Evidence that PGE2 in the dorsal and median raphe nuclei is involved in LPS-induced anorexia in rats Brigitte S. Kopf, Wolfgang Langhans, Nori Geary, Brian Hrupka 1 , Lori Asarian ⁎ ,1 Physiology and Behaviour Laboratory, Institute of Food, Nutrition and Health, ETH-Zürich, Switzerland abstract article info Article history: Received 6 December 2010 Received in revised form 8 April 2011 Accepted 13 April 2011 Available online 17 April 2011 Keywords: Prostaglandin Serotonin Eating Infection Anorexia is an element of the acute-phase immune response. Its mechanisms remain poorly understood. Activation of inducible cyclooxygenase-2 (COX-2) in blood–brain-barrier endothelial cells and subsequent release of prostaglandins (e.g., prostaglandin E2, PGE2) may be involved. Therefore, we sought to relate the effects of prostaglandins on the anorexia following gram-negative bacterial lipopolysaccharide treatment (LPS) to neural activity in the dorsal and median raphe nuclei (DRN and MnR) in rats. COX-2 antagonist (NS- 398, 10 mg/kg; IP) administration prior to LPS (100 μg/kg; IP) prevented anorexia and reduced c-Fos expression the DRN, MnR, nucleus tractus solitarii and several related forebrain areas. These data indicate that COX-2-mediated prostaglandin synthesis is necessary for LPS anorexia and much of the initial LPS-induced neural activation. Injection of NS-398 into the DRN and MnR (1 ng/site) attenuated LPS-induced anorexia to nearly the same extent as IP NS-398, suggesting that prostaglandin signaling in these areas is necessary for LPS anorexia. Because the DRN and MnR are sources of major serotonergic projections to the forebrain, these data suggest that serotonergic neurons originating in the midbrain raphe play an important role in acute-phase response anorexia. © 2011 Elsevier Inc. All rights reserved. 1. Introduction Bacterial infections and other immune challenges are met by a complex immune reaction called the acute-phase response (APR). Anorexia is a prominent element of the APR, and investigation of the anorectic effect of the bacterial toxin lipopolysaccharide (LPS) is widely used to investigate the APR's peripheral and central mechanisms. LPS is a component of the outer lipid layer of gram-negative bacteria and is released into the circulation during bacterial reproduction or lysis. LPS binding to toll-like receptor-4 in macrophages and other immune cells causes the release of pro-inflammatory signaling molecules, such as cytokines and prostaglandins (Takeda and Akira, 2005), which in turn initiate immune–neuro-endocrine cascades that ultimately lead to the APR (reviewed in Asarian and Langhans, 2010). A signaling cascade that appears crucial to brain-mediated elements of the APR involves induction of cyclo-oxygenases (e.g., COX-2) and prostaglandin H synthase, which catalyze the synthesis of prostaglandin E2 (PGE2) and other prostaglandins (Goppelt-Struebe, 1995). For example, COX-2 mRNA and protein are markedly induced in rat brain perivascular microglia and endothelial cells after LPS administration (Cao et al., 1997; Elmquist et al., 1997; Schiltz and Sawchenko, 2002; Yamagata et al., 2001). Tests of selective inhibitors of COX-1, which is not inducible, and COX-2 indicate that only COX-2 is crucial for LPS anorexia in both rats and mice (Johnson et al., 2002; Lugarini et al., 2002). That is, pretreatment of rats with a COX-1 inhibitor did not attenuate LPS anorexia, whereas pretreatment with the COX-2 inhibitor N-[2-(Cyclohexyloxy)-4-nitrophenyl] methanesulfonamide (NS-398) did (Lugarini et al., 2002). Similarly, LPS anorexia was reversed in mice with genetic deletions of COX-2, but not of COX-1 (Swiergiel and Dunn, 2001). How PGE2 acts in the brain to elicit LPS-anorexia is still unknown. One possibility is that it acts on serotonin neurons. This is suggested by the facts that serotonin antagonists reduce LPS anorexia (Hrupka and Langhans, 2001; von Meyenburg et al., 2003a) and that one subtype (EP3) of prostaglandin receptors is abundantly expressed in midbrain serotonergic neurons (Nakamura et al., 2000). Here we (1) further tested the hypothesis that brain PGE2 mediates the anorexia produced by intraperitoneal (IP) injections of LPS in rats using IP injections of the potent and specific COX-2 antagonist NS-398; (2) Pharmacology, Biochemistry and Behavior 99 (2011) 437–443 Abbreviations: 8-OH-DPAT, 8-hydroxy-N,N-dipropyl-2-aminotetralin; A1, A1 area of the ventrolateral medulla; APR, acute-phase response; Arc, arcuate nucleus of the hypothalamus; CeA, central nucleus of the amygdala; COX, cyclooxygenase; CRH, corticotropin-releasing hormone; DRN, dorsal raphe nucleus; EP3, a prostaglandin receptor subtype; ICV, intracerebroventricular; IP, intraperitoneal; LPS, bacterial lipopolysaccharide; MnR, median raphe nucleus; NS-398, N-[2-(Cyclohexyloxy)-4- nitrophenyl] methanesulfonamide; NTS, nucleus tractus solitarii; PB, phosphate buffer; PGE2, prostaglandin E2; mPGES, microsomal prostaglandin E synthase; PVN, para- ventricular nucleus of the hypothalamus; RMg, raphe magnus nucleus; RPa, raphe pallidus nucleus. ⁎ Corresponding author at: Institute of Veterinary Physiology, University of Zurich, Winterthurerstrasse 260, Zurich, 8057, Switzerland. Tel.: + 41 44 635 8836; fax: + 41 44 635 8932. E-mail address: lasarian@vetphys.uzh.ch (L. Asarian). 1 These two authors share the senior authorship of this work. 0091-3057/$ – see front matter © 2011 Elsevier Inc. All rights reserved. doi:10.1016/j.pbb.2011.04.006 Contents lists available at ScienceDirect Pharmacology, Biochemistry and Behavior journal homepage: www.elsevier.com/locate/pharmbiochembeh