Journal of Comparative Physiology B

, Volume 181, Issue 7, pp 981–990 | Cite as

Chronic hypoxic incubation blunts a cardiovascular reflex loop in embryonic American alligator (Alligator mississippiensis)

Original Paper

Abstract

Hypoxia is a naturally occurring environmental challenge for embryonic non-avian reptiles, and this study is the first to investigate the impact of chronic hypoxia on a possible chemoreflex loop in a developing non-avian reptile. We measured heart rate and blood pressure in normoxic and hypoxic-incubated (10% O2) American alligator embryos (Alligator mississippiensis) at 70 and 90/95% of development. We hypothesized that hypoxic incubation would blunt embryonic alligators’ response to a reflex loop stimulated by phenylbiguanide (PBG), a 5-HT3 receptor agonist that stimulates vagal pulmonary C-fiber afferents. PBG injection caused a hypotensive bradycardia in 70 and 95% of development embryos (paired t tests, P < 0.05), a response similar to mammals breathing inspired air (all injections made through occlusive catheter in tertiary chorioallantoic membrane artery). Hypoxic incubation blunted the bradycardic response to PBG in embryos at 95% of development (two-way ANOVA, P < 0.01). We also demonstrated that the vagally mediated afferent limb of this reflex can be partially or completely blocked in ovo with a 5-HT3 receptor blockade using ondansetron hydrochloride dihydrate (OHD), with a ganglionic blockade using hexamethonium, or with a cholinergic blockade using atropine. Atropine eliminated the hypotensive and bradycardic responses to PBG, and OHD and hexamethonium significantly blunted these responses. This cardiovascular reflex mediated by the vagus was affected by hypoxic incubation, suggesting that reptilian sympathetic and parasympathetic reflex loops have the potential for developmental plasticity in response to hypoxia. We suggest that the American alligator, with an extended length of time between each developmental stage relative to avian species, may provide an excellent model to test the cardiorespiratory effects of prolonged exposure to changes in atmospheric gases. This extended period allows for lengthy studies at each stage without the transition to a new stage, and the natural occurrence of hypoxia and hypercapnia in crocodilian nests makes this stress ecologically and evolutionarily relevant.

Keywords

Chemoreflex Chorioallantoic membrane Embryo Hypoxia Phenylbiguanide Reptile 

Abbreviations

BPM

Beats per minute

CAM

Chorioallantoic membrane

fH

Heart rate

MAP

Mean arterial pressure

OHD

Ondansetron hydrochloride dihydrate, 5-HT3 (serotonin) receptor blocker

PBG

Phenylbiguanide, 5-HT3 receptor (serotonin) agonist of vagal pulmonary C-fiber afferents

VE

Minute ventilation

VO2

Oxygen consumption rate

References

  1. Ackerman RA (1980) Physiological and ecological aspects of gas exchange by sea turtle eggs. Am Zool 20:575–583Google Scholar
  2. Adair T, Guyton AC, Montani JP, Lindsay HL, Stanek KA (1987) Whole body structural vascular adaptation to prolonged hypoxia in chick embryos. Am J Physiol Heart Circ Physiol 252:H1228–H1234Google Scholar
  3. Altimiras J, Crossley DA II (2000) Control of blood pressure mediated by baroreflex changes of heart rate in the chicken embryo (Gallus gallus). Am J Physiol Regul Integr Comp Physiol 278:R980–R986PubMedGoogle Scholar
  4. Bavis RW, Kilgore DL (2001) Effects of embryonic CO2 exposure on the adult ventilatory response in quail: does gender matter? Respir Physiol 126:183–199PubMedCrossRefGoogle Scholar
  5. Booth DT (1998) Nest temperature and respiratory gases during natural incubation in the broad-shelled river turtle, Chelodina expansa (Testudinata:Chelidae). Aust J Zool 46:183–191CrossRefGoogle Scholar
  6. Booth DT (2000) The effect of hypoxia on oxygen consumption of embryonic estuarine crocodiles (Crocodylus porosus). J Herpetol 34:478–481CrossRefGoogle Scholar
  7. Coleridge HM, Coleridge JCG (1994) Pulmonary reflexes: neural mechanisms of pulmonary defense. Annu Rev Physiol 56:69–91PubMedCrossRefGoogle Scholar
  8. Corona TB, Warburton SJ (2000) Regional hypoxia elicits regional changes in chorioallantoic membrane vascular density in alligator but not chicken embryos. Comp Biochem Physiol A 125:57–61CrossRefGoogle Scholar
  9. Crossley DA II, Altimiras J (2005) Cardiovascular development in embryos of the American alligator Alligator mississippiensis: effects of chronic and acute hypoxia. J Exp Biol 208:31–39PubMedCrossRefGoogle Scholar
  10. Crossley DA II, Burggren WW, Altimiras J (2003a) A cardiovascular regulation during hypoxia in embryos of the domestic chicken Gallus gallus. Am J Physiol Regul Integr Comp Physiol 284:219–226Google Scholar
  11. Crossley DA II, Hicks JW, Altimiras J (2003b) Ontogeny of baroreflex control in the American alligator Alligator mississippiensis. J Exp Biol 206:2895–2902PubMedCrossRefGoogle Scholar
  12. Eme J, Crossley II DA, Hicks JW (2011) Role of the left aortic arch and blood flows in embryonic American alligator (Alligator mississippiensis). J Comp Physiol B 181:391–401. doi:10.1007/s00360-010-0494-6 (online first)
  13. Ferguson MWJ (1985) Reproductive biology and embryology of the crocodilians. In: Gans C, Billet F, Maderson P (eds) Biology of the reptilia, vol 14 A. Wiley, New York, pp 329–349Google Scholar
  14. Ferner K, Mortola JP (2009) Ventilatory response to hypoxia in chicken hatchlings: a developmental window of sensitivity to embryonic hypoxia. Respir Physiol Neurobiol 165:49–53PubMedCrossRefGoogle Scholar
  15. Fu LW, Longhurst JC (1998) Reflex pressor response to arterial phenylbiguanide: role of abdominal sympathetic visceral afferents. Am J Physiol Heart Circ Physiol 275:2025–2035Google Scholar
  16. Gleed RD, Mortola JP (1991) Ventilation in newborn rats after gestation at simulated high altitude. J Appl Physiol 70:1146–1151PubMedGoogle Scholar
  17. Gu Q, Lee L-Y (2002) Alveolar hypercapnia augments pulmonary C-fiber responses to chemical stimulants: role of hydrogen ion. J Appl Physiol 93:181–188PubMedGoogle Scholar
  18. Herrera EA, Pulgar VM, Riquelme RA, Sanhueza EM, Reyes RV, Ebensperger G, Parer JT, Valdez EA, Giussani DA, Blanco CE, Hanson MA, Llanos AJ (2007) High-altitude chronic hypoxia during gestation and after birth modifies cardiovascular responses in newborn sheep. Am J Physiol Regul Integr Comp Physiol 292:R2234–R2240PubMedCrossRefGoogle Scholar
  19. Ho D, Burggren WW (2010) Epigenetics and transgenerational transfer: a physiological perspective. J Exp Biol 213:3–16PubMedCrossRefGoogle Scholar
  20. Johnson SM, Wilkerson JER, Henderson DR, Wenninger MR, Mitchell GS (2001) Serotonin elicits long-lasting enhancement of rhythmic respiratory activity in turtle brain stems in vitro. J Appl Physiol 91:2703–2712PubMedGoogle Scholar
  21. Kam YC (1993) Physiological effects of hypoxia on metabolism and growth of turtle embryos. Respir Physiol 92:127–138PubMedCrossRefGoogle Scholar
  22. Kawada T, Yamazaki T, Akiyama T, Shishido T, Inagaki M, Uemura K, Miyamoto T, Sugimachi M, Takaki H, Sunagawa K (2001) In vivo assessment of acetylcholine-releasing function at cardiac vagal nerve terminals. Am J Physiol Heart Circ Physiol 281:H139–H145PubMedGoogle Scholar
  23. Kay IS, Armstrong DJ (1990) Phenylbiguanide not phenyldiguanide is used to evoke the pulmonary chemoreflex in anesthetized rabbits. Exp Physiol 75:383–389PubMedGoogle Scholar
  24. Lee L-Y, Pisarri TE (2001) Afferent properties and reflex functions of brochopulmonary C-fibers. Resp Physiol 125:47–65CrossRefGoogle Scholar
  25. Lutz PL, Dunbar-Cooper A (1984) The nest environment of the American crocodile (Crocodylus acutus). Copeia 1:153–161CrossRefGoogle Scholar
  26. Matsumoto S, Kanno T, Yamasaki M, Nagayama T, Shimizu T (1992) Pulmonary C-fibers elicit both apneusis and tachypnea in the rabbit. Respir Physiol 87:165–181PubMedCrossRefGoogle Scholar
  27. Miller NA (2008) PO2 in loggerhead Sea turtle (Caretta caretta) nests measured using fiber-optic oxygen sensors. Copeia 4:882–888CrossRefGoogle Scholar
  28. Owerkowicz T, Elsey RM, Hicks JW (2009) Atmospheric oxygen level affects growth trajectory, cardiopulmonary allometry and metabolic rate in the American alligator (Alligator mississippiensis). J Exp Biol 212:1237–1247PubMedCrossRefGoogle Scholar
  29. Peyronnet J, Roux JC, Geloen A, Tang LQ, Pequignot JM, Lagercrantz H, Dalmaz Y (2000) Prenatal hypoxia impairs the postnatal development of neural and functional chemoafferent pathway in rat. J Physiol 524:525–537PubMedCrossRefGoogle Scholar
  30. Pulgar VM, Hong JK, Jessup JA, Massmann AG, Diz DI, Figueroa JP (2009) Mild chronic hypoxemia modifies expression of brain stem angiotensin peptide receptors and reflex responses in fetal sheep. Am J Physiol Regul Integr Comp Physiol 297:R446–R452PubMedCrossRefGoogle Scholar
  31. Rouwet EV, Tintu AN, Shellings MWM, van Bilsen M, Lutgens E, Hofstra L, Slaaf DW, Ramsay G, le Noble FAC (2002) Hypoxia induces aortic hypertrophic growth, left ventricular dysfunction and sympathetic hyperinnervation of peripheral arteries in the chick embryo. Circulation 105:2791–2796PubMedCrossRefGoogle Scholar
  32. Seymour RS, Vleck D, Vleck CM (1986) Gas exchange in the incubation mounds of megapode birds. J Comp Physiol B 156:772–782CrossRefGoogle Scholar
  33. Szdzuy K, Mortola JP (2007) Ventilatory chemosensitivity of the 1-day-old chicken hatchling after embryonic hypoxia. Am J Physiol Regul Integr Comp Physiol 293:R1640–R1649PubMedCrossRefGoogle Scholar
  34. Warburton SJ, Hastings D, Wang T (1995) Responses to chronic hypoxia in embryonic alligators. J Exp Zool 273:44–50PubMedCrossRefGoogle Scholar
  35. Williams BR, Kilgore DL (1992) Ontogenetic modification of the hypercapnic ventilatory response in the zebra finch. Respir Physiol 90:125–134PubMedCrossRefGoogle Scholar
  36. Xu F, Gu Q-H, Zhou T, Lee L-Y (2003) Acute hypoxia prolongs the apnea induced by right atrial injection of capsaicin. J Appl Physiol 94:1446–1454PubMedGoogle Scholar
  37. Zhang JW, Walker JF, Guardiola J, Yu J (2006) Pulmonary sensory and reflex responses in the mouse. J Appl Physiol 101:986–992PubMedCrossRefGoogle Scholar

Copyright information

© Springer-Verlag 2011

Authors and Affiliations

  • John Eme
    • 1
  • James W. Hicks
    • 2
  • Dane A. CrossleyII
    • 1
  1. 1.Department of Biological SciencesUniversity of North TexasDentonUSA
  2. 2.Ecology and Evolutionary BiologyUniversity of California, IrvineIrvineUSA

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