title: Orexins (hypocretins) directly interact with neuropeptide Y, POMC and glucose-responsive neurons to regulate Ca 2+ signaling in a reciprocal manner to leptin: orexigenic neuronal pathways in the mediobasal hypothalamus.
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 Ca(2+) concentration ([Ca(2+)](i)) in the isolated neurons from the ARC, which were subsequently shown to be immunoreactive for NPY. The increases in [Ca(2+)](i) were inhibited by blockers of phospholipase C (PLC), protein kinase C (PKC) and Ca(2+) uptake into endoplasmic reticulum. The stimulation of food intake and increases in [Ca(2+)](i) in NPY neurons were greater with orexin-A than with orexin-B, indicative of involvement of the orexin-1 receptor (OX(1)R). In contrast, orexin-A and -B equipotently attenuated [Ca(2+)](i) oscillations and decreased [Ca(2+)](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 [Ca(2+)](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 Ca(2+) signaling in NPY neurons via OX(1)R-PLC-PKC and IP(3) pathways. These neural pathways and intracellular signaling mechanisms may play key roles in the orexigenic action of orexins.
authors.affiliation: Department of Physiology, Division of Integrative Physiology, Jichi Medical School, Minamikawachi, Kawachi, Tochigi 329-0498, Japan.
authors.forename: Shinji
authors.initials: S
authors.lastname: Muroya
authors.forename: Hisayuki
authors.initials: H
authors.lastname: Funahashi
authors.forename: Akihiro
authors.initials: A
authors.lastname: Yamanaka
authors.forename: Daisuke
authors.initials: D
authors.lastname: Kohno
authors.forename: Kazuhide
authors.initials: K
authors.lastname: Uramura
authors.forename: Tadahiro
authors.initials: T
authors.lastname: Nambu
authors.forename: Megumi
authors.initials: M
authors.lastname: Shibahara
authors.forename: Motoki
authors.initials: M
authors.lastname: Kuramochi
authors.forename: Morikuni
authors.initials: M
authors.lastname: Takigawa
authors.forename: Masashi
authors.initials: M
authors.lastname: Yanagisawa
authors.forename: Takeshi
authors.initials: T
authors.lastname: Sakurai
authors.forename: Seiji
authors.initials: S
authors.lastname: Shioda
authors.forename: Toshihiko
authors.initials: T
authors.lastname: Yada
mesh_terms: D000818:Animals; D020013:Calcium Signaling / Q000187:drug effects*; D002352:Carrier Proteins / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions; D004435:Eating / Q000187:drug effects; D004791:Enzyme Inhibitors; D016257:Fura-2 / Q000378:metabolism; D005947:Glucose / Q000378:metabolism*; D007031:Hypothalamus / Q000166:cytology*; D007150:Immunohistochemistry; D047908:Intracellular Signaling Peptides and Proteins; D020738:Leptin / Q000494:pharmacology*; D008959:Models, Neurological; D009474:Neurons / Q000145:classification / Q000187:drug effects / Q000378:metabolism; D009478:Neuropeptide Y / Q000378:metabolism*; D009479:Neuropeptides / Q000494:pharmacology*; D000068797:Orexins; D037342:Pertussis Toxin / Q000494:pharmacology; D011333:Pro-Opiomelanocortin / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D005680:gamma-Aminobutyric Acid / Q000494:pharmacology
chemical_list: D002352:Carrier Proteins; D004791:Enzyme Inhibitors; D047908:Intracellular Signaling Peptides and Proteins; D020738:Leptin; D009478:Neuropeptide Y; D009479:Neuropeptides; D000068797:Orexins; D005680:gamma-Aminobutyric Acid; D011333:Pro-Opiomelanocortin; D037342:Pertussis Toxin; D005947:Glucose; D016257:Fura-2