title: Onset and early development of hypoxic ventilatory responses and branchial neuroepithelial cells in Xenopus laevis.
abstract: Onset and ontogeny of the O₂ chemoreceptive control of ventilation was investigated in Xenopus laevis. The density and size of branchial serotonin-immunoreactive neuroepithelial cells (5-HT-IR NECs) were also determined using confocal immunofluorescent microscopy. Larvae started gill ventilation at 3 days post-fertilization (dpf), and, at this early stage, acute hypoxic exposure produced an increase in frequency from 28 ± 4 to 60 ± 2 beats x min⁻¹. Concurrent with the onset of ventilatory responses, 5-HT-IR NECs appeared in the gill filament bud. Lung ventilation began at 5 dpf and exhibited a 3-fold increase in frequency during acute hypoxia. At 10 dpf, gill ventilatory sensitivity to hypoxia increased, as did NEC density, from 15 ± 1 (5 dpf) to 29 ± 2 (10 dpf) cells x mm of filament⁻¹. Unlike ventilation frequency, gill ventilation amplitude and lung expired volume were unaltered by acute hypoxia. Chronic exposure to moderate hypoxia, at a P(O₂) of 110 mmHg, attenuated acute responses to moderate hypoxia at 10 and 14 dpf but had no effect at more severe hypoxia or at other stages. Chronic hypoxia also stimulated 5-HT-IR NECs growth at 21 dpf. Collectively, larvae at 5 dpf exhibited strong O₂-driven gill and lung ventilatory responses, and between 10 and 21 dpf, the early hypoxic responses can be shaped by the ambient P(O₂).
authors: Developmental Physiology and Genetics Research Cluster, Department of Biological Sciences, University of North Texas, Denton, Texas 76203-5017, USA. francispan@my.unt.edu
authors: Tien-Chien F
authors: TC
authors: Pan
authors: Warren W
authors: WW
authors: Burggren
mesh_terms: D000818:Animals; D001934:Branchial Region / Q000254:growth & development* / Q000473:pathology / Q000503:physiopathology*; D005880:Gills / Q000378:metabolism / Q000473:pathology; D000860:Hypoxia / Q000503:physiopathology*; D007814:Larva / Q000254:growth & development; D046569:Neuroepithelial Cells / Q000378:metabolism* / Q000473:pathology*; D010313:Partial Pressure; D012143:Respiratory Physiological Phenomena; D012701:Serotonin / Q000378:metabolism; D014982:Xenopus laevis / Q000254:growth & development* / Q000378:metabolism
chemical_list: D012701:Serotonin