Meeting Abstract
P2.109 Jan. 5 Developmental plasticity of cardio-respiratory control in African clawed frog, Xenopus laevis PAN, T.C.*; BURGGREN, W.W.; Univ. of North Texas, Denton; Univ. of North Texas, Denton tp0073@unt.edu
Most research on the respiratory development of amphibians has focused on metamorphosis or the water-air breathing transition rather than earlier stages. In the present study, the development of breathing and cardiac response to acute hypoxia (5%, 10% and 15%) was examined in Xenopus laevis. The effect of chronic hypoxic (15%) exposure on the development of cardio-respiratory regulatory system in embryonic and larval Xenopus laevis was also investigated. Breathing frequency and heart rate were recorded with an inverted microscope by placing early larvae in a modified cell culture dish in which animals were restrained but unanesthetized. The holding chamber received a constant flow of water with controlled O2 level (21%, 15%, 10% or 5%). Normoxic larvae started gill ventilation at 4 dpf. Breathing rate reached a peak at 7 dpf (61 � 6 min-1) and then decreased gradually. Larvae from populations chronically exposed to both 21% and 15% O2 began to respond to acute hypoxia (10 minutes exposure) by increasing buccal pumping rate at 3 dpf, and the rate kept increasing following the decrease of ambient O2. Long-term exposure to hypoxia (15%) decreased the buccal pumping rate measured in 15% O2 compared with that in larvae reared in normoxia. Hypoxic bradycardia in adults was not observed in embryonic and larval stages (up to 30 days). The early breathing response to acute hypoxia shows that the respiratory reflex is established at 3 days. The depression of buccal pumping rate in larvae chronically exposed to 15% O2 may indicate the desensitization of oxygen receptors during hypoxic acclimation. Our results also suggest that the cardiac reflex responding to acute hypoxia is not fully functional in the first month of development, nor is its onset affected by chronic hypoxia.
