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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

View larger version (12K): [in a new window]   Fig. 1. Heart rate (fH; open circles) and mean arterial pressure (a; closed circles) during development in the alligator. Data are means ± S.E.M. (N=7 at 60%, N=8 at 70%, N=8 at 80%, N=9 at 90% and N=6 for hatchlings).

View larger version (19K): [in a new window]   Fig. 2. Blood pressure changes (a) elicited by different doses of (A) sodium nitroprusside (SNP) and (B) phenylephrine (PE) at different ages of development. Open bars: 25 µg kg–1 SNP and 30 µg kg–1 PE, respectively; shaded bars: 50 µg kg–1 SNP and 60 µg kg–1 PE, respectively; closed bars: 100 µg kg–1 SNP and 120 µg kg–1 PE, respectively. Data are means ± S.E.M. (N=8). Dissimilar letters indicate differences between ages. All doses except the lowest dose of SNP at 60% of development induced significant changes in pressure.

View larger version (17K): [in a new window]   Fig. 3. Representative hypertensive baroreflex responses at (A) 70%, (B) 80% and (C) 90% of development after an injection of 120 µg kg–1 of phenylephrine (the highest dose). The time of injection is indicated by the arrow. While the y-axis absolute scales vary between developmental ages, the relative scales are maintained for comparative purposes. a, arterial pressure; fH, heart rate.

View larger version (10K): [in a new window]   Fig. 4. The mean baroreflex responses at 60% (diamonds), 70% (squares), 80% (circles) and 90% (triangles) of development. Notice that decreases in blood pressure (a) with sodium nitroprusside (SNP) did not induce reciprocal changes in heart rate (fH). Data are means ± S.E.M. (N=8). Asterisks indicate a significant heart rate response (P<0.05).

View larger version (12K): [in a new window]   Fig. 5. Heart rate–mean blood pressure (fH–a) relationship in 1-week-old hatchling alligators. The data from all pharmacological manipulations are combined in a single trace (N=6); different symbols represent different animals.

View larger version (10K): [in a new window]   Fig. 6. Comparison of the heart rate–mean blood pressure (fH–a) relationship for all developmental ages. The point in each trace indicates resting values for heart rate and mean arterial pressure: open circle, 70%; triangle, 80%; square, 90%; diamond, hatchling; filled circle, 1-year-old.

View larger version (22K): [in a new window]   Fig. 7. Effect on heart rate (fH) of a bolus injection of acetylcholine (100 µg kg–1; time of injection indicated by dotted line) before (solid symbols) and after (open symbols) treatment with atropine (3 mg kg–1) at 70% (A; N=4) and 90% (B; N=5) of development. Data are means ± S.E.M.

View larger version (11K): [in a new window]   Fig. 8. Chorioallantoic membrane mean arterial pressure (a) and heart rate (fH) before (open bars) and after (closed bars) injection of phenylephrine (120 µg kg–1) in 80% and 90% embryos pre-treated with atropine (3 mg kg–1). Notice that phenylephrine has significant effects on pressure but no effects on heart rate. Data are means ± S.E.M. (N=6). Asterisks indicate a significant response to the drug (P<0.05).

View larger version (11K): [in a new window]   Fig. 9. Femoral arterial pressure and heart rate before (open bars) and after (closed bars) injection of phenylephrine (PE; 120 µg kg–1) and sodium nitroprusside (SNP; 100 µg kg–1) in hatchlings pre-treated with atropine (3 mg kg–1). Data are means ± S.E.M. (N=6). Asterisks indicate a significant response to the drug (P<0.05).