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Farnham MMJ, Tallapragada VJ, O'Connor ET, Nedoboy PE, Dempsey B, Mohammed S, Fong AY, Lung MSY, Derakhshan F, Wilson RJA, Pilowsky PM. PACAP-PAC1 Receptor Activation Is Necessary for the Sympathetic Response to Acute Intermittent Hypoxia. Front Neurosci 2019; 13:881. [PMID: 31496933 PMCID: PMC6712064 DOI: 10.3389/fnins.2019.00881] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2019] [Accepted: 08/05/2019] [Indexed: 01/29/2023] Open
Abstract
Repetitive hypoxia is a key feature of obstructive sleep apnoea (OSA), a condition characterized by intermittent airways obstruction. Patients with OSA present with persistent increases in sympathetic activity and commonly develop hypertension. The objectives of this study were to determine if the persistent increases in sympathetic nerve activity, known to be induced by acute intermittent hypoxia (AIH), are mediated through activation of the pituitary adenylate cyclase activating polypeptide (PACAP) signaling system. Here, we show that the excitatory neuropeptide PACAP, acting in the spinal cord, is important for generating the sympathetic response seen following AIH. Using PACAP receptor knockout mice, and pharmacological agents in Sprague Dawley rats, we measured blood pressure, heart rate, pH, PaCO2, and splanchnic sympathetic nerve activity, under anaesthesia, to demonstrate that the sympathetic response to AIH is mediated via the PAC1 receptor, in a cAMP-dependent manner. We also report that both intermittent microinjection of glutamate into the rostroventrolateral medulla (RVLM) and intermittent infusion of a sub-threshold dose of PACAP into the subarachnoid space can mimic the sympathetic response to AIH. All the sympathetic responses are independent of blood pressure, pH or PaCO2 changes. Our results show that in AIH, PACAP signaling in the spinal cord helps drive persistent increases in sympathetic nerve activity. This mechanism may be a precursor to the development of hypertension in conditions of chronic intermittent hypoxia, such as OSA.
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Affiliation(s)
- Melissa M J Farnham
- The Heart Research Institute, Newtown, NSW, Australia.,Faculty of Medicine, Macquarie University, North Ryde, NSW, Australia.,Department of Physiology, Faculty of Medicine, University of Sydney, Sydney, NSW, Australia
| | | | - Edward T O'Connor
- Department of Physiology and Pharmacology, Hotchkiss Brain Institute and Alberta Children's Hospital Research Institute, University of Calgary, Calgary, AB, Canada
| | - Polina E Nedoboy
- The Heart Research Institute, Newtown, NSW, Australia.,Department of Physiology, Faculty of Medicine, University of Sydney, Sydney, NSW, Australia
| | - Bowen Dempsey
- Faculty of Medicine, Macquarie University, North Ryde, NSW, Australia
| | - Suja Mohammed
- The Heart Research Institute, Newtown, NSW, Australia.,Faculty of Medicine, Macquarie University, North Ryde, NSW, Australia.,Department of Physiology, Faculty of Medicine, University of Sydney, Sydney, NSW, Australia
| | - Angelina Y Fong
- Faculty of Medicine, Macquarie University, North Ryde, NSW, Australia.,Department of Physiology, Faculty of Medicine, Dentistry and Health Sciences, University of Melbourne, Melbourne, VIC, Australia
| | - Mandy S Y Lung
- Faculty of Medicine, Macquarie University, North Ryde, NSW, Australia
| | - Fatemeh Derakhshan
- Department of Physiology and Pharmacology, Hotchkiss Brain Institute and Alberta Children's Hospital Research Institute, University of Calgary, Calgary, AB, Canada
| | - Richard J A Wilson
- Department of Physiology and Pharmacology, Hotchkiss Brain Institute and Alberta Children's Hospital Research Institute, University of Calgary, Calgary, AB, Canada
| | - Paul M Pilowsky
- The Heart Research Institute, Newtown, NSW, Australia.,Department of Physiology, Faculty of Medicine, University of Sydney, Sydney, NSW, Australia
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2
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Barrett KT, Hasan SU, Scantlebury MH, Wilson RJA. Impaired neonatal cardiorespiratory responses to hypoxia in mice lacking PAC1 or VPAC2 receptors. Am J Physiol Regul Integr Comp Physiol 2019; 316:R594-R606. [PMID: 30758978 DOI: 10.1152/ajpregu.00250.2018] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
The stress peptide pituitary adenylate cyclase activating polypeptide (PACAP) and its specific receptor PACAP type 1 receptor (PAC1) have been implicated in sudden infant death syndrome (SIDS). PACAP is also critical to the neonatal cardiorespiratory response to homeostatic stressors identified in SIDS, including hypoxia. However, which of PACAP's three receptors, PAC1, vasoactive intestinal peptide receptor type 1 (VPAC1), and/or vasoactive intestinal peptide receptor type 2 (VPAC2), are involved is unknown. In this study, we hypothesized that PAC1, but not VPAC2, is involved in mediating the cardiorespiratory response to hypoxia during neonatal development. To test this hypothesis, head-out plethysmography and surface ECG electrodes were used to assess the cardiorespiratory variables of unanesthetized postnatal day 4 PAC1 and VPAC2-knockout (KO) and wild-type (WT) mice in response to a 10% hypoxic challenge. Our results demonstrate that compared with WT pups, the early and late hypoxic rate of expired CO2 (V̇co2), V̇co2 and ventilatory responses were blunted in PAC1-KO neonates, and during the posthypoxic period, minute ventilation (V̇e), V̇co2 and heart rate were increased, while the increase in apneas normally associated with the posthypoxic period was reduced. Consistent with impaired cardiorespiratory control in these animals, the V̇e/V̇co2 slope was reduced in PAC1-KO pups, suggesting that breathing was inappropriately matched to metabolism. In contrast, VPAC2-KO pups exhibited elevated heart rate variability during hypoxia compared with WT littermates, but the effects of the VPAC2-KO genotype on breathing were minimal. These findings suggest that PAC1 plays the principal role in mediating the cardiorespiratory effects of PACAP in response to hypoxic stress during neonatal development and that defective PACAP signaling via PAC1 may contribute to the pathogenesis of SIDS.
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Affiliation(s)
- Karlene T Barrett
- Department of Physiology and Pharmacology, Hotchkiss Brain Institute and Alberta Children's Hospital Research Institute, University of Calgary , Calgary, Alberta , Canada
| | - Shabih U Hasan
- Department of Pediatrics, Alberta Children's Hospital Research Institute, University of Calgary , Calgary, Alberta , Canada
| | - Morris H Scantlebury
- Department of Pediatrics, Clinical Neuroscience, Alberta Children's Hospital Research Institute, University of Calgary , Calgary, Alberta , Canada
| | - Richard J A Wilson
- Department of Physiology and Pharmacology, Hotchkiss Brain Institute and Alberta Children's Hospital Research Institute, University of Calgary , Calgary, Alberta , Canada
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3
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Barrett KT, Daubenspeck JA, Wilson RJA. Pituitary adenylate cyclase-activating polypeptide drives cardiorespiratory responses to heat stress in neonatal mice. Am J Physiol Regul Integr Comp Physiol 2017; 313:R385-R394. [DOI: 10.1152/ajpregu.00118.2017] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2017] [Revised: 06/05/2017] [Accepted: 06/27/2017] [Indexed: 11/22/2022]
Abstract
The neuropeptide pituitary adenylate cyclase-activating polypeptide (PACAP) has emerged as a principal and rate-limiting regulator of physiological stress responses in adult rodents and has been implicated in sudden infant death syndrome (SIDS). Recent studies show that PACAP plays a role in neonatal cardiorespiratory responses to hypoxia, hypercapnia, and hypothermia, but not hyperthermia, which is often associated with SIDS. Here we tested the hypothesis that, consistent with a role in SIDS, PACAP is involved in regulating the neonatal cardiorespiratory responses to severe heat. To address this, we used head-out plethysmography and surface ECG electrodes to study the cardiorespiratory physiology of conscious neonatal PACAP-null and wild-type mice at ambient temperatures of 32°C (baseline) and 40°C (heat stress). We also assessed body surface temperature as an indicator of cutaneous heat loss. Our results show that wild-type neonatal mice respond to heat stress by increasing ventilation ( P = 0.007) and associated expired CO2 ( P = 0.041), heart rate ( P < 0.001), and cutaneous heat loss ( P < 0.001). In PACAP-null neonates, this heat response is impaired, as indicated by a decrease in ventilation ( P = 0.04) and associated expired CO2 ( P = 0.006) and a blunted increase in heart rate ( P = 0.001) and cutaneous heat loss ( P = 0.0002). In addition, heart rate variability at baseline was lower in PACAP-null neonates than wild-type controls ( P < 0.01). These results suggest that, during heat stress, PACAP is important for neonatal cardiorespiratory responses that help regulate body temperature. Abnormal PACAP regulation could, therefore, contribute to neonatal disorders in which the autonomic response to stress is impaired, such as SIDS.
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Affiliation(s)
- Karlene T. Barrett
- Department of Physiology and Pharmacology, Hotchkiss Brain Institute and Alberta Children’s Hospital Research Institute, University of Calgary, Calgary, Alberta, Canada; and
| | - John A. Daubenspeck
- Department of Physiology and Neurobiology, Geisel School of Medicine at Dartmouth, Hanover, New Hampshire
| | - Richard J. A. Wilson
- Department of Physiology and Pharmacology, Hotchkiss Brain Institute and Alberta Children’s Hospital Research Institute, University of Calgary, Calgary, Alberta, Canada; and
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4
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Rudecki AP, Gray SL. PACAP in the Defense of Energy Homeostasis. Trends Endocrinol Metab 2016; 27:620-632. [PMID: 27166671 DOI: 10.1016/j.tem.2016.04.008] [Citation(s) in RCA: 34] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/16/2016] [Revised: 04/12/2016] [Accepted: 04/12/2016] [Indexed: 11/23/2022]
Abstract
The neuropeptide pituitary adenylate cyclase-activating polypeptide (PACAP) mediates diverse physiology from neuroprotection to thermoregulation. PACAP is well established as a master regulator of the stress response, regulating psychological and physiological equilibrium via the autonomic nervous system. Neuroanatomical and functional evidence support a role for PACAP in energy metabolism, including thermogenesis, activity, mobilization of energy stores, and appetite. Through integration of this evidence we suggest PACAP be included in the growing list of neuropeptides that mediate energy homeostasis. Future work to uncover the intricacies of PACAP expression and the molecular pathways responsible for PACAP signaling may show potential for this neuropeptide as a therapeutic target as well as further elucidate the complex neuroanatomical networks involved in defending energy balance.
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Affiliation(s)
- Alexander P Rudecki
- Northern Medical Program, University of Northern British Columbia, 3333 University Way, Prince George BC, V2N 4Z9, Canada
| | - Sarah L Gray
- Northern Medical Program, University of Northern British Columbia, 3333 University Way, Prince George BC, V2N 4Z9, Canada.
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5
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Lamine A, Létourneau M, Doan ND, Maucotel J, Couvineau A, Vaudry H, Chatenet D, Vaudry D, Fournier A. Characterizations of a synthetic pituitary adenylate cyclase-activating polypeptide analog displaying potent neuroprotective activity and reduced in vivo cardiovascular side effects in a Parkinson's disease model. Neuropharmacology 2016; 108:440-50. [PMID: 26006268 DOI: 10.1016/j.neuropharm.2015.05.014] [Citation(s) in RCA: 35] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2015] [Revised: 05/07/2015] [Accepted: 05/12/2015] [Indexed: 02/08/2023]
Abstract
Parkinson's disease (PD) is characterized by a steady loss of dopamine neurons through apoptotic, inflammatory and oxidative stress processes. In that line of view, the pituitary adenylate cyclase-activating polypeptide (PACAP), with its ability to cross the blood-brain barrier and its anti-apoptotic, anti-inflammatory and anti-oxidative properties, has proven to offer potent neuroprotection in various PD models. Nonetheless, its peripheral actions, paired with low metabolic stability, hampered its clinical use. We have developed Ac-[Phe(pI)(6), Nle(17)]PACAP(1-27) as an improved PACAP-derived neuroprotective compound. In vitro, this analog stimulated cAMP production, maintained mitochondrial potential and protected SH-SY5Y neuroblastoma cells from 1-methyl-4-phenylpyridinium (MPP(+)) toxicity, as potently as PACAP. Furthermore, contrasting with PACAP, it is stable in human plasma and against dipeptidyl peptidase IV activity. When injected intravenously to 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated mice, PACAP and Ac-[Phe(pI)(6), Nle(17)]PACAP(1-27) restored tyrosine hydoxylase expression into the substantia nigra and modulated the inflammatory response. Albeit falls of mean arterial pressure (MAP) were observed with both PACAP- and Ac-[Phe(pI)(6), Nle(17)]PACAP(1-27)-treated mice, the intensity of the decrease as well as its duration were significantly less marked after iv injections of the analog than after those of the native polypeptide. Moreover, no significant changes in heart rate were measured with the animals for both compounds. Thus, Ac-[Phe(pI)(6), Nle(17)]PACAP(1-27) appears as a promising lead molecule for the development of PACAP-derived drugs potentially useful for the treatment of PD or other neurodegenerative diseases.
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Affiliation(s)
- Asma Lamine
- INRS - Institut Armand-Frappier, 531 boul. des Prairies, Laval, QC H7V 1B7, Canada; Laboratoire International Associé Samuel de Champlain, Université de Rouen, France; INSERM-U982, Laboratory of Neuronal and Neuroendocrine Differentiation and Communication, IRIB, Université de Rouen, 76821 Mont-Saint-Aignan, France
| | - Myriam Létourneau
- INRS - Institut Armand-Frappier, 531 boul. des Prairies, Laval, QC H7V 1B7, Canada; Laboratoire International Associé Samuel de Champlain, Université de Rouen, France
| | - Ngoc Duc Doan
- INRS - Institut Armand-Frappier, 531 boul. des Prairies, Laval, QC H7V 1B7, Canada; Laboratoire International Associé Samuel de Champlain, Université de Rouen, France
| | - Julie Maucotel
- Laboratoire International Associé Samuel de Champlain, Université de Rouen, France; INSERM-U982, Laboratory of Neuronal and Neuroendocrine Differentiation and Communication, IRIB, Université de Rouen, 76821 Mont-Saint-Aignan, France
| | - Alain Couvineau
- INSERM U1149/Inflammation Research Center (CRI), Université Paris-Diderot, Faculté de Médecine Site Bichat, 16, rue H. Huchard, 75018 Paris, France
| | - Hubert Vaudry
- Laboratoire International Associé Samuel de Champlain, Université de Rouen, France; INSERM-U982, Laboratory of Neuronal and Neuroendocrine Differentiation and Communication, IRIB, Université de Rouen, 76821 Mont-Saint-Aignan, France
| | - David Chatenet
- INRS - Institut Armand-Frappier, 531 boul. des Prairies, Laval, QC H7V 1B7, Canada
| | - David Vaudry
- Laboratoire International Associé Samuel de Champlain, Université de Rouen, France; INSERM-U982, Laboratory of Neuronal and Neuroendocrine Differentiation and Communication, IRIB, Université de Rouen, 76821 Mont-Saint-Aignan, France
| | - Alain Fournier
- INRS - Institut Armand-Frappier, 531 boul. des Prairies, Laval, QC H7V 1B7, Canada; Laboratoire International Associé Samuel de Champlain, Université de Rouen, France.
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Kim SJ, Kim YJ, Kakall Z, Farnham MMJ, Pilowsky PM. Intermittent hypoxia-induced cardiorespiratory long-term facilitation: A new role for microglia. Respir Physiol Neurobiol 2016; 226:30-8. [PMID: 27015670 DOI: 10.1016/j.resp.2016.03.012] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2016] [Revised: 03/18/2016] [Accepted: 03/18/2016] [Indexed: 02/07/2023]
Abstract
Intermittent hypoxia induces plasticity in neural networks controlling breathing and cardiovascular function. Studies demonstrate that mechanisms causing cardiorespiratory plasticity rely on intracellular signalling pathways that are activated by specific neurotransmitters. Peptides such as serotonin, PACAP and orexin are well-known for their physiological significance in regulating the cardiorespiratory system. Their receptor counterparts are present in cardiorespiratory centres of the brainstem medulla and spinal cord. Microglial cells are also important players in inducing plasticity. The phenotype and function of microglial cells can change based on the physiological state of the central nervous system. Here, we propose that in the autonomic nuclei of the ventral brainstem the relationship between neurotransmitters and neurokines, neurons and microglia determines the overall neural function of the central cardiorespiratory system.
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Affiliation(s)
- Seung Jae Kim
- Department of Physiology, Faculty of Medicine, The University of Sydney, Sydney, New South Wales 2006, Australia; The Heart Research Institute, 7 Eliza Street, Newtown, Sydney 2042, Australia
| | - Yeon Jae Kim
- Department of Physiology, Faculty of Medicine, The University of Sydney, Sydney, New South Wales 2006, Australia
| | - Zohra Kakall
- Department of Physiology, Faculty of Medicine, The University of Sydney, Sydney, New South Wales 2006, Australia; The Heart Research Institute, 7 Eliza Street, Newtown, Sydney 2042, Australia
| | - Melissa M J Farnham
- Department of Physiology, Faculty of Medicine, The University of Sydney, Sydney, New South Wales 2006, Australia; The Heart Research Institute, 7 Eliza Street, Newtown, Sydney 2042, Australia
| | - Paul M Pilowsky
- Department of Physiology, Faculty of Medicine, The University of Sydney, Sydney, New South Wales 2006, Australia; The Heart Research Institute, 7 Eliza Street, Newtown, Sydney 2042, Australia.
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7
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Deuchars SA, Lall VK. Sympathetic preganglionic neurons: properties and inputs. Compr Physiol 2016; 5:829-69. [PMID: 25880515 DOI: 10.1002/cphy.c140020] [Citation(s) in RCA: 44] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
The sympathetic nervous system comprises one half of the autonomic nervous system and participates in maintaining homeostasis and enabling organisms to respond in an appropriate manner to perturbations in their environment, either internal or external. The sympathetic preganglionic neurons (SPNs) lie within the spinal cord and their axons traverse the ventral horn to exit in ventral roots where they form synapses onto postganglionic neurons. Thus, these neurons are the last point at which the central nervous system can exert an effect to enable changes in sympathetic outflow. This review considers the degree of complexity of sympathetic control occurring at the level of the spinal cord. The morphology and targets of SPNs illustrate the diversity within this group, as do their diverse intrinsic properties which reveal some functional significance of these properties. SPNs show high degrees of coupled activity, mediated through gap junctions, that enables rapid and coordinated responses; these gap junctions contribute to the rhythmic activity so critical to sympathetic outflow. The main inputs onto SPNs are considered; these comprise afferent, descending, and interneuronal influences that themselves enable functionally appropriate changes in SPN activity. The complexity of inputs is further demonstrated by the plethora of receptors that mediate the different responses in SPNs; their origins and effects are plentiful and diverse. Together these different inputs and the intrinsic and coupled activity of SPNs result in the rhythmic nature of sympathetic outflow from the spinal cord, which has a variety of frequencies that can be altered in different conditions.
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Affiliation(s)
- Susan A Deuchars
- School of Biomedical Sciences, University of Leeds, Leeds, United Kingdom
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Irwin M, Greig A, Tvrdik P, Lucero MT. PACAP modulation of calcium ion activity in developing granule cells of the neonatal mouse olfactory bulb. J Neurophysiol 2014; 113:1234-48. [PMID: 25475351 DOI: 10.1152/jn.00594.2014] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Ca(2+) activity in the CNS is critical for the establishment of developing neuronal circuitry prior to and during early sensory input. In developing olfactory bulb (OB), the neuromodulators that enhance network activity are largely unknown. Here we provide evidence that pituitary adenylate cyclase-activating peptide (PACAP)-specific PAC1 receptors (PAC1Rs) expressed in postnatal day (P)2-P5 mouse OB are functional and enhance network activity as measured by increases in calcium in genetically identified granule cells (GCs). We used confocal Ca(2+) imaging of OB slices from Dlx2-tdTomato mice to visualize GABAergic GCs. To address whether the PACAP-induced Ca(2+) oscillations were direct or indirect effects of PAC1R activation, we used antagonists for the GABA receptors (GABARs) and/or glutamate receptors (GluRs) in the presence and absence of PACAP. Combined block of GABARs and GluRs yielded a 66% decrease in the numbers of PACAP-responsive cells, suggesting that 34% of OB neurons are directly activated by PACAP. Similarly, immunocytochemistry using anti-PAC1 antibody showed that 34% of OB neurons express PAC1R. Blocking either GluRs or GABARs alone indirectly showed that PACAP stimulates release of both glutamate and GABA, which activate GCs. The appearance of PACAP-induced Ca(2+) activity in immature GCs suggests a role for PACAP in GC maturation. To conclude, we find that PACAP has both direct and indirect effects on neonatal OB GABAergic cells and may enhance network activity by promoting glutamate and GABA release. Furthermore, the numbers of PACAP-responsive GCs significantly increased between P2 and P5, suggesting that PACAP-induced Ca(2+) activity contributes to neonatal OB development.
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Affiliation(s)
- Mavis Irwin
- Department of Physiology, University of Utah School of Medicine, Salt Lake City, Utah
| | - Ann Greig
- Department of Physiology, University of Utah School of Medicine, Salt Lake City, Utah
| | - Petr Tvrdik
- Department of Human Genetics, University of Utah School of Medicine, Salt Lake City, Utah; Interdepartmental Neuroscience Program, University of Utah School of Medicine, Salt Lake City, Utah; and
| | - Mary T Lucero
- Department of Physiology, University of Utah School of Medicine, Salt Lake City, Utah; Interdepartmental Neuroscience Program, University of Utah School of Medicine, Salt Lake City, Utah; and Department of Neuroscience and Physiology, American University of the Caribbean, Cupecoy, Sint Maarten, Netherlands Antilles
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9
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Pituitary Adenylate Cyclase-Activating Polypeptide (PACAP) Signalling Enhances Osteogenesis in UMR-106 Cell Line. J Mol Neurosci 2014; 54:555-73. [DOI: 10.1007/s12031-014-0389-1] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2014] [Accepted: 07/22/2014] [Indexed: 01/14/2023]
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Ho CM, Chiang CH, Lee CM, Fan YP, Su CK. Glutamatergic activities in neonatal rat spinal cord heterogeneously regulate single-fiber splanchnic nerve discharge. Auton Neurosci 2013; 177:175-80. [PMID: 23665166 DOI: 10.1016/j.autneu.2013.04.008] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2012] [Revised: 02/22/2013] [Accepted: 04/15/2013] [Indexed: 10/26/2022]
Abstract
Kynurenic acid (KYN) is a metabolite of tryptophan and is involved in various neurological disorders. Using whole-bundle nerve recording techniques, we previously observed that applications of KYN to block endogenous ionotropic glutamate receptor activities in neonatal rat spinal cords in vitro cause a reversible fluctuation of splanchnic sympathetic nerve discharge (SND). We hypothesized that the SND fluctuation was due to a heterogeneous single-fiber response. To detail individual fiber activities, we used the so-called 'oligofiber recordings'. Spontaneous single-fiber activities were recorded from the collagenase-dissociated splanchnic nerve fascicles. Applications of KYN increased, decreased or did not change firing rates. The heterogeneous responses in spontaneous spiking activities were confirmed by applications of APV or CNQX, suggesting an effect mediated by endogenous NMDA- or non-NMDA receptor activities. In addition to changes in firing rates, apparent drug-induced changes in firing patterns were also observed in some fiber activities. Using the oligofiber recording techniques, we confirmed a differential role of endogenous ionotropic glutamate receptor activities in regulating sympathetic outflows from the spinal cord of neonatal rats. Fine-tuning of ionotropic glutamate receptor activities in the spinal cord may serve as a simple way for heterogeneous regulation of various sympathetic-targeting tissues.
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Affiliation(s)
- Chiu-Ming Ho
- Department of Anesthesiology, Taipei Veterans General Hospital and National Yang-Ming University, Taipei 112, Taiwan
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Farnham MMJ, Lung MSY, Tallapragada VJ, Pilowsky PM. PACAP causes PAC1/VPAC2 receptor mediated hypertension and sympathoexcitation in normal and hypertensive rats. Am J Physiol Heart Circ Physiol 2012; 303:H910-7. [PMID: 22886412 DOI: 10.1152/ajpheart.00464.2012] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
Pituitary adenylate cyclase-activating polypeptide (PACAP) is an excitatory neuropeptide that plays an important role in hypertension and stress responses. PACAP acts at three G protein-coupled receptors [PACAP type 1 receptor (PAC(1)) and vasoactive intestinal peptide receptor types 1 and 2 (VPAC(1) and VPAC(2))] and is localized to sites involved in cardiovascular control, most significantly the rostral ventrolateral medulla (RVLM). The RVLM is crucial for the tonic and reflex control of efferent sympathetic activity. Increases in sympathetic activity are observed in most types of hypertension and heart failure. PACAP delivered intrathecally also causes massive sympathoexcitation. We aimed to determine the presence and abundance of the three PACAP receptors in the RVLM, the role, in vivo, of PACAP in the RVLM on tonic and reflex cardiovascular control, and the contribution of PACAP to hypertension in the spontaneously hypertensive rat (SHR). Data were obtained using quantitative PCR and microinjection of PACAP and its antagonist, PACAP(6-38), into the RVLM of anesthetized artificially ventilated normotensive rats or SHRs. All three receptors were present in the RVLM. PACAP microinjection into the RVLM caused sustained sympathoexcitation and tachycardia with a transient hypertension but did not affect homeostatic reflexes. The responses were partially mediated through PAC(1)/VPAC(2) receptors since the effect of PACAP was attenuated (∼50%) by PACAP(6-38). PACAP was not tonically active in the RVLM in this preparation because PACAP(6-38) on its own had no inhibitory effect. PACAP has long-lasting cardiovascular effects, but altered PACAP signaling within the RVLM is not a cause of hypertension in the SHR.
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Affiliation(s)
- M M J Farnham
- Macquarie University, Sydney, New South Wales, Australia
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