1
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MacMillan S, Burns DP, O'Halloran KD, Evans AM. SubSol-HIe is an AMPK-dependent hypoxia-responsive subnucleus of the nucleus tractus solitarius that coordinates the hypoxic ventilatory response and protects against apnoea in mice. Pflugers Arch 2024; 476:1087-1107. [PMID: 38635058 PMCID: PMC11166843 DOI: 10.1007/s00424-024-02957-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2023] [Revised: 03/24/2024] [Accepted: 03/31/2024] [Indexed: 04/19/2024]
Abstract
Functional magnetic resonance imaging (fMRI) suggests that the hypoxic ventilatory response is facilitated by the AMP-activated protein kinase (AMPK), not at the carotid bodies, but within a subnucleus (Bregma -7.5 to -7.1 mm) of the nucleus tractus solitarius that exhibits right-sided bilateral asymmetry. Here, we map this subnucleus using cFos expression as a surrogate for neuronal activation and mice in which the genes encoding the AMPK-α1 (Prkaa1) and AMPK-α2 (Prkaa2) catalytic subunits were deleted in catecholaminergic cells by Cre expression via the tyrosine hydroxylase promoter. Comparative analysis of brainstem sections, relative to controls, revealed that AMPK-α1/α2 deletion inhibited, with right-sided bilateral asymmetry, cFos expression in and thus activation of a neuronal cluster that partially spanned three interconnected anatomical nuclei adjacent to the area postrema: SolDL (Bregma -7.44 mm to -7.48 mm), SolDM (Bregma -7.44 mm to -7.48 mm) and SubP (Bregma -7.48 mm to -7.56 mm). This approximates the volume identified by fMRI. Moreover, these nuclei are known to be in receipt of carotid body afferent inputs, and catecholaminergic neurons of SubP and SolDL innervate aspects of the ventrolateral medulla responsible for respiratory rhythmogenesis. Accordingly, AMPK-α1/α2 deletion attenuated hypoxia-evoked increases in minute ventilation (normalised to metabolism), reductions in expiration time, and increases sigh frequency, but increased apnoea frequency during hypoxia. The metabolic response to hypoxia in AMPK-α1/α2 knockout mice and the brainstem and spinal cord catecholamine levels were equivalent to controls. We conclude that within the brainstem an AMPK-dependent, hypoxia-responsive subnucleus partially spans SubP, SolDM and SolDL, namely SubSol-HIe, and is critical to coordination of active expiration, the hypoxic ventilatory response and defence against apnoea.
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Affiliation(s)
- Sandy MacMillan
- Centre for Discovery Brain Sciences, College of Medicine and Veterinary Medicine, Hugh Robson Building, University of Edinburgh, Edinburgh, EH8 9XD, UK
| | - David P Burns
- Department of Physiology, School of Medicine, College of Medicine & Health, University College Cork, Cork, Ireland
| | - Ken D O'Halloran
- Department of Physiology, School of Medicine, College of Medicine & Health, University College Cork, Cork, Ireland
| | - A Mark Evans
- Centre for Discovery Brain Sciences, College of Medicine and Veterinary Medicine, Hugh Robson Building, University of Edinburgh, Edinburgh, EH8 9XD, UK.
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2
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Yang H, Tenorio Lopes L, Barioni NO, Roeske J, Incognito AV, Baker J, Raj SR, Wilson RJA. The molecular makeup of peripheral and central baroreceptors: stretching a role for Transient Receptor Potential (TRP), Epithelial Sodium Channel (ENaC), Acid Sensing Ion Channel (ASIC), and Piezo channels. Cardiovasc Res 2022; 118:3052-3070. [PMID: 34734981 DOI: 10.1093/cvr/cvab334] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/18/2021] [Revised: 09/27/2021] [Accepted: 10/29/2021] [Indexed: 12/16/2022] Open
Abstract
The autonomic nervous system maintains homeostasis of cardiovascular, respiratory, gastrointestinal, urinary, immune, and thermoregulatory function. Homeostasis involves a variety of feedback mechanisms involving peripheral afferents, many of which contain molecular receptors sensitive to mechanical deformation, termed mechanosensors. Here, we focus on the molecular identity of mechanosensors involved in the baroreflex control of the cardiovascular system. Located within the walls of the aortic arch and carotid sinuses, and/or astrocytes in the brain, these mechanosensors are essential for the rapid moment-to-moment feedback regulation of blood pressure (BP). Growing evidence suggests that these mechanosensors form a co-existing system of peripheral and central baroreflexes. Despite the importance of these molecules in cardiovascular disease and decades of research, their precise molecular identity remains elusive. The uncertainty surrounding the identity of these mechanosensors presents a major challenge in understanding basic baroreceptor function and has hindered the development of novel therapeutic targets for conditions with known arterial baroreflex impairments. Therefore, the purpose of this review is to (i) provide a brief overview of arterial and central baroreflex control of BP, (ii) review classes of ion channels currently proposed as the baroreflex mechanosensor, namely Transient Receptor Potential (TRP), Epithelial Sodium Channel (ENaC), Acid Sensing Ion Channel (ASIC), and Piezo, along with additional molecular candidates that serve mechanotransduction in other organ systems, and (iii) summarize the potential clinical implications of impaired baroreceptor function in the pathophysiology of cardiovascular disease.
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Affiliation(s)
- Hannah Yang
- Department of Physiology and Pharmacology, Cumming School of Medicine, University of Calgary, 3330 Hospital Dr. N.W., Calgary, AB T2N4N1, Canada.,Hotchkiss Brain Institute, Cumming School of Medicine, University of Calgary, 3330 Hospital Dr. N.W., Calgary, AB T2N4N1, Canada.,Alberta Children's Hospital Research Institute, Cumming School of Medicine, University of Calgary, 3330 Hospital Dr. N.W., Calgary, AB T2N4N1, Canada
| | - Luana Tenorio Lopes
- Department of Physiology and Pharmacology, Cumming School of Medicine, University of Calgary, 3330 Hospital Dr. N.W., Calgary, AB T2N4N1, Canada.,Hotchkiss Brain Institute, Cumming School of Medicine, University of Calgary, 3330 Hospital Dr. N.W., Calgary, AB T2N4N1, Canada.,Alberta Children's Hospital Research Institute, Cumming School of Medicine, University of Calgary, 3330 Hospital Dr. N.W., Calgary, AB T2N4N1, Canada
| | - Nicole O Barioni
- Department of Physiology and Pharmacology, Cumming School of Medicine, University of Calgary, 3330 Hospital Dr. N.W., Calgary, AB T2N4N1, Canada.,Hotchkiss Brain Institute, Cumming School of Medicine, University of Calgary, 3330 Hospital Dr. N.W., Calgary, AB T2N4N1, Canada.,Alberta Children's Hospital Research Institute, Cumming School of Medicine, University of Calgary, 3330 Hospital Dr. N.W., Calgary, AB T2N4N1, Canada
| | - Jamie Roeske
- Department of Physiology and Pharmacology, Cumming School of Medicine, University of Calgary, 3330 Hospital Dr. N.W., Calgary, AB T2N4N1, Canada.,Hotchkiss Brain Institute, Cumming School of Medicine, University of Calgary, 3330 Hospital Dr. N.W., Calgary, AB T2N4N1, Canada.,Alberta Children's Hospital Research Institute, Cumming School of Medicine, University of Calgary, 3330 Hospital Dr. N.W., Calgary, AB T2N4N1, Canada
| | - Anthony V Incognito
- Department of Physiology and Pharmacology, Cumming School of Medicine, University of Calgary, 3330 Hospital Dr. N.W., Calgary, AB T2N4N1, Canada.,Hotchkiss Brain Institute, Cumming School of Medicine, University of Calgary, 3330 Hospital Dr. N.W., Calgary, AB T2N4N1, Canada.,Alberta Children's Hospital Research Institute, Cumming School of Medicine, University of Calgary, 3330 Hospital Dr. N.W., Calgary, AB T2N4N1, Canada
| | - Jacquie Baker
- Department of Cardiac Sciences, Libin Cardiovascular Institute, Cumming School of Medicine, University of Calgary, 3330 Hospital Dr. N.W., Calgary, AB T2N4N1, Canada
| | - Satish R Raj
- Department of Cardiac Sciences, Libin Cardiovascular Institute, Cumming School of Medicine, University of Calgary, 3330 Hospital Dr. N.W., Calgary, AB T2N4N1, Canada
| | - Richard J A Wilson
- Department of Physiology and Pharmacology, Cumming School of Medicine, University of Calgary, 3330 Hospital Dr. N.W., Calgary, AB T2N4N1, Canada.,Hotchkiss Brain Institute, Cumming School of Medicine, University of Calgary, 3330 Hospital Dr. N.W., Calgary, AB T2N4N1, Canada.,Alberta Children's Hospital Research Institute, Cumming School of Medicine, University of Calgary, 3330 Hospital Dr. N.W., Calgary, AB T2N4N1, Canada
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3
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Elsaafien K, Harden SW, Johnson DN, Kimball AK, Sheng W, Smith JA, Scott KA, Frazier CJ, de Kloet AD, Krause EG. A Novel Organ-Specific Approach to Selectively Target Sensory Afferents Innervating the Aortic Arch. Front Physiol 2022; 13:841078. [PMID: 35399269 PMCID: PMC8987286 DOI: 10.3389/fphys.2022.841078] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2021] [Accepted: 02/16/2022] [Indexed: 12/02/2022] Open
Abstract
The brain maintains cardiovascular homeostasis, in part, via the arterial baroreflex which senses changes in blood pressure (BP) at the level of the aortic arch. Sensory afferents innervating the aortic arch employ baroreceptors to convert stretch exerted on the arterial wall into action potentials carried by the vagus nerve to second order neurons residing within the nucleus of the solitary tract (NTS). Although the baroreflex was described more than 80 years ago, the specific molecular, structural, and functional phenotype of the baroreceptors remain uncharacterized. This is due to the lack of tools that provide the genetic and target organ specificity that is required to selectively characterize baroreceptor afferents. Here, we use a novel approach to selectively target baroreceptors. Male mice on a C57BL/6J background were anesthetized with isoflurane, intubated, and artificially ventilated. Following sternotomy, the aortic arch was exposed, and a retrograde adeno-associated virus was applied to the aortic arch to direct the expression of channelrhoropsin-2 (ChR2) and/or tdTomato (tdTom) to sensory afferents presumably functioning as baroreceptors. Consistent with the structural characteristics of arterial baroreceptors, robust tdTom expression was observed in nerve endings surrounding the aortic arch, within the fibers of the aortic depressor and vagus nerves, cell bodies of the nodose ganglia (NDG), and neural projections to the caudal NTS (cNTS). Additionally, the tdTom labeled cell bodies within the NDG also expressed mRNAs coding for the mechanically gated ion channels, PIEZO-1 and PIEZO-2. In vitro electrophysiology revealed that pulses of blue light evoked excitatory post-synaptic currents in a subset of neurons within the cNTS, suggesting a functional connection between the labeled aortic arch sensory afferents and second order neurons. Finally, the in vivo optogenetic stimulation of the cell bodies of the baroreceptor expressing afferents in the NDG produced robust depressor responses. Together, these results establish a novel approach for selectively targeting sensory neurons innervating the aortic arch. This approach may be used to investigate arterial baroreceptors structurally and functionally, and to assess their role in the etiology or reversal of cardiovascular disease.
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Affiliation(s)
- Khalid Elsaafien
- Department of Pharmacodynamics, College of Pharmacy, University of Florida, Gainesville, FL, United States
- Center for Integrative Cardiovascular and Metabolic Diseases, University of Florida, Gainesville, FL, United States
| | - Scott W. Harden
- Department of Pharmacodynamics, College of Pharmacy, University of Florida, Gainesville, FL, United States
- Center for Integrative Cardiovascular and Metabolic Diseases, University of Florida, Gainesville, FL, United States
| | - Dominique N. Johnson
- Department of Physiology and Functional Genomics, College of Medicine, University of Florida, Gainesville, FL, United States
| | - Aecha K. Kimball
- Department of Physiology and Functional Genomics, College of Medicine, University of Florida, Gainesville, FL, United States
| | - Wanhui Sheng
- Department of Pharmacodynamics, College of Pharmacy, University of Florida, Gainesville, FL, United States
- Center for Integrative Cardiovascular and Metabolic Diseases, University of Florida, Gainesville, FL, United States
| | - Justin A. Smith
- Department of Pharmacodynamics, College of Pharmacy, University of Florida, Gainesville, FL, United States
| | - Karen A. Scott
- Department of Pharmacodynamics, College of Pharmacy, University of Florida, Gainesville, FL, United States
- Center for Integrative Cardiovascular and Metabolic Diseases, University of Florida, Gainesville, FL, United States
| | - Charles J. Frazier
- Department of Pharmacodynamics, College of Pharmacy, University of Florida, Gainesville, FL, United States
- Center for Integrative Cardiovascular and Metabolic Diseases, University of Florida, Gainesville, FL, United States
| | - Annette D. de Kloet
- Center for Integrative Cardiovascular and Metabolic Diseases, University of Florida, Gainesville, FL, United States
- Department of Physiology and Functional Genomics, College of Medicine, University of Florida, Gainesville, FL, United States
- Evelyn F. and William L. McKnight Brain Institute, University of Florida, Gainesville, FL, United States
- Annette D. de Kloet,
| | - Eric G. Krause
- Department of Pharmacodynamics, College of Pharmacy, University of Florida, Gainesville, FL, United States
- Center for Integrative Cardiovascular and Metabolic Diseases, University of Florida, Gainesville, FL, United States
- Evelyn F. and William L. McKnight Brain Institute, University of Florida, Gainesville, FL, United States
- *Correspondence: Eric G. Krause,
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4
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Norcliffe-Kaufmann L. Stress and the baroreflex. Auton Neurosci 2022; 238:102946. [PMID: 35086020 DOI: 10.1016/j.autneu.2022.102946] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2021] [Revised: 11/16/2021] [Accepted: 01/16/2022] [Indexed: 11/27/2022]
Abstract
The stress response to emotions elicits the release of glucocorticoids from the adrenal cortex, epinephrine from the adrenal medulla, and norepinephrine from the sympathetic nerves. The baroreflex adapts to buffer these responses to ensure that perfusion to the organs meets the demands while maintaining blood pressure within a within a narrow range. While stressor-evoked autonomic cardiovascular responses may be adaptive for the short-term, the recurrent exaggerated cardiovascular stress reactions can be maladaptive in the long-term. Prolonged stress or loss of the baroreflex's buffering capacity can predispose episodes of heightened sympathetic activity during stress leading to hypertension, tachycardia, and ventricular wall motion abnormalities. This review discusses 1) how the baroreflex responds to acute and chronic stressors, 2) how lesions in the neuronal pathways of the baroreflex alter the ability to respond or counteract the stress response, and 3) the techniques to assess baroreflex sensitivity and stress responses. Evidence suggests that loss of baroreflex sensitivity may predispose heightened autonomic responses to stress and at least in part explain the association between stress, mortality and cardiovascular diseases.
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5
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Li N, Guan Y, Tian YM, Ma HJ, Zhang X, Zhang Y, Wang S. Chronic Intermittent Hypobaric Hypoxia Ameliorates Renal Vascular Hypertension Through Up-regulating NOS in Nucleus Tractus Solitarii. Neurosci Bull 2019; 35:79-90. [PMID: 30617765 DOI: 10.1007/s12264-018-00330-z] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2018] [Accepted: 11/24/2018] [Indexed: 12/25/2022] Open
Abstract
Chronic intermittent hypobaric hypoxia (CIHH) is known to have an anti-hypertensive effect, which might be related to modulation of the baroreflex in rats with renal vascular hypertension (RVH). In this study, RVH was induced by the 2-kidney-1-clip method (2K1C) in adult male Sprague-Dawley rats. The rats were then treated with hypobaric hypoxia simulating 5000 m altitude for 6 h/day for 28 days. The arterial blood pressure (ABP), heart rate (HR), and renal sympathetic nerve activity (RSNA) were measured before and after microinjection of L-arginine into the nucleus tractus solitarii (NTS) in anesthetized rats. Evoked excitatory postsynaptic currents (eEPSCs) and spontaneous EPSCs (sEPSCs) were recorded in anterogradely-labeled NTS neurons receiving baroreceptor afferents. We measured the protein expression of neuronal nitric oxide synthase (nNOS) and endothelial NOS (eNOS) in the NTS. The results showed that the ABP in RVH rats was significantly lower after CIHH treatment. The inhibition of ABP, HR, and RSNA induced by L-arginine was less in RVH rats than in sham rats, and greater in the CIHH-treated RVH rats than the untreated RVH rats. The eEPSC amplitude in NTS neurons receiving baroreceptor afferents was lower in the RVH rats than in the sham rats and recovered after CIHH. The protein expression of nNOS and eNOS in the NTS was lower in the RVH rats than in the sham rats and this decrease was reversed by CIHH. In short, CIHH treatment decreases ABP in RVH rats via up-regulating NOS expression in the NTS.
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Affiliation(s)
- Na Li
- Department of Physiology, Hebei Medical University, Shijiazhuang, 050017, China.,Department of Physiology, Basic Medical College, Hebei University, Baoding, 071000, China
| | - Yue Guan
- Department of Physiology, Hebei Medical University, Shijiazhuang, 050017, China.,Hebei Collaborative Innovation Center for Cardio-cerebrovascular Disease, Shijiazhuang, 050000, China
| | - Yan-Ming Tian
- Department of Physiology, Hebei Medical University, Shijiazhuang, 050017, China.,Hebei Collaborative Innovation Center for Cardio-cerebrovascular Disease, Shijiazhuang, 050000, China
| | - Hui-Jie Ma
- Department of Physiology, Hebei Medical University, Shijiazhuang, 050017, China.,Hebei Collaborative Innovation Center for Cardio-cerebrovascular Disease, Shijiazhuang, 050000, China
| | - Xiangjian Zhang
- Hebei Collaborative Innovation Center for Cardio-cerebrovascular Disease, Shijiazhuang, 050000, China
| | - Yi Zhang
- Department of Physiology, Hebei Medical University, Shijiazhuang, 050017, China. .,Hebei Collaborative Innovation Center for Cardio-cerebrovascular Disease, Shijiazhuang, 050000, China.
| | - Sheng Wang
- Department of Physiology, Hebei Medical University, Shijiazhuang, 050017, China. .,Hebei Collaborative Innovation Center for Cardio-cerebrovascular Disease, Shijiazhuang, 050000, China.
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6
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Kim S, Kim SM, Oh B, Tak J, Yang E, Jin YH. Allopregnanolone Effects on Transmission in the Brain Stem Solitary Tract Nucleus (NTS). Neuroscience 2018; 379:219-227. [PMID: 29604384 DOI: 10.1016/j.neuroscience.2018.03.036] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/28/2017] [Revised: 03/20/2018] [Accepted: 03/21/2018] [Indexed: 10/17/2022]
Abstract
During pregnancy, the progesterone metabolite, allopregnanolone (ALLO), becomes elevated and has been associated with altered levels within the CNS and resulting changes in GABAA receptor function. Pregnant animals poorly compensate reflexes for a decrease in blood pressure during hemorrhage. Previous works suggested that ALLO decreases baroreflex responses by central actions, however, the underlying mechanisms are poorly understood. In this study, we tested ALLO actions on visceral afferent synaptic transmission at second-order neurons within medial portions of the nucleus tractus solitarius (NTS) using hindbrain slices from non-pregnant female rats. Solitary tract (ST) stimulation-evoked excitatory postsynaptic currents (ST-eEPSCs) in NTS neurons directly connected to vagal afferents within the ST. ST-eEPSCs were functionally identified as monosynaptic by the latency characteristics (low jitter = standard deviation of latency, ≤200 μs) to ST stimulation. Such second-order neurons all displayed spontaneous inhibitory postsynaptic currents (sIPSCs), and low micromolar concentrations of ALLO increased frequency and decay time. At submicromolar concentrations, ALLO induced a tonic, GABAergic inhibitory current and suppressed ST-eEPSCs' amplitude. While GABAA receptor antagonist, bicuculline, blocked all ALLO effects, gabazine only blocked sIPSC actions. In current-clamp mode, ALLO perfusion increased failure of ST stimulation to trigger action potentials in most neurons. Thus, our results indicate that ALLO acts to suppress visceral afferent ST synaptic transmission at first synapses by activating pharmacologically distinct GABAA subtypes at different concentration ranges. This ALLO-mediated attenuated visceral afferent signal integration in NTS may underlie reflex changes in blood pressure during gestation.
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Affiliation(s)
- Sojin Kim
- Department of Physiology, College of Medicine, Kyung Hee University, Seoul 02447, Republic of Korea
| | - Sung-Moon Kim
- Department of Biochemistry and Molecular Biology, College of Medicine, Kyung Hee University, Seoul 02447, Republic of Korea
| | - Bermseok Oh
- Department of Biochemistry and Molecular Biology, College of Medicine, Kyung Hee University, Seoul 02447, Republic of Korea
| | - Jihoon Tak
- Department of Biochemistry and Molecular Biology, College of Medicine, Kyung Hee University, Seoul 02447, Republic of Korea
| | - Eunhee Yang
- Department of Biomedical Science, Graduate School, Kyung Hee University, Republic of Korea
| | - Young-Ho Jin
- Department of Physiology, College of Medicine, Kyung Hee University, Seoul 02447, Republic of Korea.
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7
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Carter DA, Guo H, Connelly AA, Bassi JK, Fong AY, Allen AM, McDougall SJ. Viscerosensory input drives angiotensin II type 1A receptor-expressing neurons in the solitary tract nucleus. Am J Physiol Regul Integr Comp Physiol 2017; 314:R282-R293. [PMID: 29118020 DOI: 10.1152/ajpregu.00290.2017] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Homeostatic regulation of visceral organ function requires integrated processing of neural and neurohormonal sensory signals. The nucleus of the solitary tract (NTS) is the primary sensory nucleus for cranial visceral sensory afferents. Angiotensin II (ANG II) is known to modulate peripheral visceral reflexes, in part, by activating ANG II type 1A receptors (AT1AR) in the NTS. AT1AR-expressing NTS neurons occur throughout the NTS with a defined subnuclear distribution, and most of these neurons are depolarized by ANG II. In this study we determined whether AT1AR-expressing NTS neurons receive direct visceral sensory input, and whether this input is modulated by ANG II. Using AT1AR-GFP mice to make targeted whole cell recordings from AT1AR-expressing NTS neurons, we demonstrate that two-thirds (37 of 56) of AT1AR-expressing neurons receive direct excitatory, visceral sensory input. In half of the neurons tested (4 of 8) the excitatory visceral sensory input was significantly reduced by application of the transient receptor potential vallinoid type 1 receptor agonist, capsaicin, indicating AT1AR-expressing neurons can receive either C- or A-fiber-mediated input. Application of ANG II to a subset of second-order AT1AR-expressing neurons did not affect spontaneous, evoked, or asynchronous glutamate release from visceral sensory afferents. Thus it is unlikely that AT1AR-expressing viscerosensory neurons terminate on AT1AR-expressing NTS neurons. Our data suggest that ANG II is likely to modulate multiple visceral sensory modalities by altering the excitability of second-order AT1AR-expressing NTS neurons.
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Affiliation(s)
- D A Carter
- Department of Physiology, The University of Melbourne , Victoria , Australia
| | - H Guo
- Florey Institute of Neuroscience and Mental Health, The University of Melbourne , Victoria , Australia
| | - A A Connelly
- Department of Physiology, The University of Melbourne , Victoria , Australia
| | - J K Bassi
- Department of Physiology, The University of Melbourne , Victoria , Australia
| | - A Y Fong
- Department of Physiology, The University of Melbourne , Victoria , Australia
| | - A M Allen
- Department of Physiology, The University of Melbourne , Victoria , Australia.,Florey Institute of Neuroscience and Mental Health, The University of Melbourne , Victoria , Australia
| | - S J McDougall
- Florey Institute of Neuroscience and Mental Health, The University of Melbourne , Victoria , Australia
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8
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L-DOPA inhibits excitatory synaptic transmission in the rat nucleus tractus solitarius through release of dopamine. Neuroscience 2017; 360:18-27. [PMID: 28757247 DOI: 10.1016/j.neuroscience.2017.07.043] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2017] [Revised: 07/18/2017] [Accepted: 07/19/2017] [Indexed: 12/29/2022]
Abstract
The mode of action of L-DOPA on excitatory synaptic transmission in second-order neurons of the nucleus tractus solitarius (NTS) was studied using the rat brainstem slices. Superfusion of L-DOPA (10μM) reduced the frequency of miniature excitatory postsynaptic currents (mEPSCs) without any effect on the amplitude. A low concentration (1μM) was ineffective on the mEPSCs, and the highest concentration (100μM) exerted a stronger inhibitory effect. L-DOPA (10μM) decreased the amplitude of EPSCs (eEPSCs) evoked by electrical stimulation of the tractus solitarius and increased the paired-pulse ratio. The inhibitory effects of L-DOPA on mEPSCs and eEPSCs were similar to those of dopamine (100μM). The effects of L-DOPA were blocked by a competitive antagonist, L-DOPA methyl ester (100μM) and also by a D2 receptor antagonist, sulpiride (10μM), while those of dopamine were blocked by the latter but not by the former. In reserpine (5mg/kg, s.c.)-treated rats, the effects of L-DOPA on both mEPSCs and eEPSCs were completely abolished, but those of dopamine remained unchanged. The present results suggest a possibility that L-DOPA may induce the release of dopamine from the axon terminals in the NTS and the released dopamine suppresses the glutamatergic transmission through activation of the presynaptic D2 receptors.
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9
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Beaumont E, Campbell RP, Andresen MC, Scofield S, Singh K, Libbus I, KenKnight BH, Snyder L, Cantrell N. Cervical vagus nerve stimulation augments spontaneous discharge in second- and higher-order sensory neurons in the rat nucleus of the solitary tract. Am J Physiol Heart Circ Physiol 2017; 313:H354-H367. [PMID: 28476920 DOI: 10.1152/ajpheart.00070.2017] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/03/2017] [Revised: 05/01/2017] [Accepted: 05/01/2017] [Indexed: 02/07/2023]
Abstract
Vagus nerve stimulation (VNS) currently treats patients with drug-resistant epilepsy, depression, and heart failure. The mild intensities used in chronic VNS suggest that primary visceral afferents and central nervous system activation are involved. Here, we measured the activity of neurons in the nucleus of the solitary tract (NTS) in anesthetized rats using clinically styled VNS. Our chief findings indicate that VNS at threshold bradycardic intensity activated NTS neuron discharge in one-third of NTS neurons. This VNS directly activated only myelinated vagal afferents projecting to second-order NTS neurons. Most VNS-induced activity in NTS, however, was unsynchronized to vagal stimuli. Thus, VNS activated unsynchronized activity in NTS neurons that were second order to vagal afferent C-fibers as well as higher-order NTS neurons only polysynaptically activated by the vagus. Overall, cardiovascular-sensitive and -insensitive NTS neurons were similarly activated by VNS: 3/4 neurons with monosynaptic vagal A-fiber afferents, 6/42 neurons with monosynaptic vagal C-fiber afferents, and 16/21 polysynaptic NTS neurons. Provocatively, vagal A-fibers indirectly activated C-fiber neurons during VNS. Elevated spontaneous spiking was quantitatively much higher than synchronized activity and extended well into the periods of nonstimulation. Surprisingly, many polysynaptic NTS neurons responded to half the bradycardic intensity used in clinical studies, indicating that a subset of myelinated vagal afferents is sufficient to evoke VNS indirect activation. Our study uncovered a myelinated vagal afferent drive that indirectly activates NTS neurons and thus central pathways beyond NTS and support reconsideration of brain contributions of vagal afferents underpinning of therapeutic impacts.NEW & NOTEWORTHY Acute vagus nerve stimulation elevated activity in neurons located in the medial nucleus of the solitary tract. Such stimuli directly activated only myelinated vagal afferents but indirectly activated a subpopulation of second- and higher-order neurons, suggesting that afferent mechanisms and central neuron activation may be responsible for vagus nerve stimulation efficacy.
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Affiliation(s)
- Eric Beaumont
- Department of Biomedical Sciences, Quillen College of Medicine, East Tennessee State University, Johnson City, Tennessee;
| | - Regenia P Campbell
- Department of Biomedical Sciences, Quillen College of Medicine, East Tennessee State University, Johnson City, Tennessee
| | | | - Stephanie Scofield
- Department of Biomedical Sciences, Quillen College of Medicine, East Tennessee State University, Johnson City, Tennessee
| | - Krishna Singh
- Department of Biomedical Sciences, Quillen College of Medicine, East Tennessee State University, Johnson City, Tennessee.,James H. Quillen Veterans Affairs Medical Center, Johnson City, Tennessee; and
| | | | | | - Logan Snyder
- Department of Biomedical Sciences, Quillen College of Medicine, East Tennessee State University, Johnson City, Tennessee
| | - Nathan Cantrell
- Department of Biomedical Sciences, Quillen College of Medicine, East Tennessee State University, Johnson City, Tennessee
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10
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McDougall SJ, Guo H, Andresen MC. Dedicated C-fibre viscerosensory pathways to central nucleus of the amygdala. J Physiol 2016; 595:901-917. [PMID: 27616729 DOI: 10.1113/jp272898] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2016] [Accepted: 09/01/2016] [Indexed: 11/08/2022] Open
Abstract
KEY POINTS Emotions are accompanied by concordant changes in visceral function, including cardiac output, respiration and digestion. One major forebrain integrator of emotional responses, the amygdala, is considered to rely on embedded visceral afferent information, although few details are known. In the present study, we retrogradely transported dye from the central nucleus of the amygdala (CeA) to identify CeA-projecting nucleus of the solitary tract (NTS) neurons for synaptic characterization and compared them with unlabelled, near-neighboor NTS neurons. Solitary tract (ST) afferents converged onto NTS-CeA second-order sensory neurons in greater numbers, as well as indirectly via polysynaptic pathways. Unexpectedly, all mono- and polysynaptic ST afferent pathways to NTS-CeA neurons were organized exclusively as either transient receptor potential cation channel subfamily V member 1 (TRPV1)-sensitive or TRPV1-resistant, regardless of whether intervening neurons were excitatory or inhibitory. This strict sorting provides viscerosensory signals to CeA about visceral conditions with respect to being either 'normal' via A-fibres or 'alarm' via TRPV1 expressing C-fibres and, accordingly, this pathway organization probably encodes interoceptive status. ABSTRACT Emotional state is impacted by changes in visceral function, including blood pressure, breathing and digestion. A main line of viscerosensory information processing occurs first in the nucleus of the solitary tract (NTS). In the present study conducted in rats, we examined the synaptic characteristics of visceral afferent pathways to the central nucleus of the amygdala (CeA) in brainstem slices by recording from retrogradely labelled NTS projection neurons. We simultaneously recorded neuron pairs: one dye positive (i.e. NTS-CeA) and a second unlabelled neighbour. Graded shocks to the solitary tract (ST) always (93%) triggered EPSCs at CeA projecting NTS neurons. Half of the NTS-CeA neurons received at least one primary afferent input (classed 'second order') indicating that viscerosensory information arrives at the CeA conveyed via a pathway involving as few as two synapses. The remaining NTS-CeA neurons received viscerosensory input only via polysynaptic pathways. By contrast, ∼3/4 of unlabelled neighbouring neurons were directly connected to ST. NTS-CeA neurons received greater numbers of ST-related inputs compared to unlabelled NTS neurons, indicating that highly convergent viscerosensory signals reach the CeA. Remarkably, despite multifibre convergence, all single NTS-CeA neurons received inputs derived from only unmyelinated afferents [transient receptor potential cation channel subfamily V member 1 (TRPV1) expressing C-fibres] or only non-TRPV1 ST afferent inputs, and never a combination of both. Such segregation means that visceral afferent information followed separate lines to reach the CeA. Their very different physiological activation profiles mean that these parallel visceral afferent pathways encode viscerosensory signals to the amygdala that may provide interoceptive assessments to impact on behaviours.
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Affiliation(s)
- Stuart J McDougall
- Department of Physiology & Pharmacology, Oregon Health & Science University, Portland, OR, USA.,Florey Institute of Neuroscience and Mental Health, University of Melbourne, Parkville, VIC, Australia
| | - Haoyao Guo
- Florey Institute of Neuroscience and Mental Health, University of Melbourne, Parkville, VIC, Australia
| | - Michael C Andresen
- Department of Physiology & Pharmacology, Oregon Health & Science University, Portland, OR, USA
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Major Autonomic Neuroregulatory Pathways Underlying Short- and Long-Term Control of Cardiovascular Function. Curr Hypertens Rep 2016; 18:18. [DOI: 10.1007/s11906-016-0625-x] [Citation(s) in RCA: 36] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
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12
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Enhanced Firing in NTS Induced by Short-Term Sustained Hypoxia Is Modulated by Glia-Neuron Interaction. J Neurosci 2015; 35:6903-17. [PMID: 25926465 DOI: 10.1523/jneurosci.4598-14.2015] [Citation(s) in RCA: 43] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
Humans ascending to high altitudes are submitted to sustained hypoxia (SH), activating peripheral chemoreflex with several autonomic and respiratory responses. Here we analyzed the effect of short-term SH (24 h, FIO210%) on the processing of cardiovascular and respiratory reflexes using an in situ preparation of rats. SH increased both the sympatho-inhibitory and bradycardiac components of baroreflex and the sympathetic and respiratory responses of peripheral chemoreflex. Electrophysiological properties and synaptic transmission in the nucleus tractus solitarius (NTS) neurons, the first synaptic station of afferents of baroreflexes and chemoreflexes, were evaluated using brainstem slices and whole-cell patch-clamp. The second-order NTS neurons were identified by previous application of fluorescent tracer onto carotid body for chemoreceptor afferents or onto aortic depressor nerve for baroreceptor afferents. SH increased the intrinsic excitability of NTS neurons. Delayed excitation, caused by A-type potassium current (IKA), was observed in most of NTS neurons from control rats. The IKA amplitude was higher in identified second-order NTS neurons from control than in SH rats. SH also blunted the astrocytic inhibition of IKA in NTS neurons and increased the synaptic transmission in response to afferent fibers stimulation. The frequency of spontaneous excitatory currents was also increased in neurons from SH rats, indicating that SH increased the neurotransmission by presynaptic mechanisms. Therefore, short-term SH changed the glia-neuron interaction, increasing the excitability and excitatory transmission of NTS neurons, which may contribute to the observed increase in the reflex sensitivity of baroreflex and chemoreflex in in situ preparation.
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Li DP, Chen SR. Nitric oxide stimulates glutamatergic synaptic inputs to baroreceptor neurons through potentiation of Cav2.2-mediated Ca(2+) currents. Neurosci Lett 2014; 567:57-62. [PMID: 24686191 DOI: 10.1016/j.neulet.2014.03.036] [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: 01/19/2014] [Accepted: 03/06/2014] [Indexed: 11/27/2022]
Abstract
Nitric oxide (NO) increases glutamate release to the second-order neurons in the nucleus tractus solitarius (NTS). N-type Ca(2+) channel is essential for triggering glutamate release at synaptic terminals. In this study, we determined the role of Cav2.2 subunit in NO-induced increase in glutamate synaptic inputs to NTS neurons. The second-order NTS neurons and nodose ganglionic (NG) neurons were identified by applying DiA, a fluorescent lipophilic tracer, on aortic depressor nerve in rats. NO donor DEA/NO significantly increased tractus solitarius (TS)-evoked excitatory postsynaptic currents (EPSCs) in second-order NTS neurons, an effect was abolished by pretreatment of slice with ODQ, an inhibitor for soluble isoform of guanylyl cyclase. DEA/NO decreased the paired-pulse ratio of TS-evoked EPSCs, while increased the frequency, but not the amplitude, of miniature EPSCs in second-order NTS neurons. Furthermore, DEA/NO significantly increased Ba(2+) currents in identified baroreceptor NG neurons. However, DEA/NO had little effect on the Ba(2+) currents in the presence of specific N-type Ca(2+) blocker ω-conotoxin GVIA. In addition, immunocytochemistry staining revealed that Cav2.2 subunit immunoreactivates were colocalized with DiA-labeled baroreceptor nerve terminals in the NTS. Collectively, these findings suggest that NO stimulates glutamatergic synaptic inputs to second-order NTS neurons through augmentation of Cav2.2-mediated N-type Ca(2+) currents.
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Affiliation(s)
- De-Pei Li
- Department of Critical Care, The University of Texas M. D. Anderson Cancer Center, Houston, TX 77030, USA.
| | - Shao-Rui Chen
- Department of Anesthesiology and Perioperative Medicine, The University of Texas M. D. Anderson Cancer Center, Houston, TX 77030, USA
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Li YL. Angiotensin II-Superoxide Signaling and Arterial Baroreceptor Function in Type-1 Diabetes Mellitus. JOURNAL OF DIABETES & METABOLISM 2014; Suppl 12:1-6. [PMID: 24567847 DOI: 10.4172/2155-6156.s12-001] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
Diabetes is a major world health problem. Growing evidence from both clinical trials and animal experiments has clearly confirmed that arterial baroreflex dysfunction is a feature of type 1 diabetes, which links to prognosis and mortality of the type 1 diabetic patients. The arterial baroreflex normally regulates the blood pressure and heart rate through sensing changes of arterial vascular tension by the arterial baroreceptors in the aortic arch and carotid sinus. The aortic baroreceptor neuron located in the nodose ganglia is a primary afferent component of the arterial baroreflex. The functional changes of these neurons are involved in the arterial baroreflex dysfunction in the type 1 diabetes. Type 1 diabetes causes the overexpression and hyperactivation of hyperpolarization-activated cyclic nucleotide-gated (HCN) channels and further reduces cell excitability of the aortic baroreceptor neurons. The alterations of the HCN channels are regulated by angiotensin II-NADPH oxidase-superoxide signaling in the aortic baroreceptor neurons. From the present review, we can understand the possible mechanisms responsible for the attenuated arterial baroreflex in the type 1 diabetes. These findings are beneficial for improving quality of life and prognosis in patients with the type 1 diabetes mellitus.
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Affiliation(s)
- Yu-Long Li
- Department of Emergency Medicine, University of Nebraska Medical Center, USA
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Sekizawa SI, Horwitz BA, Horowitz JM, Chen CY. Protection of signal processing at low temperature in baroreceptive neurons in the nucleus tractus solitarius of Syrian hamsters, a hibernating species. Am J Physiol Regul Integr Comp Physiol 2013; 305:R1153-62. [PMID: 24068050 DOI: 10.1152/ajpregu.00165.2013] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
We previously described synaptic currents between baroreceptor fibers and second-order neurons in the nucleus tractus solitarius (NTS) that were larger in Syrian hamsters than in rats. This suggested that although electrical activity throughout the hamster brain decreased as brain temperature declined, the greater synaptic input to its NTS would support continued operation of cardiorespiratory reflexes at low body temperatures. Here, we focused on properties that would protect these neurons against potential damage from the larger synaptic inputs, testing the hypotheses that hamster NTS neurons exhibit: 1) intrinsic N-methyl-D-aspartate receptor (NMDAR) properties that limit Ca(2+) influx to a greater degree than do rat NTS neurons and 2) properties that reduce gating signals to NMDARs to a greater degree than in rat NTS neurons. Whole cell patch-clamp recordings on anatomically identified second-order NTS baroreceptive neurons showed that NMDAR-mediated synaptic currents between sensory fibers and second-order NTS neurons were larger in hamsters than in rats at 33°C and 15°C, with no difference in their permeability to Ca(2+). However, at 15°C, but not at 33°C, non-NMDAR currents evoked by glutamate released from baroreceptor fibers had significantly shorter durations in hamsters than in rats. Thus, hamster NMDARs did not exhibit lower Ca(2+) influx than did rats (negating hypothesis 1), but they did exhibit significant differences in non-NMDAR neuronal properties at low temperature (consistent with hypothesis 2). The latter (shorter duration of non-NMDAR currents) would likely limit NMDAR coincidence gating and may help protect hamster NTS neurons, enabling them to contribute to signal processing at low body temperatures.
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Accorsi-Mendonça D, Machado BH. Synaptic transmission of baro- and chemoreceptors afferents in the NTS second order neurons. Auton Neurosci 2013; 175:3-8. [DOI: 10.1016/j.autneu.2012.12.002] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2012] [Revised: 11/17/2012] [Accepted: 12/03/2012] [Indexed: 12/17/2022]
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Andresen MC, Fawley JA, Hofmann ME. Peptide and lipid modulation of glutamatergic afferent synaptic transmission in the solitary tract nucleus. Front Neurosci 2013; 6:191. [PMID: 23335875 PMCID: PMC3541483 DOI: 10.3389/fnins.2012.00191] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2012] [Accepted: 12/17/2012] [Indexed: 12/21/2022] Open
Abstract
The brainstem nucleus of the solitary tract (NTS) holds the first central neurons in major homeostatic reflex pathways. These homeostatic reflexes regulate and coordinate multiple organ systems from gastrointestinal to cardiopulmonary functions. The core of many of these pathways arise from cranial visceral afferent neurons that enter the brain as the solitary tract (ST) with more than two-thirds arising from the gastrointestinal system. About one quarter of ST afferents have myelinated axons but the majority are classed as unmyelinated C-fibers. All ST afferents release the fast neurotransmitter glutamate with remarkably similar, high-probability release characteristics. Second order NTS neurons receive surprisingly limited primary afferent information with one or two individual inputs converging on single second order NTS neurons. A- and C-fiber afferents never mix at NTS second order neurons. Many transmitters modify the basic glutamatergic excitatory postsynaptic current often by reducing glutamate release or interrupting terminal depolarization. Thus, a distinguishing feature of ST transmission is presynaptic expression of G-protein coupled receptors for peptides common to peripheral or forebrain (e.g., hypothalamus) neuron sources. Presynaptic receptors for angiotensin (AT1), vasopressin (V1a), oxytocin, opioid (MOR), ghrelin (GHSR1), and cholecystokinin differentially control glutamate release on particular subsets of neurons with most other ST afferents unaffected. Lastly, lipid-like signals are transduced by two key ST presynaptic receptors, the transient receptor potential vanilloid type 1 and the cannabinoid receptor that oppositely control glutamate release. Increasing evidence suggests that peripheral nervous signaling mechanisms are repurposed at central terminals to control excitation and are major sites of signal integration of peripheral and central inputs particularly from the hypothalamus.
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Affiliation(s)
- Michael C Andresen
- Department of Physiology and Pharmacology, Oregon Health and Science University Portland, OR, USA
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Schild JH, Kunze DL. Differential distribution of voltage-gated channels in myelinated and unmyelinated baroreceptor afferents. Auton Neurosci 2012; 172:4-12. [DOI: 10.1016/j.autneu.2012.10.014] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
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McDougall SJ, Andresen MC. Independent transmission of convergent visceral primary afferents in the solitary tract nucleus. J Neurophysiol 2012; 109:507-17. [PMID: 23114206 DOI: 10.1152/jn.00726.2012] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Cranial primary afferents from the viscera enter the brain at the solitary tract nucleus (NTS), where their information is integrated for homeostatic reflexes. The organization of sensory inputs is poorly understood, despite its critical impact on overall reflex performance characteristics. Single afferents from the solitary tract (ST) branch within NTS and make multiple contacts onto individual neurons. Many neurons receive more than one ST input. To assess the potential interaction between converging afferents and proximal branching near to second-order neurons, we probed near the recorded soma in horizontal slices from rats with focal electrodes and minimal shocks. Remote ST shocks evoked monosynaptic excitatory postsynaptic currents (EPSCs), and nearby focal shocks also activated monosynaptic EPSCs. We tested the timing and order of stimulation to determine whether focal shocks influenced ST responses and vice versa in single neurons. Focal-evoked EPSC response profiles closely resembled ST-EPSC characteristics. Mean synaptic jitters, failure rates, depression, and phenotypic segregation by capsaicin responsiveness were indistinguishable between focal and ST-evoked EPSCs. ST-EPSCs failed to affect focal-EPSCs within neurons, indicating that release sites and synaptic terminals were functionally independent and isolated from cross talk or neurotransmitter overflow. In only one instance, focal shocks intercepted and depleted the ST axon generating evoked EPSCs. Despite large numbers of functional contacts, multiple afferents do not appear to interact, and ST axon branches may be limited to close to the soma. Thus single or multiple primary afferents and their presynaptic active release sites act independently when they contact single second-order NTS neurons.
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Affiliation(s)
- Stuart J McDougall
- Department of Physiology and Pharmacology, Oregon Health and Science University, Portland, Oregon, USA.
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Accorsi-Mendonça D, Castania J, Bonagamba L, Machado B, Leão R. Synaptic profile of nucleus tractus solitarius neurons involved with the peripheral chemoreflex pathways. Neuroscience 2011; 197:107-20. [DOI: 10.1016/j.neuroscience.2011.08.054] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2011] [Revised: 08/22/2011] [Accepted: 08/24/2011] [Indexed: 10/17/2022]
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Heterosynaptic crosstalk: GABA-glutamate metabotropic receptors interactively control glutamate release in solitary tract nucleus. Neuroscience 2010; 174:1-9. [PMID: 21129447 DOI: 10.1016/j.neuroscience.2010.11.053] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/09/2010] [Revised: 11/12/2010] [Accepted: 11/24/2010] [Indexed: 11/22/2022]
Abstract
Synaptic terminals often contain metabotropic receptors that act as autoreceptors to control neurotransmitter release. Less appreciated is the heterosynaptic crossover of glutamate receptors to control GABA release and vice versa GABA receptors which control glutamate release. In the brainstem, activation of solitary tract (ST) afferents releases glutamate onto second-order neurons within the solitary tract nucleus (NTS). Multiple metabotropic receptors are expressed in NTS for glutamate (mGluRs) and for GABA (GABA(B)). The present report identifies mGluR regulation of glutamate release at second and higher order sensory neurons in NTS slices. We found strong inhibition of glutamate release to group II and III mGluR activation on mechanically isolated NTS neurons. However, the same mGluR-selective antagonists paradoxically decreased glutamate release (miniature, mEPSCs) at identified second-order NTS neurons. Unaltered amplitudes were consistent with selective presynaptic mGluR actions. GABA(B) blockade in slices resolved the paradoxical differences and revealed a group II/III mGluR negative feedback of mEPSC frequency similar to isolated neurons. Thus, the balance of glutamate control is tipped by mGluR receptors on GABA terminals resulting in predominating heterosynaptic GABA(B) inhibition of glutamate release. Regulation by mGluR or GABA(B) was not consistently evident in excitatory postsynaptic currents (EPSCs) in higher-order NTS neurons demonstrating metabotropic receptor distinctions in processing at different NTS pathway stages. These cellular localizations may figure importantly in understanding interventions such as brain-penetrant compounds or microinjections. We conclude that afferent glutamate release in NTS produces a coordinate presynaptic activation of co-localized mGluR and GABA(B) feedback on cranial afferent terminals to regulate glutamate release.
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Hisadome K, Reimann F, Gribble FM, Trapp S. Leptin directly depolarizes preproglucagon neurons in the nucleus tractus solitarius: electrical properties of glucagon-like Peptide 1 neurons. Diabetes 2010; 59:1890-8. [PMID: 20522593 PMCID: PMC2911066 DOI: 10.2337/db10-0128] [Citation(s) in RCA: 117] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/26/2010] [Accepted: 05/14/2010] [Indexed: 02/01/2023]
Abstract
OBJECTIVE Glucagon-like peptide (GLP)-1 inhibits food intake, acting both in the periphery and within the central nervous system. It is unclear if gut-derived GLP-1 can enter the brain, or whether GLP-1 from preproglucagon (PPG) cells in the lower brainstem is required to activate central GLP-1 receptors. Brainstem PPG neurons, however, have been poorly characterized, due to the difficulties in identifying these cells while viable. This study provides data on the electrical properties of brainstem PPG cells and their regulation by orexigenic and anorexigenic peptides. RESEARCH DESIGN AND METHODS Transgenic mice expressing Venus under control of the PPG promoter were used to identify PPG neurons in vitro in brainstem slice preparations for electrophysiological recordings. RESULTS The majority of PPG neurons were spontaneously active. Further electrical and molecular characterization revealed that GLP-1 receptor activation had no pre- or postsynaptic effect and that PPG neurons lack GLP-1 receptors. Similarly, they were unresponsive to PYY and ghrelin. In contrast, leptin rapidly and reversibly depolarized these neurons. Responses to electrical stimulation of the solitary tract suggest that PPG cells are mostly second-order neurons, receiving direct input from vagal afferent fibers. Both evoked and spontaneous excitatory postsynaptic currents were predominantly glutamatergic. CONCLUSIONS The study introduces PPG-promoter-Venus transgenic mice as a viable and important tool to study brainstem PPG cells. PPG neuron activity is directly modulated by leptin but was unaffected by other satiety or hunger peptides. Direct synaptic input from the solitary tract suggests that peripheral signals (including GLP-1) could modulate PPG cells via vagal afferents.
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Affiliation(s)
- Kazunari Hisadome
- Department of Surgery and Cancer, Imperial College London, London, U.K
- Biophysics Section, Blackett Laboratory, Imperial College London, London, U.K
| | - Frank Reimann
- Cambridge Institute for Medical Research, University of Cambridge, Cambridge, U.K
| | - Fiona M. Gribble
- Cambridge Institute for Medical Research, University of Cambridge, Cambridge, U.K
| | - Stefan Trapp
- Department of Surgery and Cancer, Imperial College London, London, U.K
- Biophysics Section, Blackett Laboratory, Imperial College London, London, U.K
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Exogenous brain-derived neurotrophic factor rescues synaptic dysfunction in Mecp2-null mice. J Neurosci 2010; 30:5303-10. [PMID: 20392952 DOI: 10.1523/jneurosci.5503-09.2010] [Citation(s) in RCA: 154] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Postnatal deficits in brain-derived neurotrophic factor (BDNF) are thought to contribute to pathogenesis of Rett syndrome (RTT), a progressive neurodevelopmental disorder caused by mutations in the gene encoding methyl-CpG-binding protein 2 (MeCP2). In Mecp2-null mice, a model of RTT, BDNF deficits are most pronounced in structures important for autonomic and respiratory control, functions that are severely affected in RTT patients. However, relatively little is known about how these deficits affect neuronal function or how they may be linked to specific RTT endophenotypes. To approach these issues, we analyzed synaptic function in the brainstem nucleus tractus solitarius (nTS), the principal site for integration of primary visceral afferent inputs to central autonomic pathways and a region in which we found markedly reduced levels of BDNF in Mecp2 mutants. Our results demonstrate that the amplitude of spontaneous miniature and evoked EPSCs in nTS neurons is significantly increased in Mecp2-null mice and, accordingly, that mutant cells are more likely than wild- type cells to fire action potentials in response to primary afferent stimulation. These changes occur without any increase in intrinsic neuronal excitability and are unaffected by blockade of inhibitory GABA currents. However, this synaptopathy is associated with decreased BDNF availability in the primary afferent pathway and can be rescued by application of exogenous BDNF. On the basis of these findings, we hypothesize that altered sensory gating in nTS contributes to cardiorespiratory instability in RTT and that nTS is a site at which restoration of normal BDNF signaling could help reestablish normal homeostatic controls.
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Zhang W, Mifflin S. Plasticity of GABAergic mechanisms within the nucleus of the solitary tract in hypertension. Hypertension 2010; 55:201-6. [PMID: 20048192 DOI: 10.1161/hypertensionaha.109.146407] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Affiliation(s)
- Weirong Zhang
- Department of Integrative Physiology and the Cardiovascular Research Institute, The University of North Texas Health Science Center, Fort Worth, Tex 76107-2699, USA
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Zhang W, Mifflin S. Chronic hypertension enhances presynaptic inhibition by baclofen in the nucleus of the solitary tract. Hypertension 2009; 55:481-6. [PMID: 20038748 DOI: 10.1161/hypertensionaha.109.145151] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
The selective gamma-aminobutyric acid B-subtype receptor agonist baclofen activates both presynaptic and postsynaptic receptors in the brain. Microinjection of baclofen into the nucleus of the solitary tract increases arterial pressure, heart rate, and sympathetic nerve discharge consistent with inhibition of the arterial baroreflex. The magnitude of these responses is enhanced in hypertension and is associated with increased postsynaptic GABA(B) receptor function. We tested whether a presynaptic mechanism contributes to the enhanced baclofen inhibition in hypertension. Whole-cell recordings of second-order baroreceptor neurons, identified by 4-(4-(dihexadecylamino)styryl)-N-methylpyridinium iodide labeling of aortic nerve, were obtained in brainstem slices from normotensive control and renal-wrap hypertensive rats. After 4 weeks, arterial blood pressure was 162+/-9 mm Hg in hypertensive (n=6) and 107+/-3 mm Hg in control rats (n=6/11; P<0.001). Baclofen reduced the amplitude of excitatory postsynaptic currents evoked by solitary tract stimulation and the EC(50) of this inhibition was greater in control (1.5+/-0.5 micromol/L; n=6) than in hypertensive cells (0.6+/-0.1 micromol/L; n=9; P<0.05). Baclofen (1 micromol/L) elicited greater inhibition on evoked response in hypertensive (58+/-6%; n=9) than in control cells (40+/-6%; n=8; P<0.05). Another index of presynaptic inhibition, the paired-pulse ratio (ratio of second to first evoked response amplitudes at stimulus intervals of 40 ms), was greater in hypertensive (0.60+/-0.08; n=8) than in control cells (0.48+/-0.06; n=5; P<0.05). The results suggest that in renal-wrap hypertensive rats, baclofen causes an enhanced presynaptic inhibition of glutamate release from baroreceptor afferent terminals to second-order neurons in the nucleus of the solitary tract. This enhanced presynaptic inhibition could contribute to altered baroreflex function in hypertension.
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Affiliation(s)
- Weirong Zhang
- Department of Pharmacology, University of Texas Health Science Center at San Antonio, San Antonio, Tex 76107, USA.
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Optical tracking of phenotypically diverse individual synapses on solitary tract nucleus neurons. Brain Res 2009; 1312:54-66. [PMID: 19944080 DOI: 10.1016/j.brainres.2009.11.042] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2009] [Revised: 11/04/2009] [Accepted: 11/18/2009] [Indexed: 11/23/2022]
Abstract
The solitary tract nucleus (NTS) is the termination site for cranial visceral afferents-peripheral primary afferent neurons which differ by phenotype (e.g. myelinated and unmyelinated). These afferents have very uniform glutamate release properties calculated by variance mean analysis. In the present study, we optical measured the inter-terminal release properties across individual boutons by assessing vesicle membrane turnover with the dye FM1-43. Single neurons were mechanically micro-harvested from medial NTS without enzyme treatment. The TRPV1 agonist capsaicin (CAP, 100 nM) was used to identify afferent, CAP-sensitive terminals arising from unmyelinated afferents. Isolated NTS neurons retained both glutamatergic and inhibitory terminals that generated EPSCs and IPSCs, respectively. Visible puncta on the neurons were stained positively with monoclonal antibody for synaptophysin, a presynaptic marker. Elevating extracellular K(+) concentration to 10 mM increased synaptic release measured at individual terminals by FM1-43. Within single neurons, CAP destained some but not other individual terminals. FM1-43 positive terminals that were resistant to CAP could be destained with K(+) solution. Individual terminals responded to depolarization with similar vesicle turnover kinetics. Thus, vesicular release was relatively homogenous across individual release sites. Surprisingly, conventionally high K(+) concentrations (>50 mM) produced erratic synaptic responses and at 90 mM K(+) overt neuron swelling--results that suggest precautions about assuming consistent K(+) responses in all neurons. The present work demonstrates remarkably uniform glutamate release between individual unmyelinated terminals and suggests that the homogeneous EPSC release properties of solitary tract afferents result from highly uniform release properties across multiple contacts on NTS neurons.
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Sun H, Li DP, Chen SR, Hittelman WN, Pan HL. Sensing of blood pressure increase by transient receptor potential vanilloid 1 receptors on baroreceptors. J Pharmacol Exp Ther 2009; 331:851-9. [PMID: 19726694 DOI: 10.1124/jpet.109.160473] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
The arterial baroreceptor is critically involved in the autonomic regulation of homoeostasis. The transient receptor potential vanilloid 1 (TRPV1) receptor is expressed on both somatic and visceral sensory neurons. Here, we examined the TRPV1 innervation of baroreceptive pathways and its functional significance in the baroreflex. Resiniferatoxin (RTX), an ultrapotent analog of capsaicin, was used to ablate TRPV1-expressing afferent neurons and fibers in adult rats. Immunofluorescence labeling revealed that TRPV1 immunoreactivity was present on nerve fibers and terminals in the adventitia of the ascending aorta and aortic arch, the nodose ganglion neurons, and afferent fibers in the solitary tract of the brainstem. RTX treatment eliminated TRPV1 immunoreactivities in the aorta, nodose ganglion, and solitary tract. Renal sympathetic nerve activity, blood pressure, and heart rate were recorded in anesthetized rats. The baroreflex was triggered by lowering and raising blood pressure through intravenous infusion of sodium nitroprusside and phenylephrine, respectively. Inhibition of sympathetic nerve activity and heart rate by the phenylephrine-induced increase in blood pressure was largely impaired in RTX-treated rats. The maximum gain of the baroreflex function was significantly lower in RTX-treated than vehicle-treated rats. Furthermore, blocking of TRPV1 receptors significantly blunted the baroreflex and decreased the maximum gain of baroreflex function in the high blood pressure range. Our findings provide important new information that TRPV1 is expressed along the entire baroreceptive afferent pathway. TRPV1 receptors expressed on baroreceptive nerve endings can function as mechanoreceptors to detect the increase in blood pressure and maintain the homoeostasis.
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Affiliation(s)
- Hao Sun
- Department of Anesthesiology and Perioperative Medicine, the University of Texas M. D. Anderson Cancer Center, Houston, Texas 77030, USA
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Holmes GM, Browning KN, Tong M, Qualls-Creekmore E, Travagli RA. Vagally mediated effects of glucagon-like peptide 1: in vitro and in vivo gastric actions. J Physiol 2009; 587:4749-59. [PMID: 19675064 DOI: 10.1113/jphysiol.2009.175067] [Citation(s) in RCA: 65] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
Glucagon-like peptide-1 (GLP-1) is a neuropeptide released following meal ingestion that, among other effects, decreases gastric tone and motility. The central targets and mechanism of action of GLP-1 on gastric neurocircuits have not, however, been fully investigated. A high density of GLP-1 containing neurones and receptors are present in brainstem vagal circuits, suggesting that the gastroinhibition may be vagally mediated. We aimed to investigate: (1) the response of identified gastric-projecting neurones of the dorsal motor nucleus of the vagus (DMV) to GLP-1 and its analogues; (2) the effects of brainstem application of GLP-1 on gastric tone; and (3) the vagal pathway utilized by GLP-1 to induce gastroinhibition. We conducted our experiments using whole-cell recordings from identified gastric-projecting DMV neurones and microinjection in the dorsal vagal complex (DVC) of anaesthetized rats while monitoring gastric tone. Perfusion with GLP-1 induced a concentration-dependent excitation of a subpopulation of gastric-projecting DMV neurones. The GLP-1 effects were mimicked by exendin-4 and antagonized by exendin-9-39. In an anaesthetized rat preparation, application of exendin-4 to the DVC decreased gastric tone in a concentration-dependent manner. The gastroinhibitory effects of exendin-4 were unaffected by systemic pretreatment with the pro-motility muscarinic agonist bethanechol, but were abolished by systemic administration of the nitric oxide synthase (NOS) inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME), or by bilateral vagotomy. Our data indicate that GLP-1 activates selective receptors to excite DMV neurones mainly and that the gastroinhibition observed following application of GLP-1 in the DVC is due to the activation of an inhibitory non-adrenergic, non-cholinergic input to the stomach.
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Affiliation(s)
- Gregory M Holmes
- Neuroscience, PBRC-Louisiana State University, Baton Rouge, LA 70808, USA
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Lin LH. Glutamatergic neurons say NO in the nucleus tractus solitarii. J Chem Neuroanat 2009; 38:154-65. [PMID: 19778681 DOI: 10.1016/j.jchemneu.2009.02.002] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2008] [Revised: 02/06/2009] [Accepted: 02/09/2009] [Indexed: 01/13/2023]
Abstract
Both glutamate and nitric oxide (NO) may play an important role in cardiovascular reflex and respiratory signal transmission in the nucleus tractus solitarii (NTS). Pharmacological and physiological data have shown that glutamate and NO may be linked in mediating cardiovascular regulation by the NTS. Through tract tracing, multiple-label immunofluorescent staining, confocal microscopic, and electronic microscopic methods, we and other investigators have provided anatomical evidence that supports a role for glutamate and NO as well as an interaction between glutamate and NO in cardiovascular regulation in the NTS. This review article focuses on summarizing and discussing these anatomical findings. We utilized antibodies to markers of glutamatergic neurons and to neuronal NO synthase (nNOS), the enzyme that synthesizes NO in NTS neurons, to study the anatomical relationship between glutamate and NO in rats. Not only were glutamatergic markers and nNOS both found in similar subregions of the NTS and in vagal afferents, they were also frequently colocalized in the same neurons and fibers in the NTS. In addition, glutamatergic markers and nNOS were often present in fibers that were in close apposition to each other. Furthermore, N-methyl-d-aspartate (NMDA) type glutamate receptors and nNOS were often found on the same NTS neurons. Similarly, alpha-amino-3-hydroxy-5-methylisoxozole-proprionic acid (AMPA) type glutamate receptors also frequently colocalized with nNOS in NTS neurons. These findings support the suggestion that the interaction between glutamate and NO may be mediated both through NMDA and AMPA receptors. Finally, by applying tracer to the cut aortic depressor nerve (ADN) to identify nodose ganglion (NG) neurons that transmit cardiovascular signals to the NTS, we observed colocalization of vesicular glutamate transporters (VGluT) and nNOS in the ADN neurons. Thus, taken together, these neuroanatomical data support the hypothesis that glutamate and NO may interact with each other to regulate cardiovascular and likely other visceral functions through the NTS.
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Affiliation(s)
- Li-Hsien Lin
- Department of Neurology, University of Iowa, Iowa City, IA 52242, USA.
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Frank JG, Jameson HS, Gorini C, Mendelowitz D. Mapping and identification of GABAergic neurons in transgenic mice projecting to cardiac vagal neurons in the nucleus ambiguus using photo-uncaging. J Neurophysiol 2009; 101:1755-60. [PMID: 19164103 DOI: 10.1152/jn.91134.2008] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The neural control of heart rate is determined primarily by the activity of preganglionic parasympathetic cardiac vagal neurons (CVNs) originating in the nucleus ambiguus (NA) in the brain stem. GABAergic inputs to CVNs play an essential role in determining the activity of these neurons including a robust inhibition during each inspiratory burst. The origin of GABAergic innervation has yet to be determined however. A transgenic mouse line expressing green florescent protein (GFP) in GABAergic cells was used in conjunction with caged glutamate to identify both clusters and individual GABAergic neurons that evoke inhibitory GABAergic synaptic responses in CVNs. Transverse slices were taken with CVNs patch-clamped in the whole cell configuration. Sections containing both the pre-Botzinger complex as well as the calamus scriptorius were divided into approximately 90 quadrants, each 200 x 200 microm and were sequentially photostimulated. Inhibitory post synaptic currents (IPSCs) were recorded in CVNs after a 5-ms photostimulation of 50 microM caged glutamate. The four areas that contained GABAergic cells projecting to CVNs were 200 microm medial, 400 microm medial, 200 microm ventral, and 1,200 microm dorsal and 1,000 microm medial to patched CVNs. Once foci of GABAergic cells projecting to CVNs were determined, photostimulation of individual GABAergic neurons was conducted. The results from this study suggest that GABAergic cells located in four specific areas project to CVNs, and that these cells can be individually identified and stimulated using photouncaging to recruit GABAergic neurotransmission to CVNs.
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Affiliation(s)
- J G Frank
- Dept. of Pharmacology and Physiology, The George Washington University, 2300 I Street NW, Washington, DC 20037, USA
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31
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Austgen JR, Fong AY, Foley CM, Mueller PJ, Kline DD, Heesch CM, Hasser EM. Expression of Group I metabotropic glutamate receptors on phenotypically different cells within the nucleus of the solitary tract in the rat. Neuroscience 2008; 159:701-16. [PMID: 19013221 DOI: 10.1016/j.neuroscience.2008.09.060] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2007] [Revised: 09/09/2008] [Accepted: 09/30/2008] [Indexed: 02/07/2023]
Abstract
Group I metabotropic glutamate receptors (mGluRs) are G-coupled receptors that modulate synaptic activity. Previous studies have shown that Group I mGluRs are present in the nucleus of the solitary tract (NTS), in which many visceral afferents terminate. Microinjection of selective Group I mGluR agonists into the NTS results in a depressor response and decrease in sympathetic nerve activity. There is, however, little evidence detailing which phenotypes of neurons within the NTS express Group I mGluRs. In brainstem slices, we performed immunohistochemical localization of Group I mGluRs and either glutamic acid decarboxylase 67 kDa isoform (GAD67), neuronal nitric oxide synthase (nNOS) or tyrosine hydroxylase (TH). Fluoro-Gold (FG, 2%; 15 nl) was microinjected in the caudal ventrolateral medulla (CVLM) of the rat to retrogradely label NTS neurons that project to CVLM. Group I mGluRs were distributed throughout the rostral-caudal extent of the NTS and were found within most NTS subregions. The relative percentages of Group I mGluR expressing neurons colabeled with the different markers were FG (6.9+/-0.7) nNOS (5.6+/-0.9), TH (3.9+/-1.0), and GAD67 (3.1+/-1.4). The percentage of FG containing cells colabeled with Group I mGluR (13.6+/-2.0) was greater than the percent colabeled with GAD67 (3.1+/-0.5), nNOS (4.7+/-0.5), and TH (0.1+/-0.08). Cells triple labeled for FG, nNOS, and Group I mGluRs were identified in the NTS. Thus, these data provide an anatomical substrate by which Group I mGluRs could modulate activity of CVLM projecting neurons in the NTS.
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Affiliation(s)
- J R Austgen
- Department of Medical Pharmacology and Physiology, University of Missouri, Columbia, MO 65211, USA
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Andresen MC, Peters JH. Comparison of baroreceptive to other afferent synaptic transmission to the medial solitary tract nucleus. Am J Physiol Heart Circ Physiol 2008; 295:H2032-42. [PMID: 18790834 DOI: 10.1152/ajpheart.00568.2008] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Cranial nerve visceral afferents enter the brain stem to synapse on neurons within the solitary tract nucleus (NTS). The broad heterogeneity of both visceral afferents and NTS neurons makes understanding afferent synaptic transmission particularly challenging. To study a specific subgroup of second-order neurons in medial NTS, we anterogradely labeled arterial baroreceptor afferents of the aortic depressor nerve (ADN) with lipophilic fluorescent tracer (i.e., ADN+) and measured synaptic responses to solitary tract (ST) activation recorded from dye-identified neurons in medial NTS in horizontal brain stem slices. Every ADN+ NTS neuron received constant-latency ST-evoked excitatory postsynaptic currents (EPSCs) (jitter < 192 micros, SD of latency). Stimulus-recruitment profiles showed single thresholds and no suprathreshold recruitment, findings consistent with EPSCs arising from a single, branched afferent axon. Frequency-dependent depression of ADN+ EPSCs averaged approximately 70% for five shocks at 50 Hz, but single-shock failure rates did not exceed 4%. Whether adjacent ADN- or those from unlabeled animals, other second-order NTS neurons (jitters < 200 micros) had ST transmission properties indistinguishable from ADN+. Capsaicin (CAP; 100 nM) blocked ST transmission in some neurons. CAP-sensitive ST-EPSCs were smaller and failed over five times more frequently than CAP-resistant responses, whether ADN+ or from unlabeled animals. Variance-mean analysis of ST-EPSCs suggested uniformly high probabilities for quantal glutamate release across second-order neurons. While amplitude differences may reflect different numbers of contacts, higher frequency-dependent failure rates in CAP-sensitive ST-EPSCs may arise from subtype-specific differences in afferent axon properties. Thus afferent transmission within medial NTS differed by axon class (e.g., CAP sensitive) but was indistinguishable by source of axon (e.g., baroreceptor vs. nonbaroreceptor).
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Affiliation(s)
- Michael C Andresen
- Department of Physiology and Pharmacology, Oregon Health & Science University, Portland, Oregon 97239-3098, USA.
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Bailey TW, Appleyard SM, Jin YH, Andresen MC. Organization and properties of GABAergic neurons in solitary tract nucleus (NTS). J Neurophysiol 2008; 99:1712-22. [PMID: 18272881 DOI: 10.1152/jn.00038.2008] [Citation(s) in RCA: 83] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Cranial visceral afferents enter the brain at the solitary tract nucleus (NTS). GABAergic neurons are scattered throughout the NTS, but their relation to solitary tract (ST) afferent pathways is imprecisely known. We hypothesized that most GABAergic NTS neurons would be connected only indirectly to the ST. We identified GABAergic neurons in brain stem horizontal slices using transgenic mice in which enhanced green fluorescent protein (EGFP) expression was linked to glutamic acid decarboxylase expression (GAD(+)). Finely graded electrical shocks to ST recruit ST-synchronized synaptic events with all-or-none thresholds and individual waveforms did not change with greater suprathreshold intensities--evidence consistent with initiation by single afferent axons. Most (approximately 70%) GAD(+) neurons received ST-evoked excitatory postsynaptic currents (EPSCs) that had minimally variant latencies (jitter, SD of latency <200 micros) and waveforms consistent with single, direct ST connections (i.e., monosynaptic). Increasing stimulus intensity evoked additional ST-synchronized synaptic responses with jitters >200 micros including inhibitory postsynaptic currents (IPSCs), indicating indirect connections (polysynaptic). Shocks of suprathreshold intensity delivered adjacent (50-300 microm) to the ST failed to excite non-ST inputs to second-order neurons, suggesting a paucity of axons passing near to ST that connected to these neurons. Despite expectations, we found similar ST synaptic patterns in GAD(+) and unlabeled neurons. Generally, ST information that arrived indirectly had small amplitudes (EPSCs and IPSCs) and frequency-dependent failures that reached >50% for IPSCs to bursts of stimuli. This ST afferent pathway organization is strongly use-dependent--a property that may tune signal propagation within and beyond NTS.
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Affiliation(s)
- Timothy W Bailey
- Department of Physiology and Pharmacology, Oregon Health and Science University, Portland, OR 97239-3098, USA
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McDougall SJ, Bailey TW, Mendelowitz D, Andresen MC. Propofol enhances both tonic and phasic inhibitory currents in second-order neurons of the solitary tract nucleus (NTS). Neuropharmacology 2007; 54:552-63. [PMID: 18082229 DOI: 10.1016/j.neuropharm.2007.11.001] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2007] [Revised: 10/26/2007] [Accepted: 11/04/2007] [Indexed: 02/07/2023]
Abstract
The anesthetic propofol is thought to induce rapid hypnotic sedation by facilitating a GABAergic tonic current in forebrain neurons. The depression of cardiovascular and respiratory regulation often observed during propofol suggests potential additional actions within the brainstem. Here we determined the impacts of propofol on both GABAergic and glutamatergic synaptic mechanisms in a class of solitary tract nucleus (NTS) neurons common to brainstem reflex pathways. In horizontal brainstem slices, we recorded from NTS neurons directly activated by solitary tract (ST) axons. We identified these second-order NTS neurons by time-invariant ("jitter"<200 micros), "all-or-none" glutamatergic excitatory postsynaptic currents (EPSCs) in response to shocks to the ST. In order to assess propofol actions, we measured ST-evoked, spontaneous and miniature EPSCs and inhibitory postsynaptic currents (IPSCs) during propofol exposure. Propofol prolonged miniature IPSC decay time constants by 50% above control at 1.8 microM. Low concentrations of gabazine (SR-95531) blocked phasic GABA currents. At higher concentrations, propofol (30 microM) induced a gabazine-insensitive tonic current that was blocked by picrotoxin or bicuculline. In contrast, total propofol concentrations up to 30 microM had no effect on EPSCs. Thus, propofol enhanced phasic GABA events in NTS at lower concentrations than tonic current induction, opposite to the relative sensitivity observed in forebrain regions. These data suggest that therapeutic levels of propofol facilitate phasic (synaptic) inhibitory transmission in second-order NTS neurons which likely inhibits autonomic reflex pathways during anesthesia.
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Affiliation(s)
- Stuart J McDougall
- Department of Physiology and Pharmacology L334, Oregon Health and Science University, 3181 SW Sam Jackson Park Road, Portland OR 97239-3098, USA.
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Wan S, Coleman FH, Travagli RA. Cholecystokinin-8s excites identified rat pancreatic-projecting vagal motoneurons. Am J Physiol Gastrointest Liver Physiol 2007; 293:G484-92. [PMID: 17569742 DOI: 10.1152/ajpgi.00116.2007] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
It is known that cholecystokinin (CCK) acts in a paracrine fashion to increase pancreatic exocrine secretion via vagal circuits. Recent evidence, however, suggests that CCK-8s actions are not restricted to afferent vagal fibers, but also affect brain stem structures directly. Within the brain stem, preganglionic neurons of the dorsal motor nucleus of the vagus (DMV) send efferent fibers to subdiaphragmatic viscera, including the pancreas. Our aims were to investigate whether DMV neurons responded to exogenously applied CCK-8s and, if so, the mechanism of action. Using whole cell patch-clamp recordings we show that perfusion with CCK-8s induced a concentration-dependent excitation in approximately 60% of identified pancreas-projecting DMV neurons. The depolarization was significantly reduced by tetrodotoxin, suggesting both direct (on the DMV membrane) and indirect (on local synaptic circuits) effects. Indeed, CCK-8s increased the frequency of miniature excitatory currents onto DMV neurons. The CCK-A antagonist, lorglumide, prevented the CCK-8s-mediated excitation whereas the CCK-B preferring agonist, CCK-nonsulfated, had no effect, suggesting the involvement of CCK-A receptors only. In voltage clamp, the CCK-8s-induced inward current reversed at -106 +/- 3 mV and the input resistance increased by 150 +/- 15%, suggesting an effect mediated by the closure of a potassium conductance. Indeed, CCK-8s reduced both the amplitude and the time constant of decay of a calcium-dependent potassium conductance. When tested with pancreatic polypeptide (which reduces pancreatic exocrine secretion), cells that responded to CCK-8s with an excitation were, instead, inhibited by pancreatic polypeptide. These data indicate that CCK-8s may control pancreas-exocrine secretion also via an effect on pancreas-projecting DMV neurons.
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Affiliation(s)
- Shuxia Wan
- Department of Neuroscience, Pennington Biomedical Research Center-Louisiana State University System, 6400 Perkins Rd., Baton Rouge, LA 70808, USA
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Bailey TW, Hermes SM, Whittier KL, Aicher SA, Andresen MC. A-type potassium channels differentially tune afferent pathways from rat solitary tract nucleus to caudal ventrolateral medulla or paraventricular hypothalamus. J Physiol 2007; 582:613-28. [PMID: 17510187 PMCID: PMC2075344 DOI: 10.1113/jphysiol.2007.132365] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
The solitary tract nucleus (NTS) conveys visceral information to diverse central networks involved in homeostatic regulation. Although afferent information content arriving at various CNS sites varies substantially, little is known about the contribution of processing within the NTS to these differences. Using retrograde dyes to identify specific NTS projection neurons, we recently reported that solitary tract (ST) afferents directly contact NTS neurons projecting to caudal ventrolateral medulla (CVLM) but largely only indirectly contact neurons projecting to the hypothalamic paraventricular nucleus (PVN). Since intrinsic properties impact information transmission, here we evaluated potassium channel expression and somatodendritic morphology of projection neurons and their relation to afferent information output directed to PVN or CVLM pathways. In slices, tracer-identified projection neurons were classified as directly or indirectly (polysynaptically) coupled to ST afferents by EPSC latency characteristics (directly coupled, jitter < 200 micros). In each neuron, voltage-dependent potassium currents (IK) were evaluated and, in representative neurons, biocytin-filled structures were quantified. Both CVLM- and PVN-projecting neurons had similar, tetraethylammonium-sensitive IK. However, only PVN-projecting NTS neurons displayed large transient, 4-aminopyridine-sensitive, A-type currents (IKA). PVN-projecting neurons had larger cell bodies with more elaborate dendritic morphology than CVLM-projecting neurons. ST shocks faithfully (> 75%) triggered action potentials in CVLM-projecting neurons but spike output was uniformly low (< 20%) in PVN-projecting neurons. Pre-conditioning hyperpolarization removed IKA inactivation and attenuated ST-evoked spike generation along PVN but not CVLM pathways. Thus, multiple differences in structure, organization, synaptic transmission and ion channel expression tune the overall fidelity of afferent signals that reach these destinations.
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Affiliation(s)
- T W Bailey
- Department of Physiology and Pharmacology, Oregon Health and Science University, Portland, OR 972393098, USA.
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Tolstykh G, de Paula PM, Mifflin S. Voltage-dependent calcium currents are enhanced in nucleus of the solitary tract neurons isolated from renal wrap hypertensive rats. Hypertension 2007; 49:1163-9. [PMID: 17372037 DOI: 10.1161/hypertensionaha.106.084004] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
The nucleus of the solitary tract (NTS) is the central site of termination of baroreceptor afferents. We hypothesize that changes occur in voltage-gated calcium channels (VGCCs) within NTS neurons as a consequence of hypertension. Whole-cell patch-clamp recordings were obtained from adult normotensive (109+/-2 mm Hg; n=6 from 6 sham-operated and 31 nonsurgically treated) and hypertensive (158+/-6 mm Hg; n=24) rats. In some experiments, 4-(4-[dihexadecylamino]styryl)-N-methylpyridinium iodide was applied to the aortic nerve to visualize NTS neurons receiving baroreceptor synaptic contacts. Ba(2+) currents (500 ms; -80 mV prepotential; 500 ms voltage steps in 5-mV increments to +15mV) peaked between -20 and -10 mV and were blocked by 100 mum of Cd(2+). Peak VGCCs were not different comparing non-4-(4-[dihexadecylamino]styryl)-N-methylpyridinium iodide-labeled and 4-(4- [dihexadecylamino]styryl)-N-methylpyridinium iodide-labeled NTS neurons in hypertensive and normotensive rats. The peak VGCC was significantly greater in cells from hypertensive compared with normotensive rats for both non-DiA-labeled (P=0.02) and DiA-labeled (P=0.04) neurons. To separate high-voltage activated (HVA) and low-voltage activated (LVA) components of VGCCs, voltage ramps (-110 mV to +30 mV over 50 ms) were applied from a holding potential of -60 mV (LVA channels inactivated) and a holding potential of -100 mV (both LVA and HVA currents activated). HVA currents were subtracted from HVA+LVA currents to yield the LVA current. Peak LVA currents were not different between hypertensive (8.9+/-0.8 pA/pF) and normotensive (7.8+/-0.6 pA/pF) groups of NTS neurons (P=0.27). These results demonstrate that 4 weeks of renal wrap hypertension induce an increase in Ca(2+) influx through HVA VGCCs in NTS neurons receiving arterial baroreceptor inputs.
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Affiliation(s)
- Gleb Tolstykh
- University of Texas Health Science Center at San Antonio, TX 78229-3900, USA
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Zhang W, Herrera-Rosales M, Mifflin S. Chronic hypertension enhances the postsynaptic effect of baclofen in the nucleus tractus solitarius. Hypertension 2006; 49:659-63. [PMID: 17145979 DOI: 10.1161/01.hyp.0000253091.82501.c0] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Microinjection of the inhibitory neurotransmitter gamma-aminobutyric acid B-subtype receptor agonist baclofen into the nucleus tractus solitarius increases arterial blood pressure and sympathetic nerve discharge. The baclofen-induced pressor response is enhanced in chronic hypertension. We hypothesized that a postsynaptic mechanism contributes to the enhanced responses to baclofen in hypertension. We investigated the postsynaptic effect of baclofen on second-order baroreceptor neurons, identified by 1,1'-dilinoleyl-3,3,3',3'-tetra-methylindocarbocyanine, 4-chlorobenzenesulphonate labeling of the aortic nerve, in nucleus tractus solitarius slices from sham-operated normotensive and unilateral nephrectomized, renal-wrap hypertensive rats. After 4 weeks, arterial blood pressure was 153+/-7 mm Hg in hypertensive rats (n=9) and 93+/-3 mm Hg in normotensive rats (n=8; P<0.05). There was no difference in resting membrane potential (54.5+/-0.7 versus 53.3+/-0.6 mV) or input resistance (1.07+/-0.11 versus 1.03+/-0.11 GOmega) between hypertensive and normotensive neurons (both n=18). Baclofen induced a net outward current in nucleus tractus solitarius neurons in the presence of 1 micromol/L tetrodotoxin. The EC50 of the baclofen effect was greater in normotensive cells (9.1+/-3.2 micromol/L; n=5) than hypertensive cells (3.0+/-0.5 micromol/L; n=7; P<0.05), and baclofen (10 micromol/L) induced a greater decrease in input resistance in hypertensive cells (61+/-2%; n=6) than in normotensive cells (45+/-4%; n=9; P<0.05). Both potassium and calcium channels were involved in the baclofen-evoked whole-cell current. The results suggest an enhanced postsynaptic response to activation of inhibitory neurotransmitter gamma-aminobutyric acid B-subtype receptors in second-order baroreceptor neurons in the nucleus tractus solitarius in renal-wrap hypertensive rats. This enhanced inhibition could alter baroreflex function in chronic hypertension.
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Affiliation(s)
- Weirong Zhang
- Department of Pharmacology, University of Texas Health Science Center at San Antonio, San Antonio, TX 78229, USA
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Bailey TW, Hermes SM, Andresen MC, Aicher SA. Cranial visceral afferent pathways through the nucleus of the solitary tract to caudal ventrolateral medulla or paraventricular hypothalamus: target-specific synaptic reliability and convergence patterns. J Neurosci 2006; 26:11893-902. [PMID: 17108163 PMCID: PMC6674856 DOI: 10.1523/jneurosci.2044-06.2006] [Citation(s) in RCA: 120] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2006] [Revised: 10/08/2006] [Accepted: 10/10/2006] [Indexed: 02/07/2023] Open
Abstract
Cranial visceral afferents activate central pathways that mediate systemic homeostatic processes. Afferent information arrives in the brainstem nucleus of the solitary tract (NTS) and is relayed to other CNS sites for integration into autonomic responses and complex behaviors. Little is known about the organization or nature of processing within NTS. We injected fluorescent retrograde tracers into two nuclei to identify neurons that project to sites involved in autonomic regulation: the caudal ventrolateral medulla (CVLM) or paraventricular nucleus of the hypothalamus (PVN). We found distinct differences in synaptic connections and performance in the afferent path through NTS to these neurons. Anatomical studies using confocal and electron microscopy found prominent, primary afferent synapses directly on somata and dendrites of CVLM-projecting NTS neurons identifying them as second-order neurons. In brainstem slices, afferent activation evoked large, constant latency EPSCs in CVLM-projecting NTS neurons that were consistent with the precise timing and rare failures of monosynaptic contacts on second-order neurons. In contrast, most PVN-projecting NTS neurons lacked direct afferent input and responded to afferent stimuli with highly variable, intermittently failing synaptic responses, indicating polysynaptic pathways to higher-order neurons. The afferent-evoked EPSCs in most PVN-projecting NTS neurons were smaller and unreliable but also often included multiple, convergent polysynaptic responses not observed in CVLM-projecting neurons. A few PVN-projecting NTS neurons had monosynaptic EPSC characteristics. Together, we found that cranial visceral afferent pathways are structured distinctly within NTS depending on the projection target. Such, intra-NTS pathway architecture will substantially impact performance of autonomic or neuroendocrine reflex arcs.
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Affiliation(s)
- Timothy W Bailey
- Department of Physiology and Pharmacology, Oregon Health & Science University, Portland, Oregon 97239-3098, USA.
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Zhang W, Mifflin SW. Modulation of synaptic transmission to second-order peripheral chemoreceptor neurons in caudal nucleus tractus solitarius by alpha1-adrenoreceptors. J Pharmacol Exp Ther 2006; 320:670-7. [PMID: 17082311 DOI: 10.1124/jpet.106.114033] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Norepinephrine (NE) is an important neurotransmitter in central autonomic regulation. Peripheral chemoreceptor stimulation activates central noradrenergic structures. These structures innervate and therefore could modulate neurons in caudal nucleus tractus solitarius (cNTS), which receives the first central projections from peripheral chemoreceptors. However, the role of alpha(1)-adrenoreceptors in synaptic transmission of peripheral chemoreceptor inputs in cNTS is unknown. We investigated the responses to activation of alpha(1)-adrenoreceptors on glutamatergic and GABAergic inputs in NTS slices using whole-cell recording. Second-order neurons were identified by 1,1'-dilinoleyl-3,3,3',3'-tetra-methylindocarbocyanine, 4-chlorobenzenesulphonate (DiA) labeling of carotid bodies. Electrical stimulation of ipsilateral tractus solitarius was used to evoke excitatory postsynaptic currents (eEPSCs), whereas inhibitory postsynaptic currents were evoked (eIPSCs) by electrically stimulating NTS near the recorded neuron. Application of alpha(1)-adrenoreceptor agonist phenylephrine (PE) at 20 microM significantly decreased amplitudes of eEPSCs (78 +/- 1% of control; n = 16; p < 0.01), and it increased amplitudes of eIPSCs (120 +/- 13% of control; n = 7; p < 0.01). Both effects were blocked by the alpha(1)-adrenoreceptor antagonist prazosin at 10 microM. PE did not change holding current, input resistance, and current-voltage relationship in cNTS neurons. PE significantly changed paired pulse ratios of eEPSC/eIPSCs, increased the frequency of miniature IPSCs (329 +/- 10% of control; n = 6; p < 0.05), but it decreased that of miniature EPSCs (69 +/- 6% of control; n = 5; p < 0.01). PE-induced inhibition of eEPSCs was independent of N-methyl-D-aspartate or GABA(B) receptors. These results suggest that activation of alpha(1)-adrenoreceptors reduces excitatory and enhances inhibitory inputs to second-order peripheral chemoreceptor neurons in cNTS via a presynaptic mechanism. These actions result in the inhibition of synaptic transmission and could play a role in the autonomic responses to hypoxia.
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Affiliation(s)
- Weirong Zhang
- Department of Pharmacology, The University of Texas Health Science Center at San Antonio, TX 78229-3900, USA
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Wang G, Anrather J, Glass MJ, Tarsitano MJ, Zhou P, Frys KA, Pickel VM, Iadecola C. Nox2, Ca2+, and protein kinase C play a role in angiotensin II-induced free radical production in nucleus tractus solitarius. Hypertension 2006; 48:482-9. [PMID: 16894058 DOI: 10.1161/01.hyp.0000236647.55200.07] [Citation(s) in RCA: 90] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
The dorsomedial portion of the nucleus tractus solitarius (dmNTS) is the site of termination of baroreceptor and cardiorespiratory vagal afferents and plays a critical role in cardiovascular regulation. Angiotensin II (Ang II) is a powerful signaling molecule in dmNTS neurons and exerts some of its biological effects by modulating Ca(2+) currents via reactive oxygen species (ROS) derived from reduced nicotinamide-adenine dinucleotide phosphate (NADPH) oxidase. We investigated whether a Nox2-containing NADPH oxidase is the source of the Ang II-induced ROS production and whether the signaling mechanisms of its activation require intracellular Ca(2+) or protein kinase C (PKC). Second-order dmNTS neurons were anterogradely labeled with 4-(4-[didecylamino]styryl)-N-methylpyridinium iodide transported from the vagus and isolated from the brain stem. ROS production was assessed in 4-(4-[didecylamino]styryl)-N-methylpyridinium iodide-positive dmNTS neurons using the fluorescent dye 6-carboxy-2',7'-dichlorodihydro-fluorescein di(acetoxymethyl ester). Ang II (3 to 2000 nmol/L) increased ROS production in dmNTS neurons (EC(50)=38.3 nmol/L). The effect was abolished by the ROS scavenger Mn (III) porphyrin 5,10,20-tetrakis (benzoic acid) porphyrin manganese (III), the Ang II type 1 receptor antagonist losartan, or the NADPH oxidase inhibitors apocynin or gp91ds-tat. Ang II failed to increase ROS production or to potentiate L-type Ca(2+) currents in dmNTS neurons of mice lacking Nox2. The PKC inhibitor GF109203X or depletion of intracellular Ca(2+) attenuated Ang II-elicited ROS production. We conclude that the powerful effects of Ang II on Ca(2+) currents in dmNTS neurons are mediated by PKC activation leading to ROS production via Nox2. Thus, a Nox2-containing NADPH oxidase is the critical link between Ang II and the enhancement of Ca(2+) currents that underlie the actions of Ang II on central autonomic regulation.
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Affiliation(s)
- Gang Wang
- Division of Neurobiology, Weill Medical College of Cornell University, 411 East 69th St, New York, NY 10021, USA.
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Bailey TW, Jin YH, Doyle MW, Smith SM, Andresen MC. Vasopressin inhibits glutamate release via two distinct modes in the brainstem. J Neurosci 2006; 26:6131-42. [PMID: 16763021 PMCID: PMC2680488 DOI: 10.1523/jneurosci.5176-05.2006] [Citation(s) in RCA: 91] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
The hypothalamus coordinates autonomic responses in part through arginine vasopressin (AVP) released in medial nucleus tractus solitarius (NTS). However, the mechanisms and sites of AVP action within NTS pathways are uncertain. In brainstem slices, we activated solitary tract (ST) primary afferents to release glutamate and tested whether AVP modulated synaptic transmission to second-order neurons. NTS neurons were classified as second order by ST synaptic characteristics or the presence of anterograde tracers from peripheral baroreceptor afferents. Stimulus recruitment curves indicated ST-EPSCs on individual neurons were evoked by stimulation of single ST axons. Variance-mean (V-M) analysis of ST-EPSCs in individual neurons revealed uniformly high release probability (p approximately 0.9) from an average of 19 release sites (N) and a quantal size (q) of 34.0 +/- 4.7 pA. In 26 of 49 neurons, AVP inhibited afferent synaptic transmission. In most neurons, AVP reduced ST-EPSC amplitudes (n = 20) by decreasing p to 0.65, whereas q, N, and conduction times were unaffected. The V1a antagonist SR49059 alone decreased ST-EPSC V and increased M, suggesting tonic AVP actions, and blocked exogenous AVP action (n = 4). In other neurons with identical ST release properties, AVP induced synaptic failures and increased conduction time without altering the V-M relationship of successful ST-EPSCs (n = 6). Interestingly, frequency-depressed ST-EPSCs were not affected by AVP. AVP failed to alter holding or voltage-dependent potassium currents. Thus, AVP regulates NTS neurons by two distinct novel and state-dependent mechanisms: one, an analog, graded presynaptic inhibition of terminal glutamate release and the other, a binary, extraterminal block of conducted excitation.
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Affiliation(s)
- Timothy W Bailey
- Department of Physiology and Pharmacology, Oregon Health and Science University, Portland, Oregon 97239-3098, USA.
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43
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Lin LH, Talman WT. Vesicular glutamate transporters and neuronal nitric oxide synthase colocalize in aortic depressor afferent neurons. J Chem Neuroanat 2006; 32:54-64. [PMID: 16735103 DOI: 10.1016/j.jchemneu.2006.04.004] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2006] [Revised: 04/11/2006] [Accepted: 04/11/2006] [Indexed: 11/24/2022]
Abstract
The aortic depressor nerve (ADN) primarily transmits baroreceptor signals from the aortic arch to the nucleus tractus solitarii. Cell bodies of neurons that send peripheral fibers to form the ADN are located in the nodose ganglion (NG). Studies have implicated glutamate and nitric oxide in transmission of baroreflex signals; therefore, we tested the hypothesis that ADN neurons contain either vesicular glutamate transporters (VGLUTs) or neuronal nitric oxide synthase (nNOS) or both. We applied a fluorescent tracer, tetramethyl rhodamine dextran (TRD), to rat ADN to identify ADN neurons and then performed immunofluorescent labeling for nNOS and VGLUTs 1, 2, and 3 in NG sections. We found that VGLUT2-immunoreactivity (IR) and VGLUT3-IR was present in a significantly higher proportion of TRD positive neurons than in TRD negative neurons. In contrast, the percentage of TRD positive neurons containing VGLUT1-IR or nNOS-IR did not differ from that of TRD negative neurons. We also observed that the percentage of TRD positive neurons containing both VGLUT2-IR and nNOS-IR and the percentage of TRD positive neurons containing both VGLUT3-IR and nNOS-IR were significantly higher than that of TRD negative neurons. On the other hand, colocalization of VGLUT1-IR and nNOS-IR in TRD positive neurons did not differ from that of TRD negative neurons. These results support our hypothesis and suggest prominent roles of VGLUT2-IR containing neurons and VGLUT3-IR containing neurons in transmitting cardiovascular signals via the ADN to the brain stem.
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Affiliation(s)
- L H Lin
- Department of Neurology, University of Iowa, Iowa City, IA 52242, USA.
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Reynolds PJ, Fan W, Andresen MC. Capsaicin-resistant arterial baroreceptors. J Negat Results Biomed 2006; 5:6. [PMID: 16709252 PMCID: PMC1481593 DOI: 10.1186/1477-5751-5-6] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2006] [Accepted: 05/18/2006] [Indexed: 12/28/2022] Open
Abstract
BACKGROUND Aortic baroreceptors (BRs) comprise a class of cranial afferents arising from major arteries closest to the heart whose axons form the aortic depressor nerve. BRs are mechanoreceptors that are largely devoted to cardiovascular autonomic reflexes. Such cranial afferents have either lightly myelinated (A-type) or non-myelinated (C-type) axons and share remarkable cellular similarities to spinal primary afferent neurons. Our goal was to test whether vanilloid receptor (TRPV1) agonists, capsaicin (CAP) and resiniferatoxin (RTX), altered the pressure-discharge properties of peripheral aortic BRs. RESULTS Periaxonal application of 1 microM CAP decreased the amplitude of the C-wave in the compound action potential conducting at <1 m/sec along the aortic depressor nerve. 10 microM CAP eliminated the C-wave while leaving intact the A-wave conducting in the A-delta range (<12 m/sec). These whole nerve results suggest that TRPV1 receptors are expressed along the axons of C- but not A-conducting BR axons. In an aortic arch--aortic nerve preparation, intralumenal perfusion with 1 microM CAP had no effect on the pressure-discharge relations of regularly discharging, single fiber BRs (A-type)--including the pressure threshold, sensitivity, frequency at threshold, or maximum discharge frequency (n = 8, p > 0.50) but completely inhibited discharge of an irregularly discharging BR (C-type). CAP at high concentrations (10-100 microM) depressed BR sensitivity in regularly discharging BRs, an effect attributed to non-specific actions. RTX (< or = 10 microM) did not affect the discharge properties of regularly discharging BRs (n = 7, p > 0.18). A CAP-sensitive BR had significantly lower discharge regularity expressed as the coefficient of variation than the CAP-resistant fibers (p < 0.002). CONCLUSION We conclude that functional TRPV1 channels are present in C-type but not A-type (A-delta) myelinated aortic arch BRs. CAP has nonspecific inhibitory actions that are unlikely to be related to TRV1 binding since such effects were absent with the highly specific TRPV1 agonist RTX. Thus, CAP must be used with caution at very high concentrations.
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Affiliation(s)
- Patrick J Reynolds
- Department of Physiology and Pharmacology, Oregon Health & Science University, Portland, Oregon 97239-3098, USA
| | - Wei Fan
- Vollum Institute, Oregon Health & Science University, Portland, Oregon 97239-3098, USA
| | - Michael C Andresen
- Department of Physiology and Pharmacology, Oregon Health & Science University, Portland, Oregon 97239-3098, USA
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Hermes SM, Mitchell JL, Aicher SA. Most neurons in the nucleus tractus solitarii do not send collateral projections to multiple autonomic targets in the rat brain. Exp Neurol 2006; 198:539-51. [PMID: 16487517 DOI: 10.1016/j.expneurol.2005.12.028] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2005] [Revised: 12/06/2005] [Accepted: 12/23/2005] [Indexed: 02/02/2023]
Abstract
The nucleus tractus solitarii (NTS) receives primary visceral afferents and sends projections to other autonomic nuclei at all levels of the neuroaxis. However, it is unknown if distinct populations of NTS neurons project to individual autonomic targets or if individual neurons in the NTS project to multiple autonomic targets. Understanding the basic circuitry of visceral reflex pathways is essential for the analyses of functional central autonomic networks. We examined projections from the NTS to autonomic targets within the hypothalamus (paraventricular nucleus, PVN), pons (parabrachial nucleus, PB), and medulla (caudal ventrolateral medulla, CVL) using retrograde tracing and immunohistochemistry. Dual retrograde tracer microinjections were made into pairs of targets (PVN + CVL; PVN + PB; PB + CVL), and the pattern of retrograde labeling was examined within NTS. The extent of collateralization, seen as dual retrogradely labeled neurons, was negligible for combined PVN and CVL injections and increased for injections combining PB with either PVN or CVL, but the majority of NTS neurons project to only one autonomic target. Immunohistochemistry for tyrosine hydroxylase (TH) was used to examine the pattern of TH-immunoreactivity (TH-ir) within retrogradely labeled NTS neurons. TH-ir was seen predominantly in projections to PVN, to a lesser degree in projections to PB, and was largely absent from projections to CVL. The percentage of dual retrogradely labeled neurons displaying TH-ir corresponded to the target displaying the most TH-ir, and TH-ir was not predictive of collateralization. Together, these results indicate that NTS neurons project to individual autonomic targets in the brain.
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Affiliation(s)
- Sam M Hermes
- Neurological Sciences Institute, Oregon Health & Science University, 505 NW 185th Avenue, Beaverton, OR 97006, USA
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46
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Corbett EKA, Sinfield JK, McWilliam PN, Deuchars J, Batten TFC. Differential expression of vesicular glutamate transporters by vagal afferent terminals in rat nucleus of the solitary tract: projections from the heart preferentially express vesicular glutamate transporter 1. Neuroscience 2005; 135:133-45. [PMID: 16084661 DOI: 10.1016/j.neuroscience.2005.06.010] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2005] [Accepted: 06/02/2005] [Indexed: 12/31/2022]
Abstract
The central projections and neurochemistry of vagal afferent neurones supplying the heart in the rat were investigated by injecting cholera toxin B-subunit into the pericardium. Transganglionically transported cholera toxin B-subunit was visualized in the medulla oblongata in axons and varicosities that were predominantly aggregated in the dorsomedial, dorsolateral, ventrolateral and commissural subnuclei of the caudal nucleus of the solitary tract. Unilateral vagal section in control rats prevented cholera toxin B-subunit labeling on the ipsilateral side of the nucleus of the solitary tract. Fluorescent and electron microscopic dual labeling showed colocalization of immunoreactivity for vesicular glutamate transporter 1, but only rarely vesicular glutamate transporters 2 or 3 with cholera toxin B-subunit in terminals in nucleus of the solitary tract, suggesting that cardiac vagal axons release glutamate as a neurotransmitter. In contrast, populations of vagal afferent fibers labeled by injection of cholera toxin B-subunit, tetra-methylrhodamine dextran or biotin dextran amine into the aortic nerve, stomach or nodose ganglion colocalized vesicular glutamate transporter 2 more frequently than vesicular glutamate transporter 1. The presence of other neurochemical markers of primary afferent neurones was examined in nucleus of the solitary tract axons and nodose ganglion cells labeled by pericardial cholera toxin B-subunit injections. Immunoreactivity for a 200-kDa neurofilament protein in many large, cholera toxin B-subunit-labeled nodose ganglion cells indicated that the cardiac afferent fibers labeled are mostly myelinated, whereas binding of Griffonia simplicifolia isolectin B4 to fewer small cholera toxin B-subunit-labeled ganglion cells suggested that tracer was also taken up by some non-myelinated axons. A few labeled nucleus of the solitary tract axons and ganglion cells were positive for substance P and calcitonin gene-related peptide, which are considered as peptide markers of nociceptive afferent neurones. These data suggest that the population of cardiac vagal afferents labeled by pericardial cholera toxin B-subunit injection is neurochemically varied, which may be related to a functional heterogeneity of baroreceptive, chemoreceptive and nociceptive afferent fibers. A high proportion of cardiac neurones appear to be glutamatergic, but differ from other vagal afferents in expressing vesicular glutamate transporter 1.
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Affiliation(s)
- E K A Corbett
- School of Medicine, Worsley Building, University of Leeds, Leeds LS2 9JT, UK
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47
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Belugin S, Mifflin S. Transient Voltage-Dependent Potassium Currents Are Reduced in NTS Neurons Isolated From Renal Wrap Hypertensive Rats. J Neurophysiol 2005; 94:3849-59. [PMID: 16293589 DOI: 10.1152/jn.00573.2005] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Whole cell patch-clamp measurements were made in neurons enzymatically dispersed from the nucleus of the solitary tract (NTS) to determine if alterations occur in voltage-dependent potassium channels from rats made hypertensive (HT) by unilateral nephrectomy/renal wrap for 4 wk. Some rats had the fluorescent tracer DiA applied to the aortic nerve before the experiment to identify NTS neurons receiving monosynaptic baroreceptor afferent inputs. Mean arterial pressure (MAP) was greater in 4-wk HT (165 ± 5 mmHg, n = 26, P < 0.001) rats compared with normotensive (NT) rats (109 ± 3 mmHg measured in 10 of 69 rats). Transient outward currents (TOCs) were observed in 67–82% of NTS neurons from NT and HT rats. At activation voltages from −10 to +10 mV, TOCs were significantly less in HT neurons compared with those observed in NT neurons ( P < 0.001). There were no differences in the voltage-dependent activation kinetics, the voltage dependence of steady-state inactivation, and the rise and decay time constants of the TOCs comparing neurons isolated from NT and HT rats. The 4-aminopyridine–sensitive component of the TOC was significantly less in neurons from HT compared with NT rats ( P < 0.001), whereas steady-state outward currents, whether or not sensitive to 4-aminopyridine or tetraethylammonium, were not different. Delayed excitation, studied under current clamp, was observed in 60–80% of NTS neurons from NT and HT rats and was not different comparing neurons from NT and HT rats. However, examination of the subset of NTS neurons exhibiting somatic DiA fluorescence revealed that DiA-labeled neurons from HT rats had a significantly shorter duration delayed excitation ( n = 8 cells, P = 0.022) than DiA-labeled neurons from NT rats ( n = 7 cells). Neurons with delayed excitation from HT rats had a significantly broader first action potential (AP) and a slower maximal downstroke velocity of repolarization compared with NT neurons with delayed excitation ( P = 0.016 and P = 0.014, respectively). The number of APs in the first 200 ms of a sustained depolarization was greater in HT than NT neurons ( P = 0.012). These results suggest that HT of 4-wk duration reduces TOCs in NTS neurons, and this contributes to reduced delayed excitation and increased AP responses to depolarizing inputs. Such changes could alter baroreflex function in hypertension.
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Affiliation(s)
- Sergei Belugin
- University of Texas Health Science Center at San Antonio, 78229-3900, USA
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Browning KN, Coleman FH, Travagli RA. Characterization of pancreas-projecting rat dorsal motor nucleus of vagus neurons. Am J Physiol Gastrointest Liver Physiol 2005; 288:G950-5. [PMID: 15637183 DOI: 10.1152/ajpgi.00549.2004] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
The electrophysiological and morphological properties of rat dorsal motor nucleus of the vagus (DMV) neurons innervating the pancreas were examined by using whole cell patch clamp recordings from brain stem slices and postfixation morphological reconstructions of Neurobiotin-filled neurons. Recordings were made from 178 DMV neurons whose projections had been identified by previous apposition of the fluorescent neuronal tracer DiI to the body of the pancreas. DMV neurons projecting to the pancreas had an input resistance of 434 +/- 14 M omega, an action potential duration of 3 +/- 0.1 ms, and an afterhyperpolarization of 18 +/- 0.4 mV amplitude and 108 +/- 7 ms time constant of decay; these electrophysiological properties resembled those of gastric-projecting neurons but were significantly different from those of intestinal-projecting neurons. Interestingly, 14 of 178 pancreas-projecting neurons showed the presence of a slowly developing afterhyperpolarization whose presence was not reported in DMV neurons projecting to any other gastrointestinal area. The morphological characteristics of pancreas-projecting neurons (soma area 274 +/- 12 microm2; soma diameter of 25 +/- 0.7 microm; soma form factor 0.74 +/- 0.01; segments 9.7 +/- 0.41), however, were similar to those of intestinal- but differed from those of gastric-projecting neurons. In summary, these results suggest that pancreas-projecting rat DMV neurons are heterogeneous with respect to some electrophysiological and morphological properties. These differences might underlie functional differences in the vagal modulation of pancreatic functions.
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Affiliation(s)
- Kirsteen N Browning
- Department of Neuroscience, Pennington Biomedical Research Center, Louisiana State University System, Baton Rouge, Louisiana 70808, USA
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Jin YH, Bailey TW, Andresen MC. Cranial afferent glutamate heterosynaptically modulates GABA release onto second-order neurons via distinctly segregated metabotropic glutamate receptors. J Neurosci 2005; 24:9332-40. [PMID: 15496669 PMCID: PMC6730106 DOI: 10.1523/jneurosci.1991-04.2004] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
The balance between excitation and inhibition dictates central integration. Glutamatergic and GABAergic neurotransmission dominate this process. Cranial primary afferents enter the brainstem to release glutamate (Glu) onto second-order neurons within the caudal nucleus tractus solitarius (NTS) to initiate autonomic reflexes. The simplest pathways for these reflexes contain as few as two central neurons, but display robust frequency-dependent behavior. Within NTS, multiple metabotropic Glu receptors (mGluRs) are present, but their roles are poorly understood. Using synaptically discriminated second-order NTS neurons in brainstem slices and mechanically dissociated NTS neurons with intact boutons, we show that Glu differentially controls GABA release via distinct presynaptic mGluRs. In second-order NTS neurons recorded in slices, activation of primary afferents at frequencies as low as 10 shocks per second released sufficient Glu to alter rates of spontaneous IPSCs (sIPSCs). In both approaches, group I mGluRs increased GABA release in some neurons, but, on different neurons, group II and group III mGluRs decreased the sIPSC rate. mGluR actions were remarkably rapid, with onset and reversal beginning within 100 msec. In all cases, mGluR actions were exclusively presynaptic, and mGluRs did not alter postsynaptic properties in second-order neurons in either slices or isolated neurons. Tests with capsaicin and alphabeta-methylene ATP suggest that myelinated and unmyelinated afferent pathways engage both mGluR-GABA mechanisms. Afferent Glu spillover provides heterosynaptic cross talk with GABAergic inhibition in NTS. This process may critically shape the dynamic character and use dependence for cranial afferent transmission at the first stage of autonomic reflexes.
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Affiliation(s)
- Young-Ho Jin
- Department of Physiology and Pharmacology, Oregon Health and Science University, Portland, Oregon 97239-3098, USA
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50
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Wang G, Anrather J, Huang J, Speth RC, Pickel VM, Iadecola C. NADPH oxidase contributes to angiotensin II signaling in the nucleus tractus solitarius. J Neurosci 2004; 24:5516-24. [PMID: 15201324 PMCID: PMC6729325 DOI: 10.1523/jneurosci.1176-04.2004] [Citation(s) in RCA: 146] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
Angiotensin II (AngII), acting through angiotensin type 1 (AT1) receptors, exerts powerful effects on central autonomic networks regulating cardiovascular homeostasis and fluid balance; however, the mechanisms of AngII signaling in functionally defined central autonomic neurons have not been fully elucidated. In vascular cells, reactive oxygen species (ROS) generated by the enzyme NADPH oxidase play a major role in AngII signaling. Thus, we sought to determine whether NADPH oxidase is present in central autonomic neurons and, if so, whether NADPH oxidase-derived ROS are involved in the effects of AngII on these neurons. The present studies focused on the intermediate dorsomedial nucleus of the solitary tract (dmNTS) because this region receives autonomic afferents via the vagus nerve and is an important site of AngII actions. Using double-label immunoelectron microscopy, we found that the essential NADPH oxidase subunit gp91phox is present in somatodendric and axonal profiles containing AT1 receptors. The gp91phox-labeled dendrites received inputs from large axon terminals resembling vagal afferents. In parallel experiments using patch clamp of dissociated NTS neurons anterogradely labeled via the vagus, we found that AngII potentiates the L-type Ca2+ currents, an effect mediated by AT1 receptors and abolished by the ROS scavenger Mn(III) tetrakis (4-benzoic acid) porphyrin chloride. The NADPH oxidase assembly inhibitor apocynin and the peptide inhibitor gp91phox docking sequence, but not its scrambled version, also blocked the potentiation. The results provide evidence that NADPH oxidase-derived ROS are involved in the effects of AngII on Ca2+ influx in NTS neurons receiving vagal afferents and support the notion that ROS are important signaling molecules in central autonomic networks.
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Affiliation(s)
- Gang Wang
- Division of Neurobiology, Department of Neurology and Neuroscience, Weill Medical College of Cornell University, New York, New York 10021, USA.
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