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The Journal of Experimental Biology 206, 2895-2902 (2003)
doi: 10.1242/jeb.00486

Ontogeny of baroreflex control in the American alligator Alligator mississippiensis

Dane A. Crossley, II¹, James W. Hicks^1,* and Jordi Altimiras²

¹ Department of Ecology and Evolutionary Biology, University of California at Irvine, CA 92697, USA
² Department of Biology, IFM, University of Linköping, SE-58183, Sweden

^* Author for correspondence (e-mail: dcrossle{at}uci.edu)

Accepted 12 May 2003

Baroreflex regulation appears in different species at different points in embryonic development. This study was designed to understand the development of the baroreflex in embryos of the American alligator at four different points of embryonic development (60%, 70%, 80% and 90% of a total incubation period of 72 days) and in 1-week-old hatchlings. Data from a separate study on 1-year-old alligators were included for comparison. The gain of the cardiac limb of the baroreflex was calculated from heart rate changes triggered by pharmacological manipulation of arterial pressure with sodium nitroprusside and phenylephrine. The results demonstrated that a vagally mediated hypertensive baroreflex was present during the final 30% of alligator development. A hypotensive baroreflex was not present in embryos but appeared in hatchlings, mediated by a combined effect of vagal and sympathetic efferents. Absolute baroreflex gain was maximal at 80% of incubation (41.22 beats kPa^–1 min^–1) and dropped thereafter, reaching a minimum in 1-year-old alligators (9.69 beats kPa^–1 min^–1). When the baroreflex gain was normalized to resting arterial pressure and heart rate, the maximum gain was observed in 1-year-old alligators (normalized index of 2.12 versus 0.75 in hatchlings and 0.69 as the highest gain in embryos). In conclusion, baroreflex regulation appeared during embryonic development with a substantial gain. These findings indicate that embryonic development is a period of preparation for cardiovascular regulatory mechanisms that will be necessary in adult life and that the baroreflex control mechanism is required for cardiovascular control during ontogeny.

Key words: baroreflex regulation, embryonic development, baroreflex gain, cardiovascular regulation, American alligator, Alligator mississippiensis

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				D. A. Crossley II and J. Altimiras Cardiovascular development in embryos of the American alligator Alligator mississippiensis: effects of chronic and acute hypoxia J. Exp. Biol., January 1, 2005; 208(1): 31 - 39. [Abstract] [Full Text] [PDF]