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Fernandes LG, Müller LO, Feijóo RA, Blanco PJ. Closed-loop baroreflex model with biophysically detailed afferent pathway. INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING 2024:e3849. [PMID: 39054666 DOI: 10.1002/cnm.3849] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/07/2023] [Revised: 05/22/2024] [Accepted: 06/30/2024] [Indexed: 07/27/2024]
Abstract
In this work, we couple a lumped-parameter closed-loop model of the cardiovascular system with a physiologically-detailed mathematical description of the baroreflex afferent pathway. The model features a classical Hodgkin-Huxley current-type model for the baroreflex afferent limb (primary neuron) and for the second-order neuron in the central nervous system. The pulsatile arterial wall distension triggers a frequency-modulated sequence of action potentials at the afferent neuron. This signal is then integrated at the brainstem neuron model. The efferent limb, representing the sympathetic and parasympathetic nervous system, is described as a transfer function acting on heart and blood vessel model parameters in order to control arterial pressure. Three in silico experiments are shown here: a step increase in the aortic pressure to evaluate the functionality of the reflex arch, a hemorrhagic episode and an infusion simulation. Through this model, it is possible to study the biophysical dynamics of the ionic currents proposed for the afferent limb components of the baroreflex during the cardiac cycle, and the way in which currents dynamics affect the cardiovascular function. Moreover, this system can be further developed to study in detail each baroreflex loop component, helping to unveil the mechanisms involved in the cardiovascular afferent information processing.
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Affiliation(s)
- Luciano Gonçalves Fernandes
- Instituto de Ciências Biológicas e da Saúde, Universidade Federal Rural do Rio de Janeiro, Rio de Janeiro, Brazil
- Instituto Nacional de Ciência e Tecnologia em Medicina Assistida por Computação Científica, Rio de Janeiro, Brazil
| | - Lucas Omar Müller
- Instituto Nacional de Ciência e Tecnologia em Medicina Assistida por Computação Científica, Rio de Janeiro, Brazil
- Coordenação de Métodos Matemáticos e Computacionais, Laboratório Nacional de Computação Científica, Petrópolis, Brazil
- Department of Mathematics, University of Trento, Trento, Italy
| | - Raúl Antonino Feijóo
- Instituto Nacional de Ciência e Tecnologia em Medicina Assistida por Computação Científica, Rio de Janeiro, Brazil
- Coordenação de Métodos Matemáticos e Computacionais, Laboratório Nacional de Computação Científica, Petrópolis, Brazil
| | - Pablo Javier Blanco
- Instituto Nacional de Ciência e Tecnologia em Medicina Assistida por Computação Científica, Rio de Janeiro, Brazil
- Coordenação de Métodos Matemáticos e Computacionais, Laboratório Nacional de Computação Científica, Petrópolis, Brazil
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Bagnall-Hare H, McLoone VI, Ringwood JV. On the accuracy of sequence methods for baroreflex sensitivity estimation. Phys Eng Sci Med 2024; 47:503-516. [PMID: 38564152 PMCID: PMC11166763 DOI: 10.1007/s13246-023-01380-y] [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: 03/27/2023] [Accepted: 12/22/2023] [Indexed: 04/04/2024]
Abstract
In the absence of a true gold standard for non-invasive baroreflex sensitivity estimation, it is difficult to quantify the accuracy of the variety of techniques used. A popular family of methods, usually entitled 'sequence methods' involves the extraction of (apparently) correlated sequences from blood pressure and RR-interval data and the subsequent fitting of a regression line to the data. This paper discusses the accuracy of sequence methods from a system identification perspective, using both data generated from a known mathematical model and spontaneous baroreflex data. It is shown that sequence methods can introduce significant bias in the baroreflex sensitivity estimate, even when great care is taken in sequence selection.
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Affiliation(s)
- Hasana Bagnall-Hare
- Department of Electronic Engineering, Maynooth University, Maynooth, Co. Kildare, Ireland.
| | - Violeta I McLoone
- Department of Aero, Mechanical and Electronic Engineering, South East Technological University, Waterford, Co. Carlow, Ireland
| | - John V Ringwood
- Department of Electronic Engineering, Maynooth University, Maynooth, Co. Kildare, Ireland
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3
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Ragozzino FJ, Karatsoreos IN, Peters JH. Principles of synaptic encoding of brainstem circadian rhythms. Exp Physiol 2024. [PMID: 38308846 DOI: 10.1113/ep090867] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2023] [Accepted: 01/16/2024] [Indexed: 02/05/2024]
Abstract
Circadian regulation of autonomic tone and reflex pathways pairs physiological processes with the daily light cycle. However, the underlying mechanisms mediating these changes on autonomic neurocircuitry are only beginning to be understood. The brainstem nucleus of the solitary tract (NTS) and adjacent nuclei, including the area postrema and dorsal motor nucleus of the vagus, are key candidates for rhythmic control of some aspects of the autonomic nervous system. Recent findings have contributed to a working model of circadian regulation in the brainstem which manifests from the transcriptional, to synaptic, to circuit levels of organization. Vagal afferent neurons and the NTS possess rhythmic clock gene expression, rhythmic action potential firing, and our recent findings demonstrate rhythmic spontaneous glutamate release. In addition, postsynaptic conductances also vary across the day producing subtle changes in membrane depolarization which govern synaptic efficacy. Together these coordinated pre- and postsynaptic changes provide nuanced control of synaptic transmission across the day to tune the sensitivity of primary afferent input and likely govern reflex output. Further, given the important role for the brainstem in integrating cues such as feeding, cardiovascular function and temperature, it may also be an underappreciated locus in mediating the effects of such non-photic entraining cues. This short review focuses on the neurophysiological principles that govern NTS synaptic transmission and how circadian rhythms impacted them across the day.
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Affiliation(s)
- Forrest J Ragozzino
- Department of Integrative Physiology and Neuroscience, College of Veterinary Medicine, Washington State University, Pullman, Washington, USA
| | - Ilia N Karatsoreos
- Department of Psychological and Brain Sciences, University of Massachusetts Amherst, Amherst, Massachusetts, USA
| | - James H Peters
- Department of Integrative Physiology and Neuroscience, College of Veterinary Medicine, Washington State University, Pullman, Washington, USA
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Chikamoto A, Tochinai R, Sekizawa SI, Kuwahara M. Plasticity occurs in a specific phenotype of neurons in the nucleus tractus solitarius of dystrophin gene-mutated rats. Eur J Neurosci 2023; 58:4282-4297. [PMID: 37933572 DOI: 10.1111/ejn.16179] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2023] [Revised: 10/03/2023] [Accepted: 10/09/2023] [Indexed: 11/08/2023]
Abstract
Duchenne muscular dystrophy (DMD) is a severe progressive neuromuscular disorder that causes cardiac and respiratory failure. Patients with DMD have tachycardia and autonomic nervous dysfunction at a young age, which can potentially worsen cardiorespiratory function. Therefore, we hypothesised that plasticity occurs in neurons of the cardiorespiratory brainstem nucleus (nucleus tractus solitarius [NTS]) due to DMD, thus affecting neuronal regulation because afferent information from cardiorespiratory organs changes with disease progression. Patch-clamp experiments were performed on second-order NTS neurons from Dmd-mutated (Dm) rats that showed no functional dystrophin protein expression, as confirmed by immunohistochemistry. NTS neurons are classified into two electrophysiological phenotypes: one showing a delayed onset of spiking from hyperpolarised membrane potentials, namely, delayed-onset spiking (DS)-type neurons, and the other showing a rapid onset, namely, rapid-onset spiking-type neurons. Neuroplasticity mainly occurs in DS-type neurons in Dm rats and is characterised by blunted neuronal excitability accompanied by reduced outward currents and a facilitatory effect on synaptic transmission, that is, an increased frequency of spontaneous and miniature excitatory postsynaptic currents (EPSCs) without changes in the amplitude and an increased amplitude of tractus solitarius-evoked EPSCs without changes in the paired-pulse ratio. Although we cannot rule out the possibility that the neuroplastic changes observed in Dm rats were caused by dystrophin deficiency in the neurons themselves, the plasticity could be caused by cardiorespiratory deterioration and/or adaptation in DMD patients.
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Affiliation(s)
- Akitoshi Chikamoto
- Laboratory of Veterinary Pathophysiology and Animal Health, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Tokyo, Japan
| | - Ryota Tochinai
- Laboratory of Veterinary Pathophysiology and Animal Health, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Tokyo, Japan
| | - Shin-Ichi Sekizawa
- Laboratory of Veterinary Pathophysiology and Animal Health, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Tokyo, Japan
| | - Masayoshi Kuwahara
- Laboratory of Veterinary Pathophysiology and Animal Health, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Tokyo, Japan
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Jin Z, Kim JB, Jin YH. Effect of endogenous substance P on visceral afferent signal integration in the nucleus tractus solitaries of rat brainstem slices. IBRO Neurosci Rep 2023; 15:327-334. [PMID: 38025662 PMCID: PMC10660985 DOI: 10.1016/j.ibneur.2023.10.007] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2023] [Revised: 10/23/2023] [Accepted: 10/23/2023] [Indexed: 12/01/2023] Open
Abstract
In the first synapse of the blood-pressure-regulating pathway, a neurokinin (NK) family peptide substance P (SP) is release with an excitatory neurotransmitter, glutamate, to enhance the sensitivity of the baroreflex responses. However, the underlying mechanisms of action are not yet well understood. The effects of NK receptor antagonists and agonists on solitary tract stimulation-evoked excitatory postsynaptic responses were recorded using whole-cell patch-clamp recordings of neurons in the medial portion of the nucleus tractus solitarius (mNTS) in the brainstem. SP reduced the amplitude of the evoked excitatory postsynaptic currents (eEPSCs) and shifted the holding current inward, in a dose-dependent manner. The concentrations of SP needed to induce such responses were different between capsaicin-sensitive unmyelinated (C-type) and capsaicin-resistant myelinated (A-type) neurons. The perfusion of a NK1 receptor antagonist, sendide, reduced the amplitude of eEPSCs in all tested neurons but did not affect the levels of the holding current. A Neurokinin type 1 receptor (NK1 receptor) agonist, [Sar9, Met(O2)11]-SP, reduced the amplitude of the eEPSCs and shifted the holding current inward in capsaicin-resistant neurons; however, it failed to induce any significant changes in the capsaicin-sensitive neurons. Furthermore, a selective Neurokinin type 3 receptor (NK3 receptor) antagonist, SB223412, failed to induce any changes in any tested neuron. In current-clamp experiments, sendide reduced solitary tract (ST)-stimulation evoked firing of action potentials in both A- and C-type neurons. [Sar9, Met(O2)11]-SP suppressed the firing of the action potentials in C-type but not A-type neurons. In spontaneous synaptic recordings, SP reduced frequency of the sEPSCs in CAP sensitive neuron but NK1 agonist reduced at capsaicin resistant neurons. Taken together, the findings show that ST activation leads to the co-transmission of SP and glutamate and enhances baroreflex sensitivity by potentiating the amplitude of eEPSC in an NK1 receptor activity-dependent manner.
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Affiliation(s)
- Zhenhua Jin
- Department of Physiology, College of Medicine, Kyung Hee University, Seoul 02447, Republic of Korea
| | - Jin-Bae Kim
- Division of Cardiology, Department of Internal Medicine, College of Medicine, 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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Umene R, Nakamura Y, Wu CH, Muta K, Nishino T, Inoue T. Induction of tetraspanin 13 contributes to the synergistic anti-inflammatory effects of parasympathetic and sympathetic stimulation in macrophages. Biochem Biophys Res Commun 2023; 665:187-194. [PMID: 37163939 DOI: 10.1016/j.bbrc.2023.04.118] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2023] [Accepted: 04/29/2023] [Indexed: 05/12/2023]
Abstract
The autonomic nervous system plays an important role in the regulation of peripheral inflammation. Sympathetic nervous activation stimulates inflammatory gene expression and cytokines, whereas parasympathetic nervous activation suppresses the production of inflammatory cytokines by immune cells. However, most studies on the relationship between the autonomic nervous system and immune processes have analyzed a single branch of the autonomic nerves in isolation. Therefore, this study aimed to examine the effects of sympathetic and parasympathetic stimulation on macrophages, which are controlled by autonomic regulation. Macrophages were stimulated with lipopolysaccharide (LPS) to induce TNF-α. Then, the effects of β2 adrenergic receptor and α7 nicotinic acetylcholine receptor activation on TNF-α production were assessed using concentration-dependent assays. RNA-seq data were also used to identify genes whose expression was enhanced by parasympathetic and sympathetic stimulation. The simultaneous activation of β2 adrenergic receptors and α7 nicotinic acetylcholine receptors suppressed LPS-induced TNF-α production in a concentration-dependent manner. Moreover, simultaneous activation of these receptors had synergistic anti-inflammatory effects and induced Tspan13 expression, thereby contributing to anti-inflammatory mechanisms in macrophages. Our study revealed the synergistic anti-inflammatory effects of the parasympathetic and sympathetic stimulation of macrophages. Our results suggest that targeting both sympathetic and parasympathetic signaling is a promising therapeutic approach for inflammatory diseases.
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Affiliation(s)
- Ryusuke Umene
- Department of Physiology of Visceral Function and Body Fluid, Graduate School of Biomedical Sciences, Nagasaki University, Nagasaki, Japan; Department of Nephrology, Graduate School of Biomedical Sciences, Nagasaki University, Nagasaki, Japan
| | - Yasuna Nakamura
- Department of Physiology of Visceral Function and Body Fluid, Graduate School of Biomedical Sciences, Nagasaki University, Nagasaki, Japan
| | - Chia-Hsien Wu
- Department of Physiology of Visceral Function and Body Fluid, Graduate School of Biomedical Sciences, Nagasaki University, Nagasaki, Japan
| | - Kumiko Muta
- Department of Nephrology, Graduate School of Biomedical Sciences, Nagasaki University, Nagasaki, Japan
| | - Tomoya Nishino
- Department of Nephrology, Graduate School of Biomedical Sciences, Nagasaki University, Nagasaki, Japan.
| | - Tsuyoshi Inoue
- Department of Physiology of Visceral Function and Body Fluid, Graduate School of Biomedical Sciences, Nagasaki University, Nagasaki, Japan.
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Mun J, Lee J, Park E, Park SM. Frequency-dependent depression of the NTS synapse affects the temporal response of the antihypertensive effect of auricular vagus nerve stimulation (aVNS). J Neural Eng 2022; 19. [PMID: 35905707 DOI: 10.1088/1741-2552/ac857a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2022] [Accepted: 07/29/2022] [Indexed: 11/12/2022]
Abstract
OBJECTIVES Auricular vagus nerve stimulation (aVNS) has recently emerged as a promising neuromodulation modality for blood pressure (BP) reduction due to its ease of use although its efficacy is still limited compared to direct baroreflex stimulation. Previous studies have also indicated that synaptic depression of nucleus tractus solitarius (NTS) in the baroreflex pathway depends on stimulus frequency. However, the nature of this frequency dependence phenomenon on antihypertensive effect has been unknown for aVNS. We aimed to investigate the antihypertensive effect of aVNS considering frequency-dependent depression characteristic in the NTS synapse. We explored NTS activation and BP reduction induced by aVNS and by direct secondary neuron stimulation (DS). APPROACH Both protocols were performed with recording of NTS activation and BP response with stimulation for each frequency parameter (2, 4, 20, 50, and 80 Hz). MAIN RESULTS The BP recovery time constant was significantly dependent on the frequency of DS and aVNS (DS - 2 Hz: 8.17 ± 4.98; 4 Hz: 9.73 ± 6.3; 20 Hz: 6.61 ± 3.28; 50 Hz: 4.93 ± 1.65; 80 Hz: 4.00 ± 1.43, p < 0.001, Kruskal-Wallis H-test / aVNS - 2 Hz: 4.02 ± 2.55; 4 Hz: 8.13 ± 4.05; 20 Hz: 6.40 ± 3.16; 50 Hz: 5.18 ± 2.37; 80 Hz: 3.13 ± 1.29, p < 0.05, Kruskal-Wallis H-test) despite no significant BP reduction at 2 Hz compared to sham groups (p > 0.05, Mann-Whitney U-test). SIGNIFICANCE Our observations suggest that the antihypertensive effect of aVNS is influenced by the characteristics of frequency-dependent synaptic depression in the NTS neuron in terms of the BP recovery time. These findings suggest that the antihypertensive effect of aVNS can be improved with further understanding of the neurological properties of the baroreflex associated with aVNS, which is critical to push this new modality for clinical interpretation.
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Affiliation(s)
- Junseung Mun
- Department of Convergence IT Engineering, POSTECH, IMSLAB, 2nd floor, C5 building, POSTECH 77, Cheongam-ro, Nam-gu, South Korea, Pohang, 37673, Korea (the Republic of)
| | - Jiho Lee
- Department of Convergence IT Engineering, Pohang University of Science and Technology, IMSLAB, 2nd floor, C5 building, POSTECH 77, Cheongam-ro, Nam-gu, South Korea, Pohang, 37673, Korea (the Republic of)
| | - Eunkyoung Park
- Department of Medical and Mechatronics Engineering, Soonchunhyang University, Chungnam 31538, Asan, Korea, Asan, Chungcheongnam-do, 31538, Korea (the Republic of)
| | - Sung-Min Park
- POSTECH, IMSLAB, 2nd floor, C5 building, POSTECH 77, Cheongam-ro, Nam-gu, South Korea, Pohang, 37673, Korea (the Republic of)
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Lima-Silveira L, Hasser EM, Kline DD. Cardiovascular deconditioning increases GABA signaling in the nucleus tractus solitarii. J Neurophysiol 2022; 128:28-39. [PMID: 35642806 PMCID: PMC9236861 DOI: 10.1152/jn.00102.2022] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The nucleus tractus solitarii (nTS) is the major integrative brainstem region for autonomic modulation and processing of cardiovascular reflexes. GABA and glutamate are the main inhibitory and excitatory neurotransmitters, respectively, within this nucleus. Alterations in the GABA-glutamate regulation in the nTS are related to numerous cardiovascular comorbidities. Bedridden individuals and people exposed to microgravity exhibit dysautonomia and cardiovascular deconditioning that are mimicked in the hindlimb unloading (HU) rat model. We have previously shown in the nTS that HU increases glutamatergic neurotransmission yet decreases neuronal excitability. In this study, we investigated the effects of HU on nTS GABAergic neurotransmission. We hypothesized that HU potentiates GABA signaling via increased GABAergic release and postsynaptic GABA receptor expression. Following HU or control postural exposure, GABAergic neurotransmission was assessed using whole cell patch clamp whereas the magnitude of GABA release was evaluated via an intensity-based GABA sensing fluorescence reporter (iGABASnFR). In response to GABA interneuron stimulation, the evoked inhibitory postsynaptic current (nTS-IPSC) amplitude and area, as well as iGABASnFR fluorescence, were greater in HU than in control. HU also elevated the frequency but not the amplitude of spontaneous miniature IPSCs. Picoapplication of GABA produced similar postsynaptic current responses in nTS neurons of HU and control. Moreover, HU did not alter GABAA receptor α1 subunit expression, indicating minimal alterations in postsynaptic membrane receptor expression. These results indicate that HU increases GABAergic signaling in the nTS likely via augmented release of GABA from presynaptic terminals. Altogether, our data indicate GABA plasticity contributes to the autonomic and cardiovascular alterations following cardiovascular deconditioning (CVD).NEW & NOTEWORTHY Gravity influences distribution of blood volume and autonomic function. Microgravity and prolonged bed rest induce cardiovascular deconditioning (CVD). We used hindlimb unloading (HU), a rat analog for bed rest, to investigate CVD-induced neuroplasticity in the brainstem. Our data demonstrate that HU increases GABA modulation of nucleus tractus solitarii (nTS) neurons via presynaptic plasticity. Given the importance of nTS in integrating cardiovascular reflexes, this study provides new evidence on the central mechanisms behind CVD following HU.
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Affiliation(s)
- Ludmila Lima-Silveira
- 1Department of Biomedical Sciences, University of Missouri, Columbia, Missouri,3Dalton Cardiovascular Research Center, University of Missouri, Columbia, Missouri
| | - Eileen M. Hasser
- 1Department of Biomedical Sciences, University of Missouri, Columbia, Missouri,2Department of Medical Pharmacology and Physiology, University of Missouri, Columbia, Missouri,3Dalton Cardiovascular Research Center, University of Missouri, Columbia, Missouri
| | - David D. Kline
- 1Department of Biomedical Sciences, University of Missouri, Columbia, Missouri,2Department of Medical Pharmacology and Physiology, University of Missouri, Columbia, Missouri,3Dalton Cardiovascular Research Center, University of Missouri, Columbia, Missouri
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Brandlhuber M, Benhaqi P, Brandlhuber B, Koliogiannis V, Kasparek MS, Mueller MH, Kreis ME. The role of vagal innervation on the early development of postoperative ileus in mice. Neurogastroenterol Motil 2022; 34:e14308. [PMID: 34962331 DOI: 10.1111/nmo.14308] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/07/2020] [Revised: 05/30/2021] [Accepted: 10/27/2021] [Indexed: 02/08/2023]
Abstract
BACKGROUND Postoperative ileus (POI) involves an intestinal inflammatory response that is modulated by afferent and efferent vagal activation. We aimed to identify the potential influence of the vagus nerve on POI by tracking central vagal activation and its role for peripheral inflammatory changes during the early hours after surgery. METHODS C57BL6 mice were vagotomized (V) 3-4 days prior to experiments, while control animals received sham vagotomy (SV). Subgroups underwent either laparotomy (sham operation; S-POI) or laparotomy followed by standardized small bowel manipulation to induce postoperative ileus (POI). Three hours and 9 h later, respectively, a jejunal segment was harvested and infiltration of inflammatory cells in intestinal muscularis was evaluated by fluorescein isothiocyanate (FITC) avidin and myeloperoxidase (MPO) staining. Moreover, the brain stem was harvested, and central nervous activation was investigated by Fos immunochemistry in both the nucleus of the solitary tract (NTS) and the area postrema (AP). Data are presented as mean ± SEM, and a p < 0.05 was considered statistically significant. KEY RESULTS Three hour experiments revealed no significant differences between all experimental groups, except MPO staining: 3 h after abdominal surgery, there were significantly more MPO-positive cells in vagotomized S-POI animals compared to sham-vagotomized S-POI animals (26.7 ± 7.1 vs. 5.1 ± 2.4, p < 0.01). Nine hour postoperatively intramuscular mast cells (IMMC) were significantly decreased in the intestinal muscularis of V/POI animals compared to SV/POI animals (1.5 ± 0.3 vs. 5.9 ± 0.2, p < 0.05), while MPO-positive cells were increased in V/POI animals compared to SV/POI animals (713.2 ± 99.4 vs. 46.9 ± 5.8, p < 0.05). There were less Fos-positive cells in the NTS of V/POI animals compared to SV/POI animals (64.7 ± 7.8 vs. 132.8 ± 23.9, p < 0.05) and more Fos-positive cells in the AP of V/POI animals compared to SV/POI animals 9 h postoperatively (38.0 ± 2.0 vs. 13.7 ± 0.9, p < 0.001). CONCLUSIONS AND INTERFERENCES Afferent nerve signaling to the central nervous system during the development of early POI seems to be mediated mainly via the vagus nerve and to a lesser degree via systemic circulation. During the early hours of POI, the intestinal immune response may be attenuated by vagal modulation, suggesting interactions between the central nervous system and the intestine.
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Affiliation(s)
- Martina Brandlhuber
- Department of Radiology, Grosshadern Clinic, Ludwig-Maximilians-University Munich, Munich, Germany
| | - Petra Benhaqi
- Center for Human Genetics and Laboratory Diagnostics, Medical Labs Martinsried, Martinsried, Germany
| | | | - Vanessa Koliogiannis
- Department of Radiology, Grosshadern Clinic, Ludwig-Maximilians-University Munich, Munich, Germany
| | | | - Mario H Mueller
- Department of Surgery and Minimal-Invasive Surgery, Vivantes Klinikum Neukölln, Berlin, Germany
| | - Martin E Kreis
- Department of General and Visceral Surgery, Charité University Medicine Berlin, Campus Benjamin Franklin, Berlin, Germany
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Lima-Silveira L, Martinez D, Hasser EM, Kline DD. Mechanisms Underlying Neuroplasticity in the Nucleus Tractus Solitarii Following Hindlimb Unloading in Rats. Neuroscience 2020; 449:214-227. [PMID: 33039526 DOI: 10.1016/j.neuroscience.2020.09.043] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2020] [Revised: 09/15/2020] [Accepted: 09/20/2020] [Indexed: 12/11/2022]
Abstract
Hindlimb unloading (HU) in rats induces cardiovascular deconditioning (CVD) analogous to that observed in individuals exposed to microgravity or bed rest. Among other physiological changes, HU rats exhibit autonomic imbalance and altered baroreflex function. Lack of change in visceral afferent activity that projects to the brainstem in HU rats suggests that neuronal plasticity within central nuclei processing cardiovascular afferents may be responsible for these changes in CVD and HU. The nucleus tractus solitarii (nTS) is a critical brainstem region for autonomic control and integration of cardiovascular reflexes. In this study, we used patch electrophysiology, live-cell calcium imaging and molecular methods to investigate the effects of HU on glutamatergic synaptic transmission and intrinsic properties of nTS neurons. HU increased the amplitude of monosynaptic excitatory postsynaptic currents and presynaptic calcium entry evoked by afferent tractus solitarii stimulus (TS-EPSC); spontaneous (s) EPSCs were unaffected. The addition of a NMDA receptor antagonist (AP5) reduced TS-EPSC amplitude and sEPSC frequency in HU but not control. Despite the increase in glutamatergic inputs, HU neurons were more hyperpolarized and exhibited intrinsic decreased excitability compared to controls. After block of ionotropic glutamatergic and GABAergic synaptic transmission (NBQX, AP5, Gabazine), HU neuronal membrane potential depolarized and neuronal excitability was comparable to controls. These data demonstrate that HU increases presynaptic release and TS-EPSC amplitude, which includes a NMDA receptor component. Furthermore, the decreased excitability and hyperpolarized membrane after HU are associated with enhanced GABAergic modulation. This functional neuroplasticity in the nTS may underly the CVD induced by HU.
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Affiliation(s)
- Ludmila Lima-Silveira
- Department of Biomedical Sciences, University of Missouri, 134 Research Park Dr., Columbia, MO 65211, USA; Dalton Cardiovascular Research Center, University of Missouri, 134 Research Park Dr., Columbia, MO 65211, USA.
| | - Diana Martinez
- Department of Biomedical Sciences, University of Missouri, 134 Research Park Dr., Columbia, MO 65211, USA; Dalton Cardiovascular Research Center, University of Missouri, 134 Research Park Dr., Columbia, MO 65211, USA.
| | - Eileen M Hasser
- Department of Biomedical Sciences, University of Missouri, 134 Research Park Dr., Columbia, MO 65211, USA; Department of Medical Pharmacology and Physiology, University of Missouri, 134 Research Park Dr., Columbia, MO 65211, USA; Dalton Cardiovascular Research Center, University of Missouri, 134 Research Park Dr., Columbia, MO 65211, USA.
| | - David D Kline
- Department of Biomedical Sciences, University of Missouri, 134 Research Park Dr., Columbia, MO 65211, USA; Dalton Cardiovascular Research Center, University of Missouri, 134 Research Park Dr., Columbia, MO 65211, USA.
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11
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Leptin Sensitizes NTS Neurons to Vagal Input by Increasing Postsynaptic NMDA Receptor Currents. J Neurosci 2020; 40:7054-7064. [PMID: 32817248 DOI: 10.1523/jneurosci.1865-19.2020] [Citation(s) in RCA: 20] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2019] [Revised: 12/05/2019] [Accepted: 07/27/2020] [Indexed: 11/21/2022] Open
Abstract
Leptin signaling within the nucleus of the solitary tract (NTS) contributes to the control of food intake, and injections of leptin into the NTS reduce meal size and increase the efficacy of vagus-mediated satiation signals. Leptin receptors (LepRs) are expressed by vagal afferents as well as by a population of NTS neurons. However, the electrophysiological properties of LepR-expressing NTS neurons have not been well characterized, and it is unclear how leptin might act on these neurons to reduce food intake. To address this question, we recorded from LepR-expressing neurons in horizontal brain slices containing the NTS from male and female LepR-Cre X Rosa-tdTomato mice. We found that the vast majority of NTS LepR neurons received monosynaptic innervation from vagal afferent fibers and LepR neurons exhibited large synaptic NMDA receptor (NMDAR)-mediated currents compared with non-LepR neurons. During high-frequency stimulation of vagal afferents, leptin increased the size of NMDAR-mediated currents, but not AMPAR-mediated currents. Leptin also increased the size of evoked EPSPs and the ability of low-intensity solitary tract stimulation to evoke action potentials in LepR neurons. These effects of leptin were blocked by bath applying a competitive NMDAR antagonist (DCPP-ene) or by an NMDAR channel blocker applied through the recording pipette (MK-801). Last, feeding studies using male rats demonstrate that intra-NTS injections of DCPP-ene attenuate reduction of overnight food intake following intra-NTS leptin injection. Our results suggest that leptin acts in the NTS to reduce food intake by increasing NMDAR-mediated currents, thus enhancing NTS sensitivity to vagal inputs.SIGNIFICANCE STATEMENT Leptin is a hormone that critically impacts food intake and energy homeostasis. The nucleus of the solitary tract (NTS) is activated by vagal afferents from the gastrointestinal tract, which promotes termination of a meal. Injection of leptin into the NTS inhibits food intake, while knockdown of leptin receptors (LepRs) in NTS neurons increases food intake. However, little was known about how leptin acts in the NTS neurons to inhibit food intake. We found that leptin increases the sensitivity of LepR-expressing neurons to vagal inputs by increasing NMDA receptor-mediated synaptic currents and that NTS NMDAR activation contributes to leptin-induced reduction of food intake. These findings suggest a novel mechanism by which leptin, acting in the NTS, could potentiate gastrointestinal satiation signals.
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Gauda EB, Conde S, Bassi M, Zoccal DB, Almeida Colombari DS, Colombari E, Despotovic N. Leptin: Master Regulator of Biological Functions that Affects Breathing. Compr Physiol 2020; 10:1047-1083. [PMID: 32941688 DOI: 10.1002/cphy.c190031] [Citation(s) in RCA: 17] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Obesity is a global epidemic in developed countries accounting for many of the metabolic and cardiorespiratory morbidities that occur in adults. These morbidities include type 2 diabetes, sleep-disordered breathing (SDB), obstructive sleep apnea, chronic intermittent hypoxia, and hypertension. Leptin, produced by adipocytes, is a master regulator of metabolism and of many other biological functions including central and peripheral circuits that control breathing. By binding to receptors on cells and neurons in the brainstem, hypothalamus, and carotid body, leptin links energy and metabolism to breathing. In this comprehensive article, we review the central and peripheral locations of leptin's actions that affect cardiorespiratory responses during health and disease, with a particular focus on obesity, SDB, and its effects during early development. Obesity-induced hyperleptinemia is associated with centrally mediated hypoventilation with decrease CO2 sensitivity. On the other hand, hyperleptinemia augments peripheral chemoreflexes to hypoxia and induces sympathoexcitation. Thus, "leptin resistance" in obesity is relative. We delineate the circuits responsible for these divergent effects, including signaling pathways. We review the unique effects of leptin during development on organogenesis, feeding behavior, and cardiorespiratory responses, and how undernutrition and overnutrition during critical periods of development can lead to cardiorespiratory comorbidities in adulthood. We conclude with suggestions for future directions to improve our understanding of leptin dysregulation and associated clinical diseases and possible therapeutic targets. Lastly, we briefly discuss the yin and the yang, specifically the contribution of relative adiponectin deficiency in adults with hyperleptinemia to the development of metabolic and cardiovascular disease. © 2020 American Physiological Society. Compr Physiol 10:1047-1083, 2020.
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Affiliation(s)
- Estelle B Gauda
- Division of Neonatology, Department of Pediatrics, The Hospital for Sick Children, Toronto, Ontario, Canada
| | - Silvia Conde
- CEDOC, NOVA Medical School, Faculdade de Ciências Médicas, Lisboa, Portugal
| | - Mirian Bassi
- Department of Physiology and Pathology, School of Dentistry, São Paulo State University (UNESP), Araraquara, São Paulo, Brazil
| | - Daniel B Zoccal
- Department of Physiology and Pathology, School of Dentistry, São Paulo State University (UNESP), Araraquara, São Paulo, Brazil
| | - Debora Simoes Almeida Colombari
- Department of Physiology and Pathology, School of Dentistry, São Paulo State University (UNESP), Araraquara, São Paulo, Brazil
| | - Eduardo Colombari
- Department of Physiology and Pathology, School of Dentistry, São Paulo State University (UNESP), Araraquara, São Paulo, Brazil
| | - Nikola Despotovic
- Faculty of Medicine, University of Toronto, Toronto, Ontario, Canada
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Sklerov M, Dayan E, Browner N. Functional neuroimaging of the central autonomic network: recent developments and clinical implications. Clin Auton Res 2018; 29:555-566. [PMID: 30470943 PMCID: PMC6858471 DOI: 10.1007/s10286-018-0577-0] [Citation(s) in RCA: 79] [Impact Index Per Article: 13.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2018] [Accepted: 11/07/2018] [Indexed: 12/08/2023]
Abstract
Purpose The central autonomic network (CAN) is an intricate system of brainstem, subcortical, and cortical structures that play key roles in the function of the autonomic nervous system. Prior to the advent of functional neuroimaging, in vivo studies of the human CAN were limited. The purpose of this review is to highlight the contribution of functional neuroimaging, specifically functional magnetic resonance imaging (fMRI), to the study of the CAN, and to discuss recent advances in this area. Additionally, we aim to emphasize exciting areas for future research. Methods We reviewed the existing literature in functional neuroimaging of the CAN. Here, we focus on fMRI research conducted in healthy human subjects, as well as research that has been done in disease states, to understand CAN function. To minimize confounding, papers examining CAN function in the context of cognition, emotion, pain, and affective disorders were excluded. Results fMRI has led to significant advances in the understanding of human CAN function. The CAN is composed of widespread brainstem and forebrain structures that are intricately connected and play key roles in reflexive and modulatory control of autonomic function. Conclusions fMRI technology has contributed extensively to current knowledge of CAN function. It holds promise to serve as a biomarker in disease states. With ongoing advancements in fMRI technology, there is great opportunity and need for future research involving the CAN.
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Affiliation(s)
- Miriam Sklerov
- Department of Neurology, University of North Carolina, 170 Manning Drive, CB# 7025, Chapel Hill, NC, 27599, USA.
| | - Eran Dayan
- Department of Radiology and Biomedical Research Imaging Center, University of North Carolina, 130 Mason Farm Road, CB# 7513, Chapel Hill, NC, 27599, USA
| | - Nina Browner
- Department of Neurology, University of North Carolina, 170 Manning Drive, CB# 7025, Chapel Hill, NC, 27599, USA
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Chen J, Gu H, Wurster RD, Cheng Z. Baroreflex Control of Heart Rate in Mice Overexpressing Human SOD1: Functional Changes in Central and Vagal Efferent Components. Neurosci Bull 2018; 35:91-97. [PMID: 30460537 PMCID: PMC6357281 DOI: 10.1007/s12264-018-0302-y] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2018] [Accepted: 08/06/2018] [Indexed: 12/16/2022] Open
Abstract
Excessive reactive oxygen species (ROS) (such as the superoxide radical) are commonly associated with cardiac autonomic dysfunctions. Though superoxide dismutase 1 (SOD1) overexpression may protect against ROS damage to the autonomic nervous system, superoxide radical reduction may change normal physiological functions. Previously, we demonstrated that human SOD1 (hSOD1) overexpression does not change baroreflex bradycardia and tachycardia but rather increases aortic depressor nerve activity in response to arterial pressure changes in C57B6SJL-Tg (SOD1)2 Gur/J mice. Since the baroreflex arc includes afferent, central, and efferent components, the objective of this study was to determine whether hSOD1 overexpression alters the central and vagal efferent mediation of heart rate (HR) responses. Our data indicate that SOD1 overexpression decreased the HR responses to vagal efferent nerve stimulation but did not change the HR responses to aortic depressor nerve (ADN) stimulation. Along with the previous study, we suggest that SOD1 overexpression preserves normal baroreflex function but may differentially alter the functions of the ADN, vagal efferents, and central components. While SOD1 overexpression likely enhanced ADN function and the central mediation of bradycardia, it decreased vagal efferent control of HR.
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Affiliation(s)
- Jin Chen
- Division of Neuroscience and Division of Metabolic and Cardiovascular Sciences, Burnett School of Biomedical Sciences, College of Medicine, University of Central Florida, Orlando, FL, 32816, USA
| | - He Gu
- Division of Neuroscience and Division of Metabolic and Cardiovascular Sciences, Burnett School of Biomedical Sciences, College of Medicine, University of Central Florida, Orlando, FL, 32816, USA
| | - Robert D Wurster
- Department of Cellular and Molecular Physiology, Stritch School of Medicine, Loyola University, Maywood, IL, 60153, USA
| | - Zixi Cheng
- Division of Neuroscience and Division of Metabolic and Cardiovascular Sciences, Burnett School of Biomedical Sciences, College of Medicine, University of Central Florida, Orlando, FL, 32816, USA.
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Liu Y, Wu D, Qu MY, He JL, Yuan M, Zhao M, Wang JX, He J, Wang LQ, Guo XJ, Zuo M, Zhao SY, Ma MN, Li JN, Shou W, Qiao GF, Li BY. Neuropeptide Y-mediated sex- and afferent-specific neurotransmissions contribute to sexual dimorphism of baroreflex afferent function. Oncotarget 2018; 7:66135-66148. [PMID: 27623075 PMCID: PMC5323221 DOI: 10.18632/oncotarget.11880] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2015] [Accepted: 07/16/2016] [Indexed: 01/19/2023] Open
Abstract
Background Molecular and cellular mechanisms of neuropeptide-Y (NPY)-mediated gender-difference in blood pressure (BP) regulation are largely unknown. Methods Baroreceptor sensitivity (BRS) was evaluated by measuring the response of BP to phenylephrine/nitroprusside. Serum NPY concentration was determined using ELISA. The mRNA and protein expression of NPY receptors were assessed in tissue and single-cell by RT-PCR, immunoblot, and immunohistochemistry. NPY was injected into the nodose while arterial pressure was monitored. Electrophysiological recordings were performed on nodose neurons from rats by patch-clamp technique. Results The BRS was higher in female than male and ovariectomized rats, while serum NPY concentration was similar among groups. The sex-difference was detected in Y1R, not Y2R protein expression, however, both were upregulated upon ovariectomy and canceled by estrogen replacement. Immunostaining confirmed Y1R and Y2R expression in myelinated and unmyelinated afferents. Single-cell PCR demonstrated that Y1R expression/distribution was identical between A- and C-types, whereas, expressed level of Y2R was ∼15 and ∼7 folds higher in Ah- and C-types than A-types despite similar distribution. Activation of Y1R in nodose elevated BP, while activation of Y2R did the opposite. Activation of Y1R did not alter action potential duration (APD) of A-types, but activation of Y2R- and Y1R/Y2R in Ah- and C-types frequency-dependently prolonged APD. N-type ICa was reduced in A-, Ah- and C-types when either Y1R, Y2R, or both were activated. The sex-difference in Y1R expression was also observed in NTS. Conclusions Sex- and afferent-specific expression of Neuropeptide-Y receptors in baroreflex afferent pathway may contribute to sexual-dimorphic neurocontrol of BP regulation.
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Affiliation(s)
- Yang Liu
- Department of Pharmacology, Harbin Medical University, Harbin, China
| | - Di Wu
- Key Laboratory of Cardiovascular Research of Ministry of Education, Harbin Medical University, Harbin, China
| | - Mei-Yu Qu
- Key Laboratory of Cardiovascular Research of Ministry of Education, Harbin Medical University, Harbin, China
| | - Jian-Li He
- Key Laboratory of Cardiovascular Research of Ministry of Education, Harbin Medical University, Harbin, China
| | - Mei Yuan
- Department of Pharmacology, Harbin Medical University, Harbin, China
| | - Miao Zhao
- Key Laboratory of Cardiovascular Research of Ministry of Education, Harbin Medical University, Harbin, China
| | - Jian-Xin Wang
- Key Laboratory of Cardiovascular Research of Ministry of Education, Harbin Medical University, Harbin, China
| | - Jian He
- Key Laboratory of Cardiovascular Research of Ministry of Education, Harbin Medical University, Harbin, China
| | - Lu-Qi Wang
- Key Laboratory of Cardiovascular Research of Ministry of Education, Harbin Medical University, Harbin, China
| | - Xin-Jing Guo
- Department of Pharmacology, Harbin Medical University, Harbin, China
| | - Meng Zuo
- Department of Pharmacology, Harbin Medical University, Harbin, China
| | - Shu-Yang Zhao
- Key Laboratory of Cardiovascular Research of Ministry of Education, Harbin Medical University, Harbin, China
| | - Mei-Na Ma
- Key Laboratory of Cardiovascular Research of Ministry of Education, Harbin Medical University, Harbin, China
| | - Jun-Nan Li
- Department of Pharmacology, Harbin Medical University, Harbin, China
| | - Weinian Shou
- Riley Heart Research Center, Division of Pediatric Cardiology, Herman B. Wells Center for Pediatric Research, Department of Pediatrics, Indiana University School of Medicine, Indianapolis, IN, USA
| | - Guo-Fen Qiao
- Department of Pharmacology, Harbin Medical University, Harbin, China.,Key Laboratory of Cardiovascular Research of Ministry of Education, Harbin Medical University, Harbin, China
| | - Bai-Yan Li
- Department of Pharmacology, Harbin Medical University, Harbin, China
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Donnelly WT, Xia L, Bartlett D, Leiter JC. Activation of serotonergic neurons in the medullary caudal raphe shortens the laryngeal chemoreflex in anaesthetized neonatal rats. Exp Physiol 2017; 102:1007-1018. [PMID: 28675564 DOI: 10.1113/ep086082] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2016] [Accepted: 05/25/2017] [Indexed: 12/29/2022]
Abstract
NEW FINDINGS What is the central question of this study? Does activation of serotonergic neurons in the caudal medullary raphe, some of which project to the nucleus of the solitary tract, shorten the laryngeal chemoreflex? What is the main finding and its importance? We found that serotonin originating from neurons in the caudal raphe acts through a 5-HT3 receptor located in the nucleus of the solitary tract to terminate reflex apnoea. Failure or deficiency of this arousal-related process is likely to be relevant to the pathogenesis of sudden infant death syndrome. Failure to terminate apnoea and arouse is likely to contribute to sudden infant death syndrome (SIDS). Serotonin is deficient in the brainstems of babies who have died of SIDS. We tested the hypothesis that activation of serotoninergic neurons in the caudal medullary raphe, some of which project to the nucleus of the solitary tract (NTS), would shorten the laryngeal chemoreflex (LCR). We studied anaesthetized neonatal rat pups between postnatal days 9 and 17. We injected 5-40 μl of water into the larynx to elicit the LCR and measured the duration of respiratory disruption. Microinjection of 50 nl of 100 μm AMPA into the caudal medullary raphe shortened the apnoeas (P < 0.001) and respiratory inhibition (P < 0.005) associated with the LCR. When 50 nl of 30 mm ondansetron, a 5-HT3 antagonist, was microinjected bilaterally into the NTS, AMPA microinjected into the caudal raphe no longer shortened the LCR. After bilateral microinjection of vehicle into the NTS, AMPA microinjection into the caudal raphe significantly shortened the LCR. AMPA, a glutamate receptor agonist, may activate many neurons within the caudal raphe, but blocking the 5-HT3 receptor-dependent responses in the NTS prevented the shortening of the LCR associated with AMPA microinjections into the caudal raphe. Thus, serotonin originating from neurons in the caudal raphe acts through a 5-HT3 receptor located in the NTS to terminate or shorten the LCR. Serotonin is deficient in the brainstems of babies who have died of SIDS, and deficient serotonergic termination of apnoea is likely to be relevant to the pathogenesis of SIDS.
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Affiliation(s)
- William T Donnelly
- Department of Molecular and Systems Biology, Geisel School of Medicine at Dartmouth, Lebanon, NH, USA
| | - Luxi Xia
- Department of Molecular and Systems Biology, Geisel School of Medicine at Dartmouth, Lebanon, NH, USA
| | - Donald Bartlett
- Department of Molecular and Systems Biology, Geisel School of Medicine at Dartmouth, Lebanon, NH, USA
| | - J C Leiter
- Department of Molecular and Systems Biology, Geisel School of Medicine at Dartmouth, Lebanon, NH, USA
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Kolpakova J, Li L, Hatcher JT, Gu H, Zhang X, Chen J, Cheng ZJ. Responses of Nucleus Tractus Solitarius (NTS) early and late neurons to blood pressure changes in anesthetized F344 rats. PLoS One 2017; 12:e0169529. [PMID: 28384162 PMCID: PMC5383029 DOI: 10.1371/journal.pone.0169529] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2016] [Accepted: 12/19/2016] [Indexed: 02/07/2023] Open
Abstract
Previously, many different types of NTS barosensitive neurons were identified. However, the time course of NTS barosensitive neuronal activity (NA) in response to arterial pressure (AP) changes, and the relationship of NA-AP changes, have not yet been fully quantified. In this study, we made extracellular recordings of single NTS neurons firing in response to AP elevation induced by occlusion of the descending aorta in anesthetized rats. Our findings were that: 1) Thirty-five neurons (from 46 neurons) increased firing, whereas others neurons either decreased firing upon AP elevation, or were biphasic: first decreased firing upon AP elevation and then increased firing during AP decrease. 2) Fourteen neurons with excitatory responses were activated and rapidly increased their firing during the early phase of AP increase (early neurons); whereas 21 neurons did not increase firing until the mean arterial pressure changes (ΔMAP) reached near/after the peak (late neurons). 3) The early neurons had a significantly higher firing rate than late neurons during AP elevation at a similar rate. 4) Early neuron NA-ΔMAP relationship could be well fitted and characterized by the sigmoid logistic function with the maximal gain of 29.3. 5) The increase of early NA correlated linearly with the initial heart rate (HR) reduction. 6) The late neurons did not contribute to the initial HR reduction. However, the late NA could be well correlated with HR reduction during the late phase. Altogether, our study demonstrated that the NTS excitatory neurons could be grouped into early and late neurons based on their firing patterns. The early neurons could be characterized by the sigmoid logistic function, and different neurons may differently contribute to HR regulation. Importantly, the grouping and quantitative methods used in this study may provide a useful tool for future assessment of functional changes of early and late neurons in disease models.
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Affiliation(s)
- Jenya Kolpakova
- Burnett School of Biomedical Sciences, College of Medicine, University of Central Florida, Orlando FL, United States of America
| | - Liang Li
- Burnett School of Biomedical Sciences, College of Medicine, University of Central Florida, Orlando FL, United States of America
| | - Jeffrey T. Hatcher
- Burnett School of Biomedical Sciences, College of Medicine, University of Central Florida, Orlando FL, United States of America
| | - He Gu
- Burnett School of Biomedical Sciences, College of Medicine, University of Central Florida, Orlando FL, United States of America
| | - Xueguo Zhang
- Department of Neurology, Henry Ford Hospital, Detroit, Michigan, United States of America
| | - Jin Chen
- Burnett School of Biomedical Sciences, College of Medicine, University of Central Florida, Orlando FL, United States of America
| | - Zixi Jack Cheng
- Burnett School of Biomedical Sciences, College of Medicine, University of Central Florida, Orlando FL, United States of America
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Cuéllar R, Montero S, Luquín S, García-Estrada J, Melnikov V, Virgen-Ortiz A, Lemus M, Pineda-Lemus M, de Álvarez-Buylla E. BDNF and AMPA receptors in the cNTS modulate the hyperglycemic reflex after local carotid body NaCN stimulation. Auton Neurosci 2017; 205:12-20. [PMID: 28254195 DOI: 10.1016/j.autneu.2017.02.001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2016] [Revised: 11/29/2016] [Accepted: 02/01/2017] [Indexed: 11/30/2022]
Abstract
The application of sodium cyanide (NaCN) to the carotid body receptors (CBR) (CBR stimulation) induces rapid blood hyperglycemia and an increase in brain glucose retention. The commissural nucleus tractus solitarius (cNTS) is an essential relay nucleus in this hyperglycemic reflex; it receives glutamatergic afferents (that also release brain derived neurotrophic factor, BDNF) from the nodose-petrosal ganglia that relays CBR information. Previous work showed that AMPA in NTS blocks hyperglycemia and brain glucose retention after CBR stimulation. In contrast, BDNF, which attenuates glutamatergic AMPA currents in NTS, enhances these glycemic responses. Here we investigated the combined effects of BDNF and AMPA (and their antagonists) in NTS on the glycemic responses to CBR stimulation. Microinjections of BDNF plus AMPA into the cNTS before CBR stimulation in anesthetized rats, induced blood hyperglycemia and an increase in brain arteriovenous (a-v) of blood glucose concentration difference, which we infer is due to increased brain glucose retention. By contrast, the microinjection of the TrkB antagonist K252a plus AMPA abolished the glycemic responses to CBR stimulation similar to what is observed after AMPA pretreatments. In BDNF plus AMPA microinjections preceding CBR stimulation, the number of c-fos immunoreactive cNTS neurons increased. In contrast, in the rats microinjected with K252a plus AMPA in NTS, before CBR stimulation, c-fos expression in cNTS decreased. The expression of AMPA receptors GluR2/3 did not change in any of the studied groups. These results indicate that BDNF in cNTS plays a key role in the modulation of the hyperglycemic reflex initiated by CBR stimulation.
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Affiliation(s)
- R Cuéllar
- Centro Universitario de Investigaciones Biomédicas, Universidad de Colima, Ave. 25 de Julio 965, Colima 28045, Mexico; Departamento de Neurociencias, Centro Universitario de Ciencias de la Salud, Universidad de Guadalajara, Sierra Mojada 950, Guadalajara 44340, Mexico
| | - S Montero
- Centro Universitario de Investigaciones Biomédicas, Universidad de Colima, Ave. 25 de Julio 965, Colima 28045, Mexico; Facultad de Medicina, Universidad de Colima, Ave. Universidad 333, Colima 28040, Mexico
| | - S Luquín
- Departamento de Neurociencias, Centro Universitario de Ciencias de la Salud, Universidad de Guadalajara, Sierra Mojada 950, Guadalajara 44340, Mexico
| | - J García-Estrada
- Departamento de Neurociencias, Centro Universitario de Ciencias de la Salud, Universidad de Guadalajara, Sierra Mojada 950, Guadalajara 44340, Mexico; División de Investigación Quirúrgica, Centro de Investigación Biomédica de Occidente, IMSS, Guadalajara, Mexico
| | - V Melnikov
- Facultad de Medicina, Universidad de Colima, Ave. Universidad 333, Colima 28040, Mexico
| | - A Virgen-Ortiz
- Centro Universitario de Investigaciones Biomédicas, Universidad de Colima, Ave. 25 de Julio 965, Colima 28045, Mexico
| | - M Lemus
- Centro Universitario de Investigaciones Biomédicas, Universidad de Colima, Ave. 25 de Julio 965, Colima 28045, Mexico
| | - M Pineda-Lemus
- Facultad de Medicina, Universidad de Colima, Ave. Universidad 333, Colima 28040, Mexico
| | - E de Álvarez-Buylla
- Centro Universitario de Investigaciones Biomédicas, Universidad de Colima, Ave. 25 de Julio 965, Colima 28045, Mexico.
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McCulloch PF, Warren EA, DiNovo KM. Repetitive Diving in Trained Rats Still Increases Fos Production in Brainstem Neurons after Bilateral Sectioning of the Anterior Ethmoidal Nerve. Front Physiol 2016; 7:148. [PMID: 27148082 PMCID: PMC4838619 DOI: 10.3389/fphys.2016.00148] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2015] [Accepted: 04/05/2016] [Indexed: 12/19/2022] Open
Abstract
This research was designed to investigate the role of the anterior ethmoidal nerve (AEN) during repetitive trained diving in rats, with specific attention to activation of afferent and efferent brainstem nuclei that are part of this reflexive response. The AEN innervates the nose and nasal passages and is thought to be an important component of the afferent limb of the diving response. Male Sprague-Dawley rats (N = 24) were trained to swim and dive through a 5 m underwater maze. Some rats (N = 12) had bilateral sectioning of the AEN, others a Sham surgery (N = 12). Twelve rats (6 AEN cut and 6 Sham) had 24 post-surgical dive trials over 2 h to activate brainstem neurons to produce Fos, a neuronal activation marker. Remaining rats were non-diving controls. Diving animals had significantly more Fos-positive neurons than non-diving animals in the caudal pressor area, ventral medullary dorsal horn, ventral paratrigeminal nucleus, nucleus tractus solitarius, rostral ventrolateral medulla, Raphe nuclei, A5, Locus Coeruleus, and Kölliker-Fuse area. There were no significant differences in brainstem Fos labeling in rats diving with and without intact AENs. Thus, the AENs are not required for initiation of the diving response. Other nerve(s) that innervate the nose and nasal passages, and/or suprabulbar activation of brainstem neurons, may be responsible for the pattern of neuronal activation observed during repetitive trained diving in rats. These results help define the central neuronal circuitry of the mammalian diving response.
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Affiliation(s)
- Paul F McCulloch
- Department of Physiology, Chicago College of Osteopathic Medicine, Midwestern University Downers Grove, IL, USA
| | - Erik A Warren
- Department of Physiology, Chicago College of Osteopathic Medicine, Midwestern University Downers Grove, IL, USA
| | - Karyn M DiNovo
- Department of Physiology, Chicago College of Osteopathic Medicine, Midwestern University Downers Grove, IL, USA
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Boxwell AJ, Chen Z, Mathes CM, Spector AC, Le Roux CW, Travers SP, Travers JB. Effects of high-fat diet and gastric bypass on neurons in the caudal solitary nucleus. Physiol Behav 2015. [PMID: 26216080 DOI: 10.1016/j.physbeh.2015.07.025] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
Abstract
Bariatric surgery is an effective treatment for obesity that involves both peripheral and central mechanisms. To elucidate central pathways by which oral and visceral signals are influenced by high-fat diet (HFD) and Roux-en-Y gastric bypass (RYGB) surgery, we recorded from neurons in the caudal visceral nucleus of the solitary tract (cNST, N=287) and rostral gustatory NST (rNST,N=106) in rats maintained on a HFD and lab chow (CHOW) or CHOW alone, and subjected to either RYGB or sham surgery. Animals on the HFD weighed significantly more than CHOW rats and RYGB reversed and then blunted weight gain regardless of diet. Using whole-cell patch clamp recording in a brainstem slice, we determined the membrane properties of cNST and rNST neurons associated with diet and surgery. We could not detect differences in rNST neurons associated with these manipulations. In cNST neurons, neither the threshold for solitary tract stimulation nor the amplitude of evoked EPSCs at threshold varied by condition; however suprathreshold EPSCs were larger in HFD compared to chow-fed animals. In addition, a transient outward current, most likely an IA current, was increased with HFD and RYGB reduced this current as well as a sustained outward current. Interestingly, hypothalamic projecting cNST neurons preferentially express IA and modulate transmission of afferent signals (Bailey, '07). Thus, diet and RYGB have multiple effects on the cellular properties of neurons in the visceral regions of NST, with potential to influence inputs to forebrain feeding circuits.
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Affiliation(s)
- A J Boxwell
- Ohio State Univ., Columbus, OH, United States
| | - Z Chen
- Ohio State Univ., Columbus, OH, United States
| | - C M Mathes
- Florida State Univ., Tallahassee, FL, United States
| | - A C Spector
- Florida State Univ., Tallahassee, FL, United States
| | | | - S P Travers
- Ohio State Univ., Columbus, OH, United States
| | - J B Travers
- Ohio State Univ., Columbus, OH, United States.
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Boychuk CR, Gyarmati P, Xu H, Smith BN. Glucose sensing by GABAergic neurons in the mouse nucleus tractus solitarii. J Neurophysiol 2015; 114:999-1007. [PMID: 26084907 DOI: 10.1152/jn.00310.2015] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2015] [Accepted: 06/15/2015] [Indexed: 12/23/2022] Open
Abstract
Changes in blood glucose concentration alter autonomic function in a manner consistent with altered neural activity in brain regions controlling digestive processes, including neurons in the brain stem nucleus tractus solitarii (NTS), which process viscerosensory information. With whole cell or on-cell patch-clamp recordings, responses to elevating glucose concentration from 2.5 to 15 mM were assessed in identified GABAergic NTS neurons in slices from transgenic mice that express EGFP in a subset of GABA neurons. Single-cell real-time RT-PCR was also performed to detect glutamic acid decarboxylase (GAD67) in recorded neurons. In most identified GABA neurons (73%), elevating glucose concentration from 2.5 to 15 mM resulted in either increased (40%) or decreased (33%) neuronal excitability, reflected by altered membrane potential and/or action potential firing. Effects on membrane potential were maintained when action potentials or fast synaptic inputs were blocked, suggesting direct glucose sensing by GABA neurons. Glucose-inhibited GABA neurons were found predominantly in the lateral NTS, whereas glucose-excited cells were mainly in the medial NTS, suggesting regional segregation of responses. Responses were prevented in the presence of glucosamine, a glucokinase (GCK) inhibitor. Depolarizing responses were prevented when KATP channel activity was blocked with tolbutamide. Whereas effects on synaptic input to identified GABAergic neurons were variable in GABA neurons, elevating glucose increased glutamate release subsequent to stimulation of tractus solitarius in unlabeled, unidentified neurons. These results indicate that GABAergic NTS neurons act as GCK-dependent glucose sensors in the vagal complex, providing a means of modulating central autonomic signals when glucose is elevated.
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Affiliation(s)
- Carie R Boychuk
- Department of Physiology, University of Kentucky College of Medicine, Lexington, Kentucky
| | - Peter Gyarmati
- Department of Physiology, University of Kentucky College of Medicine, Lexington, Kentucky
| | - Hong Xu
- Department of Physiology, University of Kentucky College of Medicine, Lexington, Kentucky
| | - Bret N Smith
- Department of Physiology, University of Kentucky College of Medicine, Lexington, Kentucky
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22
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Babic T, Ambler J, Browning KN, Travagli RA. Characterization of synapses in the rat subnucleus centralis of the nucleus tractus solitarius. J Neurophysiol 2014; 113:466-74. [PMID: 25355962 DOI: 10.1152/jn.00598.2014] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023] Open
Abstract
The nucleus tractus solitarius (NTS) receives subdiaphragmatic visceral sensory information via vagal A- or C-fibers. We have recently shown that, in contrast to cardiovascular NTS medialis neurons, which respond to either purinergic or vanilloid agonists, the majority of esophageal NTS centralis (cNTS) neurons respond to vanilloid agonists, whereas a smaller subset responds to both vanilloid and purinerigic agonists. The present study aimed to further investigate the neurochemical and synaptic characteristics of cNTS neurons using whole cell patch-clamp, single cell RT-PCR and immunohistochemistry. Excitatory postsynaptic currents (EPSCs) were evoked in cNTS by tractus solitarius stimulation, and in 19 of 64 neurons perfusion with the purinergic agonist αβ-methylene ATP (αβMeATP) increased the evoked EPSC amplitude significantly. Furthermore, neurons with αβMeATP-responsive synaptic inputs had different probabilities of release compared with nonresponsive neurons. Single cell RT-PCR revealed that 8 of 13 αβMeATP-responsive neurons expressed metabotropic glutamate receptor 8 (mGluR8) mRNA, which our previous studies have suggested is a marker of glutamatergic neurons, whereas only 3 of 13 expressed glutamic acid dehydroxylase, a marker of GABAergic neurons. A significantly lower proportion of αβMeATP-nonresponsive neurons expressed mGluR8 (2 of 30 neurons), whereas a greater proportion expressed glutamic acid dehydroxylase (12 of 30 neurons). Esophageal distension significantly increased the number of colocalized mGluR8- and c-Fos-immunoreactive neurons in the cNTS from 8.0 ± 4% to 20 ± 2.5%. These data indicate that cNTS comprises distinct neuronal subpopulations that can be distinguished based on their responses to purinergic agonists and that these subpopulations have distinct neurochemical and synaptic characteristics, suggesting that integration of sensory inputs from the esophagus relies on a discrete organization of synapses between vagal afferent fibers and cNTS neurons.
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Affiliation(s)
- Tanja Babic
- Department of Neural and Behavioral Sciences, Penn State University College of Medicine, Hershey, Pennsylvania
| | - Jason Ambler
- Department of Neural and Behavioral Sciences, Penn State University College of Medicine, Hershey, Pennsylvania
| | - Kirsteen N Browning
- Department of Neural and Behavioral Sciences, Penn State University College of Medicine, Hershey, Pennsylvania
| | - R Alberto Travagli
- Department of Neural and Behavioral Sciences, Penn State University College of Medicine, Hershey, Pennsylvania
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Emanueli C, Meloni M, Hasan W, Habecker BA. The biology of neurotrophins: cardiovascular function. Handb Exp Pharmacol 2014; 220:309-28. [PMID: 24668478 DOI: 10.1007/978-3-642-45106-5_12] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
This chapter addresses the role of neurotrophins in the development of the heart, blood vessels, and neural circuits that control cardiovascular function, as well as the role of neurotrophins in the mature cardiovascular system. The cardiovascular system includes the heart and vasculature whose functions are tightly controlled by the nervous system. Neurons, cardiomyocytes, endothelial cells, vascular smooth muscle cells, and pericytes are all targets for neurotrophin action during development. Neurotrophin expression continues throughout life, and several common pathologies that impact cardiovascular function involve changes in the expression or activity of neurotrophins. These include atherosclerosis, hypertension, diabetes, acute myocardial infarction, and heart failure. In many of these conditions, altered expression of neurotrophins and/or neurotrophin receptors has direct effects on vascular endothelial and smooth muscle cells in addition to effects on nerves that modulate vascular resistance and cardiac function. This chapter summarizes the effects of neurotrophins in cardiovascular physiology and pathophysiology.
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Affiliation(s)
- Costanza Emanueli
- Regenerative Medicine Section, School of Clinical Sciences, Bristol Heart Institute, University of Bristol, Bristol, UK,
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24
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Santa Cruz Chavez GC, Li BY, Glazebrook PA, Kunze DL, Schild JH. An afferent explanation for sexual dimorphism in the aortic baroreflex of rat. Am J Physiol Heart Circ Physiol 2014; 307:H910-21. [PMID: 25038145 DOI: 10.1152/ajpheart.00332.2014] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Sex differences in baroreflex (BRx) function are well documented. Hormones likely contribute to this dimorphism, but many functional aspects remain unresolved. Our lab has been investigating a subset of vagal sensory neurons that constitute nearly 50% of the total population of myelinated aortic baroreceptors (BR) in female rats but less than 2% in male rats. Termed "Ah," this unique phenotype has many of the nonoverlapping electrophysiological properties and chemical sensitivities of both myelinated A-type and unmyelinated C-type BR afferents. In this study, we utilize three distinct experimental protocols to determine if Ah-type barosensory afferents underlie, at least in part, the sex-related differences in BRx function. Electron microscopy of the aortic depressor nerve (ADN) revealed that female rats have less myelin (P < 0.03) and a smaller fiber cross-sectional area (P < 0.05) per BR fiber than male rats. Electrical stimulation of the ADN evoked compound action potentials and nerve conduction profiles that were markedly different (P < 0.01, n = 7 females and n = 9 males). Selective activation of ADN myelinated fibers evoked a BRx-mediated depressor response that was 3-7 times greater in female (n = 16) than in male (n = 17) rats. Interestingly, the most striking hemodynamic difference was functionally dependent upon the rate of myelinated barosensory fiber activation. Only 5-10 Hz of stimulation evoked a rapid, 20- to 30-mmHg reduction in arterial pressure of female rats, whereas rates of 50 Hz or higher were required to elicit a comparable depressor response from male rats. Collectively, our experimental results are suggestive of an alternative myelinated baroreceptor afferent pathway in females that may account for, at least in part, the noted sex-related differences in autonomic control of cardiovascular function.
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Affiliation(s)
- Grace C Santa Cruz Chavez
- Stark Neurosciences Research Institute, Indiana University School of Medicine, Indianapolis, Indiana; Department of Biomedical Engineering, Indiana University Purdue University Indianapolis, Indianapolis, Indiana
| | - Bai-Yan Li
- Department of Biomedical Engineering, Indiana University Purdue University Indianapolis, Indianapolis, Indiana
| | - Patricia A Glazebrook
- Rammelkamp Center for Education and Research, MetroHealth Campus, Cleveland, Ohio; and
| | - Diana L Kunze
- Rammelkamp Center for Education and Research, MetroHealth Campus, Cleveland, Ohio; and Department of Neurosciences, Case Western Reserve University, Cleveland, Ohio
| | - John H Schild
- Stark Neurosciences Research Institute, Indiana University School of Medicine, Indianapolis, Indiana; Department of Biomedical Engineering, Indiana University Purdue University Indianapolis, Indianapolis, Indiana;
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25
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Montero S, Lemus M, Luquin S, Garcia-Estrada J, Melnikov V, Leal CA, Portilla-de Buen E, Roces de Álvarez-Buylla E. Nitric oxide in the commissural nucleus tractus solitarii regulates carotid chemoreception hyperglycemic reflex and c-Fos expression. Nitric Oxide 2014; 36:87-93. [DOI: 10.1016/j.niox.2013.12.004] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2013] [Revised: 11/28/2013] [Accepted: 12/05/2013] [Indexed: 11/28/2022]
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26
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Anandamide, cannabinoid type 1 receptor, and NMDA receptor activation mediate non-Hebbian presynaptically expressed long-term depression at the first central synapse for visceral afferent fibers. J Neurosci 2013; 33:12627-37. [PMID: 23904599 DOI: 10.1523/jneurosci.1028-13.2013] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Presynaptic long-term depression (LTD) of synapse efficacy generally requires coordinated activity between presynaptic and postsynaptic neurons and a retrograde signal synthesized by the postsynaptic cell in an activity-dependent manner. In this study, we examined LTD in the rat nucleus tractus solitarii (NTS), a brainstem nucleus that relays homeostatic information from the internal body to the brain. We found that coactivation of N-methyl-D-aspartate receptors (NMDARs) and type 1 cannabinoid receptors (CB1Rs) induces LTD at the first central excitatory synapse between visceral fibers and NTS neurons. This LTD is presynaptically expressed. However, neither postsynaptic activation of NMDARs nor postsynaptic calcium influx are required for its induction. Direct activation of NMDARs triggers cannabinoid-dependent LTD. In addition, LTD is unaffected by blocking 2-arachidonyl-glycerol synthesis, but its induction threshold is lowered by preventing fatty acid degradation. Altogether, our data suggest that LTD in NTS neurons may be entirely expressed at the presynaptic level by local anandamide synthesis.
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Andresen MC, Hofmann ME, Fawley JA. The unsilent majority-TRPV1 drives "spontaneous" transmission of unmyelinated primary afferents within cardiorespiratory NTS. Am J Physiol Regul Integr Comp Physiol 2012; 303:R1207-16. [PMID: 23076872 PMCID: PMC3532589 DOI: 10.1152/ajpregu.00398.2012] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2012] [Accepted: 10/11/2012] [Indexed: 01/29/2023]
Abstract
Cranial primary afferent sensory neurons figure importantly in homeostatic control of visceral organ systems. Of the two broad classes of visceral afferents, the role of unmyelinated or C-type class remains poorly understood. This review contrasts key aspects of peripheral discharge properties of C-fiber afferents and their glutamate transmission mechanisms within the solitary tract nucleus (NTS). During normal prevailing conditions, most information arrives at the NTS through myelinated A-type nerves. However, most of visceral afferent axons (75-90%) in NTS are unmyelinated, C-type axons. Centrally, C-type solitary tract (ST) afferent terminals have presynaptic transient receptor potential vanilloid type 1 (TRPV1) receptors. Capsaicin activation of TRPV1 blocks phasic or synchronous release of glutamate but facilitates release of glutamate from a separate pool of vesicles. This TRPV1-operated pool of vesicles is active at normal temperatures and is responsible for actively driving a 10-fold higher release of glutamate at TRPV1 compared with TRPV1- terminals even in the absence of afferent action potentials. This novel TRPV1 mechanism is responsible for an additional asynchronous release of glutamate that is not present in myelinated terminals. The NTS is rich with presynaptic G protein-coupled receptors, and the implications of TRPV1-operated glutamate offer unique targets for signaling in C-type sensory afferent terminals from neuropeptides, inflammatory mediators, lipid metabolites, cytokines, and cannabinoids. From a homeostatic view, this combination could have broad implications for integration in chronic pathological disturbances in which the numeric dominance of C-type endings and TRPV1 would broadly disturb multisystem control mechanisms.
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Affiliation(s)
- Michael C Andresen
- Department of Physiology and Pharmacology, Oregon Health and Science University, Portland, OR 97239-3098, USA.
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28
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McDougall SJ, Andresen MC. Low-fidelity GABA transmission within a dense excitatory network of the solitary tract nucleus. J Physiol 2012; 590:5677-89. [PMID: 22946100 DOI: 10.1113/jphysiol.2012.241976] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
Visceral primary afferents enter the CNS at the caudal solitary tract nucleus (NTS), and activate central pathways key to autonomic and homeostatic regulation. Excitatory transmission from primary solitary tract (ST)-afferents consists of multiple contacts originating from single axons that offer a remarkably high probability of glutamate release and high safety factor for ST afferent excitation. ST afferent activation sometimes triggers polysynaptic GABAergic circuits, which feedback onto second-order NTS neurons. Although inhibitory transmission is observed at second-order neurons, much less is known about the organization and mechanisms regulating GABA transmission. Here, we used a focal pipette to deliver minimal stimulus shocks near second-order NTS neurons in rat brainstem slices and directly activated single GABAergic axons. Most minimal focal shocks activated low jitter EPSCs from single axons with characteristics resembling ST afferents. Much less commonly (9% of sites), minimal focal shocks activated monosynaptic IPSCs at fixed latency (low jitter) that often failed (30%) and had no frequency-dependent facilitation or depression. These GABA release characteristics contrasted markedly to the unfailing, large amplitudes for glutamate released during ST-EPCSs recorded from the same neurons. Surprisingly, unitary GABAergic IPSCs were only weakly calcium dependent. In some neurons, strong focal shocks evoked compound IPSCs indicating convergent summation of multiple inhibitory axons. Our studies demonstrate that second-order NTS neurons receive GABAergic transmission from a diffuse network of inhibitory axons that rely on an intrinsically less reliable and substantially weaker release apparatus than ST excitation. Effective inhibition depends on co-activation of convergent inputs to blunt excitatory drive.
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Affiliation(s)
- Stuart J McDougall
- Department of Physiology & Pharmacology, Oregon Health & Science University, Portland OR, USA.
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29
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Smith SM, Chen W, Vyleta NP, Williams C, Lee CH, Phillips C, Andresen MC. Calcium regulation of spontaneous and asynchronous neurotransmitter release. Cell Calcium 2012; 52:226-33. [PMID: 22748761 DOI: 10.1016/j.ceca.2012.06.001] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2012] [Revised: 05/23/2012] [Accepted: 06/01/2012] [Indexed: 11/28/2022]
Abstract
The molecular machinery underlying action potential-evoked, synchronous neurotransmitter release, has been intensely studied. It was presumed that two other forms of exocytosis, delayed (asynchronous) and spontaneous transmission, were mediated by the same voltage-activated Ca(2+) channels (VACCs), intracellular Ca(2+) sensors and vesicle pools. However, a recent explosion in the study of spontaneous and asynchronous release has shown these presumptions to be incorrect. Furthermore, the finding that different forms of synaptic transmission may mediate distinct physiological functions emphasizes the importance of identifying the mechanisms by which Ca(2+) regulates spontaneous and asynchronous release. In this article, we will briefly summarize new and published data on the role of Ca(2+) in regulating spontaneous and asynchronous release at a number of different synapses. We will discuss how an increase of extracellular [Ca(2+)] increases spontaneous and asynchronous release, show that VACCs are involved at only some synapses, and identify regulatory roles for other ion channels and G protein-coupled receptors. In particular, we will focus on two novel pathways that play important roles in the regulation of non-synchronous release at two exemplary synapses: one modulated by the Ca(2+)-sensing receptor and the other by transient receptor potential cation channel sub-family V member 1.
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Affiliation(s)
- Stephen M Smith
- Division of Pulmonary & Critical Care Medicine, Oregon Health & Science University, Portland, OR 97239, United States.
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Browning KN, Wan S, Baptista V, Travagli RA. Vanilloid, purinergic, and CCK receptors activate glutamate release on single neurons of the nucleus tractus solitarius centralis. Am J Physiol Regul Integr Comp Physiol 2011; 301:R394-401. [PMID: 21543639 DOI: 10.1152/ajpregu.00054.2011] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Baroreceptor inputs to nucleus of the tractus solitarius medialis (mNTS) neurons can be differentiated, among other features, by their response to vanilloid or purinergic agonists, active only on C- or A-fibers, respectively. A major aim of this study was to examine whether neurons of NTS centralis (cNTS), a subnucleus dominated by esophageal inputs, exhibit a similar dichotomy. Since it has been suggested that cholecystokinin (CCK), exerts its gastrointestinal (GI)-related effects via paracrine activation of vagal afferent C-fibers, we tested whether CCK-sensitive fibers impinging upon cNTS neurons are responsive to vanilloid but not purinergic agonists. Using whole cell patch-clamp recordings from cNTS, we recorded miniature excitatory postsynaptic currents (mEPSCs) to test the effects of the vanilloid agonist capsaicin, the purinergic agonist α,β-methylene-ATP (α,β-Met-ATP), and/or CCK-octapeptide (CCK-8s). α,β-Met-ATP, capsaicin; and CCK-8s increased EPSC frequency in 37, 71, and 46% of cNTS neurons, respectively. Approximately 30% of cNTS neurons were responsive to both CCK-8s and α,β-Met-ATP, to CCK-8s and capsaicin, or to α,β-Met-ATP and capsaicin, while 32% of neurons were responsive to all three agonists. All neurons responding to either α,β-Met-ATP or CCK-8s were also responsive to capsaicin. Perivagal capsaicin, which is supposed to induce a selective degeneration of C-fibers, decreased the number of cNTS neurons responding to capsaicin or CCK-8s but not those responding to α,β-Met-ATP. In summary, GI inputs to cNTS neurons cannot be distinguished on the basis of their selective responses to α,β-Met-ATP or capsaicin. Our data also indicate that CCK-8s increases glutamate release from purinergic and vanilloid responsive fibers impinging on cNTS neurons.
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Affiliation(s)
- Kirsteen N Browning
- Neural and Behavioral Sciences, Penn State College of Medicine, Hershey, Pennsylvania 17033-0850, USA
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31
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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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Abstract
Central synapses spontaneously release neurotransmitter at low rates. In the brainstem, cranial visceral afferent terminals in caudal solitary tract nucleus (NTS) display pronounced, activity-dependent, asynchronous release of glutamate and this extra release depends on TRPV1 receptors (TRPV1+). Asynchronous release is absent for afferents lacking TRPV1 (TRPV1-) and resting EPSC frequency was greater in TRPV1+. Here, we studied this basal activity difference by assessing thermal sensitivity of spontaneous and miniature synaptic events in TRPV1+ and TRPV1- second-order NTS neurons. The spontaneous EPSC rate decreased when temperature was decreased, increased steeply between 30 and 42°C only in TRPV1+ neurons, and was calcium-dependent. TRPV1-specific antagonist SB366791, but not TTX, strongly attenuated thermal responses. Temperature changes failed to alter EPSC frequency in TRPV1- neurons. EPSC amplitudes and decay kinetics changed little with temperature. IPSCs in these second-order NTS neurons were unaltered by temperature. Such results suggest that activated, presynaptic TRPV1+ receptors trigger continuous resting release of glutamate vesicles at physiological temperatures only in capsaicin-responsive terminals. In mechanically isolated individual neurons harvested from medial NTS, increases in temperature increased the rate of glutamate release only in TRPV1+ neurons, whereas IPSC rates were unaffected. Cadmium failed to block thermal increases in glutamate release, suggesting that calcium entry through TRPV1 channels may trigger glutamate release independently of voltage-activated calcium channels. Together, our findings indicate a new form of afferent signaling in which TRPV1 channels within central terminals of peripheral afferents tonically generate glutamate release in NTS at 37°C in the absence of afferent action potentials.
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Kline DD. Chronic intermittent hypoxia affects integration of sensory input by neurons in the nucleus tractus solitarii. Respir Physiol Neurobiol 2010; 174:29-36. [PMID: 20416405 DOI: 10.1016/j.resp.2010.04.015] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2010] [Revised: 04/13/2010] [Accepted: 04/13/2010] [Indexed: 01/19/2023]
Abstract
The autonomic nervous and respiratory systems, as well as their coupling, adapt over a wide range of conditions. Chronic intermittent hypoxia (CIH) is a model for recurrent apneas and induces alterations in breathing and increases in sympathetic nerve activity which may ultimately result in hypertension if left untreated. These alterations are believed to be due to increases in the carotid body chemoreflex pathway. Here we present evidence that the nucleus tractus solitarii (nTS), the central brainstem termination site of chemoreceptor afferents, expresses a form of synaptic plasticity that increases overall nTS activity following intermittent hypoxia. Following CIH, an increase in presynaptic spontaneous neurotransmitter release occurs under baseline conditions. Furthermore, during and following afferent stimulation there is an augmentation of spontaneous transmitter release that occurs out of synchrony with sensory stimulation. On the other hand, afferent evoked synchronous transmitter release is attenuated. Overall, this shift from synchronous to asynchronous transmitter release enhances nTS cellular discharge. The role of the neurotransmitter dopamine in CIH-induced plasticity is also discussed. Dopamine attenuates synaptic transmission in nTS cells by blockade of N-type calcium channels, and this mechanism occurs tonically following normoxia and CIH. This dopaminergic pathway, however, is not altered in CIH. Taken together, alterations in nTS synaptic activity may play a role in the changes of chemoreflex function and cardiorespiratory activity in the CIH apnea model.
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Affiliation(s)
- David D Kline
- Department of Biomedical Sciences, Dalton Cardiovascular Research Center, University of Missouri, Columbia, MO 65211, USA.
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34
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Primary afferent activation of thermosensitive TRPV1 triggers asynchronous glutamate release at central neurons. Neuron 2010; 65:657-69. [PMID: 20223201 DOI: 10.1016/j.neuron.2010.02.017] [Citation(s) in RCA: 147] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 01/13/2010] [Indexed: 11/20/2022]
Abstract
TRPV1 receptors feature prominently in nociception of spinal primary afferents but are also expressed in unmyelinated cranial visceral primary afferents linked to homeostatic regulation. Cranial visceral afferents enter the brain at the solitary tract nucleus (NTS) to control the heart, lungs, and other vital organs. Here we identify a role for central TRPV1 in the activity-dependent facilitation of glutamatergic transmission from solitary tract (ST) afferents. Fast, synchronous ST-NTS transmission from capsaicin-sensitive (TRPV1+) and -insensitive (TRPV1-) afferents was similar. However, afferent activation triggered long-lasting asynchronous glutamate release only from TRPV1+ synapses. Asynchronous release was proportional to synchronous EPSC amplitude, activity, and calcium entry. TRPV1 antagonists and low temperature blocked asynchronous release, but not evoked EPSCs. At physiological afferent frequencies, asynchronous release strongly potentiated the duration of postsynaptic spiking. This activity-dependent TPRV1-mediated facilitation is a form of synaptic plasticity that brings a unique central integrative feature to the CNS and autonomic regulation.
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35
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Wang M, Bradley RM. Synaptic characteristics of rostral nucleus of the solitary tract neurons with input from the chorda tympani and glossopharyngeal nerves. Brain Res 2010; 1328:71-8. [PMID: 20214892 DOI: 10.1016/j.brainres.2010.03.003] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2010] [Revised: 03/01/2010] [Accepted: 03/02/2010] [Indexed: 10/19/2022]
Abstract
Chorda tympani (CT) and glossopharyngeal (IXth) nerves relay taste information from anterior and posterior tongue to brainstem where they synapse with second order neurons in the rostral nucleus of solitary tract (rNST). rNST neurons monosynaptically connected to afferent gustatory input were identified both by anatomical labeling and synaptic latency measures. Anterograde tracing was used to label the CT and IXth terminal fields, and neurons surrounded by fluorescent neural profiles visualized with differential interference contrast (DIC) optics in horizontal brainstem slices. Anatomically identified neurons were patch-clamped and excitatory postsynaptic currents (EPSCs) evoked by electrically stimulating the solitary tract (ST) under GABA(A) receptor blockade. Monosynaptic connections were confirmed by measures of the standard deviation of synaptic latency (jitter). rNST neurons responded to ST stimulation with either all-or-none or graded amplitude EPSCs. Most (70%) of the rNST neurons with CT input and 30% with IX input responded with all-or-none EPSCs. The remainder of the neurons with CT and IX input responded with increasing EPSC amplitudes to greater intensity stimulus shocks. EPSCs evoked in rNST neurons by increasing shock frequency to both CT and IXth nerves resulted in reduced amplitude EPSCs characteristic of frequency-dependent synaptic depression. Our results suggest that the second order rNST neurons respond to afferent input with different patterns of EPSCs that potentially influence transmission of gustatory information. Frequency-dependent synaptic depression would act as a low pass filter important in the initial processing of gustatory derived sensory messages.
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Affiliation(s)
- Min Wang
- Department of Biologic and Materials Sciences, School of Dentistry, University of Michigan, Ann Arbor, MI 48109-1078, USA
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36
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Role of GABAB Receptors in Autonomic Control of Systemic Blood Pressure. GABABRECEPTOR PHARMACOLOGY - A TRIBUTE TO NORMAN BOWERY 2010; 58:257-86. [DOI: 10.1016/s1054-3589(10)58011-6] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
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37
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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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Moreira TH, Cruz JS, Weinreich D. Angiotensin II increases excitability and inhibits a transient potassium current in vagal primary sensory neurons. Neuropeptides 2009; 43:193-9. [PMID: 19433335 DOI: 10.1016/j.npep.2009.04.003] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/22/2009] [Revised: 04/07/2009] [Accepted: 04/08/2009] [Indexed: 11/22/2022]
Abstract
The octapeptide angiotensin II (ANG II) plays a pivotal role in the maintenance of blood pressure by activating ANG II receptors located in variety of cell types including neurons housed in the central nervous system (CNS) and in the peripheral nervous system (PNS). ANG II (100 nM) blocked spike frequency accommodation (SFA) recorded with whole-cell patch technique in acutely isolated nodose ganglion neurons (NGN) from adult rats. ANG II increased the frequency of action potentials (AP) produced by supramaximal 500 ms depolarizing currents recorded in both tonic (16 Hz vs. 58 Hz, control vs. ANG II perfusion respectively, n=9) and phasic (1Hz vs. 38 Hz, n=13) NGNs. ANG II produced no significant changes in: the resting membrane potential (-51 mV vs. -50 mV, n=65), AP overshoot (46 mV vs. 41 mV, n=25), AP undershoot (-65 mV vs. -61 mV, n=25), AP duration (1 ms vs. 1.2 ms, n=25), and AP threshold (-40 mV vs. -43 mV, n=19). CV-11974 (600 nM), a specific AT1 receptor antagonist, prevented ANG II-evoked changes SFA (n=10). ANG II (100 nM) had no significant effect on total outward potassium current (I(K)) but inhibited a fast activating and fast inactivating I(K) recorded in the presence of TEA. A kinetically similar I(K) was also inhibited by 4-AP (3mM). In phasic NGNs, 4-AP occluded the effects of 100 nM ANG II on SFA. Our results indicate that ANG II can block an A-type of I(K) and that this effect may underlie the ANG II-mediated change in SFA.
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Affiliation(s)
- Thaís Helena Moreira
- Department of Pharmacology and Experimental Therapeutics, University of Maryland, School of Medicine, 655 W. Baltimore Street, Baltimore, MD 21201, USA
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Brozoski DT, Dean C, Hopp FA, Hillard CJ, Seagard JL. Differential endocannabinoid regulation of baroreflex-evoked sympathoinhibition in normotensive versus hypertensive rats. Auton Neurosci 2009; 150:82-93. [PMID: 19464961 DOI: 10.1016/j.autneu.2009.05.243] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2009] [Revised: 04/29/2009] [Accepted: 05/06/2009] [Indexed: 11/16/2022]
Abstract
Previously, we found that endocannabinoids acting at cannabinoid 1 receptors in the nucleus tractus solitarius prolonged baroreflex inhibition of renal sympathetic nerve activity in normotensive Sprague Dawley rats. The current study investigated whether endocannabinoid signaling was altered in spontaneously hypertensive rats, a model marked by elevated sympathetic activity and depressed baroreflex responses. The effects of endocannabinoids in the nucleus tractus solitarius on baroreflex control of renal sympathetic nerve activity evoked by systemic pressor changes or by direct stimulation of nucleus tractus solitarius neurons, which produced depressor and sympathoinhibitory responses, were studied in Sprague Dawley rats, Wistar Kyoto rats, and spontaneously hypertensive rats. Evoked responses were compared before and after microinjection of AM404, which prolonged actions of endogenous endocannabinoids, or microinjection of an endocannabinoid, anandamide, into the baroreceptive region of the nucleus tractus solitarius. AM404 microinjections significantly prolonged evoked sympathoinhibition in Sprague Dawley and Wistar Kyoto rats, but had little effect in spontaneously hypertensive rats. Microinjections of anandamide prolonged sympathoinhibition in Sprague Dawley rats, with lesser effects in Wistar Kyoto rats and no effects in spontaneously hypertensive rats. Parallel studies found that density of binding sites of endocannabinoids in the nucleus tractus solitarius was significantly reduced in spontaneously hypertensive rats versus the normotensive rats. Results indicate that attenuated function of the endocannabinoid system in the nucleus tractus solitarius of spontaneously hypertensive rats resulted in less modulation of baroreflex-evoked sympathoinhibition and that reduced cannabinoid 1 receptor density could contribute to blunted baroreflex-induced sympathoinhibition and elevated sympathetic tone characteristic of spontaneously hypertensive rats.
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Affiliation(s)
- D T Brozoski
- Department of Anesthesiology, Medical College of Wisconsin, Milwaukee, WI, USA
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Suwabe T, Bradley RM. Characteristics of rostral solitary tract nucleus neurons with identified afferent connections that project to the parabrachial nucleus in rats. J Neurophysiol 2009; 102:546-55. [PMID: 19439671 DOI: 10.1152/jn.91182.2008] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Afferent information derived from oral chemoreceptors is transmitted to second-order neurons in the rostral solitary tract nucleus (rNST) and then relayed to other CNS locations responsible for complex sensory and motor behaviors. Here we investigate the characteristics of rNST neurons sending information rostrally to the parabrachial nucleus (PBN). Afferent connections to these rNST-PBN projection neurons were identified by anterograde labeling of the chorda tympani (CT), glossopharyngeal (IX), and lingual (LV) nerves. We used voltage- and current-clamp recordings in brain slices to characterize the expression of both the transient A-type potassium current, IKA and the hyperpolarization-activated inward current, Ih, important determinants of neuronal repetitive discharge characteristics. The majority of rNST-PBN neurons express IKA, and these IKA-expressing neurons predominate in CT and IX terminal fields but were expressed in approximately half of the neurons in the LV field. rNST-PBN neurons expressing Ih were evenly distributed among CT, IX and LV terminal fields. However, expression patterns of IKA and Ih differed among CT, IX, and LV fields. IKA-expressing neurons frequently coexpress Ih in CT and IX terminal fields, whereas neurons in LV terminal field often express only Ih. After GABAA receptor block all rNST-PBN neurons responded to afferent stimulation with all-or-none excitatory synaptic responses. rNST-PBN neurons had either multipolar or elongate morphologies and were distributed throughout the rNST, but multipolar neurons were more often encountered in CT and IX terminal fields. No correlation was found between the biophysical and morphological characteristics of the rNST-PBN projection neurons in each terminal field.
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Affiliation(s)
- Takeshi Suwabe
- Department of Biologic and Materials Sciences, School of Dentistry, University of Michigan, Ann Arbor, MI 48109-1078, USA
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Kline DD. Plasticity in glutamatergic NTS neurotransmission. Respir Physiol Neurobiol 2009; 164:105-11. [PMID: 18524694 DOI: 10.1016/j.resp.2008.04.013] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2008] [Revised: 04/18/2008] [Accepted: 04/21/2008] [Indexed: 01/10/2023]
Abstract
Changes in the physiological state of an animal or human can result in alterations in the cardiovascular and respiratory system in order to maintain homeostasis. Accordingly, the cardiovascular and respiratory systems are not static but readily adapt under a variety of circumstances. The same can be said for the brainstem circuits that control these systems. The nucleus tractus solitarius (NTS) is the central integration site of baroreceptor and chemoreceptor sensory afferent fibers. This central nucleus, and in particular the synapse between the sensory afferent and second-order NTS cell, possesses a remarkable degree of plasticity in response to a variety of stimuli, both acute and chronic. This brief review is intended to describe the plasticity observed in the NTS as well as the locus and mechanisms as they are currently understood. The functional consequence of NTS plasticity is also discussed.
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Affiliation(s)
- David D Kline
- Department of Biomedical Sciences and Dalton Cardiovascular Research Center, University of Missouri, 134 Research Park Dr., Columbia, MO 65211, USA.
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The dmNTS is not the source of increased blood pressure variability in baroreflex denervated rats. Auton Neurosci 2009; 148:21-7. [PMID: 19285454 DOI: 10.1016/j.autneu.2009.02.002] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2008] [Revised: 02/05/2009] [Accepted: 02/08/2009] [Indexed: 02/02/2023]
Abstract
A consistent and prominent feature, observed across many species, including our neuromuscular blocked (NMB) rat preparation, is that obliterating the baroafferent inputs to the brainstem, e.g., by sinoaortic denervation (SAD), significantly increases blood pressure variability (BPV). The sources of the BPV, however, are not completely understood, but involve both the central and the peripheral mechanisms. The key central noise source is likely in the brainstem. Previously, in NMB rats, we showed that the maximum gain of the baroreflex system is in the very low frequency (VLF) range of 0.01-0.2 Hz. In this study, using the same NMB preparation, we demonstrated that, after SAD, there was a significant increase in the VLF power of the expiratory systolic blood pressure (EsBP) spectrum, but a decrease in the VLF power of the expiratory heart inter-beat-interval (EIBI) spectrum. Because dmNTS is the only major common anatomic node for the vascular sympathetic and the cardiac parasympathetic pathways, the opposite changes in the post-SAD VLF powers of the EsBP and EIBI spectra suggest that dmNTS is unlikely the major noise source for the post-SAD BPV. Supporting this finding, we found that the dmNTS evoked response to single pulse baroreflex afferent aortic depressor nerve (ADN) stimuli was substantially more reliable than the evoked systolic blood pressure responses to the same stimuli.
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Postnatal development of axosomatic synapses in the rat nucleus tractus solitarius: Dorsal and ventral subnuclei differences. Neurosci Lett 2009; 450:217-20. [DOI: 10.1016/j.neulet.2008.12.012] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2008] [Revised: 11/27/2008] [Accepted: 12/10/2008] [Indexed: 11/30/2022]
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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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Engelhardt E, Laks J. Alzheimer disease neuropathology: understanding autonomic dysfunction. Dement Neuropsychol 2008; 2:183-191. [PMID: 29213568 PMCID: PMC5619463 DOI: 10.1590/s1980-57642009dn20300004] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2008] [Accepted: 08/22/2008] [Indexed: 12/30/2022] Open
Abstract
Alzheimer's disease is a widely studied disorder with research focusing on cognitive and functional impairments, behavioral and psychological symptoms, and on abnormal motor manifestations. Despite the importance of autonomic dysfunctions they have received less attention in systematic studies. The underlying neurodegenerative process of AD, mainly affecting cortical areas, has been studied for more than one century. However, autonomic-related structures have not been studied neuropathologically with the same intensity. The autonomic nervous system governs normal visceral functions, and its activity is expressed in relation to homeostatic needs of the organism's current physical and mental activities. The disease process leads to autonomic dysfunction or dysautonomy possibly linked to increased rates of morbidity and mortality. OBJECTIVE The aim of this review was to analyze the cortical, subcortical, and more caudal autonomic-related regions, and the specific neurodegenerative process in Alzheimer's disease that affects these structures. METHODS A search for papers addressing autonomic related-structures affected by Alzheimer's degeneration, and under normal condition was performed through MedLine, PsycInfo and Lilacs, on the bibliographical references of papers of interest, together with a manual search for classic studies in older journals and books, spanning over a century of publications. RESULTS The main central autonomic-related structures are described, including cortical areas, subcortical structures (amygdala, thalamus, hypothalamus, brainstem, cerebellum) and spinal cord. They constitute autonomic neural networks that underpin vital functions. These same structures, affected by specific Alzheimer's disease neurodegeneration, were also described in detail. The autonomic-related structures present variable neurodegenerative changes that develop progressively according to the degenerative stages described by Braak and Braak. CONCLUSION The neural networks constituted by the central autonomic-related structures, when damaged by progressive neurodegeneration, represent the neuropathological substrate of autonomic dysfunction. The presence of this dysfunction and its possible relationship with higher rates of morbidity, and perhaps of mortality, in affected subjects must be kept in mind when managing Alzheimer's patients.
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Affiliation(s)
- Eliasz Engelhardt
- MD, PhD, Coordinator of the Cognitive and Behavioral Unit
– INDC-UFRJ
| | - Jerson Laks
- MD, PhD, Coordinator of the Alzheimer’s Disease Unit –
CDA/IPUB-UFRJ
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Andresen MC, Bailey TW, Jin YH, McDougall SJ, Peters JH, Aicher SA. Cellular Heterogeneity Within the Solitary Tract Nucleus and Visceral Afferent Processing—Electrophysiological Approaches to Discerning Pathway Performance. Tzu Chi Med J 2007. [DOI: 10.1016/s1016-3190(10)60014-6] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/19/2022] Open
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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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Tang X, Dworkin BR. Baroreflexes of the rat. IV. ADN-evoked responses at the NTS. Am J Physiol Regul Integr Comp Physiol 2007; 293:R2243-53. [PMID: 17898125 DOI: 10.1152/ajpregu.00142.2007] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
In a long-term (7-21 days) neuromuscular blocked (NMB) rat preparation, using precise single-pulse aortic depressor nerve (ADN) stimulation and stable chronic evoked response (ER) recordings from the dorsal-medial solitary nucleus (dmNTS), two different response patterns were observed: continuous and discrete. For the continuous pattern, activity began approximately 3 ms after the stimulus and persisted for 45 ms; for the discrete pattern, two complexes were separated by a gap from approximately 17 to 25 ms. The early complex was probably transmitted via A-fibers: it had a low stimulus current threshold and an average conduction velocity (CV) of 0.58-5.5 m/s; the high threshold late (HTL) complex had a CV = 0.26-0.58 m/s. The average stimulus amplitude-ER magnitude transduction curves for the A and HTL complexes were sigmoidal. For individual rats, in the linear range, mean r2 = 0.96 +/- 0.03 for both complexes. The average stimulus amplitude vs. the systolic blood pressure change (delta sBP) transduction curve was also approximately linear; however, for individual rats, the relationship was not consistently reliable: mean r2 = 0.48 +/- 0.19. Approximately 90% of recording sites had respiratory, and 50% had cardiac synchronism. The NMB preparation is useful for studying central baroreflex mechanisms that operate on time scales of days or weeks, such as adaptation and other kinds of neural plasticity.
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Affiliation(s)
- Xiaorui Tang
- Dept. of Neural and Behavioral Sciences, Pennsylvania State Univ., College of Medicine, Hershey, PA 17033, USA
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Michelini LC. The NTS and integration of cardiovascular control during exercise in normotensive and hypertensive individuals. Curr Hypertens Rep 2007; 9:214-21. [PMID: 17519128 DOI: 10.1007/s11906-007-0039-x] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
Abstract
Due to upward resetting of baroreceptors, tachycardia coexists with increased pressure during dynamic exercise. This review critically evaluates current knowledge of proposed mechanisms to explain the continuous resetting of baroreflex control of heart rate and sympathetic nerve activity during and after exercise and exercise training. Of interest is the exercise-induced upward resetting that occurs in hypertensive and normotensive individuals. Accumulated evidence indicates that not only somatosensory afferents, but also inputs from central command projecting to the nucleus tractus solitarius (NTS) in the dorsal brainstem may mediate inhibition of excitatory neurotransmission on barosensitive neurons. Specific coordinated activation of vasopressinergic and oxytocinergic projections to the NTS is essential to tonically maintain baroreflex sensitivity and to adjust heart rate and cardiac output to circulatory demand at rest and during exercise in both sedentary and trained individuals. These findings reinforce the paramount importance of the NTS in integration of cardiovascular control during exercise.
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Affiliation(s)
- Lisete Compagno Michelini
- Department of Physiology and Biophysics, Biomedical Sciences Institute, University of São Paulo, Av. Prof. Lineu Prestes, 1524 05508-900, São Paulo, Brazil.
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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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