1
|
Nedoboy PE, Houlahan CB, Farnham MMJ. Pentobarbital Anesthesia Suppresses the Glucose Response to Acute Intermittent Hypoxia in Rat. Front Physiol 2021; 12:645392. [PMID: 33746780 PMCID: PMC7973217 DOI: 10.3389/fphys.2021.645392] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2020] [Accepted: 02/17/2021] [Indexed: 11/17/2022] Open
Abstract
A key feature of sleep disordered breathing syndromes, such as obstructive sleep apnea is intermittent hypoxia. Intermittent hypoxia is well accepted to drive the sympathoexcitation that is frequently associated with hypertension and diabetes, with measurable effects after just 1 h. The aim of this study was to directly measure the glucose response to 1 h of acute intermittent hypoxia in pentobarbital anesthetized rats, compared to conscious rats. However, we found that while a glucose response is measurable in conscious rats exposed to intermittent hypoxia, it is suppressed in anesthetized rats. Intermittent hypoxia for 1, 2, or 8 h increased blood glucose by 0.7 ± 0.1 mmol/L in conscious rats but had no effect in anesthetized rats (−0.1 ± 0.2 mmol/L). These results were independent of the frequency of the hypoxia challenges, fasting state, vagotomy, or paralytic agents. A supraphysiological challenge of 3 min of hypoxia was able to induce a glycemic response indicating that the reflex response is not abolished under pentobarbital anesthesia. We conclude that pentobarbital anesthesia is unsuitable for investigations into glycemic response pathways in response to intermittent hypoxia in rats.
Collapse
Affiliation(s)
- Polina E Nedoboy
- Cardiovascular Neuroscience Unit, Heart Research Institute, Newtown, NSW, Australia.,Department of Physiology, School of Medical Sciences, Faculty of Medicine and Health, The University of Sydney, Camperdown, NSW, Australia
| | - Callum B Houlahan
- Cardiovascular Neuroscience Unit, Heart Research Institute, Newtown, NSW, Australia.,Department of Physiology, School of Medical Sciences, Faculty of Medicine and Health, The University of Sydney, Camperdown, NSW, Australia
| | - Melissa M J Farnham
- Cardiovascular Neuroscience Unit, Heart Research Institute, Newtown, NSW, Australia.,Department of Physiology, School of Medical Sciences, Faculty of Medicine and Health, The University of Sydney, Camperdown, NSW, Australia
| |
Collapse
|
2
|
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: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [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.
Collapse
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
| |
Collapse
|
3
|
Kakall ZM, Nedoboy PE, Farnham MMJ, Pilowsky PM. Activation of µ-opioid receptors in the rostral ventrolateral medulla blocks the sympathetic counterregulatory response to glucoprivation. Am J Physiol Regul Integr Comp Physiol 2018; 315:R1115-R1122. [PMID: 30281326 DOI: 10.1152/ajpregu.00248.2018] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
Activation of neurons in the rostral ventrolateral medulla (RVLM) following glucoprivation initiates sympathoadrenal activation, adrenaline release, and increased glucose production. Here, we aimed to determine the role of RVLM µ-opioid receptors in the counterregulatory response to systemic glucoprivation. Experiments were performed in pentobarbital sodium anesthetized male Sprague-Dawley rats ( n = 30). Bilateral activation of RVLM µ-opioid receptors with [d-Ala2, N-Me-Phe4, Gly5-ol]-enkephalin (DAMGO) (8 mM, 50 nl) depressed adrenal sympathetic nerve activity for ~60 min ( n = 6; Δ49.9 ± 5.8%, P < 0.05). The counterregulatory response to glucoprivation (measured by adrenal sympathetic efferent nerve activity) induced by 2-deoxyglucose (2-DG) ( n = 6; Δ63.6 ± 16.5%, P < 0.05) was completely blocked 60 min after DAMGO microinjections ( n = 6; Δ10.2 ± 3.5%, P < 0.05). Furthermore, DAMGO pretreatment attenuated the increase in blood glucose levels after 2-DG infusion ( n = 6; 6.1 ± 0.7mmol/l vs. baseline 5.2 ± 0.3mmol/l, P > 0.05) compared with 2-DG alone ( n = 6; 7.6 ± 0.4mmol/l vs. baseline 6.0 ± 0.4mmol/l, P < 0.05). Thus, activation of RVLM µ-opioid receptors attenuated the neural efferent response to glucoprivation and reduced glucose production.
Collapse
Affiliation(s)
- Zohra M Kakall
- Department of Physiology, Sydney Medical School, The University of Sydney , Sydney, NSW , Australia.,Heart Research Institute , Sydney, NSW , Australia
| | - Polina E Nedoboy
- Department of Physiology, Sydney Medical School, The University of Sydney , Sydney, NSW , Australia.,Heart Research Institute , Sydney, NSW , Australia
| | - Melissa M J Farnham
- Department of Physiology, Sydney Medical School, The University of Sydney , Sydney, NSW , Australia.,Heart Research Institute , Sydney, NSW , Australia
| | - Paul M Pilowsky
- Department of Physiology, Sydney Medical School, The University of Sydney , Sydney, NSW , Australia.,Heart Research Institute , Sydney, NSW , Australia
| |
Collapse
|
4
|
Cohen EM, Farnham MMJ, Kakall Z, Kim SJ, Nedoboy PE, Pilowsky PM. Glia and central cardiorespiratory pathology. Auton Neurosci 2018; 214:24-34. [PMID: 30172674 DOI: 10.1016/j.autneu.2018.08.003] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2018] [Revised: 08/22/2018] [Accepted: 08/22/2018] [Indexed: 01/08/2023]
Abstract
Respiration and blood pressure are primarily controlled by somatic and autonomic motor neurones, respectively. Central cardiorespiratory control is critical in moment-to-moment survival, but it also has a role in the development and maintenance of chronic pathological conditions such as hypertension. The glial cells of the brain are non-neuronal cells with metabolic, immune, and developmental functions. Recent evidence shows that glia play an active role in supporting and regulating the neuronal circuitry which drives the cardiorespiratory system. Here we will review the activities of two key types of glial cell, microglia and astrocytes, in assisting normal central cardiorespiratory control and in pathology.
Collapse
Affiliation(s)
- E Myfanwy Cohen
- The Heart Research Institute, Sydney, New South Wales 2042, Australia; Sydney Medical School, University of Sydney, Sydney, New South Wales 2006, Australia
| | - Melissa M J Farnham
- The Heart Research Institute, Sydney, New South Wales 2042, Australia; Sydney Medical School, University of Sydney, Sydney, New South Wales 2006, Australia
| | - Zohra Kakall
- The Heart Research Institute, Sydney, New South Wales 2042, Australia; Sydney Medical School, University of Sydney, Sydney, New South Wales 2006, Australia
| | - Seung Jae Kim
- The Heart Research Institute, Sydney, New South Wales 2042, Australia; Sydney Medical School, University of Sydney, Sydney, New South Wales 2006, Australia
| | - Polina E Nedoboy
- The Heart Research Institute, Sydney, New South Wales 2042, Australia; Sydney Medical School, University of Sydney, Sydney, New South Wales 2006, Australia
| | - Paul M Pilowsky
- The Heart Research Institute, Sydney, New South Wales 2042, Australia; Sydney Medical School, University of Sydney, Sydney, New South Wales 2006, Australia.
| |
Collapse
|
5
|
Roy A, Farnham MMJ, Derakhshan F, Pilowsky PM, Wilson RJA. Acute intermittent hypoxia with concurrent hypercapnia evokes P2X and TRPV1 receptor-dependent sensory long-term facilitation in naïve carotid bodies. J Physiol 2018; 596:3149-3169. [PMID: 29159869 PMCID: PMC6068228 DOI: 10.1113/jp275001] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2017] [Accepted: 11/16/2017] [Indexed: 12/14/2022] Open
Abstract
KEY POINTS Activity-dependent plasticity can be induced in carotid body (CB) chemosensory afferents without chronic intermittent hypoxia (CIH) preconditioning by acute intermittent hypoxia coincident with bouts of hypercapnia (AIH-Hc). Several properties of this acute plasticity are shared with CIH-dependent sensory long-term facilitation (LTF) in that induction is dependent on 5-HT, angiotensin II, protein kinase C and reactive oxygen species. Several properties differ from CIH-dependent sensory LTF; H2 O2 appears to play no part in induction, whereas maintenance requires purinergic P2X2/3 receptor activation and is dependent on transient receptor potential vanilloid type 1 (TRPV1) receptor sensitization. Because P2X2/3 and TRPV1 receptors are located in carotid sinus nerve (CSN) terminals but not presynaptic glomus cells, a primary site of the acute AIH-Hc induced sensory LTF appears to be postsynaptic. Our results obtained in vivo suggest a role for TRPV1-dependent CB activity in acute sympathetic LTF. We propose that P2X-TRPV1-receptor-dependent sensory LTF may constitute an important early mechanism linking sleep apnoea with hypertension and/or cardiovascular disease. ABSTRACT Apnoeas constitute an acute existential threat to neonates and adults. In large part, this threat is detected by the carotid bodies, which are the primary peripheral chemoreceptors, and is combatted by arousal and acute cardiorespiratory responses, including increased sympathetic output. Similar responses occur with repeated apnoeas but they continue beyond the last apnoea and can persist for hours [i.e. ventilatory and sympathetic long-term facilitation (LTF)]. These long-term effects may be adaptive during acute episodic apnoea, although they may prolong hypertension causing chronic cardiovascular impairment. We report a novel mechanism of acute carotid body (CB) plasticity (sensory LTF) induced by repeated apnoea-like stimuli [i.e. acute intermittent hypoxia coincident with bouts of hypercapnia (AIH-Hc)]. This plasticity did not require chronic intermittent hypoxia preconditioning, was dependent on P2X receptors and protein kinase C, and involved heat-sensitive transient receptor potential vanilloid type 1 (TRPV1) receptors. Reactive oxygen species (O2 ·¯) were involved in initiating plasticity only; no evidence was found for H2 O2 involvement. Angiotensin II and 5-HT receptor antagonists, losartan and ketanserin, severely reduced CB responses to individual hypoxic-hypercapnic challenges and prevented the induction of sensory LTF but, if applied after AIH-Hc, failed to reduce plasticity-associated activity. Conversely, TRPV1 receptor antagonism had no effect on responses to individual hypoxic-hypercapnic challenges but reduced plasticity-associated activity by ∼50%. Further, TRPV1 receptor antagonism in vivo reduced sympathetic LTF caused by AIH-Hc, although only if the CBs were functional. These data demonstrate a new mechanism of CB plasticity and suggest P2X-TRPV1-dependent sensory LTF as a novel target for pharmacological intervention in some forms of neurogenic hypertension associated with recurrent apnoeas.
Collapse
Affiliation(s)
- Arijit Roy
- Department of Physiology & Pharmacology, Hotchkiss Brain Institute, Faculty of MedicineUniversity of CalgaryCalgaryAlbertaCanada
| | | | - Fatemeh Derakhshan
- Department of Physiology & Pharmacology, Hotchkiss Brain Institute, Faculty of MedicineUniversity of CalgaryCalgaryAlbertaCanada
| | | | - Richard J. A. Wilson
- Department of Physiology & Pharmacology, Hotchkiss Brain Institute, Faculty of MedicineUniversity of CalgaryCalgaryAlbertaCanada
| |
Collapse
|
6
|
Kakall ZM, Pilowsky PM, Farnham MMJ. PACAP-(6-38) or kynurenate microinjections in the RVLM prevent the development of sympathetic long-term facilitation after acute intermittent hypoxia. Am J Physiol Heart Circ Physiol 2017; 314:H563-H572. [PMID: 29212793 DOI: 10.1152/ajpheart.00596.2017] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Intermittent hypoxia causes a persistent increase in sympathetic activity that progresses to hypertension in chronic conditions such as obstructive sleep apnea. Pituitary adenylate cyclase-activating polypeptide (PACAP) is an excitatory neurotransmitter that causes long-lasting sympathetic excitation. We aimed to determine if intermittent activation of the rostral ventrolateral medulla (RVLM) causes PACAP-mediated elevation of sympathetic nerve activity, termed sympathetic long-term facilitation (sLTF). The role of PACAP in mediating sLTF in response to intermittent activation of the RVLM was investigated in urethane-anaesthetized and artificially ventilated rats ( n = 65, Sprague-Dawley). Bilateral RVLM microinjections of the PACAP type 1 receptor/vasoactive intestinal polypeptide receptor type 2 receptor antagonist PACAP-(6-38) [ n = 6, change (Δ): -16.4 ± 6.5%) or an ionotropic glutamate antagonist, kynurenate ( n = 6, Δ:-7.2 ± 2.3%), blocked the development of acute intermittent hypoxia-induced sLTF ( n = 6, Δ: 49.2 ± 14.2%). Intermittent RVLM microinjections of glutamate caused sLTF ( n = 5, Δ: 56.9 ± 14.7%) that was abolished by PACAP-(6-38) pretreatment ( n = 5, Δ:-1.2 ± 4.7%). Conversely, intermittent microinjections of PACAP in the RVLM did not elicit sLTF. Intermittent bilateral disinhibition of the RVLM by microinjection of γ-aminobutyric acid in the caudal ventrolateral medulla did not elicit sLTF. Direct activation of RVLM neurons is crucial for the development of sLTF. PACAP and glutamate act synergistically in the RVLM, with both being necessary for the sLTF response. We found that activation of glutamate but not PACAP receptors is necessary and sufficient to generate sLTF, even in the absence of intermittent hypoxia. Our results demonstrate that PACAP within the RVLM may contribute to the development of obstructive sleep apnea -induced hypertension. NEW & NOTEWORTHY Pharmacological blockade of either pituitary adenylate cyclase-activating polypeptide (PACAP) or ionotropic glutamate receptors in the rostral ventrolateral medulla prevents development of sympathetic long-term facilitation. PACAP receptor inhibition prevents the occurrence of hypoxia-induced peripheral chemoreflex sensitization. Thus, PACAP receptors may be a potential therapeutic target serving to reduce heightened sympathetic tone and hypersensitized cardiovascular reflexes.
Collapse
Affiliation(s)
- Zohra M Kakall
- Department of Physiology, Sydney Medical School, The University of Sydney , Sydney, New South Wales , Australia.,Heart Research Institute , Sydney, New South Wales , Australia
| | - Paul M Pilowsky
- Department of Physiology, Sydney Medical School, The University of Sydney , Sydney, New South Wales , Australia.,Heart Research Institute , Sydney, New South Wales , Australia
| | - Melissa M J Farnham
- Department of Physiology, Sydney Medical School, The University of Sydney , Sydney, New South Wales , Australia.,Heart Research Institute , Sydney, New South Wales , Australia
| |
Collapse
|
7
|
Kim SJ, Pilowsky PM, Farnham MMJ. Intrathecal Intermittent Orexin-A Causes Sympathetic Long-Term Facilitation and Sensitizes the Peripheral Chemoreceptor Response to Hypoxia in Rats. J Pharmacol Exp Ther 2016; 358:492-501. [PMID: 27384072 DOI: 10.1124/jpet.116.234443] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2016] [Accepted: 07/05/2016] [Indexed: 11/22/2022] Open
Abstract
Intermittent hypoxia causes a persistent increase in sympathetic nerve activity (SNA), which progresses to hypertension in conditions such as obstructive sleep apnea. Orexins (A and B) are hypothalamic neurotransmitters with arousal-promoting and sympathoexcitatory effects. We investigated whether the sustained elevation of SNA, termed sympathetic long-term facilitation, after acute intermittent hypoxia (AIH) is caused by endogenous orexin acting on spinal sympathetic preganglionic neurons. The role of orexin in the increased SNA response to AIH was investigated in urethane-anesthetized, vagotomized, and artificially ventilated Sprague-Dawley rats (n = 58). A spinally infused subthreshold dose of orexin-A (intermittent; 0.1 nmol × 10) produced long-term enhancement in SNA (41.4% ± 6.9%) from baseline. This phenomenon was not produced by the same dose of orexin-A administered as a bolus intrathecal infusion (1 nmol; 7.3% ± 2.3%). The dual orexin receptor blocker, Almorexant, attenuated the effect of sympathetic long-term facilitation generated by intermittent orexin-A (20.7% ± 4.5% for Almorexant at 30 mg∙kg(-1) and 18.5% ± 1.2% for 75 mg∙kg(-1)), but not in AIH. The peripheral chemoreflex sympathoexcitatory response to hypoxia was greatly enhanced by intermittent orexin-A and AIH. In both cases, the sympathetic chemoreflex sensitization was reduced by Almorexant. Taken together, spinally acting orexin-A is mechanistically sufficient to evoke sympathetic long-term facilitation. However, AIH-induced sympathetic long-term facilitation appears to rely on mechanisms that are independent of orexin neurotransmission. Our findings further reveal that the activation of spinal orexin receptors is critical to enhance peripheral chemoreceptor responses to hypoxia after AIH.
Collapse
Affiliation(s)
- Seung Jae Kim
- Department of Physiology, Sydney Medical School, University of Sydney, and Heart Research Institute, Sydney, New South Wales, Australia
| | - Paul M Pilowsky
- Department of Physiology, Sydney Medical School, University of Sydney, and Heart Research Institute, Sydney, New South Wales, Australia
| | - Melissa M J Farnham
- Department of Physiology, Sydney Medical School, University of Sydney, and Heart Research Institute, Sydney, New South Wales, Australia
| |
Collapse
|
8
|
Kapoor K, Bhandare AM, Nedoboy PE, Mohammed S, Farnham MMJ, Pilowsky PM. Dynamic changes in the relationship of microglia to cardiovascular neurons in response to increases and decreases in blood pressure. Neuroscience 2016; 329:12-29. [PMID: 27155147 DOI: 10.1016/j.neuroscience.2016.04.044] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2016] [Revised: 04/26/2016] [Accepted: 04/28/2016] [Indexed: 02/07/2023]
Abstract
Microglia are present throughout the central nervous system (CNS) and express receptors for every known neurotransmitter. During inflammation, microglia change into a state that either promotes removal of debris (M1), or into a state that promotes soothing (M2). Caudal- and rostral- ventrolateral medullary regions (CVLM and RVLM, respectively) of the brainstem are key nuclei involved in all aspects of the cardiovascular system. In this study, we investigate a novel role for microglia in cardiovascular control in the brainstem of adult male Sprague-Dawley (SD) rat. Here we show, that increases and decreases in blood pressure (BP) triggers alertness in the physiology of microglia in the brainstem region; inducing changes in microglial spatial distribution and the number of synapses in contact with microglial end processes. Following 6h of acute hypertension, the number of synapses in contact with microglia increased by ≈30% in both regions of the brainstem, CVLM and RVLM. Induction of acute hypotension for 6h causes microglia to reduce the number of synaptic contacts by >20% in both, CVLM and RVLM, nuclei of the brainstem. Our analysis of the morphological characteristics of microglia, and expression levels of M1 and M2, reveals that the changes induced in microglial behavior do not require any obvious dramatic changes in their morphology. Taken together, our findings suggest that microglia play a novel, unexpected, physiological role in the uninjured autonomic nuclei of CNS; we therefore speculate that microglia act cooperatively with brainstem cardiovascular neurons to maintain them in a physiologically receptive state.
Collapse
Affiliation(s)
- Komal Kapoor
- Faculty of Medicine and Health Sciences, Macquarie University, Sydney, New South Wales 2109, Australia; The Heart Research Institute, Sydney, New South Wales 2042, Australia
| | - Amol M Bhandare
- Faculty of Medicine and Health Sciences, Macquarie University, Sydney, New South Wales 2109, Australia; The Heart Research Institute, Sydney, New South Wales 2042, Australia
| | - Polina E Nedoboy
- The Heart Research Institute, Sydney, New South Wales 2042, Australia
| | - Suja Mohammed
- The Heart Research Institute, Sydney, New South Wales 2042, Australia; Department of Physiology, University of Sydney, Sydney, New South Wales 2006, Australia
| | - Melissa M J Farnham
- The Heart Research Institute, Sydney, New South Wales 2042, Australia; Department of Physiology, University of Sydney, Sydney, New South Wales 2006, Australia
| | - Paul M Pilowsky
- The Heart Research Institute, Sydney, New South Wales 2042, Australia; Department of Physiology, University of Sydney, Sydney, New South Wales 2006, Australia.
| |
Collapse
|
9
|
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] [What about the content of this article? (0)] [Affiliation(s)] [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.
Collapse
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.
| |
Collapse
|
10
|
Deng W, Farnham MMJ, Goldys EM, Mohammed S, Pilowsky PM. Gene Interference with Morpholinos in a Gold Nanoparticle-Based Delivery Platform in Rat PC12 Cells. J Biomed Nanotechnol 2015; 11:2111-23. [PMID: 26510306 DOI: 10.1166/jbn.2015.2171] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
For the first time the efficiency of gene knockdown of the pituitary adenylate cyclase-activating polypeptide (PACAP) receptor 1 (PAC1R) is demonstrated by employing gold nanocomplexes. This gene knockdown subsequently affects the action of PACAP on neurite outgrowth in PC12 cells. These nanocomplexes comprise cholera toxin B (CTB)-gold nanoparticle conjugates loaded with double-stranded morpholinos (MOs) (photo MO and antisense MO). Nanocomplexes are introduced into cells via lipid raft-dependent endocytosis. After UV light exposure, the photolinker in the photo MO is cleaved, bisecting the photo MO and releasing the antisense MO from the conjugate. The antisense MO then binds the PAC1R mRNA and decreases gene expression. The maximal efficiency of gene knockdown is observed after 24 hours, resulting in a 65% ± 12 reduction of the protein level. This reduction in PAC1R impairs the responsiveness of cells to PACAP exposure. Following PAC1R gene knockdown, only 10% ± 8 and 11%± 9 of cells exhibit neurite outgrowth after 4-day exposure to PACAP-38 and PACAP-27, respectively. These results demonstrate an efficient PAC1R gene knockdown and noticeable difference in response to PACAP action on neural cell differentiation, adding an extra dimension to determine the involvement of PACAP and its PAC1R in the neurotropic effect to PC12 cells.
Collapse
|
11
|
Farnham MMJ, O'Connor ET, Wilson RJA, Pilowsky PM. Surgical preparation of mice for recording cardiorespiratory parameters in vivo. J Neurosci Methods 2015; 248:41-5. [PMID: 25861941 DOI: 10.1016/j.jneumeth.2015.03.038] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2014] [Revised: 02/24/2015] [Accepted: 03/31/2015] [Indexed: 11/19/2022]
Abstract
BACKGROUND The explosion in the use of genetically modified mouse strains to investigate function in biology has an enormous potential to expand on pharmacological studies traditionally conducted in rats. A key limitation to date is the inability to record from multiple nerves in an anaesthetised mouse for long periods. NEW METHOD Here we describe an in vivo preparation that maintains mice in a suitable physiological state, under anaesthesia, for at least 6 hr and also enables multiple cardiorespiratory recordings over that time. RESULTS Using the method described, blood pressure, heart rate, phrenic nerve activity, splanchnic nerve activity and heart rate were able to be recorded for hours in an anaesthetised, paralysed and mechanically ventilated mouse. COMPARISON WITH EXISTING METHOD Existing anaesthetised mouse preparations are limited by difficulties in maintaining mice under anaesthesia for long periods. This time constraint therefore limits the surgical time and number of cardiorespiratory variables recorded. It also limits the type of stimuli that can be administered and the length of recorded responses. The method described here optimises these variables to overcome these challenges. CONCLUSIONS In summary, we report an approach that enables physiological and pharmacological studies previously undertaken in larger animals or 'reduced' preparations, to be conducted in vivo in mice. We anticipate that the use of this preparation will enable a deeper understanding of genetic variation, and allow a much greater level of phenotypic characterisation in genetically modified mice.
Collapse
Affiliation(s)
- Melissa M J Farnham
- Australian School of Advanced Medicine, 2 Technology Place, Macquarie University, Sydney, NSW 2109, Australia; The Heart Research Institute and The University of Sydney, 7 Eliza St, Newtown 2042, Australia.
| | - Edward T O'Connor
- Department of Physiology and Pharmacology, Hotchkiss Brain Institute and Alberta Children's Hospital Research Institute, Cumming School of Medicine, University of Calgary, 3330 Hospital Dr. N.W., Calgary, Alberta T2N4N1, Canada
| | - Richard J A Wilson
- Department of Physiology and Pharmacology, Hotchkiss Brain Institute and Alberta Children's Hospital Research Institute, Cumming School of Medicine, University of Calgary, 3330 Hospital Dr. N.W., Calgary, Alberta T2N4N1, Canada
| | - Paul M Pilowsky
- The Heart Research Institute and The University of Sydney, 7 Eliza St, Newtown 2042, Australia
| |
Collapse
|
12
|
Deng W, Goldys EM, Farnham MMJ, Pilowsky PM. Optogenetics, the intersection between physics and neuroscience: light stimulation of neurons in physiological conditions. Am J Physiol Regul Integr Comp Physiol 2014; 307:R1292-302. [PMID: 25274906 DOI: 10.1152/ajpregu.00072.2014] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Neuronal stimulation by light is a novel approach in the emerging field of optogenetics, where genetic engineering is used to introduce light-activated channels. However, light is also capable of stimulating neurons even in the absence of genetic modifications through a range of physical and biological mechanisms. As a result, rigorous design of optogenetic experiments needs to take note of alternative and parallel effects of light illumination of neuronal tissues. Thus all matters relating to light penetration are critical to the development of studies using light-activated proteins. This paper discusses ways to quantify light, light penetration in tissue, as well as light stimulation of neurons in physiological conditions. We also describe the direct effect of light on neurons investigated at different sites.
Collapse
Affiliation(s)
- Wei Deng
- Physics and Astronomy Department, Macquarie University, Sydney, Australia; and
| | - Ewa M Goldys
- Physics and Astronomy Department, Macquarie University, Sydney, Australia; and
| | | | - Paul M Pilowsky
- Heart Research Institute and Sydney University, Sydney, Australia
| |
Collapse
|
13
|
Inglott MA, Lerner EA, Pilowsky PM, Farnham MMJ. Activation of PAC(1) and VPAC receptor subtypes elicits differential physiological responses from sympathetic preganglionic neurons in the anaesthetized rat. Br J Pharmacol 2013; 167:1089-98. [PMID: 22612450 DOI: 10.1111/j.1476-5381.2012.02045.x] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023] Open
Abstract
BACKGROUND AND PURPOSE Pituitary adenylate cyclase-activating polypeptide (PACAP) is an excitatory neuropeptide with central and peripheral cardiovascular actions. Intrathecal PACAP increases splanchnic sympathetic nerve activity and heart rate, but not mean arterial pressure (MAP). We hypothesize that the three PACAP receptors (PAC(1) , VPAC(1) and VPAC(2) ) have different actions in central cardiovascular control, and that their summed effect results in the lack of MAP response observed following intrathecal PACAP injection. EXPERIMENTAL APPROACH The effects of the PACAP receptors on baseline cardiovascular parameters were investigated using selective agonists and antagonists administered into the intrathecal space of urethane-anaesthetized, vagotomized and artificially ventilated male Sprague-Dawley rats. KEY RESULTS Selective activation of the PACAP receptors had different effects on MAP. When activated by maxadilan, PAC(1) receptors increased MAP. The VPAC receptors decreased MAP when both were activated with vasoactive intestinal polypeptide or when only VPAC(1) receptors were activated. The PAC(1) and VPAC(2) receptor antagonist PACAP(6-38) had no cardiovascular effects, suggesting that PACAP is not tonically released. CONCLUSIONS AND IMPLICATIONS PACAP neurotransmission was not responsible for the moment-to-moment tonic regulation of central cardiovascular control mechanisms. Nevertheless, PACAP release within the spinal cord may have pleiotropic effects on sympathetic outflow depending on the postsynaptic receptor type. PAC(1) and VPAC receptor subtypes produced opposing changes in blood pressure when activated by intrathecal PACAP-38 in the anaesthetized Sprague-Dawley rat, resulting in no net change in MAP.
Collapse
Affiliation(s)
- Melissa A Inglott
- Australian School of Advanced Medicine, Macquarie University, Sydney, NSW, Australia
| | | | | | | |
Collapse
|
14
|
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] [What about the content of this article? (0)] [Affiliation(s)] [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.
Collapse
Affiliation(s)
- M M J Farnham
- Macquarie University, Sydney, New South Wales, Australia
| | | | | | | |
Collapse
|
15
|
Gaede AH, Inglott MA, Farnham MMJ, Pilowsky PM. Catestatin has an unexpected effect on the intrathecal actions of PACAP dramatically reducing blood pressure. Am J Physiol Regul Integr Comp Physiol 2012; 303:R719-26. [PMID: 22874427 DOI: 10.1152/ajpregu.00202.2012] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
This study focuses on presympathetic neurons of the rostral ventrolateral medulla (RVLM) that regulate sympathetic vasomotor tone. Many neurotransmitters are colocalized in RVLM neurons and are released under specific conditions to modulate efferent homeostatic responses. Of particular interest here are two peptides colocalized in catecholaminergic RVLM neurons: catestatin and pituitary adenylate cyclase-activating polypeptide (PACAP). Chromogranin A-derived catestatin is a potent endogenous noncompetitive nicotinic and adrenoreceptor antagonist. Catestatin impairs adenylate cyclase and phospholipase C action: mechanisms engaged by PACAP. Although PACAP and catestatin are likely coreleased, the possible effects of this are unknown. We aimed to determine whether catestatin affects the normal sympathoexcitatory but isotensive responses to intrathecal PACAP. Urethane-anesthetized, vagotomized, ventilated Sprague-Dawley rats (n = 22) were given an intrathecal injection of catestatin at different times prior to intrathecal administration of PACAP-38. Arterial pressure, splanchnic sympathetic nerve activity, heart rate, and reflex responses to baroreceptor and chemoreceptor activation were recorded. The key findings of this study are that pretreatment with catestatin time dependently enhances the PACAP-38 effect on mean arterial pressure and enhances sympathetic barosensitivity and chemosensitivity. The time-scale of the effect of catestatin on the response to PACAP-38 strongly suggests that catestatin is either causing changes in gene expression to exert its effects, or modifying intracellular mechanisms normally engaged by PAC(1) receptors. The ability of catestatin pretreatment to enhance barosensitivity and chemosensitivity after PACAP-38 injection supports the hypothesis that catestatin manipulates the intracellular environment within sympathetic neurons in a way that increases responses to PACAP.
Collapse
Affiliation(s)
- Andrea H Gaede
- The Australian School of Advanced Medicine, Macquarie Univ., Macquarie Park, NSW, Australia
| | | | | | | |
Collapse
|
16
|
Abstract
A critical function of cells is the maintenance of their genomic integrity. A family of phosphoinositide-3-kinase-related protein kinases, which includes ataxia telangiectasia mutated (ATM) and ataxia telangiectasia and Rad3 related (ATR) kinases, play key roles in sensing DNA damage. ATM and ATR were demonstrated in the cleavage stages of mouse embryo development. Genotoxic stress was imposed by exposure to ultraviolet (UV) radiation (causes DNA strand breaks) or cisplatin (causes strand cross-links). UV irradiation or cisplatin treatment of 2-cell embryos in the G(2) phase of the cell cycle caused DNA damage as defined by increased phosphorylation of the H2A histone family, member X (H2AFX; previously H2AX) variant. UV irradiation caused a stable G(2)-M arrest, and cisplatin treatment allowed progression through mitosis followed by activation of a G(1)-S checkpoint. Both checkpoints were transformation-related protein 53-independent. Caffeine (inhibits both ATM and ATR), but not KU55933 (ATM-selective inhibitor), reversed the G(2)-M block induced by UV, inferring a primary role for ATR in sensing this form of DNA damage. Caffeine and KU55933 were equally effective in reversing the cisplatin-induced G(1)-S block, implicating ATM as the primary sensing enzyme. Breaching of either checkpoint by treatment with caffeine or KU55933 allowed embryos to progress through several further cell cycles, yet none developed to blastocysts. The results show, to our knowledge for the first time, that the G(2)-M and G(1)-S cell-cycle checkpoints in the early embryo are differentially regulated by ATM and ATR in response to genotoxic stress and that they act as an initial point for containment of genomic damage. Under conditions of extensive or persistent DNA damage, the demise of the embryo is the ultimate method of protecting genomic integrity.
Collapse
Affiliation(s)
- X F Mu
- Human Reproduction Unit, Sydney Centre for Developmental and Regenerative Medicine, Kolling Institute of Medical Research, Sydney Medical School, University of Sydney, Sydney, New South Wales, Australia
| | | | | | | | | |
Collapse
|
17
|
Inglott MA, Farnham MMJ, Pilowsky PM. Intrathecal PACAP-38 causes prolonged widespread sympathoexcitation via a spinally mediated mechanism and increases in basal metabolic rate in anesthetized rat. Am J Physiol Heart Circ Physiol 2011; 300:H2300-7. [PMID: 21460201 DOI: 10.1152/ajpheart.01052.2010] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
The rostral ventrolateral medulla differentially regulates sympathetic output to different vascular beds, possibly through the release of various neurotransmitters and peptides that may include pituitary adenylate cyclase-activating polypeptide (PACAP). An intrathecal administration of PACAP increases splanchnic sympathetic nerve activity and heart rate, but not mean arterial blood pressure. The mechanism behind this response is unknown but may be due to a differential control of sympathetic outflows. In this study we sought 1) to investigate whether intrathecal PACAP differentially affects sympathetic outflow, 2) to determine whether the intrathecal responses to PACAP are solely due to a spinally mediated mechanism, and 3) to determine whether intrathecal PACAP affects metabolic function. Experiments using urethane-anesthetized, vagotomized, ventilated, and paralyzed adult male Sprague-Dawley rats were conducted in this study. Intrathecal injections of PACAP-38 were given, and mean arterial pressure, heart rate, the activity of regional sympathetic nerves, end-tidal CO(2), and core temperature were recorded. The novel findings of this study are that 1) intrathecal PACAP-38 causes a prolonged widespread sympathoexcitation in multiple sympathetic beds, 2) this widespread sympathoexcitation is mediated within the spinal cord itself since spinal transection does not abrogate the response, and 3) that intrathecal PACAP-38 increases basal metabolic rate. Therefore, we conclude that intrathecal PACAP acts in the spinal cord to cause a prolonged widespread sympathoexcitation and that PACAP also causes an increase in basal metabolic rate that includes an increase in brown adipose tissue thermogenesis in our rat preparation.
Collapse
Affiliation(s)
- Melissa A Inglott
- Australian School of Advanced Medicine, L1, F10A, Macquarie Univ., NSW 2109, Sydney, Australia
| | | | | |
Collapse
|
18
|
Farnham MMJ, Inglott MA, Pilowsky PM. Intrathecal PACAP-38 causes increases in sympathetic nerve activity and heart rate but not blood pressure in the spontaneously hypertensive rat. Am J Physiol Heart Circ Physiol 2010; 300:H214-22. [PMID: 20952662 DOI: 10.1152/ajpheart.00662.2010] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
The rostral ventrolateral medulla contains presympathetic neurons that project monosynaptically to sympathetic preganglionic neurons (SPN) in the spinal cord and are essential for the tonic and reflex control of the cardiovascular system. SPN directly innervate the adrenal medulla and, via postganglionic axons, affect the heart, kidneys, and blood vessels to alter sympathetic outflow and hence blood pressure. Over 80% of bulbospinal, catecholaminergic (C1) neurons contain pituitary adenylate cyclase-activating polypeptide (PACAP) mRNA. Activation of PACAP receptors with intrathecal infusion of PACAP-38 causes a robust, prolonged elevation in sympathetic tone. Given that a common feature of most forms of hypertension is elevated sympathetic tone, this study aimed to determine in the spontaneously hypertensive rat (SHR) and the Wistar Kyoto rat (normotensive control) 1) the proportion of C1 neurons containing PACAP mRNA and 2) responsiveness to intrathecal PACAP-38. We further investigated whether intrathecal infusion of the PACAP antagonist, PACAP(6-38), reduces the hypertension in the SHR. The principal findings are that 1) the proportion of PACAP mRNA-containing C1 neurons is not different between normotensive and hypertensive rats, 2) intrathecal PACAP-38 causes a strain-dependent, sustained sympathoexcitation and tachycardia with variable effects on mean arterial pressure in normotensive and hypertensive rats, and 3) PACAP(6-38) effectively attenuated the effects of intrathecal PACAP-38, but had no effect alone, on any baseline variables. This finding indicates that PACAP-38 is not tonically released in the spinal cord of rats. A role for PACAP in hypertension in conscious rats remains to be determined.
Collapse
Affiliation(s)
- Melissa M J Farnham
- Australian School of Advanced Medicine, Macquarie University, Sydney, New South Wales, Australia
| | | | | |
Collapse
|
19
|
McMullan S, Dick TE, Farnham MMJ, Pilowsky PM. Effects of baroreceptor activation on respiratory variability in rat. Respir Physiol Neurobiol 2009; 166:80-6. [PMID: 19429523 DOI: 10.1016/j.resp.2009.02.006] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2008] [Revised: 02/02/2009] [Accepted: 02/02/2009] [Indexed: 11/13/2022]
Abstract
Controversy surrounds the respiratory responses to baroreceptor activation. Although many reflexes that effect respiration (e.g. chemoreflexes and nociceptive reflexes) frequently affect cardiovascular parameters, the effect of baroreflex stimulation within normal physiological limits is generally considered to affect only blood pressure and heart rate. Even though previous authors have reported that baroreceptor activation can affect respiratory activity, the effects on respiratory frequency and amplitude are highly variable, and changes in perfusion evoked by blood pressure manipulation could account for the observed effects. Here, we determined the respiratory effects of activating arterial baroreceptors by intravenous injection of phenylephrine or angiotensin II, or by electrical stimulation of the aortic depressor nerve (ADN). In urethane-anesthetized vagotomized rats, 1, 2 and 4s trains of tetanic ADN stimulation evoked 3.1+/-1.1%, 11.2+/-13.6% and 21.9+/-8.9% increases in inspiratory (TI) time and 26.5+/-18%, 23.4+/-15.7% and 34.6+/-20.9% increases in expiratory (TE) time, respectively (P<0.05 in both cases), but no effect on the amplitude of bursts recorded in the phrenic nerve. Similar effects were observed following pressor trials evoked by intravenous PE (TE: +26.1+/-9.1%, P<0.01), but not Ang II. Intermittent ADN stimulation (single pulse, 1 Hz) significantly increased the variability of TI during periods of low respiratory drive (P<0.05) without significantly affecting any other parameters. We propose that a specific baroreceptor-respiratory response exists that is independent of changes in blood flow. In contrast to the effects of baroreceptor stimulation on sympathetic nerve activity, the baro-respiratory response is subtle and highly dependent on respiratory drive.
Collapse
Affiliation(s)
- Simon McMullan
- Australian School of Advanced Medicine, Macquarie University, 3 Innovation Road, Sydney, NSW 2109, Australia
| | | | | | | |
Collapse
|
20
|
Farnham MMJ, Li Q, Goodchild AK, Pilowsky PM. PACAP is expressed in sympathoexcitatory bulbospinal C1 neurons of the brain stem and increases sympathetic nerve activity in vivo. Am J Physiol Regul Integr Comp Physiol 2008; 294:R1304-11. [DOI: 10.1152/ajpregu.00753.2007] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
Pituitary adenylate cyclase-activating polypeptide (PACAP) is an excitatory neuropeptide present in the rat brain stem. The extent of its localization within catecholaminergic groups and bulbospinal sympathoexcitatory neurons is not established. Using immunohistochemistry and in situ hybridization, we determined the extent of any colocalization with catecholaminergic and/or bulbospinal projections from the brain stem was determined. PACAP mRNA was found in tyrosine hydroxylase-immunoreactive (TH-ir) neurons in the C1-C3 cell groups. In the rostral ventrolateral medulla (RVLM), PACAP mRNA was found in 84% of the TH-ir neurons and 82% of bulbospinal TH-ir neurons. The functional significance of these PACAP mRNA positive bulbospinal neurons was tested by intrathecal administration of PACAP-38 in anaesthetized rats. Splanchnic sympathetic nerve activity doubled (110%) and heart rate rose significantly (19%), although blood pressure was unaffected. In addition, as previously reported, PACAP was found in the A1 cell group but not in the A5 cell group or in the locus coeruleus. The RVLM is the primary site responsible for the tonic and reflex control of blood pressure through the activity of bulbospinal presympathetic neurons, the majority of which contain TH. The results indicate 1) that pontomedullary neurons containing both TH and PACAP that project to the intermediolateral cell column originate from C1-C3 and not A5, and 2) intrathecal PACAP-38 causes a prolonged, sympathoexcitatory effect.
Collapse
|