title: Partial Raphe Dysfunction in Neurotransmission Is Sufficient to Increase Mortality after Anoxic Exposures in Mice at a Critical Period in Postnatal Development.
abstract: 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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Department of Physiology and Neurobiology, Geisel School of Medicine at Dartmouth, Lebanon, New Hampshire 03756.
authors.forename: Karlene T
authors.initials: KT
authors.lastname: Barrett
authors.affiliation: Department of Genetics, Harvard Medical School, Boston, Massachusetts 02115, and.
authors.forename: Ryan T
authors.identifier: http://orcid.org/0000-0002-0120-9565
authors.initials: RT
authors.lastname: Dosumu-Johnson
authors.affiliation: Department of Physiology and Neurobiology, Geisel School of Medicine at Dartmouth, Lebanon, New Hampshire 03756.
authors.forename: J Andrew
authors.initials: JA
authors.lastname: Daubenspeck
authors.affiliation: Department of Genetics, Harvard Medical School, Boston, Massachusetts 02115, and.
authors.forename: Rachael D
authors.initials: RD
authors.lastname: Brust
authors.affiliation: Department of Genetics, Harvard Medical School, Boston, Massachusetts 02115, and.
authors.forename: Vasileios
authors.identifier: http://orcid.org/0000-0002-8207-9933
authors.initials: V
authors.lastname: Kreouzis
authors.affiliation: Department of Psychology, University of Toronto, Toronto, Ontario M5S, Canada.
authors.forename: Jun Chul
authors.identifier: http://orcid.org/0000-0001-9920-3307
authors.initials: JC
authors.lastname: Kim
authors.affiliation: Department of Physiology and Neurobiology, Geisel School of Medicine at Dartmouth, Lebanon, New Hampshire 03756.
authors.forename: Aihua
authors.initials: A
authors.lastname: Li
authors.affiliation: Department of Genetics, Harvard Medical School, Boston, Massachusetts 02115, and.
authors.forename: Susan M
authors.initials: SM
authors.lastname: Dymecki
authors.affiliation: Department of Physiology and Neurobiology, Geisel School of Medicine at Dartmouth, Lebanon, New Hampshire 03756, Eugene.Nattie@Dartmouth.edu.
authors.forename: Eugene E
authors.initials: EE
authors.lastname: Nattie
mesh_terms: D000375:Aging / Q000523:psychology; D000818:Animals; D000831:Animals, Newborn; D003423:Critical Period, Psychological; D020868:Gene Silencing; D006339:Heart Rate; D006801:Humans; D000860:Hypoxia / Q000401:mortality* / Q000503:physiopathology*; D007231:Infant, Newborn; D051379:Mice; D008822:Mice, Transgenic; D011903:Raphe Nuclei / Q000187:drug effects / Q000503:physiopathology*; D015656:Respiratory Mechanics; D050486:Serotonin Plasma Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism; D013398:Sudden Infant Death; D009435:Synaptic Transmission / Q000187:drug effects; D013744:Tetanus Toxin / Q000633:toxicity; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism; D014365:Tryptophan Hydroxylase / Q000235:genetics / Q000378:metabolism
chemical_list: C484684:Fev protein, mouse; D050486:Serotonin Plasma Membrane Transport Proteins; C493231:Slc6a4 protein, mouse; D013744:Tetanus Toxin; D014157:Transcription Factors; C487802:Tph2 protein, mouse; D014365:Tryptophan Hydroxylase
keywords: autoresuscitation; serotonergic system; sudden infant death syndrome