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Abstract
Assessing and communicating the full value of biomedical research is essential to answer calls from the government and the public demanding accountability for the spending of public funds. In academic settings, however, research success is measured largely in terms of grant funding received or the number of peer-reviewed publications produced. These credible and time-tested metrics miss the full picture of the scientific process, which continues to confer benefits to patients, communities, and the health care system well after an article is published. In this context, in 2012, the Association of American Medical Colleges, in collaboration with RAND Europe, initiated a program to provide resources and guidance for leaders of medical schools and teaching hospitals interested in evaluating-in novel ways complementary to traditional methods-the outcomes and impacts of the research that emanates from their institutions. This Perspective provides context for this initiative and delineates the process through which researchers, evaluation experts, and other stakeholders-including legislators, health system leaders, and community members-identified and vetted novel "metrics that matter" in advance of a pilot test at the University of Wisconsin-Madison, which sought to assess and communicate its community-engaged science and scholarship.
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Affiliation(s)
- Ann C Bonham
- A.C. Bonham is immediate past chief scientific officer, Association of American Medical Colleges, Washington, DC. P.M. Alberti is senior director, Health Equity Research and Policy, Association of American Medical Colleges, Washington, DC
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Heinig SJ, Dev A, Bonham AC. The U.S. Public's Investment in Medical Research: An Evolving Social Contract. Am J Med Sci 2016; 351:69-76. [PMID: 26802760 DOI: 10.1016/j.amjms.2015.10.016] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2015] [Accepted: 10/13/2015] [Indexed: 10/22/2022]
Abstract
Medical researchers and their institutions are operating under extraordinary financial stress. More than a decade after completion of the 5-year doubling of the National Institutes of Health budget, the medical research community must confront a significant loss in National Institutes of Health purchasing power and downward pressures in federal discretionary spending. In part, this trend results from a federal budget stalemate over the growth in entitlement programs, particularly spending on medical care. This article considers the changing nature of the federal investment in medical research and the potential for medical researchers and institutions conducting the full spectrum of research to improve health system performance and health equity. In our view, continued federal investments reflect an evolving social contract for research serving the public good; the term contract is used metaphorically to represent a figurative, implicit agreement between the scientific community and the public's representatives in government. Under this conceptual contract, the American people--who are ultimately the funders of research, research training and infrastructure--expect outcomes that lead to better health, security or other benefits. The evolving contract includes expectations for more accountability, transparency, sharing of results and resources, and better integration of research systems and cultures that used to take pride in boundaries and distinctions. We outline here some of the major movements of organizations realigning to social support, which are increasingly essential to sustain public investment in medical research.
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Affiliation(s)
| | - Anurupa Dev
- Association of American Medical Colleges, Washington, DC
| | - Ann C Bonham
- Association of American Medical Colleges, Washington, DC
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Abstract
MD-PhD programs provide rigorous, integrated training for physician-scientists, enabling them to frame scientific questions in unique ways and to apply clinical insight to fundamental science. Few would question the influential contributions of MD-PhD physician-scientists in advancing medical science. In this issue of Academic Medicine, Jeffe et al affirm high levels of excellence in educational outcomes from MD-PhD training programs at U.S. MD-granting medical schools, especially programs that receive funding from the NIH Medical Scientist Training Program (MSTP). The author of this commentary observes that, in the face of current economic pressures, comprehensive, longitudinal national outcomes data from MSTP- and non-MSTP-funded MD-PhD programs will help verify the value provided by MD-PhD physician-scientists. She proposes that MD-PhD programs should better prepare the next generation of physician-scientists for future research environments, which will provide new technologies, venues, and modalities. These research environments will be more closely integrated within health care delivery systems, extend into diverse communities and regions, and employ complex technologies. MD-PhD physician-scientists also will train and gain expertise in broadening areas of research, such as health policy, health economics, clinical epidemiology, and medical informatics. Program leaders are ideally situated to foster innovative learning environments and methodologies. By sharing their innovations, they can help ensure production of a diverse MD-PhD physician-scientist workforce, prepared to engage in myriad research opportunities to meet patient and population needs in a new environment.
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Affiliation(s)
- Ann C Bonham
- Dr. Bonham is chief scientific officer, Association of American Medical Colleges, Washington, DC
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Abstract
Equity in health and health care in America continues to be a goal unmet. Certain demographic groups in the United States-including racial and ethnic minorities and individuals with lower socioeconomic status-have poorer health outcomes across a wide array of diseases, and have higher all-cause mortality. Yet despite growing understanding of how social-, structural-, and individual-level factors maintain and create inequities, solutions to reduce or eliminate them have been elusive. In this article, the authors envision how disparities-related provisions in the Affordable Care Act and other recent legislation could be linked with new value-based health care requirements and payment models to create incentives for narrowing health care disparities and move the nation toward equity.Specifically, the authors explore how recent legislative actions regarding payment reform, health information technology, community health needs assessments, and expanding health equity research could be woven together to build an evidence base for solutions to health care inequities. Although policy interventions at the clinical and payer levels alone will not eliminate disparities, given the significant role the social determinants of health play in the etiology and maintenance of inequity, such policies can allow the health care system to better identify and leverage community assets; provide high-quality, more equitable care; and demonstrate that equity is a value in health.
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Affiliation(s)
- Philip M Alberti
- Dr. Alberti is senior director, Health Equity Research and Policy, Association of American Medical Colleges, Washington, DC. Dr. Bonham is chief scientific officer, Association of American Medical Colleges, Washington, DC. Dr. Kirch is president and CEO, Association of American Medical Colleges, Washington, DC
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Knowlton AA, Rainwater JA, Chiamvimonvat N, Bonham AC, Robbins JA, Henderson S, Meyers FJ. Training the translational research teams of the future: UC Davis-HHMI Integrating Medicine into Basic Science program. Clin Transl Sci 2013; 6:339-46. [PMID: 24127920 DOI: 10.1111/cts.12068] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022] Open
Abstract
There is a need for successful models of how to recruit, train, and retain bench scientists at the earliest stages of their careers into translational research. One recent, promising model is the University of California Davis Howard Hughes Medical Institute Integrating Medicine into Basic Science (HHMI-IMBS) program, part of the HHMI Med into Grad initiative. This paper outlines the HHMI-IMBS program's logic, design, and curriculum that guide the goal of research that moves from bedside to bench. That is, a curriculum that provides graduate students with guided translational training, clinical exposure, team science competencies, and mentors from diverse disciplines that will advance the students careers in clinical translational research and re-focusing of research to answer clinical dilemmas. The authors have collected data on 55 HHMI-IMBS students to date. Many of these students are still completing their graduate work. In the current study the authors compare the initial two cohorts (15 students) with a group of 29 control students to examine the program success and outcomes. The data indicate that this training program provides an effective, adaptable model for training future translational researchers. HHMI-IMBS students showed improved confidence in conducting translational research, greater interest in a future translational career, and higher levels of research productivity and collaborations than a comparable group of predoctoral students.
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Affiliation(s)
- Anne A Knowlton
- Cardiovascular Division, Department of Medicine, School of Medicine, University of California, Sacramento, California, USA; Department of Medical Pharmacology, School of Medicine, University of California, Davis, California, USA; Northern California VA, Sacramento, California, USA
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Sekizawa SI, Joad JP, Pinkerton KE, Bonham AC. Distinct tachykinin NK(1) receptor function in primate nucleus tractus solitarius neurons is dysregulated after second-hand tobacco smoke exposure. Br J Pharmacol 2011; 163:782-91. [PMID: 21323902 PMCID: PMC3111680 DOI: 10.1111/j.1476-5381.2011.01271.x] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2010] [Revised: 12/14/2010] [Accepted: 01/10/2011] [Indexed: 11/30/2022] Open
Abstract
BACKGROUND AND PURPOSE Second-hand tobacco smoke (SHS) exposure in children increases the risk of asthma and sudden infant death syndrome. Epidemiological and experimental data have suggested SHS can alter neuroplasticity in the CNS, associated with substance P. We hypothesized that exposure to SHS in young primates changed the effect of substance P on the plasticity of neurons in the nucleus tractus solitarius (NTS), where airway sensory information is first processed in the CNS. EXPERIMENTAL APPROACH Thirteen-month-old rhesus monkeys were exposed to filtered air (FA, n= 5) or SHS (n= 5) for >6 months from 50 days of their fetal age. Whole-cell patch-clamp recordings were performed on NTS neurons in brainstem slices from these animals to record the intrinsic cell excitability in the absence or presence of the NK(1) receptor antagonist, SR140333 (3 µM). KEY RESULTS Neurons were electrophysiologically classified based on their spiking onset from a hyperpolarized membrane potential into two phenotypes: rapid-onset spiking (RS) and delayed-onset spiking (DS) types. In RS neurons, SR140333 reduced the spiking response, similarly in both FA- and SHS-exposed animals. In DS neurons, SR140333 almost abolished the spiking response in FA-exposed animals, but had no effect in SHS-exposed animals. CONCLUSIONS AND IMPLICATIONS The contribution of NK(1) receptors to cell excitability depended on firing phenotype of primate NTS neurons and was disrupted by SHS exposure, specifically in DS neurons. Our findings reveal a novel NK(1) receptor function in the primate brainstem and support the hypothesis that chronic exposure to SHS in children causes tachykinin-related neuroplastic changes in the CNS.
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Abstract
With growing constraints on government spending, policy makers are investing in comparative effectiveness research (CER) to attempt to bring the power of science to bear on the problems of suboptimal outcomes and high cost in the U.S. health care system. This commitment of resources to CER reflects confidence that better evidence can help clinicians and patients make better decisions, consistent with the long tradition of medical schools' and teaching hospitals' use of science to inform medical care. Thus, CER offers a great opportunity, albeit with some considerable challenges, for academic medicine to play a central role in comprehensive health care reform. Certainly, many scientists conducting CER will learn their methodological rigor in the training programs of academic health centers. Numerous new CER research teams will be needed, establishing effective partnerships far outside the walls of the traditional academic setting. And the clinicians interpreting the medical literature and applying the insights from CER to the unique problems of individual patients will need to learn this evidence-based, patient-centered care from the educators, mentors, and role models at U.S. medical and other health science schools and teaching hospitals. Achieving this will require investment in research infrastructure, adaptations of institutional culture, development of new disciplines and research methods, establishment of new collaborations, training of new faculty, and the expansion and refocusing of educational capacity. By successfully responding to this challenge, academic medicine can further strengthen its long-standing commitment to the scientific practice of medicine and the use of evidence in patient-centered, personalized care.
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Affiliation(s)
- Eugene C Rich
- Center on Health Care Effectiveness, Mathematica Policy Research, 600 Maryland Ave. SW, Washington, DC 20024, USA
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Abstract
A single bout of exercise can lead to a postexercise decrease in blood pressure in hypertensive individuals, called postexercise hypotension. Compelling evidence suggests that the central baroreflex pathway plays a crucial role in the development of postexercise hypotension. This review focuses on the exercise-induced changes in brainstem nuclei involved in blood pressure regulation.
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Affiliation(s)
- Chao-Yin Chen
- Department of Pharmacology, University of California, Davis, CA 95616, USA.
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Bonham AC, Solomon MZ. Moving Comparative Effectiveness Research Into Practice: Implementation Science And The Role Of Academic Medicine. Health Aff (Millwood) 2010; 29:1901-5. [DOI: 10.1377/hlthaff.2010.0790] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Affiliation(s)
- Ann C. Bonham
- Ann C. Bonham ( ) is chief scientific officer at the Association of American Medical Colleges, in Washington, D.C
| | - Mildred Z. Solomon
- Mildred Z. Solomon is senior director of implementation science at the Association of American Medical Colleges and an associate clinical professor of medical ethics in the Department of Global Health and Social Medicine, Harvard Medical School, in Boston, Massachusetts
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Bonham AC, Rich EC, Davis DA, Longnecker DE, Heinig SJ. Commentary: Putting evidence to work: an expanded research agenda for academic medicine in the era of health care reform. Acad Med 2010; 85:1551-1553. [PMID: 20703148 DOI: 10.1097/acm.0b013e3181effdbc] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/29/2023]
Abstract
The historic Patient Protection and Affordable Care Act (HR 3590) signed into law by President Obama has brought into sharp focus the need and opportunity for an expanded continuum of biomedical research. An updated research agenda must build on basic science and classical clinical investigation to place a more deliberate emphasis on patient- and population-outcome-oriented science and to apply science to help transform our current inefficient and expensive health care system into a more evidence-based system of effective, coordinated, safe, and patient-centered health care. If academic medicine is to play a leading role in this 21st-century transformation of health care through research, as it did in the 20th century, those in the community must think strategically about what needs to be done to be part of the solution for transforming the nation's health care delivery systems and prevention strategies, and the changes in institutional, organizational, and individual behaviors and values required to get there. Not all institutions will engage in the science called for in health care reform, but for those institutions with the interest, capacity, and resources to move forward, what is needed?
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Affiliation(s)
- Ann C Bonham
- Association of American Medical Colleges, Washington, DC 20037, USA.
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Sekizawa SI, Joad JP, Pinkerton KE, Bonham AC. Secondhand smoke exposure alters K+ channel function and intrinsic cell excitability in a subset of second-order airway neurons in the nucleus tractus solitarius of young guinea pigs. Eur J Neurosci 2010; 31:673-84. [PMID: 20384811 DOI: 10.1111/j.1460-9568.2010.07093.x] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Extended exposure to secondhand smoke (SHS) in infants and young children increases the incidence of cough, wheeze, airway hyper-reactivity and the prevalence and earlier onset of asthma. The adverse effects may result from environmentally-induced plasticity in the neural network regulating cough and airway function. Using whole-cell patch-clamp recordings in brainstem slices containing anatomically identified second-order lung afferent neurons in the nucleus tractus solitarius (NTS), we determined the effects of extended SHS exposure in young guinea pigs for a duration equivalent to human childhood on the intrinsic excitability of NTS neurons. SHS exposure resulted in marked decreases in the intrinsic excitability of a subset of lung afferent second-order NTS neurons. The neurons exhibited a decreased spiking capacity, prolonged action potential duration, reduced afterhyperpolarization, decrease in peak and steady-state outward currents, and membrane depolarization. SHS exposure effects were mimicked by low concentrations of the K+ channel blockers 4-aminopyridine and/or tetraethyl ammonium. The data suggest that SHS exposure downregulates K+ channel function in a subset of NTS neurons, resulting in reduced cell excitability. The changes may help to explain the exaggerated neural reflex responses in children exposed to SHS.
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Affiliation(s)
- Shin-Ichi Sekizawa
- Department of Pharmacology, School of Medicine, GBSF Room 3617, 451 Health Sciences Drive, University of California Davis, Davis, CA 95616-0635, USA
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Sekizawa SI, Bechtold AG, Tham RC, Kott KS, Hyde DM, Joad JP, Bonham AC. House-dust mite allergen and ozone exposure decreases histamine H3 receptors in the brainstem respiratory nuclei. Toxicol Appl Pharmacol 2010; 247:204-10. [PMID: 20600210 DOI: 10.1016/j.taap.2010.06.014] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2010] [Revised: 06/11/2010] [Accepted: 06/22/2010] [Indexed: 10/19/2022]
Abstract
Allergic airway diseases in children are a common and a growing health problem. Changes in the central nervous system (CNS) have been implicated in contributing to some of the symptoms. We hypothesized that airway allergic diseases are associated with altered histamine H3 receptor expression in the nucleus tractus solitarius (NTS) and caudal spinal trigeminal nucleus, where lung/airway and nasal sensory afferents terminate, respectively. Immunohistochemistry for histamine H3 receptors was performed on brainstem sections containing the NTS and the caudal spinal trigeminal nucleus from 6- and 12-month-old rhesus monkeys who had been exposed for 5 months to house dust mite allergen (HDMA)+O3 or to filtered air (FA). While histamine H3 receptors were found exclusively in astrocytes in the caudal spinal trigeminal nucleus, they were localized to both neuronal terminals and processes in the NTS. HDMA+O3 exposure significantly decreased histamine H3 receptor immunoreactivity in the NTS at 6 months and in the caudal spinal trigeminal nucleus at 12 months of age. In conclusion, exposing young primates to HDMA+O3 changed histamine H3 receptor expression in CNS pathways involving lung and nasal afferent nerves in an age-related manner. Histamine H3 receptors may be a therapeutic target for allergic asthma and rhinitis in children.
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Affiliation(s)
- Shin-ichi Sekizawa
- Department of Pharmacology, School of Medicine, University of California Davis, GBSF Rm. 3617, 451 Health Sciences Drive, Davis, CA 95616-0635, USA.
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Howell LP, Chen CY, Joad JP, Green R, Callahan EJ, Bonham AC. Issues and challenges of non-tenure-track research faculty: the UC Davis School of Medicine experience. Acad Med 2010; 85:1041-1047. [PMID: 20505407 DOI: 10.1097/acm.0b013e3181dbfbf3] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/29/2023]
Abstract
Nationally, medical schools are appointing growing numbers of research faculty into non-tenure-track positions, paralleling a similar trend in universities. The American Association of University Professors (AAUP) issued a statement expressing concern that the marked growth in non-tenure-track faculty can undermine educational quality, academic freedom, and collegiality. Like other medical schools, the UC Davis School of Medicine has had a rise in non-tenure-track faculty in order to enhance its research mission, in particular in the Salaried Adjunct faculty track (SalAdj). SalAdj faculty have more difficulty in achieving promotion, report inequitable treatment and less quality of life, have less opportunity to participate in governance, and feel second-class and insecure. These issues reflect those described by the AAUP. The authors describe the efforts at UC Davis to investigate and address these issues, implementation of a plan for improvement based on task force recommendations, and the lessons learned. Supporting transfer to faculty tracks in the academic senate, enhancing financial support, ensuring eligibility for internal grants, and equitable space assignments have contributed to an improved career path and more satisfaction among SalAdj faculty. Challenges in addressing these issues include limited availability of tenure-track positions, financial resources, adequate communication regarding change, and compliance with existing faculty search policies.
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Sekizawa SI, Joad JP, Pinkerton KE, Bonham AC. Secondhand tobacco smoke exposure differentially alters nucleus tractus solitarius neurons at two different ages in developing non-human primates. Toxicol Appl Pharmacol 2009; 242:199-208. [PMID: 19850058 DOI: 10.1016/j.taap.2009.10.009] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2009] [Revised: 10/07/2009] [Accepted: 10/10/2009] [Indexed: 10/20/2022]
Abstract
Exposing children to secondhand tobacco smoke (SHS) is associated with increased risk for asthma, bronchiolitis and SIDS. The role for changes in the developing CNS contributing to these problems has not been fully explored. We used rhesus macaques to test the hypothesis that SHS exposure during development triggers neuroplastic changes in the nucleus tractus solitarius (NTS), where lung sensory information related to changes in airway and lung function is first integrated. Pregnant monkeys were exposed to filtered air (FA) or SHS for 6 h/day, 5 days/week starting at 50-day gestational age. Mother/infant pairs continued the exposures postnatally to age 3 or 13 months, which may be equivalent to approximately 1 or 4 years of human age, respectively. Whole-cell recordings were made of second-order NTS neurons in transverse brainstem slices. To target the consequences of SHS exposure based on neuronal subgroups, we classified NTS neurons into two phenotypes, rapid-onset spiking (RS) and delayed-onset spiking (DS), and then evaluated intrinsic and synaptic excitabilities in FA-exposed animals. RS neurons showed greater cell excitability especially at age of 3 months while DS neurons received greater amplitudes of excitatory postsynaptic currents (EPSCs). Developmental neuroplasticity such as increases in intrinsic and synaptic excitabilities were detected especially in DS neurons. In 3 month olds, SHS exposure effects were limited to excitatory changes in RS neurons, specifically increases in evoked EPSC amplitudes and increased spiking responses accompanied by shortened action potential width. By 13 months, the continued SHS exposure inhibited DS neuronal activity; decreases in evoked EPSC amplitudes and blunted spiking responses accompanied by prolonged action potential width. The influence of SHS exposure on age-related and phenotype specific changes may be associated with age-specific respiratory problems, for which SHS exposure can increase the risk, such as SIDS and bronchiolitis in infants and asthma in older children.
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Affiliation(s)
- Shin-Ichi Sekizawa
- Department of Pharmacology, University of California Davis, Davis, CA 95616, USA.
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Pham H, Bonham AC, Pinkerton KE, Chen CY. Central neuroplasticity and decreased heart rate variability after particulate matter exposure in mice. Environ Health Perspect 2009; 117:1448-53. [PMID: 19750112 PMCID: PMC2737024 DOI: 10.1289/ehp.0900674] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/09/2009] [Accepted: 05/20/2009] [Indexed: 05/02/2023]
Abstract
BACKGROUND Epidemiologic studies show that exposure to fine particulate matter [aerodynamic diameter < or = 2.5 microm (PM(2.5))] increases the total daily cardiovascular mortality. Impaired cardiac autonomic function, which manifests as reduced heart rate variability (HRV), may be one of the underlying causes. However, the cellular mechanism(s) by which PM(2.5) exposure induces decreased HRV is not known. OBJECTIVES We tested the hypothesis that exposure to PM(2.5) impairs HRV by decreasing the excitability of the cardiac vagal neurons in the nucleus ambiguus. We also determined the effect of iron on PM-exposure-induced decrease in HRV. METHODS We measured 24-hr HRV in time domains from electrocardiogram telemetry recordings obtained in conscious, freely moving mice after 3 days of exposure to PM(2.5) in the form of soot only or iron-soot. In parallel studies, we determined the intrinsic properties of identified cardiac vagal neurons, retrogradely labeled with a fluorescent dye applied to the sinoatrial node. RESULTS Soot-only exposure decreased short-term HRV (root mean square of successive difference). With the addition of iron, all HRV parameters were significantly reduced. In nonexposed mice, vagal blockade significantly reduced all HRV parameters, suggesting that HRV is, in part, under vagal regulation in mice. Iron-soot exposure had no significant effect on resting membrane potential but decreased spiking responses of the identified cardiac vagal neurons to depolarizations (p < 0.05). The decreased spiking response was accompanied with a higher minimal depolarizing current required to evoke spikes and a lower peak discharge frequency. CONCLUSIONS The data suggest that PM-induced neuroplasticity of cardiac vagal neurons may be one mechanism contributing to the cardiovascular consequences associated with PM(2.5) exposure seen in humans.
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Affiliation(s)
| | | | - Kent E. Pinkerton
- Center for Health and the Environment, University of California at Davis, Davis, California, USA
| | - Chao-Yin Chen
- Department of Pharmacology and
- Address correspondence to C.-Y. Chen, Department of Pharmacology, University of California, Davis, GBSF 3510C, One Shields Ave., Davis, CA 95616 USA. Telephone: (530) 754-6458. Fax: (530) 752-7710. E-mail:
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Howell LP, Joad JP, Callahan E, Servis G, Bonham AC. Generational forecasting in academic medicine: a unique method of planning for success in the next two decades. Acad Med 2009; 84:985-93. [PMID: 19638760 DOI: 10.1097/acm.0b013e3181acf408] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/25/2023]
Abstract
Multigenerational teams are essential to the missions of academic health centers (AHCs). Generational forecasting using Strauss and Howe's predictive model, "the generational diagonal," can be useful for anticipating and addressing issues so that each generation is effective. Forecasts are based on the observation that cyclical historical events are experienced by all generations, but the response of each generation differs according to its phase of life and previous defining experiences. This article relates Strauss and Howe's generational forecasts to AHCs. Predicted issues such as work-life balance, indebtedness, and succession planning have existed previously, but they now have different causes or consequences because of the unique experiences and life stages of current generations. Efforts to address these issues at the authors' AHC include a work-life balance workgroup, expanded leave, and intramural grants.
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Affiliation(s)
- Lydia Pleotis Howell
- Department of Pathology and Laboratory Medicine, University of California, Davis, School of Medicine, Davis, California 95817, USA.
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Pham H, Pinkerton KE, Bonham AC, Chen C. Particulate matter exposure‐induced decreased heart rate variability is associated with a reduced excitability of cardiac vagal neurons in mice. FASEB J 2009. [DOI: 10.1096/fasebj.23.1_supplement.612.1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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Bechtold AG, Bonham AC. Elimination of nucleus of the solitary tract (NTS) neurokinin‐1 receptor (NK1R) expressing neurons enhances heart rate adaption and attenuates body weight loss during chronic restraint stress in spontaneously hypertensive rats. FASEB J 2009. [DOI: 10.1096/fasebj.23.1_supplement.1008.4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
| | - Ann C Bonham
- PharmacologyUniversity of California‐DavisDavisCA
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Bechtold AG, Bonham AC. Elimination of nucleus of the solitary tract (NTS) neurokinin‐1 receptor (NK1R) expressing neurons enhances arterial pressure response to acute restraint, but attenuates enhancement of the arterial pressure response and adaption of post‐restraint hypotension during sub‐acute restraint in spontaneously hypertensive rats. FASEB J 2009. [DOI: 10.1096/fasebj.23.1_supplement.959.6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
| | - Ann C Bonham
- PharmacologyUniversity of California‐DavisDavisCA
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Abstract
Cough is the most common symptom for which individuals seek medical attention and spend health-care dollars. Despite the burden induced by cough, the current treatments for cough are only partially effective. Delineating the sites and mechanisms in the cough central network for changes in the cough reflex could lead to new therapeutic strategies and drug target sites for more effective treatments. The first synaptic target in the CNS for the cough-related sensory input is the second-order neurons in the nucleus tractus solitarius (NTS); these neurons reorganize the primary sensory information into a coherent output. The NTS neurons have been shown to undergo neuroplasticity under a variety of conditions, such as respiratory disorders, stress, and exposures to environmental pollutants. The NTS contains a rich innervation of substance P immunoreactive nerve terminals, suggesting that substance P might be important in altered cough reflex response. This chapter summarizes our current findings on the role of substance P in enhanced cough reflex as well as the potential NTS targets for the action of substance P.
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Affiliation(s)
- C-Y Chen
- Department of Pharmacology, University of California, Davis School of Medicine, 4150 V Street, 1104 PSSB, Sacramento, CA 95817, USA
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Sekizawa SI, Chen CY, Bechtold AG, Tabor JM, Bric JM, Pinkerton KE, Joad JP, Bonham AC. Extended secondhand tobacco smoke exposure induces plasticity in nucleus tractus solitarius second-order lung afferent neurons in young guinea pigs. Eur J Neurosci 2008; 28:771-81. [PMID: 18657181 DOI: 10.1111/j.1460-9568.2008.06378.x] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Infants and young children experiencing extended exposure to secondhand smoke (SHS) have an increased occurrence of asthma, as well as increased cough, wheeze, mucus production and airway hyper-reactivity. Plasticity in lung reflex pathways has been implicated in causing these symptoms, as have changes in substance P-related mechanisms. Using whole-cell voltage-clamp recordings and immunohistochemistry in brainstem slices containing anatomically identified second-order lung afferent nucleus tractus solitarius (NTS) neurons, we determined whether extended SHS exposure during the equivalent period of human childhood modified evoked or spontaneous excitatory synaptic transmission, and whether those modifications were altered by endogenous substance P. SHS exposure enhanced evoked synaptic transmission between sensory afferents and the NTS second-order neurons by eliminating synaptic depression of evoked excitatory postsynaptic currents (eEPSCs), an effect reversed by the neurokinin-1-receptor antagonist (SR140333). The recruitment of substance P in enhancing evoked synaptic transmission was further supported by an increased number of substance P-expressing lung afferent central terminals synapsing onto the second-order lung afferent neurons. SHS exposure did not change background spontaneous EPSCs. The data suggest that substance P in the NTS augments evoked synaptic transmission of lung sensory input following extended exposure to a pollutant. The mechanism may help to explain some of the exaggerated respiratory responses of children exposed to SHS.
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Affiliation(s)
- Shin-Ichi Sekizawa
- Department of Pharmacology, University of California Davis, Davis, CA 95616, USA
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Chen CY, Chow D, Chiamvimonvat N, Glatter KA, Li N, He Y, Pinkerton KE, Bonham AC. Short-term secondhand smoke exposure decreases heart rate variability and increases arrhythmia susceptibility in mice. Am J Physiol Heart Circ Physiol 2008; 295:H632-9. [PMID: 18552155 DOI: 10.1152/ajpheart.91535.2007] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Exposure to secondhand smoke (SHS), a major indoor air pollutant, is linked to increased cardiovascular morbidity and mortality, including cardiac arrhythmias. However, the mechanisms underlying the epidemiological findings are not well understood. Impaired cardiac autonomic function, indexed by reduced heart rate variability (HRV), may represent an underlying cause. The present study takes advantage of well-defined short-term SHS exposure (3 days, 6 h/day) on HRV and the susceptibility to arrhythmia in mice. With the use of electrocardiograph telemetry recordings in conscious mice, HRV parameters in the time domain were measured during the night after each day of exposure and 24 h after 3 days of exposure to either SHS or filtered air. The susceptibility to arrhythmia was determined after 3 days of exposure. Exposure to a low concentration of SHS [total suspended particle (TSP), 2.4 +/- 3.2; and nicotine, 0.3 +/- 0.1 mg/m(3)] had no significant effect on HRV parameters. In contrast, the exposure to a higher but still environmentally relevant concentration of SHS (TSP, 30 +/- 1; and nicotine, 5 +/- 1 mg/m(3)) significantly reduced HRV starting after the first day of exposure and continuing 24 h after the last day of exposure. Moreover, the exposed mice showed a significant increase in ventricular arrhythmia susceptibility and atrioventricular block. The data suggest that SHS exposure decreased HRV beyond the exposure period and was associated with an increase in arrhythmia susceptibility. The data provide insights into possible mechanisms underlying documented increases in cardiovascular morbidity and mortality in humans exposed to SHS.
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Affiliation(s)
- Chao-Yin Chen
- Dept. of Pharmacology, Univ. of California, Davis, GBSF 3510C, 1 Shields Ave., Davis, CA 95616, USA.
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Bechtold AG, Tabor J, Bonham AC. Neurokinin‐1 receptor expressing neurons in the nucleus of the solitary tract are required for full expression of post‐exercise hypotension in spontaneously hypertensive rats. FASEB J 2008. [DOI: 10.1096/fasebj.22.1_supplement.1171.20] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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Sekizawa S, Hoffman M, Bonham AC. Post‐synaptic effects of Group II metabotropic glutamate receptors (mGluRs) on second‐order baroreceptor neurons of the nucleus tractus solitarius (NTS) in rats. FASEB J 2008. [DOI: 10.1096/fasebj.22.1_supplement.1171.13] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
| | | | - Ann C. Bonham
- PharmacologyUniversity of California DavisSacramentoCA
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Abstract
Epidemiological studies have shown that exposure to air pollution is associated with respiratory symptoms and decreases in lung function. This paper reviews recent literature showing that exposure to particulate matter, irritant gases, environmental tobacco smoke (ETS), mixed pollutants, and molds is associated with an increase in cough and wheeze. Some pollutants, like particulate matter and mixed pollutants, appear to increase cough at least as much as wheeze. Others, like irritant gases, appear to increase wheeze more than cough. For ETS, exposure during childhood is associated with cough and wheeze in adulthood, suggesting that the pollutant permanently alters some important aspect of the lungs, immune system or nervous system. We have shown in animal studies that pollutants change the neural control of airways and cough. Second hand smoke (SHS) exposure lengthened stimulated apnoea, increased the number of stimulated coughs, and augmented the degree of stimulated bronchoconstriction. The mechanisms included enhanced reactivity of the peripheral sensory neurones and second-order neurones in the nucleus tractus solitarius (NTS). NTS effects were due to a substance P mechanism at least in part. Ozone and allergen increased the intrinsic excitability of second-order neurones in the NTS. The animal studies suggest that the cough and wheeze experienced by humans exposed to pollutants may involve plasticity in the nervous system.
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Affiliation(s)
- Jesse P Joad
- Department of Pediatrics, University of California, Davis, 2516 Stockton Blvd., Sacramento, CA 95817, USA.
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Chen C, Chow D, Pinkerton KE, Bonham AC. Biphasic heart rate variability response to short‐term second‐hand smoke exposure in mice. FASEB J 2007. [DOI: 10.1096/fasebj.21.5.a474] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
| | | | - Kent E Pinkerton
- Center for the Health and EnvironmentUC‐Davis, One Shields AveDavisCA95616
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28
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Chen C, Pinkerton KE, Bonham AC. Time‐dependent decrease in heart rate variability to particulate matter exposure in mice. FASEB J 2007. [DOI: 10.1096/fasebj.21.5.a473-d] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
| | - Kent E Pinkerton
- Center for the Health and EnvironmentUC‐Davis, One Shields AveDavisCA95616
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Chen C, Bechtold AG, Bonham AC. Postexercise hypotension is associated with a reduced NK1 receptor mechanism on GABAergic inter neurons in nucleus tractus solitarii (NTS) in spontaneously hypertensive rats (SHRs). FASEB J 2007. [DOI: 10.1096/fasebj.21.5.a463-d] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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Bechtold AG, Zhang Y, Accorsi‐Mendonca D, Chen C, Bonham AC. Exercise decreases the spiking response to excitation of a subpopulation of 2nd‐order aortic baroreceptor neurons in the nucleus tractus solitarii (NTS) of spontaneously hypertensive rats (SHRs). FASEB J 2007. [DOI: 10.1096/fasebj.21.5.a463-c] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
- Andrea G Bechtold
- Pharmacology and ToxicologyUniversity of California‐DavisGenome and Biomedical Sciences Facility, 451 E. Health Sciences DriveDavisCA95616
| | - Yi‐Ming Zhang
- Pharmacology and ToxicologyUniversity of California‐DavisGenome and Biomedical Sciences Facility, 451 E. Health Sciences DriveDavisCA95616
| | - Daniela Accorsi‐Mendonca
- Pharmacology and ToxicologyUniversity of California‐DavisGenome and Biomedical Sciences Facility, 451 E. Health Sciences DriveDavisCA95616
| | - Chao‐Yin Chen
- Pharmacology and ToxicologyUniversity of California‐DavisGenome and Biomedical Sciences Facility, 451 E. Health Sciences DriveDavisCA95616
| | - Ann C Bonham
- Pharmacology and ToxicologyUniversity of California‐DavisGenome and Biomedical Sciences Facility, 451 E. Health Sciences DriveDavisCA95616
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31
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Sekizawa S, Bonham AC, Pinkerton KE, Joad JP. Developmental changes in two types of neurons in the nucleus tractus solitarius (NTS) of non‐human primates. FASEB J 2007. [DOI: 10.1096/fasebj.21.6.a1442-d] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
- Shin‐ichi Sekizawa
- Medical Pharmacology and ToxicologyUniversity of CaliforniaGBSF Rm. 3617, 451 East Health Sciences DriveDavisCA95616
| | - Ann C Bonham
- Medical Pharmacology and ToxicologyUniversity of CaliforniaGBSF Rm. 3617, 451 East Health Sciences DriveDavisCA95616
| | - Kent E Pinkerton
- Center for Health and the EnvironmentUniversity of CaliforniaOne Shields AvenueDavisCA95616
| | - Jesse P Joad
- PediatricsUniversity of California2516 Stockton BlvdDavisCA95817
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Bonham AC, Sekizawa SI, Chen CY, Joad JP. Plasticity of brainstem mechanisms of cough. Respir Physiol Neurobiol 2006; 152:312-9. [PMID: 16554189 DOI: 10.1016/j.resp.2006.02.010] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2005] [Revised: 02/07/2006] [Accepted: 02/09/2006] [Indexed: 11/27/2022]
Abstract
The cough reflex is a brainstem reflex, consisting of specific sensory afferent nerves which trigger the reflex, by transmitting the sensory input over vagal or laryngeal nerves to a brainstem circuitry which processes and ultimately transforms the sensory input into a complex motor output to generate cough. The first synaptic target for the primary cough-related sensory input is the second-order neurons in the nucleus tractus solitarius (NTS). This position in the reflex pathway and intricate local circuits within the nucleus make it a strategic site where the sensory information can be modified. Plasticity at this synapse will change the nature of the output--exaggerating it, suppressing it or transforming it into some other complex pattern. This review integrates evidence implicating the NTS in exaggerated cough with proof of the concept that NTS neurons undergo plasticity to contribute to an exaggeration of cough.
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Affiliation(s)
- Ann C Bonham
- Department of Pharmacology, University of California, Davis School of Medicine, 4150 V Street, 1104 PSSB, Sacramento, CA 95817, USA.
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Chen C, Bonham AC. NK1 receptor mechanism mediates exercise‐induced reduction in inhibitory inputs to baroreceptor second‐order neurons in nucleus tractus solitarii (NTS) in spontaneously hypertensive rats (SHRs). FASEB J 2006. [DOI: 10.1096/fasebj.20.4.a361-b] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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Abstract
The nucleus tractus solitarius (NTS) is the first central nervous system (CNS) site for synaptic contact of the primary afferent fibers from the lungs and airways. The signal processing at these synapses will determine the output of the sensory information from the lungs and airways to all downstream synapses in the reflex pathways. The second-order NTS neurons bring to bear their own intrinsic and synaptic properties to temporally and spatially integrate the sensory information with inputs from local networks, higher brain regions, and circulating mediators, to orchestrate a coherent reflex output. There is growing evidence that NTS neurons share the rich repertoire of forms of plasticity demonstrated throughout the CNS. This review focuses on existing evidence for plasticity in the NTS, potential targets for plasticity in the NTS, and the impact of this plasticity on lung and airway reflexes.
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Affiliation(s)
- Ann C Bonham
- Department of Medical Pharmacology, University of California, Davis, CA, USA.
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35
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Sekizawa SI, Bonham AC. Group I Metabotropic Glutamate Receptors on Second-Order Baroreceptor Neurons Are Tonically Activated and Induce a Na+–Ca2+Exchange Current. J Neurophysiol 2006; 95:882-92. [PMID: 16192328 DOI: 10.1152/jn.00772.2005] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023] Open
Abstract
The nucleus tractus solitarius (NTS) is essential for coordinating baroreflex control of blood pressure. The baroreceptor sensory fibers make glutamatergic synapses onto second-order NTS neurons. Glutamate spillover activates Group II and III presynaptic metabotropic glutamate receptors (mGluRs) on the baroreceptor central terminals to inhibit synaptic transmission, but the role of postsynaptic mGluRs is less understood. We used whole cell patch-clamping in anatomically identified second-order baroreceptor neurons in a brain stem slice to test whether Group I, II, and III mGluRs had postsynaptic effects at this first central synapse in the baroreceptor afferent pathway. The Group I agonist DHPG induced a depolarization and spiking that was mimicked by endogenous glutamate. Group I mGluR blockade prevented the depolarization and slightly hyperpolarized the neurons, suggesting a small tonic Group I mGluR activation. The DHPG-induced inward current consisted of voltage-dependent and -independent components; the former was blocked by TEA and the latter was blocked by replacing extracellular NaCl with LiCl or Tris-HCl. The DHPG current was potentiated in a Ca2+-free external solution and was diminished by intracellular dialysis with BAPTA and by perfusion with Na+–Ca2+exchanger blockers, KB-R7943 or 3′,4′-dichlorobenzamil. Intracellular dialysis with GDPβS or heparin and perfusion with the PLC inhibitor U-73122 or the Ca2+-calmodulin inhibitor W-7 significantly decreased the DHPG current. The data suggest that Group I mGluRs on baroreceptor neurons are functional; are activated by endogenous glutamate; and activate a Na+–Ca2+exchanger through G-protein, PLC, IP3, and Ca2+-calmodulin mechanisms to excite the cell, thus providing postsynaptic mechanisms to enhance or prolong baroreceptor signal transmission.
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Affiliation(s)
- Shin-ichi Sekizawa
- Department of Pharmacology, School of Medicine, University of California, Davis, CA 95817, USA
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36
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Abstract
Cough is associated with plasticity of putative cough afferent fibres, but whether plasticity in the brainstem network contributes is less well understood. A key site in the CNS network is the nucleus tractus solitarius (NTS), the first synaptic contact of the primary afferent fibres. We sought to develop a conscious guinea pig model to detect enhanced cough, to focus on the NTS as a potential site for plasticity, and to test a role for substance P in the NTS since the neuropeptide has been implicated in plasticity of the vagal afferent fibres. Guinea pigs were exposed to second-hand tobacco smoke (SHS) or filtered air (FA) from 1-6 weeks of age. At 5 weeks, cannulae were implanted in the NTS. At 6 weeks, either vehicle or a neurokinin 1 (NK-1) receptor antagonist was injected into the NTS of the conscious guinea pigs who were then exposed to citric acid aerosol. SHS exposure significantly enhanced citric acid-induced cough (56%, P<0.05), an effect attenuated by NTS NK-1 receptor blockade (P<0.05). The findings suggest that one possible mechanism for plasticity in cough is related to substance P effects in the NTS. Future studies will be required to investigate the possible mechanisms underlying the role of substance P as well as other mechanisms in generating SHS-induced cough.
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Affiliation(s)
- A C Bonham
- Department of Pharmacology, University of California Davis, Tupper Hall Room 1310, One Shields Avenue, Davis, CA 95616-0635, USA
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37
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Abstract
The nucleus tractus solitarii (NTS) is essential for coordinating arterial baroreflex control of blood pressure. The primary baroreceptor afferent fibres make their first excitatory synaptic contact at second-order NTS neurones with glutamate as the major neurotransmitter. Glutamate regulates its own release by activating presynaptic metabotropic glutamate autoreceptors (mGluRs) on the baroreceptor central terminals to suppress its further release in frequency-dependent manner. Gamma-aminobutyric acid (GABA) interneurones provide the major inhibitory synaptic input. It is the integration of excitatory and inhibitory inputs that shapes the NTS output of baroreceptor signals. We hypothesized that glutamate released from the primary central afferent terminals can spill over to presynaptic mGluRs on GABA interneurones to suppress GABA release at the second-order baroreceptor neurones. We assessed GABA transmission in second-order baroreceptor neurones identified by attached aortic depressor nerve (ADN) boutons. The medial NTS was stimulated to evoke GABA inhibitory postsynaptic currents (eIPSCs). Glutamate spillover, generated by brief 2 s, 25 Hz trains of stimuli applied to the tractus solitarius (TS), induced a small (10%) but significant reduction in the eIPSC amplitudes. The depression was enhanced to a 25% decrease by increasing glutamate in the cleft with a glutamate-uptake inhibitor (M-trans-pyrrolidine-2,4-dicarboxylic acid, 1 mum), blocked by a Group II mGluR antagonist (LY341495, 200 nm) and mimicked by a Group II agonist ((2S,3S,4S)-CCG/(2S,1'S,2'S)-2-carboxycyclopropyl; L-CCG-I). A presynaptic mGluR locus was established by the mGluR agonist-mediated increase in the paired-pulse ratio of two consecutive eIPSCs in conjunction with the decrease in the first eIPSC, and a decrease in the frequency (39-46% reduction at EC(50) concentration), but not amplitude, of spontaneous and miniature GABA IPSCs. The data indicate that endogenous glutamate activation of Group II presynaptic mGluRs can decrease GABA release at the first central synapses, suggesting a heterosynaptic role for the Group II mGluRs in shaping baroreceptor signal transmission.
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Affiliation(s)
- Chao-Yin Chen
- Department of Medical Pharmacology and Toxicology, Tupper Hall Room 1311, University of California-Davis, One Shields Avenue, Davis, CA 95616, USA
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Sekizawa SI, Joad JP, Bonham AC. Substance P presynaptically depresses the transmission of sensory input to bronchopulmonary neurons in the guinea pig nucleus tractus solitarii. J Physiol 2004; 552:547-59. [PMID: 14561836 PMCID: PMC2343393 DOI: 10.1113/jphysiol.2003.051326] [Citation(s) in RCA: 55] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
Substance P modulates the reflex regulation of respiratory function by its actions both peripherally and in the CNS, particularly in the nucleus tractus solitarii (NTS), the first central site for synaptic contact of the lung and airway afferent fibres. There is considerable evidence that the actions of substance P in the NTS augment respiratory reflex output, but the precise effects on synaptic transmission have not yet been determined. Therefore, we determined the effects of substance P on synaptic transmission at the first central synapses by using whole-cell voltage clamping in an NTS slice preparation. Studies were performed on second-order neurons in the slice anatomically identified as receiving monosynaptic input from sensory nerves in the lungs and airways. This was done by the fluorescent labelling of terminal boutons after 1,1'-dioctadecyl-3,3,3',3'-tetra-methylindocarbo-cyanine perchlorate (DiI) was applied via tracheal instillation. Substance P (1.0, 0.3 and 0.1 microM) significantly decreased the amplitude of excitatory postsynaptic currents (eEPSCs) evoked by stimulation of the tractus solitarius, in a concentration-dependent manner. The decrease was accompanied by an increase in the paired-pulse ratio of two consecutive eEPSCs, and a decrease in the frequency, but not the amplitude, of spontaneous EPSCs and miniature EPSCs, findings consistent with a presynaptic site of action. The effects were consistently and significantly attenuated by a neurokinin-1 (NK1) receptor antagonist (SR140333, 3 muM). The data suggest a new site of action for substance P in the NTS (NK1 receptors on the central terminals of sensory fibres) and a new mechanism (depression of synaptic transmission) for regulating respiratory reflex function.
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Affiliation(s)
- Shin-ichi Sekizawa
- Department of Pharmacology and Toxicology and Department of Pediatrics, University of California Davis, Davis, CA 95616, USA
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Joad JP, Munch PA, Bric JM, Evans SJ, Pinkerton KE, Chen CY, Bonham AC. Passive smoke effects on cough and airways in young guinea pigs: role of brainstem substance P. Am J Respir Crit Care Med 2003; 169:499-504. [PMID: 14644932 DOI: 10.1164/rccm.200308-1139oc] [Citation(s) in RCA: 73] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
Abstract
Children raised with extended exposure to environmental tobacco smoke (ETS) experience increased cough and wheeze. This study was designed to determine whether extended ETS exposure enhances citric acid-induced cough and bronchoconstriction in young guinea pigs via a neurokinin-1 (NK-1) receptor mechanism at the first central synapse of lung afferent neurons, the nucleus tractus solitarius. Guinea pigs were exposed to ETS from 1 to 6 weeks of age. At 5 weeks of age, guide cannulae were implanted bilaterally in the medial nucleus tractus solitarius at a site that produced apnea in response to the glutamate agonist D,L-homocysteic acid. At 6 weeks of age, either vehicle or a NK-1 receptor antagonist, SR 140333, was injected into the nucleus tractus solitarius of the conscious guinea pigs who were then exposed to citric acid aerosol. ETS exposure significantly enhanced citric acid-induced cough by 56% and maximal Penh (a measure of airway obstruction) by 43%, effects that were attenuated by the NK-1 receptor antagonist in the nucleus tractus solitarius. We conclude that in young guinea pigs extended exposure to ETS increases citric acid-induced cough and bronchoconstriction in part by an NK-1 receptor mechanism in the nucleus tractus solitarius.
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Affiliation(s)
- Jesse P Joad
- Department of Pediatrics, School of Medicine, University of California, Davis, Sacramento, CA 95817, USA.
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Chen CY, Bonham AC, Plopper CG, Joad JP. Neuroplasticity in nucleus tractus solitarius neurons after episodic ozone exposure in infant primates. J Appl Physiol (1985) 2003; 94:819-27. [PMID: 12433861 DOI: 10.1152/japplphysiol.00552.2002] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Acute ozone exposure evokes adverse respiratory responses, particularly in children. With repeated ozone exposures, however, despite the persistent lung inflammation and increased sensory nerve excitability, the central nervous system reflex responses, i.e., rapid shallow breathing and decreased lung function, adapt, suggesting changes in central nervous system signaling. We determined whether repeated ozone exposures altered the behavior of nucleus tractus solitarius (NTS) neurons where reflex respiratory motor outputs are first coordinated. Whole cell recordings were performed on NTS neurons in brain stem slices from infant monkeys exposed to filtered air or ozone (0.5 ppm, 8 h/day for 5 days every 14 days for 11 episodes). Although episodic ozone exposure depolarized the membrane potential, increased the membrane resistance, and increased neuronal spiking responses to depolarizing current injections (P < 0.05), it decreased the excitability to vagal sensory fiber activation (P < 0.05), suggesting a diminished responsiveness to sensory transmission, despite overall increases in excitability. Substance P, implicated in lung and NTS signaling, contributed to the increased responsiveness to current injections but not to the diminished sensory transmission. The finding that NTS neurons undergo plasticity with repeated ozone exposures may help to explain the adaptation of the respiratory motor responses.
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Affiliation(s)
- Chao-Yin Chen
- Department of Internal Medicine, School of Medicine, University of California at Davis, 95616, USA
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Abstract
In hypertensive subjects, a single bout of dynamic exercise results in an immediate lowering of blood pressure back toward normal. This postexercise hypotension (PEH) also occurs in the spontaneously hypertensive rat (SHR). In both humans and SHRs, PEH features a decrease in sympathetic nerve discharge, suggesting the involvement of central nervous system pathways. Given that substance P is released in the nucleus tractus solitarius (NTS) by activation of baroreceptor and skeletal muscle afferent fibers during muscle contraction, we hypothesized that substance P acting at neurokinin-1 (NK-1) receptors in the NTS might contribute to PEH. We tested the hypothesis by determining, in conscious SHRs, whether NTS microinjections of the NK-1 receptor antagonist SR-140333 before exercise attenuated PEH. The antagonist, in a dose (60 pmol) that blocked substance P- and spared D,L-homocysteic acid-induced depressor responses, significantly attenuated the PEH by 37%, whereas it had no effect on blood pressure during exercise. Vehicle microinjection had no effect. The antagonist also had no effect on heart rate responses during both exercise and the PEH period. The data suggest that a substance P (NK-1) receptor mechanism in the NTS contributes to PEH.
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Affiliation(s)
- Chao-Yin Chen
- Department of Internal Medicine, Division of Cardiovascular Medicine, University of California-Davis, TB 172, One Shields Avenue, Davis, CA 95616, USA.
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Abstract
A single bout of exercise results in a postexercise hypotension (PEH) that is accompanied by a reduced baroreflex function. Based on the role of rostral ventrolateral medulla (RVLM) neurons in controlling sympathetic nerve activity (SNA) and blood pressure, the role of gamma-aminobutyric acid (GABA) in controlling RVLM neuronal activity, and the reduced baroreflex-SNA relationship during PEH, we determined whether: 1) RVLM neuronal activity is decreased during PEH, 2) GABA(A)-receptor mechanisms mediate the decrease, and 3) baroreflex control of RVLM activity is reduced. Spontaneously hypertensive rats (SHR) were subjected to 40 min of treadmill or sham exercise (Sham PEH). PEH lasted 10 h in conscious and anesthetized SHR, indicating that the anesthetics did not affect the expression of PEH. Extracellular RVLM neuronal activity having a cardiac and sympathetic rhythm, lumbar SNA, and blood pressure were recorded at rest and during baroreflex function curves. Resting RVLM neuronal activity was lower and was increased to a greater extent by GABA(A)-receptor antagonism in PEH versus Sham PEH (P < 0.05). Baroreflex control of RVLM neuronal activity operated with a reduced gain (P < 0.05). Thus increased GABA signaling at RVLM neurons may contribute to PEH.
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Affiliation(s)
- Radhika Kajekar
- Department of Internal Medicine, University of California at Davis, Davis, California 95616, USA
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Abstract
1. The nucleus tractus solitarius (NTS) is the first central site where the reflex control of autonomic, including baroreceptor, reflex function is coordinated. Autonomic signals are transmitted from the first-order visceral afferent fibres to second-order NTS neurons by L-glutamate. It is well established that activation of the alpha-amino-3-hydroxy-5-methyl-4-isoxazole proprionic acid (AMPA) receptors, which mediate the fast component of L-glutamate signalling, is required for generating changes in membrane potentials of the second-order NTS neurons. The contribution of the slower-developing, longer-lasting N-methyl-D-aspartate (NMDA) receptor-mediated component of glutamate signalling to synaptic transmission at these synapses is less well understood. 2. The aim of this work is to highlight evidence that functional NMDA receptors exist on second-order NTS neurons in autonomic, including baroreceptor, afferent pathways by determining whether NMDA receptors can be activated by: (i) exogenous application of NMDA; and (ii) endogenous release of L-glutamate from autonomic afferent fibres. Studies were performed on second-order neurons in transverse and horizontal brainstem slices containing the intermediate NTS and the tractus solitarius. Second-order NTS neurons were identified by electrophysiological criteria or by attached fluorescent-labelled aortic depressor nerve (ADN) boutons. 3. N-Methyl-D-aspartate (50 nmol(-2) micromol) dose-dependently evoked excitatory post-synaptic currents in second-order NTS neurons (P = 0.004; n = 4). The NMDA receptor-mediated currents were also synaptically evoked by low-frequency stimulation of the autonomic afferent fibres in the tractus solitarius. The NMDA receptor-mediated currents were blocked by the NMDA receptor antagonist AP5 (n = 7; P = 0.027). 4. The findings suggest that functional NMDA receptors exist on second-order NTS neurons. While the NMDA receptor- mediated currents may not be required for signal transmission when the second-order neurons are at resting membrane potential, their activation may help to modulate autonomic signal transmission in the NTS under conditions in which the membrane is depolarized by high frequency or convergent inputs.
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Affiliation(s)
- Ann C Bonham
- Department of Internal Medicine, University of California, Davis, California 95616, USA.
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Chen CY, Ling Eh EH, Horowitz JM, Bonham AC. Synaptic transmission in nucleus tractus solitarius is depressed by Group II and III but not Group I presynaptic metabotropic glutamate receptors in rats. J Physiol 2002; 538:773-86. [PMID: 11826164 PMCID: PMC2290096 DOI: 10.1113/jphysiol.2001.012948] [Citation(s) in RCA: 81] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
Presynaptic metabotropic glutamate receptors (mGluRs) serve as autoreceptors throughout the CNS to inhibit glutamate release and depress glutamatergic transmission. Both presynaptic and postsynaptic mGluRs have been implicated in shaping autonomic signal transmission in the nucleus tractus solitarius (NTS). We sought to test the hypothesis that activation of presynaptic mGluRs depresses neurotransmission between primary autonomic afferent fibres and second-order NTS neurones. In second-order NTS neurones, excitatory postsynaptic currents (EPSCs) synaptically evoked by stimulation of primary sensory afferent fibres in the tractus solitarius (ts) and currents postsynaptically evoked by alpha-amino-3-hydroxy-4-isoxazoleproprionic acid (AMPA) were studied in the presence and absence of mGluR agonists and antagonists. Real-time quantitative RT-PCR (reverse transcription-polymerase chain reaction) was used to determine whether the genes for the mGluR subtypes were expressed in the cell bodies of the primary autonomic afferent fibres. Agonist activation of Group II and III but not Group I mGluRs reduced the peak amplitude of synaptically (ts) evoked EPSCs in a concentration-dependent manner while having no effect on postsynaptically (AMPA) evoked currents recorded in the same neurones. At the highest concentrations, the Group II agonist, (2S,3S,4S)-CCG/(2S,1'S,2'S)-2-carboxycyclopropyl (L-CCG-I), decreased the amplitude of the ts-evoked EPSCs by 39 % with an EC50 of 21 microM, and the Group III agonist, L(+)-2-amino-4-phosphonobutyric acid (L-AP4), decreased the evoked EPSCs by 71 % with an EC50 of 1 mM. mRNA for all eight mGluR subtypes was detected in the autonomic afferent fibre cell bodies in the nodose and jugular ganglia. Group II and III antagonists ((2S,3S,4S)-2-methyl-2-(carboxycyclopropyl)glycine (MCCG) and (RS)-alpha-methylserine-O-phosphate (MSOP)), at concentrations that blocked the respective agonist-induced synaptic depression, attenuated the frequency-dependent synaptic depression associated with increasing frequencies of ts stimulation by 13-34 % and 13-19 %, respectively (P < 0.05, for each). We conclude that Group II and III mGluRs (synthesized in the cell bodies of the primary autonomic afferent fibres and transported to the central terminals in the NTS) contribute to the depression of autonomic signal transmission by attenuating presynaptic release of glutamate.
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Affiliation(s)
- Chao-Yin Chen
- Division of Cardiovascular Medicine, University of California, Davis, CA 95616, USA
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Chen CY, Bonham AC, Schelegle ES, Gershwin LJ, Plopper CG, Joad JP. Extended allergen exposure in asthmatic monkeys induces neuroplasticity in nucleus tractus solitarius. J Allergy Clin Immunol 2001; 108:557-62. [PMID: 11590381 DOI: 10.1067/mai.2001.118132] [Citation(s) in RCA: 67] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Abstract
BACKGROUND Extended exposure to allergen exacerbates asthma symptoms, in part via complex interactions between inflammatory cells and mediators. One consequence of these interactions is the triggering of local and central nervous system (CNS) neuronal activity that might further exacerbate the asthma-like symptoms by causing bronchoconstriction, mucous secretion, increased microvascular leak, and cough. One CNS region that might be particularly important is the caudomedial nucleus tractus solitarius (NTS). NTS neurons not only integrate primary afferent inputs from lung sensory nerve fibers but also have direct exposure to inhaled allergens and allergen-induced blood-borne inflammatory mediators via a deficient blood-brain barrier. Given the capacity of CNS neurons to undergo plasticity, allergen-induced changes in NTS neuronal properties could contribute to the exaggerated respiratory responses to extended allergen exposure. OBJECTIVE In a recently developed rhesus monkey model of allergic asthma, we tested the hypothesis that extended exposure to allergen increases the intrinsic excitability of NTS neurons. METHODS Three adult monkeys were sensitized and then repeatedly exposed to aerosols of house dust mite allergen; 4 monkeys served as controls. Whole-cell current-clamp recordings were made to measure 3 indices of excitability: resting membrane potential, input resistance, and number of action potentials evoked by current injections. RESULTS Extended allergen exposure depolarized the resting membrane potential by 14% and increased the number of action potentials evoked by current injections (5-fold). CONCLUSION The finding that NTS neurons in a primate model of allergic asthma undergo intrinsic increases in excitability suggests that CNS mechanisms might contribute to the exaggerated symptoms in asthmatic individuals exposed to allergen.
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Affiliation(s)
- C Y Chen
- Department of Internal Medicine, School of Medicine, University of California at Davis, Sacramento, 95817, USA
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Bonham AC, Chen CY, Mutoh T, Joad JP. Lung C-fiber CNS reflex: role in the respiratory consequences of extended environmental tobacco smoke exposure in young guinea pigs. Environ Health Perspect 2001; 109 Suppl 4:573-578. [PMID: 11544166 PMCID: PMC1240584 DOI: 10.1289/ehp.01109s4573] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
Environmental tobacco smoke (ETS) exposure harms the respiratory health of children and is associated with an increased risk of asthma and sudden infant death syndrome (SIDS). The mechanisms by which ETS causes these effects are not understood. We hypothesized that one mechanism is an upregulation of the lung C-fiber central nervous system (CNS) reflex responses, which would result in exaggerated reflex responses of apnea, bronchoconstriction, and mucous hypersecretion. The purpose of this work is to highlight evidence obtained in an animal model of postnatal ETS exposure supporting the hypothesis and present data suggesting that actions of the neuropeptide substance P in the nucleus tractus solitarius (NTS) may contribute. Exposing young guinea pigs to sidestream smoke, the surrogate for ETS, for 5 weeks during the equivalent of human childhood, increased the excitability of afferent lung C fibers and NTS neurons in the CNS reflex pathway and prolonged the expiratory apnea. The findings suggest that an increased excitability of NTS neurons that can augment reflex output may contribute to respiratory symptoms in children exposed to ETS. Besides ETS exposure, substance P can also excite NTS neurons and augment lung C-fiber CNS reflex responses. Others have shown that substance P synthesis in lung C fibers is upregulated by another environmental stimulant, allergen. Thus, an upregulation of the substance P system at NTS synapses could contribute to the increased NTS excitability and enhanced reflex responses to lung C-fiber stimulation, providing a potential mechanism to help explain the association of ETS exposure with respiratory symptoms and SIDS.
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Affiliation(s)
- A C Bonham
- Department of Internal Medicine, School of Medicine, Kobe University, Kobe, Japan.
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Abstract
Bronchopulmonary C fibers defend the lungs against injury from inhaled agents by a central nervous system reflex consisting of apnea, cough, bronchoconstriction, hypotension, and bradycardia. Glutamate is the putative neurotransmitter at the first central synapses in the nucleus of the solitary tract (NTS), but substance P, also released in the NTS, may modulate the transmission. To test the hypothesis that substance P in the NTS augments bronchopulmonary C fiber input and hence reflex output, we stimulated the C fibers with left atrial capsaicin (LA CAP) injections and compared the changes in phrenic nerve discharge, tracheal pressure (TP), arterial blood pressure (ABP), and heart rate (HR) in guinea pigs before and after substance P injections (200 microM, 25 nl) in the NTS. Substance P significantly augmented LA CAP-evoked increases in expiratory time by 10-fold and increases in TP and decreases in ABP and HR by threefold, effects prevented by neurokinin-1 (NK1) receptor antagonism. Thus substance P acting at NTS NK1 receptors can exaggerate bronchopulmonary C fiber reflex output. Because substance P synthesis in vagal airway C fibers may be enhanced in pathological conditions such as allergic asthma, the findings may help explain some of the associated respiratory symptoms including cough and bronchoconstriction.
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Affiliation(s)
- T Mutoh
- Departments of Internal Medicine and Pharmacology, University of California, Davis, Sacramento, California 95616, USA
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Mutoh T, Joad JP, Bonham AC. Chronic passive cigarette smoke exposure augments bronchopulmonary C-fibre inputs to nucleus tractus solitarii neurones and reflex output in young guinea-pigs. J Physiol 2000; 523 Pt 1:223-33. [PMID: 10673557 PMCID: PMC2269785 DOI: 10.1111/j.1469-7793.2000.00223.x] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
Abstract
1. Children chronically exposed to environmental tobacco smoke (passive cigarette smoke) have more wheeze, cough, bronchoconstriction, airway hyper-reactivity and mucous secretion, which may result, in part, from stimulation of the vagal bronchopulmonary C-fibre reflex. 2. Environmental tobacco smoke increases the sensitivity of bronchopulmonary C-fibre endings, but the physiological relevance of this sensitization is unknown. If this exposure augments the reflex responses via a central mechanism, then the responses of higher-order neurones in the reflex pathway and some components of the reflex output should also be augmented. 3. Guinea-pigs were chronically exposed to sidestream tobacco smoke (surrogate for environmental tobacco smoke) or filtered air for 5 days week-1 from age 1 to 6 weeks (age equivalent of human childhood) and were then anaesthetized, paralysed, ventilated and prepared with pneumothoraces. Baseline and left atrial capsaicin (0.5 and 2.0 microg kg-1)- evoked changes in the impulse activity of vagal C-fibre-activated neurones in nucleus tractus solitarii (NTS), phrenic nerve activity, tracheal pressure, arterial blood pressure and heart rate were compared in the two groups. 4. Sidestream smoke exposure significantly augmented the peak (P = 0.02) and duration (P = 0.01) of the NTS neuronal responses and the prolongation of expiratory time (P = 0.003) at the higher capsaicin dose. 5. Thus, the sensitization of the bronchopulmonary C-fibre endings by chronic exposure to sidestream tobacco smoke is transmitted to the NTS and is associated with a prolonged reflexively evoked expiratory apnoea. The findings may help to explain some related respiratory symptoms in children and be a factor in sudden infant death syndrome.
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Affiliation(s)
- T Mutoh
- Departments of Internal Medicine and Pharmacology and Department of Pediatrics, University of California, Davis, CA 95616, USA
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Abstract
The frequency of baroreceptor volleys to the central nervous system can influence the fidelity of baroreceptor signal transmission and thus may affect baroreflex regulation of blood pressure. We examined 1) the extent to which frequency-dependent depression of aortic baroreceptor signals was initiated at the first central synapse between primary baroreceptor fibers and second-order nucleus tractus solitarii (NTS) neurons; 2) whether the pattern of baroreceptor input influenced the depression; and 3) the potential relevance to baroreflex sympathoinhibition. In urethan-anesthetized rats, NTS action potential responses of neurons classified as second or higher order and averaged lumbar sympathetic nerve activity responses were simultaneously measured during 100 aortic depressor nerve stimuli delivered in constant or phasic patterns (0.8-48 Hz). Frequency-dependent depression was initiated at second-order neurons, with NTS responses decreasing to a 72% response rate at 48 Hz; the depression was greater at higher-order neurons; responses decreased to a 30% response rate. The depression was slightly but significantly greater with phasic inputs. Curve fitting suggested that synaptic depression may limit baroreflex sympathoinhibition. Thus frequency limits on baroreceptor inputs at NTS synapses may affect baroreflex function.
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Affiliation(s)
- Z Liu
- Division of Cardiovascular Medicine and Department of Pharmacology, University of California, Davis, California 95616, USA
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Abstract
With increasing frequencies of autonomic afferent input to the nucleus tractus solitarii (NTS), postsynaptic responses are depressed. To test the hypothesis that a presynaptic mechanism contributes to this frequency-dependent depression, we used whole cell, voltage-clamp recordings in an NTS slice. First, we determined whether solitary tract stimulation (0.4-24 Hz) resulted in frequency-dependent depression of excitatory postsynaptic currents (EPSCs) in second-order neurons. Second, because decreases in presynaptic glutamate release result in a parallel depression of alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) and N-methyl-D-aspartic acid (NMDA) receptor-mediated components of EPSCs, we determined whether the magnitude, time course, and recovery from the depression were the same in both EPSC components. Third, to determine whether AMPA receptor desensitization contributed, we examined the depression during cyclothiazide. EPSCs decreased in a frequency-dependent manner by up to 76% in second- and 92% in higher-order neurons. AMPA and NMDA EPSC components were depressed with the same magnitude (by 83% and 83%) and time constant (113 and 103 ms). The time constant for the recovery was also not different (1.2 and 0.8 s). Cyclothiazide did not affect synaptic depression at >/=3 Hz. The data suggest that presynaptic mechanism(s) at the first NTS synapse mediate frequency-dependent synaptic depression.
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Affiliation(s)
- C Y Chen
- Division of Cardiovascular Medicine, Department of Pharmacology, University of California, Davis, California 95616, USA
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