The gut–brain peptide neuromedin U is involved in the mammalian circadian oscillator system Keiko Nakahara, a,1 Reiko Hanada, b,1 Noboru Murakami, a, * Hitoshi Teranishi, b Hideko Ohgusu, b Nobuhiro Fukushima, b Maiko Moriyama, b Takanori Ida, a Kenji Kangawa, c and Masayasu Kojima b a Department of Veterinary Physiology, Faculty of Agriculture, Miyazaki University, Miyazaki 889-2192, Japan b Molecular Genetics, Institute of Life science, Kurume University, Kurume, Fukuoka 839-0861, Japan c Department of Biochemistry, National Cardiovascular Center Research Institute, Fujishirodai 5-7-1, Suita, Osaka 565-8565, Japan Received 18 March 2004 Abstract Immunohistochemical analysis revealed the presence of a gut–brain peptide, neuromedin U (NMU), in the suprachiasmatic nucleus (SCN), which is the site of the master circadian oscillator. The expression of NMU mRNA exhibited a circadian rhythm, with the peak expression in the SCN occurring at CT4–8 h. The two NMU-binding receptors (NMU-R1 and NMU-R2) were also expressed in the SCN, but their phase angles were different. Intracerebroventricular injection (ICV) of NMU induced the expression of Fos protein in the SCN cells and caused a phase-dependent phase shift of the circadian locomotor activity rhythm. The mag- nitude of the phase shift was dose dependent. This NMU-induced phase shift was of the nonphotic type. Quantitative reverse transcriptase-polymerase chain reaction (RT-PCR) analysis revealed increases in the expression in the SCN of immediate early genes, such as c-fos, NGFI-A, NGFI-B, and JunB. Furthermore, ICV injection of NMU increased the expression of Per1, but not Per2, in the SCN. These results indicate that NMU may play some important role in the circadian oscillator by exerting an autocrine or paracrine action in the SCN. Ó 2004 Elsevier Inc. All rights reserved. Keywords: Circadian rhythm; Fos; Neuromedin U; Per; Phase shift; Suprachiasmatic nucleus Neuromedin U (NMU), which was originally identi- fied in the porcine spinal cord, was so named because of its potent uterine-contraction-inducing activity [1]. NMU is a highly conserved gut–brain peptide present in a wide range of animals from mammals to amphibians, indicating that it plays an essential role in neuroendo- crine function [2,3]. NMU is distributed widely in the gastrointestinal tract, pituitary gland, and central ner- vous system [4–6]. The peripheral activities of NMU include smooth muscle contraction [1], blood pressure elevation [7], and modification of intestinal ion transport [8], whereas centrally, NMU suppresses feeding [9,10] and induces the release of stress-mediating molecules such as adrenocorticotropic hormone (ACTH) and corticosterone [11,12]. Two homologous orphan G-protein-coupled receptors have been identified as NMU receptors: NMU-R1 and NMU-R2 [9,10,13]. These two receptors are expressed in numerous tissues, although NMU-R1 is found primarily in the periphery whereas NMU-R2 is expressed prefer- entially in the central nervous system, and especially in the hypothalamic paraventricular nucleus (PVN), the wall of the third ventricle, and the CA1 region of the hippo- campus [9,13]. The widespread distribution of these two NMU receptors suggests additional functions of NMU in the central nervous system. Recently, we and other groups found that NMU exists in the hypothalamic SCN [9], indicating that NMU might be involved in the regulation of circadian rhythm, since it is well known that the SCN functions as a biological clock [14–16]. In the study presented here, * Corresponding author. Fax: +81-985-58-7265. E-mail address: a0d201u@cc.miyazaki-u.ac.jp (N. Murakami). 1 These authors contributed equally to this work. 0006-291X/$ - see front matter Ó 2004 Elsevier Inc. All rights reserved. doi:10.1016/j.bbrc.2004.04.014 Biochemical and Biophysical Research Communications 318 (2004) 156–161 BBRC www.elsevier.com/locate/ybbrc