Hypothalamic Neuronal Histamine in Genetically Obese Animals: Its Implication of Leptin Action in the Brain

Identification of genes regulated by lipids from seaweed Susabinori (Pyropia yezoensis) involved in the improvement of hepatic steatosis: Insights from RNA-Seq analysis in obese db/db mice

Hepatic steatosis is an early stage in the progression of non-alcoholic fatty liver disease (NAFLD) and can lead to the development of non-alcoholic steatohepatitis (NASH), a major cause of liver-related morbidity and mortality. Identification of dietary components that can alleviate hepatic steatosis is crucial for developing effective therapeutic strategies for NAFLD. Recently, we demonstrated the impact of lipids extracted from the marine red alga Susabinori (Pyropia yezoensis) in a murine model of type 2-diabete (db/db). We found that Susabinori lipids (SNL), abundant in eicosapentaenoic acid (EPA)-containing polar lipids, protected against obesity-induced hepatic steatosis in db/db mice. To understand the specific genes or biological pathways underlying the effects of SNL, we conducted RNA-Seq analysis of the hepatic transcriptome. By performing comparative analysis of differentially expressed genes between normal mice and db/db mice consuming a control diet, as well as SNL-fed db/db mice, we identified the 15 SNL-dependent up-regulated genes that were down-regulated in db/db mice but up-regulated by SNL feeding. Gene ontology and pathway analysis on these 15 genes demonstrated a significant association with the metabolisms of arachidonic acid (AA) and linoleic acid (LA). Furthermore, we observed alterations in the expression levels of monoacylglycerol lipase (Magl) and fatty acid-binding protein 4 (Fabp4) in the SNL-fed db/db mice, both of which are implicated in AA and LA metabolism. Additionally, the livers of SNL-fed db/db mice exhibited reduced levels of AA and LA, but a high accumulation of EPA. In conclusion, the SNL diet might affect the metabolisms of AA and LA, which contribute to the improvement of hepatic steatosis. Our findings provide insights into the molecular mechanisms underlying the beneficial effects of SNL.

Regulation of metabolic health by dietary histidine in mice

Low-protein (LP) diets are associated with a decreased risk of diabetes in humans, and promote leanness and glycaemic control in both rodents and humans. While the effects of an LP diet on glycaemic control are mediated by reduced levels of the branched-chain amino acids, we have observed that reducing dietary levels of the other six essential amino acids leads to changes in body composition. Here, we find that dietary histidine plays a key role in the response to an LP diet in male C57BL/6J mice. Specifically reducing dietary levels of histidine by 67% reduces the weight gain of young, lean male mice, reducing both adipose and lean mass without altering glucose metabolism, and rapidly reverses diet-induced obesity and hepatic steatosis in diet-induced obese male mice, increasing insulin sensitivity. This normalization of metabolic health was associated not with caloric restriction or increased activity, but with increased energy expenditure. Surprisingly, the effects of histidine restriction do not require the energy balance hormone Fgf21. Histidine restriction that was started in midlife promoted leanness and glucose tolerance in aged males but not females, but did not affect frailty or lifespan in either sex. Finally, we demonstrate that variation in dietary histidine levels helps to explain body mass index differences in humans. Overall, our findings demonstrate that dietary histidine is a key regulator of weight and body composition in male mice and in humans, and suggest that reducing dietary histidine may be a translatable option for the treatment of obesity. KEY POINTS: Protein restriction (PR) promotes metabolic health in rodents and humans and extends rodent lifespan. Restriction of specific individual essential amino acids can recapitulate the benefits of PR. Reduced histidine promotes leanness and increased energy expenditure in male mice. Reduced histidine does not extend the lifespan of mice when begun in midlife. Dietary levels of histidine are positively associated with body mass index in humans.

Effects of Developmental Failure of Swallowing Threshold on Obesity and Eating Behaviors in Children Aged 5-15 Years

Background: The aim of the present study was to identify factors related to developmental failure of swallowing threshold in children aged 5−15 years. Methods: A total of 83 children aged 5−15 years were included in this study. A self-administered lifestyle questionnaire was completed, along with hand grip strength and oral function tests. Swallowing threshold was determined based on the concentration of dissolved glucose obtained from gummy jellies when the participants signaled that they wanted to swallow the chewed gummy jellies. Developmental failure of swallowing threshold was defined as glucose concentrations in the lowest 20th percentile. After univariate analysis, multivariate binary logistic regression analysis was used to identify factors associated with developmental failure of swallowing threshold. Results: Hand grip strength was significantly correlated with masticatory performance (r = 0.611, p < 0.01). Logistic regression analysis revealed factors related to developmental failure of swallowing threshold, i.e., overweight/obesity (Odds ratio) (OR) = 5.343, p = 0.031, 95% CI = 1.168−24.437) and eating between meals at least once a day (OR = 4.934, p = 0.049, 95% CI = 1.004−24.244). Conclusions: Developmental failure of swallowing threshold was closely associated with childhood obesity in 5- to 15-year-old children.

Crosstalk of hypothalamic chemerin, histamine, and AMPK in diet-and olanzapine-induced obesity in rats

AIM

Contradiction overwhelms chemerin link to feeding behavior. Neither the chemerin central role on appetite regulation nor its relation to hypothalamic histamine and AMPK is verified.

MAIN METHODS

Food intake, body weight and hypothalamic biochemical changes were assessed after a single intra-cerebroventricular or intraperitoneal injection (ip) (1 μg/kg or 16 μg/kg, respectively) or chronic ip administration (8 μg/kg/day) of chemerin for 14 or 28 days. Hypothalamic neurobiochemical changes in chemerin/histamine/AMPK induced by either 8-week high fat diet (HFD) or food restriction were also investigated. To confirm chemerin-histamine crosstalk, these neurobiochemical changes were assessed under settings of H1-receptor agonism and/or antagonism by betahistine and/or olanzapine, respectively for 3 weeks.

KEY FINDINGS

Chemerin-injected rats exhibited anorexigenic behavior in both acute and chronic studies that was associated with a decreased AMPK activity in the arcuate nucleus (ARC). However, with long-term administration, chemerin anorexigenic effect gradually ceased. Contrarily to food restriction, 8-week HFD increased ARC expression of chemerin and its receptor CMKLR1, reducing food intake via an interplay of H1-receptors and AMPK activity. Blockage of H1-receptors by olanzapine disrupted chemerin signaling pathway with an increased AMPK activity, augmenting food intake. These changes were reversed to normal by betahistine coadministration.

SIGNIFICANCE

Chemerin is an anorexigenic adipokine, whose dysregulation is implicated in diet, and olanzapine-induced obesity through a histamine/AMPK axis in the ARC. Hypothalamic chemerin/CMKLR1 expression is a dynamic time-dependent response to changes in body weight and/or food intake. Targeting chemerin as a novel therapeutic approach against antipsychotic- or diet-induced obesity is worth to be further delineated.

The factors related to decreases in masticatory performance and masticatory function until swallowing using gummy jelly in subjects aged 20-79 years

Background

There is growing international interest in the prevention of decreased oral function for managing oral health in older people.

Objective

The aims of the present study were to identify factors related to decreases in masticatory performance and masticatory function until swallowing in subjects aged 20‐79 years old.

Methods

A total of 152 subjects, ranging in age from 20 to 79 years, were divided into six groups according to their chronological age: 20‐29, 30‐39, 40‐49, 50‐59, 60‐69 and 70‐79 years. Grip strength, maximum occlusal force, maximum tongue pressure, masticatory performance and swallowing threshold were measured in all subjects. Masticatory performance and swallowing threshold were determined according to the concentration of dissolved glucose obtained from gummy jellies; decreased masticatory performance and decreased swallowing threshold were defined as glucose concentrations in the lowest 20th percentile. A multivariate binary logistic regression analysis was used to identify factors associated with decreased masticatory performance and decreased swallowing threshold. A self‐administered lifestyle questionnaire was also completed.

Results

Logistic regression analyses revealed that factors related to decreased masticatory performance included use of more than one kind of medicine for treating chronic diseases and removable denture use, while factors related to decreased swallowing threshold included eating between meals once or more per day, poorer mental health and decreased saliva flow.

Conclusions

Different factors are related to decreased masticatory performance and decreased swallowing threshold, although both of these phenomena are closely associated with general health status.

Novel Tetrahydroquinazolinamines as Selective Histamine 3 Receptor Antagonists for the Treatment of Obesity

The histamine 3 receptor (H3R) is a presynaptic receptor, which modulates several neurotransmitters including histamine and various essential physiological processes, such as feeding, arousal, cognition, and pain. The H3R is considered as a drug target for the treatment of several central nervous system disorders. We have synthesized and identified a novel series of 4-aryl-6-methyl-5,6,7,8-tetrahydroquinazolinamines that act as selective H3R antagonists. Among all the synthesized compounds, in vitro and docking studies suggested that the 4-methoxy-phenyl-substituted tetrahydroquinazolinamine compound 4c has potent and selective H3R antagonist activity (IC₅₀ < 0.04 μM). Compound 4c did not exhibit any activity on the hERG ion channel and pan-assay interference compounds liability. Pharmacokinetic studies showed that 4c crosses the blood brain barrier, and in vivo studies demonstrated that 4c induces anorexia and weight loss in obese, but not in lean mice. These data reveal the therapeutic potential of 4c as an anti-obesity candidate drug via antagonizing the H3R.

Knockout of l-Histidine Decarboxylase Prevents Cholangiocyte Damage and Hepatic Fibrosis in Mice Subjected to High-Fat Diet Feeding via Disrupted Histamine/Leptin Signaling

Feeding a high-fat diet (HFD) coupled with sugar, mimicking a Western diet, causes fatty liver disease in mice. Histamine induces biliary proliferation and fibrosis and regulates leptin signaling. Wild-type (WT) and l-histidine decarboxylase (Hdc-/-) mice were fed a control diet or an HFD coupled with a high fructose corn syrup equivalent. Hematoxylin and eosin and Oil Red O staining were performed to determine steatosis. Biliary mass and cholangiocyte proliferation were evaluated by immunohistochemistry. Senescence and fibrosis were measured by quantitative PCR and immunohistochemistry. Hepatic stellate cell activation was detected by immunofluorescence. Histamine and leptin levels were measured by enzyme immunoassay. Leptin receptor (Ob-R) was evaluated by quantitative PCR. The HDC/histamine/histamine receptor axis, ductular reaction, and biliary senescence were evaluated in patients with nonalcoholic fatty liver disease, nonalcoholic steatohepatitis, or end-stage liver disease. Hdc-/- HFD mice had increased steatosis compared with WT HFD mice. WT HFD mice had increased biliary mass, biliary proliferation, senescence, fibrosis, and hepatic stellate cell activation, which were reduced in Hdc-/- HFD mice. In Hdc-/- HFD mice, serum leptin levels increased, whereas biliary Ob-R expression decreased. Nonalcoholic steatohepatitis patients had increased HDC/histamine/histamine receptor signaling. Hdc-/- HFD mice are susceptible to obesity via dysregulated leptin/Ob-R signaling, whereas the lack of HDC protects from HFD-induced fibrosis and cholangiocyte damage. HDC/histamine/leptin signaling may be important in managing obesity-induced biliary damage.

Modulatory influences of estradiol and other anorexigenic hormones on metabotropic, Gi/o-coupled receptor function in the hypothalamic control of energy homeostasis

The appetite suppressant actions of estradiol are due to its ability to attenuate orexigenic signals and potentiate anorexigenic signals. The work from my laboratory has shown that male guinea pigs are more sensitive to the hyperphagic and hypothermic effects of cannabinoids than their female counterparts. Cannabinoid sensitivity is further dampened by the activational effects of estradiol. This occurs via the hypothalamic feeding circuitry, where estradiol rapidly attenuates the cannabinoid CB1 receptor-mediated presynaptic inhibition of glutamatergic input onto anorexigenic proopiomelanocortin (POMC) neurons in the arcuate nucleus. This disruption is blocked by the estrogen receptor antagonist ICI 182,780, and associated with increased expression of phosphatidylinositol-3-kinase (PI3K). Moreover, the ability of estradiol to reduce both the cannabinoid-induced hyperphagia and glutamate release onto POMC neurons is abrogated by the PI3K inhibitor PI 828. The peptide orphanin FQ/nociceptin (OFQ/N) activates opioid receptor-like (ORL)1 receptors to hyperpolarize and inhibit POMC neurons via the activation of postsynaptic G protein-gated, inwardly-rectifying (GIRK) channels. We have demonstrated that the fasting-induced hyperphagia observed in ORL1-null mice is blunted compared to wild type controls. In addition, the ORL1 receptor-mediated activation of GIRK channels in POMC neurons from ovariectomized female rats is markedly impaired by estradiol. The estrogenic attenuation of presynaptic CB1 and postsynaptic ORL1 receptor function may be part of a more generalized mechanism through which anorexigenic hormones suppress orexigenic signaling. Indeed, we have found that leptin robustly suppresses the OFQ/N-induced activation of GIRK channels in POMC neurons. Furthermore, its ability to augment excitatory input onto POMC neurons is blocked by PI 828. Thus, estradiol and other hormones like leptin reduce energy intake at least partly by activating PI3K to disrupt the pleiotropic functions of Gi/o-coupled receptors that inhibit anorexigenic POMC neurons.

Loss of histaminergic modulation of thermoregulation and energy homeostasis in obese mice

Histamine acts centrally to increase energy expenditure and reduce body weight by mechanisms not fully understood. It has been suggested that in the obese state hypothalamic histamine signaling is altered. Previous studies have also shown that histamine acting in the preoptic area controls thermoregulation. We aimed to study the influence of preoptic histamine on body temperature and energy homeostasis in control and obese mice. Activating histamine receptors in the preoptic area by increasing the concentration of endogenous histamine or by local injection of specific agonists induced an elevation of core body temperature and decreased respiratory exchange ratio (RER). In addition, the food intake was significantly decreased. The hyperthermic effect was associated with a rapid increase in mRNA expression of uncoupling proteins in thermogenic tissues, the most pronounced being that of uncoupling protein (UCP) 1 in brown adipose tissue and of UCP2 in white adipose tissue. In diet-induced obese mice histamine had much diminished hyperthermic effects as well as reduced effect on RER. Similarly, the ability of preoptic histamine signaling to increase the expression of uncoupling proteins was abolished. We also found that the expression of mRNA encoding the H1 receptor subtype in the preoptic area was significantly lower in obese animals. These results indicate that histamine signaling in the preoptic area modulates energy homeostasis by regulating body temperature, metabolic parameters and food intake and that the obese state is associated with a decrease in neurotransmitter's influence.

Intersection between metabolic dysfunction, high fat diet consumption, and brain aging

Deleterious neurochemical, structural, and behavioral alterations are a seemingly unavoidable aspect of brain aging. However, the basis for these alterations, as well as the basis for the tremendous variability in regards to the degree to which these aspects are altered in aging individuals, remains to be elucidated. An increasing number of individuals regularly consume a diet high in fat, with high-fat diet consumption known to be sufficient to promote metabolic dysfunction, although the links between high-fat diet consumption and aging are only now beginning to be elucidated. In this review we discuss the potential role for age-related metabolic disturbances serving as an important basis for deleterious perturbations in the aging brain. These data not only have important implications for understanding the basis of brain aging, but also may be important to the development of therapeutic interventions which promote successful brain aging.

Obesity and vulnerability of the CNS

The incidence of obesity is increasing worldwide, and is especially pronounced in developed western countries. While the consequences of obesity on metabolic and cardiovascular physiology are well established, epidemiological and experimental data are beginning to establish that the central nervous system (CNS) may also be detrimentally affected by obesity and obesity-induced metabolic dysfunction. In particular, data show that obesity in human populations is associated with cognitive decline and enhanced vulnerability to brain injury, while experimental studies in animal models confirm a profile of heightened vulnerability and decreased cognitive function. This review will describe findings from human and animal studies to summarize current understanding of how obesity affects the brain. Furthermore, studies aimed at identifying key elements of body-brain dialog will be discussed to assess how various metabolic and adipose-related signals could adversely affect the CNS. Overall, data suggest that obesity-induced alterations in metabolism may significantly synergize with age to impair brain function and accelerate age-related diseases of the nervous system. Thus, enhanced understanding of the effects of obesity and obesity-related metabolic dysfunction on the brain are especially critical as increasing numbers of obese individuals approach advanced age.

Cannabinoid-induced hyperphagia: correlation with inhibition of proopiomelanocortin neurons?

We tested the hypothesis that cannabinoids modulate feeding in male guinea pigs, and correlated cannabinoid-induced changes in feeding behavior with alterations in glutamatergic synaptic currents impinging upon proopiomelanocortin (POMC) neurons of the hypothalamic arcuate nucleus. Feeding experiments were performed as follows: after a three-day acclimation period, animals were weighed and injected with either the CB1 receptor agonist WIN 55,212-2 (1 mg/kg, s.c.), antagonist AM251 (3 mg/kg, s.c.) or their cremophore/ethanol/saline vehicle (1:1:18; 1 ml/kg, s.c.) each day for seven days. WIN 55,212-2 increased, whereas AM251 decreased, the rate of cumulative food intake. The agonist effect was manifest primarily by increases in meal frequency and the amount of food eaten per meal. By contrast, the antagonist effect was associated with decreases in meal frequency, duration and weight loss. For the electrophysiological experiments, we performed whole-cell patch-clamp recordings from POMC neurons in hypothalamic slices. WIN 55,212-2 decreased the amplitude of evoked, glutamatergic excitatory postsynaptic currents (eEPSCs) and increased the S2:S1 ratio. Conversely, AM251 increased eEPSC amplitude per se, and blocked the inhibitory effects of the agonist. WIN 55,212-2 also decreased miniature EPSC (mEPSC) frequency; whereas AM251 increased mEPSC frequency per se, and again blocked the inhibitory effect of the agonist. A subpopulation of cells exhibited an agonist-induced outward current, which was blocked by AM251, associated with increased conductance and reversed polarity near the Nernst equilibrium potential for K(+). These data demonstrate that cannabinoids regulate appetite in the guinea pig in part through both presynaptic and postsynaptic actions on anorexigenic POMC neurons.

Histamine in the brain: Beyond sleep and memory

A few decades elapsed between the attribution of unwanted side effects of classic antihistamine compounds to the blockade of central H(1) receptors, and the acceptance of the concept that the histaminergic system commands general states of metabolism and consciousness. In the early 80s, two laboratories discovered independently that histaminergic neurons are located in the posterior hypothalamus and project to the whole CNS [Panula P, Yang HY, Costa E. Histamine-containing neurons in the rat hypothalamus. Proc Natl Acad Sci 1984;81:2572-76, Watanabe T, Taguchi Y, Hayashi H, Tanaka J, Shiosaka S, Tohyama M, Kubota H, Terano Y, Wada H. Evidence for the presence of a histaminergic neuron system in the rat brain: an immunohistochemical analysis. Neurosci Lett 1983;39:249-54], suggesting a global nature of histamine regulatory effects. Recently, functional studies demonstrated that activation of the central histaminergic system alters CNS functions in both behavioral and homeostatic contexts, which include sleep and wakefulness, learning and memory, anxiety, locomotion, feeding and drinking, and neuroendocrine regulation. These actions are achieved through interactions with other neurotransmitter systems, and the interplay between histaminergic neurons and other neurotransmitter systems are becoming clear. Hence, numerous laboratories are pursuing novel compounds targeting the three known histamine receptors found in the brain for various therapeutic indications. Preclinical studies are focusing on three major areas of interest and intense research is mainly oriented towards providing drugs for the treatment of sleep, cognitive and feeding disorders. This commentary is intended to summarize some of the latest findings that suggest functional roles for the interplay between histamine and other neurotransmitter systems, and to propose novel interactions as physiological substrates that may partially underlie some of the behavioral changes observed following manipulation of the histaminergic system.

Histamine and the regulation of body weight

Energy intake and expenditure is regulated by a complex interplay between peripheral and central factors. An exhaustive list of peptides and neurotransmitters taking part in this complex regulation of body weight exists. Among these is histamine, which acts as a central neurotransmitter. In the present article we review current evidence pointing at an important role of histamine in the regulation of appetite and metabolism. Studies using both knockout mouse models as well as pharmacological studies have revealed that histamine acts as an anorexigenic agent via stimulation of histamine H(1) receptors. One effect of histamine in the regulation of appetite is to act as a mediator of the inhibitory effect of leptin on appetite. It seems that histamine may attenuate and delay the development of leptin resistance in high-fat-diet-induced obesity. Furthermore, histamine may also act to accelerate lipolysis. Based on the current evidence of the involvement of histamine in the regulation of body weight, the histaminergic system is an obvious target for the development of pharmacological agents to control obesity. At present, H(3) receptor antagonists that stimulate the histaminergic system may be the most promising histaminergic drugs for antiobesity therapy.

Histamine induces the expression of uncoupling protein 2 (UCP2) and acid-binding protein (aP2) in white adipocytes

BACKGROUND

The aim of the present study was to investigate whether histamine induces up-regulated expression of uncoupling protein 2 (UCP2) and fat acid-binding protein (aP2) in white adipocytes (differentiated 3T3-L1 cells).

METHODS

Differentiation of 3T3-L1 preadipocytes to adipocytes was induced by the addition of 5 microg/mL insulin, 1 micromol/L dexamethasone, 10 mmol/L 1-isobutyl-3-methylxanthine, 1% dimethylsulfoxide, and 10% fetal bovine serum in Dulbecco's modification of Eagle's medium. Total RNA from differentiated 3T3-L1 cells was extracted and semi-quantitative RT-PCR was performed to determine the levels of UCP2 and aP2 mRNA. The expression level of UCP2 protein was determined by Western blot analysis.

RESULTS

Histamine at a concentration of 30 micromol/L significantly increased the expression of UCP2 mRNA and UCP2 protein, and expression levels reached a peak value. There were significant differences in the expression levels of UCP2 mRNA and UCP2 protein in adipocytes treated with 30 micromol/L histamine at various time points within 48 h, and their levels reached a peak value after 6 h of incubation. In addition, histamine increased the expression level of aP2 mRNA in adipocytes. Expression of aP2 mRNA in adipocytes reached the highest value at a concentration of 20 micromol/L histamine after 6-h incubation. Finally, we found that diphenhydramine (a H1 receptor antagonist) significantly decreased expression levels of UCP2 mRNA and protein, as well as aP2 mRNA. There were significant differences in expression levels of UCP2 and aP2 mRNA in adipocytes treated at concentrations of 20 micromol/L histamine and diphenhydramine, respectively.

CONCLUSIONS

These data reveal that histamine up-regulated the expression of UCP2 and aP2 in vitro in white adipocytes.

Food intake and reward mechanisms in patients with schizophrenia: implications for metabolic disturbances and treatment with second-generation antipsychotic agents

Obesity is highly prevalent among patients with schizophrenia and is associated with detrimental health consequences. Although excessive consumption of fast food and pharmacotherapy with such second-generation antipsychotic agents (SGAs) as clozapine and olanzapine has been implicated in the schizophrenia/obesity comorbidity, the pathophysiology of this link remains unclear. Here, we propose a mechanism based on brain reward function, a relevant etiologic factor in both schizophrenia and overeating. A comprehensive literature search on neurobiology of schizophrenia and of eating behavior was performed. The collected articles were critically reviewed and relevant data were extracted and summarized within four key areas: (1) energy homeostasis, (2) food reward and hedonics, (3) reward function in schizophrenia, and (4) metabolic effects of the SGAs. A mesolimbic hyperdopaminergic state may render motivational/incentive reward system insensitive to low salience/palatability food. This, together with poor cognitive control from hypofunctional prefrontal cortex and enhanced hedonic impact of food, owing to exaggerated opioidergic drive (clinically manifested as pain insensitivity), may underlie unhealthy eating habits in patients with schizophrenia. Treatment with SGAs purportedly improves dopamine-mediated reward aspects, but at the cost of increased appetite and worsened or at least not improved opiodergic capacity. These effects can further deteriorate eating patterns. Pathophysiological and therapeutic implications of these insights need further validation via prospective clinical trials and neuroimaging studies.

Altered sleep regulation in leptin-deficient mice

Recent epidemiological, clinical, and experimental studies have demonstrated important links between sleep duration and architecture, circadian rhythms, and metabolism, although the genetic pathways that interconnect these processes are not well understood. Leptin is a circulating hormone and major adiposity signal involved in long-term energy homeostasis. In this study, we tested the hypothesis that leptin deficiency leads to impairments in sleep-wake regulation. Male ob/ob mice, a genetic model of leptin deficiency, had significantly disrupted sleep architecture with an elevated number of arousals from sleep [wild-type (WT) mice, 108.2 ± 7.2 vs. ob/ob mice, 148.4 ± 4.5, P < 0.001] and increased stage shifts (WT, 519.1 ± 25.2 vs. ob/ob, 748.0 ± 38.8, P < 0.001) compared with WT mice. Ob/ob mice also had more frequent, but shorter-lasting sleep bouts compared with WT mice, indicating impaired sleep consolidation. Interestingly, ob/ob mice showed changes in sleep time, with increased amounts of 24-h non-rapid eye movement (NREM) sleep (WT, 601.5 ± 10.8 vs. ob/ob, 669.2 ± 13.4 min, P < 0.001). Ob/ob mice had overall lower body temperature (WT, 35.1 ± 0.2 vs. ob/ob, 33.4 ± 0.2°C, P < 0.001) and locomotor activity counts (WT, 25125 ± 2137 vs. ob/ob, 5219 ± 1759, P < 0.001). Ob/ob mice displayed an attenuated diurnal rhythm of sleep-wake stages, NREM delta power, and locomotor activity. Following sleep deprivation, ob/ob mice had smaller amounts of NREM and REM recovery sleep, both in terms of the magnitude and the duration of the recovery response. In combination, these results indicate that leptin deficiency disrupts the regulation of sleep architecture and diurnal rhythmicity.

The neuronal histamine H(1) and pro-opiomelanocortin-melanocortin 4 receptors: independent regulation of food intake and energy expenditure

Hypothalamic neuronal histamine and its H(1) receptor (H(1)-R) form part of the leptin signaling pathway in the brain, and regulate body weight and adiposity by affecting food intake and energy expenditure. The pro-opiomelanocortin (POMC)-melanocortin 4 receptor (MC4-R) is also important for leptin signaling. We investigated whether and how these two neuronal pathways interact in regulating energy metabolism. From studies of agouti yellow (A(y)/a) obese mice, a model of a defect in POMC-MC4-R signaling, we concluded that the histamine H(1)-R signaling pathway is independent of the POMC-MC4-R complex in regulating food intake, energy metabolism, and adiposity.

Increased susceptibility to diet-induced obesity in histamine-deficient mice

BACKGROUND AND AIM

The neurotransmitter histamine is involved in the regulation of appetite and in the development of age-related obesity in mice. Furthermore, histamine is a mediator of the anorexigenic action of leptin. The aim of the present study was to investigate a possible role of histamine in the development of high-fat diet (HFD)-induced obesity.

METHODS

Histamine-deficient histidine decarboxylase knock-out (HDC-KO) mice and C57BL/6J wild-type (WT) mice were given either a standard diet (STD) or HFD for 8 weeks. Body weight, 24-hour caloric intake, epididymal adipose tissue size, plasma leptin concentration and quantitative expression of leptin receptor (Ob-R) mRNA were measured.

RESULTS

Both HDC-KO and WT mice fed an HFD for 8 weeks increased their body weight significantly more than STD-fed mice. A significant difference in body weight gain between HDC-KO mice fed an HFD or an STD was seen after 2 weeks, whereas a significant difference in body weight gain was first observed after 5 weeks in WT mice. After 8 weeks 24-hour caloric intake was significantly lower in HFD- than in STD-fed WT mice. In HDC-KO mice no difference in caloric intake was observed between HFD- and STD-fed mice. After 8 weeks epididymal adipose tissue size and plasma leptin concentration had increased significantly in HFD-fed WT and HDC-KO mice compared to their STD-fed controls. Epididymal adipose tissue size was higher in HDC-KO than WT mice, both in STD- and HFD-fed mice. A significant decrease in Ob-R mRNA in HFD-fed HDC-KO mice compared to STD-fed HDC-KO mice was observed, while no such difference was observed in WT mice.

CONCLUSION

Based on our results, we conclude that histamine plays a role in the development of HFD-induced obesity.

Glucagon‐like peptide‐1, corticotropin‐releasing hormone, and hypothalamic neuronal histamine interact in the leptin‐signaling pathway to regulate feeding behavior

Glucagon-like peptide-1 (GLP-1), corticotropin-releasing hormone (CRH), and hypothalamic neuronal histamine suppress food intake, a target of leptin action in the brain. This study examined the interactions of GLP-1, CRH, and histamine downstream from the leptin-signaling pathway in regulating feeding behavior. Infusion of GLP-1 into the third cerebral ventricle (i3vt) at a dose of 1 mug significantly decreased the initial 1 h cumulative food intake in rats as compared with phosphate-buffered saline (PBS) controls. The GLP-1-induced suppression of feeding was partially attenuated by intraperitoneal pretreatment with alpha-fluoromethylhistidine (FMH), a specific suicide inhibitor of histidine decarboxylase, which depletes hypothalamic neuronal histamine. Pretreatment with alpha-helical CRH (10 microg/rat, i3vt), a nonselective CRH antagonist, abolished the GLP-1-induced suppression of feeding completely. I3vt infusion of GLP-1 increased the CRH content and histamine turnover assessed using the pargyline-induced accumulation of tele-methyl histamine (t-MH), a major metabolite of neuronal histamine, in the hypothalamus. The central infusion of CRH also induced the increase of histamine turnover and CRH receptor type 1 was localized on the cell body of histamine neuron. Pretreatment with exendin(9-39), a GLP-1 receptor antagonist, attenuated the leptin-induced increase in CRH content of the hypothalamus. Finally, i3vt infusion of leptin also increased histamine turnover in the hypothalamus. Pretreatment with exendin(9-39), alpha-helical CRH or both antagonists attenuated the leptin-induced responses of t-MH levels in the hypothalamus. These results suggest that CRH or hypothalamic neuronal histamine mediates the GLP-1-induced suppression of feeding behavior, that CRH mediates GLP-1 signaling to neuronal histamine and that a functional link from GLP-1 to neuronal histamine via CRH constitutes the leptin-signaling pathway regulating feeding behavior.

Assessment of pharmacology and potential anti-obesity properties of H3receptor antagonists/inverse agonists

Histamine is a key neurotransmitter that alters central nervous system functions in both behavioural and homeostatic contexts through its actions on the histamine (H) subreceptors H(1), H(2) and H(3) G-protein-coupled receptors. H(3)receptors have a diverse central nervous system distribution where they function as both homo- and hetero-receptors to modulate the synthesis and/or release of several neurotransmitters. H(3) receptors are constitutively active, which implies that antagonists of H(3) receptors may also function as inverse agonists to alter the basal state of the receptor and uncouple constitutive receptor-G-protein interactions. Reference H(3) antagonists such as thioperamide and ciproxifan, administered either centrally or systemically, have been shown to cause changes in food consumption and/or body weight in proof-of-concept studies. More recently, several non-imidazole-based H(3) antagonists/inverse agonists have also been described with efficacy in at least one animal model of human obesity. Considerable preclinical effort remains necessary before such compounds achieve therapeutic success or failure. Moreover, ongoing research in a number of laboratories has shed new insights into the effects of H(3) ligands in the control of feeding, appetite and body weight, which offer different results and conclusions. The goal of this review is to appraise these findings and forecast whether any H(3) antagonists/inverse agonists will provide clinical utility to treat human obesity.

Simultaneous fluorometric measurement of histamine and tele-methylhistamine levels in rodent brain by high-performance liquid chromatography

An improved high-performance liquid chromatography (HPLC) method was developed for simultaneous analysis of histamine (HA) and tele-methylhistamine (tele-MHA) levels in mouse and rat brain. The method consists of a solid-phase extraction (SPE) and subsequent HPLC with postcolumn derivatization of the amines with o-phthalaldehyde. The recovery rates of HA and tele-MHA during the SPE procedure were 82.8+/-3.4 and 86.0+/-1.7%, respectively. The detection limits for HA and tele-MHA were 8 and 12pg, respectively, with sufficient linearity up to 30pg. Using this newly developed system, we observed that the brain tele-MHA levels in H3 receptor knockout mice were significantly higher than those of wild-type mice by 2.1-fold. Furthermore, we also observed that the brain HA and tele-MHA levels in Zucker rats were significantly lower than those of lean rats by 76.6+/-5.3 and 77.8+/-5.0%, respectively. These observations coincided well with those of previous studies using radioimmunoassay or HPLC with precolumn OPA derivatization, confirming the utilization of the assay system.