title: Ghrelin directly interacts with neuropeptide-Y-containing neurons in the rat arcuate nucleus: Ca2+ signaling via protein kinase A and N-type channel-dependent mechanisms and cross-talk with leptin and orexin.
abstract: Ghrelin is a newly discovered peptide that is released from the stomach and from neurons in the hypothalamic arcuate nucleus (ARC) and potently stimulates growth hormone release and food intake. Neuropeptide-Y (NPY) neurons in the ARC play an important role in the stimulation of food intake. The present study aimed to determine whether ghrelin directly activates NPY neurons and, if so, to explore its signaling mechanisms. Whether the neurons that respond to ghrelin could be regulated by orexin and leptin was also examined. We isolated single neurons from the ARC of rats and measured the cytosolic Ca(2+) concentration ([Ca(2+)](i)) with fura-2 fluorescence imaging. Ghrelin (10(-12) to 10(-8) mol/l) concentration-dependently increased [Ca(2+)](i), which occurred in 35% of the ARC neurons. Approximately 80% of these ghrelin-responsive neurons were proved to be NPY-containing by immunocytochemical staining, and 58% of them were glucose-sensitive neurons as judged by their responses to lowering glucose concentrations. The [Ca(2+)](i) responses to ghrelin were markedly attenuated by inhibitors of protein kinase A (PKA) but not protein kinase C and by a blocker of N-type but not L-type Ca(2+) channels. Orexin increased [Ca(2+)](i) and leptin attenuated ghrelin-induced [Ca(2+)](i) increases in the majority (80%) of ghrelin-responsive NPY neurons. These results demonstrate that ghrelin directly interacts with NPY neurons in the ARC to induce Ca(2+) signaling via PKA and N-type Ca(2+) channel-dependent mechanisms. The integration of stimulatory effects of ghrelin and orexin and inhibitory effect of leptin may play an important role in the regulation of the activity of NPY neurons and thereby feeding.
authors.affiliation: Department of Physiology, Jichi Medical School, School of Medicine, Minamikawachi, Tochigi, Japan.
authors.forename: Daisuke
authors.initials: D
authors.lastname: Kohno
authors.forename: Hong-Zhi
authors.initials: HZ
authors.lastname: Gao
authors.forename: Shinji
authors.initials: S
authors.lastname: Muroya
authors.forename: Sakae
authors.initials: S
authors.lastname: Kikuyama
authors.forename: Toshihiko
authors.initials: T
authors.lastname: Yada
mesh_terms: D000818:Animals; D001111:Arcuate Nucleus of Hypothalamus / Q000187:drug effects / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism*; D020864:Calcium Channels, N-Type / Q000502:physiology; D002352:Carrier Proteins / Q000494:pharmacology; D017868:Cyclic AMP-Dependent Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D054439:Ghrelin; D005947:Glucose / Q000494:pharmacology; D047908:Intracellular Signaling Peptides and Proteins; D020738:Leptin / Q000494:pharmacology; D008297:Male; D009474:Neurons / Q000737:chemistry / Q000187:drug effects / Q000378:metabolism*; D009478:Neuropeptide Y / Q000032:analysis*; D009479:Neuropeptides / Q000494:pharmacology; D000068797:Orexins; D036361:Peptide Hormones / Q000494:pharmacology*; D011493:Protein Kinase C / Q000037:antagonists & inhibitors; D051381:Rats; D017207:Rats, Sprague-Dawley; D020239:Receptor Cross-Talk; D015398:Signal Transduction
chemical_list: D020864:Calcium Channels, N-Type; D002352:Carrier Proteins; D004791:Enzyme Inhibitors; D054439:Ghrelin; D047908:Intracellular Signaling Peptides and Proteins; D020738:Leptin; D009478:Neuropeptide Y; D009479:Neuropeptides; D000068797:Orexins; D036361:Peptide Hormones; D017868:Cyclic AMP-Dependent Protein Kinases; D011493:Protein Kinase C; D005947:Glucose; D002118:Calcium