{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,10,19]],"date-time":"2026-10-19T09:57:28Z","timestamp":1792403848228,"version":"4.4.0"},"reference-count":39,"publisher":"American Physiological Society","issue":"5","content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["American Journal of Physiology-Regulatory, Integrative and Comparative Physiology"],"published-print":{"date-parts":[[2010,5]]},"abstract":"<jats:p>Neonatal rodents deficient in medullary serotonin neurons have respiratory instability and enhanced spontaneous bradycardias. This study asks if, in Pet-1<jats:sup>\u2212\/\u2212<\/jats:sup>mice over development: 1) the respiratory instability leads to hypoxia; 2) greater bradycardia is related to the degree of hypoxia or concomitant hypopnea; and 3) hyperthermia exacerbates bradycardias. Pet-1<jats:sup>+\/+<\/jats:sup>, Pet-1<jats:sup>+\/\u2212<\/jats:sup>, and Pet-1<jats:sup>\u2212\/\u2212<\/jats:sup>mice [postnatal days (P) 4\u20135, P11\u201312, P14\u201315] were held at normal body temperature (T<jats:sub>b<\/jats:sub>) and were then made 2\u00b0C hypo- and hyperthermic. Using a pneumotach-mask system with ECG, we measured heart rate, metabolic rate (V\u0307o<jats:sub>2<\/jats:sub>), and ventilation. We also calculated indexes for apnea-induced hypoxia (total hypoxia: apnea incidence \u00d7 O<jats:sub>2<\/jats:sub>consumed during apnea = \u03bcl\u00b7g<jats:sup>\u22121<\/jats:sup>\u00b7min<jats:sup>\u22121<\/jats:sup>) and bradycardia (total bradycardia: bradycardia incidence \u00d7 magnitude = beats missed\/min). Resting heart rate was significantly lower in all Pet-1<jats:sup>\u2212\/\u2212<\/jats:sup>animals, irrespective of T<jats:sub>b<\/jats:sub>. At P4\u20135, Pet-1<jats:sup>\u2212\/\u2212<\/jats:sup>animals had approximately four- to eightfold greater total bradycardia ( P &lt; 0.001), owing to an approximately two- to threefold increase in bradycardia magnitude and a near doubling in bradycardia incidence. Pet-1<jats:sup>\u2212\/\u2212<\/jats:sup>animals had a significantly reduced V\u0307o<jats:sub>2<\/jats:sub>at all T<jats:sub>b<\/jats:sub>; thus there was no genotype effect on total hypoxia. At P11\u201312, total bradycardia was nearly threefold greater in hyperthermic Pet-1<jats:sup>\u2212\/\u2212<\/jats:sup>animals compared with controls ( P &lt; 0.01). In both genotypes, bradycardia magnitude was positively related to the degree of hypopnea ( P = 0.02), but there was no genotype effect on degree of hypopnea or total hypoxia. At P14\u201315, genotype had no effect on total bradycardia, but Pet-1<jats:sup>\u2212\/\u2212<\/jats:sup>animals had up to seven times more total hypoxia ( P &lt; 0.001), owing to longer and more frequent apneas and a normalized V\u0307o<jats:sub>2<\/jats:sub>. We infer from these data that 1) Pet-1<jats:sup>\u2212\/\u2212<\/jats:sup>neonates are probably not hypoxic from respiratory dysfunction until P14\u201315; 2) neither apnea-related hypoxia nor greater hypopnea contribute to the enhanced bradycardias of Pet-1<jats:sup>\u2212\/\u2212<\/jats:sup>neonates from approximately P4 to approximately P12; and 3) an enhancement of a temperature-sensitive reflex may contribute to the greater bradycardia in hyperthermic Pet-1<jats:sup>\u2212\/\u2212<\/jats:sup>animals at approximately P12.<\/jats:p>","DOI":"10.1152\/ajpregu.00110.2010","type":"journal-article","created":{"date-parts":[[2010,3,11]],"date-time":"2010-03-11T03:33:44Z","timestamp":1268278424000},"page":"R1333-R1342","source":"Crossref","is-referenced-by-count":37,"title":["Bradycardia in serotonin-deficient<i>Pet-1<\/i><sup>\u2212\/\u2212<\/sup>mice: influence of respiratory dysfunction and hyperthermia over the first 2 postnatal 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