shu-9119 and Anorexia

Growing evidence suggests that the pituitary adenylate cyclase-activating polypeptide (PACAP)/PAC1 receptor system represents one of the main regulators of the behavioral, endocrine, and autonomic responses to stress. Although induction of anorexia is a well-documented effect of PACAP, the central sites underlying this phenomenon are poorly understood. The present studies addressed this question by examining the neuroanatomical, behavioral, and pharmacological mechanisms mediating the anorexia produced by PACAP in the central nucleus of the amygdala (CeA), a limbic structure implicated in the emotional components of ingestive behavior. Male rats were microinfused with PACAP (0-1 μg per rat) into the CeA and home-cage food intake, body weight change, microstructural analysis of food intake, and locomotor activity were assessed. Intra-CeA (but not intra-basolateral amygdala) PACAP dose-dependently induced anorexia and body weight loss without affecting locomotor activity. PACAP-treated rats ate smaller meals of normal duration, revealing that PACAP slowed feeding within meals by decreasing the regularity and maintenance of feeding from pellet-to-pellet; postprandial satiety was unaffected. Intra-CeA PACAP-induced anorexia was blocked by coinfusion of either the melanocortin receptor 3/4 antagonist SHU 9119 or the tyrosine kinase B (TrKB) inhibitor k-252a, but not the CRF receptor antagonist D-Phe-CRF(12-41). These results indicate that the CeA is one of the brain areas through which the PACAP system promotes anorexia and that PACAP preferentially lessens the maintenance of feeding in rats, effects opposite to those of palatable food. We also demonstrate that PACAP in the CeA exerts its anorectic effects via local melanocortin and the TrKB systems, and independently from CRF.

Topics: Analysis of Variance; Animals; Anorexia; Body Weight; Central Amygdaloid Nucleus; Corticotropin-Releasing Hormone; Disease Models, Animal; Dose-Response Relationship, Drug; Eating; Feeding Behavior; Male; Melanocortins; Melanocyte-Stimulating Hormones; Motor Activity; Pituitary Adenylate Cyclase-Activating Polypeptide; Rats; Rats, Wistar; Receptor, trkB; Time Factors; Vasodilator Agents

Aminoprocalcitonin (N-PCT), a neuroendocrine peptide encoded by the calcitonin-I (CALC-I) gene, suppresses food intake when administered centrally in rats. However, the neural pathways underlying this effect remain unclear. N-PCT and calcitonin receptors (CT-R) have been identified in hypothalamic regions involved in energy homeostasis, including the arcuate nucleus (ARC). Here, we hypothesized an involvement of the hypothalamic ARC in mediating the anorexic effects of central N-PCT based on its content of peptidergic neurons involved in feeding and its expression of N-PCT and CT-R. Fasting strongly reduced expression of the N-PCT precursor gene CALC-I in the ARC, and central immunoneutralization of endogenous N-PCT increased food intake. Intracerebroventricular administration of N-PCT reduced food intake in fed and fasted rats, and its effect was attenuated by a neutralizing anti-N-PCT antibody. Immunohistochemistry for N-PCT showed that it is expressed in astrocytes and neurons in the ARC and is colocalized with anorexigenic proopiomelanocortin (POMC) neurons. Fasting reduced coexpression of N-PCT and POMC, and N-PCT administration activated hypothalamic neurons, including rostral POMC neurons. We also found that N-PCT stimulates POMC mRNA expression in fed and fasted rats, whereas it reduced the expression of orexigenic peptides neuropeptide Y (NPY) and agouti-related peptide (AgRP) only in fasted rats in which those mRNAs are normally elevated. Finally, we showed that the melanocortin-3/4 receptor antagonist SHU 9119 attenuates the intake-suppressive effect of N-PCT. These data demonstrate that hypothalamic N-PCT is involved in control of energy balance and that its anorexigenic effects are mediated through the melanocortin system.

Topics: Agouti-Related Protein; Animals; Anorexia; Antibodies, Neutralizing; Arcuate Nucleus of Hypothalamus; Calcitonin; Calcitonin Gene-Related Peptide; Eating; Energy Metabolism; Feeding Behavior; Male; Melanocyte-Stimulating Hormones; Neuropeptide Y; Protein Precursors; Rats; Rats, Wistar; Receptor, Melanocortin, Type 3; Receptor, Melanocortin, Type 4; Receptors, Melanocortin; Signal Transduction

Neuronostatin, a recently discovered peptide derived from the somatostatin preprohormone, significantly inhibited both food and water intake when administered centrally in adult male rats. Because neuronostatin is highly produced in the hypothalamus, an area of the brain through which important feeding circuits, including the central melanocortin system, communicate, we sought to determine if the anorexigenic and antidipsogenic effects of neuronostatin would be reversed by pretreatment with the melanocortin 3/4 receptor antagonist, SHU9119. SHU9119 pretreatment reversed the effect of neuronostatin on both food and water intake. We have shown recently that the central oxytocin system is a potential downstream mediator of the anorexignic action of alpha-MSH. We therefore tested whether the effects of neuronostatin also were dependent upon central oxytocin receptors. Neuronostatin-induced anorexia was not reversed by pretreatment with the oxytocin receptor antagonist, OVT, suggesting that neuronostatin acts through a unique subset of POMC neurons that do not signal via central oxytocin receptors.

Topics: Animals; Anorexia; Appetite Regulation; Drinking; Hormone Antagonists; Injections, Intraventricular; Male; Melanocortins; Melanocyte-Stimulating Hormones; Neurons; Oxytocin; Peptide Fragments; Peptide Hormones; Rats; Rats, Sprague-Dawley; Receptor, Melanocortin, Type 3; Receptor, Melanocortin, Type 4; Receptors, Oxytocin; Signal Transduction; Somatostatin; Time Factors

Of the central nervous system receptors that could mediate the energy balance effects of leptin, those of the hypothalamic arcuate nucleus receive the greatest attention. Melanocortin receptors (MC-Rs) contribute to the feeding and energetic effects of hypothalamically delivered leptin. Energy balance effects of leptin are also mediated by extrahypothalamic neurons including the hindbrain nucleus tractus solitarius. Hindbrain leptin receptors play a role in leptin's anorectic effects, but their contribution to its energetic effects and their functional interaction with melanocortin systems within the hindbrain remains unexplored. Here rats implanted with telemetric devices for recording energetic/cardiovascular responses were examined to determine whether: 1) hindbrain (fourth ventricular) leptin receptor stimulation triggers energetic and cardiovascular effects, 2) these effects are altered by a 6-wk high-fat diet maintenance, and 3) hindbrain MC-Rs mediate the thermogenic, cardiovascular, and anorexic effects of hindbrain leptin delivery. Results show that hindbrain leptin receptor stimulation produced long-lasting (>6 h) increases in core temperature and heart rate and also decreased food intake and body weight. These responses were not altered by high-fat maintenance, in contrast to what has been reported for forebrain leptin delivery. Fourth ventricular pretreatment with MC-R antagonist SHU 9119 completely abolished the hyperthermia, anorexia, and body weight loss seen with hindbrain-directed leptin but had no effects of its own. These data highlight a role for hindbrain leptin receptors in the initiation of energetic and anorexic responses and show that MCRs are part of the downstream mediation of hindbrain leptin-induced energy balance effects, paralleling effects observed for hypothalamic leptin receptors.

Topics: Animals; Anorexia; Body Temperature; Body Weight; Dietary Fats; Eating; Energy Metabolism; Fever; Glucose Tolerance Test; Heart Rate; Injections; Leptin; Male; Melanocyte-Stimulating Hormones; Rats; Rats, Sprague-Dawley; Receptors, Melanocortin; Rhombencephalon

In response to nutrient stimuli, the mediobasal hypothalamus (MBH) drives multiple neuroendocrine and behavioral mechanisms to regulate energy balance. While central leucine reduces food intake and body weight, the specific neuroanatomical sites of leucine sensing, downstream neural substrates, and neurochemical effectors involved in this regulation remain largely unknown. Here we demonstrate that MBH leucine engages a neural energy regulatory circuit by stimulating POMC (proopiomelanocortin) neurons of the MBH, oxytocin neurons of the paraventricular hypothalamus, and neurons within the brainstem nucleus of the solitary tract to acutely suppress food intake by reducing meal size. We identify central p70 S6 kinase and Erk1/2 pathways as intracellular effectors required for this response. Activation of endogenous leucine intracellular metabolism produced longer-term reductions in meal number. Our data identify a novel, specific hypothalamus-brainstem circuit that links amino acid availability and nutrient sensing to the control of food intake.

Topics: Animals; Anorexia; Body Weight; Bone Morphogenetic Protein Receptors, Type I; Brain Stem; Butadienes; Dose-Response Relationship, Drug; Drug Administration Schedule; Eating; Enzyme Inhibitors; Feeding Behavior; Green Fluorescent Proteins; Hypothalamus; In Vitro Techniques; Injections, Intraventricular; Keto Acids; Leucine; Male; Melanocortins; Melanocyte-Stimulating Hormones; Mice; Mice, Inbred C57BL; Mice, Transgenic; Neural Pathways; Neurons; Nitriles; Oxytocin; Pro-Opiomelanocortin; Proto-Oncogene Proteins c-fos; Rats; Rats, Sprague-Dawley; Signal Transduction; Threonine; Time Factors; Tyrosine; Vasotocin

Melanocortin receptors are considered promising candidates for the treatment of behavioral and metabolic disorders ranging from obesity to anorexia and cachexia. These experiments examined the response of mice to peripheral injections of two compounds. PG932 is a derivative of SHU9119 which is non-selective antagonist of melanocortin-3 and melanocortin-4 receptors (Mc3r and Mc4r). PG946 is a derivative of a hybrid of alpha- and beta-MSH, and is a moderately selective Mc3r antagonist. SHU9119 increases food intake when administered intracerebroventricularly but is without effect when injected into the periphery. In contrast, PG932 was found to be highly effective at stimulating food intake when administered peripherally by intraperitoneal injection. The orexigenic effect of PG932 required functional Mc4r, suggesting that inhibition of this receptor is involved in the stimulation of food intake. PG946 did not significantly affect on feeding behavior. PG932 is thus a useful new compound for studies examining the regulation of appetite and energy balance, and may also prove useful for the treatment of cachectic conditions.

Topics: Animals; Anorexia; Dizziness; Dose-Response Relationship, Drug; Eating; Injections, Intraperitoneal; Injections, Intraventricular; Lipopolysaccharides; Melanocyte-Stimulating Hormones; Mice; Mice, Inbred C57BL; Mice, Knockout; Peptides, Cyclic; Receptor, Melanocortin, Type 3; Receptor, Melanocortin, Type 4

Activity-based anorexia (ABA) mimics starvation and hyperactivity of anorexia nervosa patients in rats. Activation of the melanocortin (MC) system leads to hypophagia and increased energy expenditure in ad libitum fed rats. Therefore, activation of the MC system might underlie the development and propagation of ABA. Pro-opiomelanocortin (POMC) gene expression is normally decreased during negative energy balance. Strikingly, we found a transient up-regulation of POMC mRNA levels in the arcuate nucleus during the development of ABA, indicating a hyperactive MC system. However, wheel running and food intake were not influenced by treating ABA rats with the competitive antagonist SHU9119. This suggests that agonism of MC receptors by endogenous alpha-melanocyte-stimulating hormone (alpha-MSH) levels does not underlie ABA. Instead, treatment with the inverse agonist AgRP(83-132) did ameliorate signs of ABA. This implies that modulation of constitutive MC receptor activity rather than antagonizing putative alpha-MSH release contributes to the development and propagation of ABA.

Topics: Agouti-Related Protein; Animals; Anorexia; Body Weight; Female; Humans; Melanocyte-Stimulating Hormones; Motor Activity; Peptide Fragments; Pro-Opiomelanocortin; Rats; Rats, Wistar; Receptors, Melanocortin

The cytokine interleukin-1 (IL-1), which mediates many responses to infection and injury, induces anorexia and fever through direct actions in the central nervous system. The melanocortin neuropeptides, such as alpha melanocyte-stimulating hormone (alpha-MSH), reportedly antagonize many actions of IL-1, including fever and anorexia. However, it is unknown whether endogenous melanocortins modulate anorexia induced by IL-1. The objective of the present study was to establish the effect of endogenous melanocortins on IL-1-induced anorexia and fever in the rat. Intracerebroventricular (i.c.v.) injection of IL-1beta caused a significant reduction in food intake and body weight gain, and a rise in core body temperature in conscious rats. Coadministration of the melanocortin-3/4 receptor (MC3/4-R) antagonist, SHU9119, reversed IL-1beta-induced reductions in food intake and body weight, but did not affect the febrile response to IL-1beta. These data suggest IL-1beta may elicit its effects on food intake through the melanocortin system, predominantly via the MC3-R or MC4-R. In contrast, IL-1beta-induced fever does not appear to be mediated or modulated by MC3-R or MC4-R activity.

Topics: alpha-MSH; Animals; Anorexia; Appetite Depressants; Body Temperature; Brain; Eating; Fever; Injections, Intraventricular; Interleukin-1; Kinetics; Male; Melanocyte-Stimulating Hormones; Pyrogens; Rats; Rats, Sprague-Dawley; Receptors, Corticotropin; Receptors, Melanocortin; Weight Loss

Anorexia is a debilitating manifestation of many malignancies. The etiology of cancer anorexia is poorly understood, and effective treatment options are limited. To investigate the role of central melanocortin receptor signaling in the pathogenesis of cancer anorexia, we assessed the effects on food intake of the melanocortin receptor antagonist SHU9119 administered into the third cerebral ventricle of Lobund-Wistar rats that were anorexic from prostate cancer. In anorexic tumor-bearing rats, daily treatment with SHU9119 (0.35 nmol, intracerebroventricularly) increased food intake from 71 +/- 3% to 110 +/- 6% of preanorectic baseline and caused significant weight gain (13 +/- 5 vs. 5 +/- 1 g/3 d, SHU9119 vs. baseline in tumor-bearing rats). In control rats pair-fed to the intake of tumor-bearing animals, SHU9119 was ineffective at increasing food intake. The specificity of the SHU9119 feeding response was assessed using two other orexigenic peptides, NPY and the novel hormone ghrelin. Treatment of tumor-bearing rats with intracerebroventricular ghrelin (10 microg) increased food intake, but the effect was blunted relative to that in controls. Intracerebroventricular injections of NPY (1 microg) also failed to reverse anorexia in tumor-bearing rats. Because SHU9119 completely reverses cancer anorexia in this model, whereas ghrelin and NPY do not, increased central nervous system melanocortin signaling is implicated in the pathogenesis of this disorder. This suggests that new targets for the treatment of cancer anorexia may be found in the melanocortin pathways.

Topics: Adenocarcinoma; Animals; Anorexia; Body Weight; Brain; Eating; Ghrelin; Injections, Intraventricular; Male; Melanocyte-Stimulating Hormones; Neuropeptide Y; Peptide Hormones; Peptides; Prostatic Neoplasms; Rats; Rats, Wistar; Receptors, Corticotropin; Receptors, Melanocortin; Reference Values; Third Ventricle

Inflammation and microbial infection produce symptoms, including fever, anorexia, and hypoactivity, that are thought to be mediated by endogenous proinflammatory cytokines. Melanocortins are known to act centrally to suppress effects on fever and other sequelae of proinflammatory cytokine actions in the central nervous system, but the roles of melanocortins in anorexia and hypoactivity occurring during the acute phase response are unknown. The present study was designed to determine the effects of exogenous and endogenous alpha-melanocyte stimulating hormone (alpha-MSH) on lipopolysaccharide (LPS)-induced anorexia in relation to their effects on fever. Rats were fasted overnight to promote feeding behavior, then injected intraperitoneally with LPS (100 micrograms/kg ip), followed 30 min later by intracerebroventricular injection of either alpha-MSH or the melanocortin receptor subtype 3/subtype 4 (MC3-R/MC4-R) antagonist SHU-9119. Food intake, locomotor activity, and body temperature (Tb) were monitored during the ensuing 24-h period. Each of two intracerebroventricular doses of alpha-MSH (30 and 300 ng) potentiated the suppressive effects of LPS on food intake and locomotion, despite the fact that the higher dose alleviated LPS-induced fever. In control rats that were not treated with LPS, only the higher dose of alpha-MSH significantly inhibited food intake, and Tb and locomotor activity were unaffected. To assess the roles of endogenous central melanocortins, LPS-treated rats received intracerebroventricular SHU-9119 (200 ng). Central MC3-R/MC4-R blockade did not affect Tb or food intake in the absence of LPS treatment, but it reversed the LPS-induced reduction in 24-h food intake and increased LPS-induced fever without altering the LPS-induced suppression of locomotion. Taken together, the results suggest that exogenous and endogenous melanocortins acting centrally exert divergent influences on different aspects of the acute phase response, suppressing LPS-induced fever but contributing to LPS-induced anorexia and hypoactivity.

Topics: alpha-MSH; Animals; Anorexia; Body Temperature; Brain; Eating; Endotoxins; Injections, Intraventricular; Lipopolysaccharides; Male; Melanocyte-Stimulating Hormones; Motor Activity; Rats; Rats, Sprague-Dawley; Receptors, Cell Surface; Reference Values

Topics: Animals; Anorexia; Body Weight; Eating; Glucagon-Like Peptides; Leptin; Male; Melanocyte-Stimulating Hormones; Paraventricular Hypothalamic Nucleus; Peptides; Proteins; Proto-Oncogene Proteins c-fos; Rats; Receptors, Corticotropin; Receptors, Melanocortin; Signal Transduction