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Cummings KJ, Leiter JC, Trachtenberg FL, Okaty BW, Darnall RA, Haas EA, Harper RM, Nattie EE, Krous HF, Mena OJ, Richerson GB, Dymecki SM, Kinney HC, Haynes RL. Altered 5-HT2A/C receptor binding in the medulla oblongata in the sudden infant death syndrome (SIDS): Part II. Age-associated alterations in serotonin receptor binding profiles within medullary nuclei supporting cardiorespiratory homeostasis. J Neuropathol Exp Neurol 2024; 83:144-160. [PMID: 38323418 PMCID: PMC10880067 DOI: 10.1093/jnen/nlae004] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2024] Open
Abstract
The failure of chemoreflexes, arousal, and/or autoresuscitation to asphyxia may underlie some sudden infant death syndrome (SIDS) cases. In Part I, we showed that some SIDS infants had altered 5-hydroxytryptamine (5-HT)2A/C receptor binding in medullary nuclei supporting chemoreflexes, arousal, and autoresuscitation. Here, using the same dataset, we tested the hypotheses that the prevalence of low 5-HT1A and/or 5-HT2A/C receptor binding (defined as levels below the 95% confidence interval of controls-a new approach), and the percentages of nuclei affected are greater in SIDS versus controls, and that the distribution of low binding varied with age of death. The prevalence and percentage of nuclei with low 5-HT1A and 5-HT2A/C binding in SIDS were twice that of controls. The percentage of nuclei with low 5-HT2A/C binding was greater in older SIDS infants. In >80% of older SIDS infants, low 5-HT2A/C binding characterized the hypoglossal nucleus, vagal dorsal nucleus, nucleus of solitary tract, and nuclei of the olivocerebellar subnetwork (important for blood pressure regulation). Together, our findings from SIDS infants and from animal models of serotonergic dysfunction suggest that some SIDS cases represent a serotonopathy. We present new hypotheses, yet to be tested, about how defects within serotonergic subnetworks may lead to SIDS.
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Affiliation(s)
- Kevin J Cummings
- Department of Biomedical Sciences, Dalton Cardiovascular Research Center, University of Missouri, Columbia, Missouri, USA
| | - James C Leiter
- Department of Molecular and Systems Biology, Geisel School of Medicine at Dartmouth, Hanover, New Hampshire, USA
| | | | - Benjamin W Okaty
- Department of Genetics, Harvard Medical School, Boston, Massachusetts, USA
| | - Robert A Darnall
- Department of Molecular and Systems Biology, Geisel School of Medicine at Dartmouth, Hanover, New Hampshire, USA
| | - Elisabeth A Haas
- Department of Research, Rady’s Children’s Hospital, San Diego, California, USA
| | - Ronald M Harper
- Department of Neurobiology and the Brain Research Institute, David Geffen School of Medicine at UCLA, Los Angeles, California, USA
| | - Eugene E Nattie
- Department of Molecular and Systems Biology, Geisel School of Medicine at Dartmouth, Hanover, New Hampshire, USA
| | - Henry F Krous
- Department of Pediatrics, University of California San Diego, San Diego, California, USA
- Departments of Pathology and Pediatrics, Rady Children’s Hospital, San Diego, California, USA
| | - Othon J Mena
- San Diego County Medical Examiner Office, San Diego, California, USA
| | - George B Richerson
- Departments of Neurology and Molecular Physiology & Biophysics, University of Iowa, Iowa City, Iowa, USA
| | - Susan M Dymecki
- Department of Genetics, Harvard Medical School, Boston, Massachusetts, USA
| | - Hannah C Kinney
- Department of Pathology, CJ Murphy Laboratory for SIDS Research, Boston Children’s Hospital and Harvard Medical School, Boston, Massachusetts, USA
| | - Robin L Haynes
- Department of Pathology, CJ Murphy Laboratory for SIDS Research, Boston Children’s Hospital and Harvard Medical School, Boston, Massachusetts, USA
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Wojcik MH, Poduri AH, Holm IA, MacRae CA, Goldstein RD. The fundamental need for unifying phenotypes in sudden unexpected pediatric deaths. Front Med (Lausanne) 2023; 10:1166188. [PMID: 37332751 PMCID: PMC10273404 DOI: 10.3389/fmed.2023.1166188] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2023] [Accepted: 05/03/2023] [Indexed: 06/20/2023] Open
Abstract
A definitive, authoritative approach to evaluate the causes of unexpected, and ultimately unexplained, pediatric deaths remains elusive, relegating final conclusions to diagnoses of exclusion in the vast majority of cases. Research into unexplained pediatric deaths has focused primarily on sudden infant deaths (under 1 year of age) and led to the identification of several potential, albeit incompletely understood, contributory factors: nonspecific pathology findings, associations with sleep position and environment that may not be uniformly relevant, and the elucidation of a role for serotonin that is practically difficult to estimate in any individual case. Any assessment of progress in this field must also acknowledge the failure of current approaches to substantially decrease mortality rates in decades. Furthermore, potential commonalities with pediatric deaths across a broader age spectrum have not been widely considered. Recent epilepsy-related observations and genetic findings, identified post-mortem in both infants and children who died suddenly and unexpectedly, suggest a role for more intense and specific phenotyping efforts as well as an expanded role for genetic and genomic evaluation. We therefore present a new approach to reframe the phenotype in sudden unexplained deaths in the pediatric age range, collapsing many distinctions based on arbitrary factors (such as age) that have previously guided research in this area, and discuss its implications for the future of postmortem investigation.
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Affiliation(s)
- Monica H. Wojcik
- Robert’s Program for Sudden Unexpected Death in Pediatrics, Boston Children’s Hospital, Boston, MA, United States
- Division of Newborn Medicine, Department of Pediatrics, Boston Children’s Hospital, Boston, MA, United States
- Division of Genetics and Genomics, Department of Pediatrics, Boston Children’s Hospital, Boston, MA, United States
- Harvard Medical School, Boston, MA, United States
| | - Annapurna H. Poduri
- Robert’s Program for Sudden Unexpected Death in Pediatrics, Boston Children’s Hospital, Boston, MA, United States
- Harvard Medical School, Boston, MA, United States
- F.M. Kirby Neurobiology Center, Boston Children's Hospital, Boston, MA, United States
- Epilepsy Genetics Program, Department of Neurology, Boston Children's Hospital and Harvard Medical School, Boston, MA, United States
| | - Ingrid A. Holm
- Robert’s Program for Sudden Unexpected Death in Pediatrics, Boston Children’s Hospital, Boston, MA, United States
- Division of Genetics and Genomics, Department of Pediatrics, Boston Children’s Hospital, Boston, MA, United States
- Harvard Medical School, Boston, MA, United States
| | - Calum A. MacRae
- Harvard Medical School, Boston, MA, United States
- Department of Medicine, Brigham and Women's Hospital, Boston, MA, United States
| | - Richard D. Goldstein
- Robert’s Program for Sudden Unexpected Death in Pediatrics, Boston Children’s Hospital, Boston, MA, United States
- Harvard Medical School, Boston, MA, United States
- Division of General Pediatrics, Department of Pediatrics, Boston Children's Hospital, Boston, MA, United States
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Yackle K. Transformation of Our Understanding of Breathing Control by Molecular Tools. Annu Rev Physiol 2023; 85:93-113. [PMID: 36323001 PMCID: PMC9918693 DOI: 10.1146/annurev-physiol-021522-094142] [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: 02/12/2023]
Abstract
The rhythmicity of breath is vital for normal physiology. Even so, breathing is enriched with multifunctionality. External signals constantly change breathing, stopping it when under water or deepening it during exertion. Internal cues utilize breath to express emotions such as sighs of frustration and yawns of boredom. Breathing harmonizes with other actions that use our mouth and throat, including speech, chewing, and swallowing. In addition, our perception of breathing intensity can dictate how we feel, such as during the slow breathing of calming meditation and anxiety-inducing hyperventilation. Heartbeat originates from a peripheral pacemaker in the heart, but the automation of breathing arises from neural clusters within the brainstem, enabling interaction with other brain areas and thus multifunctionality. Here, we document how the recent transformation of cellular and molecular tools has contributed to our appreciation of the diversity of neuronal types in the breathing control circuit and how they confer the multifunctionality of breathing.
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Affiliation(s)
- Kevin Yackle
- Department of Physiology, University of California, San Francisco, California, USA;
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Genes involved in paediatric apnoea and death based on knockout animal models: Implications for sudden infant death syndrome (SIDS). Paediatr Respir Rev 2022; 44:53-60. [PMID: 34750067 DOI: 10.1016/j.prrv.2021.09.003] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/01/2021] [Accepted: 09/14/2021] [Indexed: 12/14/2022]
Abstract
The mechanism of death in Sudden infant death syndrome (SIDS) remains unknown but it is hypothesised that cardiorespiratory failure of brainstem origin results in early post-natal death. For a subset of SIDS infants, an underlying genetic cause may be present, and genetic abnormalities affecting brainstem respiratory control may result in abnormalities that are detectable before death. Genetic knockout mice models were developed in the 1990s and have since helped to elucidate the physiological roles of a number of genes. This systematic review aimed to identify which genes, when knocked out, result in the phenotypes of abnormal cardiorespiratory control and/or early post-natal death. Three major genes were identified: Pet1- a serotonin transcription factor, the neurotrophin pituitary adenylate cyclase activating polypeptide (PACAP) and its receptor (PAC1). Knockouts targeting these genes had blunted hypercapnic and/or hypoxic responses and early post-natal death. The hypothesis that these genes have a role in SIDS is supported by their being identified as abnormal in SIDS cohorts. Future research in SIDS cohorts will be important to determine whether these genetic abnormalities coexist and their potential applicability as biomarkers.
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Koh HY, Haghighi A, Keywan C, Alexandrescu S, Plews-Ogan E, Haas EA, Brownstein CA, Vargas SO, Haynes RL, Berry GT, Holm IA, Poduri AH, Goldstein RD. Genetic Determinants of Sudden Unexpected Death in Pediatrics. Genet Med 2022; 24:839-850. [PMID: 35027292 PMCID: PMC9164313 DOI: 10.1016/j.gim.2021.12.004] [Citation(s) in RCA: 21] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2021] [Revised: 12/07/2021] [Accepted: 12/08/2021] [Indexed: 02/06/2023] Open
Abstract
PURPOSE This study aimed to evaluate genetic contributions to sudden unexpected death in pediatrics (SUDP). METHODS We phenotyped and performed exome sequencing for 352 SUDP cases. We analyzed variants in 294 "SUDP genes" with mechanisms plausibly related to sudden death. In a subset of 73 cases with parental data (trios), we performed exome-wide analyses and conducted cohort-wide burden analyses. RESULTS In total, we identified likely contributory variants in 37 of 352 probands (11%). Analysis of SUDP genes identified pathogenic/likely pathogenic variants in 12 of 352 cases (SCN1A, DEPDC5 [2], GABRG2, SCN5A [2], TTN [2], MYBPC3, PLN, TNNI3, and PDHA1) and variants of unknown significance-favor-pathogenic in 17 of 352 cases. Exome-wide analyses of the 73 cases with family data additionally identified 4 de novo pathogenic/likely pathogenic variants (SCN1A [2], ANKRD1, and BRPF1) and 4 de novo variants of unknown significance-favor-pathogenic. Comparing cases with controls, we demonstrated an excess burden of rare damaging SUDP gene variants (odds ratio, 2.94; 95% confidence interval, 2.37-4.21) and of exome-wide de novo variants in the subset of 73 with trio data (odds ratio, 3.13; 95% confidence interval, 1.91-5.16). CONCLUSION We provide strong evidence for a role of genetic factors in SUDP, involving both candidate genes and novel genes for SUDP and expanding phenotypes of disease genes not previously associated with sudden death.
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Affiliation(s)
- Hyun Yong Koh
- Robert's Program for Sudden Unexpected Death in Pediatrics, Boston Children's Hospital, Boston, MA; F.M. Kirby Neurobiology Center, Boston Children's Hospital, Boston, MA; Epilepsy Genetics Program, Department of Neurology, Boston Children's Hospital and Harvard Medical School, Boston, MA; Division of Genetics and Genomics, Department of Pediatrics and Manton Center for Orphan Diseases Research, Boston Children's Hospital, MA
| | - Alireza Haghighi
- Department of Genetics, Harvard Medical School, Boston, MA; Department of Medicine, Brigham and Women's Hospital and Harvard Medical School, Boston, MA; Broad Institute of MIT and Harvard, Cambridge, MA
| | - Christine Keywan
- Robert's Program for Sudden Unexpected Death in Pediatrics, Boston Children's Hospital, Boston, MA
| | - Sanda Alexandrescu
- Robert's Program for Sudden Unexpected Death in Pediatrics, Boston Children's Hospital, Boston, MA; Departments of Pathology, Boston Children's Hospital and Harvard Medical School, Boston, MA
| | - Erin Plews-Ogan
- Robert's Program for Sudden Unexpected Death in Pediatrics, Boston Children's Hospital, Boston, MA; Harvard Medical School, Boston, MA
| | - Elisabeth A Haas
- Department of Research, Rady Children's Hospital-San Diego, San Diego, CA
| | - Catherine A Brownstein
- Robert's Program for Sudden Unexpected Death in Pediatrics, Boston Children's Hospital, Boston, MA; Division of Genetics and Genomics, Department of Pediatrics and Manton Center for Orphan Diseases Research, Boston Children's Hospital, MA; Department of Pediatrics, Harvard Medical School, Boston, MA
| | - Sara O Vargas
- Robert's Program for Sudden Unexpected Death in Pediatrics, Boston Children's Hospital, Boston, MA; Departments of Pathology, Boston Children's Hospital and Harvard Medical School, Boston, MA
| | - Robin L Haynes
- Departments of Pathology, Boston Children's Hospital and Harvard Medical School, Boston, MA
| | - Gerard T Berry
- Robert's Program for Sudden Unexpected Death in Pediatrics, Boston Children's Hospital, Boston, MA; Division of Genetics and Genomics, Department of Pediatrics and Manton Center for Orphan Diseases Research, Boston Children's Hospital, MA; Department of Pediatrics, Harvard Medical School, Boston, MA
| | - Ingrid A Holm
- Robert's Program for Sudden Unexpected Death in Pediatrics, Boston Children's Hospital, Boston, MA; Division of Genetics and Genomics, Department of Pediatrics and Manton Center for Orphan Diseases Research, Boston Children's Hospital, MA; Broad Institute of MIT and Harvard, Cambridge, MA; Department of Pediatrics, Harvard Medical School, Boston, MA
| | - Annapurna H Poduri
- Robert's Program for Sudden Unexpected Death in Pediatrics, Boston Children's Hospital, Boston, MA; F.M. Kirby Neurobiology Center, Boston Children's Hospital, Boston, MA; Epilepsy Genetics Program, Department of Neurology, Boston Children's Hospital and Harvard Medical School, Boston, MA; Broad Institute of MIT and Harvard, Cambridge, MA; Department of Neurology, Harvard Medical School, Boston, MA
| | - Richard D Goldstein
- Robert's Program for Sudden Unexpected Death in Pediatrics, Boston Children's Hospital, Boston, MA; Broad Institute of MIT and Harvard, Cambridge, MA; Department of Pediatrics, Harvard Medical School, Boston, MA; Division of General Pediatrics, Department of Pediatrics, Boston Children's Hospital, Boston, MA.
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Spinieli RL, Ben Musa R, Kielhofner J, Cornelius-Green J, Cummings KJ. Orexin contributes to eupnea within a critical period of postnatal development. Am J Physiol Regul Integr Comp Physiol 2021; 321:R558-R571. [PMID: 34405704 PMCID: PMC8560369 DOI: 10.1152/ajpregu.00156.2021] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2021] [Revised: 08/10/2021] [Accepted: 08/10/2021] [Indexed: 02/03/2023]
Abstract
Orexin neurons are active in wakefulness and mostly silent in sleep. In adult rats and humans, orexin facilitates the hypercapnic ventilatory response but has little effect on resting ventilation. The influence of orexin on breathing in the early postnatal period, and across states of vigilance, have not been investigated. This is relevant as the orexin system may be impaired in Sudden Infant Death Syndrome (SIDS) cases. We addressed three hypotheses: 1) orexin provides a drive to breathe in infancy; 2) the effect of orexin depends on stage of postnatal development; and 3) orexin has a greater influence on breathing in wakefulness compared with sleep. Whole body plethysmography was used to monitor breathing of infant rats at three ages: postnatal days (P) 7-8, 12-14, and 17-19. Respiratory variables were analyzed in wakefulness (W), quiet sleep (QS), and active sleep (AS), following suvorexant (5 mg/kg ip), a dual orexin receptor antagonist, or vehicle (DMSO). Effects of suvorexant on ventilatory responses to graded hypercapnia ([Formula: see text] = 0.02, 0.04, 0.06), hypoxia ([Formula: see text] = 0.10), and hyperoxia ([Formula: see text] = 1.0) at P12-14 were also tested. At P12-14, but not at other ages, suvorexant significantly reduced respiratory frequency in all states, reduced the ventilatory equivalent in QW and QS, and increased [Formula: see text] to ∼5 mmHg. Suvorexant had no effect on ventilatory responses to graded hypercapnia or hypoxia. Hyperoxia eliminated the effects of suvorexant on respiratory frequency at P12-14. Our data suggest that orexin preserves eupneic frequency and ventilation in rats, specifically at ∼2 wk of age, perhaps by facilitating tonic peripheral chemoreflex activity.
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Affiliation(s)
- Richard L Spinieli
- Department of Biomedical Sciences, College of Veterinary Medicine, University of Missouri, Columbia, Missouri
| | - Ruwaida Ben Musa
- Department of Biomedical Sciences, College of Veterinary Medicine, University of Missouri, Columbia, Missouri
| | - Jane Kielhofner
- Department of Biomedical Sciences, College of Veterinary Medicine, University of Missouri, Columbia, Missouri
| | | | - Kevin J Cummings
- Dalton Cardiovascular Research Center, University of Missouri, Columbia, Missouri
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Mouradian GC, Kilby M, Alvarez S, Kaplan K, Hodges MR. Mortality and ventilatory effects of central serotonin deficiency during postnatal development depend on age but not sex. Physiol Rep 2021; 9:e14946. [PMID: 34228894 PMCID: PMC8259800 DOI: 10.14814/phy2.14946] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2021] [Revised: 06/04/2021] [Accepted: 06/07/2021] [Indexed: 11/24/2022] Open
Abstract
Serotonin (5-HT) influences brain development and has predominantly excitatory neuromodulatory effects on the neural respiratory control circuitry. Infants that succumb to sudden infant death syndrome (SIDS) have reduced brainstem 5-HT levels and Tryptophan hydroxylase 2 (Tph2). Furthermore, there are age- and sex-dependent risk factors associated with SIDS. Here we utilized our established Dark Agouti transgenic rat lacking central serotonin KO to test the hypotheses that CNS 5-HT deficiency leads to: (1) high mortality in a sex-independent manner, (2) age-dependent alterations in other CNS aminergic systems, and (3) age-dependent impairment of chemoreflexes during post-natal development. KO rat pups showed high neonatal mortality but not in a sex-dependent manner and did not show altered hypoxic or hypercapnic ventilatory chemoreflexes. However, KO rat pups had increased apnea-related metrics during a specific developmental age (P12-16), which were preceded by transient increases in dopaminergic system activity (P7-8). These results support and extend the concept that 5-HT per se is a critical factor in supporting respiratory control during post-natal development.
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Affiliation(s)
- Gary C. Mouradian
- Department of PhysiologyMedical College of WisconsinMilwaukeeWIUSA
- Neuroscience Research CenterMedical College of WisconsinMilwaukeeWIUSA
| | - Madeline Kilby
- Department of PhysiologyMedical College of WisconsinMilwaukeeWIUSA
| | - Santiago Alvarez
- Department of PhysiologyMedical College of WisconsinMilwaukeeWIUSA
| | - Kara Kaplan
- Department of PhysiologyMedical College of WisconsinMilwaukeeWIUSA
| | - Matthew R. Hodges
- Department of PhysiologyMedical College of WisconsinMilwaukeeWIUSA
- Neuroscience Research CenterMedical College of WisconsinMilwaukeeWIUSA
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8
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Abstract
The development of the control of breathing begins in utero and continues postnatally. Fetal breathing movements are needed for establishing connectivity between the lungs and central mechanisms controlling breathing. Maturation of the control of breathing, including the increase of hypoxia chemosensitivity, continues postnatally. Insufficient oxygenation, or hypoxia, is a major stressor that can manifest for different reasons in the fetus and neonate. Though the fetus and neonate have different hypoxia sensing mechanisms and respond differently to acute hypoxia, both responses prevent deviations to respiratory and other developmental processes. Intermittent and chronic hypoxia pose much greater threats to the normal developmental respiratory processes. Gestational intermittent hypoxia, due to maternal sleep-disordered breathing and sleep apnea, increases eupneic breathing and decreases the hypoxic ventilatory response associated with impaired gasping and autoresuscitation postnatally. Chronic fetal hypoxia, due to biologic or environmental (i.e. high-altitude) factors, is implicated in fetal growth restriction and preterm birth causing a decrease in the postnatal hypoxic ventilatory responses with increases in irregular eupneic breathing. Mechanisms driving these changes include delayed chemoreceptor development, catecholaminergic activity, abnormal myelination, increased astrocyte proliferation in the dorsal respiratory group, among others. Long-term high-altitude residents demonstrate favorable adaptations to chronic hypoxia as do their offspring. Neonatal intermittent hypoxia is common among preterm infants due to immature respiratory systems and thus, display a reduced drive to breathe and apneas due to insufficient hypoxic sensitivity. However, ongoing intermittent hypoxia can enhance hypoxic sensitivity causing ventilatory overshoots followed by apnea; the number of apneas is positively correlated with degree of hypoxic sensitivity in preterm infants. Chronic neonatal hypoxia may arise from fetal complications like maternal smoking or from postnatal cardiovascular problems, causing blunting of the hypoxic ventilatory responses throughout at least adolescence due to attenuation of carotid body fibers responses to hypoxia with potential roles of brainstem serotonin, microglia, and inflammation, though these effects depend on the age in which chronic hypoxia initiates. Fetal and neonatal intermittent and chronic hypoxia are implicated in preterm birth and complicate the respiratory system through their direct effects on hypoxia sensing mechanisms and interruptions to the normal developmental processes. Thus, precise regulation of oxygen homeostasis is crucial for normal development of the respiratory control network. © 2021 American Physiological Society. Compr Physiol 11:1653-1677, 2021.
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Affiliation(s)
- Gary C. Mouradian
- Department of Physiology, Medical College of Wisconsin, Milwaukee, Wisconsin, USA
| | - Satyan Lakshminrusimha
- Department of Pediatrics, UC Davis Children’s Hospital, UC Davis Health, UC Davis, Davis, California, USA
| | - Girija G. Konduri
- Department of Pediatrics, Medical College of Wisconsin, Milwaukee, Wisconsin, USA
- Children’s Research Institute, Medical College of Wisconsin, Milwaukee, Wisconsin, USA
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Cummings KJ. Eupnea and gasping in vivo are facilitated by the activation of 5-HT 2A receptors. J Neurophysiol 2021; 125:1543-1551. [PMID: 33760672 DOI: 10.1152/jn.00088.2021] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Eupnea and gasping in infancy depend on central nervous system (CNS) serotonin (5-hydroxytryptamine; 5-HT). Although previous in vitro preparations have provided some evidence that 5-HT acts through type 2 A receptors (5-HT2A) to facilitate eupnea and gasping, here the hypothesis addressed is that 5-HT2A receptor activation is necessary for eupnea and the proper generation of gasping in vivo. To test this, we administered 2,5-dimethoxy-4-iodoamphetamine (DOI; 0.25 mg/kg i.p.), a 5-HT2A agonist, 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT; 0.25 mg/kg i.p.), a 5-HT1A agonist, or vehicle (saline) to 7-9-day-old tryptophan hydroxylase 2 knockout (TPH2-/-) mice. A second experiment assessed the effect of MDL-11,939 (MDL; 10 mg/kg i.p.), the specific 5-HT2A antagonist, or vehicle (DMSO) on the gasping of wild-type (TPH2+/+) animals. Drugs were given 15 min prior to five episodes of severe hypoxia that elicited gasping. TPH2-/- breathed more slowly but had the same V̇e and V̇e/V̇o2 compared with TPH2+/+. As previously reported, the gasping of TPH2-/- was significantly delayed (P < 0.001) and occurred at a significantly lower frequency compared with TPH2+/+ (P = 0.04). For both genotypes, DOI hastened eupneic frequency but had no effect on V̇e or V̇e/V̇o2. The gasping of TPH2-/-, although unaffected by 8-OH-DPAT, was indistinguishable from the gasping of TPH2+/+ following DOI. In TPH2+/+, application of MDL led to hypoventilation (P = 0.01), a delay in the appearance of gasping (P = 0.005), and reduced gasp frequency (P = 0.05). These data show that, in vivo, 5-HT2A receptors facilitate both eupnea and gasping. As has been shown in vitro, 5-HT2A probably promotes gasping by exciting hypoxia-resistant pacemaker neurons.NEW & NOTEWORTHY Previous in vitro studies suggest that 5-HT2A receptors contribute to eupnea and are necessary for fictive gasping. The current study shows that the impaired gasping displayed by neonatal TPH2-/- mice, deficient in CNS serotonin, is restored by 5-HT2A receptor activation. Following 5-HT2A blockade, wild-type mice hypoventilated and their gasping resembled that of TPH2-/- mice. This study shows that both eupnea and gasping in vivo rely on the activation of 5-HT2A receptors.
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Affiliation(s)
- Kevin J Cummings
- Department of Biomedical Sciences, College of Veterinary Medicine, University of Missouri, Columbia, Missouri and Dalton Cardiovascular Research Center, University of Missouri, Columbia, Missouri
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10
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Barrett KT, Hasan SU, Scantlebury MH, Wilson RJA. Impaired cardiorespiratory responses to hypercapnia in neonatal mice lacking PAC1 but not VPAC2 receptors. Am J Physiol Regul Integr Comp Physiol 2021; 320:R116-R128. [PMID: 33146556 DOI: 10.1152/ajpregu.00161.2020] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The evidence is mounting for a role for abnormal signaling of the stress peptide pituitary adenylate cyclase activating polypeptide (PACAP) and its canonical receptor PAC1 in the pathogenesis of sudden infant death syndrome. In this study, we investigated whether the PACAP receptors PAC1 or VPAC2 are involved in the neonatal cardiorespiratory response to hypercapnic stress. We used head-out plethysmography and surface ECG electrodes to assess cardiorespiratory responses to an 8% hypercapnic challenge in unanesthetized and spontaneously breathing 4-day-old PAC1 or VPAC2 knockout (KO) and wild-type mouse pups. We demonstrate that compared with WTs, breathing frequency (RR) and minute ventilation ([Formula: see text]) in PAC1 KO pups were significantly blunted in response to hypercapnia. Although heart rate was unaltered in PAC1 KO pups during hypercapnia, heart rate recovery posthypercapnia was impaired. In contrast, cardiorespiratory impairments in VPAC2 KO pups were limited to only an overall higher tidal volume (VT), independent of treatment. These findings suggest that PACAP signaling through the PAC1 receptor plays a more important role than signaling through the VPAC2 receptor in neonatal respiratory responses to hypercapnia. Thus deficits in PACAP signaling primarily via PAC1 may contribute to the inability of infants to mount an appropriate protective response to homeostatic stressors in childhood disorders such as SIDS.
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Affiliation(s)
- Karlene T Barrett
- Department of Physiology and Pharmacology, Hotchkiss Brain Institute and Alberta Children's Hospital Research Institute, University of Calgary, Alberta, Canada
| | - Shabih U Hasan
- Department of Pediatrics, Alberta Children's Hospital Research Institute, University of Calgary, Alberta, Canada
| | - Morris H Scantlebury
- Department of Pediatrics, Clinical Neuroscience, Alberta Children's Hospital Research Institute, University of Calgary, Alberta, Canada
| | - Richard J A Wilson
- Department of Physiology and Pharmacology, Hotchkiss Brain Institute and Alberta Children's Hospital Research Institute, University of Calgary, Alberta, Canada
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11
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Allen K, Anderson TM, Chajewska U, Ramirez J, Mitchell EA. Factors associated with age of death in sudden unexpected infant death. Acta Paediatr 2021; 110:174-183. [PMID: 32304589 PMCID: PMC7574313 DOI: 10.1111/apa.15308] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/13/2020] [Revised: 04/03/2020] [Accepted: 04/14/2020] [Indexed: 12/28/2022]
Abstract
Aim This study aimed to systematically analyse the pregnancy, birth and demographic‐related factors associated with age of death in sudden unexpected infant death (SUID). Methods Data were analysed from the Centers for Disease Control and Prevention's Cohort Linked Birth/Infant Death data set (2011‐2013; 11 737 930 live births). SUID was defined as deaths from sudden infant death syndrome, ill‐defined causes, or accidental suffocation and strangulation in bed. There were 9668 SUID cases (7‐364 days; gestation >28 weeks; 0.82/1000 live births). The odds of death at different ages were compared to determine which variables significantly affect the SUID age of death. Results Forty‐three features indicated a significant change in age of death with two main patterns: (a) younger chronologic age at death was associated with maternal smoking and factors associated with lower socio‐economic status, and (b) older age was associated with low birthweight, prematurity and admission to the neonatal intensive care unit. However, when age was corrected for gestation, these factors were associated with younger age. Conclusion Factors that varied with age of death are well‐documented risk factors for SUID. The majority of these risk factors were associated with younger age at death after allowing for gestational age at birth.
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Affiliation(s)
| | | | | | - Jan‐Marino Ramirez
- Seattle Children’s Research Institute Seattle WA USA
- Departments of Neurological Surgery and Pediatrics University of Washington School of Medicine Seattle WA USA
| | - Edwin A. Mitchell
- Department of Paediatrics: Child and Youth Health University of Auckland Auckland New Zealand
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12
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Blackburn J, Chapur VF, Stephens JA, Zhao J, Shepler A, Pierson CR, Otero JJ. Revisiting the Neuropathology of Sudden Infant Death Syndrome (SIDS). Front Neurol 2020; 11:594550. [PMID: 33391159 PMCID: PMC7773837 DOI: 10.3389/fneur.2020.594550] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2020] [Accepted: 11/10/2020] [Indexed: 01/08/2023] Open
Abstract
Background: Sudden infant death syndrome (SIDS) is one of the leading causes of infant mortality in the United States (US). The extent to which SIDS manifests with an underlying neuropathological mechanism is highly controversial. SIDS correlates with markers of poor prenatal and postnatal care, generally rooted in the lack of access and quality of healthcare endemic to select racial and ethnic groups, and thus can be viewed in the context of health disparities. However, some evidence suggests that at least a subset of SIDS cases may result from a neuropathological mechanism. To explain these issues, a triple-risk hypothesis has been proposed, whereby an underlying biological abnormality in an infant facing an extrinsic risk during a critical developmental period SIDS is hypothesized to occur. Each SIDS decedent is thus thought to have a unique combination of these risk factors leading to their death. This article reviews the neuropathological literature of SIDS and uses machine learning tools to identify distinct subtypes of SIDS decedents based on epidemiological data. Methods: We analyzed US Period Linked Birth/Infant Mortality Files from 1990 to 2017 (excluding 1992–1994). Using t-SNE, an unsupervised machine learning dimensionality reduction algorithm, we identified clusters of SIDS decedents. Following identification of these groups, we identified changes in the rates of SIDS at the state level and across three countries. Results: Through t-SNE and distance based statistical analysis, we identified three groups of SIDS decedents, each with a unique peak age of death. Within the US, SIDS is geographically heterogeneous. Following this, we found low birth weight and normal birth weight SIDS rates have not been equally impacted by implementation of clinical guidelines. We show that across countries with different levels of cultural heterogeneity, reduction in SIDS rates has also been distinct between decedents with low vs. normal birth weight. Conclusions: Different epidemiological and extrinsic risk factors exist based on the three unique SIDS groups we identified with t-SNE and distance based statistical measurements. Clinical guidelines have not equally impacted the groups, and normal birth weight infants comprise more of the cases of SIDS even though low birth weight infants have a higher SIDS rate.
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Affiliation(s)
- Jessica Blackburn
- Division of Neuropathology, Department of Pathology, The Ohio State University College of Medicine, Columbus, OH, United States.,Division of Anatomy, Department of Biomedical Education & Anatomy, The Ohio State University College of Medicine, Columbus, OH, United States
| | - Valeria F Chapur
- Instituto de Ecoregiones Andinas (INECOA)/Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Buenos Aires, Argentina.,Instituto de Biología de la Altura (INBIAL)/Universidad Nacional de Jujuy (UNJU), San Salvador de Jujuy, Argentina
| | - Julie A Stephens
- Department of Biomedical Informatics, Center for Biostatistics, The Ohio State University College of Medicine, Columbus, OH, United States
| | - Jing Zhao
- Department of Biomedical Informatics, Center for Biostatistics, The Ohio State University College of Medicine, Columbus, OH, United States
| | - Anne Shepler
- Division of Neuropathology, Department of Pathology, The Ohio State University College of Medicine, Columbus, OH, United States.,Franklin County Forensic Science Center, Columbus, OH, United States
| | - Christopher R Pierson
- Division of Neuropathology, Department of Pathology, The Ohio State University College of Medicine, Columbus, OH, United States.,Division of Anatomy, Department of Biomedical Education & Anatomy, The Ohio State University College of Medicine, Columbus, OH, United States.,Department of Pathology and Laboratory Medicine, Nationwide Children's Hospital, Columbus, OH, United States
| | - José Javier Otero
- Division of Neuropathology, Department of Pathology, The Ohio State University College of Medicine, Columbus, OH, United States
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13
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Kinney HC, Haynes RL. The Serotonin Brainstem Hypothesis for the Sudden Infant Death Syndrome. J Neuropathol Exp Neurol 2020; 78:765-779. [PMID: 31397480 DOI: 10.1093/jnen/nlz062] [Citation(s) in RCA: 41] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2019] [Revised: 05/28/2019] [Accepted: 06/25/2019] [Indexed: 01/04/2023] Open
Abstract
The sudden infant death syndrome (SIDS) is the leading cause of postneonatal infant mortality in the United States today, with an overall rate of 0.39/1000 live births. It is defined as the sudden and unexpected death of an infant <12 months of age that remains unexplained after a complete autopsy, death scene investigation, and review of the clinical history. The serotonin brainstem hypothesis has been a leading hypothesis for SIDS over the last 2 decades. Our laboratory has studied this hypothesis over time with a variety of tissue techniques, including tissue receptor autoradiography, high performance liquid chromatography, Western blot analysis, immunocytochemistry, and proteomics. The purpose of this article is to review the progress in our laboratory toward supporting this hypothesis. We conclude that an important subset of SIDS infants has serotonergic abnormalities resulting from a "core lesion" in the medullary reticular formation comprised of nuclei that contain serotonin neurons. This lesion could lead to a failure of protective brainstem responses to homeostatic challenges during sleep in a critical developmental period which cause sleep-related sudden death.
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Affiliation(s)
- Hannah C Kinney
- Department of Pathology, Boston Children's Hospital and Harvard Medical School, Boston, Massachusetts
| | - Robin L Haynes
- Department of Pathology, Boston Children's Hospital and Harvard Medical School, Boston, Massachusetts
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14
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Cummings KJ, Leiter JC. Take a deep breath and wake up: The protean role of serotonin preventing sudden death in infancy. Exp Neurol 2020; 326:113165. [PMID: 31887304 PMCID: PMC6956249 DOI: 10.1016/j.expneurol.2019.113165] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2019] [Revised: 12/14/2019] [Accepted: 12/26/2019] [Indexed: 01/24/2023]
Abstract
Recordings from infants who died suddenly and unexpectedly demonstrate the occurrence of recurring apneas, ineffective gasping, and finally, failure to restore eupnea and arouse prior to death. Immunohistochemical and autoradiographic data demonstrate a constellation of serotonergic defects in the caudal raphe nuclei in infants who died of Sudden Infant Death Syndrome (SIDS). The purpose of this review is to synthesize what is known about adaptive responses of the infant to severely hypoxic conditions, which unleash a flood of neuromodulators that inhibit cardiorespiratory function, thermogenesis, and arousal and the emerging role of serotonin, which combats this cardiorespiratory inhibition to foster autoresuscitation, eupnea, and arousal to ensure survival following an hypoxic episode. The laryngeal and carotid body chemoreflexes are potent in newborns and infants, and both reflexes can induce apnea and bradycardia, which may be adaptive initially, but must be terminated if an infant is to survive. Serotonin has a unique ability to touch on each of the processes that may be required to recover from hypoxic reflex apnea: gasping, the restoration of heart rate and blood pressure, termination of apneas and, eventually, stimulation of eupnea and arousal. Recurrent apneic events, bradycardia, ineffective gasping and a failure to terminate apneas and restore eupnea are observed in animals harboring defects in the caudal serotonergic system models - all of these phenotypes are reminiscent of and compatible with the cardiorespiratory recordings made in infants who subsequently died of SIDS. The caudal serotonergic system provides an organized, multi-pronged defense against reflex cardiorespiratory inhibition and the hypoxia that accompanies prolonged apnea, bradycardia and hypotension, and any deficiency of caudal serotonergic function will increase the propensity for sudden unexplained infant death.
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Affiliation(s)
- Kevin J Cummings
- Department of Biomedical Sciences, University of Missouri-Columbia, Dalton Cardiovascular Research Center, 134 Research Park Drive, Columbia, MO 65203, USA
| | - James C Leiter
- Department of Molecular and Systems Biology, Geisel School of Medicine at Dartmouth, One Rope Ferry Road, Hanover, NH 03755, USA.
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15
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Erickson JT. Central serotonin and autoresuscitation capability in mammalian neonates. Exp Neurol 2020; 326:113162. [DOI: 10.1016/j.expneurol.2019.113162] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2019] [Revised: 11/04/2019] [Accepted: 12/23/2019] [Indexed: 01/08/2023]
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16
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Hatini PG, Commons KG. Serotonin abnormalities in Dravet syndrome mice before and after the age of seizure onset. Brain Res 2019; 1724:146399. [PMID: 31445030 DOI: 10.1016/j.brainres.2019.146399] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2019] [Revised: 08/12/2019] [Accepted: 08/20/2019] [Indexed: 01/19/2023]
Abstract
Dravet syndrome (DS) is a genetic form of severe epilepsy often associated with mutation of the SCN1A gene encoding the voltage gated sodium channel Nav1.1. Typically refractive to conventional therapy, serotonin neurotransmission may be an innovative target for treatment. To further understand the role of serotonin in this disorder, in this study we examined the state of the endogenous serotonin system in an Scn1a+/- mouse model of DS. Examined at an age before seizures appear, we found the hypothermic effect of 5-HT1A receptor agonist administration was attenuated. HPLC analysis of brain monoamine content revealed modestly reduced serotonin levels in tissue samples of the midbrain that included the dorsal raphe nucleus but no changes elsewhere in the brain. The reduced sensitivity to 5-HT1A agonist administration seen at young ages reversed after the age of seizure development when mice showed an exaggerated hypothermic response. Likewise, adult DS mice showed a pronounced hypersensitivity to a 5-HT2A/2C agonist. As adults however monoamine levels were not detectably altered. Thus there are alterations in the endogenous serotonin system that both precede and follow the appearance of seizure in DS mice, most strikingly in the response to agonist administration.
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Affiliation(s)
- Paul G Hatini
- Department of Anesthesiology, Perioperative and Pain Medicine, Children's Hospital, Boston, Department of Anæsthesia, Harvard Medical School, United States
| | - Kathryn G Commons
- Department of Anesthesiology, Perioperative and Pain Medicine, Children's Hospital, Boston, Department of Anæsthesia, Harvard Medical School, United States.
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17
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Cummings KJ, Hodges MR. The serotonergic system and the control of breathing during development. Respir Physiol Neurobiol 2019; 270:103255. [PMID: 31362064 DOI: 10.1016/j.resp.2019.103255] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2019] [Revised: 06/28/2019] [Accepted: 07/12/2019] [Indexed: 01/26/2023]
Abstract
Serotonin (5-hydroxytryptamine 5-HT) was first discovered in the late 1940's as an endogenous bioactive amine capable of inducing vasoconstriction, and in the mid-1950's was found in the brain. It was in these early years that some of the first demonstrations were made regarding a role for brain 5-HT in neurological function and behavior, including data implicating reduced brain levels of 5-HT in clinical depression. Since that time, advances in molecular biology and physiological approaches in basic science research have intensely focused on 5-HT in the brain, and the many facets of its role during embryonic development, post-natal maturation, and neural function in adulthood continues to be established. This review focuses on what is known about the developmental roles for the 5-HT system, which we define as the neurons producing 5-HT along with pre-and post-synaptic receptors, in a vital homeostatic motor behavior - the control of breathing. We will cover what is known about the embryonic origins and fate specification of 5-HT neurons, and how the 5-HT system influences pre- and post-natal maturation of the ventilatory control system. In addition, we will focus on the role of the 5-HT system in specific respiratory behaviors during fetal, neonatal and postnatal development, and the relevance of dysfunction in this system in respiratory-related human pathologies including Sudden Infant Death Syndrome (SIDS).
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Affiliation(s)
- Kevin J Cummings
- Department of Biomedical Sciences, University of Missouri, Columbia, MO 65211, USA; Dalton Cardiovascular Research Center, University of Missouri, Columbia, MO 65211, USA.
| | - Matthew R Hodges
- Department of Physiology, Medical College of Wisconsin, Milwaukee, WI 53226, USA; Neuroscience Research Center, Medical College of Wisconsin, Milwaukee, WI 53226, USA
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18
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Funk GD, Biancardi V. Commentary: Acute perturbation of Pet1-neuron activity in neonatal mice impairs cardiorespiratory homeostatic recovery. Front Physiol 2019; 10:232. [PMID: 30949061 PMCID: PMC6436076 DOI: 10.3389/fphys.2019.00232] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2019] [Accepted: 02/21/2019] [Indexed: 11/26/2022] Open
Affiliation(s)
- Gregory D Funk
- Department of Physiology, Faculty of Medicine and Dentistry, Neuroscience and Mental Health Institute, Women and Children's Health Research Institute, University of Alberta, Edmonton, AB, Canada
| | - Vivian Biancardi
- Department of Physiology, Faculty of Medicine and Dentistry, Neuroscience and Mental Health Institute, Women and Children's Health Research Institute, University of Alberta, Edmonton, AB, Canada
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19
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Anderson TM, Lavista Ferres JM, Ren SY, Moon RY, Goldstein RD, Ramirez JM, Mitchell EA. Maternal Smoking Before and During Pregnancy and the Risk of Sudden Unexpected Infant Death. Pediatrics 2019; 143:peds.2018-3325. [PMID: 30858347 PMCID: PMC6564075 DOI: 10.1542/peds.2018-3325] [Citation(s) in RCA: 104] [Impact Index Per Article: 20.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Accepted: 01/16/2019] [Indexed: 01/16/2023] Open
Abstract
OBJECTIVES Maternal smoking during pregnancy is an established risk factor for sudden unexpected infant death (SUID). Here, we aim to investigate the effects of maternal prepregnancy smoking, reduction during pregnancy, and smoking during pregnancy on SUID rates. METHODS We analyzed the Centers for Disease Control and Prevention Birth Cohort Linked Birth/Infant Death Data Set (2007-2011: 20 685 463 births and 19 127 SUIDs). SUID was defined as deaths at <1 year of age with International Classification of Diseases, 10th Revision codes R95 (sudden infant death syndrome), R99 (ill-defined or unknown cause), or W75 (accidental suffocation or strangulation in bed). RESULTS SUID risk more than doubled (adjusted odds ratio [aOR] = 2.44; 95% confidence interval [CI] 2.31-2.57) with any maternal smoking during pregnancy and increased twofold between no smoking and smoking 1 cigarette daily throughout pregnancy. For 1 to 20 cigarettes per day, the probability of SUID increased linearly, with each additional cigarette smoked per day increasing the odds by 0.07 from 1 to 20 cigarettes; beyond 20 cigarettes, the relationship plateaued. Mothers who quit or reduced their smoking decreased their odds compared with those who continued smoking (reduced: aOR = 0.88, 95% CI 0.79-0.98; quit: aOR = 0.77, 95% CI 0.67-0.87). If we assume causality, 22% of SUIDs in the United States can be directly attributed to maternal smoking during pregnancy. CONCLUSIONS These data support the need for smoking cessation before pregnancy. If no women smoked in pregnancy, SUID rates in the United States could be reduced substantially.
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Affiliation(s)
- Tatiana M. Anderson
- Center for Integrative Brain Research, Seattle
Children’s Research Institute, Seattle, Washington
| | | | | | - Rachel Y. Moon
- Department of Pediatrics, School of Medicine,
University of Virginia, Charlottesville, Virginia
| | - Richard D. Goldstein
- Boston Children’s Hospital and Harvard Medical
School, Harvard University, Boston, Massachusetts
| | - Jan-Marino Ramirez
- Center for Integrative Brain Research, Seattle
Children’s Research Institute, Seattle, Washington;,Department of Neurological Surgery and Pediatrics,
School of Medicine, University of Washington, Seattle, Washington; and
| | - Edwin A. Mitchell
- Department of Paediatrics: Child and Youth Health,
The University of Auckland, Auckland, New Zealand
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20
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Dosumu-Johnson RT, Cocoran AE, Chang Y, Nattie E, Dymecki SM. Acute perturbation of Pet1-neuron activity in neonatal mice impairs cardiorespiratory homeostatic recovery. eLife 2018; 7:37857. [PMID: 30350781 PMCID: PMC6199134 DOI: 10.7554/elife.37857] [Citation(s) in RCA: 27] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2018] [Accepted: 09/09/2018] [Indexed: 12/02/2022] Open
Abstract
Cardiorespiratory recovery from apneas requires dynamic responses of brainstem circuitry. One implicated component is the raphe system of Pet1-expressing (largely serotonergic) neurons, however their precise requirement neonatally for homeostasis is unclear, yet central toward understanding newborn cardiorespiratory control and dysfunction. Here we show that acute in vivo perturbation of Pet1-neuron activity, via triggering cell-autonomously the synthetic inhibitory receptor hM4Di, resulted in altered baseline cardiorespiratory properties and diminished apnea survival. Respiratory more than heart rate recovery was impaired, uncoupling their normal linear relationship. Disordered gasp recovery from the initial apnea distinguished mice that would go on to die during subsequent apneas. Further, the risk likelihood of apnea-related mortality associated with suppression of Pet1 neurons was higher for animals with baseline elevated ventilatory equivalents for oxygen. These findings establish that Pet1 neurons play an active role in neonatal cardiorespiratory homeostasis and provide mechanistic plausibility for the serotonergic abnormalities associated with SIDS. Our survival depends on our heart and lungs working together to supply our cells with oxygen and remove carbon dioxide waste. The brain coordinates this process by controlling the activity of the heart and lungs. Yet sometimes a person may experience an event called an apnea and briefly stop breathing. If this happens, oxygen levels in the body fall while carbon dioxide levels rise. This in turn triggers a recovery process called autoresuscitation, which includes a series of large breaths or gasps, and each gasp is accompanied by increased heart rate due to specialized parts of the nervous system. This response usually restores normal breathing. Failure of autoresuscitation may underlie many cases of sudden infant death syndrome, or SIDS (also known as “cot death” or “crib death”). SIDS is the leading cause of death in young infants in the western world, and many infants who die from SIDS show abnormalities in the brain cells that produce a chemical called serotonin. Evidence suggests that serotonin helps control breathing. This raised the question: does the autoresuscitation recovery response rely on serotonin-producing neurons? To find out, Dosumu-Johnson et al. used one-week-old mouse pups that had been genetically engineered to respond to an injected drug by rapidly inhibiting their serotonin neurons. These animals are about the same age in mouse terms as infants at greatest risk for SIDS (~2-4 months of age). Inhibiting serotonin neurons made it harder for the mouse pups to recover from artificially induced apneas. Although their heart rate showed largely normal recovery – at least at first – their breathing did not. They took fewer gasps, and were more likely to die following such episodes. These findings shed new light on how young animals control their breathing and heart rate when mounting an autoresuscitation recovery from an apnea. The observed uncoupling of breathing and heart rate recovery responses suggests that different brain cells and circuits control the two. The results also suggest that abnormalities in the activity of serotonin neurons may make infants more susceptible to SIDS. As well as offering a possible explanation to families who have lost a child to SIDS, these findings could be used to develop screening tools to identify other infants at risk. They also point to potential cellular targets for drugs that could ultimately help prevent further cases.
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Affiliation(s)
| | - Andrea E Cocoran
- Department of Molecular & Systems Biology, The Geisel School of Medicine at Dartmouth, Hanover, United States
| | - YoonJeung Chang
- Department of Genetics, Harvard Medical School, Boston, United States
| | - Eugene Nattie
- Department of Molecular & Systems Biology, The Geisel School of Medicine at Dartmouth, Hanover, United States
| | - Susan M Dymecki
- Department of Genetics, Harvard Medical School, Boston, United States
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21
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Mouradian GC, Hodges MR. The central role of serotonin. eLife 2018; 7:e42291. [PMID: 30350782 PMCID: PMC6199130 DOI: 10.7554/elife.42291] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2018] [Accepted: 10/10/2018] [Indexed: 11/24/2022] Open
Abstract
The neurotransmitter serotonin helps to co-ordinate the respiratory and cardiovascular responses of newborns to oxygen deprivation.
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Affiliation(s)
- Gary C Mouradian
- Department of PhysiologyMedical College of WisconsinMilwaukeeUnited States
| | - Matthew R Hodges
- Department of PhysiologyMedical College of WisconsinMilwaukeeUnited States
- Neuroscience Research CenterMedical College of WisconsinMilwaukeeUnited States
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22
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Lee SY, Sirieix CM, Nattie E, Li A. Pre- and early postnatal nicotine exposure exacerbates autoresuscitation failure in serotonin-deficient rat neonates. J Physiol 2018; 596:5977-5991. [PMID: 30008184 DOI: 10.1113/jp275885] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2018] [Accepted: 05/22/2018] [Indexed: 11/08/2022] Open
Abstract
KEY POINTS Sudden infant death syndrome (SIDS) is one of the leading causes of death during the first year of life and abnormalities linked to serotonin (5-HT) have been identified in many SIDS cases. Cigarette smoking and associated exogenous stressors, e.g. developmental nicotine exposure, may compound these serotonergic defects and any associated defects in cardiorespiratory function. Using neonatal rodent pups subjected to medullary 5-HT deficiency and perinatal nicotine exposure, we examined the impact of this interplay of factors on the neonates' ability to autoresuscitate at specific ages. In perinatal nicotine-exposed 5-HT deficient pups, impaired autoresuscitation along with significantly delayed post-anoxic recovery of normal breathing and heart rate was observed at postnatal day 10 (P10). We found that the interaction between 5-HT deficiency and perinatal nicotine exposure can significantly increase pups' vulnerability to environmental stressors and exacerbate defects in cardiorespiratory protective reflexes to repetitive anoxia during the development period. ABSTRACT Cigarette smoking during pregnancy increases the risk of sudden infant death syndrome (SIDS), and nicotine replacements, a key ingredient of cigarettes, have been recently prescribed to women who wish to quit smoking during their pregnancy. Serotonin (5-HT) abnormalities have been consistently identified in many SIDS cases. Here we investigated the effects of perinatal nicotine exposure in mild 5-HT deficiency rat neonates on autoresuscitation, a protective cardiorespiratory reflex. The mild 5-HT deficiency was induced by a maternal tryptophan-deficient diet, and nicotine was delivered from embryonic day (E) 4 to postnatal day (P) 10 at 6 mg kg-1 day-1 through an osmotic pump. In P10 rats, nicotine exposure exacerbates autoresuscitation failure (mortality) in mildly 5-HT-deficient rats to a greater extent than in controls (P = 0.029). The recovery of eupnoea and heart rate to baseline values following repetitive anoxic events (which elicit an apnoea accompanied by a bradycardia) is significantly delayed in 5-HT-deficient rats treated with nicotine, making them more susceptible to failure of autoresuscitation (eupnoea recovery: P = 0.0053; heart rate recovery: P = < 0.0001). Neither 5-HT deficiency nor nicotine exposure alone appears to affect the ability to autoresuscitate significantly when compared among the four treatments. The increased vulnerability to environmental stressors, e.g. severe hypoxia, asphyxia, or anoxia, in these nicotine-exposed 5-HT-deficient neonates during postnatal developmental period is evident.
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Affiliation(s)
- Stella Y Lee
- Department of Physiology and Neurobiology, Geisel school of Medicine at Dartmouth, Lebanon, NH, 03756, USA
| | - Chrystelle M Sirieix
- Department of Physiology and Neurobiology, Geisel school of Medicine at Dartmouth, Lebanon, NH, 03756, USA
| | - Eugene Nattie
- Department of Physiology and Neurobiology, Geisel school of Medicine at Dartmouth, Lebanon, NH, 03756, USA
| | - Aihua Li
- Department of Physiology and Neurobiology, Geisel school of Medicine at Dartmouth, Lebanon, NH, 03756, USA.,Department of Molecular and Systems Biology, Geisel school of Medicine at Dartmouth, Lebanon, NH, 03756, USA
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23
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Barrett KT, Daubenspeck JA, Wilson RJA. Pituitary adenylate cyclase-activating polypeptide drives cardiorespiratory responses to heat stress in neonatal mice. Am J Physiol Regul Integr Comp Physiol 2017; 313:R385-R394. [DOI: 10.1152/ajpregu.00118.2017] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2017] [Revised: 06/05/2017] [Accepted: 06/27/2017] [Indexed: 11/22/2022]
Abstract
The neuropeptide pituitary adenylate cyclase-activating polypeptide (PACAP) has emerged as a principal and rate-limiting regulator of physiological stress responses in adult rodents and has been implicated in sudden infant death syndrome (SIDS). Recent studies show that PACAP plays a role in neonatal cardiorespiratory responses to hypoxia, hypercapnia, and hypothermia, but not hyperthermia, which is often associated with SIDS. Here we tested the hypothesis that, consistent with a role in SIDS, PACAP is involved in regulating the neonatal cardiorespiratory responses to severe heat. To address this, we used head-out plethysmography and surface ECG electrodes to study the cardiorespiratory physiology of conscious neonatal PACAP-null and wild-type mice at ambient temperatures of 32°C (baseline) and 40°C (heat stress). We also assessed body surface temperature as an indicator of cutaneous heat loss. Our results show that wild-type neonatal mice respond to heat stress by increasing ventilation ( P = 0.007) and associated expired CO2 ( P = 0.041), heart rate ( P < 0.001), and cutaneous heat loss ( P < 0.001). In PACAP-null neonates, this heat response is impaired, as indicated by a decrease in ventilation ( P = 0.04) and associated expired CO2 ( P = 0.006) and a blunted increase in heart rate ( P = 0.001) and cutaneous heat loss ( P = 0.0002). In addition, heart rate variability at baseline was lower in PACAP-null neonates than wild-type controls ( P < 0.01). These results suggest that, during heat stress, PACAP is important for neonatal cardiorespiratory responses that help regulate body temperature. Abnormal PACAP regulation could, therefore, contribute to neonatal disorders in which the autonomic response to stress is impaired, such as SIDS.
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Affiliation(s)
- Karlene T. Barrett
- Department of Physiology and Pharmacology, Hotchkiss Brain Institute and Alberta Children’s Hospital Research Institute, University of Calgary, Calgary, Alberta, Canada; and
| | - John A. Daubenspeck
- Department of Physiology and Neurobiology, Geisel School of Medicine at Dartmouth, Hanover, New Hampshire
| | - Richard J. A. Wilson
- Department of Physiology and Pharmacology, Hotchkiss Brain Institute and Alberta Children’s Hospital Research Institute, University of Calgary, Calgary, Alberta, Canada; and
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24
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Donnelly WT, Xia L, Bartlett D, Leiter JC. Activation of serotonergic neurons in the medullary caudal raphe shortens the laryngeal chemoreflex in anaesthetized neonatal rats. Exp Physiol 2017; 102:1007-1018. [PMID: 28675564 DOI: 10.1113/ep086082] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2016] [Accepted: 05/25/2017] [Indexed: 12/29/2022]
Abstract
NEW FINDINGS What is the central question of this study? Does activation of serotonergic neurons in the caudal medullary raphe, some of which project to the nucleus of the solitary tract, shorten the laryngeal chemoreflex? What is the main finding and its importance? We found that serotonin originating from neurons in the caudal raphe acts through a 5-HT3 receptor located in the nucleus of the solitary tract to terminate reflex apnoea. Failure or deficiency of this arousal-related process is likely to be relevant to the pathogenesis of sudden infant death syndrome. Failure to terminate apnoea and arouse is likely to contribute to sudden infant death syndrome (SIDS). Serotonin is deficient in the brainstems of babies who have died of SIDS. We tested the hypothesis that activation of serotoninergic neurons in the caudal medullary raphe, some of which project to the nucleus of the solitary tract (NTS), would shorten the laryngeal chemoreflex (LCR). We studied anaesthetized neonatal rat pups between postnatal days 9 and 17. We injected 5-40 μl of water into the larynx to elicit the LCR and measured the duration of respiratory disruption. Microinjection of 50 nl of 100 μm AMPA into the caudal medullary raphe shortened the apnoeas (P < 0.001) and respiratory inhibition (P < 0.005) associated with the LCR. When 50 nl of 30 mm ondansetron, a 5-HT3 antagonist, was microinjected bilaterally into the NTS, AMPA microinjected into the caudal raphe no longer shortened the LCR. After bilateral microinjection of vehicle into the NTS, AMPA microinjection into the caudal raphe significantly shortened the LCR. AMPA, a glutamate receptor agonist, may activate many neurons within the caudal raphe, but blocking the 5-HT3 receptor-dependent responses in the NTS prevented the shortening of the LCR associated with AMPA microinjections into the caudal raphe. Thus, serotonin originating from neurons in the caudal raphe acts through a 5-HT3 receptor located in the NTS to terminate or shorten the LCR. Serotonin is deficient in the brainstems of babies who have died of SIDS, and deficient serotonergic termination of apnoea is likely to be relevant to the pathogenesis of SIDS.
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Affiliation(s)
- William T Donnelly
- Department of Molecular and Systems Biology, Geisel School of Medicine at Dartmouth, Lebanon, NH, USA
| | - Luxi Xia
- Department of Molecular and Systems Biology, Geisel School of Medicine at Dartmouth, Lebanon, NH, USA
| | - Donald Bartlett
- Department of Molecular and Systems Biology, Geisel School of Medicine at Dartmouth, Lebanon, NH, USA
| | - J C Leiter
- Department of Molecular and Systems Biology, Geisel School of Medicine at Dartmouth, Lebanon, NH, USA
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Sun JJ, Nanu R, Ray RS. A low cost, simplified, and scaleable pneumotachograph and face mask for neonatal mouse respiratory measurements. J Pharmacol Toxicol Methods 2017; 86:1-11. [PMID: 28213294 DOI: 10.1016/j.vascn.2017.02.019] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2016] [Revised: 02/07/2017] [Accepted: 02/13/2017] [Indexed: 11/29/2022]
Abstract
INTRODUCTION Neonatal respiratory disorders are a leading cause of perinatal mortality due to complications resulting from premature births and prenatal exposure to drugs of abuse, but optimal treatments for these symptoms are still unclear due to a variety of confounds and risk factors. Mouse models present an opportunity to study the underlying mechanisms and efficacy of potential treatments of these conditions with controlled variables. However, measuring respiration in newborn mice is difficult and commercial components are expensive and often require modification, creating a barrier and limiting our understanding of the short and long-term effects of birth complications on respiratory function. METHODS Here, we present an inexpensive and simple flow through pneumotachograph and face mask design that can be easily scaled for parallel, high-throughput assays measuring respiration in neonatal mouse pups. The final apparatus consists of three main parts: a water-jacketed chamber, an integrated support tray for the pup, and a pneumotachograph consisting of a two side-arm air channel that is attached to a pressure transducer. RESULTS The pneumotach showed a linear response and clean, steady respiratory traces in which apneas and sighs were clearly visible. Administration of caffeine in P0.5 CD1 wildtype neonates resulted in an increase in tidal volume, minute ventilation, and minute ventilation normalized to oxygen consumption as well as a decrease in periodic instability. DISCUSSION The described methods offer a relatively simple and inexpensive approach to constructing a pneumotachograph for non-invasive measurements of neonatal mouse respiration, enhancing accessibility and enabling the high-throughput and parallel characterizations of neonatal respiratory disorders and potential pharmacological therapies.
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Affiliation(s)
- Jenny J Sun
- Baylor College of Medicine, Department of Neuroscience, Room T707, 1 Baylor Plaza, Houston, TX 77030, United States.
| | - Roshan Nanu
- Baylor College of Medicine, Department of Neuroscience, Room T707, 1 Baylor Plaza, Houston, TX 77030, United States
| | - Russell S Ray
- Baylor College of Medicine, Department of Neuroscience, Room T703, 1 Baylor Plaza, Houston, TX 77030, United States.
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Activity of Tachykinin1-Expressing Pet1 Raphe Neurons Modulates the Respiratory Chemoreflex. J Neurosci 2017; 37:1807-1819. [PMID: 28073937 DOI: 10.1523/jneurosci.2316-16.2016] [Citation(s) in RCA: 30] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2016] [Revised: 11/30/2016] [Accepted: 12/30/2016] [Indexed: 11/21/2022] Open
Abstract
Homeostatic control of breathing, heart rate, and body temperature relies on circuits within the brainstem modulated by the neurotransmitter serotonin (5-HT). Mounting evidence points to specialized neuronal subtypes within the serotonergic neuronal system, borne out in functional studies, for the modulation of distinct facets of homeostasis. Such functional differences, read out at the organismal level, are likely subserved by differences among 5-HT neuron subtypes at the cellular and molecular levels, including differences in the capacity to coexpress other neurotransmitters such as glutamate, GABA, thyrotropin releasing hormone, and substance P encoded by the Tachykinin-1 (Tac1) gene. Here, we characterize in mice a 5-HT neuron subtype identified by expression of Tac1 and the serotonergic transcription factor gene Pet1, referred to as the Tac1-Pet1 neuron subtype. Transgenic cell labeling showed Tac1-Pet1 soma resident largely in the caudal medulla. Chemogenetic [clozapine-N-oxide (CNO)-hM4Di] perturbation of Tac1-Pet1 neuron activity blunted the ventilatory response of the respiratory CO2 chemoreflex, which normally augments ventilation in response to hypercapnic acidosis to restore normal pH and PCO2Tac1-Pet1 axonal boutons were found localized to brainstem areas implicated in respiratory modulation, with highest density in motor regions. These findings demonstrate that the activity of a Pet1 neuron subtype with the potential to release both 5-HT and substance P is necessary for normal respiratory dynamics, perhaps via motor outputs that engage muscles of respiration and maintain airway patency. These Tac1-Pet1 neurons may act downstream of Egr2-Pet1 serotonergic neurons, which were previously established in respiratory chemoreception, but do not innervate respiratory motor nuclei.SIGNIFICANCE STATEMENT Serotonin (5-HT) neurons modulate physiological processes and behaviors as diverse as body temperature, respiration, aggression, and mood. Using genetic tools, we characterize a 5-HT neuron subtype defined by expression of Tachykinin1 and Pet1 (Tac1-Pet1 neurons), mapping soma localization to the caudal medulla primarily and axonal projections to brainstem motor nuclei most prominently, and, when silenced, observed blunting of the ventilatory response to inhaled CO2Tac1-Pet1 neurons thus appear distinct from and contrast previously described Egr2-Pet1 neurons, which project primarily to chemosensory integration centers and are themselves chemosensitive.
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Ramirez S, Allen T, Villagracia L, Chae Y, Ramirez JM, Rubens DD. Inner ear lesion and the differential roles of hypoxia and hypercarbia in triggering active movements: Potential implication for the Sudden Infant Death Syndrome. Neuroscience 2016; 337:9-16. [PMID: 27634772 DOI: 10.1016/j.neuroscience.2016.08.054] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2016] [Revised: 08/29/2016] [Accepted: 08/31/2016] [Indexed: 01/12/2023]
Abstract
Infants that succumb to Sudden Infant Death Syndrome (SIDS) have been identified with inner ear dysfunction (IED) at birth and on autopsy. We previously investigated whether IED could play a mechanistic role in SIDS. We discovered that animals with IED displayed significant suppression of movement arousal to a hypoxic-hypercarbic gas mixture under light anesthesia. In the current study we investigated the role of each gas in triggering movements and the response to hypercarbia during natural sleep without anesthesia. Seventeen-day-old CD-1 mice received intra-tympanic gentamicin (IT-Gent) injections to precipitate IED. The movement response to hypercarbia, hypoxia and hypoxia-hypercarbia was compared to controls under light anesthesia. Hypercarbia did not stimulate vigorous movements in any animals under either sleep condition. Hypoxia triggered vigorous movements in controls (p<0.05) and a decreased response in IT-Gent animals under light anesthesia. This contrasted with combined hypoxia-hypercarbia, in which IT-Gent animals displaced significantly suppressed movements compared to controls (p<0.05). Our findings portray that a degree of intact inner ear function is necessary for instigating the movement response. Additionally, hypoxia is the trigger for the movement response while carbon dioxide (CO2) suppresses it. The finding that carbon dioxide did not stimulate movement during natural sleep is an important finding. This contrasts with other studies that have identified hypercarbia as an arousal stimulus with EEG. Further studies are warranted to evaluate the precise role of the inner ear in the movement response and potential association with SIDS. The early detection of IED in SIDS predisposed cases could be invaluable.
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Affiliation(s)
- Sanja Ramirez
- Center for Integrative Brain Research, Seattle Children's Research Institute, 1900 Ninth Avenue, Seattle, WA 98101, United States
| | - Travis Allen
- Department of Anesthesia, Seattle Children's Hospital, 4800 Sandpoint Way NE, Seattle, WA 98105, United States; Center for Integrative Brain Research, Seattle Children's Research Institute, 1900 Ninth Avenue, Seattle, WA 98101, United States; Department of Anesthesia, University of Washington, Seattle, WA, United States
| | - Lindsay Villagracia
- Center for Integrative Brain Research, Seattle Children's Research Institute, 1900 Ninth Avenue, Seattle, WA 98101, United States
| | - Yooree Chae
- Center for Integrative Brain Research, Seattle Children's Research Institute, 1900 Ninth Avenue, Seattle, WA 98101, United States
| | - Jan M Ramirez
- Center for Integrative Brain Research, Seattle Children's Research Institute, 1900 Ninth Avenue, Seattle, WA 98101, United States; Department of Pediatrics, University of Washington, Seattle, WA, United States
| | - Daniel D Rubens
- Department of Anesthesia, Seattle Children's Hospital, 4800 Sandpoint Way NE, Seattle, WA 98105, United States; Center for Integrative Brain Research, Seattle Children's Research Institute, 1900 Ninth Avenue, Seattle, WA 98101, United States; Department of Anesthesia, University of Washington, Seattle, WA, United States.
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Barrett KT, Wilson RJA, Scantlebury MH. TRPV1 deletion exacerbates hyperthermic seizures in an age-dependent manner in mice. Epilepsy Res 2016; 128:27-34. [PMID: 27810513 DOI: 10.1016/j.eplepsyres.2016.10.016] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2016] [Revised: 09/07/2016] [Accepted: 10/24/2016] [Indexed: 01/19/2023]
Abstract
Febrile seizures (FS) are the most common seizure disorder to affect children. Although there is mounting evidence to support that FS occur when children have fever-induced hyperventilation leading to respiratory alkalosis, the underlying mechanisms of hyperthermia-induced hyperventilation and links to FS remain poorly understood. As transient receptor potential vanilloid-1 (TRPV1) receptors are heat-sensitive, play an important role in adult thermoregulation and modulate respiratory chemoreceptors, we hypothesize that TRPV1 activation is important for hyperthermia-induced hyperventilation leading to respiratory alkalosis and decreased FS thresholds, and consequently, TRPV1 KO mice will be relatively protected from hyperthermic seizures. To test our hypothesis we subjected postnatal (P) day 8-20 TRPV1 KO and C57BL/6 control mice to heated dry air. Seizure threshold temperature, latency and the rate of rise of body temperature during hyperthermia were assessed. At ages where differences in seizure thresholds were identified, head-out plethysmography was used to assess breathing and the rate of expired CO2 in response to hyperthermia, to determine if the changes in seizure thresholds were related to respiratory alkalosis. Paradoxically, we observed a pro-convulsant effect of TRPV1 deletion (∼4min decrease in seizure latency), and increased ventilation in response to hyperthermia in TRPV1 KO compared to control mice at P20. This pro-convulsant effect of TRPV1 absence was not associated with an increased rate of expired CO2, however, these mice had a more rapid rise in body temperature following exposure to hyperthermia than controls, and the expected linear relationship between body weight and seizure latency was absent. Based on these findings, we conclude that deletion of the TRPV1 receptor prevents reduction in hyperthermic seizure susceptibility in older mouse pups, via a mechanism that is independent of hyperthermia-induced respiratory alkalosis, but possibly involves impaired development of thermoregulatory mechanisms, although at present the mechanism remain unknown.
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Affiliation(s)
- Karlene T Barrett
- Department of Pediatrics, University of Calgary, 3330 Hospital Drive NW, Calgary, AB, T2N 4N1, Canada; Alberta Children's Hospital Research Institute, University of Calgary, 3330 Hospital Drive NW, Calgary, AB, T2N 4N1, Canada
| | - Richard J A Wilson
- Alberta Children's Hospital Research Institute, University of Calgary, 3330 Hospital Drive NW, Calgary, AB, T2N 4N1, Canada; Department of Physiology and Pharmacology, University of Calgary, 3330 Hospital Drive NW, Calgary, AB, T2N 4N1, Canada; Hotchkiss Brain Institute, University of Calgary, 3330 Hospital Drive NW, Calgary, AB, T2N 4N1, Canada
| | - Morris H Scantlebury
- Department of Pediatrics, University of Calgary, 3330 Hospital Drive NW, Calgary, AB, T2N 4N1, Canada; Alberta Children's Hospital Research Institute, University of Calgary, 3330 Hospital Drive NW, Calgary, AB, T2N 4N1, Canada; Department of Clinical Neuroscience, University of Calgary, 3330 Hospital Drive NW, Calgary, AB, T2N 4N1, Canada.
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McDonald FB, Chandrasekharan K, Wilson RJA, Hasan SU. Interactive effects of maternal cigarette smoke, heat stress, hypoxia, and lipopolysaccharide on neonatal cardiorespiratory and cytokine responses. Am J Physiol Regul Integr Comp Physiol 2016; 311:R1113-R1124. [PMID: 27733384 DOI: 10.1152/ajpregu.00062.2016] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2016] [Revised: 10/03/2016] [Accepted: 10/06/2016] [Indexed: 11/22/2022]
Abstract
Maternal cigarette smoke (CS) exposure exhibits a strong epidemiological association with Sudden Infant Death Syndrome, but other environmental stressors, including infection, hyperthermia, and hypoxia, have also been postulated as important risk factors. This study examines whether maternal CS exposure causes maladaptations within homeostatic control networks by influencing the response to lipopolysaccharide, heat stress, and/or hypoxia in neonatal rats. Pregnant dams were exposed to CS or parallel sham treatments daily for the length of gestation. Offspring were studied at postnatal days 6-8 at ambient temperatures (Ta) of 33°C or 38°C. Within each group, rats were allocated to control, saline, or LPS (200 µg/kg) treatments. Cardiorespiratory patterns were examined using head-out plethysmography and ECG surface electrodes during normoxia and hypoxia (10% O2). Serum cytokine concentrations were quantified from samples taken at the end of each experiment. Our results suggest maternal CS exposure does not alter minute ventilation (V̇e) or heart rate (HR) response to infection or high temperature, but independently increases apnea frequency. CS also primes the inflammatory system to elicit a stronger cytokine response to bacterial insult. High Ta independently depresses V̇e but augments the hypoxia-induced increase in V̇e Moreover, higher Ta increases HR during normoxia and hypoxia, and in the presence of an immune challenge, increases HR during normoxia, and reduces the increase normally associated with hypoxia. Thus, while most environmental risk factors increase the burden on the cardiorespiratory system in early life, hyperthermia and infection blunt the normal HR response to hypoxia, and gestational CS independently destabilizes breathing by increasing apneas.
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Affiliation(s)
- Fiona B McDonald
- Department of Physiology and Pharmacology, Hotchkiss Brain Institute and Alberta Children's Hospital Research Institute, Faculty of Medicine, University of Calgary, Alberta, Canada; and
| | - Kumaran Chandrasekharan
- Section of Neonatal-Perinatal Medicine, Department of Pediatrics, Faculty of Medicine, Health Sciences Centre, University of Calgary, Alberta, Canada
| | - Richard J A Wilson
- Department of Physiology and Pharmacology, Hotchkiss Brain Institute and Alberta Children's Hospital Research Institute, Faculty of Medicine, University of Calgary, Alberta, Canada; and
| | - Shabih U Hasan
- Section of Neonatal-Perinatal Medicine, Department of Pediatrics, Faculty of Medicine, Health Sciences Centre, University of Calgary, Alberta, Canada
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McDonald FB, Chandrasekharan K, Wilson RJA, Hasan SU. Cardiorespiratory control and cytokine profile in response to heat stress, hypoxia, and lipopolysaccharide (LPS) exposure during early neonatal period. Physiol Rep 2016; 4:4/2/e12688. [PMID: 26811056 PMCID: PMC4760388 DOI: 10.14814/phy2.12688] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
Sudden infant death syndrome (SIDS) is one of the most common causes of postneonatal infant mortality in the developed world. An insufficient cardiorespiratory response to multiple environmental stressors (such as prone sleeping positioning, overwrapping, and infection), during a critical period of development in a vulnerable infant, may result in SIDS. However, the effect of multiple risk factors on cardiorespiratory responses has rarely been tested experimentally. Therefore, this study aimed to quantify the independent and possible interactive effects of infection, hyperthermia, and hypoxia on cardiorespiratory control in rats during the neonatal period. We hypothesized that lipopolysaccharide (LPS) administration will negatively impact cardiorespiratory responses to increased ambient temperature and hypoxia in neonatal rats. Sprague-Dawley neonatal rat pups were studied at postnatal day 6-8. Rats were examined at an ambient temperature of 33°C or 38°C. Within each group, rats were allocated to control, saline, or LPS (200 μg/kg) treatments. Cardiorespiratory and thermal responses were recorded and analyzed before, during, and after a hypoxic exposure (10% O2). Serum samples were taken at the end of each experiment to measure cytokine concentrations. LPS significantly increased cytokine concentrations (such as TNFα, IL-1β, MCP-1, and IL-10) compared to control. Our results do not support a three-way interaction between experimental factors on cardiorespiratory control. However, independently, heat stress decreased minute ventilation during normoxia and increased the hypoxic ventilatory response. Furthermore, LPS decreased hypoxia-induced tachycardia. Herein, we provide an extensive serum cytokine profile under various experimental conditions and new evidence that neonatal cardiorespiratory responses are adversely affected by dual interactions of environmental stress factors.
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Affiliation(s)
- Fiona B McDonald
- Department of Physiology and Pharmacology, Hotchkiss Brain Institute & Alberta Children's Hospital Research Institute, Faculty of Medicine, University of Calgary, Calgary, Alberta, Canada
| | - Kumaran Chandrasekharan
- Fetal and Neonatal Physiology, Department of Pediatrics, Faculty of Medicine B271, Health Sciences Center, University of Calgary, Calgary, Alberta, Canada
| | - Richard J A Wilson
- Department of Physiology and Pharmacology, Hotchkiss Brain Institute & Alberta Children's Hospital Research Institute, Faculty of Medicine, University of Calgary, Calgary, Alberta, Canada
| | - Shabih U Hasan
- Fetal and Neonatal Physiology, Department of Pediatrics, Faculty of Medicine B271, Health Sciences Center, University of Calgary, Calgary, Alberta, Canada
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Partial Raphe Dysfunction in Neurotransmission Is Sufficient to Increase Mortality after Anoxic Exposures in Mice at a Critical Period in Postnatal Development. J Neurosci 2016; 36:3943-53. [PMID: 27053202 DOI: 10.1523/jneurosci.1796-15.2016] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2015] [Accepted: 02/26/2016] [Indexed: 12/22/2022] Open
Abstract
UNLABELLED Sudden infant death syndrome (SIDS) cases often have abnormalities of the brainstem raphe serotonergic (5-HT) system. We hypothesize that raphe dysfunction contributes to a failure to autoresuscitate from multiple hypoxic events, leading to SIDS. We studied autoresuscitation in two transgenic mouse models in which exocytic neurotransmitter release was impaired via conditional expression of the light chain from tetanus toxin (tox) in raphe neurons expressing serotonergic bacterial artificial chromosome drivers Pet1 or Slc6a4. These used recombinase drivers targeted different portions of medullary raphe serotonergic, tryptophan hydroxylase 2 (Tph2)(+) neurons by postnatal day (P) 5 through P12: approximately one-third in triple transgenic Pet1::Flpe, hβactin::cre, RC::PFtox mice; approximately three-fourths inSlc6a4::cre, RC::Ptox mice; with the first model capturing a near equal number of Pet1(+),Tph2(+) versus Pet1(+),Tph2(low or negative) raphe cells. At P5, P8, and P12, "silenced" mice and controls were exposed to five, ∼37 s bouts of anoxia. Mortality was 5-10 times greater in "silenced" pups compared with controls at P5 and P8 (p = 0.001) but not P12, with cumulative survival not differing between experimental transgenic models. "Silenced" pups that eventually died took longer to initiate gasping (p = 0.0001), recover heart rate (p = 0.0001), and recover eupneic breathing (p = 0.011) during the initial anoxic challenges. Variability indices for baseline breathing distinguished "silenced" from controls but did not predict mortality. We conclude that dysfunction of even a portion of the raphe, as observed in many SIDS cases, can impair ability to autoresuscitate at critical periods in postnatal development and that baseline indices of breathing variability can identify mice at risk. SIGNIFICANCE STATEMENT Many sudden infant death syndrome (SIDS) cases exhibit a partial (∼26%) brainstem serotonin deficiency. Using recombinase drivers, we targeted different fractions of serotonergic and raphe neurons in mice for tetanus toxin light chain expression, which prevented vesicular neurotransmitter release. In one model, approximately one-third of medullary Tph2(+) neurons are silenced by postnatal (P) days 5 and 12, along with some Pet1(+),Tph2(low or negative) raphe cells; in the other, approximately three-fourths of medullary Tph2(+) neurons, also with some Tph2(low or negative) cells. Both models demonstrated excessive mortality to anoxia (a postulated SIDS stressor) at P5 and P8. We demonstrated fatal vulnerability to anoxic stress at a specific time in postnatal life induced by a partial defect in raphe function. This models features of SIDS.
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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: 17] [Impact Index Per Article: 2.1] [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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Goldstein RD, Kinney HC, Willinger M. Sudden Unexpected Death in Fetal Life Through Early Childhood. Pediatrics 2016; 137:e20154661. [PMID: 27230764 PMCID: PMC4894250 DOI: 10.1542/peds.2015-4661] [Citation(s) in RCA: 35] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Accepted: 03/07/2016] [Indexed: 11/24/2022] Open
Abstract
In March 2015, the Eunice Kennedy Shriver National Institute of Child Health and Human Development held a workshop entitled "Sudden Unexpected Death in Fetal Life Through Early Childhood: New Opportunities." Its objective was to advance efforts to understand and ultimately prevent sudden deaths in early life, by considering their pathogenesis as a potential continuum with some commonalities in biological origins or pathways. A second objective of this meeting was to highlight current issues surrounding the classification of sudden infant death syndrome (SIDS), and the implications of variations in the use of the term "SIDS" in forensic practice, and pediatric care and research. The proceedings reflected the most current knowledge and understanding of the origins and biology of vulnerability to sudden unexpected death, and its environmental triggers. Participants were encouraged to consider the application of new technologies and "omics" approaches to accelerate research. The major advances in delineating the intrinsic vulnerabilities to sudden death in early life have come from epidemiologic, neural, cardiac, metabolic, genetic, and physiologic research, with some commonalities among cases of unexplained stillbirth, SIDS, and sudden unexplained death in childhood observed. It was emphasized that investigations of sudden unexpected death are inconsistent, varying by jurisdiction, as are the education, certification practices, and experience of death certifiers. In addition, there is no practical consensus on the use of "SIDS" as a determination in cause of death. Major clinical, forensic, and scientific areas are identified for future research.
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Affiliation(s)
- Richard D Goldstein
- Department of Psychosocial Oncology and Palliative Care, Dana-Farber Cancer Institute, Department of Medicine, and
| | - Hannah C Kinney
- Department of Pathology, Boston Children's Hospital, Harvard Medical School, Boston, Massachusetts; and
| | - Marian Willinger
- Pregnancy and Perinatology Branch, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland
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Thach BT. Potential Central Nervous System Involvement in Sudden Unexpected Infant Deaths and the Sudden Infant Death Syndrome. Compr Physiol 2016; 5:1061-8. [PMID: 26140709 DOI: 10.1002/cphy.c130052] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Sudden unexpected infant death (SUID) in infancy which includes Sudden Infant Death Syndrome (SIDS) is the commonest diagnosed cause of death in the United States for infants 1 month to 1 year of age. Central nervous system mechanisms likely contribute to many of these deaths. We discuss some of these including seizure disorders, prolonged breath holding, arousal from sleep and its habituation, laryngeal reflex apnea potentiated by upper airway infection, and failure of brainstem-mediated autoresuscitation. In the conclusions section, we speculate how lives saved through back sleeping might result in later developmental problems in certain infants who otherwise might have died while sleeping prone.
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Affiliation(s)
- Bradley T Thach
- Professor of Pediatrics Emeritus, Washington University School of Medicine, St. Louis, Missouri, USA
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35
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Givan SA, Cummings KJ. Intermittent severe hypoxia induces plasticity within serotonergic and catecholaminergic neurons in the neonatal rat ventrolateral medulla. J Appl Physiol (1985) 2016; 120:1277-87. [PMID: 26968026 DOI: 10.1152/japplphysiol.00048.2016] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2016] [Accepted: 03/09/2016] [Indexed: 11/22/2022] Open
Abstract
5-HT neurons contribute to autoresuscitation and survival during intermittent severe hypoxia (IsH). In adults, catecholaminergic neurons in the ventrolateral medulla (VLM) contribute to the autonomic response to hypoxia. We hypothesized that 1) catecholaminergic neurons in the neonatal VLM are activated following IsH, 2) this activation is compromised following an acute loss of brain stem 5-HT, and 3) IsH induces cellular and/or transcriptomic plasticity within catecholaminergic and serotonergic neurons that are within or project to the VLM, respectively. To test these hypotheses, we treated rat pups with 6-fluorotryptophan, a tryptophan hydroxylase (TPH) inhibitor, and then exposed treated and vehicle controls to IsH or air. Along with immunohistochemistry to detect tyrosine hydroxylase (TH)- or Fos-positive neurons, we used RNA sequencing to resolve the effects of IsH and 5-HT deficiency on the expression of serotonergic and catecholaminergic system genes in the VLM. 5-HT deficiency compromised autoresuscitation and survival. IsH significantly increased the number of identifiable TH-positive VLM neurons, an effect enhanced by 5-HT deficiency (P = 0.003). Contrary to our hypothesis, 5-HT-deficient pups had significantly more Fos-positive neurons following IsH (P = 0.008) and more activated TH-positive neurons following IsH or air (P = 0.04). In both groups the expression of the 5-HT transporter and TPH2 was increased following IsH. In 5-HT-deficient pups, the expression of the inhibitory 5-HT1A receptor was decreased following IsH, while the expression of DOPA decarboxylase was increased. These data show that the serotonergic and catecholaminergic systems in the VLM of the neonatal rat are dynamically upregulated by IsH, potentially adapting cardiorespiratory responses to severe hypoxia.
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Affiliation(s)
- Scott A Givan
- Department of Molecular Microbiology and Immunology, Informatics Research Core Facility, University of Missouri, Columbia, Missouri; and
| | - Kevin J Cummings
- Department of Biomedical Sciences, University of Missouri, Columbia, Missouri
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36
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MacFarlane PM, Mayer CA, Litvin DG. Microglia modulate brainstem serotonergic expression following neonatal sustained hypoxia exposure: implications for sudden infant death syndrome. J Physiol 2016; 594:3079-94. [PMID: 26659585 DOI: 10.1113/jp271845] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2015] [Accepted: 12/07/2015] [Indexed: 11/08/2022] Open
Abstract
KEY POINTS Neonatal sustained hypoxia exposure modifies brainstem microglia and serotonin expression. The altered brainstem neurochemistry is associated with impaired ventilatory responses to acute hypoxia and mortality. The deleterious effects of sustained hypoxia exposure can be prevented by an inhibitor of activated microglia. These observations demonstrate a potential cause of the brainstem serotonin abnormalities thought to be involved in sudden infant death syndrome. ABSTRACT We showed previously that the end of the second postnatal week (days P11-15) represents a period of development during which the respiratory neural control system exhibits a heightened vulnerability to sustained hypoxia (SH, 11% O2 , 5 days) exposure. In the current study, we investigated whether the vulnerability to SH during the same developmental time period is associated with changes in brainstem serotonin (5-HT) expression and whether it can be prevented by the microglia inhibitor minocycline. Using whole-body plethysmography, SH attenuated the acute (5 min) hypoxic ventilatory response (HVR) and caused a high incidence of mortality compared to normoxia rats. SH also increased microglia cell numbers and decreased 5-HT immunoreactivity in the nucleus of the solitary tract (nTS) and dorsal motor nucleus of the vagus (DMNV). The attenuated HVR, mortality, and changes in nTS and DMNV immunoreactivity was prevented by minocycline (25 mg kg(-1) /2 days during SH). These data demonstrate that the 5-HT abnormalities in distinct respiratory neural control regions can be initiated by prolonged hypoxia exposure and may be modulated by microglia activity. These observations share several commonalities with the risk factors thought to underlie the aetiology of sudden infant death syndrome, including: (1) a vulnerable neonate; (2) a critical period of development; (3) evidence of hypoxia; (4) brainstem gliosis (particularly the nTS and DMNV); and (5) 5-HT abnormalities.
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Affiliation(s)
- P M MacFarlane
- Department of Pediatrics, Rainbow Babies & Children's Hospital, Case Western Reserve University, Cleveland, OH, 44106, USA
| | - C A Mayer
- Department of Pediatrics, Rainbow Babies & Children's Hospital, Case Western Reserve University, Cleveland, OH, 44106, USA
| | - D G Litvin
- Department of Physiology and Biophysics, Case Western Reserve University, Cleveland, OH, 44106, USA
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Kaplan K, Echert AE, Massat B, Puissant MM, Palygin O, Geurts AM, Hodges MR. Chronic central serotonin depletion attenuates ventilation and body temperature in young but not adult Tph2 knockout rats. J Appl Physiol (1985) 2016; 120:1070-81. [PMID: 26869713 DOI: 10.1152/japplphysiol.01015.2015] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2015] [Accepted: 02/09/2016] [Indexed: 12/26/2022] Open
Abstract
Genetic deletion of brain serotonin (5-HT) neurons in mice leads to ventilatory deficits and increased neonatal mortality during development. However, it is unclear if the loss of the 5-HT neurons or the loss of the neurochemical 5-HT led to the observed physiologic deficits. Herein, we generated a mutant rat model with constitutive central nervous system (CNS) 5-HT depletion by mutation of the tryptophan hydroxylase 2 (Tph2) gene in dark agouti (DA(Tph2-/-)) rats. DA(Tph2-/-) rats lacked TPH immunoreactivity and brain 5-HT but retain dopa decarboxylase-expressing raphe neurons. Mutant rats were also smaller, had relatively high mortality (∼50%), and compared with controls had reduced room air ventilation and body temperatures at specific postnatal ages. In adult rats, breathing at rest and hypoxic and hypercapnic chemoreflexes were unaltered in adult male and female DA(Tph2-/-) rats. Body temperature was also maintained in adult DA(Tph2-/-) rats exposed to 4°C, indicating unaltered ventilatory and/or thermoregulatory control mechanisms. Finally, DA(Tph2-/-) rats treated with the 5-HT precursor 5-hydroxytryptophan (5-HTP) partially restored CNS 5-HT and showed increased ventilation (P < 0.05) at a developmental age when it was otherwise attenuated in the mutants. We conclude that constitutive CNS production of 5-HT is critically important to fundamental homeostatic control systems for breathing and temperature during postnatal development in the rat.
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Affiliation(s)
- Kara Kaplan
- Department of Physiology, Medical College of Wisconsin, Milwaukee, Wisconsin
| | - Ashley E Echert
- Department of Physiology, Medical College of Wisconsin, Milwaukee, Wisconsin
| | - Ben Massat
- Department of Physiology, Medical College of Wisconsin, Milwaukee, Wisconsin
| | | | - Oleg Palygin
- Department of Physiology, Medical College of Wisconsin, Milwaukee, Wisconsin; Neuroscience Research Center, Medical College of Wisconsin, Milwaukee, Wisconsin; and
| | - Aron M Geurts
- Department of Physiology, Medical College of Wisconsin, Milwaukee, Wisconsin; Cardiovascular Center, Medical College of Wisconsin, Milwaukee, Wisconsin
| | - Matthew R Hodges
- Department of Physiology, Medical College of Wisconsin, Milwaukee, Wisconsin; Neuroscience Research Center, Medical College of Wisconsin, Milwaukee, Wisconsin; and
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Praveen V, Praveen S. Microbiome-Gut-Brain Axis: A Pathway for Improving Brainstem Serotonin Homeostasis and Successful Autoresuscitation in SIDS-A Novel Hypothesis. Front Pediatr 2016; 4:136. [PMID: 28111624 PMCID: PMC5216028 DOI: 10.3389/fped.2016.00136] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/24/2016] [Accepted: 11/30/2016] [Indexed: 12/16/2022] Open
Abstract
Sudden infant death syndrome (SIDS) continues to be a major public health issue. Following its major decline since the "Back to Sleep" campaign, the incidence of SIDS has plateaued, with an annual incidence of about 1,500 SIDS-related deaths in the United States and thousands more throughout the world. The etiology of SIDS, the major cause of postneonatal mortality in the western world, is still poorly understood. Although sleeping in prone position is a major risk factor, SIDS continues to occur even in the supine sleeping position. The triple-risk model of Filiano and Kinney emphasizes the interaction between a susceptible infant during a critical developmental period and stressor/s in the pathogenesis of SIDS. Recent evidence ranges from dysregulated autonomic control to findings of altered neurochemistry, especially the serotonergic system that plays an important role in brainstem cardiorespiratory/thermoregulatory centers. Brainstem serotonin (5-HT) and tryptophan hydroxylase-2 (TPH-2) levels have been shown to be lower in SIDS, supporting the evidence that defects in the medullary serotonergic system play a significant role in SIDS. Pathogenic bacteria and their enterotoxins have been associated with SIDS, although no direct evidence has been established. We present a new hypothesis that the infant's gut microbiome, and/or its metabolites, by its direct effects on the gut enterochromaffin cells, stimulates the afferent gut vagal endings by releasing serotonin (paracrine effect), optimizing autoresuscitation by modulating brainstem 5-HT levels through the microbiome-gut-brain axis, thus playing a significant role in SIDS during the critical period of gut flora development and vulnerability to SIDS. The shared similarities between various risk factors for SIDS and their relationship with the infant gut microbiome support our hypothesis. Comprehensive gut-microbiome studies are required to test our hypothesis.
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Affiliation(s)
| | - Shama Praveen
- Providence Little Company of Mary Medical Center , Torrance, CA , USA
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Darnall RA, Schneider RW, Tobia CM, Commons KG. Eliminating medullary 5-HT neurons delays arousal and decreases the respiratory response to repeated episodes of hypoxia in neonatal rat pups. J Appl Physiol (1985) 2015; 120:514-25. [PMID: 26702023 DOI: 10.1152/japplphysiol.00560.2014] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2014] [Accepted: 12/21/2015] [Indexed: 11/22/2022] Open
Abstract
Arousal from sleep is a critical defense mechanism when infants are exposed to hypoxia, and an arousal deficit has been postulated as contributing to the etiology of the sudden infant death syndrome (SIDS). The brainstems of SIDS infants are deficient in serotonin (5-HT) and tryptophan hydroxylase (TPH) and have decreased binding to 5-HT receptors. This study explores a possible connection between medullary 5-HT neuronal activity and arousal from sleep in response to hypoxia. Medullary raphe 5-HT neurons were eliminated from neonatal rat pups with intracisterna magna (CM) injections of 5,7-dihydroxytryptamine (DHT) at P2-P3. Each pup was then exposed to four episodes of hypoxia during sleep at three developmental ages (P5, P15, and P25) to produce an arousal response. Arousal, heart rate, and respiratory rate responses of DHT-injected pups were compared with pups that received CM artificial cerebrospinal fluid (aCSF) and those that received DHT but did not have a significant reduction in medullary 5-HT neurons. During each hypoxia exposure, the time to arousal from the onset of hypoxia (latency) was measured together with continuous measurements of heart and respiratory rates, oxyhemoglobin saturation, and chamber oxygen concentration. DHT-injected pups with significant losses of medullary 5-HT neurons exhibited significantly longer arousal latencies and decreased respiratory rate responses to hypoxia compared with controls. These results support the hypothesis that in newborn and young rat pups, 5-HT neurons located in the medullary raphe contribute to the arousal response to hypoxia. Thus alterations medullary 5-HT mechanisms might contribute to an arousal deficit and contribute to death in SIDS infants.
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Affiliation(s)
- Robert A Darnall
- Department of Physiology and Neurobiology and Department of Pediatrics, Geisel School of Medicine at Dartmouth, Lebanon, New Hampshire;
| | | | | | - Kathryn G Commons
- Department of Anesthesiology, Perioperative and Pain Medicine, Boston Children's Hospital, and Department of Anesthesia, Harvard Medical School, Boston, Massachusetts
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Puzerey PA, Kodama NX, Galán RF. Abnormal cell-intrinsic and network excitability in the neocortex of serotonin-deficient Pet-1 knockout mice. J Neurophysiol 2015; 115:813-25. [PMID: 26609119 DOI: 10.1152/jn.00996.2014] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2014] [Accepted: 11/24/2015] [Indexed: 12/18/2022] Open
Abstract
Neurons originating from the raphe nuclei of the brain stem are the exclusive source of serotonin (5-HT) to the cortex. Their serotonergic phenotype is specified by the transcriptional regulator Pet-1, which is also necessary for maintaining their neurotransmitter identity across development. Transgenic mice in which Pet-1 is genetically ablated (Pet-1(-/-)) show a dramatic reduction (∼80%) in forebrain 5-HT levels, yet no investigations have been carried out to assess the impact of such severe 5-HT depletion on the function of target cortical neurons. Using whole cell patch-clamp methods, two-dimensional (2D) multielectrode arrays (MEAs), 3D morphological neuronal reconstructions, and animal behavior, we investigated the impact of 5-HT depletion on cortical cell-intrinsic and network excitability. We found significant changes in several parameters of cell-intrinsic excitability in cortical pyramidal cells (PCs) as well as an increase in spontaneous synaptic excitation through 5-HT3 receptors. These changes are associated with increased local network excitability and oscillatory activity in a 5-HT2 receptor-dependent manner, consistent with previously reported hypersensitivity of cortical 5-HT2 receptors. PC morphology was also altered, with a significant reduction in dendritic complexity that may possibly act as a compensatory mechanism for increased excitability. Consistent with this interpretation, when we carried out experiments with convulsant-induced seizures to asses cortical excitability in vivo, we observed no significant differences in seizure parameters between wild-type and Pet-1(-/-) mice. Moreover, MEA recordings of propagating field potentials showed diminished propagation of activity across the cortical sheath. Together these findings reveal novel functional changes in neuronal and cortical excitability in mice lacking Pet-1.
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Affiliation(s)
- Pavel A Puzerey
- Department of Neurosciences, School of Medicine, Case Western Reserve University, Cleveland, Ohio
| | - Nathan X Kodama
- Department of Neurosciences, School of Medicine, Case Western Reserve University, Cleveland, Ohio
| | - Roberto F Galán
- Department of Neurosciences, School of Medicine, Case Western Reserve University, Cleveland, Ohio
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Magnusson J, Cummings KJ. Plasticity in breathing and arterial blood pressure following acute intermittent hypercapnic hypoxia in infant rat pups with a partial loss of 5-HT neurons. Am J Physiol Regul Integr Comp Physiol 2015; 309:R1273-84. [PMID: 26354844 DOI: 10.1152/ajpregu.00241.2015] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2015] [Accepted: 09/05/2015] [Indexed: 12/29/2022]
Abstract
The role of serotonin (5-HT) neurons in cardiovascular responses to acute intermittent hypoxia (AIH) has not been studied in the neonatal period. We hypothesized that a partial loss of 5-HT neurons would reduce arterial blood pressure (BP) at rest, increase the fall in BP during hypoxia, and reduce the long-term facilitation of breathing (vLTF) and BP following AIH. We exposed 2-wk-old, 5,7-dihydroxytryptamine-treated and controls to AIH (10% O2; n = 13 control, 14 treated), acute intermittent hypercapnia (5% CO2; n = 12 and 11), or acute intermittent hypercapnic hypoxia (AIHH; 10% O2, 5% CO2; n = 15 and 17). We gave five 5-min challenges of AIH and acute intermittent hypercapnia, and twenty ∼20-s challenges of AIHH to mimic sleep apnea. Systolic BP (sBP), diastolic BP, mean arterial pressure, heart rate (HR), ventilation (V̇e), and metabolic rate (V̇o2) were continuously monitored. 5,7-Dihydroxytryptamine induced an ∼35% loss of 5-HT neurons from the medullary raphe. Compared with controls, pups deficient in 5-HT neurons had reduced resting sBP (∼6 mmHg), mean arterial pressure (∼5 mmHg), and HR (56 beats/min), and experienced a reduced drop in BP during hypoxia. AIHH induced vLTF in both groups, reflected in increased V̇e and V̇e/V̇o2, and decreased arterial Pco2. The sBP of pups deficient in 5-HT neurons, but not controls, was increased 1 h following AIHH. Our data suggest that a relatively small loss of 5-HT neurons compromises resting BP and HR, but has no influence on ventilatory plasticity induced by AIHH. AIHH may be useful for reversing cardiorespiratory defects related to partial 5-HT system dysfunction.
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Affiliation(s)
- Jennifer Magnusson
- 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
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Bergman NJ. Proposal for mechanisms of protection of supine sleep against sudden infant death syndrome: an integrated mechanism review. Pediatr Res 2015; 77:10-9. [PMID: 25268147 DOI: 10.1038/pr.2014.140] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/01/2014] [Accepted: 07/11/2014] [Indexed: 02/06/2023]
Abstract
UNLABELLED Supine sleep decreases sudden infant death syndrome (SIDS) incidence, however the mechanisms for this are unclear. The triple risk model for SIDS requires that one or more underlying abnormalities of breathing or autonomic control are present; these are rare, but brainstem defects are found in most SIDS cases. Supine sleep increases sympathetic nervous system tone, and level of state organization, and may therefore act as a stressor. This is evidenced by physiological arousal, and by delayed neurodevelopment in supine compared to prone sleepers. It is argued here that prone sleep position is the biological normative standard in healthy infants, supporting autonomic regulation. During rapid eye movement (REM) sleep (and other circumstances), a parasympathetic-mediated adverse autonomic event (AAE) may be spontaneously triggered. In healthy infants, gasping initiates autoresuscitation and recovery. HYPOTHESIS The underlying vulnerability to SIDS is specific to autoresuscitation from an AAE, the initial serotonin-dependent gasp is commonly compromised. Serotonin metabolism defects also influence sleep architecture, increasing the likelihood of AAE. The mechanism whereby supine sleep decreases SIDS may therefore be a stressor effect, disturbing sleep architecture to decrease REM and AAEs, and increasing sympathetic tone, which may prevent and counteract the purely parasympathetic-mediated AAE, thereby decreasing the risk of SIDS.
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Affiliation(s)
- Nils J Bergman
- Department of Human Biology, University of Cape Town, Western Cape, South Africa
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Zhang B, McDonald FB, Cummings KJ, Frappell PB, Wilson RJ. Novel method for conscious airway resistance and ventilation estimation in neonatal rodents using plethysmography and a mechanical lung. Respir Physiol Neurobiol 2014; 201:75-83. [DOI: 10.1016/j.resp.2014.07.004] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2013] [Revised: 07/04/2014] [Accepted: 07/04/2014] [Indexed: 11/29/2022]
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Rivera-Angulo AJ, Peña-Ortega F. Isocitrate supplementation promotes breathing generation, gasping, and autoresuscitation in neonatal mice. J Neurosci Res 2013; 92:375-88. [DOI: 10.1002/jnr.23330] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2013] [Revised: 10/15/2013] [Accepted: 10/25/2013] [Indexed: 02/01/2023]
Affiliation(s)
- Ana-Julia Rivera-Angulo
- Departamento de Neurobiología del Desarrollo y Neurofisiología; Instituto de Neurobiología; Universidad Nacional Autónoma de México-Campus Juriquilla; Querétaro México
| | - Fernando Peña-Ortega
- Departamento de Neurobiología del Desarrollo y Neurofisiología; Instituto de Neurobiología; Universidad Nacional Autónoma de México-Campus Juriquilla; Querétaro México
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Yang HT, Cummings KJ. Brain stem serotonin protects blood pressure in neonatal rats exposed to episodic anoxia. J Appl Physiol (1985) 2013; 115:1733-41. [PMID: 24136109 DOI: 10.1152/japplphysiol.00970.2013] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
In neonatal rodents, a loss of brain stem serotonin [5-hydroxytryptamine (5-HT)] in utero or at birth compromises anoxia-induced gasping and the recovery of heart rate (HR) and breathing with reoxygenation (i.e., autoresuscitation). How mean arterial pressure (MAP) is influenced after an acute loss of brain stem 5-HT content is unknown. We hypothesized that a loss of 5-HT for ∼1 day would compromise MAP during episodic anoxia. We injected 6-fluorotryptophan (20 mg/kg ip) into rat pups (postnatal days 9-10 or 11-13, n = 22 treated, 24 control), causing a ∼70% loss of brain stem 5-HT. Pups were exposed to a maximum of 15 anoxic episodes, separated by 5 min of room air to allow autoresuscitation. In younger pups, we measured breathing frequency and tidal volume using "head-out" plethysmography and HR from the electrocardiogram. In older pups, we used whole body plethysmography to detect gasping, while monitoring MAP. Gasp latency and the time required for respiratory, HR, and MAP recovery following each episode were determined. Despite normal gasp latency, breathing frequency and a larger tidal volume (P < 0.001), 5-HT-deficient pups survived one-half the number of episodes as controls (P < 0.001). The anoxia-induced decrease in MAP experienced by 5-HT-deficient pups was double that of controls (P = 0.017), despite the same drop in HR (P = 0.48). MAP recovery was delayed ∼10 s by 5-HT deficiency (P = 0.001). Our data suggest a loss of brain stem 5-HT leads to a pronounced, premature loss of MAP in response to episodic anoxia. These data may help explain why some sudden infant death syndrome cases die from what appears to be cardiovascular collapse during apparent severe hypoxia.
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Affiliation(s)
- Hsiao T Yang
- Department of Biomedical Sciences, University of Missouri, Columbia, Missouri
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Iceman KE, Richerson GB, Harris MB. Medullary serotonin neurons are CO2 sensitive in situ. J Neurophysiol 2013; 110:2536-44. [PMID: 24047906 DOI: 10.1152/jn.00288.2013] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Brainstem central chemoreceptors are critical to the hypercapnic ventilatory response, but their location and identity are poorly understood. When studied in vitro, serotonin-synthesizing (5-HT) neurons within the rat medullary raphé are intrinsically stimulated by CO2/acidosis. The contributions of these neurons to central chemosensitivity in vivo, however, are controversial. Lacking is documentation of CO2-sensitive 5-HT neurons in intact experimental preparations and understanding of their spatial and proportional distribution. Here we test the hypothesis that 5-HT neurons in the rat medullary raphé are sensitive to arterial hypercapnia. We use extracellular recording and hypercapnic challenge of spontaneously active medullary raphé neurons in the unanesthetized in situ perfused decerebrate brainstem preparation to assess chemosensitivity of individual cells. Juxtacellular labeling of a subset of recorded neurons and subsequent immunohistochemistry for the 5-HT-synthesizing enzyme tryptophan hydroxylase (TPH) identify or exclude this neurotransmitter phenotype in electrophysiologically characterized chemosensitive and insensitive cells. We show that the medullary raphé houses a heterogeneous population, including chemosensitive and insensitive 5-HT neurons. Of 124 recorded cells, 16 cells were juxtacellularly filled, visualized, and immunohistochemically identified as 5-HT synthesizing, based on TPH-immunoreactivity. Forty-four percent of 5-HT cells were CO2 stimulated (increased firing rate with hypercapnia), while 56% were unstimulated. Our results demonstrate that medullary raphé neurons are heterogeneous and clearly include a subset of 5-HT neurons that are excited by arterial hypercapnia. Together with data identifying intrinsically CO2-sensitive 5-HT neurons in vitro, these results support a role for such cells as central chemoreceptors in the intact system.
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Affiliation(s)
- Kimberly E Iceman
- Department of Biology and Wildlife, University of Alaska, Fairbanks, Alaska
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Allen T, Garcia Iii AJ, Tang J, Ramirez JM, Rubens DD. Inner ear insult ablates the arousal response to hypoxia and hypercarbia. Neuroscience 2013; 253:283-91. [PMID: 24021919 DOI: 10.1016/j.neuroscience.2013.08.059] [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: 04/03/2013] [Revised: 08/26/2013] [Accepted: 08/28/2013] [Indexed: 11/27/2022]
Abstract
INTRODUCTION Sudden Infant Death Syndrome (SIDS) remains the leading cause of infant mortality in Western societies. A prior study identified an association between hearing suppression on the newborn hearing test and subsequent death from SIDS. This is the first finding of an abnormality in SIDS cases prior to death. A following study identified that inner ear dysfunction precipitates a marked suppression of the hypercapnic ventilatory response (HCVR). Failure of arousal has been proposed to be a key component in SIDS. The objective of the present study was to assess whether inner ear dysfunction not only weakens the hypercapnic response, but also plays a role in suppressing the arousal response to suffocating gas mixtures. METHODS Wild-type mice (n=28) received intra-tympanic gentamicin (IT-Gent) injections bilaterally or unilaterally to precipitate inner ear hair cell dysfunction. Three control groups (n=22) received intra-tympanic saline (IT-Saline) bilaterally or unilaterally (right or left), or intra-peritoneal gentamicin (IP-Gent). The body movement arousal responses to severe hypoxia-hypercarbia combined (5% CO2 in nitrogen) were tested under light anesthesia 8 days following the administration of gentamicin or saline. RESULTS After injections, the bilateral and unilateral IT-Gent-treated animals behaved similarly to controls, however the HCVR as well as the arousal movements in response to severe hypoxia-hypercarbia were suppressed in IT-Gent-treated animals compared to control animals (P<0.05). Thus the HCVR was significantly decreased in the bilateral (n=9) and unilateral IT-Gent-treated mice (n=19) compared to bilateral (n=7) and unilateral IT-Saline (n=9) control groups (p<0.05). Arousal movements were suppressed in the bilateral IT-Gent group (n=9) compared to bilateral IT-Saline controls (n=7, P<0.0001) and in the unilateral IT-Gent group (n=19) compared to unilateral IT-Saline controls (n=10, P<0.0001). DISCUSSION The findings support the theory that inner ear dysfunction could be relevant in the pathophysiology of SIDS. The inner ear appears to play a key role in arousal from suffocating gas mixtures that has not been previously identified.
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Affiliation(s)
- T Allen
- Department of Anesthesia, Seattle Children's Hospital, 4800 Sandpoint Way NE, Seattle, WA 98115, United States.
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Massey CA, Kim G, Corcoran AE, Haynes RL, Paterson DS, Cummings KJ, Dymecki SM, Richerson GB, Nattie EE, Kinney HC, Commons KG. Development of brainstem 5-HT1A receptor-binding sites in serotonin-deficient mice. J Neurochem 2013; 126:749-57. [PMID: 23692315 DOI: 10.1111/jnc.12311] [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: 04/26/2013] [Revised: 05/06/2013] [Accepted: 05/10/2013] [Indexed: 11/27/2022]
Abstract
The sudden infant death syndrome is associated with a reduction in brainstem serotonin 5-hydroxytryptamine (5-HT) and 5-HT(1A) receptor binding, yet it is unknown if and how these findings are linked. In this study, we used quantitative tissue autoradiography to determine if post-natal development of brainstem 5-HT(1A) receptors is altered in two mouse models where the development of 5-HT neurons is defective, the Lmx1b(f/f/p) , and the Pet-1⁻/⁻ mouse. 5-HT(1A) receptor agonist-binding sites were examined in both 5-HT-source nuclei (autoreceptors) and in sites that receive 5-HT innervation (heteroreceptors). In control mice between post-natal day (P) 3 and 10, 5-HT(1A) receptor binding increased in several brainstem sites; by P25, there were region-specific increases and decreases, refining the overall binding pattern. In the Lmx1b(f/f/p) and Pet-1⁻/⁻ mice, 5-HT(1A)-autoreceptor binding was significantly lower than in control mice at P3, and remained low at P10 and P25. In contrast, 5-HT(1A) heteroreceptor levels were comparable between control and 5-HT-deficient mice. These data define the post-natal development of 5-HT(1A)-receptor binding in the mouse brainstem. Furthermore, the data suggest that 5-HT(1A)-heteroreceptor deficits detected in sudden infant death syndrome are not a direct consequence of a 5-HT neuron dysfunction nor reduced brain 5-HT levels. To elucidate the developmental relationship between serotonin (5-HT) levels and 5-HT(1A) receptors in the brainstem, we examined 5-HT(1A) binding in two 5-HT-deficient mouse models. In nuclei containing 5-HT neurons, 5-HT(1A) binding was decreased (autoreceptors), while binding was maintained in projection sites (heteroreceptors). Thus, brainstem 5-HT(1A)-heteroreceptor-binding sites do not appear developmentally sensitive to reduced brain 5-HT levels.
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Affiliation(s)
- Caitlin A Massey
- Department of Anesthesiology, Boston Children's Hospital and Harvard Medical School, Boston, Massachusetts, USA
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The physiological determinants of sudden infant death syndrome. Respir Physiol Neurobiol 2013; 189:288-300. [PMID: 23735486 DOI: 10.1016/j.resp.2013.05.032] [Citation(s) in RCA: 67] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2013] [Revised: 05/19/2013] [Accepted: 05/27/2013] [Indexed: 01/08/2023]
Abstract
It is well-established that environmental and biological risk factors contribute to Sudden Infant Death Syndrome (SIDS). There is also growing consensus that SIDS requires the intersection of multiple risk factors that result in the failure of an infant to overcome cardio-respiratory challenges. Thus, the critical next steps in understanding SIDS are to unravel the physiological determinants that actually cause the sudden death, to synthesize how these determinants are affected by the known risk factors, and to develop novel ideas for SIDS prevention. In this review, we will examine current and emerging perspectives related to cardio-respiratory dysfunctions in SIDS. Specifically, we will review: (1) the role of the preBötzinger complex (preBötC) as a multi-functional network that is critically involved in the failure to adequately respond to hypoxic and hypercapnic challenges; (2) the potential involvement of the preBötC in the gender and age distributions that are characteristic for SIDS; (3) the link between SIDS and prematurity; and (4) the potential relationship between SIDS, auditory function, and central chemosensitivity. Each section underscores the importance of marrying the epidemiological and pathological data to experimental data in order to understand the physiological determinants of this syndrome. We hope that a better understanding will lead to novel ways to reduce the risk to succumb to SIDS.
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Sowers LP, Massey CA, Gehlbach BK, Granner MA, Richerson GB. Sudden unexpected death in epilepsy: fatal post-ictal respiratory and arousal mechanisms. Respir Physiol Neurobiol 2013; 189:315-23. [PMID: 23707877 DOI: 10.1016/j.resp.2013.05.010] [Citation(s) in RCA: 62] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2013] [Revised: 05/13/2013] [Accepted: 05/14/2013] [Indexed: 01/04/2023]
Abstract
Sudden unexplained death in epilepsy (SUDEP) is the cause of premature death of up to 17% of all patients with epilepsy and as many as 50% with chronic refractory epilepsy. However, SUDEP is not widely recognized to exist. The etiology of SUDEP remains unclear, but growing evidence points to peri-ictal respiratory, cardiac, or autonomic nervous system dysfunction. How seizures affect these systems remains uncertain. Here we focus on respiratory mechanisms believed to underlie SUDEP. We highlight clinical evidence that indicates peri-ictal hypoxemia occurs in a large percentage of patients due to central apnea, and identify the proposed anatomical regions of the brain governing these responses. In addition, we discuss animal models used to study peri-ictal respiratory depression. We highlight the role 5-HT neurons play in respiratory control, chemoreception, and arousal. Finally, we discuss the evidence that 5-HT deficits contribute to SUDEP and sudden infant death syndrome and the striking similarities between the two.
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Affiliation(s)
- Levi P Sowers
- Department of Neurology, University of Iowa Hospitals and Clinics, 200 Hawkins Drive, Iowa City, IA 52242, United States; Roy J. and Lucille A. Carver College of Medicine, University of Iowa Hospitals and Clinics, 200 Hawkins Drive, Iowa City, IA 52242, United States
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