Meeting Abstract

P3.150  Thursday, Jan. 6  Xenopus laevis does not need to use lungs to breath ROSE, C.S.*; JAMES, B.D.; James Madison University rosecs@jmu.edu

Amphibians differ from other tetrapods in utilizing gills and lungs as larvae. While lung use is considered obligatory in frogs, when tadpoles start using lungs and when lung use becomes obligatory is unclear. We addressed this issue by studying lung development and air breathing in Xenopus, and the effects of air deprivation. To study natural development, specimens at embryonic and early tadpoles stages were BrdU-treated, processed for wax histology, and examined in frontal, transverse and sagittal sections. To air-deprive specimens, embryos were placed in a screen cage and reared in well-aerated water. Specimens were fixed either directly from the cage or after varying intervals following removal from the cage. All specimens were examined for relative size of lungs in the pleuroperitoneal cavity; BrdU-treated specimens were also examined for cell division in lung tissue. Lungs develop at a mid embryonic stage; lung breathing starts at an early tadpole stage and coincides with the onset of continuous swimming. Of 15 air-deprived animals, 3 had no lungs and 12 had undersized lungs. Of 25 air-restored animals, 1 had no lungs, 16 had undersized lungs and 8 had full sized lungs. The results demonstrate that lung use is not obligatory in Xenopus raised in well-aerated water. Preventing access to air stunts or prevents lung growth into the pleuroperitoneal cavity, and restoring access to air allows for, but does not ensure, partial or complete recovery of lung development. Lung recovery generally happens within one week after restoring access, and its frequency decreases after the tadpole stage. This might result from the differentiation of bronchial tissues precluding a growth response to inhaled air, increased pressure from other organs as evidenced by fusion of lung tissue to the cavity lining, and/or frogs losing the inclination to breath air.