Food Perception Primes Hepatic ER Homeostasis via Melanocortin-Dependent Control of mTOR Activation.

Adaptation of liver to the postprandial state requires coordinated regulation of protein synthesis and folding aligned with changes in lipid metabolism. Here we demonstrate that sensory food perception is sufficient to elicit early activation of hepatic mTOR signaling, Xbp1 splicing, increased expression of ER-stress genes, and phosphatidylcholine synthesis, which translate into a rapid morphological ER remodeling. These responses overlap with those activated during refeeding, where they are maintained and constantly increased upon nutrient supply. Sensory food perception activates POMC neurons in the hypothalamus, optogenetic activation of POMC neurons activates hepatic mTOR signaling and Xbp1 splicing, whereas lack of MC4R expression attenuates these responses to sensory food perception. Chemogenetic POMC-neuron activation promotes sympathetic nerve activity (SNA) subserving the liver, and norepinephrine evokes the same responses in hepatocytes in vitro and in liver in vivo as observed upon sensory food perception. Collectively, our experiments unravel that sensory food perception coordinately primes postprandial liver ER adaption through a melanocortin-SNA-mTOR-Xbp1s axis. VIDEO ABSTRACT.

Evidence for a feeding related association between melanocortin in the NTS and Neuropeptide-Y in the PVN.

Melanocortin and neuropeptide-Y (NPY) are both involved in feeding and energy regulation, and they have opposite effects in the paraventricular nucleus of the hypothalamus (PVN). The present study examined an interaction between melanocortin in the nucleus of the solitary tract (NTS) and NPY in the PVN. Male Sprague-Dawley rats were implanted with cannulae in the injection sites of interest. In Experiment 1, subjects received either the melanocortin 3/4-receptor (MC3/4) antagonist SHU9119 (0, 10, 50 and 100 pmol/0.5 µl) or the MC3/4 agonist MTII (0, 10, 50, 100 and 200 pmol/0.5 µl) into the NTS. Food intake was measured at 1, 2, 4, 6 and 24-h post-injection. Administration of SHU9119 into the NTS significantly and dose-dependently increased food intake at 1, 2, 4, 6 and 6-24-h, and administration of MTII into the NTS significantly and dose-dependently decreased 24-h free feeding. In Experiment 2, subjects received the MC3/4 agonist MTII (0, 10, 50, 100 and 200 pmol/0.5 µl) into the NTS just prior to NPY (0 and 1µg/0.5 µl) in the PVN. PVN injection of NPY stimulated feeding, and administration of MTII (50, 100 and 200 pmol) into the NTS significantly and dose-dependently decreased NPY-induced feeding at 2, 4, 6 and 6-24-h. These data suggest that there could be a neuronal association between melanocortin in the NTS and NPY in the PVN, and that the melanocortin system in the NTS has an antagonistic effect on NPY-induced feeding in the PVN.

The Melanocortin System: A Promising Target for the Development of New Antidepressant Drugs.

Major depression is one of the most prevalent mental disorders, causing significant human suffering and socioeconomic loss. Since conventional antidepressants are not sufficiently effective, there is an urgent need to develop new antidepressant medications. Despite marked advances in the neurobiology of depression, the etiology and pathophysiology of this disease remain poorly understood. Classical and newer hypotheses of depression suggest that an imbalance of brain monoamines, dysregulation of the hypothalamic-pituitary-adrenal axis (HPAA) and immune system, or impaired hippocampal neurogenesis and neurotrophic factors pathways are cause of depression. It is assumed that conventional antidepressants improve these closely related disturbances. The purpose of this review was to discuss the possibility of affecting these disturbances by targeting the melanocortin system, which includes adrenocorticotropic hormone-activated receptors and their peptide ligands (melanocortins). The melanocortin system is involved in the regulation of various processes in the brain and periphery. Melanocortins, including peripherally administered non-corticotropic agonists, regulate HPAA activity, exhibit anti-inflammatory effects, stimulate the levels of neurotrophic factors, and enhance hippocampal neurogenesis and neurotransmission. Therefore, endogenous melanocortins and their analogs are able to complexly affect the functioning of those body's systems that are closely related to depression and the effects of antidepressants, thereby demonstrating a promising antidepressant potential.

Melanocortin MC4R receptor is required for energy expenditure but not blood pressure effects of angiotensin II within the mouse brain.

The brain renin-angiotensin system (RAS) is implicated in control of blood pressure (BP), fluid intake, and energy expenditure (EE). Angiotensin II (ANG II) within the arcuate nucleus of the hypothalamus contributes to control of resting metabolic rate (RMR) and thereby EE through its actions on Agouti-related peptide (AgRP) neurons, which also contribute to EE control by leptin. First, we determined that although leptin stimulates EE in control littermates, mice with transgenic activation of the brain RAS (sRA) exhibit increased EE and leptin has no additive effect to exaggerate EE in these mice. These findings led us to hypothesize that leptin and ANG II in the brain stimulate EE through a shared mechanism. Because AgRP signaling to the melanocortin MC4R receptor contributes to the metabolic effects of leptin, we performed a series of studies examining RMR, fluid intake, and BP responses to ANG II in mice rendered deficient for expression of MC4R via a transcriptional block (Mc4r-TB). These mice were resistant to stimulation of RMR in response to activation of the endogenous brain RAS via chronic deoxycorticosterone acetate (DOCA)-salt treatment, whereas fluid and electrolyte effects remained intact. These mice were also resistant to stimulation of RMR via acute intracerebroventricular (ICV) injection of ANG II, whereas BP responses to ICV ANG II remained intact. Collectively, these data demonstrate that the effects of ANG II within the brain to control RMR and EE are dependent on MC4R signaling, whereas fluid homeostasis and BP responses are independent of MC4R signaling.

Antistress Action of Melanocortin Derivatives Associated with Correction of Gene Expression Patterns in the Hippocampus of Male Rats Following Acute Stress.

Natural melanocortins (MCs) have been used in the successful development of drugs with neuroprotective properties. Here, we studied the behavioral effects and molecular genetic mechanisms of two synthetic MC derivatives-ACTH(4-7)PGP (Semax) and ACTH(6-9)PGP under normal and acute restraint stress (ARS) conditions. Administration of Semax or ACTH(6-9)PGP (100 µg/kg) to rats 30 min before ARS attenuated ARS-induced behavioral alterations. Using high-throughput RNA sequencing (RNA-Seq), we identified 1359 differentially expressed genes (DEGs) in the hippocampus of vehicle-treated rats subjected to ARS, using a cutoff of >1.5 fold change and adjusted p-value (Padj) < 0.05, in samples collected 4.5 h after the ARS. Semax administration produced > 1500 DEGs, whereas ACTH(6-9)PGP administration led to <400 DEGs at 4.5 h after ARS. Nevertheless, ~250 overlapping DEGs were identified, and expression of these DEGs was changed unidirectionally by both peptides under ARS conditions. Modulation of the expression of genes associated with biogenesis, translation of RNA, DNA replication, and immune and nervous system function was produced by both peptides. Furthermore, both peptides upregulated the expression levels of many genes that displayed decreased expression after ARS, and vice versa, the MC peptides downregulated the expression levels of genes that were upregulated by ARS. Consequently, the antistress action of MC peptides may be associated with a correction of gene expression patterns that are disrupted during ARS.

[Melanocortin peptides : Fundamentals, translational research, clinical dermatology, and future perspectives]. / Melanokortinpeptide : Grundlagen, translationale Forschung, klinische Dermatologie und Zukunftsperspektiven.

Melanocortins are peptides that share a common central pharmacophor. Melanin pigmentation of interfollicular epidermis and hair via MC1R remains the key physiologic function of the naturally occurring melanocortin peptides in skin. Moreover, the melanocortins are crucially involved in the ultraviolet light-induced tanning response. Under pathophysiologic conditions, melanocortin peptides induce cutaneous hyperpigmentation, likewise via the MC1R axis, e.g. in patients with Addison's disease, ectopic precursor pro-opiomelanocortin (POMC) syndrome and in those with abnormally elevated melanocortin blood levels. Translational research on α­MSH (melanocyte-stimulating hormones) and their antagonists has further revealed a variety of other biological activities beyond pigmentation. They include cytoprotection, antioxidative effects, regulation of collagen metabolism and fibrosis, sebum production, and cutaneous wound healing. These findings have also promoted the development of novel therapies in clinical dermatology including the exploitation of afamelanotide. In 2015, this agent became the first in-class synthetic α­MSH analogue to be approved in dermatology for the treatment of erythropoetic protoporphyria. In addition to afamelanotide, setmelanotide has recently emerged as a highly selective MC4R agonist useful for the treatment of distinct forms of genetically determined obesity, e.g., POMC deficiency. Future perspectives in dermatology reside in treatment of other difficult-to-treat skin diseases with α­MSH analogues, either with topical or systemic formulations. Moreover, synthetic melanocortin peptide derivatives lacking the central pharmacophor but with maintained anti-inflammatory effects could become a promising strategy for the design of new therapies in dermatology.

Peripherally administered melanocortins induce mice fat browning and prevent obesity.

BACKGROUND/OBJECTIVES: The browning of white adipose tissue (WAT) has been in the spotlight during the last years, becoming an attractive approach to combat obesity. Melanocortin neuropeptides, such as α-melanocyte-stimulating hormone (α-MSH), are well-known regulators of appetite at the central nervous system, but its role in adipocyte metabolism is poorly elucidated. This study sought to verify if α-MSH can induce transdifferentiation of white to brown/beige adipocytes and to determine whether it can ameliorate the obesity phenotype. METHODS: The browning effect of α-MSH was determined in isolated adipocytes using the 3T3-L1 cell line and in inguinal subcutaneous adipose tissue (ingWAT) of diet-induced obese (DIO) mice by quantifying the expression of browning hallmark genes, oxygen consumption, and mitochondrial biogenesis. α-MSH protection from diet-induced obesity was evaluated by analyzing mice body weight, fat mass, and lipid and glucose serum profiles. RESULTS: Here, we report that α-MSH activates a thermogenic gene program and increases the mitochondrial respiratory rate in 3T3-L1 adipocytes and ingWAT of DIO mice. Without affecting food intake, peripheral administration of α-MSH decreases body weight and ingWAT mass, promoting a significant rise in the number of smaller adipocytes, whereas it lowered the larger ones. Additionally, there was an increase in the mass of brown adipose tissue. Browning activation occurs concomitantly with improvement on serum lipid profile, insulin resistance, and glucose homeostasis. CONCLUSIONS: This study highlights the anti-obesity properties of melanocortins by promoting ingWAT browning and provides new perspectives for future designing of more effective therapeutic strategies.

Are melanocortin peptides future therapeutics for cutaneous wound healing?

Cutaneous wound healing is a complex process divided into different phases, that is an inflammatory, proliferative and remodelling phase. During these phases, a variety of resident skin cell types but also cells of the immune system orchestrate the healing process. In the last year, it has been shown that the majority of cutaneous cell types express the melanocortin 1 receptor (MC1R) that binds α-melanocyte-stimulating hormone (α-MSH) with high affinity and elicits pleiotropic biological effects, for example modulation of inflammation and immune responses, cytoprotection, antioxidative defense and collagen turnover. Truncated α-MSH peptides such as Lys-Pro-Val (KPV) as well as derivatives like Lys-d-Pro-Thr (KdPT), the latter containing the amino acid sequence 193-195 of interleukin-1ß, have been found to possess anti-inflammatory effects but to lack the pigment-inducing activity of α-MSH. We propose here that such peptides are promising future candidates for the treatment of cutaneous wounds and skin ulcers. Experimental approaches in silico, in vitro, ex vivo and in animal models are outlined. This is followed by an unbiased discussion of the pro and contra arguments of such peptides as future candidates for the therapeutic management of cutaneous wounds and a review of the so-far available data on melanocortin peptides and derivatives in wound healing.

The Use of Human Induced Pluripotent Stem Cells for Testing Neuroprotective Activity of Pharmacological Compounds.

Development of therapeutic preparations involves several steps, starting with the synthesis of chemical compounds and testing them in different models for selecting the most effective and safest ones to clinical trials and introduction into medical practice. Cultured animal cells (both primary and transformed) are commonly used as models for compound screening. However, cell models display a number of disadvantages, including insufficient standardization (primary cells) and disruption of cell genotypes (transformed cells). Generation of human induced pluripotent stem cells (IPSCs) offers new possibilities for the development of high-throughput test systems for screening potential therapeutic preparations with different activity spectra. Due to the capacity to differentiate into all cell types of an adult organism, IPSCs are a unique model that allows examining the activity and potential toxicity of tested compounds during the entire differentiation process in vitro. In this work, we demonstrated the efficiency of IPSCs and their neuronal derivatives for selecting substances with the neuroprotective activity using two classes of compounds - melanocortin family peptides and endocannabinoids. None of the tested compounds displayed cyto- or embryotoxicity. Both melanocortin peptides and endocannabinoids exerted neuroprotective effect in the neuronal precursors and IPSC-derived neurons subjected to hydrogen peroxide. The endocannabinoid N-docosahexaenoyl dopamine exhibited the highest neuroprotective effect (~70%) in the differentiated cultures enriched with dopaminergic neurons; the effect of melanocortin Semax was ~40%. The possibility of using other IPSC derivatives for selecting compounds with the neuroprotective activity is discussed.

Bench-top to clinical therapies: A review of melanocortin ligands from 1954 to 2016.

The discovery of the endogenous melanocortin agonists in the 1950s have resulted in sixty years of melanocortin ligand research. Early efforts involved truncations or select modifications of the naturally occurring agonists leading to the development of many potent and selective ligands. With the identification and cloning of the five known melanocortin receptors, many ligands were improved upon through bench-top in vitro assays. Optimization of select properties resulted in ligands adopted as clinical candidates. A summary of every melanocortin ligand is outside the scope of this review. Instead, this review will focus on the following topics: classic melanocortin ligands, selective ligands, small molecule (non-peptide) ligands, ligands with sex-specific effects, bivalent and multivalent ligands, and ligands advanced to clinical trials. Each topic area will be summarized with current references to update the melanocortin field on recent progress. This article is part of a Special Issue entitled: Melanocortin Receptors - edited by Ya-Xiong Tao.

Design, synthesis, structural and functional characterization of novel melanocortin agonists based on the cyclotide kalata B1.

BACKGROUND: Cyclotides are useful scaffolds to stabilize bioactive peptides. RESULTS: Four melanocortin analogues of kalata B1 were synthesized. One is a selective MC4R agonist. CONCLUSION: The analogues retain the native kalata B1 scaffold and introduce a designed pharmacological activity, validating cyclotides as protein engineering scaffolds. SIGNIFICANCE: A novel type of melanocortin agonist has been developed, with potential as a drug lead for treating obesity. Obesity is an increasingly important global health problem that lacks current treatment options. The melanocortin receptor 4 (MC4R) is a target for obesity therapies because its activation triggers appetite suppression and increases energy expenditure. Cyclotides have been suggested as scaffolds for the insertion and stabilization of pharmaceutically active peptides. In this study, we explored the development of appetite-reducing peptides by synthesizing MC4R agonists based on the insertion of the His-Phe-Arg-Trp sequence into the cyclotide kalata B1. The ability of the analogues to fold similarly to kalata B1 but display MC4R activity were investigated. Four peptides were synthesized using t-butoxycarbonyl peptide chemistry with a C-terminal thioester to facilitate backbone cyclization. The structures of the peptides were found to be similar to kalata B1, evaluated by Hα NMR chemical shifts. KB1(GHFRWG;23-28) had a K(i) of 29 nm at the MC4R and was 107 or 314 times more selective over this receptor than MC1R or MC5R, respectively, and had no detectable binding to MC3R. The peptide had higher affinity for the MC4R than the endogenous agonist, α-melanocyte stimulation hormone, but it was less potent at the MC4R, with an EC(50) of 580 nm for activation of the MC4R. In conclusion, we synthesized melanocortin analogues of kalata B1 that preserve the structural scaffold and display receptor binding and functional activity. KB1(GHFRWG;23-28) is potent and selective for the MC4R. This compound validates the use of cyclotides as scaffolds and has the potential to be a new lead for the treatment of obesity.

A sodium-activated potassium channel supports high-frequency firing and reduces energetic costs during rapid modulations of action potential amplitude.

We investigated the ionic mechanisms that allow dynamic regulation of action potential (AP) amplitude as a means of regulating energetic costs of AP signaling. Weakly electric fish generate an electric organ discharge (EOD) by summing the APs of their electric organ cells (electrocytes). Some electric fish increase AP amplitude during active periods or social interactions and decrease AP amplitude when inactive, regulated by melanocortin peptide hormones. This modulates signal amplitude and conserves energy. The gymnotiform Eigenmannia virescens generates EODs at frequencies that can exceed 500 Hz, which is energetically challenging. We examined how E. virescens meets that challenge. E. virescens electrocytes exhibit a voltage-gated Na(+) current (I(Na)) with extremely rapid recovery from inactivation (τ(recov) = 0.3 ms) allowing complete recovery of Na(+) current between APs even in fish with the highest EOD frequencies. Electrocytes also possess an inwardly rectifying K(+) current and a Na(+)-activated K(+) current (I(KNa)), the latter not yet identified in any gymnotiform species. In vitro application of melanocortins increases electrocyte AP amplitude and the magnitudes of all three currents, but increased I(KNa) is a function of enhanced Na(+) influx. Numerical simulations suggest that changing I(Na) magnitude produces corresponding changes in AP amplitude and that K(Na) channels increase AP energy efficiency (10-30% less Na(+) influx/AP) over model cells with only voltage-gated K(+) channels. These findings suggest the possibility that E. virescens reduces the energetic demands of high-frequency APs through rapidly recovering Na(+) channels and the novel use of KNa channels to maximize AP amplitude at a given Na(+) conductance.

Melanocortins as potential therapeutic agents in severe hypoxic conditions.

Melanocortin peptides with the adrenocorticotropin/melanocyte-stimulating hormone (ACTH/MSH) sequences and synthetic analogs have protective and life-saving effects in experimental conditions of circulatory shock, myocardial ischemia, ischemic stroke, traumatic brain injury, respiratory arrest, renal ischemia, intestinal ischemia and testicular ischemia, as well as in experimental heart transplantation. Moreover, melanocortins improve functional recovery and stimulate neurogenesis in experimental models of cerebral ischemia. These beneficial effects of ACTH/MSH-like peptides are mostly mediated by brain melanocortin MC(3)/MC(4) receptors, whose activation triggers protective pathways that counteract the main ischemia/reperfusion-related mechanisms of damage. Induction of signaling pathways and other molecular regulators of neural stem/progenitor cell proliferation, differentiation and integration seems to be the key mechanism of neurogenesis stimulation. Synthesis of stable and highly selective agonists at MC(3) and MC(4) receptors could provide the potential for development of a new class of drugs for a novel approach to management of severe ischemic diseases.

Mechanisms of action of adrenocorticotropic hormone and other melanocortins relevant to the clinical management of patients with multiple sclerosis.

The therapeutic benefits of adrenocorticotropic hormone in multiple sclerosis are usually ascribed to its corticotropic actions. Evidence is presented that adrenocorticotropic hormone, approved for multiple sclerosis relapses, acts via corticosteroid-independent melanocortin pathways to engender down-modulating actions on immune-system cells and the cytokines they synthesize. Immune response-dampening effects are also brought about by agent-induced neurotransmitters that inhibit immunocytes. The likelihood that adrenocorticotropic hormone promotes microglial quiescence and counteracts glucocorticoid-mediated bone resorption is discussed.

Effects of the central melanocortin system on feed intake, metabolic hormones and insulin action in the sheep.

Voluntary feed intake is insufficient to meet the nutrient demands associated with late pregnancy in prolific ewes and early lactation in high-yielding dairy cows. Under these conditions, peripheral signals such as growth hormone and ceramides trigger adaptations aimed at preserving metabolic well-being. Recent work in rodents has shown that the central nervous system-melanocortin (CNS-MC) system, consisting of alpha-melanocyte-stimulating hormone (α-MSH) and agouti-related peptide (AGRP) acting respectively as agonist and antagonist on central MC receptors, contributes to the regulation of some of the same adaptations. To assess the effects of the CNC-MC on peripheral adaptations in ruminants, ewes were implanted with an intracerebroventricular cannula in the third ventricle and infused over days with artificial cerebrospinal fluid (aCSF), the α-MSH analog melanotan-I (MTI), or AGRP. Infusion of MTI at 0.03 nmol/h reduced intake, expressed as a fold of maintenance energy requirement (M), from 1.8 to 1.1 M (P < 0.0001), whereas AGRP at 0.3 nmol/h increased intake from 1.8 to 2.0 M (P < 0.01); these doses were used in all subsequent experiments. To assess the effect of MTI on plasma variables, sheep were fed ad libitum and infused with aCSF or MTI or pair-fed to MTI-treated sheep and infused with aCSF (aCSFPF). Feed intake of the MTI and aCSFPF groups was 40% lower than the aCSF group (P < 0.0001). MTI increased plasma triiodothyronine and thyroxine in an intake-independent manner (P < 0.05 or less) but was devoid of effects on plasma glucose, insulin, and cortisol. None of these variables were altered by AGRP infusion in sheep fed at a fixed intake of 1.6 M. To assess the effect of CNS-MC activation on insulin action, ewes were infused with aCSF or MTI over the last 3 d of a 14-d period when energy intake was limited to 0.3 M and studied under basal conditions and during hyperinsulinemic-euglycemic clamps. MTI had no effect on plasma glucose, plasma insulin, or glucose entry rate under basal conditions but blunted the ability of insulin to inhibit endogenous glucose production during hyperinsulinemic-euglycemic clamps (P < 0.0001). Finally, MTI tended to reduce plasma leptin in sheep fed at 0.3 M (P < 0.08), and this effect became significant at 0.6 M (P < 0.05); MTI had no effect on plasma adiponectin irrespective of feeding level. These data suggest a role for the CNC-MC in regulating metabolic efficiency and peripheral insulin action.

Highly productive ruminants face short-term nutritional deficits during demanding phases of their life cycle. They remain productive and healthy during these periods through a series of metabolic adaptations. Current models in ruminant biology attribute the coordination of these adaptations to circulating hormones and bioactive metabolites but have not considered the possibility that the central nervous system (CNS) is also involved. The latter appears likely given recent work in rodents implicating the CNS-melanocortin system in the regulation of some of these adaptations. To test this possibility, mature ewes were surgically implanted with a cannula accessing the brain allowing chronic infusion of melanocortins, and used in experiments assessing peripheral effects. These experiments showed that the CNS-melanocortin system regulates the circulating concentrations of some metabolic hormones as well as the ability of insulin to regulate glucose production. Overall, these studies suggest a role for the CNS-melanocortin system in regulating metabolic adaptations in ruminants.

Circadian and social cues regulate ion channel trafficking.

Electric fish generate and sense electric fields for navigation and communication. These signals can be energetically costly to produce and can attract electroreceptive predators. To minimize costs, some nocturnally active electric fish rapidly boost the power of their signals only at times of high social activity, either as night approaches or in response to social encounters. Here we show that the gymnotiform electric fish Sternopygus macrurus rapidly boosts signal amplitude by 40% at night and during social encounters. S. macrurus increases signal magnitude through the rapid and selective trafficking of voltage-gated sodium channels into the excitable membranes of its electrogenic cells, a process under the control of pituitary peptide hormones and intracellular second-messenger pathways. S. macrurus thus maintains a circadian rhythm in signal amplitude and adapts within minutes to environmental events by increasing signal amplitude through the rapid trafficking of ion channels, a process that directly modifies an ongoing behavior in real time.

Cytoprotective effects of ß-melanocortin in the rat gastrointestinal tract.

Recently discovered anti-inflammatory and immunomodulatory properties of melanocortin peptides led to the conclusion that they might serve as new anti-inflammatory therapeutics. The purpose of this work was to examine the effectiveness of ß-melanocortin (ß-MSH) in two experimental models: ethanol-induced gastric lesions and TNBS (2,4,6-trinitrobenzenesulfonic acid)-induced colitis in male Wistar rats. Three progressive doses of ß-MSH were used: 0.125, 0.250 and 0.500 mg/kg. Our results suggest that ß-MSH acts as a protective substance in the gastric lesions model, which can be seen as a statistically significant reduction of hemorrhagic lesions at all three doses, compared to the control group. The most efficient dose was 0.250 mg/kg. Statistically significant reduction in mucosal surface affected by necrosis and the reduction of overall degree of inflammation in the colitis model indicates an anti-inflammatory effect of ß-MSH at a dose of 0.250 mg/kg. The results justify further research on ß-MSH peptide and its derivates in the inflammatory gastrointestinal diseases, and point out the possibility of using ß-MSH in studies of digestive system pharmacology.

Developmental switch in neuropeptide Y and melanocortin effects in the paraventricular nucleus of the hypothalamus.

Homeostatic regulation of energy balance in rodents changes dramatically during the first 3 postnatal weeks. Neuropeptide Y (NPY) and melanocortin neurons in the arcuate nucleus, a primary energy homeostatic center in adults, do not fully innervate the paraventricular nucleus (PVN) until the third postnatal week. We have identified two classes of PVN neurons responsive to these neuropeptides, tonically firing neurosecretory (NS) and burst-firing preautonomic (PA) cells. In neonates, NPY could inhibit GABAergic inputs to nearly all NS and PA neurons, while melanocortin regulation was minimal. However, there was a dramatic, age-dependent decrease in NPY responses specifically in the PA neurons, and a 3-fold increase in melanocortin responses in NS cells. These age-dependent changes were accompanied by changes in spontaneous GABAergic currents onto these neurons. This primarily NPYergic regulation in the neonates likely promotes the positive energy balance necessary for growth, while the developmental switch correlates with maturation of homeostatic regulation of energy balance.

Treatment of cerebral ischemia with melanocortins acting at MC4 receptors induces marked neurogenesis and long-lasting functional recovery.

Melanocortins produce neuroprotection against ischemic stroke with subsequent long-lasting functional recovery, through melanocortin MC(4) receptor activation. Here we investigated whether the long-lasting beneficial effect of melanocortins in stroke conditions is associated with a stimulation of neurogenesis. Gerbils were subjected to transient global cerebral ischemia by occluding both common carotid arteries for 10 min; then, they were prepared for 5-bromo-2'-deoxyuridine (BrdU) labeling of proliferating cells. Delayed treatment (up to 9 h after the ischemic injury) for 11 days with the melanocortin analog [Nle(4),D-Phe(7)]α-melanocyte-stimulating hormone (NDP-α-MSH) improved learning and memory throughout the 50-day observation period. Immunohistochemical examination of the hippocampus on day 50 showed, in the dentate gyrus, an elevated number of BrdU immunoreactive cells colocalized with NeuN (used as indicator of mature neurons) and Zif268 (used as indicator of functionally integrated neurons). Retrospective analysis during the early stage of neural stem/progenitor cell development (days 3 and 4 after stroke) showed, in NDP-α-MSH-treated gerbils, a high degree of daily cell proliferation and revealed that NDP-α-MSH favorably affects Wnt-3A signaling pathways and doublecortin expression. Pharmacologic blockade of MC(4) receptors prevented all effects of NDP-α-MSH. These data indicate that treatment of cerebral ischemia with MC(4) receptor agonists induces, with a broad window of therapeutic opportunity, long-lasting functional recovery associated with a large number of mature and likely functional newborn neurons in brain injured areas. Our findings reveal previously undescribed effects of melanocortins which might have major clinical implications.