Orexins (hypocretins) directly interact with neuropeptide Y, POMC and glucose-responsive neurons to regulate Ca2+ signaling in a reciprocal manner to leptin: orexigenic neuronal pathways in the mediobasal hypothalamus

Authors

  • Shinji Muroya,

    1. Department of Physiology, Division of Integrative Physiology, Jichi Medical School, Minamikawachi, Kawachi, Tochigi 329-0498, Japan
    2. Department of Psychiatry, Kagoshima University Graduate School of Medical and Dental Sciences, Kagoshima 890-8520, Japan
    Search for more papers by this author
  • Hisayuki Funahashi,

    1. Department of Anatomy, Showa University School of Medicine, Tokyo 142-8555, Japan
    Search for more papers by this author
  • Akihiro Yamanaka,

    1. Department of Pharmacology, Institute of Basic Medical Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8575, Japan
    Search for more papers by this author
  • Daisuke Kohno,

    1. Department of Physiology, Division of Integrative Physiology, Jichi Medical School, Minamikawachi, Kawachi, Tochigi 329-0498, Japan
    Search for more papers by this author
  • Kazuhide Uramura,

    1. Department of Physiology, Division of Integrative Physiology, Jichi Medical School, Minamikawachi, Kawachi, Tochigi 329-0498, Japan
    2. Department of Psychiatry, Kagoshima University Graduate School of Medical and Dental Sciences, Kagoshima 890-8520, Japan
    Search for more papers by this author
  • Tadahiro Nambu,

    1. Department of Pharmacology, Institute of Basic Medical Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8575, Japan
    Search for more papers by this author
  • Megumi Shibahara,

    1. Department of Pharmacology, Institute of Basic Medical Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8575, Japan
    Search for more papers by this author
  • Motoki Kuramochi,

    1. Department of Physiology, Division of Integrative Physiology, Jichi Medical School, Minamikawachi, Kawachi, Tochigi 329-0498, Japan
    Search for more papers by this author
  • Morikuni Takigawa,

    1. Department of Psychiatry, Kagoshima University Graduate School of Medical and Dental Sciences, Kagoshima 890-8520, Japan
    Search for more papers by this author
  • Masashi Yanagisawa,

    1. Howard Hughes Medical Institute, Department of Molecular Genetics, University of Texas South-western Medical Center at Dallas, 75235-9050, USA
    Search for more papers by this author
  • Takeshi Sakurai,

    1. Department of Pharmacology, Institute of Basic Medical Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8575, Japan
    Search for more papers by this author
  • Seiji Shioda,

    1. Department of Anatomy, Showa University School of Medicine, Tokyo 142-8555, Japan
    Search for more papers by this author
  • Toshihiko Yada

    1. Department of Physiology, Division of Integrative Physiology, Jichi Medical School, Minamikawachi, Kawachi, Tochigi 329-0498, Japan
    Search for more papers by this author

: Dr T. Yada, as above.
E-mail: tyada@jichi.ac.jp

Abstract

Orexin-A and -B (hypocretin-1 and -2) have been implicated in the stimulation of feeding. Here we show the effector neurons and signaling mechanisms for the orexigenic action of orexins in rats. Immunohistochemical methods showed that orexin axon terminals contact with neuropeptide Y (NPY)- and proopiomelanocortin (POMC)-positive neurons in the arcuate nucleus (ARC) of the rats. Microinjection of orexins into the ARC markedly increased food intake. Orexins increased cytosolic Ca2+ concentration ([Ca2+]i) in the isolated neurons from the ARC, which were subsequently shown to be immunoreactive for NPY. The increases in [Ca2+]i were inhibited by blockers of phospholipase C (PLC), protein kinase C (PKC) and Ca2+ uptake into endoplasmic reticulum. The stimulation of food intake and increases in [Ca2+]i in NPY neurons were greater with orexin-A than with orexin-B, indicative of involvement of the orexin-1 receptor (OX1R). In contrast, orexin-A and -B equipotently attenuated [Ca2+]i oscillations and decreased [Ca2+]i levels in POMC-containing neurons. These effects were counteracted by pertussis toxin, suggesting involvement of the orexin-2 receptor and Gi/Go subtypes of GTP-binding proteins. Orexins also decreased [Ca2+]i levels in glucose-responsive neurons in the ventromedial hypothalamus (VMH), a satiety center. Leptin exerted opposite effects on these three classes of neurons. These results demonstrate that orexins directly regulate NPY, POMC and glucose-responsive neurons in the ARC and VMH, in a manner reciprocal to leptin. Orexin-A evokes Ca2+ signaling in NPY neurons via OX1R–PLC–PKC and IP3 pathways. These neural pathways and intracellular signaling mechanisms may play key roles in the orexigenic action of orexins.

Ancillary