Search

Chemerin is a recently identified adipokine that is involved in the regulation of adipogenesis, energy metabolism, and inflammation. The aim of the present study was to investigate the role of chemerin on food intake, body weight and hypothalamic peptidergic and aminergic modulators which play a pivotal role in feeding regulation in rats. Male adult Wistar rats were intraperitoneally injected, daily for 17 days at 9.00am, with either vehicle (saline; N=12) or chemerin (8μg/kg; N=12) and (16μg/kg; N=12). Food intake was recorded 24h after each administration. Animals were sacrificed 24h after the last injection. Total RNA was extracted from hypothalami and reverse transcribed to evaluate gene expression of agouti-related peptide (AgRP), neuropeptide Y (NPY), orexin-A, corticotrophin releasing hormone (CRH), pro-opiomelanocortin (POMC) and cocaine and amphetamine-regulated transcript (CART). Furthermore, we evaluated the effect of chemerin on dopamine, norepinephrine and serotonin steady state concentrations in rat hypothalamus homogenate, and monoamine release from rat hypothalamic synaptosomes. Chemerin administration (8 and 16μg/kg) decreased both food intake and body weight compared to vehicle, possibly associated with a significant increase in serotonin synthesis and release, in the hypothalamus. On the other hand, the pattern of gene expression following chemerin administration indicates a minor role played by chemerin as a peripheral appetite-regulating signal., (Copyright © 2013 Elsevier Inc. All rights reserved.)

Omentin-1, a visceral fat depot-specific secretory protein, is inversely correlated with obesity and insulin resistance. We investigated, in rats, the effects of chronic omentin-1 administration (8 μg/kg, intraperitoneally, once daily for 14-days) on feeding behavior and related hypothalamic peptides and neurotransmitters. Food intake and body weight were recorded daily throughout the study. We found a significantly increased food intake compared to controls, but only in days 10-14, while body weight significantly increased since day 12 (P<0.05). Compared with vehicle, omentin-1 treatment led to a significant reduction in both cocaine and amphetamine-regulated transcript (CART) (P<0.05) and corticotrophin releasing hormone (CRH) (P<0.05) gene expression, while pro-opiomelanocortin (POMC), agouti-related peptide (AgRP), neuropeptide Y (NPY) and orexin-A gene expression were not modified with respect to vehicle-treated rats. We also found an increase in hypothalamic levodopa (l-dopa) (P<0.05) and norepinephrine (NE) (P<0.01) synthesis, without any effect on dopamine (DA) and serotonin (5-hydroxytryptamine, 5-HT) metabolism. Furthermore, in hypothalamic synaptosomes, omentin-1 (10-100 ng/ml) stimulated basal NE release (ANOVA, P<0.0001; post hoc, P<0.001 vs. vehicle), in a dose-dependent manner, leaving unaffected both basal and depolarization-induced DA and 5-HT release. Finally, when synaptosomes were co-perfused with leptin and omentin-1, we observed that leptin was able to reverse omentin-1-induced stimulation of NE. In conclusion, the orexigenic effects of omentin-1 could be related, at least in part, to decreased CART and CRH gene expression and increased NE synthesis and release in the hypothalamus., (Copyright © 2013 Elsevier Inc. All rights reserved.)

Visfatin, also known as pre-B cell colony enhancing factor (PBEF) or nicotinamide phosphoribosyltransferase (NAMPT), is a cytokine that is produced by adipose tissue, skeletal muscle, liver and immune cells. We studied the effects of visfatin/PBEF/NAMPT on feeding behavior, hypothalamic steady state concentrations of aminergic neurotransmitters and hypothalamic mRNA levels of anorexigenic peptides, such as cocaine- and amphetamine-regulated transcript (CART) peptide, corticotropin-releasing hormone (CRH), proopiomelanocortin (POMC), and orexigenic peptides, such as agouti-related peptide (AgRP) and neuropeptide Y (NPY). Forty-eight rats were injected in the arcuate nucleus (ARC) of the hypothalamus with either saline or visfatin/PBEF/NAMPT (3 microg). Food intake was recorded 1, 2 and 24 h following injection, and either dopamine (DA), norepinephrine (NE), serotonin (5-hydroxytryptamine, 5-HT) or peptide gene expression were evaluated 2 and 24 h after visfatin/PBEF/NAMPT administration. Compared to vehicle, visfatin/PBEF/NAMPT significantly increased food intake, as evaluated 1, 2 and 24 h post-injection. Visfatin/PBEF/NAMPT treatment led to a significant decrease of DA steady state concentration, CART and CRH mRNA levels. Consequently, visfatin/PBEF/NAMPT could play an orexigenic role in the ARC, and the effect could be mediated by modulation of DA, CART and CRH activity in the hypothalamus.

Visceral adipose tissue-derived serpin (vaspin) improves glucose tolerance and insulin sensitivity in diet-induced obese mice. Chemerin may increase insulin sensitivity in adipose tissue and seems to be associated with several key aspects of metabolic syndrome. Decreased levels of omentin-1 are associated with increasing obesity and insulin resistance. Our study aimed to investigate the effects of vaspin, chemerin and omentin-1 acute administration on feeding and hypothalamic gene expression of peptides which play a key role in feeding regulation. 35 rats were injected into the arcuate nucleus (ARC) of the hypothalamus with either saline (n=8), vaspin (1μg/kg; n=9), chemerin (8μg/kg; n=9), or omentin-1 (8μg/kg; n=9). Food intake in the following 24h was recorded, thereafter rats were sacrificed. Total RNA was extracted from hypothalami and reverse transcribed to evaluate hypothalamic gene expression of agouti-related peptide (AgRP), neuropeptide Y (NPY), orexin-A, cocaine- and amphetamine-regulated transcript (CART), corticotrophin releasing hormone (CRH) and proopiomelanocortin (POMC), by real-time reverse transcription polymerase chain reaction. Compared to vehicle, vaspin injection significantly decreased feeding, while chemerin and omentin-1 had no effect in the tested dose. Vaspin treatment significantly decreased NPY and increased POMC gene expression. Chemerin treatment led to a significant increase of both AgRP and POMC gene expression. Omentin-1 treatment did not modify gene expression of the investigated peptides. Therefore, vaspin is an adipokine triggering anorectic pathways in the hypothalamus, where reduction of NPY and increase of POMC mRNA levels mediate feeding inhibition. Chemerin and omentin-1 have no effect on feeding in the tested dose., (Copyright © 2011 Elsevier Inc. All rights reserved.)

We have investigated the effects of the gastric peptide obestatin injected into the arcuate nucleus of the rat hypothalamus on the hypothalamic mRNA expression of peptides which play master roles as feeding behavior modulators. We have also evaluated the effects of obestatin on dopamine, norepinephrine and serotonin release from rat hypothalamic synaptosomes in vitro. After 4 daily intrahypothalamic injections of obestatin (1 nmol/kg), we recorded a significant reduction of daily caloric intake and body weight gain. Gene expressions of either anorexigenic (cocaine- and amphetamine-regulated transcript, corticotropin releasing hormone, proopiomelanocortin) or orexigenic (agouti-related peptide, neuropeptide Y, orexin-A) peptide mRNAs in the hypothalamus, as evaluated by real-time quantitative PCR, were not different in respect to vehicle treated rats. Moreover, ghrelin/obestatin prepropeptide gene expression in the hypothalamus was not affected by obestatin treatment. In hypothalamic synaptosomes perfused with obestatin (1-100 nM), we found a dose-dependent inhibition of depolarization-induced dopamine release, while norepinephrine and serotonin releases were not modified by obestatin treatment. When ghrelin (1 nM) and obestatin (1 nM) were co-perfused, we observed that ghrelin reversed obestatin-induced inhibition of dopamine release, and obestatin was able to block ghrelin-induced inhibition of serotonin release. We can conclude that obestatin plays an anorectic role in the hypothalamus which could be partially mediated by the acute inhibition of dopamine release, with the possible involvement of antagonism of the hypothalamic serotonin inhibitory effects of ghrelin., (Copyright (c) 2010. Published by Elsevier B.V.)

Glucagon-like peptide 1 (7-36) amide (GLP-1) and exendin-4 are gastrointestinal hormones as well as neuropeptides involved in glucose homeostasis and feeding regulation, both peripherally and at the central nervous system (CNS), acting through the same GLP-1 receptor. Aminergic neurotransmitters play a role in the modulation of feeding in the hypothalamus and we have previously found that peripheral hormones and neuropeptides, which are known to modulate feeding in the central nervous system, are able to modify catecholamine and serotonin release in the hypothalamus. In the present paper we have evaluated the effects of GLP-1 and exendin-4 on dopamine, norepinephrine, and serotonin release from rat hypothalamic synaptosomes, in vitro. We found that glucagon-like peptide 1 (7-36) amide and exendin-4 did not modify either basal or depolarization-induced dopamine and norepinephrine release; on the other hand glucagon-like peptide 1 (7-36) amide and exendin-4 stimulated serotonin release, in a dose dependent manner. We can conclude that the central anorectic effects of GLP-1 agonists could be partially mediated by increased serotonin release in the hypothalamus, leaving the catecholamine release unaffected.

Peptide YY (1-36) and peptide YY (3-36) are gut-derived hormones which are involved in feeding control in the hypothalamus. The hypothalamic mechanisms of feeding have been shown to be modulated by aminergic neurotransmitters, which could mediate the anorectic or orexigenic effects of neuropeptides and hormones. We have investigated the role of peptide YY (1-36) and peptide YY (3-36) on dopamine, norepinephrine, and serotonin release from hypothalamic synaptosomes in vitro. We found that peptide YY (3-36) inhibited depolarization-induced dopamine and norepinephrine release, leaving unaffected serotonin release, while peptide YY (1-36) did not modify either basal or stimulated amine release. We can hypothesize that the effects of peptide YY (3-36) could be mediated by inhibited hypothalamic dopamine and norepinephrine release, which could partially account for the anorectic activity of the peptide. On the other hand, peptide YY (1-36), which has a feeding stimulatory role, does not affect aminergic neurotransmission in the hypothalamus.

Adiponectin (Adipocyte Complement-Related Protein of 30 kDa, ACRP30) and resistin are adipocyte-derived polypeptide hormones playing a role in metabolic homeostasis. Their plasma levels are inversely (adiponectin) or directly (resistin) correlated to obesity and they have opposite effects on insulin sensitivity. Adipose tissue hormones such as leptin have been shown to modulate neurotransmitters which control feeding in the hypothalamus. We have studied the effects of adiponectin and resistin on dopamine, norepinephrine and serotonin release from hypothalamic neuronal endings (synaptosomes) in vitro. We have found that adiponectin does not modify either basal or depolarization-induced amine release, while resistin inhibits the stimulated release of dopamine and norepinephrine, leaving unaffected serotonin release. We can conclude that, similarly to leptin, but differently from adiponectin, the adipose tissue hormone resistin could affect the central mechanisms of feeding by inhibiting catecholamine release in the hypothalamus., (Copyright 2004 Elsevier B.V.)

Chromatin-derived acidic peptides (ACPs) have been shown to acutely modulate hypothalamic catecholamine release. To investigate whether this effect is mediated through membrane polysialylated neural-cell adhesion molecule (PSA-N-CAM), we pretreated rat hypothalamic synaptosomes with neuraminidase enzyme, which partially cleaves sialic acid residues from N-CAM, and perfused them with ACP-1 (Asp-Asp-Ser-Asp-Glu-Glu-Asn) or a more lipophilic derivative, ACP-2 ([Ala-Ile-Ser-Pro]-Asp-Asp-Ser-Asp-Glu-Glu-Asn). We have found that neuraminidase completely abolish the inhibitory effect of ACP-1 on dopamine release, while the inhibitory activity of ACP-1 on norepinephrine release is partially lost. On the other hand, ACP-2 inhibition of dopamine release is not modified by neuraminidase pretreatment.

The pH fluctuations have been often interpreted as an insufficient regulation or as a consequence of the onset of pathological events, such as ischemia, in which a significant decrease in pH levels occurs. Neurotransmitter release appears to be affected by pH drop significantly. In this study, we investigated the effect of an extracellular and an intracellular acidification on tritiated dopamine release ([3H]-DA release), from superfused rat hypothalamic synaptosomes. When compared to basal release, extracellular acidification, due to a reduction in the external pH of the nominally carbonic-free superfusion media, provoked a significant increase in [3H]-DA release that showed a sensitiveness to calcium omission. Intraterminal acidification, obtained blocking the Na(+)/H(+) exchanger by 5-(N-ethyl-N-isopropyl)-amiloride (EIPA) and 5-(N,N-dimethyl)-amiloride (DMA), induced a significant increase in [3H]-DA outflow which occurred in a calcium-dependent manner (80% inhibition in absence of calcium from superfusion media). To further promote an intraterminal acidification through a H(+) inner accumulation, the proton ionophore nigericin was used. At every dose employed (10 microM), this compound induced a significant increase in [3H]-DA outflow, compared to basal release. Nigericin-evoked [3H]-DA release showed a 50% decrease when calcium was omitted from superfusion media. When BAPTA-AM, a chelator of intracellular calcium, was added, nigericin-evoked [3H]-DA was completely abolished. These data indicate that [3H]-DA release can be induced by extracellular acidification due to a lowering of external pH and by an intraterminal acidification due to an internal proton accumulation. The mechanism that can trigger this exocytotic process appears to depend on calcium presence, and in particular, on an increased intraterminal calcium availability.

Ghrelin and amylin are gut-derived hormones that stimulate and inhibit food intake, respectively. Feeding is modulated by aminergic neurotransmitters in the hypothalamus. We have evaluated the effects of ghrelin and amylin on dopamine, norepinephrine and serotonin release from rat hypothalamic synaptosomes. We found that ghrelin did not modify dopamine or norepinephrine release, but inhibited serotonin release. On the other hand, amylin inhibited dopamine release, without affecting norepinephrine or serotonin. We conclude that the appetite-stimulating activity of ghrelin could be mediated by inhibited serotonin release, while the anorectic effects of amylin could involve inhibited release of dopamine in the hypothalamus.

We have studied the effects of cocaine- and amphetamine-regulated transcript (CART) peptide-(55-102), leptin, orexin-A and orexin-B on basal and depolarization (K(+) 15 mM)-induced serotonin (5-hydroxytryptamine, 5-HT) release from rat hypothalamic neuronal endings (synaptosomes) in vitro. We have found that leptin and CART peptide-(55-102) have no effect on 5-HT release, while orexin-A and orexin-B inhibit depolarization-stimulated serotonin release. We can conclude that leptin and CART peptide-(55-102), which play a physiological role as feeding inhibitors, do not acutely affect 5-HT release from hypothalamic synaptosomes; on the other hand, feeding induced by orexin-A and orexin-B could be partially explained by decreased 5-HT release.

We have studied the neuromodulatory effects of three synthetic peptides, structurally related to chromatin-derived acidic peptides (ACPs): ACP-1 (Asp-Asp-Ser-Asp-Glu-Glu-Asn), corresponding to the C-terminal fragment of the largest subunit of eukaryotic RNA polymerase II; a more lipophilic derivative, ACP-2 (Ala-Ile-Ser-Pro-Asp-Asp-Ser-Asp-Glu-Glu-Asn); and its phosphorylated form ACP-3 (Ala-Ile-Ser-Pro-Asp-Asp-Ser(P)-Asp-Glu-Glu-Asn). Rat hypothalamic synaptosomes, loaded with [(3)H]norepinephrine or [(3)H]dopamine, were perfused with the above peptides, both basally and during a depolarizing stimulus. We have found: ACP-1 inhibited both dopamine and norepinephrine release; ACP-2 inhibited dopamine release, without affecting norepinephrine release; ACP-3 was almost ineffective, except for a weak dopamine inhibiting effect only at a higher concentration.

Cocaine- and amphetamine-regulated transcript (CART) peptide-(55-102) and thyrotropin releasing hormone (TRH) play an anorectic role in the hypothalamus. Catecholamines are also involved in appetite control and we have previously found that leptin, an adipocyte-derived anorectic hormone, inhibits hypothalamic norepinephrine and dopamine release. We have studied the effect of CART peptide-(55-102) and TRH on basal and depolarization (K+ 15 mM)-induced norepinephrine and dopamine release from rat hypothalamic neuronal endings (synaptosomes) in vitro. We have found that basal catecholamine release was not modified; both CART peptide-(55-102) and TRH, the former with a higher sensitivity, dose-dependently inhibited depolarization-induced dopamine release, and did not affect the stimulated norepinephrine release. Considering the role played by dopamine in the central mechanisms of reward, these findings suggest that the inhibition of dopamine release could underlie the decreased appetitive behaviour induced by CART peptide-(55-102) and TRH.

Noradrenergic and dopaminergic afferents arising from the brain stem to the hypothalamus still play a poorly characterised role in food intake control. We have studied the effect of leptin, an adipocyte-derived hormone which has been implicated in the regulation of feeding behaviour, on [3H]norepinephrine and [3H]dopamine release from perfused hypothalamic neuronal endings (synaptosomes) in vitro. We have found that leptin (0.01-10 nM) does not modify basal, while it inhibits depolarization-induced norepinephrine and dopamine release. We can hypothesize that at least part of the anorectic activity of leptin in the hypothalamus is effected through an inhibition of noradrenergic and dopaminergic firing.

Leptin, an adipocyte-derived 16 kDa polypeptide hormone, has been found to regulate food intake and thermogenesis by modulating stimulatory and inhibitory pathways in the feeding circuitry of the hypothalamus, among which corticotropin releasing hormone (CRH). Nitric oxide (NO) and prostaglandins have been shown to be involved in both CRH neurosecretion and feeding regulation. We have investigated the role of NO, prostaglandin E2 and prostaglandin F2alpha as mediators of the hypothalamic effects of leptin and their possible involvement in leptin-stimulated CRH secretion. Using primary cultures of neonatal (5- to 6-day-old) rat hypothalamic cells, we confirmed that leptin (0.1-10 nM) stimulates CRH secretion. This effect was not blocked by L-N(G)-nitro-methyl-arginine (L-NAME, 100 microM), a NO-synthase competitive inhibitor; and leptin did not stimulate NO production. Cyclooxygenase inhibition by indomethacin (10 microM) did not modify leptin-induced CRH secretion, while leptin stimulated prostaglandin E2, and prostaglandin F2alpha secretion. In conclusion, leptin-induced hypothalamic CRH secretion is not modulated by NO-synthase- or cyclooxygenase-mediated mechanisms; leptin does not stimulate NO production, but it stimulates prostaglandin E2 and F2alpha production, which could add to the growing list of mediators of leptin signaling in the hypothalamus.

In previous experiments we have shown the role of nitric oxide (NO) in basal and interleukin-1 beta (IL-1 beta)-induced CRH and ACTH release in vitro. Now, we have studied the possible production of NO from hypothalamic cell cultures, particularly after IL-1 beta stimulation or L-NOArg inhibition, by high performance liquid chromatographic (HPLC) assay of L-citrulline production, adding further evidence for a role of NO in IL-1 beta activity in the hypothalamus.

NG-Nitro-L-arginine, an inhibitor of nitric oxide synthase, does not influence CRH basal release but is able to modify ACTH basal secretion and to block interleukin-1 beta-induced CRH and ACTH release from rat hypothalamic and anterior pituitary cell cultures in vitro. The data suggest a different involvement of NO at hypothalamic and pituitary level.