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Koh Y, Kwok C, Voskoboinik A, Kalman JM, Wong M. Serotonin antidepressants and atrial fibrillation burden from cardiac implantable electronic devices. J Arrhythm 2023; 39:876-883. [PMID: 38045466 PMCID: PMC10692859 DOI: 10.1002/joa3.12948] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2023] [Revised: 09/16/2023] [Accepted: 10/17/2023] [Indexed: 12/05/2023] Open
Abstract
Objective Depression and anxiety show a bidirectional relationship with atrial fibrillation (AF). Antidepressant use is associated with a reduction in the incidence of AF. However, no studies have examined the relationship between antidepressant use and AF burden (time in AF). This retrospective cohort study examined cardiac implantable device-detected AF episodes and their relationship with antidepressant use, among other treatment factors. Methods Consecutive patients from the Western Health Cardiology Department attending pacemaker checks between 2015 and 2021 were included. Patients with permanent AF were excluded, yielding 285 patients with no or paroxysmal AF, with a total of 772 patient encounters. Generalized estimating equations were used to model two processes: binary AF (present/absent) and the number of days in AF for patients with AF. Results Each yearly increase with age was associated with an increase in the odds of developing AF (OR 1.03 [1.00-1.05], p = .027). Male gender conferred a reduction in AF incidence (OR 0.30 [0.13-0.68], p = .004). Digoxin use was associated with incident AF (OR 4.43 [1.07-18.4], p = .04). Sotalol and heart-failure beta blocker use were associated with a decrease in AF burden (IRR 0.30 [0.12-0.78], p = .013 and 0.33 [0.14-0.81], p = .015). Selective serotonin reuptake inhibitor antidepressant use was associated with reduced AF burden (IRR 0.27 [0.09-0.81], p = .019), as was selective serotonin/noradrenaline reuptake inhibitor use (IRR 0.07 [0.03-0.15], p < .001). Conclusions Older age, female gender and digoxin are associated with a higher odds of developing incident AF. Sotalol, heart failure beta blockers and serotonin-based antidepressants are associated with reduced AF burden. Further prospective study into the effects of antidepressants on atrial arrhythmias is warranted.
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Affiliation(s)
- Youlin Koh
- Department of CardiologyWestern HealthSt AlbansVictoriaAustralia
- Department of CardiologyRoyal Melbourne HospitalMelbourneVictoriaAustralia
| | - Cecilia Kwok
- Department of CardiologyWestern HealthSt AlbansVictoriaAustralia
| | - Aleksandr Voskoboinik
- Department of CardiologyWestern HealthSt AlbansVictoriaAustralia
- Department of CardiologyAlfred HealthMelbourneVictoriaAustralia
| | - Jonathan M. Kalman
- Department of CardiologyRoyal Melbourne HospitalMelbourneVictoriaAustralia
| | - Michael Wong
- Department of CardiologyWestern HealthSt AlbansVictoriaAustralia
- Department of CardiologyRoyal Melbourne HospitalMelbourneVictoriaAustralia
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2
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Xu F, Zhao L, Zhuang J, Gao X. Peripheral Neuroplasticity of Respiratory Chemoreflexes, Induced by Prenatal Nicotinic Exposure: Implication for SIDS. Respir Physiol Neurobiol 2023; 313:104053. [PMID: 37019251 DOI: 10.1016/j.resp.2023.104053] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2023] [Revised: 03/23/2023] [Accepted: 04/02/2023] [Indexed: 04/05/2023]
Abstract
Sudden Infant Death Syndrome (SIDS) occurs during sleep in seemingly healthy infants. Maternal cigarette smoking and hypoxemia during sleep are assumed to be the major causal factors. Depressed hypoxic ventilatory response (dHVR) is observed in infants with high risk of SIDS, and apneas (lethal ventilatory arrest) appear during the fatal episode of SIDS. Disturbance of the respiratory center has been proposed to be involved, but the pathogenesis of SIDS is still not fully understood. Peripherally, the carotid body is critical to generate HVR, and bronchopulmonary and superior laryngeal C-fibers (PCFs and SLCFs) are important for triggering central apneas; however, their roles in the pathogenesis of SIDS have not been explored until recently. There are three lines of recently accumulated evidence to show the disorders of peripheral sensory afferent-mediated respiratory chemoreflexes in rat pups with prenatal nicotinic exposure (a SIDS model) in which acute severe hypoxia leads to dHVR followed by lethal apneas. (1) The carotid body-mediated HVR is suppressed with a reduction of the number and sensitivity of glomus cells. (2) PCF-mediated apneic response is largely prolonged via increased PCF density, pulmonary IL-1β and serotonin (5-hydroxytryptamine, 5-HT) release, along with the enhanced expression of TRPV1, NK1R, IL1RI and 5-HT3R in pulmonary C-neurons to strengthen these neural responses to capsaicin, a selective stimulant to C-fibers. (3) SLCF-mediated apnea and capsaicin-induced currents in superior laryngeal C-neurons are augmented by upregulation of TRPV1 expression in these neurons. These results, along with hypoxic sensitization/stimulation of PCFs, gain insight into the mechanisms of prenatal nicotinic exposure-induced peripheral neuroplasticity responsible for dHVR and long-lasting apnea during hypoxia in rat pups. Therefore, in addition to the disturbance in the respiratory center, the disorders of peripheral sensory afferent-mediated chemoreflexes may also be involved in respiratory failure and death denoted in SIDS victims.
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3
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Magnusson JL, Emter CA, Cummings KJ. Sex- and age-based differences in the effect of central serotonin on arterial blood pressure regulation. J Appl Physiol (1985) 2020; 129:1310-1323. [PMID: 32909922 DOI: 10.1152/japplphysiol.00414.2020] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Medullary serotonin (5-hydroxytryptamine; 5-HT) neurons project to multiple autonomic nuclei in the central nervous system (CNS). Infant rats lacking 5-HT have low arterial blood pressure (ABP) in quiet sleep, but the role of 5-HT in ABP regulation across vigilance states in adults has not been studied. We hypothesized that in adults, CNS 5-HT deficiency leads to hypotension mainly in quiet wakefulness (QW) and non-rapid eye movement (NREM) sleep, when 5-HT neurons are active. We tested male and female tryptophan hydroxylase 2 knockout rats (TPH2-/-), specifically deficient in CNS 5-HT, and wild-type (TPH2+/+) controls at 2-3, 5-8, and 12-13 mo of age. Compared with TPH2+/+, mean arterial pressure of 5-8- and 12-13-mo-old (middle-aged) male TPH2-/- rats was significantly elevated (∼10 mmHg) in QW and rapid eye movement (REM) sleep. Middle-aged male TPH2-/- rats also had more frequent extreme hypertensive events during prolonged episodes of REM sleep. Female TPH2-/- had normal ABP. The low- and very-low-frequency components of systolic ABP variability were significantly higher in middle-aged male, but not female, TPH2-/- rats compared with in TPH2+/+ rats, suggesting elevated sympathetic vascular tone in male TPH2-/- rats. However, the hypertension of male TPH2-/- rats was not ameliorated by ganglionic blockade. Hearts and lungs of middle-aged male TPH2-/- rats were significantly heavier than those of TPH2+/+ rats. We show that a loss of CNS 5-HT leads to high ABP only in middle-aged males during wakefulness and REM sleep, possibly due to increased vascular tone. It should be investigated whether elevated ventricular afterload associated with CNS 5-HT deficiency initiates cardiac remodeling or alters pulmonary hemodynamics.NEW & NOTEWORTHY The role of serotonin in arterial blood pressure (ABP) regulation across states of vigilance is unknown. We hypothesized that adult rats devoid of CNS serotonin (TPH2-/-) have low ABP in wakefulness and NREM sleep, when serotonin neurons are active. However, TPH2-/- rats experience higher ABP than TPH2+/+ rats in wakefulness and REM only, a phenotype present only in older males and not females. CNS serotonin may be critical for preventing high ABP in males with aging.
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Affiliation(s)
- Jennifer L Magnusson
- Department of Biomedical Sciences, College of Veterinary Medicine, University of Missouri, Columbia, Missouri
| | - Craig A Emter
- Department of Biomedical Sciences, College of Veterinary Medicine, University of Missouri, Columbia, Missouri
| | - Kevin J Cummings
- Department of Biomedical Sciences, College of Veterinary Medicine, University of Missouri, Columbia, Missouri.,Dalton Cardiovascular Research Center, University of Missouri, Columbia, Missouri
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4
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Hu MX, Milaneschi Y, Lamers F, Nolte IM, Snieder H, Dolan CV, Penninx BWJH, de Geus EJC. The association of depression and anxiety with cardiac autonomic activity: The role of confounding effects of antidepressants. Depress Anxiety 2019; 36:1163-1172. [PMID: 31622521 PMCID: PMC6916630 DOI: 10.1002/da.22966] [Citation(s) in RCA: 33] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/16/2019] [Revised: 08/22/2019] [Accepted: 10/02/2019] [Indexed: 12/19/2022] Open
Abstract
BACKGROUND Depression and anxiety may unfavorably impact on cardiac autonomic dysregulation. However, it is unclear whether this relationship results from a causal effect or may be attributable to confounding factors. We tested the relationship between depression and anxiety with heart rate (HR) and heart rate variability (HRV) across a 9-year follow-up (FU) period and investigated possible confounding by antidepressant use and genetic pleiotropy. METHODS Data (no. of observations = 6,994, 65% female) were obtained from the longitudinal Netherlands Study of Depression and Anxiety, with repeated waves of data collection of HR, HRV, depression, anxiety, and antidepressant use. Summary statistics from meta-analyses of genome-wide association studies were used to derive polygenic risk scores of depression, HR, and HRV. RESULTS Across the 9-year FU, generalized estimating equations analyses showed that the relationship between cardiac autonomic dysregulation and depression/anxiety rendered nonsignificant after adjusting for antidepressant use. A robust association was found between antidepressant use (especially tricyclic antidepressants, selective serotonin, and noradrenalin reuptake inhibitors) and unfavorable cardiac autonomic activity across all waves. However, no evidence was found for a genetic correlation of depression with HR and HRV, indicating that confounding by genetic pleiotropy is minimal. CONCLUSIONS Our results indicate that the association between depression/anxiety and cardiac autonomic dysregulation does not result from a causal pathway or genetic pleiotropy, and these traits might therefore not be inevitably linked. Previously reported associations were likely confounded by the use of certain classes of antidepressants.
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Affiliation(s)
- Mandy X. Hu
- Department of Psychiatry, Amsterdam Public Health Research Institute, Amsterdam UMCVrije Universiteit AmsterdamAmsterdamThe Netherlands
| | - Yuri Milaneschi
- Department of Psychiatry, Amsterdam Public Health Research Institute, Amsterdam UMCVrije Universiteit AmsterdamAmsterdamThe Netherlands
| | - Femke Lamers
- Department of Psychiatry, Amsterdam Public Health Research Institute, Amsterdam UMCVrije Universiteit AmsterdamAmsterdamThe Netherlands
| | - Ilja M. Nolte
- Department of Epidemiology, Medical Center GroningenUniversity of GroningenGroningenThe Netherlands
| | - Harold Snieder
- Department of Epidemiology, Medical Center GroningenUniversity of GroningenGroningenThe Netherlands
| | - Conor V. Dolan
- Department of Biological PsychologyVU UniversityAmsterdamThe Netherlands
| | - Brenda W. J. H. Penninx
- Department of Psychiatry, Amsterdam Public Health Research Institute, Amsterdam UMCVrije Universiteit AmsterdamAmsterdamThe Netherlands
| | - Eco J. C. de Geus
- Department of Biological PsychologyVU UniversityAmsterdamThe Netherlands
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5
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Zubcevic J, Richards EM, Yang T, Kim S, Sumners C, Pepine CJ, Raizada MK. Impaired Autonomic Nervous System-Microbiome Circuit in Hypertension. Circ Res 2019; 125:104-116. [PMID: 31219753 PMCID: PMC6588177 DOI: 10.1161/circresaha.119.313965] [Citation(s) in RCA: 62] [Impact Index Per Article: 12.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Hypertension affects an estimated 103 million Americans, yet gaps in knowledge continue to limit its successful management. Rapidly emerging evidence is linking gut dysbiosis to many disorders and diseases including hypertension. The evolution of the -omics techniques has allowed determination of the abundance and potential function of gut bacterial species by next-generation bacterial sequencing, whereas metabolomics techniques report shifts in bacterial metabolites in the systemic circulation of hypertensive patients and rodent models of hypertension. The gut microbiome and host have evolved to exist in balance and cooperation, and there is extensive crosstalk between the 2 to maintain this balance, including during regulation of blood pressure. However, an understanding of the mechanisms of dysfunctional host-microbiome interactions in hypertension is still lacking. Here, we synthesize some of our recent data with published reports and present concepts and a rationale for our emerging hypothesis of a dysfunctional gut-brain axis in hypertension. Hopefully, this new information will improve the understanding of hypertension and help to address some of these knowledge gaps.
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Affiliation(s)
- Jasenka Zubcevic
- Department of Physiological Sciences, College of Veterinary Medicine; University of Florida, Gainesville FL32610
| | - Elaine M. Richards
- Department of Physiology and Functional Genomics, College of Medicine, University of Florida, Gainesville FL32610
| | - Tao Yang
- Department of Physiology and Functional Genomics, College of Medicine, University of Florida, Gainesville FL32610
| | - Seungbum Kim
- Department of Physiology and Functional Genomics, College of Medicine, University of Florida, Gainesville FL32610
| | - Colin Sumners
- Department of Physiology and Functional Genomics, College of Medicine, University of Florida, Gainesville FL32610
| | - Carl J Pepine
- Division of Cardiovascular Medicine, Department of Medicine, College of Medicine, University of Florida, Gainesville FL32610
| | - Mohan K Raizada
- Department of Physiology and Functional Genomics, College of Medicine, University of Florida, Gainesville FL32610
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6
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Bright FM, Vink R, Byard RW. The potential role of substance P in brainstem homeostatic control in the pathogenesis of sudden infant death syndrome (SIDS). Neuropeptides 2018; 70:1-8. [PMID: 29908886 DOI: 10.1016/j.npep.2018.02.006] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/30/2017] [Revised: 02/25/2018] [Accepted: 02/25/2018] [Indexed: 12/30/2022]
Abstract
Victims of sudden infant death syndrome (SIDS) are believed to have an underlying dysfunction in medullary homeostatic control that impairs critical responses to life threatening challenges such as hypoxia, hypercarbia and asphyxia, often during a sleep period. This failure is thought to result from abnormalities in a network of neural pathways in the medulla oblongata that control respiration, chemosensitivity, autonomic function and arousal. Studies have mainly focused on the role of serotonin, 5-hydroxytyptamine (5HT), although the neuropeptide substance P (SP) has also been shown to play an integral role in the modulation of medullary homeostatic function, often in conjunction with 5-HT. Actions of SP include regulation of respiratory rhythm generation, integration of cardiovascular control, modulation of the baroreceptor reflex and mediation of the chemoreceptor reflex in response to hypoxia. Abnormalities in SP neurotransmission may, therefore, also play a significant role in homeostatic dysfunction of the neurotransmitter network in SIDS. This review focuses on the pathways within the medulla involving SP and its tachykinin NK1 receptor, their potential relationship with the medullary 5-HT system, and possible involvement in the pathogenesis of SIDS.
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Affiliation(s)
- Fiona M Bright
- Discipline of Anatomy and Pathology, Adelaide Medical School, University of Adelaide, SA, Australia.
| | - Robert Vink
- Sansom Institute for Health Research, University of South Australia, Adelaide, SA, Australia
| | - Roger W Byard
- Discipline of Anatomy and Pathology, Adelaide Medical School, University of Adelaide, SA, Australia
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7
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Zhang HQ, Zhang Y, Liu L, Li JL, Lu YC, Yu YY, Li H, Zhang T, Chan YS, Zhang FX, Li YQ. Neural connection supporting endogenous 5-hydroxytryptamine influence on autonomic activity in medial prefrontal cortex. Auton Neurosci 2016; 203:25-32. [PMID: 27932203 DOI: 10.1016/j.autneu.2016.11.005] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2016] [Revised: 11/17/2016] [Accepted: 11/29/2016] [Indexed: 12/26/2022]
Abstract
5-hydroxytryptamine (5-HT) transmission in the medial prefrontal cortex (mPFC) enhances or suppresses signal outflow to influence emotion-/cognition-based function performances and, putatively, the autonomic responses. The top-down cortical modulation of autonomic activities may be mediated in part through projections from mPFC to brain stem dorsal vagal complex (DVC). The abundant and heterogeneous densities of 5-HT fibers across laminae in mPFC suggest serotonergic innervation of mPFC-DVC projection neurons whereby endogenous 5-HT acts to regulate autonomic activities. The present study investigated the physical relationship between 5-HT fibers and the autonomic-related mPFC neurons by examining and quantitatively characterizing the 5-HT contacts upon retrogradely labeled mPFC-DVC projection neurons in pre- and infra-limbic cortices (PrL/IL) with light and electron microscopies combined with immunocytochemistry for 5-HT and presynaptic vesicle marker synaptophysin (Syn). 5-HT varicosities were observed, under confocal microscope, to form close appositions to or, at ultrastructural level, to form asymmetric axodendritic synapses and direct contacts upon the target neurons. About 16% of the entire 5-HTergic varicosities in lamina V of PrL/IL coexpressed Syn and about 24% of the peri-somatic 5-HTergic swellings demonstrated Syn-immunoreactivity (ir), suggesting a low frequency of putative synapses estimated at optical level. Ultrastructurally, examination of thirty-seven serially cut thin 5-HT boutons closely apposed to the labeled dendritic profiles demonstrated that only three contacts presented with identifiable asymmetric, synaptic membrane specializations. These data provide the first and direct morphological evidence supporting that endogenous 5-HT may be released mainly via direct contacts bearing no identifiable synaptic specializations as well as synapses, targeting autonomic-related mPFC neurons for autonomic regulation.
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Affiliation(s)
- Hao-Qiang Zhang
- Department of Anatomy and K.K. Leung Brain Research Centre, The Fourth Military Medical University, Xi'an, People's Republic of China; Department of Orthopedics, Xi-Jing Hospital, The Fourth Military Medical University, Xi'an, People's Republic of China
| | - Yong Zhang
- Department of Anatomy and K.K. Leung Brain Research Centre, The Fourth Military Medical University, Xi'an, People's Republic of China
| | - Lin Liu
- Department of Anatomy and K.K. Leung Brain Research Centre, The Fourth Military Medical University, Xi'an, People's Republic of China; Department of Dermatology, Xi-Jing Hospital, The Fourth Military Medical University, Xi'an, People's Republic of China
| | - Jin-Lian Li
- Department of Anatomy and K.K. Leung Brain Research Centre, The Fourth Military Medical University, Xi'an, People's Republic of China
| | - Ya-Cheng Lu
- Department of Anatomy and K.K. Leung Brain Research Centre, The Fourth Military Medical University, Xi'an, People's Republic of China
| | - Ying-Ying Yu
- Department of Anatomy and K.K. Leung Brain Research Centre, The Fourth Military Medical University, Xi'an, People's Republic of China; Department of Anatomy, Histology and Embryology, Basic Medical College, Fujian Medical University, Fuzhou, China
| | - Hui Li
- Department of Anatomy and K.K. Leung Brain Research Centre, The Fourth Military Medical University, Xi'an, People's Republic of China
| | - Ting Zhang
- Department of Anatomy and K.K. Leung Brain Research Centre, The Fourth Military Medical University, Xi'an, People's Republic of China
| | - Ying-Shing Chan
- Department of Physiology, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong, People's Republic of China
| | - Fu-Xing Zhang
- Department of Anatomy and K.K. Leung Brain Research Centre, The Fourth Military Medical University, Xi'an, People's Republic of China.
| | - Yun-Qing Li
- Department of Anatomy and K.K. Leung Brain Research Centre, The Fourth Military Medical University, Xi'an, People's Republic of China.
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8
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Faingold CL, Randall M, Zeng C, Peng S, Long X, Feng HJ. Serotonergic agents act on 5-HT 3 receptors in the brain to block seizure-induced respiratory arrest in the DBA/1 mouse model of SUDEP. Epilepsy Behav 2016; 64:166-170. [PMID: 27743549 PMCID: PMC5123739 DOI: 10.1016/j.yebeh.2016.09.034] [Citation(s) in RCA: 36] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/09/2016] [Revised: 09/13/2016] [Accepted: 09/16/2016] [Indexed: 11/18/2022]
Abstract
Drugs that enhance the action of serotonin (5-hydroxytrypamine, 5-HT), including several selective serotonin reuptake inhibitors (SSRIs), reduce susceptibility to seizure-induced respiratory arrest (S-IRA) that leads to death in the DBA/1 mouse model of sudden unexpected death in epilepsy (SUDEP). However, it is not clear if specific 5-HT receptors are important in the action of these drugs and whether the brain is the major site of action of these agents in this SUDEP model. The current study examined the actions of agents that affect the 5-HT3 receptor subtype on S-IRA and whether intracerebroventricular (ICV) microinjection of an SSRI would reduce S-IRA susceptibility in DBA/1 mice. The data indicate that systemic administration of SR 57227, a 5-HT3 agonist, was effective in blocking S-IRA in doses that did not block seizures, and the S-IRA blocking effect of the SSRI, fluoxetine, was abolished by coadministration of a 5-HT3 antagonist, ondansetron. Intracerebroventricular administration of fluoxetine in the present study was also able to block S-IRA without blocking seizures. These findings suggest that 5-HT3 receptors play an important role in the block of S-IRA by serotonergic agents, such as SSRIs, which is consistent with the abnormal expression of 5-HT3 receptors in the brainstem of DBA mice observed previously. Taken together, these data indicate that systemically administered serotonergic agents act, at least, in part, in the brain, to reduce S-IRA susceptibility in DBA/1 mice and that 5-HT3 receptors may be important to this effect.
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Affiliation(s)
- Carl L Faingold
- Department of Pharmacology and Neurology, Southern Illinois University, School of Medicine, Springfield, IL, USA.
| | - Marcus Randall
- Department of Pharmacology and Neurology, Southern Illinois University, School of Medicine, Springfield, IL, USA
| | - Chang Zeng
- Department of Anesthesia, Critical Care and Pain Medicine, Massachusetts General Hospital and Harvard Medical School, Boston, MA, USA; Health Management Center, Xiangya Hospital, Central South University, Changsha, China
| | - Shifang Peng
- Health Management Center, Xiangya Hospital, Central South University, Changsha, China
| | - Xiaoyan Long
- Department of Neurology, Xiangya Hospital, Central South University, Changsha, China
| | - Hua-Jun Feng
- Department of Anesthesia, Critical Care and Pain Medicine, Massachusetts General Hospital and Harvard Medical School, Boston, MA, USA.
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Donnelly WT, Bartlett D, Leiter JC. Serotonin in the solitary tract nucleus shortens the laryngeal chemoreflex in anaesthetized neonatal rats. Exp Physiol 2016; 101:946-61. [PMID: 27121960 DOI: 10.1113/ep085716] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2016] [Accepted: 04/08/2016] [Indexed: 11/08/2022]
Abstract
What is the central question of this study? 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 died of SIDS. Therefore, we tested the hypothesis that serotonin in the nucleus of the solitary tract (NTS) would shorten reflex apnoea. What is the main finding and its importance? Serotonin microinjected into the NTS shortened the apnoea and respiratory inhibition associated with the laryngeal chemoreflex. Moreover, this effect was achieved through a 5-HT3 receptor. This is a new insight that is likely to be relevant to the pathogenesis of SIDS. The laryngeal chemoreflex (LCR), an airway-protective reflex that causes apnoea and bradycardia, has long been suspected as an initiating event in the sudden infant death syndrome. Serotonin (5-HT) and 5-HT receptors may be deficient in the brainstems of babies who die of sudden infant death syndrome, and 5-HT seems to be important in terminating apnoeas directly or in causing arousals or as part of the process of autoresuscitation. We hypothesized that 5-HT in the brainstem would limit the duration of the LCR. We studied anaesthetized rat pups between 7 and 21 days of age and made microinjections into the cisterna magna or into the nucleus of the solitary tract (NTS). Focal, bilateral microinjections of 5-HT into the caudal NTS significantly shortened the LCR. The 5-HT1a receptor antagonist, WAY 100635, did not affect the LCR consistently, nor did a 5-HT2 receptor antagonist, ketanserin, alter the duration of the LCR. The 5-HT3 specific agonist, 1-(3-chlorophenyl)-biguanide, microinjected bilaterally into the caudal NTS significantly shortened the LCR. Thus, endogenous 5-HT released within the NTS may curtail the respiratory depression that is part of the LCR, and serotonergic shortening of the LCR may be attributed to activation of 5-HT3 receptors within the NTS. 5-HT3 receptors are expressed presynaptically on C fibre afferents of the superior laryngeal nerve, and serotonergic shortening of the LCR may be mediated presynaptically by enhanced activation of inhibitory interneurons within the NTS.
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Affiliation(s)
- William T Donnelly
- Department of Physiology and Neurobiology, Geisel School of Medicine at Dartmouth, Lebanon, NH, 03756, USA
| | - Donald Bartlett
- Department of Physiology and Neurobiology, Geisel School of Medicine at Dartmouth, Lebanon, NH, 03756, USA
| | - J C Leiter
- Department of Physiology and Neurobiology, Geisel School of Medicine at Dartmouth, Lebanon, NH, 03756, USA
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Activation of 5-hyrdoxytryptamine 7 receptors within the rat nucleus tractus solitarii modulates synaptic properties. Brain Res 2016; 1635:12-26. [PMID: 26779891 DOI: 10.1016/j.brainres.2016.01.017] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2015] [Revised: 01/08/2016] [Accepted: 01/09/2016] [Indexed: 12/22/2022]
Abstract
Serotonin (5-HT) is a potent neuromodulator with multiple receptor types within the cardiorespiratory system, including the nucleus tractus solitarii (nTS)--the central termination site of visceral afferent fibers. The 5-HT7 receptor facilitates cardiorespiratory reflexes through its action in the brainstem and likely in the nTS. However, the mechanism and site of action for these effects is not clear. In this study, we examined the expression and function of 5-HT7 receptors in the nTS of Sprague-Dawley rats. 5-HT7 receptor mRNA and protein were identified across the rostrocaudal extent of the nTS. To determine 5-HT7 receptor function, we examined nTS synaptic properties following 5-HT7 receptor activation in monosynaptic nTS neurons in the in vitro brainstem slice preparation. Application of 5-HT7 receptor agonists altered tractus solitarii evoked and spontaneous excitatory postsynaptic currents which were attenuated with a selective 5-HT7 receptor antagonist. 5-HT7 receptor-mediated changes in excitatory postsynaptic currents were also altered by block of 5-HT1A and GABAA receptors. Interestingly, 5-HT7 receptor activation also reduced the amplitude but not frequency of GABAA-mediated inhibitory currents. Together these results indicate a complex role for 5-HT7 receptors in the nTS that mediate its diverse effects on cardiorespiratory parameters.
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11
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Speech prosody, reward, and the corticobulbar system: an integrative perspective. Behav Brain Sci 2015; 37:573-4; discussion 577-604. [PMID: 25514963 DOI: 10.1017/s0140525x13004214] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Speech prosody is essential for verbal communication. In this commentary I provide an integrative overview, arguing that speech prosody is subserved by the same anatomical and neurochemical mechanisms involved in the processing of reward/affective outcomes.
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12
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O'Regan C, Kenny RA, Cronin H, Finucane C, Kearney PM. Antidepressants strongly influence the relationship between depression and heart rate variability: findings from The Irish Longitudinal Study on Ageing (TILDA). Psychol Med 2015; 45:623-636. [PMID: 25075912 PMCID: PMC4413849 DOI: 10.1017/s0033291714001767] [Citation(s) in RCA: 64] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/26/2013] [Revised: 06/18/2014] [Accepted: 07/01/2014] [Indexed: 12/27/2022]
Abstract
BACKGROUND Heart rate variability (HRV) is known to be reduced in depression; however, is unclear whether this is a consequence of the disorder or due to antidepressant medication. METHODS We analysed data on 4750 participants from the first wave of The Irish Longitudinal Study on Ageing (TILDA). Time [standard deviation of normal to normal intervals (SDNN ms2)] and frequency domain [low frequency (LF) and high frequency (HF)] measures of HRV were derived from 3-lead surface electrocardiogram records obtained during 10 min of supine rest. Depression was assessed using the Center for Epidemiologic Studies - Depression scale. RESULTS Participants on antidepressants [with (n = 80) or without depression (n = 185)] differed significantly from controls (not depressed and not taking antidepressants n = 4107) on all measures of HRV. Depressed participants not taking antidepressants (n = 317) did not differ from controls on any measures of HRV. In linear regression analysis adjusted for relevant factors all antidepressants were associated with lower measures HRV. Participants on selective serotonin reuptake inhibitors (SSRIs) had higher measures of HRV relative to participants on tricyclic antidepressants or serotonin-norepinephrine reuptake inhibitors respectively. CONCLUSIONS Our results suggest that reductions in HRV observed among depressed older adults are driven by the effects of antidepressant medications. SSRIs have less impact on HRV than other antidepressants but they are still associated with lower measures of HRV. Study limitations include the use of a self-report measure of depression and floor effects of age on HRV could have limited our ability to detect an association between HRV and depression.
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Affiliation(s)
- C. O'Regan
- The Irish Longitudinal Study on Ageing (TILDA), Trinity College Dublin, Ireland
| | - R. A. Kenny
- The Irish Longitudinal Study on Ageing (TILDA), Trinity College Dublin, Ireland
| | - H. Cronin
- The Irish Longitudinal Study on Ageing (TILDA), Trinity College Dublin, Ireland
| | - C. Finucane
- The Irish Longitudinal Study on Ageing (TILDA), Trinity College Dublin, Ireland
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13
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Engster KM, Frommelt L, Hofmann T, Nolte S, Fischer F, Rose M, Stengel A, Kobelt P. Peripheral injected cholecystokinin-8S modulates the concentration of serotonin in nerve fibers of the rat brainstem. Peptides 2014; 59:25-33. [PMID: 25017242 DOI: 10.1016/j.peptides.2014.07.003] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/26/2014] [Revised: 07/02/2014] [Accepted: 07/02/2014] [Indexed: 02/05/2023]
Abstract
Serotonin and cholecystokinin (CCK) play a role in the short-term inhibition of food intake. It is known that peripheral injection of CCK increases c-Fos-immunoreactivity (Fos-IR) in the nucleus of the solitary tract (NTS) in rats, and injection of the serotonin antagonist ondansetron decreases the number of c-Fos-IR cells in the NTS. This supports the idea of serotonin contributing to the effects of CCK. The aim of the present study was to elucidate whether peripherally injected CCK-8S modulates the concentration of serotonin in brain feeding-regulatory nuclei. Ad libitum fed male Sprague-Dawley rats received 5.2 and 8.7 nmol/kg CCK-8S (n=3/group) or 0.15M NaCl (n=3-5/group) injected intraperitoneally (ip). The number of c-Fos-IR neurons, and the fluorescence intensity of serotonin in nerve fibers were assessed in the paraventricular nucleus (PVN), arcuate nucleus (ARC), NTS and dorsal motor nucleus of the vagus (DMV). CCK-8S increased the number of c-Fos-ir neurons in the NTS (mean±SEM: 72±4, and 112±5 neurons/section, respectively) compared to vehicle-treated rats (7±2 neurons/section, P<0.05), but did not modulate c-Fos expression in the DMV or ARC. Additionally, CCK-8S dose-dependently increased the number of c-Fos-positive neurons in the PVN (218±15 and 128±14, respectively vs. 19±5, P<0.05). In the NTS and DMV we observed a decrease of serotonin-immunoreactivity 90 min after injection of CCK-8S (46±2 and 49±8 pixel/section, respectively) compared to vehicle (81±8 pixel/section, P<0.05). No changes of serotonin-immunoreactivity were observed in the PVN and ARC. Our results suggest that serotonin is involved in the mediation of CCK-8's effects in the brainstem.
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Affiliation(s)
- Kim-Marie Engster
- Medical Clinic, Department of Psychosomatic Medicine, Charité - Universitätsmedizin Berlin, Germany
| | - Lisa Frommelt
- Medical Clinic, Department of Psychosomatic Medicine, Charité - Universitätsmedizin Berlin, Germany
| | - Tobias Hofmann
- Medical Clinic, Department of Psychosomatic Medicine, Charité - Universitätsmedizin Berlin, Germany
| | - Sandra Nolte
- Medical Clinic, Department of Psychosomatic Medicine, Charité - Universitätsmedizin Berlin, Germany
| | - Felix Fischer
- Medical Clinic, Department of Psychosomatic Medicine, Charité - Universitätsmedizin Berlin, Germany
| | - Matthias Rose
- Medical Clinic, Department of Psychosomatic Medicine, Charité - Universitätsmedizin Berlin, Germany
| | - Andreas Stengel
- Medical Clinic, Department of Psychosomatic Medicine, Charité - Universitätsmedizin Berlin, Germany
| | - Peter Kobelt
- Medical Clinic, Department of Psychosomatic Medicine, Charité - Universitätsmedizin Berlin, Germany.
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14
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McGinnis WR, Audhya T, Edelson SM. Proposed toxic and hypoxic impairment of a brainstem locus in autism. INTERNATIONAL JOURNAL OF ENVIRONMENTAL RESEARCH AND PUBLIC HEALTH 2013; 10:6955-7000. [PMID: 24336025 PMCID: PMC3881151 DOI: 10.3390/ijerph10126955] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 09/20/2013] [Revised: 11/07/2013] [Accepted: 11/11/2013] [Indexed: 01/15/2023]
Abstract
Electrophysiological findings implicate site-specific impairment of the nucleus tractus solitarius (NTS) in autism. This invites hypothetical consideration of a large role for this small brainstem structure as the basis for seemingly disjointed behavioral and somatic features of autism. The NTS is the brain's point of entry for visceral afference, its relay for vagal reflexes, and its integration center for autonomic control of circulatory, immunological, gastrointestinal, and laryngeal function. The NTS facilitates normal cerebrovascular perfusion, and is the seminal point for an ascending noradrenergic system that modulates many complex behaviors. Microvascular configuration predisposes the NTS to focal hypoxia. A subregion--the "pNTS"--permits exposure to all blood-borne neurotoxins, including those that do not readily transit the blood-brain barrier. Impairment of acetylcholinesterase (mercury and cadmium cations, nitrates/nitrites, organophosphates, monosodium glutamate), competition for hemoglobin (carbon monoxide, nitrates/nitrites), and higher blood viscosity (net systemic oxidative stress) are suggested to potentiate microcirculatory insufficiency of the NTS, and thus autism.
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Affiliation(s)
- Woody R. McGinnis
- Autism Research Institute, 4182 Adams Avenue, San Diego, CA 92116, USA; E-Mail:
- Author to whom correspondence should be addressed; E-Mail: ; Tel.: +1-541-326-8822; Fax: +1-619-563-6840
| | - Tapan Audhya
- Division of Endocrinology, Department of Medicine, New York University Medical School, New York, NY 10016, USA; E-Mail:
| | - Stephen M. Edelson
- Autism Research Institute, 4182 Adams Avenue, San Diego, CA 92116, USA; E-Mail:
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15
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Austgen JR, Kline DD. Endocannabinoids blunt the augmentation of synaptic transmission by serotonin 2A receptors in the nucleus tractus solitarii (nTS). Brain Res 2013; 1537:27-36. [PMID: 24041777 DOI: 10.1016/j.brainres.2013.09.006] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2013] [Revised: 08/06/2013] [Accepted: 09/09/2013] [Indexed: 12/21/2022]
Abstract
Serotonin (5-Hydroxytryptamine, 5-HT) and the 5-HT2 receptor modulate cardiovascular and autonomic function in part through actions in the nTS, the primary termination and integration point for cardiorespiratory afferents in the brainstem. In other brain regions, 5-HT2 receptors (5-HT2R) modify synaptic transmission directly, as well as through 5-HT2AR-induced endocannabinoid release. This study examined the role of 5-HT2AR as well as their interaction with endocannabinoids on neurotransmission in the nucleus tractus solitarii (nTS). Excitatory postsynaptic currents (EPSCs) in monosynaptic nTS neurons were recorded in the horizontal brainstem slice during activation and blockade of 5-HT2ARs. 5-HT2AR activation augmented solitary tract (TS) evoked EPSC amplitude whereas 5-HT2AR blockade depressed TS-EPSC amplitude at low and high TS stimulation rates. The 5-HT2AR-induced increase in neurotransmission was reduced by endocannabinoid receptor block and increased endogenous endocannabinoids in the synaptic cleft during high frequency, but not low, TS stimulation. Endocannabinoids did not tonically modify EPSCs. These data suggest 5-HT acting through the 5-HT2AR is an excitatory neuromodulator in the nTS and its effects are modulated by the endocannabinoid system.
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Affiliation(s)
- James R Austgen
- Department of Biomedical Sciences & Dalton Cardiovascular Research Center, University of Missouri, 134 Research Park Drive, Columbia, MO 65211, USA
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16
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Paterson DS. Serotonin gene variants are unlikely to play a significant role in the pathogenesis of the sudden infant death syndrome. Respir Physiol Neurobiol 2013; 189:301-14. [PMID: 23851109 DOI: 10.1016/j.resp.2013.07.001] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2013] [Revised: 07/01/2013] [Accepted: 07/01/2013] [Indexed: 11/20/2022]
Abstract
Sudden infant death syndrome (SIDS) is defined as the sudden and unexpected death of an infant less than 12 months of age that is related to a sleep period and remains unexplained after a complete autopsy, death scene investigation, and review of the clinical history. The cause of SIDS is unknown, but a major subset of SIDS is proposed to result from abnormalities in serotonin (5-HT) and related neurotransmitters in regions of the lower brainstem that result in failure of protective homeostatic responses to life-threatening challenges during sleep. Multiple studies have implicated gene variants that affect different elements of 5-HT neurotransmission in the pathogenesis of these abnormalities in SIDS. In this review I discuss the data from these studies together with some new data correlating genotype with brainstem 5-HT neurochemistry in the same SIDS cases and conclude that these gene variants are unlikely to play a major role in the pathogenesis of the medullary 5-HT abnormalities observed in SIDS.
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Affiliation(s)
- David S Paterson
- Department of Pathology, Enders Building Room 1109, Boston Children's Hospital and Harvard Medical School, 300 Longwood Ave, Boston, MA 02115, United States.
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17
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Serotonin activates catecholamine neurons in the solitary tract nucleus by increasing spontaneous glutamate inputs. J Neurosci 2013; 32:16530-8. [PMID: 23152635 DOI: 10.1523/jneurosci.1372-12.2012] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Serotonin (5-HT) is a critical neurotransmitter in the control of autonomic functions. 5-HT(3) receptors participate in vagal afferent feedback to decrease food intake and regulate cardiovascular reflexes; however, the phenotype of the solitary tract nucleus (NTS) neurons involved is not known. A(2)/C(2) catecholamine (CA) neurons in the NTS are directly activated by visceral afferents and are important for the control of food intake and cardiovascular function, making them good candidates to respond to and mediate the effects of serotonin at the level of the NTS. This study examines serotonin's effects on NTS-CA neurons using patch-clamp techniques and transgenic mice expressing an enhanced green fluorescent protein driven by the tyrosine hydroxylase (TH) promoter (TH-EGFP) to identify catecholamine neurons. Serotonin increased the frequency of spontaneous glutamate excitatory postsynaptic currents (sEPSCs) in >90% of NTS-TH-EGFP neurons, an effect blocked by the 5-HT(3) receptor antagonist ondansetron and mimicked by the 5-HT(3) receptor agonists SR5227 and mCPBG. In contrast, 5-HT(3) receptor agonists increased sEPSCs on a minority (<30%) of non-TH neurons. 5-HT(3) receptor agonists increased the frequency, but not the amplitude, of mini-EPSCs, suggesting that their actions are presynaptic. 5-HT(3) receptor agonists increased the firing rate of TH-EGFP neurons, an effect dependent on the increased spontaneous glutamate inputs as it was blocked by the ionotropic glutamate antagonist NBQX, but independent of visceral afferent activation. These results demonstrate a cellular mechanism by which serotonin activates NTS-TH neurons and suggest a pathway by which it can increase catecholamine release in target regions to modulate food intake, motivation, stress, and cardiovascular function.
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18
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Waki H, Gouraud SS, Bhuiyan MER, Takagishi M, Yamazaki T, Kohsaka A, Maeda M. Transcriptome of the NTS in exercise-trained spontaneously hypertensive rats: implications for NTS function and plasticity in regulating blood pressure. Physiol Genomics 2012; 45:58-67. [PMID: 23132760 DOI: 10.1152/physiolgenomics.00074.2012] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023] Open
Abstract
The nucleus tractus solitarii (NTS) controls the cardiovascular system during exercise, and alteration of its function may underlie exercise-induced cardiovascular adaptation. To understand the molecular basis of the NTS's plasticity in regulating blood pressure (BP) and its potential contribution to the antihypertensive effects, we characterized the gene expression profiles at the level of the NTS after long-term daily wheel running in spontaneously hypertensive rats (SHRs). Genome-wide microarray analysis was performed to screen for differentially expressed genes in the NTS between exercise-trained (12 wk) and control SHRs. Pathway analysis using the Kyoto Encyclopedia of Genes and Genomes database revealed that daily exercise altered the expression levels of NTS genes that are functionally associated with metabolic pathways (5 genes), neuroactive ligand-receptor interactions (4 genes), cell adhesion molecules (3 genes), and cytokine-cytokine receptor interactions (3 genes). One of the genes that belonged to the neuroactive ligand-receptor interactions category was histamine receptor H(1). Since we confirmed that the pressor response induced by activation of this receptor is increased after long-term daily exercise, it is suggested that functional plasticity in the histaminergic system may mediate the facilitation of blood pressure control in response to exercise but may not be involved in the lowered basal BP level found in exercise-trained SHRs. Since abnormal inflammatory states in the NTS are known to be prohypertensive in SHRs, altered gene expression of the inflammatory molecules identified in this study may be related to the antihypertensive effects in exercise-trained SHRs, although such speculation awaits functional validation.
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Affiliation(s)
- Hidefumi Waki
- Department of Physiology, Wakayama Medical University School of Medicine, Wakayama, Japan.
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19
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Austgen JR, Dantzler HA, Barger BK, Kline DD. 5-hydroxytryptamine 2C receptors tonically augment synaptic currents in the nucleus tractus solitarii. J Neurophysiol 2012; 108:2292-305. [PMID: 22855775 DOI: 10.1152/jn.00049.2012] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
The nucleus tractus solitarii (nTS) is the primary termination and integration point for visceral afferents in the brain stem. Afferent glutamate release and its efficacy on postsynaptic activity within this nucleus are modulated by additional neuromodulators and transmitters, including serotonin (5-HT) acting through its receptors. The 5-HT(2) receptors in the medulla modulate the cardiorespiratory system and autonomic reflexes, but the distribution of the 5-HT(2C) receptor and the role of these receptors during synaptic transmission in the nTS remain largely unknown. In the present study, we examined the distribution of 5-HT(2C) receptors in the nTS and their role in modulating excitatory postsynaptic currents (EPSCs) in monosynaptic nTS neurons in the horizontal brain stem slice. Real-time RT-PCR and immunohistochemistry identified 5-HT(2C) receptor message and protein in the nTS and suggested postsynaptic localization. In nTS neurons innervated by general visceral afferents, 5-HT(2C) receptor activation increased solitary tract (TS)-EPSC amplitude and input resistance and depolarized membrane potential. Conversely, 5-HT(2C) receptor blockade reduced TS-EPSC and miniature EPSC amplitude, as well as input resistance, and hyperpolarized membrane potential. Synaptic parameters in nTS neurons that receive sensory input from carotid body chemoafferents were also attenuated by 5-HT(2C) receptor blockade. Taken together, these data suggest that 5-HT(2C) receptors in the nTS are located postsynaptically and augment excitatory neurotransmission.
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Affiliation(s)
- James R Austgen
- Department of Biomedical Sciences and Dalton Cardiovascular Research Center, University of Missouri, Columbia, MO, USA
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20
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Watts SW, Morrison SF, Davis RP, Barman SM. Serotonin and blood pressure regulation. Pharmacol Rev 2012; 64:359-88. [PMID: 22407614 DOI: 10.1124/pr.111.004697] [Citation(s) in RCA: 252] [Impact Index Per Article: 21.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
5-Hydroxytryptamine (5-HT; serotonin) was discovered more than 60 years ago as a substance isolated from blood. The neural effects of 5-HT have been well investigated and understood, thanks in part to the pharmacological tools available to dissect the serotonergic system and the development of the frequently prescribed selective serotonin-reuptake inhibitors. By contrast, our understanding of the role of 5-HT in the control and modification of blood pressure pales in comparison. Here we focus on the role of 5-HT in systemic blood pressure control. This review provides an in-depth study of the function and pharmacology of 5-HT in those tissues that can modify blood pressure (blood, vasculature, heart, adrenal gland, kidney, brain), with a focus on the autonomic nervous system that includes mechanisms of action and pharmacology of 5-HT within each system. We compare the change in blood pressure produced in different species by short- and long-term administration of 5-HT or selective serotonin receptor agonists. To further our understanding of the mechanisms through which 5-HT modifies blood pressure, we also describe the blood pressure effects of commonly used drugs that modify the actions of 5-HT. The pharmacology and physiological actions of 5-HT in modifying blood pressure are important, given its involvement in circulatory shock, orthostatic hypotension, serotonin syndrome and hypertension.
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Affiliation(s)
- Stephanie W Watts
- Department of Pharmacology & Toxicology, Michigan State University, East Lansing, MI 48824-1317, USA.
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21
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Takenaka R, Ohi Y, Haji A. Distinct modulatory effects of 5-HT on excitatory synaptic transmissions in the nucleus tractus solitarius of the rat. Eur J Pharmacol 2011; 671:45-52. [DOI: 10.1016/j.ejphar.2011.09.164] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2011] [Revised: 08/17/2011] [Accepted: 09/15/2011] [Indexed: 01/19/2023]
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22
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Yeung LY, Kung HF, Yew DT. Localization of 5-HT1A and 5-HT2A positive cells in the brainstems of control age-matched and Alzheimer individuals. AGE (DORDRECHT, NETHERLANDS) 2010; 32:483-95. [PMID: 20508993 PMCID: PMC2980600 DOI: 10.1007/s11357-010-9152-x] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/16/2009] [Accepted: 05/11/2010] [Indexed: 04/17/2023]
Abstract
Serotonin receptor 1A and 2A positive cells in postmortem brainstems were demonstrated via immunohistochemistry in eight control age-matched elderly individuals and eight Alzheimer patients. The 5-HT1A positive cells were found in substantia nigra, pontile nucleus, and vagal as well as dorsal raphe nucleus, while 5-HT2A receptor positive cells were found in motor, sensory and spinal trigeminal nuclei, pontile nucleus, substantia nigra, and nucleus solitarius. A comparison in density of positive cells per unit area was made between control age-matched and Alzheimer individuals. Statistically significant differences (p ≤ 0.01) in density were observed in 5-HT1A cells in pontile, dorsal raphe, and vagal nuclei between control age-matched and Alzheimer, and in 5-HT2A positive cells in the sensory trigeminal nucleus, between control and Alzheimer. This de novo study indicated the presence of 5-HT1A and 5-HT2A receptor positive cells in the above nuclei of human brainstem and revealed differences in density between control age-matched and Alzheimer, indicating possible functional derangements in Alzheimer patients in these areas. In addition, colocalization studies indicated that 5-HT1A receptors were in cholinergic cells and gamma-aminobutyric acid positive fibers were linked to 5-HT2A receptor positive cells. It is hoped that understanding these two important 5-HT receptors and their localization might lead to advances in future therapeutic development.
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Affiliation(s)
- L. Y. Yeung
- School of Biomedical Sciences, Faculty of Medicine, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong S.A.R. China
| | - H. F. Kung
- Stanley Ho Centre for Emerging Infectious Diseases, School of Public Health, Faculty of Medicine, Chinese University of Hong Kong, Shatin, New Territories, Hong Kong S.A.R. Hong Kong
| | - David T. Yew
- School of Biomedical Sciences, Faculty of Medicine, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong S.A.R. China
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Licht CMM, de Geus EJC, van Dyck R, Penninx BWJH. Longitudinal evidence for unfavorable effects of antidepressants on heart rate variability. Biol Psychiatry 2010; 68:861-8. [PMID: 20843507 DOI: 10.1016/j.biopsych.2010.06.032] [Citation(s) in RCA: 157] [Impact Index Per Article: 11.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/23/2010] [Revised: 06/18/2010] [Accepted: 06/26/2010] [Indexed: 10/19/2022]
Abstract
BACKGROUND It was previously shown that antidepressants are associated with diminished vagal control over the heart. Longitudinal studies are needed to test the causality of this association further. METHODS Longitudinal data were obtained in the Netherlands Study of Depression and Anxiety. At baseline and at 2-year follow-up, heart rate and cardiac vagal control as indexed by respiratory sinus arrhythmia were measured in 2114 subjects (mean age = 42.0 years; 66.2% female), who either used antidepressants at one or two time points (n = 603) or did not use antidepressants at any time point (n = 1511). Linear mixed-model analyses were conducted to compare changes in respiratory sinus arrhythmia and heart rate over time across antidepressant-naive subjects, subjects who started using an antidepressant during follow-up, subjects who stopped using an antidepressant, and persistent antidepressant users. Analyses were adjusted for demographics, health, and lifestyle factors. RESULTS Compared with continuous nonusers, subjects who started the use of a tricyclic antidepressant or a serotonergic and noradrenergic antidepressant showed a significantly greater increase in heart rate and a decrease of respiratory sinus arrhythmia at 2 years. Subjects who started the use of selective serotonin reuptake inhibitors also showed a decrease in respiratory sinus arrhythmia, but their heart rate did not increase. Discontinuing antidepressants systematically caused opposite effects; levels returned in the direction of those observed among nonusers. CONCLUSIONS These 2-year longitudinal results indicate that all antidepressants cause a decrease in cardiac vagal control. After discontinuing antidepressants, autonomic function recovers, suggesting that the unfavorable effects are (partly) reversible.
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Affiliation(s)
- Carmilla M M Licht
- Department of Psychiatry, EMGO Institute for Health and Care Research, Vrije Universiteit Medical Center, Amsterdam, The Netherlands.
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Dean JB, Putnam RW. The caudal solitary complex is a site of central CO(2) chemoreception and integration of multiple systems that regulate expired CO(2). Respir Physiol Neurobiol 2010; 173:274-87. [PMID: 20670695 DOI: 10.1016/j.resp.2010.07.002] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2010] [Revised: 06/30/2010] [Accepted: 07/01/2010] [Indexed: 12/16/2022]
Abstract
The solitary complex is comprised of the nucleus tractus solitarius (NTS, sensory) and dorsal motor nucleus of the vagus (DMV, motor), which functions as an integrative center for neural control of multiple systems including the respiratory, cardiovascular and gastroesophageal systems. The caudal NTS-DMV is one of the several sites of central CO(2) chemoreception in the brain stem. CO(2) chemosensitive neurons are fully responsive to CO(2) at birth and their responsiveness seems to depend on pH-sensitive K(+) channels. In addition, chemosensitive neurons are highly sensitive to conditions such as hypoxia (e.g., neural plasticity) and hyperoxia (e.g., stimulation), suggesting they employ redox and nitrosative signaling mechanisms. Here we review the cellular and systems physiological evidence supporting our hypothesis that the caudal NTS-DMV is a site for integration of respiratory, cardiovascular and gastroesophageal systems that work together to eliminate CO(2) during acute and chronic respiratory acidosis to restore pH homeostasis.
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Affiliation(s)
- Jay B Dean
- Dept. of Molecular Pharmacology & Physiology, Hyperbaric Biomedical Research Laboratory, University of South Florida, Tampa, FL 33612, USA.
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25
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Abnormal serotonin receptor expression in DBA/2 mice associated with susceptibility to sudden death due to respiratory arrest. Epilepsy Res 2010; 88:183-8. [DOI: 10.1016/j.eplepsyres.2009.11.004] [Citation(s) in RCA: 68] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2009] [Revised: 10/30/2009] [Accepted: 11/12/2009] [Indexed: 11/21/2022]
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Abstract
Sleep-induced apnea and disordered breathing refers to intermittent, cyclical cessations or reductions of airflow, with or without obstructions of the upper airway (OSA). In the presence of an anatomically compromised, collapsible airway, the sleep-induced loss of compensatory tonic input to the upper airway dilator muscle motor neurons leads to collapse of the pharyngeal airway. In turn, the ability of the sleeping subject to compensate for this airway obstruction will determine the degree of cycling of these events. Several of the classic neurotransmitters and a growing list of neuromodulators have now been identified that contribute to neurochemical regulation of pharyngeal motor neuron activity and airway patency. Limited progress has been made in developing pharmacotherapies with acceptable specificity for the treatment of sleep-induced airway obstruction. We review three types of major long-term sequelae to severe OSA that have been assessed in humans through use of continuous positive airway pressure (CPAP) treatment and in animal models via long-term intermittent hypoxemia (IH): 1) cardiovascular. The evidence is strongest to support daytime systemic hypertension as a consequence of severe OSA, with less conclusive effects on pulmonary hypertension, stroke, coronary artery disease, and cardiac arrhythmias. The underlying mechanisms mediating hypertension include enhanced chemoreceptor sensitivity causing excessive daytime sympathetic vasoconstrictor activity, combined with overproduction of superoxide ion and inflammatory effects on resistance vessels. 2) Insulin sensitivity and homeostasis of glucose regulation are negatively impacted by both intermittent hypoxemia and sleep disruption, but whether these influences of OSA are sufficient, independent of obesity, to contribute significantly to the "metabolic syndrome" remains unsettled. 3) Neurocognitive effects include daytime sleepiness and impaired memory and concentration. These effects reflect hypoxic-induced "neural injury." We discuss future research into understanding the pathophysiology of sleep apnea as a basis for uncovering newer forms of treatment of both the ventilatory disorder and its multiple sequelae.
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Affiliation(s)
- Jerome A Dempsey
- The John Rankin Laboratory of Pulmonary Medicine, Departments of Population Health Sciences and of Orthopedics and Rehabilitation, School of Medicine and Public Health, University of Wisconsin, Madison, Wisconsin 53706, USA.
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Liu Q, Wong-Riley MTT. Postnatal changes in the expressions of serotonin 1A, 1B, and 2A receptors in ten brain stem nuclei of the rat: implication for a sensitive period. Neuroscience 2009; 165:61-78. [PMID: 19800944 DOI: 10.1016/j.neuroscience.2009.09.078] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2009] [Revised: 09/25/2009] [Accepted: 09/28/2009] [Indexed: 01/08/2023]
Abstract
A critical period in respiratory network development occurs in the rat around postnatal days (P) 12-13, when abrupt neurochemical, metabolic, and physiological changes were evident. As serotonin and its receptors are involved in respiratory modulation, and serotonergic abnormality is implicated in sudden infant death syndrome, we hypothesized that 5-HT receptors are significantly downregulated during the critical period. This was documented recently for 5-HT(2A)R in several respiratory nuclei. The present study represents a comprehensive analysis of postnatal development of 5-HT(1A)R and 5-HT(1B)R in 10 brain stem nuclei and 5-HT(2A)R in six nuclei not previously examined. Optical densitometric analysis of immunohistochemically-reacted neurons from P2 to P21 indicated four developmental patterns of expression: (1) Pattern I: a high level of expression at P2-P11, an abrupt and significant reduction at P12, followed by a plateau until P21 (5-HT(1A)R and 5-HT(1B)R in raphé magnus [RM], raphé obscurus [ROb], raphé pallidus [RP], pre-Bötzinger complex [PBC], nucleus ambiguus [Amb], and hypoglossal nucleus [XII; 5-HT(1A)R only]). (2) Pattern II: a high level at P2-P9, a gradual decline from P9 to P12, followed by a plateau until P21 (5-HT(1A)R and 5-HT(1B)R in the retrotrapezoid nucleus (RTN)/parafacial respiratory group (pFRG)). (3) Pattern III: a high level at P2-P11, followed by a gradual decline until P21 (5-HT(1A)R in the ventrolateral subnucleus of solitary tract nucleus [NTS(VL)] and the non-respiratory cuneate nucleus [CN]). (4) Pattern IV: a relatively constant level maintained from P2 to P21 (5-HT(1A)R in the commissural subnucleus of solitary tract nucleus (NTS(COM)); 5-HT(1B)R in XII, NTS(VL), NTS(COM), and CN; and 5-HT(2A)R in RM, ROb, RP, RTN/pFRG, NTS(VL), and NTS(COM)). Thus, a significant reduction in the expression of 5-HT(1A)R, 5-HT(1B)R, and 5-HT(2A)R in multiple respiratory-related nuclei at P12 is consistent with reduced serotonergic transmission during the critical period, thereby rendering the animals less able to respond adequately to ventilatory distress.
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Affiliation(s)
- Q Liu
- Department of Cell Biology, Neurobiology and Anatomy, Medical College of Wisconsin, Milwaukee, 53226, USA
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Mikhailova SD, Semushkina TM, Storozhakov GI. Effect of Serotonin on Impulse Activity of Bulbar Cardiovascular Neurons. Bull Exp Biol Med 2009; 147:167-9. [DOI: 10.1007/s10517-009-0468-4] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
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Kinney HC, Richerson GB, Dymecki SM, Darnall RA, Nattie EE. The brainstem and serotonin in the sudden infant death syndrome. ANNUAL REVIEW OF PATHOLOGY-MECHANISMS OF DISEASE 2009; 4:517-50. [PMID: 19400695 DOI: 10.1146/annurev.pathol.4.110807.092322] [Citation(s) in RCA: 230] [Impact Index Per Article: 15.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
The sudden infant death syndrome (SIDS) is the sudden death of an infant under one year of age that is typically associated with sleep and that remains unexplained after a complete autopsy and death scene investigation. A leading hypothesis about its pathogenesis is that many cases result from defects in brainstem-mediated protective responses to homeostatic stressors occurring during sleep in a critical developmental period. Here we review the evidence for the brainstem hypothesis in SIDS with a focus upon abnormalities related to the neurotransmitter serotonin in the medulla oblongata, as these are the most robust pathologic findings to date. In this context, we synthesize the human autopsy data with genetic, whole-animal, and cellular data concerning the function and development of the medullary serotonergic system. These emerging data suggest an important underlying mechanism in SIDS that may help lead to identification of infants at risk and specific interventions to prevent death.
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Affiliation(s)
- Hannah C Kinney
- Department of Pathology, Children's Hospital Boston and Harvard Medical School, Boston, MA 02115, USA.
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Tada M, Kakita A, Toyoshima Y, Onodera O, Ozawa T, Morita T, Nishizawa M, Takahashi H. Depletion of medullary serotonergic neurons in patients with multiple system atrophy who succumbed to sudden death. Brain 2009; 132:1810-9. [PMID: 19429902 DOI: 10.1093/brain/awp110] [Citation(s) in RCA: 74] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
Multiple system atrophy (MSA) is a neurodegenerative disorder characterized by prominent autonomic failure with ataxia and/or parkinsonism. The leading cause of death in MSA is sudden death. We have shown that the early development of autonomic failure is an independent risk factor for sudden death. The depletion of sympathetic preganglionic neurons in the spinal intermediolateral cell column (IML) and its afferent medullary catecholaminergic and serotonergic neurons has been proposed to be partly responsible for autonomic failure in MSA. In this study, we investigated whether the depletion of neurons in any of these autonomic neuron groups contributes to sudden death in MSA. Out of 52 autopsy-proven patients with MSA, we selected 12 individuals who had died within 3.5 years after disease onset to define the accurate levels of slices and identify early neuropathological changes of autonomic nuclei in MSA. Four patients succumbed to sudden death and eight patients died through established causes. Serial 10 mum sections were obtained from the 8th segment of the thoracic cord and the rostral medulla oblongata. Sections from the medulla oblongata were immunostained for thyrosine hydroxylase and tryptophan hydroxylase. The total cell number in the five sections was computed for comparison. Compared with the control, the MSA group showed a marked depletion of neurons in the IML (38.0 +/- 7.1 versus 75.2 +/- 7.6 cells, P < 0.001), thyrosine hydroxylase-immunoreactive neurons in the ventrolateral medulla (VLM) (17.4 +/- 5.1 versus 72.8 +/- 13.6 cells, P < 0.01) and tryptophan hydroxylase-immunoreactive neurons in the VLM (15.6 +/- 9.2 versus 60.8 +/- 17.0 cells, P < 0.01), nucleus raphe obscurus (19.3 +/- 4.4 versus 75.3 +/- 8.6 cells, P < 0.001), nucleus raphe pallidus (2.1 +/- 2.7 versus 9.0 +/- 3.4 cells, P < 0.03), and arcuate nucleus (0.4 +/- 0.8 versus 2.3 +/- 1.5 cells, P < 0.05). Moreover, in patients who succumbed to sudden death, when compared with patients who had established causes of death, we found a marked depletion of tryptophan hydroxylase-immunoreactive neurons in the VLM (7.3 +/- 3.5 versus 21.8 +/- 6.5 cells, P < 0.02) and nucleus raphe obscurus (15.0 +/- 2.0 versus 22.5 +/- 2.1 cells, P < 0.01). The results indicate that the spinal IML and medullary catecholaminergic and serotonergic systems are involved even in the early stages of MSA, and the dysfunction of the medullary serotonergic system regulating cardiovascular and respiratory systems could be responsible for sudden death in patients with MSA.
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Affiliation(s)
- Mari Tada
- Department of Pathology, Brain Research Institute, University of Niigata, Niigata, Japan
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Kanamaru M, Homma I. Dorsomedial medullary 5-HT2 receptors mediate immediate onset of initial hyperventilation, airway dilation, and ventilatory decline during hypoxia in mice. Am J Physiol Regul Integr Comp Physiol 2009; 297:R34-41. [PMID: 19386986 DOI: 10.1152/ajpregu.90802.2008] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The dorsomedial medulla oblongata (DMM) includes the solitary tract nucleus and the hypoglossal nucleus, to which 5-HT neurons project. Effects of 5-HT in the DMM on ventilatory augmentation and airway dilation are mediated via 5-HT2 receptors, which interact with the CO(2) drive. The interaction may elicit cycles between hyperventilation with airway dilation and hypoventilation with airway narrowing. In the present study, effects of 5-HT2 receptors in the DMM on hypoxic ventilatory and airway responses were investigated, while 5-HT release in the DMM was monitored. Adult male mice were anesthetized, and then a microdialysis probe was inserted into the DMM. The mice were placed in a double-chamber plethysmograph. After recovery from anesthesia, the mice were exposed to hypoxic gas (7% O(2) in N(2)) for 5 min with or without a 5-HT2 receptor antagonist (LY-53857) perfused in the DMM. 5-HT release in the DMM was increased by hypoxia regardless of the presence of LY-53857. Immediate onset and the peak of initial hypoxic hyperventilatory responses were delayed. Subsequent ventilatory decline and airway dilation during initial hypoxic hyperventilation were suppressed with LY-53857. These results suggest that 5-HT release increased by hypoxia acts on 5-HT2 receptors in the DMM, which contributes to the immediate onset of initial hypoxic hyperventilation, airway dilation, and subsequent ventilatory decline. Hypoxic ventilatory and airway responses mediated via 5-HT2 receptors in the DMM may play roles in immediate rescue and defensive adaptation for hypoxia and may be included in periodic breathing and the pathogenesis of obstructive sleep apnea.
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Affiliation(s)
- Mitsuko Kanamaru
- Dept. of Physiology, Showa Univ. School of Medicine, 1-5-8 Hatanodai, Shinagawa-ku, Tokyo 142-8555, Japan.
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Paterson DS, Darnall R. 5-HT2A receptors are concentrated in regions of the human infant medulla involved in respiratory and autonomic control. Auton Neurosci 2009; 147:48-55. [PMID: 19213611 DOI: 10.1016/j.autneu.2009.01.004] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2008] [Revised: 12/22/2008] [Accepted: 01/05/2009] [Indexed: 12/26/2022]
Abstract
The serotonergic (5-HT) system in the human medulla oblongata is well-recognized to play an important role in the regulation of respiratory and autonomic function. In this study, using both immunocytochemistry (n=5) and tissue section autoradiography with the radioligand (125)I-1-(2,5-dimethoxy-4-iodo-phenyl)2-aminopropane (n=7), we examine the normative development and distribution of the 5-HT(2A) receptor in the human medulla during the last part of gestation and first postnatal year when dramatic changes are known to occur in respiratory and autonomic control, in part mediated by the 5-HT(2A) receptor. High 5-HT(2A) receptor binding was observed in the dorsal motor nucleus of the vagus (preganglionic parasympathetic output) and hypoglossal nucleus (airway patency); intermediate binding was present in the nucleus of the solitary tract (visceral sensory input), gigantocellularis, intermediate reticular zone, and paragigantocellularis lateralis. Negligible binding was present in the raphé obscurus and arcuate nucleus. The pattern of 5-HT(2A) immunoreactivity paralleled that of binding density. By 15 gestational weeks, the relative distribution of the 5-HT(2A) receptor was similar to that in infancy. In all nuclei sampled, 5-HT(2A) receptor binding increased with age, with significant increases in the hypoglossal nucleus (p=0.027), principal inferior olive (p=0.044), and medial accessory olive (0.038). Thus, 5-HT(2A) receptors are concentrated in regions involved in autonomic and respiratory control in the human infant medulla, and their developmental profile changes over the first year of life in the hypoglossal nucleus critical to airway patency and the inferior olivary complex essential to cerebellar function.
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Affiliation(s)
- David S Paterson
- Department of Pathology, Children's Hospital Boston, Harvard Medical School, Boston, MA 02115, USA.
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Mackie AR, Byron KL. Cardiovascular KCNQ (Kv7) potassium channels: physiological regulators and new targets for therapeutic intervention. Mol Pharmacol 2008; 74:1171-9. [PMID: 18684841 DOI: 10.1124/mol.108.049825] [Citation(s) in RCA: 86] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
Potassium channels play an important role in electrical signaling of excitable cells such as neurons, cardiac myocytes, and vascular smooth muscle cells (VSMCs). In particular, the KCNQ (Kv7) family of voltage-activated K(+) channels functions to stabilize negative resting membrane potentials and thereby opposes electrical excitability. Of the five known members of the mammalian Kv7 family, Kv7.1 was originally recognized for its role in cardiac myocytes, where it contributes to repolarization of the cardiac action potential. Kv7.2 to Kv7.5 were first discovered in neurons, in which they play a well characterized role in neurotransmitter-stimulated action potential firing. Over the past 5 years, important new roles for Kv7 channels have been identified. Kv7 channels have been found to be expressed in VSMCs from several vascular beds where they contribute to the regulation of vascular tone. There is evidence that Kv7.5 channels in VSMCs are targeted by the hormone vasopressin to mediate its physiological vasoconstrictor actions and evidence that neuronal Kv7 channels in the baroreceptors of the aortic arch adjust the sensitivity of the mechanosensitive neurons to changes in arterial blood pressure. These newly identified physiological roles for Kv7 channels in the cardiovascular system warrant increased attention because pharmacological modulators of this family of channels are being used clinically to treat a variety of neurological disorders. This raises questions about the cardiovascular side effects associated with existing therapies, but there is also obvious potential to capitalize on the established and evolving pharmacology of these channels to develop new therapies for cardiovascular diseases.
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Affiliation(s)
- Alexander R Mackie
- Loyola University Medical Center, 2160 S. First Avenue, Maywood, IL 60153, USA
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Dergacheva O, Wang X, Kamendi H, Cheng Q, Pinol RM, Jameson H, Gorini C, Mendelowitz D. 5HT2 receptor activation facilitates P2X receptor mediated excitatory neurotransmission to cardiac vagal neurons in the nucleus ambiguus. Neuropharmacology 2008; 54:1095-102. [PMID: 18396300 DOI: 10.1016/j.neuropharm.2008.02.016] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2007] [Revised: 02/21/2008] [Accepted: 02/28/2008] [Indexed: 12/20/2022]
Abstract
Parasympathetic preganglionic cardiac vagal neurons (CVNs) which dominate the control of heart rate are located within the nucleus ambiguus (NA). Serotonin (5HT), and in particular 5HT2 receptors, play an important role in cardiovascular function in the brainstem. However, there is a lack of information on the mechanisms of action of 5HT2 receptors in modulating parasympathetic cardiac activity. This study tests whether activation of 5HT2 receptors alters excitatory glutamatergic and purinergic neurotransmission to CVNs. Application of alpha-methyl-5-hydroxytryptamine (alpha-Me-5HT), a 5HT2 agonist, reversibly increased both the frequency and amplitude of miniature excitatory postsynaptic currents (mEPSCs) in CVNs. Similar responses were obtained with alpha-methyl-5-(2-thienylmethoxy)-1H-indole-3-ethanamine hydrochloride (BW723C86), and m-chlorophenylpiperazine (m-CPP), 5HT2B and 5HT2B/C receptor agonists, respectively. The facilitation evoked by alpha-Me-5HT was prevented by the 5HT2B/C receptor antagonist SB206553 hydrochloride (SB206553). Interestingly, the blockage of both NMDA and non-NMDA glutamatergic receptors did not prevent alpha-Me-5HT-evoked facilitation of mEPSCs, however, the responses were blocked by the P2 receptor antagonist pyridoxal-phosphate-6-azophenyl-2',4'-disulfonic acid (PPADS). The responses evoked by alpha-Me-5HT were mimicked by application of alpha,beta-methylene ATP (alpha,beta-Me-ATP), a P2X receptor agonist, which were also blocked by PPADS. In summary, these results indicate activation of 5HT2 receptors facilitates excitatory purinergic, but not glutamatergic, neurotransmission to CVNs.
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Affiliation(s)
- Olga Dergacheva
- Department of Pharmacology and Physiology, The George Washington University, 2300 Eye Street NW, Washington, DC 20037, USA
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Kanamaru M, Homma I. Compensatory airway dilation and additive ventilatory augmentation mediated by dorsomedial medullary 5-hydroxytryptamine 2 receptor activity and hypercapnia. Am J Physiol Regul Integr Comp Physiol 2007; 293:R854-60. [PMID: 17537836 DOI: 10.1152/ajpregu.00829.2006] [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: 11/22/2022]
Abstract
5-HT2 receptor activity in the hypoglossal nucleus and hypercapnia is associated with airway dilation. 5-HT neurons in the medullary raphe and hypercapnia are responsible for tidal volume change. In this study, the effects of 5-HT2 receptors in the dorsomedial medulla oblongata (DMM), which receives projections from the medullary raphe, and hypercapnia on airway resistance and respiratory variables were studied in mice while monitoring 5-HT release in the DMM. A microdialysis probe was inserted into the DMM of anesthetized adult mice. Each mouse was placed in a double-chamber plethysmograph. After recovery from anesthesia, the mice were exposed to stepwise increases in CO2 inhalation (5%, 7%, and 9% CO2 in O2) at 8-min intervals with a selective serotonin reuptake inhibitor, fluoxetine, or fluoxetine plus a 5-HT2 receptor antagonist, LY-53857 in the DMM. In response to fluoxetine plus LY-53857 coperfusion, specific airway resistance was increased, and tidal volume and minute ventilation were decreased. CO2 inhalation with fluoxetine plus LY-53857 coperfusion in the DMM largely decreased airway resistance and additively increased minute ventilation. Thus, 5-HT2 receptor activity in the DMM increases basal levels of airway dilation and ventilatory volume, dependent on central inspiratory activity and the volume threshold of the inspiratory off-switch mechanism. Hypercapnia with low 5-HT2 receptor activity in the DMM largely recovers airway dilation and additively increases ventilatory volume. Interaction between 5-HT2 receptor activity in the DMM and CO2 drive may elicit a cycle of hyperventilation with airway dilation and hypoventilation with airway narrowing.
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Affiliation(s)
- Mitsuko Kanamaru
- Department of Physiology, Showa University School of Medicine, 1-5-8 Hatanodai, Shina gawa-ku, Tokyo 142-8555, Japan
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Comet MA, Bernard JF, Hamon M, Laguzzi R, Sévoz-Couche C. Activation of nucleus tractus solitarius 5-HT2A but not other 5-HT2 receptor subtypes inhibits the sympathetic activity in rats. Eur J Neurosci 2007; 26:345-54. [PMID: 17623018 DOI: 10.1111/j.1460-9568.2007.05673.x] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
Our first aim was to elucidate the mechanisms underlying the hypotensive response elicited by 5-HT(2) receptor activation in the nucleus tractus solitarius (NTS). In pentobarbitone-anaesthetized rats, intra-NTS administration of 2,5-dimethoxy-4-iodoamphetamine (DOI), a wide spectrum 5-HT(2) receptor agonist, but not an antagonist of selective 5-HT(2B) and 5-HT(2C) receptors, produced a decrease in blood pressure and heart rate. The maximal cardiovascular changes obtained by DOI (0.5 pmol) could be almost completely abolished by prior intra-NTS microinjection (10 pmol) of MDL-100907, a selective 5-HT(2A) receptor antagonist, but not by 5-HT(2B) or 5-HT(2C) receptor antagonists. In addition, using extracellular recordings we found that the large majority of identified cardiovascular rostroventrolateral medulla (RVLM) neurons were almost totally inhibited by NTS 5-HT(2A) receptor stimulation. We then investigated whether intra-NTS administration of a subthreshold dose (0.05 pmol) of DOI, known to facilitate the cardiovagal component of the baroreflex, could also modulate the sympathoinhibitory component of this reflex. These experiments showed that neither the decrease in the activity of the cardiovascular RVLM neurons and lumbar sympathetic nerve activities produced by aortic occlusion (gain of the baroreflex), nor the hypotensive response elicited by aortic nerve stimulation, were potentiated by the microinjection of DOI under such conditions. These data show that activation of 5-HT(2A), but not 5-HT(2B) or 5-HT(2C), receptors, located on NTS neurons, elicits depressor and bradycardic responses, and that this 5-HT(2A)-mediated hypotension is produced via the inhibition of RVLM cardiovascular neurons. In addition, NTS 5-HT(2A) receptor activation facilitates the cardiac but not the sympathetic baroreflex response.
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Affiliation(s)
- M-A Comet
- Université Pierre et Marie Curie-Paris 6, Faculté de Médecine Pierre et Marie Curie, Site Pitié-Salpêtrière, IFR 70 des Neurosciences, UMR S677, F-75013 Paris, France
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Suwabe T, Bradley RM. Effects of 5-Hydroxytryptamine and Substance P on Neurons of the Inferior Salivatory Nucleus. J Neurophysiol 2007; 97:2605-11. [PMID: 17267757 DOI: 10.1152/jn.00859.2006] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
The parasympathetic secretomotor innervation of the salivary glands originates from a longitudinal column of neurons in the medulla called the salivatory nucleus. The neurons innervating the parotid and von Ebner salivary glands are situated in the caudal extremity of the column designated as the inferior salivatory nucleus (ISN). Immunocytochemical investigations have demonstrated the presence of a number of neuropeptides surrounding the ISN neurons. We have examined the neurophysiological effect of two of these neuropeptides on neurons of the ISN identified by retrograde transport of a fluorescent label. Both serotonin (5-HT) and substance P (SP) excited virtually all neurons in the ISN. Application of these neuropeptides resulted in membrane depolarization that was concentration dependent. Although the majority of ISN neurons that were depolarized by SP application exhibited an increase in input resistance, application of 5-HT induced widely varied change in input resistance. Membrane depolarization elicited action potential discharges that increased in frequency with increasing concentration of 5-HT and SP. Blocking action potential conduction from surrounding neurons did not eliminate the depolarizing effects of 5-HT and SP, indicating that both neuropeptides acted directly on the ISN neurons. Finally, the use of 5-HT agonists and antagonists indicates that 5-HT acts via a 5-HT2A receptor, and the use of SP agonists suggests that SP acts via neuokinin-1 and -2 receptors. These data show that 5-HT and SP excite most of the ISN neurons innervating the lingual von Ebner glands possibly modulating the synaptic drive to these neurons derived from afferent gustatory input.
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Affiliation(s)
- Takeshi Suwabe
- Dept. of Biologic and Materials Sciences, School of Dentistry, University of Michigan, Ann Arbor, MI 48109-1078, USA
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Li A, Zhou S, Nattie E. Simultaneous inhibition of caudal medullary raphe and retrotrapezoid nucleus decreases breathing and the CO2 response in conscious rats. J Physiol 2006; 577:307-18. [PMID: 16825298 PMCID: PMC2000693 DOI: 10.1113/jphysiol.2006.114504] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2006] [Accepted: 07/06/2006] [Indexed: 12/23/2022] Open
Abstract
The medullary raphe (MR) and the retrotrapezoid nucleus (RTN) in the ventral medulla are two of many central chemoreceptor sites. We examine their combined function in conscious rats by focal inhibition using microdialysis. Inhibition of RTN neurons with the GABA(A) receptor agonist muscimol, with simultaneous dialysis of artificial cerebrospinal fluid (ACSF) in or near to the caudal MR, causes hypoventilation (decrease in the ratio of minute ventilation to oxygen consumption, V(E)/V(O2)) and reduces the ventilatory response to 7% CO(2) by 24%. Inhibition of caudal MR serotonergic neurons with the 5-HT(1A) receptor agonist (R)-(+)-8-hydroxy-2(di-n-propylamino)tetralin (8-OH-DPAT), with simultaneous dialysis of ACSF in or near to the RTN, causes hypoventilation but has no significant effect on the CO(2) response. Inhibition of both the RTN and the caudal MR simultaneously produces enhanced hypoventilation and a 51% decrease in the CO(2) response. The effects of treatment on the CO(2) response are similar in wakefulness and in non-rapid eye movement sleep. Comparison of the effect of 8-OH-DPAT microdialysed into a more rostral portion of the MR, where the CO(2) response is reduced by 22%, demonstrates heterogeneity within the MR of the function of serotonergic neurons in breathing. We conclude that serotonergic neurons within the caudal MR provide a non-CO(2)-dependent tonic drive to breathe and potentiate the effects of RTN neurons that contribute to a resting chemical 'drive to breathe' as well as the response to added CO(2). These effects of caudal MR serotonergic neurons could be at a chemoreceptor site, e.g. the RTN, or at 'downstream' sites involved in rhythm and pattern generation.
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Affiliation(s)
- Aihua Li
- Department of Physiology, Borwell Building, Dartmouth Medical School, Lebanon, NH 03756-0001, USA
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Sévoz-Couche C, Comet MA, Bernard JF, Hamon M, Laguzzi R. Cardiac baroreflex facilitation evoked by hypothalamus and prefrontal cortex stimulation: role of the nucleus tractus solitarius 5-HT2Areceptors. Am J Physiol Regul Integr Comp Physiol 2006; 291:R1007-15. [PMID: 16763082 DOI: 10.1152/ajpregu.00052.2006] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
We previously showed that serotonin (5-HT2) receptor activation in the nucleus of the tractus solitarius (NTS) produced hypotension, bradycardia, and facilitation of the baroreflex bradycardia. Activation of the preoptic area (POA) of the hypothalamus, which is involved in shock-evoked passive behaviors, induces similar modifications. In addition, previous studies showed that blockade of the infralimbic (IL) part of the medial prefrontal cortex, which sends projections to POA, produced an inhibitory influence on the baroreflex cardiac response. Thus, to assess the possible implication of NTS 5-HT2receptors in passive cardiovascular responses, we analyzed in anesthetized rats the effects of NTS inhibition and NTS 5-HT2receptor blockade on the cardiovascular modifications induced by chemical (0.3 M d,l-homocysteic acid) and electrical (50 Hz, 150–200 μA) stimulation of IL or POA. Intra-NTS microinjections of muscimol, a GABAAreceptor agonist, prevented the decreases in blood pressure and heart rate normally evoked by IL or POA activation. In addition, we found that intra-NTS microinjection of R(+)-α-(2,3-dimethoxyphenyl)-1-[2-(4-fluorophenylethyl)]-4-piperidine-methanol, a specific 5-HT2Areceptor antagonist, did not affect the decreases in cardiovascular baseline parameters induced by IL or POA stimulation but prevented the facilitation of the aortic baroreflex bradycardia normally observed during IL (+65 and +60%) or POA (+70 and +69%) electrical and chemical stimulation, respectively. These results show that NTS 5-HT2Areceptors play a key role in the enhancement of the cardiac response of the baroreflex but not in the changes in basal heart rate and blood pressure induced by IL or POA stimulation.
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Affiliation(s)
- C Sévoz-Couche
- UMR 677 INSERM/UPMC, Faculté de Médecine Pierre et Marie Curie-Site Pitié-Salpêtrière, 91 Bd de l'Hôpital, 75634 Paris Cedex 13, France.
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Bonham AC, Chen CY, Sekizawa SI, Joad JP. Plasticity in the nucleus tractus solitarius and its influence on lung and airway reflexes. J Appl Physiol (1985) 2006; 101:322-7. [PMID: 16484366 DOI: 10.1152/japplphysiol.00143.2006] [Citation(s) in RCA: 60] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
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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Kouvelas D, Singewald N, Kaehler ST, Philippu A. Sinoaortic denervation abolishes blood pressure-induced GABA release in the locus coeruleus of conscious rats. Neurosci Lett 2006; 393:194-9. [PMID: 16233953 DOI: 10.1016/j.neulet.2005.09.063] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2005] [Revised: 09/22/2005] [Accepted: 09/26/2005] [Indexed: 10/25/2022]
Abstract
Male Sprague-Dawley rats underwent sinoaortic denervation (SAD) or sham operation. We examined changes in the release rates of GABA, glutamate and arginine in the locus coeruleus (LC) elicited by experimental blood pressure increases (i.v. noradrenaline infusion for 3 min, 4 microg kg(-1)min(-1)) or decreases (i.v. sodium nitroprusside infusion for 3 min, 150 microg kg(-1)min(-1)). The release of the neurotransmitters was monitored by the push-pull superfusion technique. Mean blood pressure did not differ between sham-operated and SAD rats but blood pressure lability was greatly enhanced in SAD rats and accompanied by increased basal release of glutamate in the LC. GABA release was not affected. A rise in blood pressure induced by noradrenaline enhanced GABA release in the LC of sham-operated rats. This effect was abolished by SAD. Glutamate release did not respond to hypertension either in SAD or in sham-operated rats. Nitroprusside led to a fall in blood pressure which was more pronounced and lasted longer in SAD than in sham-operated rats. In SAD rats, glutamate release was enhanced by nitroprusside. The depressor response had no effect on glutamate release in sham-operated rats. GABA release did not respond to this stimulus in either SAD or sham-operated rats. SAD and blood pressure changes did not influence the release rate of arginine. In conclusion, experimental hypertension increases GABAergic activity in the LC by stimulating peripheral baroreceptors. In SAD rats, augmented blood pressure lability seems to be at least partly due to elevated glutamate outflow within the LC.
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Affiliation(s)
- Dimitrios Kouvelas
- Department of Pharmacology, School of Medicine, Aristotle University of Thessaloniki, P.O. Box 1532, 54006 Thessaloniki, Greece.
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Martin-Cora FJ, Fornal CA, Jacobs BL. Single-unit responses of serotonergic medullary raphe neurons to cardiovascular challenges in freely moving cats. Eur J Neurosci 2005; 22:3195-204. [PMID: 16367786 DOI: 10.1111/j.1460-9568.2005.04519.x] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
Single-unit activity of serotonergic neurons in the nuclei raphe obscurus (NRO) and raphe pallidus (NRP) were recorded in conjunction with heart rate in freely moving cats in response to systemic administration of vasoactive drugs and to graded haemorrhage. Bolus administration of phenylephrine hydrochloride and sodium nitroprusside (20 microg/kg, i.v.) produced a marked, transient reflex bradycardia (-42 b.p.m.) and tachycardia (+60 b.p.m.), respectively. The activity of NRO/NRP serotonergic neurons remained unchanged after phenylephrine and nitroprusside administration. The administration of hydralazine (1 mg/kg, i.v.), a long-acting vasodilator, produced sustained tachycardia (+60 b.p.m.), which was not accompanied by changes in neuronal activity, despite prolonged reflex activation of the sympathetic nervous system. The initial withdrawal of up to 15% of total blood volume increased heart rate (+12 b.p.m.), whereas the removal of 22.5% of total blood decreased heart rate (-44 b.p.m.). The activity of NRO/NRP serotonergic neurons remained unaltered throughout graded haemorrhage trials, despite the changes in sympathetic outflow. Thus, serotonergic NRO and NRP neurons appear to be insensitive to alterations in blood pressure and baroreceptor activity, and this lack of responsiveness does not support a specific role for these cells in cardiovascular regulation. Furthermore, these neurons do not appear to be involved in physiological mechanisms underlying alterations in autonomic outflow invoked by hypertension and hypotension. Taken within the context of our previous work, the present data suggest that medullary serotonergic neurons may modulate autonomic outflow, but only in relation to their primary role in motor control.
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Affiliation(s)
- Francisco J Martin-Cora
- Department of Physiology, School of Medicine, USC, Santiago de Compostela, Galicia 15782, Spain.
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Kinney HC. Abnormalities of the brainstem serotonergic system in the sudden infant death syndrome: a review. Pediatr Dev Pathol 2005; 8:507-24. [PMID: 16222475 DOI: 10.1007/s10024-005-0067-y] [Citation(s) in RCA: 64] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/20/2005] [Accepted: 06/24/2005] [Indexed: 10/25/2022]
Affiliation(s)
- Hannah C Kinney
- Department of Pathology, Children's Hospital Boston, Enders Building 1112, 300 Longwood Avenue, Boston, Massachusetts 02115, USA.
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Kinney HC, Myers MM, Belliveau RA, Randall LL, Trachtenberg FL, Fingers ST, Youngman M, Habbe D, Fifer WP. Subtle Autonomic and Respiratory Dysfunction in Sudden Infant Death Syndrome Associated With Serotonergic Brainstem Abnormalities: A Case Report. J Neuropathol Exp Neurol 2005; 64:689-94. [PMID: 16106217 DOI: 10.1097/01.jnen.0000174334.27708.43] [Citation(s) in RCA: 54] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
Abstract
Sudden infant death syndrome (SIDS) is characterized by a sleep-related death in a seemingly healthy infant. Previously, we reported abnormalities in the serotonergic (5-HT) system of the medulla in SIDS cases in 2 independent datasets, including in the Northern Plains American Indians. The medullary 5-HT system is composed of 5-HT neurons in the raphé, extra-raphé, and arcuate nucleus at the ventral surface. This system is thought to modulate respiratory and autonomic function, and thus abnormalities within it could potentially lead to imbalances in sympathetic and parasympathetic tone. We report the case of a full-term American Indian boy who died of SIDS at 2 postnatal weeks, and who had subtle respiratory and autonomic dysfunction measured prospectively on the second postnatal day. Cardiorespiratory assessment of heart rate variability suggested that the ratio of parasympathetic to sympathetic tone was higher than normal in active sleep and lower than normal in quiet sleep in this case. At autopsy, arcuate nucleus hypoplasia and 5-HT receptor-binding abnormalities in the arcuate nucleus and other components of the medullary 5-HT system were found. This case suggests that medullary 5-HT system abnormalities may be able to be identified by such physiological tests before death. Replication of these findings in a large population may lead to the development of predictive cardiorespiratory assessment tools for future screening to identify infants with medullary 5-HT abnormalities and SIDS risk.
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Affiliation(s)
- Hannah C Kinney
- Department of Pathology, Children's Hospital and Harvard Medical School, Boston, Massachusetts 02115, USA.
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Comet MA, Sévoz-Couche C, Hanoun N, Hamon M, Laguzzi R. 5-HT-mediated inhibition of cardiovagal baroreceptor reflex response during defense reaction in the rat. Am J Physiol Heart Circ Physiol 2004; 287:H1641-9. [PMID: 15165987 DOI: 10.1152/ajpheart.01204.2003] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Previous studies showed that the cardiac response of the baroreceptor reflex (bradycardia) is inhibited during the defense reaction evoked by direct electrical or chemical stimulation of the periaqueductal gray (dPAG) in the rat. Whether central serotonin and nucleus tractus solitarius (NTS) serotonin3 (5-HT3) receptors might participate in this inhibition was investigated in urethane-anesthetized and atenolol-pretreated rats. Our results showed that both electrical and chemical stimulation of the dPAG produced a drastic reduction of the cardiovagal component of the baroreceptor reflex triggered by either intravenous administration of phenylephrine or aortic nerve stimulation. This inhibitory effect of dPAG stimulation on the baroreflex bradycardia was not observed in rats that had been pretreated with p-chlorophenylalanine (300 mg/kg ip daily for 3 days) to inhibit serotonin synthesis. Subsequent 5-hydroxytryptophan administration (60 mg/kg ip), which was used to restore serotonin synthesis, allowed the inhibitory effect of dPAG stimulation on both aortic and phenylephrine-induced cardiac reflex responses to be recovered in p-chlorophenylalanine-pretreated rats. On the other hand, in nonpretreated rats, the inhibitory effect of dPAG stimulation on the cardiac baroreflex response could be markedly reduced by prior intra-NTS microinjection of granisetron, a 5-HT3 receptor antagonist, or bicuculline, a GABAA receptor antagonist. These results show that serotonin plays a key role in the dPAG stimulation-induced inhibition of the cardiovagal baroreceptor reflex response. Moreover, they support the idea that 5-HT3 and GABAA receptors in the NTS contribute downstream to the inhibition of the baroreflex response caused by dPAG stimulation.
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Affiliation(s)
- Marie-Anne Comet
- Institut National de la Santé et de la Recherche Médicale U.288, CHU Pitié-Salpêtrière, 91 Boulevard de l'Hôpital, 75634 Paris Cedex 13, France
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