Glucagon-like peptide-1 reduces pancreatic ß-cell mass through hypothalamic neural pathways in high-fat diet-induced obese rats.

We examined whether glucagon-like peptide-1 (GLP-1) affects ß-cell mass and proliferation through neural pathways, from hepatic afferent nerves to pancreatic efferent nerves via the central nervous system, in high-fat diet (HFD)-induced obese rats. The effects of chronic administration of GLP-1 (7-36) and liraglutide, a GLP-1 receptor agonist, on pancreatic morphological alterations, c-fos expression and brain-derived neurotrophic factor (BDNF) content in the hypothalamus, and glucose metabolism were investigated in HFD-induced obese rats that underwent hepatic afferent vagotomy (VgX) and/or pancreatic efferent sympathectomy (SpX). Chronic GLP-1 (7-36) administration to HFD-induced obese rats elevated c-fos expression and BDNF content in the hypothalamus, followed by a reduction in pancreatic ß-cell hyperplasia and insulin content, thus resulting in improved glucose tolerance. These responses were abolished by VgX and SpX. Moreover, administration of liraglutide similarly activated the hypothalamic neural pathways, thus resulting in a more profound amelioration of glucose tolerance than native GLP-1 (7-36). These data suggest that GLP-1 normalizes the obesity-induced compensatory increase in ß-cell mass and glucose intolerance through a neuronal relay system consisting of hepatic afferent nerves, the hypothalamus, and pancreatic efferent nerves.

Distribution of histaminergic neuronal cluster in the rat and mouse hypothalamus.

Histidine decarboxylase (HDC) catalyzes the biosynthesis of histamine from L-histidine and is expressed throughout the mammalian nervous system by histaminergic neurons. Histaminergic neurons arise in the posterior mesencephalon during the early embryonic period and gradually develop into two histaminergic substreams around the lateral area of the posterior hypothalamus and the more anterior peri-cerebral aqueduct area before finally forming an adult-like pattern comprising five neuronal clusters, E1, E2, E3, E4, and E5, at the postnatal stage. This distribution of histaminergic neuronal clusters in the rat hypothalamus appears to be a consequence of neuronal development and reflects the functional differentiation within each neuronal cluster. However, the close linkage between the locations of histaminergic neuronal clusters and their physiological functions has yet to be fully elucidated because of the sparse information regarding the location and orientation of each histaminergic neuronal clusters in the hypothalamus of rats and mice. To clarify the distribution of the five-histaminergic neuronal clusters more clearly, we performed an immunohistochemical study using the anti-HDC antibody on serial sections of the rat hypothalamus according to the brain maps of rat and mouse. Our results confirmed that the HDC-immunoreactive (HDCi) neuronal clusters in the hypothalamus of rats and mice are observed in the ventrolateral part of the most posterior hypothalamus (E1), ventrolateral part of the posterior hypothalamus (E2), ventromedial part from the medial to the posterior hypothalamus (E3), periventricular part from the anterior to the medial hypothalamus (E4), and diffusely extended part of the more dorsal and almost entire hypothalamus (E5). The stereological estimation of the total number of HDCi neurons of each clusters revealed the larger amount of the rat than the mouse. The characterization of histaminergic neuronal clusters in the hypothalamus of rats and mice may provide useful information for further investigations.

Nesfatin-1, corticotropin-releasing hormone, thyrotropin-releasing hormone, and neuronal histamine interact in the hypothalamus to regulate feeding behavior.

Nesfatin-1, corticotropin-releasing hormone (CRH), thyrotropin-releasing hormone (TRH), and hypothalamic neuronal histamine act as anorexigenics in the hypothalamus. We examined interactions among nesfatin-1, CRH, TRH, and histamine in the regulation of feeding behavior in rodents. We investigated whether the anorectic effect of nesfatin-1, α-fluoromethyl histidine (FMH; a specific suicide inhibitor of histidine decarboxylase that depletes hypothalamic neuronal histamine), a CRH antagonist, or anti-TRH antibody affects the anorectic effect of nesfatin-1, whether nesfatin-1 increases CRH and TRH contents and histamine turnover in the hypothalamus, and whether histamine increases nesfatin-1 content in the hypothalamus. We also investigated whether nesfatin-1 decreases food intake in mice with targeted disruption of the histamine H1 receptor (H1KO mice) and if the H1 receptor (H1-R) co-localizes in nesfatin-1 neurons. Nesfatin-1-suppressed feeding was partially attenuated in rats administered with FMH, a CRH antagonist, or anti-TRH antibody, and in H1KO mice. Nesfatin-1 increased CRH and TRH levels and histamine turnover, whereas histamine increased nesfatin-1 in the hypothalamus. Immunohistochemical analysis revealed H1-R expression on nesfatin-1 neurons in the paraventricular nucleus of the hypothalamus. These results indicate that CRH, TRH, and hypothalamic neuronal histamine mediate the suppressive effects of nesfatin-1 on feeding behavior.

A novel anti-inflammatory role for spleen-derived interleukin-10 in obesity-induced hypothalamic inflammation.

Obesity can be associated with systemic low-grade inflammation that contributes to obesity-related metabolic disorders. Recent studies raise the possibility that hypothalamic inflammation contributes to the pathogenesis of diet-induced obesity (DIO), while another study reported that obesity decreases the expression of pro-inflammatory cytokines in spleen. The following study examines the hypothesis that obesity suppresses the splenic synthesis of the anti-inflammatory cytokine, interleukin (IL)-10, thereby resulting in chronic hypothalamic inflammation. The results showed that due to oxidative stress or apoptosis, the synthesis of splenic IL-10 was decreased in DIO when compared with non-obesity rats. Splenectomy (SPX) accelerated DIO-induced inflammatory responses in the hypothalamus. Interestingly, SPX suppressed the DIO-induced increases in food intake and body weight and led to a hypothalamic pro-inflammatory state that was similar to that produced by DIO, indicating that hypothalamic inflammation exerts a dual effect on energy metabolism. These SPX-induced changes were inhibited by the systemic administration of IL-10. Moreover, SPX had no effect on hypothalamic inflammatory responses in IL-10-deficient mice. These data suggest that spleen-derived IL-10 plays an important role in the prevention of hypothalamic inflammation and may be a therapeutic target for the treatment of obesity and hypothalamic inflammation.

Regional distribution and the dynamics of n-decanoyl ghrelin, another acyl-form of ghrelin, upon fasting in rodents.

n-Decanoyl ghrelin (D-ghrelin), a member of ghrelin-derived peptides, is found in plasma and the stomach; however, there have so far been no studies describing its dynamics. A D-ghrelin-specific radioimmunoassay was established to examine the tissue distribution and the kinetics of D-ghrelin in mice. The effect of D-ghrelin on food intake was also examined and compared to n-octanoyl ghrelin (O-ghrelin). D-ghrelin was detected throughout the gastrointestinal tissue and plasma with highest level in the stomach. An immunofluorescent study revealed the co-localization of D- and O-ghrelin in the same stomach cells. Upon fasting, the levels of D-ghrelin in the stomach and plasma significantly increased, while that of O-ghrelin in the stomach declined. D-ghrelin increased the 2 h food consumption in mice as O-ghrelin does. These findings indicate that D-ghrelin is mainly produced in the stomach to work in concert with O-ghrelin. The different kinetics of D- and O-ghrelin in the stomach upon fasting implies the possibility of D-ghrelin-specific bioregulation.

Acute central administration of immepip, a histamine H3 receptor agonist, suppresses hypothalamic histamine release and elicits feeding behavior in rats.

Histamine suppresses feeding behavior via histamine H1 receptors in the hypothalamus. This study was performed to examine whether the acute reduction of histamine release in the hypothalamus caused by immepip, a histamine H3 agonist, modulates the feeding behavior of rats. Rats had a catheter implanted in the third cerebral ventricle (i3v) and were given central injections of phosphate-buffered-saline or immepip (100-300 pmol/rat). Following the i3v administration of immepip, the rats developed dose-dependent hypokinesia within 10 min of administration. Next to hypokinesia, the rats showed significant dose-dependent feeding behavior. High-performance liquid chromatography (HPLC) confirmed the reduction in histamine release in the hypothalamus of rats following i3v administration of immepip. These results suggest that i3v administration of immepip, an H3 receptor agonist, suppresses hypothalamic histamine release and elicits feeding behavior in rats.

Chikuyou-sekkou-to, a traditional Chinese herbal medicine, modulates eating behavior and thermal response induced by tumor necrosis factor-alpha in rats.

We investigated the effects of Chikuyou-sekkou-to (TJS-167), a traditional Chinese herbal medicine, on changes in eating behavior and rectal temperature induced by administration of tumor necrosis factor-alpha (TNF-alpha) in rats. Infusion of TNF-alpha into the third cerebral ventricle in doses of 1 to 4 mug/rat suppressed 24-hour cumulative food and water intake dose-dependently, compared to an infusion of phosphate-buffered saline (PBS) (p < 0.05 for each). The infusion of 2 microg/rat TNF-alpha into the third cerebral ventricle elevated rectal temperature compared to PBS controls (p < 0.05). In rats fed diets containing TJS-167 (1.38 g/kg/day) for 1 week, the suppressive effect of TNF-alpha (2 microg/rat) on food intake was alleviated significantly, compared to rats fed a standard diet (p < 0.05). The elevation of rectal temperature induced by TNF-alpha was attenuated significantly in the TJS-167-treated group compared to the control (p < 0.05). These results indicate that oral administration of TJS-167 may be effective in preventing or reducing TNF-alpha-induced inflammatory responses, such as appetite loss and elevation of body temperature.

Hypothalamic neuronal histamine modulates febrile response but not anorexia induced by lipopolysaccharide.

This study examined the contribution of hypothalamic neuronal histamine (HA) to the anorectic and febrile responses induced by lipopolysaccharide (LPS), an exogenous pyrogen, and the endogenous pyrogens interleukin-1beta (IL-1beta) and tumor necrosis factor-alpha (TNF-alpha). Intraperitoneal (ip) injection of LPS, IL-1beta, or TNF-alpha suppressed 24-hr cumulative food intake and increased rectal temperature in rats. To analyze the histaminergic contribution, rats were pretreated with intracerebroventricular (icv) injection of 2.44 mmol/kg or ip injection of 244 mmol/kg of alpha-fluoromethylhistidine (FMH), a suicide inhibitor of histidine decarboxylase (HDC), to deplete neural HA. The depletion of neural HA augmented the febrile response to ip injection of LPS and IL-1beta and alleviated the anorectic response to ip injection of IL-1beta. However, the depletion of neural HA did not modify the LPS-induced anorectic response or TNF-alpha-induced febrile and anorectic responses. Consistent with these results, the rate of hypothalamic HA turnover, assessed by the accumulation of tele-methylhistamine (t-MH), was elevated with ip injections of LPS and IL-1beta, but unaffected by TNF-alpha at equivalent doses. This suggests that (i) LPS and IL-1beta activate hypothalamic neural HA turnover; (ii) hypothalamic neural HA suppresses the LPS- and IL-1beta-induced febrile responses and accelerates the IL-1beta-induced anorectic response; and (iii) TNF-alpha modulates the febrile and anorectic responses via a neural HA-independent pathway. Therefore, hypothalamic neural HA is involved in the IL-1beta-dominant pathway, rather than the TNF-alpha-dominant pathway, preceding the systemic inflammatory response induced by exogenous pyrogens, such as LPS. Further research on this is needed.

Involvement of hypothalamic histamine H1 receptor in the regulation of feeding rhythm and obesity.

Histamine H(1) receptors (H(1)-Rs) are found in peripheral tissues and in regions of the hypothalamus that are concerned with regulating body composition. In the present study, we investigated the detailed mechanisms of histamine H(1)-Rs in the development of obesity. Histamine H(1)-R knockout (H1KO) mice gradually developed mature-onset obesity, which was accompanied by hyperphagia and decreased expression of uncoupling protein-1 (UCP-1) mRNA. Both younger nonobese (12-week-old) and older obese (48-week-old) H1KO mice exhibited impairment of the responsiveness to the leptin. In addition, disruption of the diurnal rhythm of feeding occurred before the onset of obesity in H1KO mice. Correction of these abnormal feeding rhythms by means of scheduled feeding caused a reduction in obesity and associated metabolic disorders in H1KO mice. Furthermore, central administration of a histamine H(1)-R agonist affected feeding behavior, body weight, and c-fos-like immunoreactivity in the hypothalamus. Taken together, these findings suggest that histamine H(1)-Rs are crucial for the regulation of feeding rhythm and in mediating the effects of leptin. Early disruption of H(1)-R-mediated functions in H1KO mice may lead to hyperphagia and decreased expression of UCP-1 mRNA, which may contribute to the development of obesity in these animals. In addition, centrally acting histamine H(1)-R may be a novel therapeutic target for the treatment of obesity and related metabolic disorders.

Obesity in insulin receptor substrate-2-deficient mice: disrupted control of arcuate nucleus neuropeptides.

OBJECTIVE: Disturbances in insulin signaling have been shown to induce obesity and/or hyperphagia in brain insulin receptor or insulin receptor substrate-2 (IRS-2) knockout (KO) mice. This study aimed to examine the central and peripheral mechanisms underlying the phenotype in IRS-2 KO mice. RESEARCH METHODS AND PROCEDURES: We measured the histological characterization of adipose tissues, mRNA levels of pro-opiomelanocortin, agouti-related protein, and neuropeptide Y in the hypothalamus and uncoupling proteins (UCPs) in peripheral tissues of IRS-2 KO mice. RESULTS: Female IRS-2 KO mice showed increased daily food intake. Body weight and adiposity were increased in both sexes, although these differences were more pronounced in female than in male IRS-2 KO mice. Both male and female IRS-2 KO mice showed decreased UCP1 mRNA expression in brown adipose tissue with defective thermoregulation, and UCP2 mRNA expression was increased in the white adipose tissue of female knockout mice. Furthermore, arcuate nucleus mRNA expression of pro-opiomelanocortin, was decreased in both male and female IRS-2 KO mice, whereas expression of agouti-related protein and neuropeptide Y were increased in female IRS-2 KO mice. DISCUSSION: In IRS-2 KO mice, disrupted control of hypothalamic neuropeptide levels and UCP mRNA expression may contribute to the development of obesity.

Hypothalamic neuronal histamine in genetically obese animals: its implication of leptin action in the brain.

Leptin regulates feeding behavior and energy metabolism by affecting hypothalamic neuromodulators. The present study was designed to examine hypothalamic neuronal histamine, a recently identified mediator of leptin signaling in the brain, in genetic obese animals. Concentrations of hypothalamic histamine and tele-methylhistamine (t-MH), a major histamine metabolite, were significantly lower in obese (ob/ob) and diabetic (db/db) mice, and Zucker fatty (fa/fa) rats, leptin-deficient and leptin-receptor defective animals, respectively, relative to lean littermates (P < 0.05 for each). A bolus infusion of leptin (1.0 microg) into the lateral ventricle (ilvt) significantly elevated the turnover rate of hypothalamic neuronal histamine, as assessed by pargyline-induced accumulation of t-MH, in ob/ob mice compared with phosphate-buffered saline (PBS) infusions (P < 0.05). However, this same treatment did not affect hypothalamic histamine turnover in db/db mice. In agouti yellow (A(y)/a) mice, animals defective in pro-opiomelanocortin (POMC) signaling, normal levels of histamine, and t-MH were seen in the hypothalamus at 4 weeks of age when obesity had not yet developed. These amine levels in A(y)/a mice showed no change until 16 weeks of age, although the mice were remarkably obese by this time. Infusions of corticotropin releasing hormone (CRH), one of neuropeptide related to leptin signaling, into the third ventricle (i3vt) increased histamine turnover in the hypothalamus of Wistar King A rats (P < 0.05 versus PBS infusion). Infusion of neuropeptide Y (NPY) or alpha-melanocyte stimulating hormone (MSH), a POMC-derived peptide failed to increase histamine turnover. These results indicate that lowered activity of hypothalamic neuronal histamine in ob/ob and db/db mice, and fa/fa rats may be due to insufficiency of leptin action in the brains of these animals. These results also suggest that disruption of POMC signaling in A(y)/a mice may not impact on neuronal histamine. Moreover, CRH but neither POMC-derived peptide nor NPY may act as a signal to neuronal histamine downstream of the leptin signaling pathway.

Peripheral, but not central, administration of adiponectin reduces visceral adiposity and upregulates the expression of uncoupling protein in agouti yellow (Ay/a) obese mice.

To examine the peripheral and central roles of adiponectin in energy intake and expenditure, we investigated the effects of adiponectin on food intake, adiposity, sympathetic nerve activity (SNA), and mRNA expressions of uncoupling protein (UCP) in the brown adipose tissue (BAT), white adipose tissue (WAT) and skeletal muscle in agouti yellow (A(y)/a) obese mice. Intraperitoneal administration of adiponectin (1.5 mg/kg for 7 days) attenuated body weight gain and reduced visceral adiposity in A(y)/a obese mice compared with PBS-treated controls. In addition, adiponectin treatment increased the expression of UCP1 mRNA in BAT, UCP2 mRNA in WAT, and UCP3 mRNA in skeletal muscle compared with PBS-treated A(y)/a controls. Acute peripheral administration of adiponectin (1.5 mg/kg, one injection) also increased SNA in the BAT accompanied by an increase in rectal temperature. Finally, these above responses as well as expression of c-Fos-like immunohistochemistry in the hypothalamus were not induced by central application of adiponectin (0-15 micro g/kg). Taken together, adiponectin effectively regulated visceral adiposity, SNA, and UCP mRNA expression peripherally, suggesting that this substance can be used as a therapeutic tool, administered peripherally, in the treatment of visceral obesity and related metabolic disorders.

Corticotropin-releasing hormone-mediated pathway of leptin to regulate feeding, adiposity, and uncoupling protein expression in mice.

To examine the functional role of CRH in the regulation of energy homeostasis by leptin, we measured the effects of the CRH antagonist, alpha-helical CRH 8-41 (alphaCRH) on a number of factors affected by leptin activity. These included food intake, body weight, hypothalamic c-fos-like immunoreactivity (c-FLI), weight and histological characterization of white adipose tissue, and mRNA expressions of uncoupling protein (UCP) in brown adipose tissue (BAT) in C57Bl/6 mice. Central infusion of leptin into the lateral cerebroventricle (icv) caused significant induction of c-FLI in the paraventricular nucleus (PVN), ventromedial hypothalamic nucleus (VMH), dorsomedial hypothalamic nucleus, and arcuate nucleus. In all these nuclei, the effect of leptin on expression of cFLI in the PVN and VMH was decreased by treatment with alphaCRH. Administration of leptin markedly decreased cumulative food intake and body weight with this effect being attenuated by pretreatment with alphaCRH. In peripheral tissue, leptin up-regulated BAT UCP1 mRNA expression and reduced fat depositions in this tissue. Those changes in BAT were also decreased by treatment with alphaCRH. As a consequence of the effects on food intake or energy expenditure, treatment with alphaCRH attenuated the leptin-induced reduction of body adiposity, fat cell size, triglyceride contents, and ob mRNA expression in white adipose tissue. Taken together, these results indicate that CRH neurons in the PVN and VMH may be an important mediator for leptin that contribute to regulation of feeding, adiposity, and UCP expression.

Neuronal histamine regulates food intake, adiposity, and uncoupling protein expression in agouti yellow (A(y)/a) obese mice.

Hypothalamic neuronal histamine and its H(1) receptor (H(1)-R) form a part of the leptin-signaling pathway in the brain and have been shown to regulate body weight and adiposity in diabetic (db/db) and diet-induced obese mice by affecting food intake and uncoupling protein mRNA expression. The proopiomelanocortin (POMC) melanocortin-4 receptor (MC-4R) is also important for leptin signaling. The present study had two aims: first, to clarify the antiobesity action of neuronal histamine in agouti yellow (A(y)/a) obese mice, a model of obesity in which POMC/MC-4R signaling is disrupted by blockade of MC-4R and second, to investigate the functional relationship between neuronal histamine and POMC/MC-4R signaling. Central administration of histamine into the lateral cerebroventricle decreased cumulative food intake and body weight in A(y)/a obese mice. Histamine treatment also decreased mRNA expression of ob gene in epididymal white adipose tissue and up-regulated uncoupling protein 1 mRNA expression in brown adipose tissue. These effects were attenuated in A(y)/a obese mice with histamine H(1)-receptor (H(1)-R) knockout. Histamine treatment induced c-Fos-like immunoreactivity in both paraventricular and arcuate nucleus. There was no significant difference in histamine-induced c-Fos-like immunoreactivity in the hypothalamus between A(y)/a obese mice and lean littermates, indicating histamine signaling was not disrupted at the hypothalamic level in A(y)/a obese mice. These results suggest that neuronal histamine have an antiobese action, even in A(y)/a obese mice despite a deficiency in POMC/MC-4R signaling. In addition, it appears that the histamine H(1)-R signaling pathway may be independent or downstream of the POMC/MC-4R signaling.

Hypothalamic histamine neurons activate lipolysis in rat adipose tissue.

The contribution of hypothalamic histamine neurons to the central regulation of peripheral lipid metabolism was investigated in rats using in vivo microdialysis system. A bolus infusion of L-histamine at doses of 10--10(3) nmol/rat into the third cerebral ventricle (i3vt) dose-dependently increased glycerol concentration in the perfusate from the epididymal adipose tissue. I3vt infusion of 10(2) nmol/rat thioperamide, an autoinhibitory H(3) receptor antagonist that activates histamine neurons to increase synthesis and release of neuronal histamine, convincingly mimicked histamine action in the augmented lipolysis. Intraperitoneal pretreatment with propranolol, a beta-adrenoceptor antagonist, abolished the thioperamide-induced lipolytic action. An electrophysiological study demonstrated that efferent sympathetic nerves innervating the epididymal fat were activated after the i3vt infusion of thioperamide. Hypothalamic histamine neurons thus regulate peripheral lipid metabolism through the accelerating lipolytic action by activation of sympathetic beta-adrenoceptor.

Histidine suppresses food intake through its conversion into neuronal histamine.

Hypothalamic neuronal histamine has been shown to regulate feeding behavior and energy metabolism as a target of leptin action in the brain. The present study aimed to examine the involvement of L-histidine, a precursor of neuronal histamine, in the regulation of feeding behavior in rats. Intraperitoneal (ip) injection of L-histidine at doses of 0.35 and 0.70 mmol/kg body weight significantly decreased the 24-hr cumulative food and water intakes compared to phosphate buffered saline injected controls (P < 0.05 for each). This suppression of feeding was mimicked dose-dependently by intracerebroventricular infusion of histidine at doses of 0.5, 1.0, and 2.0 micromol/rat (P < 0.05 for each). Pretreatment of the rats with an ip bolus injection of alpha-fluoromethylhistidine, a suicide inhibitor of a histidine decarboxylase (HDC), at a dosage of 224 micromol/kg blocked the conversion of histidine into histamine and attenuated the suppressive effect of histidine on food intake from 64.2% to 88.1% of the controls (P < 0.05). Administration of 0.35 mmol/kg histidine ip increased the concentration of hypothalamic neuronal histamine compared with the controls (P < 0.05). HDC activity was increased simultaneously by histidine administration compared with the controls (P < 0.05). The present findings indicate that L-histidine suppresses food intake through its conversion into histamine in the hypothalamus.