:4 to active drug/placebo. MC4-NN2-0453 was well tolerated and raised no safety concerns except for nonserious skin-related adverse events, this along with lack of weight loss effect led to premature termination of the trial. Headache, sexual-arousal disturbance, and penile erection were also reported. Single-dose pharmacokinetics showed dose-linearity and dose-proportionality. Maximum plasma concentration was observed after 50-100 hours, which then declined with a of approximately 250 hours. Plasma concentration reached steady state after 4 weeks for 0.75 and 1.5 mg/day multiple-dose cohorts, and the was similar to single dose. There were no significant pharmacodynamic effects, including effect on body weight.

Stress and eating: a dual role for bombesin-like peptides

The current obesity “epidemic” in the developed world is a major health concern; over half of adult Canadians are now classified as overweight or obese. Although the reasons for high obesity rates remain unknown, an important factor appears to be the role stressors play in overconsumption of food and weight gain. In this context, increased stressor exposure and/or perceived stress may influence eating behavior and food choices. Stress-induced anorexia is often noted in rats exposed to chronic stress (e.g., repeated restraint) and access to standard Chow diet; associated reduced consumption and weight loss. However, if a similar stressor exposure takes place in the presence of palatable, calorie dense food, rats often consume an increase proportion of palatable food relative to Chow, leading to weight gain and obesity. In humans, a similar desire to eat palatable or “comfort” foods has been noted under stressful situations; it is thought that this response may potentially be attributable to stress-buffering properties and/or through activation of reward pathways. The complex interplay between stress-induced anorexia and stress-induced obesity is discussed in terms of the overlapping circuitry and neurochemicals that mediate feeding, stress and reward pathways. In particular, this paper draws attention to the bombesin family of peptides (BBs) initially shown to regulate food intake and subsequently shown to mediate stress response as well. Evidence is presented to support the hypothesis that BBs may be involved in stress-induced anorexia under certain conditions, but that the same peptides could also be involved in stress-induced obesity. This hypothesis is based on the unique distribution of BBs in key cortico-limbic brain regions involved in food regulation, reward, incentive salience and motivationally driven behavior.

Melanocortins protect against progression of Alzheimer's disease in triple-transgenic mice by targeting multiple pathophysiological pathways

Besides specific triggering causes, Alzheimer's disease (AD) involves pathophysiological pathways that are common to acute and chronic neurodegenerative disorders. Melanocortins induce neuroprotection in experimental acute neurodegenerative conditions, and low melanocortin levels have been found in occasional studies performed in AD-type dementia patients. Here we investigated the possible neuroprotective role of melanocortins in a chronic neurodegenerative disorder, AD, by using 12-week-old (at the start of the study) triple-transgenic (3xTg-AD) mice harboring human transgenes APPSwe, PS1M146V, and tauP301L. Treatment of 3xTg-AD mice, once daily until the end of the study (30 weeks of age), with the melanocortin analog [Nle(4),D-Phe(7)]-α-melanocyte-stimulating hormone (NDP-α-MSH) reduced cerebral cortex/hippocampus phosphorylation/level of all AD-related biomarkers investigated (mediators of amyloid/tau cascade, oxidative/nitrosative stress, inflammation, apoptosis), decreased neuronal loss, induced over-expression of the synaptic activity-dependent gene Zif268, and improved cognitive functions, relative to saline-treated 3xTg-AD mice. Pharmacological blockade of melanocortin MC4 receptors prevented all neuroprotective effects of NDP-α-MSH. Our study identifies, for the first time, a class of drugs, MC4 receptor-stimulating melanocortins, that are able to counteract the progression of experimental AD by targeting pathophysiological mechanisms up- and down-stream of β-amyloid and tau. These data could have important clinical implications.

Cloning, distribution and effects of fasting status of melanocortin 4 receptor (MC4R) in Schizothorax prenanti

Melanocortin 4 receptor (MC4R) has an important role in the regulation of energy homeostasis in both mammals and fish. In this study, MC4R was characterized in S. prenanti (Schizothorax prenanti) and designated as SpMC4R. SpMC4R cDNA is composed of 1004 nucleotides with a 978 nucleotide open reading frame encoding a protein of 326 amino acids. The SpMC4R contained predicted regions that were structural features of MCR subtypes of vertebrates. In addition, phylogenetic analyses suggested that S. prenanti MC4R was closely related to fish MC4Rs. The SpMC4R mRNA was detected in embryos at developmental stages. Further, its mRNA was detectable in unfertilized eggs. Using real-time RT-PCR, MC4R is widely expressed, with highest levels of expression in brain and ovary. An experiment was conducted to determine the expression profile of MC4R during short-term and long-term fasting of the brain. The expression level of MC4R in unfed fish was significantly increased at 6, 9 and 24h post-fasting (hpf) and 14days fasting than in fed fish, this suggests that MC4R is conserved peptide that might be involved in the regulation of food intake and other physiological function in S. prenanti.

Ontogenic expression of putative feeding peptides in the rat fetal brain and placenta

The well-demonstrated "fetal programming" paradigm is based on the observation that environmental changes can reset the developmental path and thus, gene expression during intrauterine development. As appetite-regulatory neural pathways develop in utero, we sought to determine the ontogenic expression of putative orexigenic and anorexigenic feeding-regulatory peptides in the fetal rat brain and placenta during the last third of gestation. Pregnant Sprague-Dawley rats (n = 12) at D14, D16 and D18 were sacrificed and fetal whole brain and placenta removed and examined for mRNA levels of orexigenic (neuropeptide Y (NPY), agouti-related peptide (AgRP)) and anorexigenic (cocaine and amphetamine regulated transcript (CART), pro-opiomelanocortin (POMC)) peptides and leptin receptor (OB-Rb) using real-time reverse transcription polymerase chain reactions (RT-PCR). For adult comparisons, the hypothalamus, cortex and cerebellum from male rats were also examined for feeding peptides. In the fetal brain and placenta, mRNA levels of AgRP decreased 10-fold from D14 to D16 and was undetectable at D18. Appetite inhibitory factors OB-Rb and CART mRNA levels increased from D14 to D18 in the brain and placenta. NPY and POMC expression remained unchanged from D14 to D18. The pattern of expression of feeding regulatory peptides in the fetal brain most closely resembled the expression profile of the adult cerebral cortex. The continued maturation of feeding regulatory mechanisms in late gestation indicates the potential for in utero programming of ingestive behavior.

MC4-R signaling within the nucleus accumbens shell, but not the lateral hypothalamus, modulates ethanol palatability in rats

The Melanocortin (MC) system is one of the crucial neuropeptidergic systems that modulate energy balance. The roles of endogenous MC and MC-4 receptor (MC4-R) signaling within the hypothalamus in the control of homeostatic aspects of feeding are well established. Additional evidence points to a key role for the central MC system in ethanol consumption. Recently, we have shown that nucleus accumbens (NAc), but not lateral hypothalamic (LH), infusion of a selective MC4-R agonist decreases ethanol consumption. Given that MC signaling might contribute to non-homeostatic aspects of feeding within limbic circuits, we assessed here whether MC4-R signaling within the NAc and the lateral hypothalamus (LH) alters normal ingestive hedonic and/or aversive responses to ethanol in rats as measured by a taste reactivity test. Adult male Sprague-Dawley rats were given NAc- or LH- bilateral infusion of the selective MC4-R agonist cyclo (NH-CH(2)-CH(2)-CO-His-D-Phe-Arg-Trp-Glu)-NH(2) (0, 0.75 or 1.5μg/0.5μl/site) and following 30 min, the animals received 1 ml of ethanol solution (6% w/v) intraoral for 1 minute and aversive and hedonic behaviors were recorded. We found that NAc-, but not LH-administration, of a selective MC4-R agonist decreased total duration of hedonic reactions and significantly increased aversive reactions relative to saline-infused animals which support the hypothesis that MC signaling within the NAc may contribute to ethanol consumption by modulating non-homeostatic aspects (palatability) of intake.

Arcuate NPY controls sympathetic output and BAT function via a relay of tyrosine hydroxylase neurons in the PVN

Neuropepetide Y (NPY) is best known for its powerful stimulation of food intake and its effects on reducing energy expenditure. However, the pathways involved and the regulatory mechanisms behind this are not well understood. Here we demonstrate that NPY derived from the arcuate nucleus (Arc) is critical for the control of sympathetic outflow and brown adipose tissue (BAT) function. Mechanistically, a key change induced by Arc NPY signaling is a marked Y1 receptor-mediated reduction in tyrosine hydroxylase (TH) expression in the hypothalamic paraventricular nucleus (PVN), which is also associated with a reduction in TH expression in the locus coeruleus (LC) and other regions in the brainstem. Consistent with this, Arc NPY signaling decreased sympathetically innervated BAT thermogenesis, involving the downregulation of uncoupling protein 1 (UCP1) expression in BAT. Taken together, these data reveal a powerful Arc-NPY-regulated neuronal circuit that controls BAT thermogenesis and sympathetic output via TH neurons.

A debate on current eating disorder diagnoses in light of neurobiological findings: is it time for a spectrum model?

BACKGROUND

Sixty percent of eating disorders do not meet criteria for anorexia- or bulimia nervosa, as defined by the Diagnostic and Statistical Manual version 4 (DSM-IV). Instead they are diagnosed as 'eating disorders not otherwise specified' (EDNOS). Discrepancies between criteria and clinical reality currently hampering eating disorder diagnoses in the DSM-IV will be addressed by the forthcoming DSM-V. However, future diagnoses for eating disorders will rely on current advances in the fields of neuroimaging and genetics for classification of symptoms that will ultimately improve treatment.

DISCUSSION

Here we debate the classification issues, and discuss how brain imaging and genetic discoveries might be interwoven into a model of eating disorders to provide better classification and treatment. The debate concerns: a) current issues in the classification of eating disorders in the DSM-IV, b) changes proposed for DSM-V, c) neuroimaging eating disorder research and d) genetic eating disorder research.

SUMMARY

We outline a novel evidence-based 'impulse control' spectrum model of eating disorders. A model of eating disorders is proposed that will aid future diagnosis of symptoms, coinciding with contemporary suggestions by clinicians and the proposed changes due to be published in the DSM-V.

Control of food intake by MC4-R signaling in the lateral hypothalamus, nucleus accumbens shell and ventral tegmental area: interactions with ethanol

The melanocortin system is involved in animal models of obesity and anorexia-cachexia and MC4 receptors (MC4-R) are currently a target system for the development of drugs aimed to treat obesity and eating disorders in humans. Previous evidence suggest that feeding peptides might lack their orexigenic activity while stimulate ethanol intake. The present study comparatively evaluated food intake (4-h interval) in Sprague-Dawley (SD) rats drinking ethanol (6% w/v, 2 bottle choice paradigm) (EE group) and ethanol-naïve (EN) rats in response to bilateral infusion of the selective MC4-R antagonist HS014 (0, 0.02 or 0.05 μg/0.5 μl/site) or the selective MC4-R agonist cyclo(NH-CH(2)-CH(2)-CO-His-d-Phe-Arg-Trp-Glu)-NH(2) (0, 0.75 or 1.5 μg/0.5 μl/site), into the lateral hypothalamus (LH), the nucleus accumbens (NAc), or the ventral tegmental area (VTA). The main findings in the study are: (1) LH-infusions of the MC4-R antagonist increased and the agonist reduced feeding and total calories consumed, while ethanol intake remained unaltered. (2) NAc- and VTA-infusions of the selective agonist reduced food, ethanol and total calories intake. (3) NAc- and VTA-infusions of the MC4-R antagonist increased feeding in EN rats, but not in EE animals which showed a mild increase in ethanol intake, while total calories consumed remained unaltered. Present data show that having ethanol available reduces feeding elicited by NAc and VTA-MC4-R blockade. Additionally, while MC4-R signaling in the LH appears to modulate homeostatic aspects of feeding, it may contribute to non-homeostatic aspects of ingestive behaviors in the VTA and the NAc.

Food deprivation explains effects of mouthbrooding on ovaries and steroid hormones, but not brain neuropeptide and receptor mRNAs, in an African cichlid fish

Feeding behavior and reproduction are coordinately regulated by the brain via neurotransmitters, circulating hormones, and neuropeptides. Reduced feeding allows animals to engage in other behaviors important for fitness, including mating and parental care. Some fishes cease feeding for weeks at a time in order to provide care to their young by brooding them inside the male or female parent's mouth. Maternal mouthbrooding is known to impact circulating hormones and subsequent reproductive cycles, but neither the full effects of food deprivation nor the neural mechanisms are known. Here we ask what effects mouthbrooding has on several physiological processes including gonad and body mass, brain neuropeptide and receptor gene expression, and circulating steroid hormones in a mouthbrooding cichlid species, Astatotilapia burtoni. We ask whether any observed changes can be explained by food deprivation, and show that during mouthbrooding, ovary size and circulating levels of androgens and estrogens match those seen during food deprivation. Levels of gonadotropin-releasing hormone 1 (GnRH1) mRNA in the brain were low in food-deprived females compared to controls and in mouthbrooding females compared to gravid females. Levels of mRNA encoding two peptides involved in regulating feeding, hypocretin and cholecystokinin, were increased in the brains of food-deprived females. Brain mRNA levels of two receptors, GnRH receptor 2 and NPY receptor Y8c, were elevated in mouthbrooding females compared to the fed condition, but NPY receptor Y8b mRNA was differently regulated by mouthbrooding. These results suggest that many, but not all, of the characteristic physiological changes that occur during mouthbrooding are consequences of food deprivation.

Characterization of melanocortin 4 receptor in Snakeskin Gourami and its expression in relation to daily feed intake and short-term fasting

In this study, melanocortin 4 receptor (MC4R) was characterized in Snakeskin Gourami (Trichogaster pectoralis) and designated as TpMC4R. The TpMC4R contained predicted regions that were structural features of MC4R subtypes of vertebrates. In addition, phylogenetic analyses showed that TpMC4R were in MC4R orthologues and closely related to piscine MC4Rs. The TpMC4R transcripts were detected in embryos at all developmental stages. Further, its mRNA was detectable in unfertilized eggs, suggesting that TpMC4R could be classified as maternal mRNA. Using real-time RT-PCR, graded expression at each central and peripheral tissue was demonstrated. Localization of TpMC4R expression in the brain was performed by in situ hybridization. An experiment was conducted to determine the expression profile of TpMC4R during daily feeding in each region of the brain. Fish were fed twice a day at 10:00 and 16:00, and the level of TpMC4R expression was analyzed at 9:00, 11:00, 13:00 and 15:00. The expression level of TpMC4R was significantly reduced at 15:00 compared to that at all previous times (9:00, 11:00 and 13:00). Moreover, significantly higher expression levels of TpMC4R were observed at 18- and 24-h fasting periods. The finding of variation in MC4R expression level during daily feeding and fasting period revealed some direct and/or indirect relations of the MC4R expression to circadian feeding rhythm and short-term food deprivation in fish.

Conformational study on cyclic melanocortin ligands and new insight into their binding mode at the MC4 receptor

The melanocortin receptors are involved in many physiological functions, including pigmentation, sexual function, feeding behavior, and energy homeostasis, making them potential targets to treat obesity, sexual dysfunction, etc. Understanding the basis of the ligand-receptor interactions is crucial for the design of potent and selective ligands for these receptors. The conformational preferences of the cyclic melanocortin ligands MTII (Ac-Nle(4)-c[Asp(5)-His(6)-DPhe(7)-Arg(8)-Trp(9)-Lys(10)]-NH(2)) and SHU9119 (Ac-Nle(4)-c[Asp(5)-His(6)-DNal(2')(7)-Arg(8)-Trp(9)-Lys(10)]-NH(2)), which show agonist and antagonist activity at the h-MC4R, respectively, were comprehensively investigated by solution NMR spectroscopy in different environments. In particular, water and water/DMSO (8:2) solutions were used as isotropic solutions and an aqueous solution of DPC (dodecylphosphocholine) micelles was used as a membrane mimetic environment. NMR-derived conformations of these two ligands were docked within h-MC4R models. NMR and docking studies revealed intriguing differences which can help explain the different activities of these two ligands.

Y4 receptors and pancreatic polypeptide regulate food intake via hypothalamic orexin and brain-derived neurotropic factor dependent pathways

Gut-derived peptides are known to regulate food intake by activating specific receptors in the brain, but the target nuclei and neurons influenced are largely unknown. Here we show that peripherally administered pancreatic polypeptide (PP) stimulates neurons in key nuclei of the hypothalamus critical for appetite and satiety regulation. In the lateral hypothalamic area (LHA), also known as the feeding center, neurons expressing the orexigenic neuropeptide orexin co-localize with the early neuronal activation marker c-Fos upon i.p. injection of PP into mice. In the ventromedial hypothalamus (VMH), also known as the satiety center, neurons activated by PP, as indicated by induction of c-Fos immunoreactivity, express the anorexigenic brain-derived neurotrophic factor (BDNF). Activation of neurons in the LHA and VMH in response to PP occurs via a Y4 receptor-dependent process as it is not seen in Y4 receptor knockout mice. We further demonstrate that in response to i.p. PP, orexin mRNA expression in the LHA is down-regulated, with Y4 receptors being critical for this effect as it is not seen in Y4 receptor knockout mice, whereas BDNF mRNA expression is up-regulated in the VMH in response to i.p. PP in the fasted, but not in the non-fasted state. Taken together these data suggest that PP can regulate food intake by suppressing orexigenic pathways by down-regulation of orexin and simultaneously increasing anorexigenic pathways by up-regulating BDNF.

Critical role of arcuate Y4 receptors and the melanocortin system in pancreatic polypeptide-induced reduction in food intake in mice

Background

Pancreatic polypeptide (PP) is a potent anti-obesity agent known to inhibit food intake in the absence of nausea, but the mechanism behind this process is unknown.

Methodology/Principal Findings

Here we demonstrate that in response to i.p. injection of PP in wild type but not in Y4 receptor knockout mice, immunostaining for the neuronal activation marker c-Fos is induced specifically in neurons of the nucleus tractus solitarius and the area postrema in the brainstem, notably in cells also showing immunostaining for tyrosine hydroxylase. Importantly, strong c-Fos activation is also detected in the arcuate nucleus of the hypothalamus (ARC), particularly in neurons that co-express alpha melanocyte stimulating hormone (α-MSH), the anorexigenic product of the proopiomelanocortin (POMC) gene. Interestingly, other hypothalamic regions such as the paraventricular nucleus, the ventromedial nucleus and the lateral hypothalamic area also show c-Fos induction after PP injection. In addition to c-Fos activation, PP injection up-regulates POMC mRNA expression in the ARC as detected by in situ hybridization. These effects are a direct consequence of local Y4 signaling, since hypothalamus-specific conditional Y4 receptor knockout abolishes PP-induced ARC c-Fos activation and blocks the PP-induced increase in POMC mRNA expression. Additionally, the hypophagic effect of i.p. PP seen in wild type mice is completely absent in melanocortin 4 receptor knockout mice.

Conclusions/Significance

Taken together, these findings show that PP reduces food intake predominantly via stimulation of the anorexigenic α-MSH signaling pathway, and that this effect is mediated by direct action on local Y4 receptors within the ARC, highlighting a potential novel avenue for the treatment of obesity.

Functional recovery after delayed treatment of ischemic stroke with melanocortins is associated with overexpression of the activity-dependent gene Zif268

Melanocortin peptides afford strong neuroprotection and improve functional recovery in experimental ischemic stroke; they also have established neurotrophic actions. The expression of the immediate early gene Zif268 is dependent on synaptic activity and is involved in injury repair and memory formation. Here, we investigated the role of Zif268 in learning and memory recovery after delayed treatment of ischemic stroke with the melanocortin analog [Nle(4), D-Phe(7)]alpha-MSH (NDP-alpha-MSH). A 10-min period of global cerebral ischemia was induced by occluding both common carotid arteries in gerbils. Treatment with a nanomolar dose of NDP-alpha-MSH (every 12h for 11 days) was performed starting 3h or 9h after stroke induction; where indicated, gerbils were pretreated with the melanocortin MC(4) receptor antagonist HS024. Animals were subjected to the Morris water-maze test (four sessions from 4 to 50 days after the ischemic episode). Fifty days after stroke, histological damage and Zif268 expression were investigated in the hippocampus. Treatment with NDP-alpha-MSH significantly reduced hippocampal damage, including neuronal death, and improved learning and memory recovery. This protective effect was long-lasting (50 days, at least) and associated with Zif268 overexpression, with both schedules of NDP-alpha-MSH treatment. Pharmacological blockade of MC(4) receptors prevented these effects. Our data indicate that MC(4) receptor-mediated actions of melanocortins could trigger repair mechanisms able to improve neuronal functionality and synaptic plasticity, and to promote long-lasting functional recovery from ischemic stroke with Zif268 gene involvement.

High ambient temperature reverses hypothalamic MC4 receptor overexpression in an animal model of anorexia nervosa

The potential involvement of the melanocortin system in the beneficial effects of heat application in rats submitted to activity-based anorexia (ABA), an analogous model of anorexia nervosa (AN), was studied. Once ABA rats had lost 20% of body weight, half of the animals were exposed to a high ambient temperature (HAT) of 32 degrees C, whereas the rest were maintained at 21 degrees C. Control sedentary rats yoked to ABA animals received the same treatment. ABA rats (21 degrees C) showed increased Melanocortin 4 (MC4) receptor and Agouti gene Related Peptide (AgRP) expression, and decreased pro-opiomelanocortin (POMC) mRNA levels (Real Time PCR), with respect to controls. Heat application increased weight gain and food intake, and reduced running rate in ABA rats, when compared with ABA rats at 21 degrees C. However, no changes in body weight and food intake were observed in sedentary rats exposed to heat. Moreover, heat application reduced MC4 receptor, AgRP and POMC expression in ABA rats, but no changes were observed in control rats. These results indicate that hypothalamic MC4 receptor overexpression could occur on the basis of the characteristic hyperactivity, weight loss, and self-starvation of ABA rats, and suggest the involvement of hypothalamic melanocortin neural circuits in behavioural changes shown by AN patients. Changes in AgRP and POMC expression could represent an adaptative response to equilibrate energy balance. Moreover, the fact that HAT reversed hypothalamic MC4 receptor overexpression in ABA rats indicates the involvement of brain melanocortin system in the reported beneficial effects of heat application in AN. A combination of MC4 receptor antagonists and heat application could improve the clinical management of AN.

Nesfatin-1 increases anxiety- and fear-related behaviors in the rat

RATIONALE

Nesfatin-1, derived from the protein NEFA/nucleobindin2 (NUCB2), is a newly identified peptide that acts as a potent satiety agent. It has been reported that peptides involved in the regulation of ingestive behavior are also involved in the regulation of the stress response. However, the relation between nesfatin-1 and stressor-related behaviors like anxiety and/or fear has not yet been investigated.

OBJECTIVE

The effects of intracerebroventricular (ICV) injection of nesfatin-1 (0, 5, and 25 pmol/3 microl) were assessed in several paradigms that are thought to reflect anxiety and/or fear in rats.

RESULTS

Consistent with an anxiogenic effect, nesfatin-1 dose-dependently decreased the percentage of time spent on the open arms of the elevated plus maze, increased latency to approach, and decreased consumption of a palatable snack in an anxiogenic (unfamiliar) environment. Moreover, ICV nesfatin-1 increased the fear-potentiated startle response and the time spent freezing to both context and conditioned cues in a conditioned emotional response test.

CONCLUSIONS

These findings suggest that in addition to its role as a satiety peptide, nesfatin-1 may also be involved in the mediation of anxiety- and/or fear-related responses.

The role of the Agouti-Related Protein in energy balance regulation

The Agouti-Related Protein (AgRP) is a powerful orexigenic peptide that increases food intake when ubiquitously overexpressed or when administered centrally. AgRP-deficiency, on the other hand, leads to increased metabolic rate and a longer lifespan when mice consume a high fat diet. In humans, AgRP polymorphisms have been consistently associated with resistance to fatness in Blacks and Whites and resistance to the development of type-2 diabetes in African Blacks. Systemically administered AgRP accumulates in the liver, the adrenal gland and fat tissue while recent findings suggest that AgRP may also have inverse agonist effects, both centrally and peripherally. AgRP could thus modulate energy balance via different actions. Its absence or reduced functionality may offer a benefit both in terms of bringing about negative energy balance in obesigenic environments, as well as leading to an increased lifespan.

Nesfatin-1 increases anxiety- and fear-related behaviors in the rat

RATIONALE

Nesfatin-1, derived from the protein NEFA/nucleobindin2 (NUCB2), is a newly identified peptide that acts as a potent satiety agent. It has been reported that peptides involved in the regulation of ingestive behavior are also involved in the regulation of the stress response. However, the relation between nesfatin-1 and stressor-related behaviors like anxiety and/or fear has not yet been investigated.

OBJECTIVE

The effects of intracerebroventricular (ICV) injection of nesfatin-1 (0, 5, and 25 pmol/3 microl) were assessed in several paradigms that are thought to reflect anxiety and/or fear in rats.

RESULTS

Consistent with an anxiogenic effect, nesfatin-1 dose-dependently decreased the percentage of time spent on the open arms of the elevated plus maze, increased latency to approach, and decreased consumption of a palatable snack in an anxiogenic (unfamiliar) environment. Moreover, ICV nesfatin-1 increased the fear-potentiated startle response and the time spent freezing to both context and conditioned cues in a conditioned emotional response test.

CONCLUSIONS

These findings suggest that in addition to its role as a satiety peptide, nesfatin-1 may also be involved in the mediation of anxiety- and/or fear-related responses.

Maternal nutrition and the programming of obesity: The brain

The increasing incidence of obesity in the developed and developing world in the last decade has led to a need to define our understanding of the physiological mechanisms which can predispose individuals to weight gain in infancy, childhood and adulthood. There is now a considerable body of evidence which has shown that the pathway to obesity may begin very early in life, and that exposure to an inappropriate level of nutrition during prenatal and/or early postnatal development can predispose individuals to obesity in later life The brain is at the heart of the regulation of appetite and food preferences, and it is increasingly being recognized that the development of central appetitive structures is acutely sensitive to the nutritional environment both before and immediately after birth. This review will summarize the body of work which has highlighted the critical role of the brain in the early origins of obesity and presents some perspectives as to the potential application of these research findings in the clinical setting.

Effects of fluoxetine administration on hypothalamic melanocortin system in obese Zucker rats

The aim of the present work was to study the potential involvement of melanocortin system in the anorectic mechanism of fluoxetine, a selective serotonin reuptake inhibitors, in obese Zucker rats. Male obese Zucker (fa/fa) rats were administered fluoxetine (10 mg/kg; i.p.) daily for two weeks. The control group was given 0.9% NaCl solution. RT-PCR for pro-opiomelanocortin (POMC), Agouti gene related peptide (AgRP) and melanocortin receptor 4 (MC4-R) in the hypothalamus, as well as regional immunostaining for alpha-melanocyte stimulating hormone (alpha-MSH) and MC4-R were carried out. Fluoxetine administration increased POMC expression and reduced MC4-R expression in the hypothalamus, without changes in AgRP mRNA levels. Moreover, an increase in the numbers of alpha-MSH positively immunostained neural cells in the hypothalamic arcuate nucleus (ARC), as well as a significant decrease in the numbers of neural cells positively immunostained for MC4-R in the paraventricular nucleus (PVN), without changes in lateral hypothalamic area (LHA), were observed. These results suggest the involvement of alpha-MSH in central fluoxetine anorectic action.

Synthesis and biological activity of novel peptide mimetics as melanocortin receptor agonists

A series of novel peptidomimetic analogs was prepared containing cyclohexyl, phenyl, or heterocyclic groups to ostensibly orient the guanidine or mimic of an arginine in a putative melanocortin receptor ligand pharmacophore. Some binding affinity at the melanocortin receptors MC(3) and MC(4) was noted. In silico docking also indicated that the relative positions of the hydrogen-bonding sites and hydrophobic regions of the compounds are reasonably well matched to the receptor-binding site. This may present a lead entry into a selective series of MC(4)R agonists.

MTII attenuates ghrelin- and food deprivation-induced increases in food hoarding and food intake

Food deprivation triggers a constellation of physiological and behavioral changes including increases in peripherally-produced ghrelin and centrally-produced agouti-related protein (AgRP). Upon refeeding, food intake is increased in most species, however hamsters primarily increase food hoarding. Food deprivation-induced increases in food hoarding by Siberian hamsters are mimicked by peripheral ghrelin and central AgRP injections. Because food deprivation stimulates ghrelin as well as AgRP synthesis/release, food deprivation-induced increases in hoarding may be mediated by melanocortin 3 or 4 receptor (MC3/4-R) antagonism via AgRP, the MC3/4-R inverse agonist. Therefore, we asked: Can a MC3/4-R agonist block food deprivation- or ghrelin-induced increases in foraging, food hoarding and food intake? This was accomplished by injecting melanotan II (MTII), a synthetic MC3/4-R agonist, into the 3rd ventricle in food deprived, fed or peripheral ghrelin injected hamsters and housed in a running wheel-based food delivery foraging system. Three foraging conditions were used: a) no running wheel access, non-contingent food, b) running wheel access, non-contingent food or c) a foraging requirement for food (10 revolutions/pellet). Food deprivation was a more potent stimulator of foraging and hoarding than ghrelin. Concurrent injections of MTII completely blocked food deprivation- and ghrelin-induced increases in food intake and attenuated, but did not always completely block, food deprivation- and ghrelin-induced increases in food hoarding. Collectively, these data suggest that the MC3/4-R are involved in ghrelin- and food deprivation-induced increases in food intake, but other neurochemical systems, such as previously demonstrated with neuropeptide Y, also are involved in increases in food hoarding as well as foraging.

The melanocortinergic pathway is rapidly recruited by emotional stress and contributes to stress-induced anorexia and anxiety-like behavior

Neurons producing melanocortin receptor agonist, alpha-MSH derived from proopiomelanocortin, and antagonist, agouti-related protein, are known to be sensitive to metabolic stress such as food deprivation and glucoprivation. However, how these neurons respond to emotional/psychological stress remained to be elucidated. We report here that acute emotional stressors, i.e. restraint and forced swim, evoked mRNA expression of c-fos, a neuronal activation marker, in a high percentage of proopiomelanocortin neurons (up to 53% for restraint stress and 62% for forced swim), with marked variations along the rostro-caudal axis of the arcuate nucleus. In contrast, only a small population of agouti-related protein neurons in this brain region was activated. These neuronal activation patterns were correlated with behavioral reactions. Both stressors suppressed feeding and induced anxiety-like behavior in the elevated plus-maze test, as reflected by a reduction in the percentage of entries and time spent in the open arms. Central pretreatment with SHU9119, a melanocortin receptor antagonist, dose dependently attenuated the anorectic and anxiogenic effects elicited by acute restraint or forced swim. These results indicate that the melancortinergic pathway can be rapidly recruited by acute emotional stress, and that activation of melanocortin signaling is involved in mediating stress-induced anorexia and anxiety.

Melanocortin subtype 4 receptor agonists: Structure–activity relationships about the 4-alkyl piperidine core

SAR about the piperidine core in a series of MC4R agonists is described. A number of alkyl substituents that furnish compounds with good affinity and functional potency are reported.

Substituted NDP-MSH peptides paired with mutant melanocortin-4 receptors demonstrate the role of transmembrane 6 in receptor activation

The melanocortin-4 receptor (MC4R) is involved in regulating energy homeostasis and is a potential therapeutic target for obesity and cachexia. Molecular interactions between peptide ligands and MC4R have been studied in detail. Less is known regarding the role of these interactions in the mechanism of MC4R activation. The aim of this study was to investigate the molecular mechanism of human MC4R activation by [Nle4, d-Phe7]alpha-melanocyte-stimulating hormone (NDP-MSH), by first defining the role of the His6-d-Phe7-Arg8-Trp9 residues in receptor activation (Emax for stimulation of cAMP accumulation) using modified peptides, then understanding how their interaction with the receptor modulates activation using site-directed mutagenesis and a molecular model of NDP-MSH bound to the active state of the receptor. Alanine substitution indicated that the d-Phe7, Arg8, and Trp9 side chains contribute binding energy but are not essential for the receptor activation event. Conversely, His6 to Ala6 substitution reduced receptor activation but did not affect affinity. Chlorine substitutions on the d-Phe7 side chain also inhibited receptor activation. F261(6.51)A and F284(7.35)A receptor mutations acted as gain-of-function mutations, restoring efficacy to the His6 and d-Phe7 substituted peptides that had lost efficacy at the wild-type receptor. Based on a model of NDP-MSH and MC4R interaction, the antagonist behavior of these peptides is consistent with the prevention of transmembrane 6 (TM6) rotation. This data supports the hypothesis that increasing the size of d-Phe7 directly interferes with TM6 rotation, preventing receptor activation. We further propose that removing the interaction with the His6 side chain reorients the peptide within the binding pocket, indirectly impeding TM6 rotation by strengthening peptide interaction with F261(6.51) and F284(7.35). These findings refine the molecular basis for the mechanism of ligand-stimulated hMC4R activation and will be useful for the development of hMC4R agonists and antagonists.

Brain-adipose tissue neural crosstalk

The preponderance of basic obesity research focuses on its development as affected by diet and other environmental factors, genetics and their interactions. By contrast, we have been studying the reversal of a naturally-occurring seasonal obesity in Siberian hamsters. In the course of this work, we determined that the sympathetic innervation of white adipose tissue (WAT) is the principal initiator of lipid mobilization not only in these animals, but in all mammals including humans. We present irrefutable evidence for the sympathetic nervous system (SNS) innervation of WAT with respect to neuroanatomy (including its central origins as revealed by transneuronal viral tract tracers), neurochemistry (norepinephrine turnover studies) and function (surgical and chemical denervation). A relatively unappreciated role of WAT SNS innervation also is reviewed--the control of fat cell proliferation as shown by selective chemical denervation that triggers adipocyte proliferation, although the precise mechanism by which this occurs presently is unknown. There is no, however, equally strong evidence for the parasympathetic innervation of this tissue; indeed, the data largely are negative severely questioning its existence and importance. Convincing evidence also is given for the sensory innervation of WAT (as shown by tract tracing and by markers for sensory nerves in WAT), with suggestive data supporting a possible role in conveying information on the degree of adiposity to the brain. Collectively, these data offer an additional or alternative view to the predominate one of the control of body fat stores via circulating factors that serve as efferent and afferent communicators.

Further structure-activity studies of lactam derivatives of MT-II and SHU-9119: their activity and selectivity at human melanocortin receptors 3, 4, and 5

Recently we have demonstrated that replacing His(6) by constrained amino acids(2) in the well-known antagonist SHU-9119 resulted in potent and selective antagonist ligands especially at the hMC3R and hMC5 receptors. With the aim to further explore position 6 in the sequence of SHU-9119 and MT-II, we have designed, synthesized, and pharmacologically characterized a series of peptide analogues of MT-II and SHU-9119 at the human melanocortin receptors subtypes MC3R, MC4R and MC5R. All these peptides were modified at position 6 with constrained amino acids which are commercially available. In this study, we have identified new selective ligands for the hMC4R, and an antagonist for the hMC3/hMC4 receptors. Additionally, we have discovered an interesting new selective antagonist at the hMC3R, Ac-Nle-c[Asp-betaAla-DNal(2')-Arg-Trp-Lys]-NH(2) (2, PG-106) which represents an important tool in further biological investigations of the hMC3R. PG-106 will be useful in further efforts to differentiate the substructural features responsible for selectivity at the hMC3R, hMC4R, and hMC5R.

Thematic review series: adipocyte biology. Sympathetic and sensory innervation of white adipose tissue

During our study of the reversal of seasonal obesity in Siberian hamsters, we found an interaction between receptors for the pineal hormone melatonin and the sympathetic nervous system (SNS) outflow from brain to white adipose tissue (WAT). This ultimately led us and others to conclude that the SNS innervation of WAT is the primary initiator of lipid mobilization in these as well as other animals, including humans. There is strong neurochemical (norepinephrine turnover), neuroanatomical (viral tract tracing), and functional (sympathetic denervation-induced blockade of lipolysis) evidence for the role of the SNS in lipid mobilization. Recent findings suggest the presence of WAT sensory innervation based on strong neuroanatomical (viral tract tracing, immunohistochemical markers of sensory nerves) and suggestive functional (capsaicin sensory denervation-induced WAT growth) evidence, the latter implying a role in conveying adiposity information to the brain. By contrast, parasympathetic nervous system innervation of WAT is characterized by largely negative neuroanatomical evidence (viral tract tracing, immunohistochemical and biochemical markers of parasympathetic nerves). Functional evidence (intraneural stimulation and in situ microdialysis) for the role of the SNS innervation in lipid mobilization in human WAT is convincing, with some controversy regarding the level of sympathetic nerve activity in human obesity.

Novel selective human melanocortin-3 receptor ligands: use of the 4-amino-1,2,4,5-tetrahydro-2-benzazepin-3-one (Aba) scaffold

In search of new selective antagonists and/or agonists for the human melanocortin receptor subtypes hMC1R to hMC5R to elucidate the specific biological roles of each GPCR, we modified the structures of the superagonist MT-II (Ac-Nle-c[Asp-His-D-Phe-Arg-Trp-Lys]-NH(2)) and the hMC3R/hMC4R antagonist SHU9119 (Ac-Nle-c[Asp-His-D-Nal(2')-Arg-Trp-Lys]-NH(2)) by replacing the His-d-Phe and His-d-Nal(2') fragments in MT-II and SHU9119, respectively, with Aba-Xxx (4-amino-1,2,4,5-tetrahydro-2-benzazepin-3-one-Xxx) dipeptidomimetics (Xxx=D-Phe/pCl-D-Phe/D-Nal(2')). Employment of the Aba mimetic yielded novel selective high affinity hMC3R and hMC3R/hMC5R antagonists.

Expression and localization of melanocortin-1 receptor in human adipose tissues of severely obese patients

OBJECTIVE

The melanocortin system is a key regulator in the hypothalamus of energy intake and expenditure. It is frequently linked with obesity and apparently modulates sympathetic outflow to white adipose tissues. The role of the melanocortins within adipose tissues, however, is not entirely clear. This study was aimed at determining the quantitative expression of the five melanocortin receptors (MC1-R to MC5-R) in subcutaneous and omental fat of obese patients and non-obese subjects.

RESEARCH METHODS AND PROCEDURES

Expression of MC1-R to MC5-R, proopiomelanocortin, agouti signaling protein, leptin, leptin receptor, and uncoupling protein-1 was investigated in human fat samples by quantitative reverse transcription-polymerase chain reaction. MC1-R expression was also studied in preadipocytes, adipocytes, and monocytic THP-1 cells and by immunohistochemical localization in adipose tissues.

RESULTS

Notable expression was found for MC1-R, whereas no mRNA for MC2-R and MC3-R was detected; MC4-R and MC5-R mRNA was occasionally detectable but at very low levels. MC1-R mRNA in subcutaneous fat was increased in obese patients as compared with controls; omental fat of both groups had slightly higher MC1-R expression than subcutaneous fat and did not differ between patient groups. Immunohistochemical analysis of the MC1-R in adipose tissue sections showed that MC1-R expression was higher in macrophages but also present in adipocytes.

DISCUSSION

The expression of MC1-R and the lack of MC2-R in human adipose tissues indicate that the melanocortins may regulate cell proliferation and/or inflammatory signals rather than lipolysis. Also, the increased expression of MC1-R in subcutaneous fat of obese subjects may reflect one aspect of the pathophysiology of obesity.

Effects of estradiol on acute and recurrent insulin-induced hypoglycemia-associated patterns of arcuate neuropeptide Y, proopiomelanocortin, and cocaine- and amphetamine-related transcript gene expression in the ovariectomized rat

The ovarian steroid hormone, estradiol, is one of several peripheral metabolic signal modulators that are integrated at the level of the arcuate nucleus of the hypothalamus (ARH), and is implicated in the control of ARH neuropeptides that maintain energy balance, including neuropeptide Y (NPY) and proopiomelanocortin (POMC). The present studies utilized quantitative real-time RT-PCR techniques to examine the hypothesis that estradiol regulates ARH NPY, POMC, and cocaine- and amphetamine-related transcript (CART) gene expression during acute insulin-induced hypoglycemia (IIH) and that adaptive modifications in transcriptional reactivity during recurring exposure are steroid dependent. ARH tissue was obtained by micropunch dissection from estradiol benzoate- and oil-implanted ovariectomized (OVX) rats that were treated by subcutaneous injection of one or four doses of the intermediate insulin formulation, Humulin NPH, over as many days, or vehicle alone. Our data show that in OVX plus estradiol benzoate and OVX plus oil groups, a single injection of insulin did not modify gene expression profiles, with the exception of acute hypoglycemic reduction of ARH NPY transcripts in the presence of estrogen. Prior exposure to daily hypoglycemia significantly diminished basal NPY and POMC mRNA levels in estradiol benzoate-, but not oil-implanted OVX rats, but elevated baseline CART transcripts in oil-treated animals. Recurring IIH enhanced ARH NPY gene expression relative to baseline, irrespective of the estradiol manipulation, but net tissue levels were greater in the absence of estrogen. In contrast, reexposure to hypoglycemia decreased POMC and CART gene transcription in estradiol benzoate- and oil-implanted OVX animals, respectively, relative to the single-dose groups. These studies show that estrogen modulates the impact of precedent exposure to IIH on basal and/or hypoglycemia-associated patterns of expression of ARH neuropeptide genes of characterized significance for energy homeostasis. The novel evidence for transcriptional acclimation of NPY, POMC, and CART to recurring IIH supports the possibility that adaptation of compensatory behavioral and physiological responses to acute versus chronic exposure to this metabolic stress may reflect neural regulatory mechanisms involving one or more neurotransmitters encoded by these genes.