Amygdalar opioids modulate hypothalamic melanocortin-induced anorexia

Convergent Energy State-Dependent Antagonistic Signaling by Cocaine- and Amphetamine-Regulated Transcript (CART) and Neuropeptide Y (NPY) Modulates the Plasticity of Forebrain Neurons to Regulate Feeding in Zebrafish

Dynamic reconfiguration of circuit function subserves the flexibility of innate behaviors tuned to physiological states. Internal energy stores adaptively regulate feeding-associated behaviors and integrate opposing hunger and satiety signals at the level of neural circuits. Across vertebrate lineages, the neuropeptides cocaine- and amphetamine-regulated transcript (CART) and neuropeptide Y (NPY) have potent anorexic and orexic functions, respectively, and show energy-state-dependent expression in interoceptive neurons. However, how the antagonistic activities of these peptides modulate circuit plasticity remains unclear. Using behavioral, neuroanatomical, and activity analysis in adult zebrafish of both sexes, along with pharmacological interventions, we show that CART and NPY activities converge on a population of neurons in the dorsomedial telencephalon (Dm). Although CART facilitates glutamatergic neurotransmission at the Dm, NPY dampens the response to glutamate. In energy-rich states, CART enhances NMDA receptor (NMDAR) function by protein kinase A/protein kinase C (PKA/PKC)-mediated phosphorylation of the NR1 subunit of the NMDAR complex. Conversely, starvation triggers NPY-mediated reduction in phosphorylated NR1 via calcineurin activation and inhibition of cAMP production leading to reduced responsiveness to glutamate. Our data identify convergent integration of CART and NPY inputs by the Dm neurons to generate nutritional state-dependent circuit plasticity that is correlated with the behavioral switch induced by the opposing actions of satiety and hunger signals.SIGNIFICANCE STATEMENT Internal energy needs reconfigure neuronal circuits to adaptively regulate feeding behavior. Energy-state-dependent neuropeptide release can signal energy status to feeding-associated circuits and modulate circuit function. CART and NPY are major anorexic and orexic factors, respectively, but the intracellular signaling pathways used by these peptides to alter circuit function remain uncharacterized. We show that CART and NPY-expressing neurons from energy-state interoceptive areas project to a novel telencephalic region, Dm, in adult zebrafish. CART increases the excitability of Dm neurons, whereas NPY opposes CART activity. Antagonistic signaling by CART and NPY converge onto NMDA-receptor function to modulate glutamatergic neurotransmission. Thus, opposing activities of anorexic CART and orexic NPY reconfigure circuit function to generate flexibility in feeding behavior.

Melanocortin receptor agonist melanotan-II microinjected in the nucleus accumbens decreases appetitive and consumptive responding for food

RATIONALE

Obesity is a major health problem worldwide. An understanding of the factors that drive feeding behaviors is key to the development of pharmaceuticals to decrease appetite and consumption. Proopiomelanocortin (POMC), the melanocortin peptide precursor, is essential in the regulation of body weight and ingestive behaviors. Deletion of POMC or impairment of melanocortin signaling in the brain results in hyperphagic obesity. Neurons in the hypothalamic arcuate nucleus produce POMC and project to many areas including the nucleus accumbens (NAcc), which is well established in the rewarding and reinforcing effects of both food and drugs of abuse.

OBJECTIVE

These studies sought to determine the role of melanocortins in the NAcc on consumption of and motivation to obtain access to standard rodent chow.

METHODS

Male, C57BL/6J mice were microinjected bilaterally into the NAcc (100 nl/side) with the melanocortin receptor 3/4 agonist melanotan-II (MT-II; 0.1, 0.3, and 1 nmol), and ingestive behaviors were examined in both home cage and operant food self-administration experiments. In addition, the ability of MT-II in the NAcc to produce aversive properties or affect metabolic rate were tested.

RESULTS

MT-II injected into the NAcc significantly decreased consumption in both home cage and operant paradigms, and furthermore decreased appetitive responding to gain access to food. There was no development of conditioned taste avoidance or change in metabolic parameters following anorexic doses of MT-II.

CONCLUSIONS

MT-II in the NAcc decreased both the motivation to eat and the amount of food consumed without inducing an aversive state or affecting metabolic rate, suggesting a role for melanocortin signaling in the NAcc that is selective for appetite and satiety without affecting metabolism or producing an aversive state.

Adjustment of Whey:Casein Ratio from 20:80 to 60:40 in Milk Formulation Affects Food Intake and Brainstem and Hypothalamic Neuronal Activation and Gene Expression in Laboratory Mice

Adjustment of protein content in milk formulations modifies protein and energy levels, ensures amino acid intake and affects satiety. The shift from the natural whey:casein ratio of ~20:80 in animal milk is oftentimes done to reflect the 60:40 ratio of human milk. Studies show that 20:80 versus 60:40 whey:casein milks differently affect glucose metabolism and hormone release; these data parallel animal model findings. It is unknown whether the adjustment from the 20:80 to 60:40 ratio affects appetite and brain processes related to food intake. In this set of studies, we focused on the impact of the 20:80 vs. 60:40 whey:casein content in milk on food intake and feeding-related brain processes in the adult organism. By utilising laboratory mice, we found that the 20:80 whey:casein milk formulation was consumed less avidly and was less preferred than the 60:40 formulation in short-term choice and no-choice feeding paradigms. The relative PCR analyses in the hypothalamus and brain stem revealed that the 20:80 whey:casein milk intake upregulated genes involved in early termination of feeding and in an interplay between reward and satiety, such as melanocortin 3 receptor (MC3R), oxytocin (OXT), proopiomelanocortin (POMC) and glucagon-like peptide-1 receptor (GLP1R). The 20:80 versus 60:40 whey:casein formulation intake differently affected brain neuronal activation (assessed through c-Fos, an immediate-early gene product) in the nucleus of the solitary tract, area postrema, ventromedial hypothalamic nucleus and supraoptic nucleus. We conclude that the shift from the 20:80 to 60:40 whey:casein ratio in milk affects short-term feeding and relevant brain processes.

Evaluation of the MC4R gene across eMERGE network identifies many unreported obesity-associated variants

BACKGROUND/OBJECTIVES

Melanocortin-4 receptor (MC4R) plays an essential role in food intake and energy homeostasis. More than 170 MC4R variants have been described over the past two decades, with conflicting reports regarding the prevalence and phenotypic effects of these variants in diverse cohorts. To determine the frequency of MC4R variants in large cohort of different ancestries, we evaluated the MC4R coding region for 20,537 eMERGE participants with sequencing data plus additional 77,454 independent individuals with genome-wide genotyping data at this locus.

SUBJECTS/METHODS

The sequencing data were obtained from the eMERGE phase III study, in which multisample variant call format calls have been generated, curated, and annotated. In addition to penetrance estimation using body mass index (BMI) as a binary outcome, GWAS and PheWAS were performed using median BMI in linear regression analyses. All results were adjusted for principal components, age, sex, and sites of genotyping.

RESULTS

Targeted sequencing data of MC4R revealed 125 coding variants in 1839 eMERGE participants including 30 unreported coding variants that were predicted to be functionally damaging. Highly penetrant unreported variants included (L325I, E308K, D298N, S270F, F261L, T248A, D111V, and Y80F) in which seven participants had obesity class III defined as BMI ≥ 40 kg/m2. In GWAS analysis, in addition to known risk haplotype upstream of MC4R (best variant rs6567160 (P = 5.36 × 10-25, Beta = 0.37), a novel rare haplotype was detected which was protective against obesity and encompassed the V103I variant with known gain-of-function properties (P = 6.23 × 10-08, Beta = -0.62). PheWAS analyses extended this protective effect of V103I to type 2 diabetes, diabetic nephropathy, and chronic renal failure independent of BMI.

CONCLUSIONS

MC4R screening in a large eMERGE cohort confirmed many previous findings, extend the MC4R pleotropic effects, and discovered additional MC4R rare alleles that probably contribute to obesity.

Endogenous opioid modulation of food intake and body weight: Implications for opioid influences upon motivation and addiction

This review is part of a special issue dedicated to Opioid addiction, and examines the influential role of opioid peptides, opioid receptors and opiate drugs in mediating food intake and body weight control in rodents. This review postulates that opioid mediation of food intake was an example of "positive addictive" properties that provide motivational drives to maintain opioid-seeking behavior and that are not subject to the "negative addictive" properties associated with tolerance, dependence and withdrawal. Data demonstrate that opiate and opioid peptide agonists stimulate food intake through homeostatic activation of sensory, metabolic and energy-related In contrast, general, and particularly mu-selective, opioid receptor antagonists typically block these homeostatically-driven ingestive behaviors. Intake of palatable and hedonic food stimuli is inhibited by general, and particularly mu-selective, opioid receptor antagonists. The selectivity of specific opioid agonists to elicit food intake was confirmed through the use of opioid receptor antagonists and molecular knockdown (antisense) techniques incapacitating specific exons of opioid receptor genes. Further extensive evidence demonstrated that homeostatic and hedonic ingestive situations correspondingly altered the levels and expression of opioid peptides and opioid receptors. Opioid mediation of food intake was controlled by a distributed brain network intimately related to both the appetitive-consummatory sites implicated in food intake as well as sites intimately involved in reward and reinforcement. This emergent system appears to sustain the "positive addictive" properties providing motivational drives to maintain opioid-seeking behavior.

Oxytocin administration in the basolateral and central nuclei of amygdala moderately suppresses food intake

Oxytocin (OT) at acting central nuclei decreases meal size and reduces intake of palatable sweet solutions. It remains largely unclear as to which brain sites mediate OT's effect on palatability versus energy or the combination of those aspects of consumption. Here, we expanded the search for sites that mediate anorexigenic properties of OT by focusing on two subdivisions of the amygdala, its central (CNA) and basolateral (BLA) nuclei. We injected OT directly into the BLA or CNA in rats and assessed intake of standard chow induced by energy deprivation and intake of sweet solutions in nondeprived animals. We examined whether these effects are reversible by OT receptor (OTr) antagonism and whether OT presence in BLA or CNA induces taste aversion. We also determined the effect of energy deprivation and exposure to sweet saccharin on BLA and CNA expression of OTr mRNA. OT administration in BLA at 0.3 μg and in CNA at 1 μg reduced standard chow intake after deprivation by ~25%. Only administration of OT in BLA was effective in suppressing consumption of sucrose and saccharin solutions. The anorexigenic effects of OT in BLA and CNA were attenuated by OTr antagonist, L-368,899, pretreatment. OT at anorexigenic doses did not promote acquisition of taste aversion. BLA OTr mRNA expression was affected by exposure to palatable saccharin, whereas that of CNA OTr, by energy deprivation. OT in the amygdala moderately decreases food intake. The functional relationship between amygdalar OT and energy intake versus palatability-driven intake depends on the discrete localization of the OTr within this complex structure.

Effect of Oxytocin on Hunger Discrimination

Centrally and peripherally administered oxytocin (OT) decreases food intake and activation of the endogenous OT systems, which is associated with termination of feeding. Evidence gathered thus far points to OT as a facilitator of early satiation, a peptide that reduces the need for a meal that has already begun. It is not known, however, whether OT can diminish a feeling of hunger, thereby decreasing a perceived need to seek calories. Therefore, in the current project, we first confirmed that intraperitoneal (i.p.) OT at 0.3-1 mg/kg reduces food intake in deprived and non-deprived rats. We then used those OT doses in a unique hunger discrimination protocol. First, rats were trained to discriminate between 22- and 2-h food deprivation (hungry vs. sated state) in a two-lever operant procedure. After rats acquired the discrimination, they were food-restricted for 22 h and given i.p. OT before a generalization test session. OT did not decrease 22-h deprivation-appropriate responding to match that following 2-h food deprivation, thus, it did not reduce the perceived level of hunger. In order to better understand the mechanisms behind this ineffectiveness of OT, we used c-Fos immunohistochemistry to determine whether i.p. OT activates a different subset of feeding-related brain sites under 22- vs. 2-h deprivation. We found that in sated animals, OT induces c-Fos changes in a broader network of hypothalamic and brain stem sites compared to those affected in the hungry state. Finally, by employing qPCR analysis, we asked whether food deprivation vs. sated state have an impact on OT receptor expression in the brain stem, a CNS "entry" region for peripheral OT. Fasted animals had significantly lower OT receptor mRNA levels than their ad libitum-fed counterparts. We conclude that OT does not diminish a feeling of hunger before a start of a meal. Instead OT's anorexigenic properties are manifested once consumption has already begun which is-at least to some extent-driven by changes in brain responsiveness to OT treatment in the hungry vs. fed state. OT should be viewed as a mediator of early satiation rather than as a molecule that diminishes perceived hunger.

Endogenous opioids and feeding behavior: A decade of further progress (2004-2014). A Festschrift to Dr. Abba Kastin

Functional elucidation of the endogenous opioid system temporally paralleled the creation and growth of the journal, Peptides, under the leadership of its founding editor, Dr. Abba Kastin. He was prescient in publishing annual and uninterrupted reviews on Endogenous Opiates and Behavior that served as a microcosm for the journal under his stewardship. This author published a 2004 review, "Endogenous opioids and feeding behavior: a thirty-year historical perspective", summarizing research in this field between 1974 and 2003. The present review "closes the circle" by reviewing the last 10 years (2004-2014) of research examining the role of endogenous opioids and feeding behavior. The review summarizes effects upon ingestive behavior following administration of opioid receptor agonists, in opioid receptor knockout animals, following administration of general opioid receptor antagonists, following administration of selective mu, delta, kappa and ORL-1 receptor antagonists, and evaluating opioid peptide and opioid receptor changes in different food intake models.

Central amygdala PKC-δ(+) neurons mediate the influence of multiple anorexigenic signals

Feeding can be inhibited by multiple cues, including those associated with satiety, sickness or unpalatable food. How such anorexigenic signals inhibit feeding at the neural circuit level is not completely understood. Although some inhibitory circuits have been identified, it is not yet clear whether distinct anorexigenic influences are processed in a convergent or parallel manner. The amygdala central nucleus (CEA) has been implicated in feeding control, but its role is controversial. The lateral subdivision of CEA (CEl) contains a subpopulation of GABAergic neurons that are marked by protein kinase C-δ (PKC-δ). We found that CEl PKC-δ(+) neurons in mice were activated by diverse anorexigenic signals in vivo, were required for the inhibition of feeding by such signals and strongly suppressed food intake when activated. They received presynaptic inputs from anatomically distributed neurons activated by different anorexigenic agents. Our data suggest that CEl PKC-δ(+) neurons constitute an important node that mediates the influence of multiple anorexigenic signals.

Central amygdala opioid transmission is necessary for increased high-fat intake following 24-h food deprivation, but not following intra-accumbens opioid administration

Previous research has demonstrated a dissociation of certain neural mediators that contribute to the increased consumption of a high-fat diet that follows intra-accumbens (Acb) administration of μ-opioid receptor agonists vs. 24-h food deprivation. These two models, both which induce rapid consumption of the diet, have been shown to involve a distributed corticolimbic circuitry, including the amygdala. Specifically, the central amygdala (CeA) has been shown to be involved in high-fat feeding within both opioid and food-deprivation driven models. The present experiments were conducted to examine the more specific role of CeA opioid transmission in mediating high-fat feeding driven by either intra-Acb administration of the μ-opioid agonist d-Ala2-NMe-Phe4-Glyol5-enkephalin (DAMGO) or 24-h home cage food deprivation. Injection of DAMGO into the Acb (0.25 μg/0.5 μl/side) increased consumption of the high-fat diet, but this feeding was unaffected by administration of opioid antagonist, naltrexone (5 μg/0.25 μl/side) administered into the CeA. In contrast, intra-CeA naltrexone administration attenuated high-fat intake driven by 24-h food deprivation, demonstrating a specific role for CeA opioid transmission in high-fat consumption. Intra-CeA naltrexone administration alone had no effect on baseline feeding levels within either feeding model. These findings suggest that CeA opioid transmission mediates consumption of a palatable high-fat diet driven by short-term negative-energy balance (24-h food deprivation), but not intra-Acb opioid receptor activation.

Common genetic variation near MC4R has a sex-specific impact on human brain structure and eating behavior

Obesity is associated with genetic and environmental factors but the underlying mechanisms remain poorly understood. Recent genome-wide association studies (GWAS) identified obesity- and type 2 diabetes-associated genetic variants located within or near genes that modulate brain activity and development. Among the top hits is rs17782313 near MC4R, encoding for the melanocortin-4-receptor, which is expressed in brain regions that regulate eating. Here, we hypothesized rs17782313-associated changes in human brain regions that regulate eating behavior. Therefore, we examined effects of common variants at rs17782313 near MC4R on brain structure and eating behavior. Only in female homozygous carriers of the risk allele we found significant increases of gray matter volume (GMV) in the right amygdala, a region known to influence eating behavior, and the right hippocampus, a structure crucial for memory formation and learning. Further, we found bilateral increases in medial orbitofrontal cortex, a multimodal brain structure encoding the subjective value of reinforcers, and bilateral prefrontal cortex, a higher order regulation area. There was no association between rs17782313 and brain structure in men. Moreover, among female subjects only, we observed a significant increase of ‘disinhibition’, and, more specifically, on ‘emotional eating’ scores of the Three Factor Eating Questionnaire in carriers of the variant rs17782313’s risk allele. These findings suggest that rs17782313’s effect on eating behavior is mediated by central mechanisms and that these effects are sex-specific.

Tolerance and sensitization to chronic escalating dose heroin following extended withdrawal in Fischer rats: possible role of mu-opioid receptors

RATIONALE/OBJECTIVES

Heroin addiction is characterized by recurrent cycles of drug use, abstinence, and relapse. It is likely that neurobiological changes during chronic heroin exposure persist across withdrawal and impact behavioral responses to re-exposure. We hypothesized that, after extended withdrawal, heroin-withdrawn rats would express behavioral tolerance and/or sensitization in response to heroin re-exposure and that these responses might be associated with altered mu-opioid receptor (MOPr) activity.

METHODS

Male Fischer rats were exposed chronically to escalating doses of heroin (7.5-75 mg/kg/day), experienced acute spontaneous withdrawal and extended (10-day) abstinence, and were re-exposed chronically to heroin. Homecage behaviors and locomotor activity in response to heroin, as well as somatic withdrawal signs, were recorded. Separate groups of rats were sacrificed after extended abstinence and MOPr expression and G-protein coupling were analyzed using [(3)H]DAMGO and [(35)S]GTPγS assays.

RESULTS

The depth of behavioral stupor was lower during the initial days of heroin re-exposure compared to the initial days of the first exposure period. Behavioral responses (e.g., stereotypy) and locomotion were elevated in response to heroin re-exposure at low doses. Rats conditioned for heroin place preference during the chronic re-exposure period expressed heroin preference during acute withdrawal; this preference was stronger than rats conditioned during chronic heroin exposure that followed chronic saline and injection-free periods. Extended withdrawal was associated with increased MOPr expression in the caudate-putamen and frontal and cingulate cortices. No changes in G-protein coupling were identified.

CONCLUSIONS

Aspects of tolerance/sensitization to heroin are present even after extended abstinence and may be associated with altered MOPr density.

Antinociceptive effects induced by injection of the galanin receptor 1 agonist M617 into central nucleus of amygdala in rats

The present study was performed to explore the antinociceptive effects of M617, a selective galanin receptor 1 agonist, in the central nucleus of amygdala (CeA) of rats. Intra-CeA injection of 0.1 nmol, 0.5 nmol and 1 nmol of M617 induced dose-dependent increases in hindpaw withdrawal latencies (HWLs) to noxious thermal and mechanical stimulations in rats. Furthermore, rats received intra-CeA administration of M617 and galanin. The HWL to noxious thermal and mechanical stimulations increased markedly, and there were no significant differences in HWLs of rats received intra-CeA administration of M617 and galanin. The results demonstrated that intra-CeA injection of M617 induced significant antinociceptive effects in CeA of rats, indicating that galanin receptor 1 may be involved in M617-induced antinociception in the CeA of rats.

Feed-forward mechanisms: addiction-like behavioral and molecular adaptations in overeating

Food reward, not hunger, is the main driving force behind eating in the modern obesogenic environment. Palatable foods, generally calorie-dense and rich in sugar/fat, are thus readily overconsumed despite the resulting health consequences. Important advances have been made to explain mechanisms underlying excessive consumption as an immediate response to presentation of rewarding tastants. However, our understanding of long-term neural adaptations to food reward that oftentimes persist during even a prolonged absence of palatable food and contribute to the reinstatement of compulsive overeating of high-fat high-sugar diets, is much more limited. Here we discuss the evidence from animal and human studies for neural and molecular adaptations in both homeostatic and non-homeostatic appetite regulation that may underlie the formation of a "feed-forward" system, sensitive to palatable food and propelling the individual from a basic preference for palatable diets to food craving and compulsive, addiction-like eating behavior.

Hypothalamic opioid-melanocortin appetitive balance and addictive craving

Whilst the parallels between drug and food craving are receiving increasing attention, the recently elucidated complex physiology of the hypothalamic appetite regulatory centres has been largely overlooked in the efforts to understand drug craving which is one of the most refractory and problematic aspects of drug and behavioural addictions. Important conceptual gains could be made by researchers from both appetite and addiction neuroscience if they were to have an improved understanding of each others' disciplines. It is well known in addiction medicine that the use of many substances is elevated in opiate dependency. There is voluminous evidence of very high rates of drug use in opiate agonist maintained patients, and the real possibility exists that opiate agonist therapy therefore increases drug craving. Conversely, opiate antagonist therapy with naloxone or naltrexone has been shown to reduce most chemical and behavioural addictions, and naltrexone is now being developed together with bupropion as the anti-obesity drug "Contrave". Hypothalamic melanocortins, particularly α-MSH, are known to constitute the main brake to consumptive behaviour of food. There is a well described antagonism between melanocortins and opioids at many loci including the hypothalamus. Administration of exogenous opiates is known to both suppress α-MSH and to stimulate hedonic food consumption. Opiate maintenance programs are associated with weight gain. As monoamines, opioids and cannabinoids are known to be involved in appetite regulation, and as endorphin opioids are known to be perturbed in other addictions, further exploration of the hypothalamic appetite regulatory centre would appear to be an obvious, albeit presently largely overlooked, locus in which to study drug and other craving mechanisms.

Endogenous opiates and behavior: 2009

This paper is the 32nd consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2009 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior (Section 2), and the roles of these opioid peptides and receptors in pain and analgesia (Section 3); stress and social status (Section 4); tolerance and dependence (Section 5); learning and memory (Section 6); eating and drinking (Section 7); alcohol and drugs of abuse (Section 8); sexual activity and hormones, pregnancy, development and endocrinology (Section 9); mental illness and mood (Section 10); seizures and neurologic disorders (Section 11); electrical-related activity and neurophysiology (Section 12); general activity and locomotion (Section 13); gastrointestinal, renal and hepatic functions (Section 14); cardiovascular responses (Section 15); respiration and thermoregulation (Section 16); and immunological responses (Section 17).

Hypothalamic control of energy metabolism via the autonomic nervous system

The hypothalamic control of hepatic glucose production is an evident aspect of energy homeostasis. In addition to the control of glucose metabolism by the circadian timing system, the hypothalamus also serves as a key relay center for (humoral) feedback information from the periphery, with the important role for hypothalamic leptin receptors as a striking example. The hypothalamic biological clock uses its projections to the preautonomic hypothalamic neurons to control the daily rhythms in plasma glucose concentration, glucose uptake, and insulin sensitivity. Euglycemic, hyperinsulinemic clamp experiments combined with either sympathetic-, parasympathetic-, or sham-denervations of the autonomic input to the liver have further delineated the hypothalamic pathways that mediate the control of the circadian timing system over glucose metabolism. In addition, these experiments clearly showed both that next to the biological clock peripheral hormones may "use" the preautonomic neurons in the hypothalamus to affect hepatic glucose metabolism, and that similar pathways may be involved in the control of lipid metabolism in liver and white adipose tissue.

GABA-A and GABA-B receptors mediate feeding elicited by the GABA-B agonist baclofen in the ventral tegmental area and nucleus accumbens shell in rats: reciprocal and regional interactions

Food intake is significantly increased following administration of GABA-B and GABA-A agonists into the nucleus accumbens (NAC) shell and ventral tegmental area (VTA) with receptor-selective antagonist pretreatment capable of blocking these responses within sites. Regional interactions in feeding studies have been evaluated by administering an antagonist in one site of interest prior to administration of the feeding-active agonist in a second site of interest and have identified important relationships, particularly for opioid-opioid interactions. To evaluate whether regional and reciprocal VTA and NAC shell interactions occur for GABA-mediated feeding, the present study examined whether feeding elicited by the GABA-B agonist, baclofen, microinjected into the NAC shell was dose-dependently blocked by pretreatment with either the GABA-B antagonist, saclofen, or the GABA-A antagonist, bicuculline, into the VTA, and then whether VTA baclofen-induced feeding was dose-dependently blocked by NAC shell pretreatment of either saclofen or bicuculline in rats. Rats were stereotaxically implanted with bilateral pairs of cannulae aimed at the VTA and NAC shell and were assessed for food intake following vehicle and baclofen (200 ng) in each site. Baclofen produced similar magnitudes of increased food intake following VTA and NAC shell treatment. Baclofen administration in the VTA and NAC shell was preceded 20 min earlier with administration of bicuculline (0, 7.5, 75, 150, 300 ng) or saclofen (0, 0.5, 1.5, 3, 5 μg) into the other site with intake measured 1, 2 and 4h after agonist treatment. VTA saclofen dose-dependently and significantly blocked feeding elicited by NAC shell baclofen. Correspondingly, NAC shell saclofen dose-dependently and significantly blocked feeding elicited by VTA baclofen, indicating a robust and bidirectional GABA-B/GABA-B receptor interaction between sites. Whereas VTA bicuculline significantly blocked the increased feeding elicited by NAC shell baclofen, NAC shell bicuculline reduced but did not block feeding elicited by VTA baclofen, indicating a unidirectional interaction GABA-B/GABA-A receptor interaction between sites. Unlike within-site receptor specificity governing the ability of GABA agonist mediation of food intake, the present study demonstrates that GABA, like opioids, employs a distributed brain network in mediating its ingestive effects, and that under certain circumstances, uses multiple receptor subtypes to underlie its regional effects.

Chronic sugar intake dampens feeding-related activity of neurons synthesizing a satiety mediator, oxytocin

Increased tone of orexigens mediating reward occurs upon repeated consumption of sweet foods. Interestingly, some of these reward orexigens, such as opioids, diminish activity of neurons synthesizing oxytocin, a nonapeptide that promotes satiety and feeding termination. It is not known, however, whether consumption-related activity of the central oxytocin system is modified under chronic sugar feeding reward itself. Therefore, we examined how chronic consumption of a rewarding high-sucrose (HS) vs. bland cornstarch (CS) diet affected the activity of oxytocin cells in the hypothalamus at the time of meal termination. Schedule-fed (2h/day) rats received either a HS or CS powdered diet for 20 days. On the 21st day, they were given the same or the opposite diet, and food was removed after the main consummatory activity was completed. Animals were perfused 60 min after feeding termination and brains were immunostained for oxytocin and the marker of neuronal activity, c-Fos. The percentage of c-Fos-positive oxytocin cells in the hypothalamic paraventricular nucleus was significantly lower in rats chronically exposed to the HS than to the CS diet, regardless of which diet they received on the final day. A similar pattern was observed in the supraoptic nucleus. We conclude that the chronic rather than acute sucrose intake reduces activity of the anorexigenic oxytocin system. These findings indicate that chronic consumption of sugar blunts activity of pathways that mediate satiety. We speculate that a reduction in central satiety signaling precipitated by regular intake of foods high in sugar may lead to generalized overeating.

The action of leptin on appetite-regulating cells in the ovine hypothalamus: demonstration of direct action in the absence of the arcuate nucleus

It is widely accepted that leptin acts on first-order neurons in the arcuate nucleus (ARC) with information then relayed to other hypothalamic centers. However, the extent to which leptin mediates its central actions solely, or even primarily, via this route is unclear. We used a model of hypothalamo-pituitary disconnection (HPD) to determine whether leptin action on appetite-regulating systems requires the ARC. This surgical preparation eliminates the ARC. We measured effects of iv leptin to activate hypothalamic neurons (Fos labeling). In ARC-intact animals, leptin increased the percentage of Fos-positive melanocortin neurons and reduced percentages of Fos-positive neuropeptide Y neurons compared with saline-treated animals. HPD itself increased Fos labeling in the lateral hypothalamic area (LHA). Leptin influenced Fos labeling in the dorsomedial nucleus (DMH), ventromedial nucleus, and paraventricular nucleus (PVN) in HPD and normal animals, with effects on particular cell types varying. In the LHA and DMH, leptin decreased orexin cell activation in HPD and ARC-intact sheep. HPD abolished leptin-induced expression of Fos in melanin-concentrating hormone cells in the LHA and in CRH cells in the PVN. In contrast, HPD accentuated activation in oxytocin neurons. Our data from sheep with lesions encompassing the ARC do not suggest a primacy of action of leptin in this nucleus. We demonstrate that first order to second order signaling may not represent the predominant means by which leptin acts in the brain to generate integrated responses. We provide evidence that leptin exerts direct action on cells of the DMH, ventromedial nucleus, and PVN.

The role of the autonomic nervous liver innervation in the control of energy metabolism

Despite a longstanding research interest ever since the early work by Claude Bernard, the functional significance of autonomic liver innervation, either sympathetic or parasympathetic, is still ill defined. This scarcity of information not only holds for the brain control of hepatic metabolism, but also for the metabolic sensing function of the liver and the way in which this metabolic information from the liver affects the brain. Clinical information from the bedside suggests that successful human liver transplantation (implying a complete autonomic liver denervation) causes no life threatening metabolic derangements, at least in the absence of severe metabolic challenges such as hypoglycemia. However, from the benchside, data are accumulating that interference with the neuronal brain-liver connection does cause pronounced changes in liver metabolism. This review provides an extensive overview on how metabolic information is sensed by the liver, and how this information is processed via neuronal pathways to the brain. With this information the brain controls liver metabolism and that of other organs and tissues. We will pay special attention to the hypothalamic pathways involved in these liver-brain-liver circuits. At this stage, we still do not know the final destination and processing of the metabolic information that is transferred from the liver to the brain. On the other hand, in recent years, there has been a considerable increase in the understanding which brain areas are involved in the control of liver metabolism via its autonomic innervation. However, in view of the ever rising prevalence of type 2 diabetes, this potentially highly relevant knowledge is still by far too limited. Thus the autonomic innervation of the liver and its role in the control of metabolism needs our continued and devoted attention.

Antinociceptive effects of galanin in the central nucleus of amygdala of rats, an involvement of opioid receptors

The central nucleus of amygdala (CeA) is a very important brain structure involved in multiple physiological functions, especially in pain modulation. There are high densities of galanin and galanin receptors found in the CeA. The present study was performed to explore the antinociceptive effects of galanin in the CeA of rats, and possible involvements of opioid receptors in the galanin-induced antinociception. Intra-CeA injection of galanin induced dose-dependent increases in hindpaw withdrawal latencies (HWLs) to noxious thermal and mechanical stimulations in rats. Interestingly, the amtinociceptive effect induced by intra-CeA injection of galanin was blocked by intra-CeA injection of naloxone, a common opioid receptor antagonist, indicating an involvement of opioid receptors in the galanin-induced antinociception in the CeA of rats. Moreover, intra-CeA injection of either selective mu-opioid receptor antagonist beta-funaltrexamine (beta-FNA) or delta-opioid receptor antagonist naltrindole, but not kappa-opioid receptor antagonist nor-binaltorphimine (nor-BNI), significantly attenuated the galanin-induced increases in HWLs in the CeA of rats. Taken together, the results demonstrate that galanin induces antinociceptive effects in the CeA of rats, and both mu- and delta-opioid receptors are involved in the galanin-induced antinociception.