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Velázquez-Marrero C, Custer EE, Marrero H, Ortiz-Miranda S, Lemos JR. Voltage-induced Ca 2+ release by ryanodine receptors causes neuropeptide secretion from nerve terminals. J Neuroendocrinol 2020; 32:e12840. [PMID: 32227430 DOI: 10.1111/jne.12840] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/14/2019] [Revised: 02/21/2020] [Accepted: 02/24/2020] [Indexed: 11/28/2022]
Abstract
Depolarisation-secretion coupling is assumed to be dependent only on extracellular calcium ([Ca2+ ]o ). Ryanodine receptor (RyR)-sensitive stores in hypothalamic neurohypophysial system (HNS) terminals produce sparks of intracellular calcium ([Ca2+ ]i ) that are voltage-dependent. We hypothesised that voltage-elicited increases in intraterminal calcium are crucial for neuropeptide secretion from presynaptic terminals, whether from influx through voltage-gated calcium channels and/or from such voltage-sensitive ryanodine-mediated calcium stores. Increases in [Ca2+ ]i upon depolarisation in the presence of voltage-gated calcium channel blockers, or in the absence of [Ca2+ ]o , still give rise to neuropeptide secretion from HNS terminals. Even in 0 [Ca2+ ]o , there was nonetheless an increase in capacitance suggesting exocytosis upon depolarisation. This was blocked by antagonist concentrations of ryanodine, as was peptide secretion elicited by high K+ in 0 [Ca2+ ]o . Furthermore, such depolarisations lead to increases in [Ca2+ ]i . Pre-incubation with BAPTA-AM resulted in > 50% inhibition of peptide secretion elicited by high K+ in 0 [Ca2+ ]o . Nifedipine but not nicardipine inhibited both the high K+ response for neuropeptide secretion and intraterminal calcium, suggesting the involvement of CaV1.1 type channels as sensors in voltage-induced calcium release. Importantly, RyR antagonists also modulate neuropeptide release under normal physiological conditions. In conclusion, our results indicate that depolarisation-induced neuropeptide secretion is present in the absence of external calcium, and calcium release from ryanodine-sensitive internal stores is a significant physiological contributor to neuropeptide secretion from HNS terminals.
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Affiliation(s)
| | - Edward E Custer
- Departments of Microbiology and Physiological Systems, Neurobiology & Program in Neuroscience, University of Massachusetts Medical School, Worcester, MA, USA
| | - Héctor Marrero
- Institute of Neurobiology, University of Puerto Rico, San Juan, PR, USA
| | - Sonia Ortiz-Miranda
- Departments of Microbiology and Physiological Systems, Neurobiology & Program in Neuroscience, University of Massachusetts Medical School, Worcester, MA, USA
| | - José R Lemos
- Departments of Microbiology and Physiological Systems, Neurobiology & Program in Neuroscience, University of Massachusetts Medical School, Worcester, MA, USA
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2
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Lemos JR, Custer EE, Ortiz-Miranda S. Purinergic receptor types in the hypothalamic-neurohypophysial system. J Neuroendocrinol 2018; 30:10.1111/jne.12588. [PMID: 29512852 PMCID: PMC6128781 DOI: 10.1111/jne.12588] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/01/2017] [Accepted: 02/28/2018] [Indexed: 11/27/2022]
Abstract
Many different types of purinergic receptors are present in the Hypothalamic-Neurohypophysial System (HNS), which synthesizes and releases vasopressin and oxytocin. The specific location of purinergic receptor subtypes has important functional repercussions for neuronal activity and synaptic output. Yet, until the advent of receptor KOs, this had been hindered by the low selectivity of the available pharmacological tools. The HNS offers an excellent opportunity to differentiate the functional properties of these purinergic receptors in cell bodies vs. terminals of the same physiological system. P2X2, P2X3, P2X4 and P2X7 receptors are present in vasopressin terminals while oxytocin terminals exclusively express the P2X7 subtype. The latter is not functional in the cell bodies of the HNS. These purinergic receptor subtypes are permeable to sodium vs. calcium in varying amounts and this could play an important role in the release of vasopressin vs. oxytocin during bursting activity. Endogenous ATP and its metabolite, adenosine, have autocrine and paracrine modulatory effects on the release of these neuropeptides during physiological stimulation. Finally, we hypothesize that during such action potential bursts, ATP potentiates the release of vasopressin but not of oxytocin, and that adenosine, via A1 receptors, inhibits the release of both neuropeptides. This article is protected by copyright. All rights reserved.
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Affiliation(s)
| | | | - Sonia Ortiz-Miranda
- Neurobiology Depts. & Prog. Neurosci., Univ. Mass. Med. School, Worcester, MA 01605
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3
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Maícas-Royo J, Leng G, MacGregor DJ. A Predictive, Quantitative Model of Spiking Activity and Stimulus-Secretion Coupling in Oxytocin Neurons. Endocrinology 2018; 159:1433-1452. [PMID: 29342276 PMCID: PMC5934744 DOI: 10.1210/en.2017-03068] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/26/2017] [Accepted: 01/08/2018] [Indexed: 12/19/2022]
Abstract
Oxytocin neurons of the rat hypothalamus project to the posterior pituitary, where they secrete their products into the bloodstream. The pattern and quantity of that release depends on the afferent inputs to the neurons, on their intrinsic membrane properties, and on nonlinear interactions between spiking activity and exocytosis: A given number of spikes will trigger more secretion when they arrive close together. Here we present a quantitative computational model of oxytocin neurons that can replicate the results of a wide variety of published experiments. The spiking model mimics electrophysiological data of oxytocin cells responding to cholecystokinin (CCK), a peptide produced in the gut after food intake. The secretion model matches results from in vitro experiments on stimulus-secretion coupling in the posterior pituitary. We mimic the plasma clearance of oxytocin with a two-compartment model, replicating the dynamics observed experimentally after infusion and injection of oxytocin. Combining these models allows us to infer, from measurements of oxytocin in plasma, the spiking activity of the oxytocin neurons that produced that secretion. We have tested these inferences with experimental data on oxytocin secretion and spiking activity in response to intravenous injections of CCK. We show how intrinsic mechanisms of the oxytocin neurons determine this relationship: In particular, we show that the presence of an afterhyperpolarization (AHP) in oxytocin neurons dramatically reduces the variability of their spiking activity and even more markedly reduces the variability of oxytocin secretion. The AHP thus acts as a filter, protecting the final product of oxytocin cells from noisy fluctuations.
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Affiliation(s)
- Jorge Maícas-Royo
- Centre for Discovery Brain Sciences, University of Edinburgh, Edinburgh, United Kingdom
| | - Gareth Leng
- Centre for Discovery Brain Sciences, University of Edinburgh, Edinburgh, United Kingdom
| | - Duncan J MacGregor
- Centre for Discovery Brain Sciences, University of Edinburgh, Edinburgh, United Kingdom
- Correspondence: Duncan J. MacGregor, PhD, Centre for Discovery Brain Sciences, University of Edinburgh, Hugh Robson Building, George Square, Edinburgh EH8 9XD, United Kingdom. E-mail:
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4
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Wu L, Meng J, Shen Q, Zhang Y, Pan S, Chen Z, Zhu LQ, Lu Y, Huang Y, Zhang G. Caffeine inhibits hypothalamic A 1R to excite oxytocin neuron and ameliorate dietary obesity in mice. Nat Commun 2017; 8:15904. [PMID: 28654087 PMCID: PMC5490268 DOI: 10.1038/ncomms15904] [Citation(s) in RCA: 52] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2017] [Accepted: 05/10/2017] [Indexed: 12/14/2022] Open
Abstract
Caffeine, an antagonist of the adenosine receptor A1R, is used as a dietary supplement to reduce body weight, although the underlying mechanism is unclear. Here, we report that adenosine level in the cerebrospinal fluid, and hypothalamic expression of A1R, are increased in the diet-induced obesity (DIO) mouse. We find that mice with overexpression of A1R in the neurons of paraventricular nucleus (PVN) of the hypothalamus are hyperphagic, have glucose intolerance and high body weight. Central or peripheral administration of caffeine reduces the body weight of DIO mice by the suppression of appetite and increasing of energy expenditure. We also show that caffeine excites oxytocin expressing neurons, and blockade of the action of oxytocin significantly attenuates the effect of caffeine on energy balance. These data suggest that caffeine inhibits A1Rs expressed on PVN oxytocin neurons to negatively regulate energy balance in DIO mice.
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Affiliation(s)
- Liufeng Wu
- Key Laboratory of Environmental Health, Ministry of Education, Department of Toxicology, School of Public Health, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei 430030, China
| | - Jia Meng
- Key Laboratory of Environmental Health, Ministry of Education, Department of Toxicology, School of Public Health, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei 430030, China
| | - Qing Shen
- Key Laboratory of Environmental Health, Ministry of Education, Department of Toxicology, School of Public Health, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei 430030, China
| | - Yi Zhang
- Key Laboratory of Environmental Health, Ministry of Education, Department of Toxicology, School of Public Health, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei 430030, China
| | - Susu Pan
- Key Laboratory of Environmental Health, Ministry of Education, Department of Toxicology, School of Public Health, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei 430030, China
| | - Zhuo Chen
- Key Laboratory of Environmental Health, Ministry of Education, Department of Toxicology, School of Public Health, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei 430030, China
| | - Ling-Qiang Zhu
- Institute for Brain Research, Collaborative Innovation Center for Brain Science, Huazhong University of Science and Technology, Wuhan, Hubei 430030, China.,Department of Pathophysiology, School of Basic Medicine, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei 430030, China
| | - Youming Lu
- Institute for Brain Research, Collaborative Innovation Center for Brain Science, Huazhong University of Science and Technology, Wuhan, Hubei 430030, China.,Department of Physiology, School of Basic Medicine, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei 430030, China
| | - Yuan Huang
- Key Laboratory of Environmental Health, Ministry of Education, Department of Toxicology, School of Public Health, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei 430030, China
| | - Guo Zhang
- Key Laboratory of Environmental Health, Ministry of Education, Department of Toxicology, School of Public Health, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei 430030, China.,Institute for Brain Research, Collaborative Innovation Center for Brain Science, Huazhong University of Science and Technology, Wuhan, Hubei 430030, China
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Abstract
Adenosine-5'-triphosphate is released by neuroendocrine, endocrine, and other cell types and acts as an extracellular agonist for ligand-gated P2X cationic channels and G protein-coupled P2Y receptors in numerous organs and tissues, including the endocrine system. The breakdown of ATP by ectonucleotidases not only terminates its extracellular messenger functions, but also provides a pathway for the generation of two additional agonists: adenosine 5'-diphosphate, acting via some P2Y receptors, and adenosine, a native agonist for G protein-coupled adenosine receptors, also expressed in the endocrine system. This article provides a review of purinergic signaling pathways in the hypothalamic magnocellular neurosecretory cells and neurohypophysis, hypothalamic parvocellular neuroendocrine system, adenohypophysis, and effector glands organized in five axes: hypothalamic-pituitary-gonadal, hypothalamic-pituitary-thyroid, hypothalamic-pituitary-adrenal, hypothalamic-pituitary-growth hormone, and hypothalamic-pituitary-prolactin. We attempted to summarize current knowledge of purinergic receptor subtypes expressed in the endocrine system, including their roles in intracellular signaling, hormone secretion, and other cell functions. We also briefly review the release mechanism for adenosine-5'-triphosphate by neuroendocrine, endocrine and surrounding cells, the enzymes involved in adenosine-5'-triphosphate hydrolysis to adenosine-5'-diphosphate and adenosine, and the relevance of this pathway for sequential activation of receptors and termination of signaling.
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6
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μ-Opioid inhibition of Ca2+ currents and secretion in isolated terminals of the neurohypophysis occurs via ryanodine-sensitive Ca2+ stores. J Neurosci 2014; 34:3733-42. [PMID: 24599471 DOI: 10.1523/jneurosci.2505-13.2014] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
μ-Opioid agonists have no effect on calcium currents (I(Ca)) in neurohypophysial terminals when recorded using the classic whole-cell patch-clamp configuration. However, μ-opioid receptor (MOR)-mediated inhibition of I(Ca) is reliably demonstrated using the perforated-patch configuration. This suggests that the MOR-signaling pathway is sensitive to intraterminal dialysis and is therefore mediated by a readily diffusible second messenger. Using the perforated patch-clamp technique and ratio-calcium-imaging methods, we describe a diffusible second messenger pathway stimulated by the MOR that inhibits voltage-gated calcium channels in isolated terminals from the rat neurohypophysis (NH). Our results show a rise in basal intracellular calcium ([Ca(2+)]i) in response to application of [D-Ala(2)-N-Me-Phe(4),Gly5-ol]-Enkephalin (DAMGO), a MOR agonist, that is blocked by D-Phe-Cys-Tyr-D-Trp-Orn-Thr-Pen-Thr-NH2 (CTOP), a MOR antagonist. Buffering DAMGO-induced changes in [Ca(2+)]i with BAPTA-AM completely blocked the inhibition of both I(Ca) and high-K(+)-induced rises in [Ca(2+)]i due to MOR activation, but had no effect on κ-opioid receptor (KOR)-mediated inhibition. Given the presence of ryanodine-sensitive stores in isolated terminals, we tested 8-bromo-cyclic adenosine diphosphate ribose (8Br-cADPr), a competitive inhibitor of cyclic ADP-ribose (cADPr) signaling that partially relieves DAMGO inhibition of I(Ca) and completely relieves MOR-mediated inhibition of high-K(+)-induced and DAMGO-induced rises in [Ca(2+)]i. Furthermore, antagonist concentrations of ryanodine completely blocked MOR-induced increases in [Ca(2+)]i and inhibition of I(Ca) and high-K(+)-induced rises in [Ca(2+)]i while not affecting KOR-mediated inhibition. Antagonist concentrations of ryanodine also blocked MOR-mediated inhibition of electrically-evoked increases in capacitance. These results strongly suggest that a key diffusible second messenger mediating the MOR-signaling pathway in NH terminals is [Ca(2+)]i released by cADPr from ryanodine-sensitive stores.
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Zemkova H, Kucka M, Li S, Gonzalez-Iglesias AE, Tomic M, Stojilkovic SS. Characterization of purinergic P2X4 receptor channels expressed in anterior pituitary cells. Am J Physiol Endocrinol Metab 2010; 298:E644-51. [PMID: 20009029 PMCID: PMC2838522 DOI: 10.1152/ajpendo.00558.2009] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Anterior pituitary cells express cation-conducting P2X receptor channels (P2XRs), but their molecular identity, electrophysiological properties, cell-specific expression pattern, and physiological roles have been only partially characterized. In this study, we show by quantitative RT-PCR that mRNA transcripts for the P2X(4) subunit are the most abundant in rat anterior pituitary tissue and confirm the P2X(4)R protein expression by Western blot analysis. Single-cell patch-clamp recordings show that extracellular ATP induced an inward depolarizing current in a majority of thyrotropin-releasing hormone-responsive pituitary cells, which resembled the current profile generated by recombinant P2X(4)R. The channels were activated and desensitized in a dose-dependent manner and deactivated rapidly. Activation of these channels led to stimulation of electrical activity and promotion of voltage-gated and voltage-insensitive Ca(2+) influx. In the presence of ivermectin, a specific allosteric modulator of P2X(4)Rs, there was an approximately fourfold increase in the maximum amplitude of the ATP-induced inward current, accompanied by an increase in the sensitivity of receptors for ATP, slowed deactivation of receptors, and enhanced ATP-induced prolactin release. These results indicate that thyrotropin-releasing hormone-responsive cells, including lactotrophs, express homomeric and/or heteromeric P2X(4)Rs, which facilitate Ca(2+) influx and hormone secretion.
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Affiliation(s)
- Hana Zemkova
- Section on Cellular Signaling, Program in Developmental Neuroscience, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892-4510, USA
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8
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Stojilkovic SS, He ML, Koshimizu TA, Balik A, Zemkova H. Signaling by purinergic receptors and channels in the pituitary gland. Mol Cell Endocrinol 2010; 314:184-91. [PMID: 19467293 PMCID: PMC2815212 DOI: 10.1016/j.mce.2009.05.008] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/13/2009] [Revised: 05/14/2009] [Accepted: 05/17/2009] [Indexed: 10/20/2022]
Abstract
Adenosine 5'-triphosphate is frequently released by cells and acts as an agonist for G protein-coupled P2Y receptors and ligand-gated P2X cationic channels in numerous tissues. The breakdown of ATP by ectonucleotidases not only terminates its extracellular messenger functions, but also provides a pathway for the generation of two additional agonists: adenosine 5'-diphosphate, acting via some P2Y receptors, and adenosine, a native agonist for G protein-coupled adenosine receptors. In the pituitary gland, adenosine 5'-triphosphate is released from the endings of magnocellular hypothalamic neurons and by anterior pituitary cells through pathway(s) that are still not well characterized. This gland also expresses several members of each family of purinergic receptors. P2X and adenosine receptors are co-expressed in the somata and nerve terminals of vasopressin-releasing neurons as well as in some secretory pituitary cells. P2X receptors stimulate electrical activity and modulate InsP(3)-dependent calcium release from intracellular stores, whereas adenosine receptors terminate electrical activity. Calcium-mobilizing P2Y receptors are expressed in pituicytes, folliculo-stellate cells and some secretory cells of the anterior pituitary.
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Affiliation(s)
- Stanko S Stojilkovic
- Section on Cellular Signaling, Program in Developmental Neuroscience, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892-4510, USA.
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9
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Marrero HG, Lemos JR. Ionic conditions modulate stimulus-induced capacitance changes in isolated neurohypophysial terminals of the rat. J Physiol 2009; 588:287-300. [PMID: 19933755 DOI: 10.1113/jphysiol.2009.180778] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Peptidergic nerve terminals of the neurohypophysis (NH) secrete both oxytocin and vasopressin upon stimulation with peptide-specific bursts of action potentials from magnocellular neurons. These bursts vary in both frequency and action potential duration and also induce in situ ionic changes both inside and outside the terminals in the NH. These temporary effects include the increase of external potassium and decrease of external calcium, as well as the increase in internal sodium and chloride concentrations. In order to determine any mechanism of action that these ionic changes might have on secretion, stimulus-induced capacitance recordings were performed on isolated terminals of the NH using action potential burst patterns of varying frequency and action potential width. The results indicate that in NH terminals: (1) increased internal chloride concentration improves the efficiency of action potential-induced capacitance changes, (2) increasing external potassium increases stimulus-induced capacitance changes, (3) decreasing external calcium decreases the capacitance induced by low frequency broadened action potentials, while no capacitance change is observed with high frequency un-broadened action potentials, and (4) increasing internal sodium increases the capacitance change induced by low frequency bursts of broadened action potentials, more than for high frequency bursts of narrow action potentials. These results are consistent with previous models of stimulus-induced secretion, where optimal secretory efficacy is determined by particular characteristics of action potentials within a burst. Our results suggest that positive effects of increased internal sodium and external potassium during a burst may serve as a compensatory mechanism for secretion, counterbalancing the negative effects of reduced external calcium. In this view, high frequency un-broadened action potentials (initial burst phase) would condition the terminals by increasing internal sodium for optimal secretion by the physiological later phase of broadened action potentials. Thus, ionic changes occurring during a burst may help to make such stimulation more efficient at inducing secretion. Furthermore, these effects are thought to occur within the initial few seconds of incoming burst activity at both oxytocin and vasopressin types of NH nerve terminals.
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Affiliation(s)
- Héctor G Marrero
- Physiology Department & Program in Neuroscience, University of Massachusetts, Medical School, Worcester, MA 01655, USA.
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10
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Stojilkovic SS. Purinergic regulation of hypothalamopituitary functions. Trends Endocrinol Metab 2009; 20:460-8. [PMID: 19800813 PMCID: PMC2766266 DOI: 10.1016/j.tem.2009.05.005] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/04/2009] [Revised: 05/11/2009] [Accepted: 05/12/2009] [Indexed: 10/20/2022]
Abstract
The hypothalamus controls the release of hormones by the pituitary and is involved in control of food and water intake, sexual behavior, reproduction and daily cycles in physiological state and behavior, temperature regulation and emotional responses. Adenosine-5'-triphosphate (ATP) and its metabolic products contribute to these functions, acting as agonists for adenosine and P2Y receptors and two-transmembrane domain P2X receptor channels. This review summarizes the recent findings on purinergic receptor expression and their roles in signaling and cellular function in secretory and supporting cells of the hypothalamopituitary system. ATP secretion by these tissues, the enzymes involved in ATP hydrolysis, and the relevance of this pathway for sequential activation of receptors and termination of signaling are also discussed.
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Affiliation(s)
- Stanko S Stojilkovic
- Section on Cellular Signaling, Program in Developmental Neuroscience, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892-4510, USA.
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11
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Effects of Ketamine on the Balance of Ions Ca2+, Mg2+, Cu2+ and Zn2+ in the Ischemia-reperfusion Affected Spinal Cord Tissues in Rabbits. Neurochem Res 2009; 34:2192-6. [DOI: 10.1007/s11064-009-0019-4] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 06/02/2009] [Indexed: 12/15/2022]
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12
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Kiss DS, Zsarnovszky A, Horvath K, Gyorffy A, Bartha T, Hazai D, Sotonyi P, Somogyi V, Frenyo LV, Diano S. Ecto-nucleoside triphosphate diphosphohydrolase 3 in the ventral and lateral hypothalamic area of female rats: morphological characterization and functional implications. Reprod Biol Endocrinol 2009; 7:31. [PMID: 19383175 PMCID: PMC2676295 DOI: 10.1186/1477-7827-7-31] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/25/2009] [Accepted: 04/22/2009] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Based on its distribution in the brain, ecto-nucleoside triphosphate diphosphohydrolase 3 (NTPDase3) may play a role in the hypothalamic regulation of homeostatic systems, including feeding, sleep-wake behavior and reproduction. To further characterize the morphological attributes of NTPDase3-immunoreactive (IR) hypothalamic structures in the rat brain, here we investigated: 1.) The cellular and subcellular localization of NTPDase3; 2.) The effects of 17beta-estradiol on the expression level of hypothalamic NTPDase3; and 3.) The effects of NTPDase inhibition in hypothalamic synaptosomal preparations. METHODS Combined light- and electron microscopic analyses were carried out to characterize the cellular and subcellular localization of NTPDase3-immunoreactivity. The effects of estrogen on hypothalamic NTPDase3 expression was studied by western blot technique. Finally, the effects of NTPDase inhibition on mitochondrial respiration were investigated using a Clark-type oxygen electrode. RESULTS Combined light- and electron microscopic analysis of immunostained hypothalamic slices revealed that NTPDase3-IR is linked to ribosomes and mitochondria, is predominantly present in excitatory axon terminals and in distinct segments of the perikaryal plasma membrane. Immunohistochemical labeling of NTPDase3 and glutamic acid decarboxylase (GAD) indicated that gamma-amino-butyric-acid- (GABA) ergic hypothalamic neurons do not express NTPDase3, further suggesting that in the hypothalamus, NTPDase3 is predominantly present in excitatory neurons. We also investigated whether estrogen influences the expression level of NTPDase3 in the ventrobasal and lateral hypothalamus. A single subcutaneous injection of estrogen differentially increased NTPDase3 expression in the medial and lateral parts of the hypothalamus, indicating that this enzyme likely plays region-specific roles in estrogen-dependent hypothalamic regulatory mechanisms. Determination of mitochondrial respiration rates with and without the inhibition of NTPDases confirmed the presence of NTPDases, including NTPDase3 in neuronal mitochondria and showed that blockade of mitochondrial NTPDase functions decreases state 3 mitochondrial respiration rate and total mitochondrial respiratory capacity. CONCLUSION Altogether, these results suggest the possibility that NTPDases, among them NTPDase3, may play an estrogen-dependent modulatory role in the regulation of intracellular availability of ATP needed for excitatory neuronal functions including neurotransmission.
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Affiliation(s)
- David S Kiss
- Department of Physiology & Biochemistry, Szent Istvan University Faculty of Veterinary Science, Budapest, Hungary
| | - Attila Zsarnovszky
- Department of Physiology & Biochemistry, Szent Istvan University Faculty of Veterinary Science, Budapest, Hungary
- Department of Obstetrics, Gynecology & Reproductive Sciences, Yale University School of Medicine, New Haven, CT 06510, USA
| | - Krisztina Horvath
- Department of Physiology & Biochemistry, Szent Istvan University Faculty of Veterinary Science, Budapest, Hungary
| | - Andrea Gyorffy
- Department of Physiology & Biochemistry, Szent Istvan University Faculty of Veterinary Science, Budapest, Hungary
| | - Tibor Bartha
- Department of Physiology & Biochemistry, Szent Istvan University Faculty of Veterinary Science, Budapest, Hungary
| | - Diana Hazai
- Department of Anatomy & Histology, Szent Istvan University Faculty of Veterinary Science, Budapest, Hungary
| | - Peter Sotonyi
- Department of Anatomy & Histology, Szent Istvan University Faculty of Veterinary Science, Budapest, Hungary
| | - Virag Somogyi
- Department of Physiology & Biochemistry, Szent Istvan University Faculty of Veterinary Science, Budapest, Hungary
| | - Laszlo V Frenyo
- Department of Physiology & Biochemistry, Szent Istvan University Faculty of Veterinary Science, Budapest, Hungary
| | - Sabrina Diano
- Department of Obstetrics, Gynecology & Reproductive Sciences, Yale University School of Medicine, New Haven, CT 06510, USA
- Department of Neurobiology, Yale University School of Medicine, New Haven, CT 06510, USA
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13
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Knott TK, Marrero HG, Custer EE, Lemos JR. Endogenous ATP potentiates only vasopressin secretion from neurohypophysial terminals. J Cell Physiol 2008; 217:155-61. [PMID: 18481265 DOI: 10.1002/jcp.21485] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Exogenous ATP induces inward currents and causes the release of arginine-vasopressin (AVP) from isolated neurohypophysial terminals (NHT); both effects are inhibited by the P2X2 and P2X3 antagonists, suramin and PPADS. Here we examined the role of endogenous ATP in the neurohypophysis. Stimulation of NHT caused the release of both AVP and ATP. ATP induced a potentiation in the stimulated release of AVP, but not of oxytocin (OT), which was blocked by the presence of suramin. In loose-patch clamp recordings, from intact neurohypophyses, suramin or PPADS produces an inhibition of action potential currents in a static bath, that can be mimicked by a hyperpolarization of the resting membrane potential (RMP). Correspondingly, in a static versus perfused bath there is a depolarization of the RMP of NHT, which was reduced by either suramin or PPADS. We measured an accumulation of ATP (3.7 +/- 0.7 microM) released from NHT in a static bath. Applications of either suramin or PPADS to a static bath decreased burst-stimulated capacitance increases in NHT. Finally, only vasopressin release from electrically stimulated intact neurohypophyses was reduced in the presence of Suramin or PPADS. These data suggest that there was sufficient accumulation of ATP released from the neurohypophysis during stimulations to depolarize its nerve terminals. This would occur via the opening of P2X2 and P2X3 receptors, inducing an influx of Ca2+. The subsequent elevation in [Ca2+](i) would further increase the stimulated release of only vasopressin from NHT terminals. Such purinergic feedback mechanisms could be physiologically important at most CNS synapses.
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Affiliation(s)
- Thomas K Knott
- Department of Physiology & Program in Neuroscience, University of Massachusetts Medical School, 55 Lake Avenue North, Worcester, Massachusetts 01655, USA
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Giannaccini G, Betti L, Palego L, Fabbrini L, Schmid L, Castagna M, Giusti L, Mascia G, Lucacchini A. Species Comparison of Adenosine Receptor Subtypes in Brain and Testis. Neurochem Res 2007; 33:852-60. [DOI: 10.1007/s11064-007-9525-4] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2007] [Accepted: 10/01/2007] [Indexed: 11/28/2022]
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