Direct versus indirect actions of ghrelin on hypothalamic NPY neurons.
<h4>Objectives</h4>Assess direct versus indirect action(s) of ghrelin on hypothalamic NPY neurons.<h4>Materials and methods</h4>Electrophysiology was used to measure ion channel activity in NPY-GFP neurons in slice preparations. Ca2+ imaging was used to monitor ghrelin activa...
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2017-01-01
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| author | Hiroshi Hashiguchi Zhenyu Sheng Vanessa Routh Volodymyr Gerzanich J Marc Simard Joseph Bryan |
| author_facet | Hiroshi Hashiguchi Zhenyu Sheng Vanessa Routh Volodymyr Gerzanich J Marc Simard Joseph Bryan |
| author_sort | Hiroshi Hashiguchi |
| collection | DOAJ |
| description | <h4>Objectives</h4>Assess direct versus indirect action(s) of ghrelin on hypothalamic NPY neurons.<h4>Materials and methods</h4>Electrophysiology was used to measure ion channel activity in NPY-GFP neurons in slice preparations. Ca2+ imaging was used to monitor ghrelin activation of isolated NPY GFP-labeled neurons. Immunohistochemistry was used to localize Trpm4, SUR1 and Kir6.2 in the hypothalamus.<h4>Results</h4>Acylated ghrelin depolarized the membrane potential (MP) of NPY-GFP neurons in brain slices. Depolarization resulted from a decreased input resistance (IR) in ~70% of neurons (15/22) or an increased IR in the remainder (7/22), consistent with the opening or closing of ion channels, respectively. Although tetrodotoxin (TTX) blockade of presynaptic action potentials reduced ghrelin-induced changes in MP and IR, ghrelin still significantly depolarized the MP and decreased IR in TTX-treated neurons, suggesting that ghrelin directly opens cation channel(s) in NPY neurons. In isolated NPY-GFP neurons, ghrelin produced a sustained rise of [Ca2+]c, with an EC50 ~110 pM. Pharmacologic studies confirmed that the direct action of ghrelin was through occupation of the growth hormone secretagogue receptor, GHS-R, and demonstrated the importance of the adenylate cyclase/cAMP/protein kinase A (PKA) and phospholipase C/inositol triphosphate (PLC/IP3) pathways as activators of 5' AMP-activated protein kinase (AMPK). Activation of isolated neurons was not affected by CNQX or TTX, but reducing [Na+]o suppressed activation, suggesting a role for Na+-permeable cation channels. SUR1 and two channel partners, Kir6.2 and Trpm4, were identified immunologically in NPY-GFP neurons in situ. The actions of SUR1 and Trpm4 modulators were informative: like ghrelin, diazoxide, a SUR1 agonist, elevated [Ca2+]c and glibenclamide, a SUR1 antagonist, partially suppressed ghrelin action, while 9-phenanthrol and flufenamic acid, selective Trpm4 antagonists, blocked ghrelin actions on isolated neurons. Ghrelin activation was unaffected by nifedipine and ω-conotoxin, inhibitors of L- and N-type Ca2+ channels, respectively, while Ni2+, mibefradil, and TTA-P2 completely or partially inhibited ghrelin action, implicating T-type Ca2+ channels. Activation was also sensitive to a spider toxin, SNX-482, at concentrations selective for R-type Ca2+ channels. Nanomolar concentrations of GABA markedly inhibited ghrelin-activation of isolated NPY-GFP neurons, consistent with chronic suppression of ghrelin action in vivo.<h4>Conclusions</h4>NPY neurons express all the molecular machinery needed to respond directly to ghrelin. Consistent with recent studies, ghrelin stimulates presynaptic inputs that activate NPY-GFP neurons in situ. Ghrelin can also directly activate a depolarizing conductance. Results with isolated NPY-GFP neurons suggest the ghrelin-activated, depolarizing current is a Na+ conductance with the pharmacologic properties of SUR1/Trpm4 non-selective cation channels. In the isolated neuron model, the opening of SUR1/Trpm4 channels activates T- and SNX482-sensitive R-type voltage dependent Ca2+ channels, which could contribute to NPY neuronal activity in situ. |
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| institution | DOAJ |
| issn | 1932-6203 |
| language | English |
| publishDate | 2017-01-01 |
| publisher | Public Library of Science (PLoS) |
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| series | PLoS ONE |
| spelling | doaj-art-09f172a9a5674a6fae11b4fa6d55bbc22025-08-20T02:46:04ZengPublic Library of Science (PLoS)PLoS ONE1932-62032017-01-01129e018426110.1371/journal.pone.0184261Direct versus indirect actions of ghrelin on hypothalamic NPY neurons.Hiroshi HashiguchiZhenyu ShengVanessa RouthVolodymyr GerzanichJ Marc SimardJoseph Bryan<h4>Objectives</h4>Assess direct versus indirect action(s) of ghrelin on hypothalamic NPY neurons.<h4>Materials and methods</h4>Electrophysiology was used to measure ion channel activity in NPY-GFP neurons in slice preparations. Ca2+ imaging was used to monitor ghrelin activation of isolated NPY GFP-labeled neurons. Immunohistochemistry was used to localize Trpm4, SUR1 and Kir6.2 in the hypothalamus.<h4>Results</h4>Acylated ghrelin depolarized the membrane potential (MP) of NPY-GFP neurons in brain slices. Depolarization resulted from a decreased input resistance (IR) in ~70% of neurons (15/22) or an increased IR in the remainder (7/22), consistent with the opening or closing of ion channels, respectively. Although tetrodotoxin (TTX) blockade of presynaptic action potentials reduced ghrelin-induced changes in MP and IR, ghrelin still significantly depolarized the MP and decreased IR in TTX-treated neurons, suggesting that ghrelin directly opens cation channel(s) in NPY neurons. In isolated NPY-GFP neurons, ghrelin produced a sustained rise of [Ca2+]c, with an EC50 ~110 pM. Pharmacologic studies confirmed that the direct action of ghrelin was through occupation of the growth hormone secretagogue receptor, GHS-R, and demonstrated the importance of the adenylate cyclase/cAMP/protein kinase A (PKA) and phospholipase C/inositol triphosphate (PLC/IP3) pathways as activators of 5' AMP-activated protein kinase (AMPK). Activation of isolated neurons was not affected by CNQX or TTX, but reducing [Na+]o suppressed activation, suggesting a role for Na+-permeable cation channels. SUR1 and two channel partners, Kir6.2 and Trpm4, were identified immunologically in NPY-GFP neurons in situ. The actions of SUR1 and Trpm4 modulators were informative: like ghrelin, diazoxide, a SUR1 agonist, elevated [Ca2+]c and glibenclamide, a SUR1 antagonist, partially suppressed ghrelin action, while 9-phenanthrol and flufenamic acid, selective Trpm4 antagonists, blocked ghrelin actions on isolated neurons. Ghrelin activation was unaffected by nifedipine and ω-conotoxin, inhibitors of L- and N-type Ca2+ channels, respectively, while Ni2+, mibefradil, and TTA-P2 completely or partially inhibited ghrelin action, implicating T-type Ca2+ channels. Activation was also sensitive to a spider toxin, SNX-482, at concentrations selective for R-type Ca2+ channels. Nanomolar concentrations of GABA markedly inhibited ghrelin-activation of isolated NPY-GFP neurons, consistent with chronic suppression of ghrelin action in vivo.<h4>Conclusions</h4>NPY neurons express all the molecular machinery needed to respond directly to ghrelin. Consistent with recent studies, ghrelin stimulates presynaptic inputs that activate NPY-GFP neurons in situ. Ghrelin can also directly activate a depolarizing conductance. Results with isolated NPY-GFP neurons suggest the ghrelin-activated, depolarizing current is a Na+ conductance with the pharmacologic properties of SUR1/Trpm4 non-selective cation channels. In the isolated neuron model, the opening of SUR1/Trpm4 channels activates T- and SNX482-sensitive R-type voltage dependent Ca2+ channels, which could contribute to NPY neuronal activity in situ.https://journals.plos.org/plosone/article/file?id=10.1371/journal.pone.0184261&type=printable |
| spellingShingle | Hiroshi Hashiguchi Zhenyu Sheng Vanessa Routh Volodymyr Gerzanich J Marc Simard Joseph Bryan Direct versus indirect actions of ghrelin on hypothalamic NPY neurons. PLoS ONE |
| title | Direct versus indirect actions of ghrelin on hypothalamic NPY neurons. |
| title_full | Direct versus indirect actions of ghrelin on hypothalamic NPY neurons. |
| title_fullStr | Direct versus indirect actions of ghrelin on hypothalamic NPY neurons. |
| title_full_unstemmed | Direct versus indirect actions of ghrelin on hypothalamic NPY neurons. |
| title_short | Direct versus indirect actions of ghrelin on hypothalamic NPY neurons. |
| title_sort | direct versus indirect actions of ghrelin on hypothalamic npy neurons |
| url | https://journals.plos.org/plosone/article/file?id=10.1371/journal.pone.0184261&type=printable |
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