Energy Balance Effects of Central Melanocortin, Cocaine and Amphetamine Related Transcript and Leptin: Moving Outside of the Hypothalamic Box.

Due to increasing rates of obesity and its comorbidities, there is tremendous interest in the central nervous system (CNS) control of energy balance. This basic science interest is guided in part by the need to develop effective drugs for the overweight and the obese patient. Despite a large literature, our understanding of the circuits and neurochemical receptors that mediate energy balance is still limited. The studies described here address this limitation by defining neural circuits that mediate melanocortin´s effects on energy balance. Disruption in CNS melanocortin receptor (MCR) signaling is the single largest monogenic cause of human obesity and also produces severe hyperphagia and reduced energy expenditure in rodents. Forebrain ventricular application of MCR agonists, triggers sympathetically mediated expenditure responses that have been attributed to signaling at hypothalamic structures. However, caudal flow of the injected ligands in CSF makes them available to extrahypothalamic sites. Given the widespread distribution of MCRs it is impossible to define which MCR-bearing neurons - among them several hypothalamic and hindbrain nuclei- contribute to the observed effects. Here we characterized the respective contributions of the hypothalamic and caudal hindbrain MCRs to energetic and intake control with ventricular (3rd and 4th v) as well as selective parnechymal MCR agonist delivery. Results demonstrate that thermogenic, cardiovascular and anorexic responses of similar size and duration can be obtained by stimulation of several hypothalamic and hindbrain MCR populations. Using an antagonist treatment we evaluated the endogenous hindbrain MCR contributions to the intake and thermogenic responses driven by leptin (a hormone produced by the adipose tissue) and an exposure to palatable, high-energy diet. Results indicated that hindbrain MCRs are required for mediation of anorexic and thermogenic effects of hindbrain leptin and for limiting overeating induced by palatable high-energy diet. The data presented here confirm the hypothesis that the melanocortin system’s contribution to food intake and energy expenditure is distributed across spatially distinct regions of the brain. Taken together results demonstrate the presence of an independent hindbrain MCR-driven energy balance circuitry that responds to peripheral inputs (e.g. leptin) and physiological challenges (e.g. high-energy diet) similarly to what has been earlier ascribed to the hypothalamic MCR populations

An appetite for aggressive behavior? Female rats, too, derive reward from winning aggressive interactions

While aggression is an adaptive behavior mostly triggered by competition for resources, it can also in and of itself be rewarding. Based on the common notion that female rats are not aggressive, much of aggression research has been centered around males, leading to a gap in the understanding of the female aggression neurobiology. Therefore, we asked whether intact virgin female rats experience reward from an aggressive interaction and assessed aggression seeking behavior in rats of both sexes. To validate the involvement of reward signaling, we measured mesolimbic dopamine turnover and determined the necessity of dopamine signaling for expression of aggression-seeking. Together our data indicate that female rats exhibit aggressive behavior outside of maternal context, experience winning aggressive behaviors as rewarding, and do so to a similar extent as male rats and in a dopamine-dependent manner

Influence of ghrelin on the central serotonergic signaling system in mice

AbstractThe central ghrelin signaling system engages key pathways of importance for feeding control, recently shown to include those engaged in anxiety-like behavior in rodents. Here we sought to determine whether ghrelin impacts on the central serotonin system, which has an important role in anxiety. We focused on two brain areas, the amygdala (of importance for the mediation of fear and anxiety) and the dorsal raphe (i.e. the site of origin of major afferent serotonin pathways, including those that project to the amygdala). In these brain areas, we measured serotonergic turnover (using HPLC) and the mRNA expression of a number of serotonin-related genes (using real-time PCR). We found that acute central administration of ghrelin to mice increased the serotonergic turnover in the amygdala. It also increased the mRNA expression of a number of serotonin receptors, both in the amygdala and in the dorsal raphe. Studies in ghrelin receptor (GHS-R1A) knock-out mice showed a decreased mRNA expression of serotonergic receptors in both the amygdala and the dorsal raphe, relative to their wild-type littermates. We conclude that the central serotonin system is a target for ghrelin, providing a candidate neurochemical substrate of importance for ghrelin's effects on mood

Vagal Blocking for Obesity Control : a Possible Mechanism-Of-Action

14 September 2016 Erratum to: Vagal Blocking for Obesity Control: a Possible Mechanism-Of-Action Helene Johannessen, David Revesz, Yosuke Kodama, Nikki Cassie, Karolina P Skibicka, Perry Barrett, Suzanne Dickson, Jens Holst, Jens Rehfeld, Geoffrey van der Plasse, Roger Adan, Bård Kulseng, Elinor Ben-Menachem, Chun-Mei Zhao, Duan Chen, 2016, 2016. Obesity surgery. In the original article on page 4 the figures are referred to as (Fig. 1b-d) and (Fig. 1e) in the text. The correct reference is (Fig. 1b-e) and (Fig. 1f), respectively. In the original article on page 5 the figures are referred to as (Fig. 3c) and (Fig. 3d) in the text. The correct reference is (Fig. 3c,d) and (Fig. 3e,f), respectively. Peer reviewedPostprin

Ghrelin increases intake of rewarding food in rodents

We investigated whether ghrelin action at the level of the ventral tegmental area (VTA), a key node in the mesolimbic reward system, is important for the rewarding and motivational aspects of the consumption of rewarding/palatable food. Mice with a disrupted gene encoding the ghrelin receptor (GHS-R1A) and rats treated peripherally with a GHS-R1A antagonist both show suppressed intake of rewarding food in a free choice (chow/rewarding food) paradigm. Moreover, accumbal dopamine release induced by rewarding food was absent in GHS-R1A knockout mice. Acute bilateral intra-VTA administration of ghrelin increased 1-hour consumption of rewarding food but not standard chow. In comparison with sham rats, VTA-lesioned rats had normal intracerebroventricular ghrelin-induced chow intake, although both intake of and time spent exploring rewarding food was decreased. Finally, the ability of rewarding food to condition a place preference was suppressed by the GHS-R1A antagonist in rats. Our data support the hypothesis that central ghrelin signaling at the level of the VTA is important for the incentive value of rewarding food

Key role for hypothalamic interleukin-6 in food-motivated behavior and body weight regulation

The pro-inflammatory role of interleukin-6 (IL-6) is well-characterized. Blockade of IL-6, by Tocilizumab, is used in patients with rheumatoid arthritis and those diagnosed with cytokine storm. However, brain-produced IL-6 has recently emerged as  a critical mediator of gut/adipose communication with the brain. Central nervous system (CNS) IL-6 is engaged by peripheral and central signals regulating energy homeostasis. IL-6 is critical for mediating hypophagia and weight loss effects of a GLP-1 analog, exendin-4, a clinically utilized drug. However, neuroanatomical substrates and behavioral mechanisms of brain IL-6 energy balance control remain poorly understood. We propose that the lateral hypothalamus (LH) is an IL-6-harboring brain region, key to food intake and food reward control. Microinjections of IL-6 into the LH reduced chow and palatable food intake in male rats. In contrast, female rats responded with reduced motivated behavior for sucrose, measured by the progressive ratio operant conditioning test, a behavioral mechanism previously not linked to IL-6. To test whether IL-6, produced in the LH, is necessary for ingestive and motivated behaviors, and body weight homeostasis, viroge-netic knockdown by infusion of AAV-siRNA-IL6 into the LH was utilized. Attenuation of LH IL-6 resulted in a potent increase in sucrose-motivated behavior, without any effect on ingestive behavior or body weight in female rats. In  contrast, the  treatment did  not  affect any  parameters measured (chow intake, sucrose-motivated behavior, locomotion, and body weight) in chow-fed males. However, when challenged with a high-fat/high- sugar diet, the male LH IL-6 knockdown rats displayed rapid weight gain and hyperphagia. Together, our data suggest that LH-produced IL-6 is necessary and sufficient for ingestive behavior and weight homeostasis in male rats. In females, IL-6 in the LH plays a critical role in food-motivated, but not ingestive behavior control or weight regulation. Thus, collectively these data support the idea that brain-produced IL-6 engages the hypothalamus to control feeding behavior.</p

Peripherally restricted oxytocin is sufficient to reduce food intake and motivation, while <scp>CNS</scp> entry is required for locomotor and taste avoidance effects

ObjectivesOxytocin (OT) has a well‐established role in reproductive behaviours; however, it recently emerged as an important regulator of energy homeostasis. In addition to central nervous system (CNS), OT is found in the plasma and OT receptors (OT‐R) are found in peripheral tissues relevant to energy balance regulation. Here, we aim to determine whether peripheral OT‐R activation is sufficient to alter energy intake and expenditure.Methods and ResultsWe first show that systemic OT potently reduced food intake and food‐motivated behaviour for a high‐fat reward in male and female rats. As it is plausible that peripherally, intraperitoneally (IP) injected OT crosses the blood‐brain barrier (BBB) to produce some of the metabolic effects within the CNS, we screened, with a novel fluorescently labelled‐OT (fAF546‐OT, Roxy), for the presence of IP‐injected Roxy in CNS tissue relevant to feeding control and compared such with BBB‐impermeable fluorescent OT‐B$_{12}$ (fCy5‐OT‐B$_{12;}$ BRoxy). While Roxy did penetrate the CNS, BRoxy did not. To evaluate the behavioural and thermoregulatory impact of exclusive activation of peripheral OT‐R, we generated a novel BBB‐impermeable OT (OT‐B$_{12}$), with equipotent binding at OT‐R in vitro. In vivo, IP‐injected OT and OT‐B$_{12}$ were equipotent at food intake suppression in rats of both sexes, suggesting that peripheral OT acts on peripheral OT‐R to reduce feeding behaviour. Importantly, OT induced a potent conditioned taste avoidance, indistinguishable from that induced by LiCl, when applied peripherally. Remarkably, and in contrast to OT, OT‐B$_{12}$ did not induce any conditioned taste avoidance. Limiting the CNS entry of OT also resulted in a dose‐dependent reduction of emesis in male shrews. While both OT and OT‐B$_{12}$ proved to have similar effects on body temperature, only OT resulted in home‐cage locomotor depression.ConclusionsTogether our data indicate that limiting systemic OT CNS penetrance preserves the anorexic effects of the peptide and reduces the clinically undesired side effects of OT: emesis, taste avoidance and locomotor depression. Thus, therapeutic targeting of peripheral OT‐R may be a viable strategy to achieve appetite suppression with better patient outcomes

Interleukin-6 in the central amygdala is bioactive and co-localised with glucagon-like peptide-1 receptor

Neuronal circuits involving the central amygdala (CeA) are gaining prominence as important centres for regulation of metabolic functions. As a part of the subcortical food motivation circuitry, CeA is associated with food motivation and hunger. We have previously shown that interleukin (IL)-6 can act as a downstream mediator of the metabolic effects of glucagon-like peptide-1 (GLP-1) receptor (R) stimulation in the brain, although the sites of these effects are largely unknown. In the present study, we used the newly generated and validated RedIL6 reporter mouse strain to investigate the presence of IL-6 in the CeA, as well as possible interactions between IL-6 and GLP-1 in this nucleus. IL-6 was present in the CeA, mostly in cells in the medial and lateral parts of this structure, and a majority of IL-6-containing cells also co-expressed GLP-1R. Triple staining showed GLP-1 containing fibres co-staining with synaptophysin close to or overlapping with IL-6 containing cells. GLP-1R stimulation enhanced IL-6 mRNA levels. IL-6 receptor-alpha (IL-6R alpha) was found to a large part in neuronal CeA cells. Using electrophysiology, we determined that cells with neuronal properties in the CeA could be rapidly stimulated by IL-6 administration in vitro. Moreover, microinjections of IL-6 into the CeA could slightly reduce food intake in vivo in overnight fasted rats. In conclusion, IL-6 containing cells in the CeA express GLP-1R, are close to GLP-1-containing synapses, and demonstrate increased IL-6 mRNA in response to GLP-1R agonist treatment. IL-6, in turn, exerts biological effects in the CeA, possibly via IL-6R alpha present in this nucleus

Parabrachial Interleukin-6 reduces body weight and food intake and increases thermogenesis to regulate energy metabolism

Chronic low-grade inflammation and increased serum levels of the cytokine IL-6 accompany obesity. For brain-produced IL-6, the mechanisms by which it controls energy balance and its role in obesity remain unclear. Here, we show that brain-produced IL-6 is decreased in obese mice and rats in a neuroanatomically and sex-specific manner. Reduced IL-6 mRNA localized to lateral parabrachial nucleus (lPBN) astrocytes, microglia, and neurons, including paraventricular hypothalamus-innervating lPBN neurons. IL-6 microinjection into lPBN reduced food intake and increased brown adipose tissue (BAT) thermogenesis in male lean and obese rats by increasing thyroid and sympathetic outflow to BAT. Parabrachial IL-6 interacted with leptin to reduce feeding. siRNA-mediated reduction of lPBN IL-6 leads to increased weight gain and adiposity, reduced BAT thermogenesis, and increased food intake. Ambient cold exposure partly normalizes the obesity-induced suppression of lPBN IL-6. These results indicate that lPBN-produced IL-6 regulates feeding and metabolism and pinpoints (patho)physiological contexts interacting with lPBN IL-6This research was funded by the Swedish Research Council ( 2014-2945 to K.P.S.; 2017-00792 to I.W.A.; and 2013-7107 to Patrik Rorsman), the Novo Nordisk Foundation Excellence project grant (to K.P.S. and I.W.A.), the Ragnar Söderberg Foundation (to K.P.S.), Harald Jeanssons Stiftelse and Greta Jeanssons Stiftelse (to K.P.S.), Magnus Bergvalls Stiftelse (to K.P.S.), the Wallenberg Foundation and the Center for Molecular and Translational Medicine (to K.P.S.), postdoctoral stipendium from The Swedish Brain Foundation (to D.M.), the ERC ( BFU2015-70664-R and StG-281408 ) (to R.N.), and the NIH ( DK-21397 ) (to H.J.G.)S