Lipopolysaccharide (LPS)- and muramyl dipeptide (MDP)-induced anorexia during refeeding following acute fasting: characterization of brain cytokine and neuropeptide systems mRNAs

doi:10.1016/S0006-8993(98)00280-7

Brain Research

Volume 795, Issues 1–2, 8 June 1998, Pages 77-86

https://doi.org/10.1016/S0006-8993(98)00280-7 Get rights and content

Abstract

We investigated the effectiveness of lipopolysaccharide (LPS) and muramyl dipeptide (MDP) administered into the brain to induce anorexia in acutely fasted Wistar rats allowed to refeed. We also assayed for changes in mRNA levels of IL-1 system components, TNF-α, TGF-β1, glycoprotein 130 (gp 130), leptin receptor (OB-R), pro-opiomelanocortin (POMC), neuropeptide Y (NPY), glucocorticoid receptor (GR), and CRF receptor (CRF-R) in selected brain regions. The data show that LPS and MDP induced anorexia differentially during refeeding. LPS-induced anorexia was of a stronger magnitude and duration than that of MDP. RNase protection assays showed that LPS and MDP significantly increased the expression of IL-1β, IL-1 receptor type I, and TNF-α mRNAs in the cerebellum, hippocampus, and hypothalamus; LPS was more potent in all cases. MDP treatment, on the other hand, induced a stronger increase in hypothalamic levels of IL-1 receptor antagonist (IL-1Ra) and TGF-β1 mRNAs relative to LPS. In addition, competitive RT–PCR analysis showed that LPS induced an eleven-fold increase in IL-1α mRNA in the hypothalamus relative to vehicle. These findings suggest that LPS and MDP mediate anorexia through different cytokine mechanisms. A stronger up-regulation of anti-inflammatory cytokines (IL-1Ra and TGF-β1) mRNA expression by MDP may be involved in the weaker MDP-induced anorexia relative to LPS. No significant changes were observed in the peptide components examined except for an up-regulation in cerebellar gp 130 mRNA and down-regulation of hypothalamic GR mRNA expression in response to LPS or MDP. This study shows that LPS and MDP induce anorexia in fasted rats allowed to refeed, and suggests an important role for endogenous cytokine–cytokine interactions.

Introduction

Bacterial products such as lipopolysaccharide (LPS, from Gram negative bacteria) and muramyl dipeptide (MDP, from Gram positive bacteria) have been shown to reduce food intake 8, 16and to increase cytokine production 9, 17, 30. On the other hand, acute fasting induces hyperphagia when animals are allowed to refeed [6]. To characterize LPS- and MDP-induced anorexia during a condition of enhanced feeding drive (i.e., following food deprivation), we investigated the feeding response and mRNA response profiles of various cytokines to LPS and MDP administration into the brain of fasted rats allowed to refeed ad libitum. We also assayed mRNA levels of various components of peptide systems that have been shown to modulate feeding behavior 18, 19, 33. It is unknown whether LPS or MDP induce anorexia in fasted rats allowed to refeed by modulating cytokines and/or feeding-regulatory peptides. Hence, this approach allows the study of cytokine–cytokine and cytokine–peptide interactions that may underlie anorexia induced by LPS or MDP.

Specifically, animals were fasted for 39.5 h, then challenged with the intracerebroventricular (i.c.v.) administration of LPS or MDP, followed by 5 h of ad libitum feeding. We then determined brain (cerebellar, hippocampal, hypothalamic) mRNA levels of interleukin-1 (IL-1) system components: the ligands IL-1α and IL-1β, two pro-inflammatory cytokines 7, 20; IL-1 receptor type I (IL-1RI), the signaling receptor [28]; IL-1 receptor accessory proteins (IL-1R AcP I and II, membrane bound and soluble forms, respectively), with the membrane bound form conferring responsiveness 11, 21, 36; and IL-1 receptor antagonist (IL-1Ra), an endogenous competitive inhibitor of IL-1 action [1]. We also determined mRNA levels for tumor necrosis factor-α (TNF-α), a pro-inflammatory cytokine [20], and transforming growth factor-β1 (TGF-β1), a potential anti-inflammatory cytokine 4, 20, 31. Messenger RNA levels of the following components were also assayed: pro-opiomelanocortin (POMC), the precursor of β-endorphin and MSH; neuropeptide Y (NPY), a potent feeding inducer peptide 5, 18, 27which can interact antagonistically with IL-1β[29]; glycoprotein 130 (gp 130), a common signal transducer among receptors for members of the IL-6 subfamily [23]that is homologous to the leptin receptor 2, 32; leptin receptor (OB-R); glucocorticoid receptor (GR); and corticotropin releasing factor receptor (CRF-R).

Our previous work found that levels of IL-1α mRNA were below the sensitivity of RNase protection assay. Hence, we used the more sensitive competitive RT–PCR analysis to determine IL-1α mRNA profile in response to LPS treatment. RNase protection assays were used for all other components.

The results show that LPS and MDP inhibit feeding in fasted rats allowed to refeed, and differentially modulate the mRNA expression of various cytokines and peptide system components.

Section snippets

Subjects and maintenance

Male Wistar (VAF) rats weighing between 250 and 275 g at the beginning of the experiments were used. Rats were randomly assigned into groups and placed in individual cages. They were maintained ad libitum on powdered rat food (Labdiet, PMI Feeds, St. Louis, MO) and tap water as previously described [26]. Room temperature was maintained at 21±2°C, and artificial illumination was from 0600 to 1800 h (12:12 h light:dark cycle). All rats were handled daily. After several days of adaptation to the

Food intake

The treatments differentially affected cumulative food intake over the 5-h refeeding period (F(2,24)=7, p<0.004). Cumulative food intake data collected at 1-h and 3-h post-infusion show that both LPS (n=9) and MDP (n=9) significantly (p<0.05) decreased food intake relative to the vehicle (n=9). Values at 1-h were: 6.2±0.3 g for LPS, 7.4±1.0 g for MDP, and 9.0±0.6 g for vehicle; and at 3-h: 6.3±0.3 g for LPS; 8.1±0.8 g for MDP; and 9.9±0.6 g for vehicle. Pairwise comparisons also showed

Discussion

This study shows that i.c.v. administered LPS and MDP induce anorexia of different magnitudes and durations in fasted rats allowed to refeed ad libitum. Treatments also differentially affected cytokine and peptide system components mRNA levels in the brain regions examined. Specifically, LPS and MDP administration significantly increased IL-1β, IL-1RI, and TNF-α mRNA levels in the cerebellum, hippocampus, and hypothalamus. MDP also significantly increased hippocampal IL-1R AcP I and

Acknowledgements

We thank Dr. Ronald P. Hart (Department of Biological Sciences, Rutgers University) for providing the rat IL-1β, IL-1Ra, IL-1RI and IL-1R AcP cDNAs, Dr. Karl Decker (Biochemisches Institut der Albert Ludwigs Universität) for providing the rat TNF-α cDNA, Dr. David Danielpour (National Cancer Institute) for providing the rat TGF-β1 cDNA, Dr. Gerald M. Fuller (Department of Cell Biology and Anatomy, University of Alabama at Birmingham) for providing the rat glycoprotein 130 cDNA, Dr. Charles I.

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Research reportLipopolysaccharide (LPS)- and muramyl dipeptide (MDP)-induced anorexia during refeeding following acute fasting: characterization of brain cytokine and neuropeptide systems mRNAs

Abstract

Introduction

Section snippets

Subjects and maintenance

Food intake

Discussion

Acknowledgements

J. Neuroimmunol.

Peptides

Blood

Mol. Brain Res.

Brain Res. Bull.

J. Biol. Chem.

Mol. Cell. Endocrinol.

Biochem. Biophys. Res. Commun.

Biochem. Biophys. Res. Commun.

Nutrition

Mol. Brain Res.

Neurosci. Biobehav. Rev.

Brain Res. Bull.

J. Neuroimmunol.

Pharmacol. Biochem. Behav.

Physiol. Behav.

Mol. Brain Res.

Peptides

Research report
Lipopolysaccharide (LPS)- and muramyl dipeptide (MDP)-induced anorexia during refeeding following acute fasting: characterization of brain cytokine and neuropeptide systems mRNAs