Nitric oxide is a central component in neuropeptide regulation of appetite

doi:10.1016/j.peptides.2010.12.015

Peptides

Volume 32, Issue 4, April 2011, Pages 776-780

https://doi.org/10.1016/j.peptides.2010.12.015 Get rights and content

Abstract

In recent years, there have been a large number of neuropeptides discovered that regulate food intake. Many of these peptides regulate food intake by increasing or decreasing nitric oxide (NO). In the current study, we compared the effect of the food modulators ghrelin, NPY and CCK in NOS KO mice. Satiated homozygous and heterozygous NOS KO mice and their wild type controls were administered ghrelin ICV. Food intake was measured for 2 h post injection. Ghrelin did not increase food intake in the homozygous NOS KO mice compared to vehicle treated NOS KO mice, whereas food intake was increased in the wild type controls compared to vehicle treated wild type controls. NPY was administered ICV and food intake measured for 2 h. Homozygous NOS KO mice showed no increase in food intake after NPY administration, whereas the wild type controls did. In our final study, we administered CCK intraperitoneally to homozygous and heterozygous NOS KO mice and their wild type controls after overnight food deprivation. Food intake was measured for 1 h after injection. CCK inhibited food intake in wild type mice after overnight food deprivation, however, CCK failed to inhibit food intake in the NOS KO mice. The heterozygous mice showed partial food inhibition after the CCK. The current results add further support to the theory that NO is a central mediator in food intake.

Research highlights

► This study compares the effect of the food modulators ghrelin, NPY and CCK in NOS KO mice. ► Ghrelin did not increase food intake in the homozygous NOS KO mice while wild type controls did experience increased food intake. ► Nitric oxide did show to be a central mediator in food intake in this study.

Introduction

Studies of peptides that are involved in the pathway of energy intake and expenditure have suggested that nitric oxide (NO) is a common regulator in the function of all these peptides. A number of studies have shown that NO is involved in the regulation of food intake in a variety of species including rats, chicks, broilers, Leghorns, marsupial Sminthopsis crassicaudata, mice, and dogs [21], [22], [24], [27], [28], [31], [36], [38]. The complex pathway involved in energy intake and expenditure includes agouti-related protein (AgRP), neuropeptide Y (NPY), proopiomelanocortin (PMOC) and cocaine- and amphetamine-related transcript (CART) in the arcuate neucleus and the paraventricular nucleus, melanocortin 4 receptor (MC4R) in the paraventricular and ventromedial hypothalamus (PVH/VMH) and orexin and melanin-concentrating hormone (MCH) in the lateral hypothalamus [14]. In addition, multiple other areas in the brain, e.g., cortico-limbic system and brainstem are involved in regulating food intake. Substances from the periphery that regulate the process in these regions include leptin, insulin, peptide in YY (PYY), glucagon-like peptide-1 (GLP-1), cholecystokinin (CCK) and ghrelin. Previous studies have shown nitric oxide regulates the function of many of these peptides including of leptin, NPY, orexin and ghrelin [12], [17], [25]. Peptides that enhance feeding increase NO, whereas peptides that decrease food intake decrease NO. Nitric oxide has been shown in mice to increase with advancing age [26].

NO is synthesized within cells by nitric oxide synthase (NOS) from arginine with the aid of molecular oxygen and nicotinamide adenine dinucleotide phosphate (NADPH). In neurons, NO is produced by neuronal nitric oxide synthase (nNOS), representing one of the three NOS isoforms expressed in most tissues [29], [35] Studies have linked nNOS to many physiological processes, including cardiac function, immune function, reproductive function, CNS neuronal function, muscular function and feeding [1], [2], [3], [9], [33].

Food intake enhanced by food deprivation or the administration of ghrelin, NPY or orexin-A can each be blocked by co-administration of Nω-nitro-l-arginine methyl ester (l-NAME) a nitric oxide synthase (NOS) inhibitor [12], [16], [17]. Leptin which decreases food intake has been found to decrease NO levels in the hypothalamus. Both short-term and chronic injections of leptin have been found to decrease nitric oxide synthase and, in nNOS knockout mice, the leptin affect on feeding was greatly reduced [5]. Chronic blockage of NO synthesis reduces adiposity and improves insulin resistance [34].

To further examine whether NO is involved in the regulation of peptides which alter food intake, we examined the ability of NPY and ghrelin to increase feeding and CCK to decrease feeding in a neuronal NOS knockout mouse (NOS KO) compared to the wild type controls.

Section snippets

Mice

The subjects for the experiments were 12 week male and female mice homozygous, heterozygous NOS KO mice and wild type controls (C57BL/J6) obtained from our breeding colony which was started from breeding pairs obtained from Jackson Laboratories (BarHarbor, ME). Phenotypically they are similar to the mice described by Haung et al. [18]. Sentinels from the colony are tested regularly to ensure the colony is virus and pathogen free. Food (5001 Rodent Diet, PMI Nutrition International, LLC,

The effect of overnight food deprivation on food intake in NOS KO mice

We examined the effect of overnight food deprivation on food intake during the first hour after refeeding. The two-way ANOVA for food intake produced a significant effect for strain F(2,27) 25.21, P < 0.0008 and time F(1,27) = 32.31, P < 0.0001, but not for interaction F(2,27) = 0.89, P NS. Bonferroni post test indicated that the NOS KO mice ate significantly less than the wild type controls at both 30 and 60 min post food induction. There was no difference between wild type controls and the

Discussion

Nitric oxide has been shown to be involved in the regulation of feeding and the effect of feeding peptides in the CNS. Here, we examined the response of NOS KO mice to CCK, NPY and ghrelin, three peptides known to be involved in the regulation of food intake. We found that none of the three compounds altered food intake in the NOS KO mice. NPY and ghrelin failed to enhance food intake in NOS KO mice yet they both significantly enhanced food intake in wild type controls. CCK failed to inhibit

Author contributions

Drs. Morley, Farr and Banks designed the study and wrote the manuscript; Dr. Farr supervised experiments; Dr. Hileman checked genetic type; Rebecca Sale assisted in food intake assessment.

Conflicts of Interest

All authors state that they have no conflicts of interest regarding this study.

Funding

Funding was provided by the Veterans Administration.

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Nitric oxide is a central component in neuropeptide regulation of appetite

Abstract

Research highlights

Introduction

Section snippets

Mice

The effect of overnight food deprivation on food intake in NOS KO mice

Discussion

Author contributions

Conflicts of Interest

Funding

Pharm Biochem Behav

Pharm Biochem Behav

Pharm Biochem Behav

Peptides

Peptides

Cell

Brain Res

Peptides

Peptides

Cell

Peptides

Comp Biochem Physiol A Mol Integr Physiol

Nitric Oxide

Life Sci

Eur J Pharmacol

Life Sci

Neurosci Lett

Neurobiol Aging

Neurobiol Aging