Journal of Comparative Physiology B

, Volume 183, Issue 7, pp 947–957 | Cite as

Chronic hypoxic incubation blunts thermally dependent cholinergic tone on the cardiovascular system in embryonic American alligator (Alligator mississippiensis)

  • Chris Marks
  • John Eme
  • Ruth M. Elsey
  • Dane A. CrossleyII
Original Paper

Abstract

Environmental conditions play a major role in shaping reptilian embryonic development, but studies addressing the impact of interactions between chronic and acute environmental stressors on embryonic systems are lacking. In the present study, we investigated thermal dependence of cholinergic and adrenergic cardiovascular tone in embryonic American alligators (Alligator mississippiensis) and assessed possible phenotypic plasticity in a chronic hypoxic incubation treatment. We compared changes in heart rate (fH) and mean arterial blood pressure (PM) for chronically hypoxic and normoxic-incubated embryos after cholinergic and adrenergic blockade following three different acute temperature treatments: (1) 30 °C (control incubation temperature), (2) acute, progressive decrease 30–24 °C then held at 24 °C, and (3) acute, progressive increase 30–36 °C then held at 36 °C. fH progressively fell in response to decreasing temperature and rose in response to increasing temperature. PM did not significantly change with decreasing temperature, but was lowered significantly with increasing acute temperature in the normoxic group at 90 % of development only. Propranolol administration (β adrenergic antagonist) produced a significant fH decrease at 24, 30, and 36 °C that was similar at all temperatures for all groups. For normoxic-incubated embryos at 90 % of development, atropine administration (cholinergic antagonist) significantly increased fH in both 24 and 36 °C treatments, but not in the 30 °C control treatment. This atropine response at 24 and 36 °C demonstrated acute thermally dependent cholinergic tone on fH late in development for normoxic-incubated, but not chronically hypoxic-incubated embryos. Collectively, data indicated that cardiovascular control mechanisms in embryonic alligators may be activated by thermal extremes, and the maturation of control mechanisms was delayed by chronic hypoxia.

Keywords

Atropine Embryo Hypoxia Propranolol Reptile Temperature 

Abbreviations

CAM

Chorioallantoic membrane

fH

Heart rate

PM

Mean arterial pressure

TE

Temperature of embryo, from thermocouple probe inserted into allantoic fluid

N70 or N90

Alligator embryos incubated in chronic normoxia, measured at 70 or 90 % of embryonic development, respectively

H70 or H90

Alligator embryos incubated in chronic hypoxia (10 % O2) beginning at 20 % of development, measured at 70 or 90 % of embryonic development, respectively

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Copyright information

© Springer-Verlag Berlin Heidelberg 2013

Authors and Affiliations

  • Chris Marks
    • 1
  • John Eme
    • 1
  • Ruth M. Elsey
    • 2
  • Dane A. CrossleyII
    • 1
  1. 1.Department of Biological SciencesUniversity of North TexasDentonUSA
  2. 2.Louisiana Department of Wildlife and FisheriesRockefeller Wildlife RefugeGrand ChenierUSA

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