Anesthesia for Echocardiography and Magnetic Resonance Imaging in the African Clawed Frog (Xenopus laevis)

Abstract

This report describes an anesthesia technique that we used to study cardiovascular anatomy and physiology with echocardiography and cardiac magnetic resonance (CMR) in 46 African clawed frogs (Xenopus laevis) (n = 24 for electrocardiography and n = 22 for CMR). For administration of anesthesia, 3 holding tanks, one each for transportation, sedation, and recovery, were filled with filtered water, with 0.05% buffered tricaine methasulfonate solution (MS-222) added into the sedation tank. Fifteen minutes after the frog was placed in the sedation tank, a paper towel was soaked in MS-222 solution, and the frog was placed in a supine position and rolled 3 to 4 times in the soaked paper with the head and legs exposed. Vital signs were monitored and recorded throughout the procedure. After imagining, frogs were unrolled from the paper towel, placed in the recovery tank, and later returned to their home tank. Monitoring was discontinued when the frogs resumed typical activity. No mortality or complications were observed in frogs that underwent this procedure. Mean duration ± 1 SD of anesthesia induction was 12 ± 5 min in the echocardiography group and 14 ± 6 min in the CMR group. The mean duration of anesthesia maintenance was 60 ± 18 min in the echocardiography group and 118 ± 37 min in the CMR group. An additional dose of anesthesia was necessary during maintenance for 9 of 24 (37%) frogs in the echocardiography group and 6 of 22 (27%) frogs in the CMR group. At the end of the procedure, the mean oxygen saturation was 66 ± 9% in the echocardiography group and 85 ± 6% in the CMR group, and heart rate was 48 ± 13 beats/min in the echocardiography group and 42 ± 7 beats/min in the CMR group. We conclude that the anesthesia technique of immersion in MS-222 is suitable for performing echocardiography and CMR imaging in this species without complications.

Single ventricle: amphibians and human beings

“…What seem extremely interesting are the observations of the similarities between the anatomical and physiological findings in frogs and salamanders and the few reported cases with single ventricle who survived until adult age without surgery [7,19,23,24]. The presence of intact interatrial septum, by preventing any mixing at atrial level, may well justify that, in the absence of complete mixing in the single ventricular chamber, and with certain morphological characteristics, the amphibians can live unrestrictive long life.…”

“…In the circulatory system of frogs and salamanders, the two circulations are fused at the level of single ventricle, but then they are split at the pulmonary and systemic branches, where the amount of blood flow distributed between the outlet arteries is determined by the ration of the peripheral resistances in the two territories [24]. The relative oxygen concentration in the pulmonary and systemic arteries has not yet been measured in relationship to intra-cardiac anatomy, but we must assume that it is possible and hopefully it will be soon available [7].…”

“…The simplest final product of the cardiac dysfunction in single ventricle is expressed by cyanosis and dyspnea [1][2][3][4][5][6]28]. It is likely that the pulmonary vascular resistance are variable in different functional states, especially in frogs and salamanders, with the resulting QP:QS, ration between the pulmonary blood flow (QP) and systemic blood flow (QS), depending upon variable circumstances and environments [7,24], as in human beings with single ventricle. In general, the cardiac hemodynamics is primarily controlled by pressures and resistance, and not by metabolic markers, such as oxygen concentration.…”

“…Mathematical and computational fluid dynamic models were used to study the blood flow distribution in single ventricle [20,21], and a better design of circulation, altering the traditional surgical options [22]. Research could greatly benefit from studies performed on animals born with single ventricle, even if the only animal models available in nature are amphibians, like axolotl salamander (Ambystoma mexicanum) [7] and frogs (Xenopus laevis) [23,24], and reptiles.These experimental studies on amphibians, performed with echocardiography and cardiac magnetic resonance imaging, revealed that salamanders and frogs have two elements in common in their double inlet form of single ventricle: intact interatrial septum and excessively trabeculated ventricular chamber.…”

“…Mathematical and computational fluid dynamic models were used to study the blood flow distribution in single ventricle [20,21], and a better design of circulation, altering the traditional surgical options [22]. Research could greatly benefit from studies performed on animals born with single ventricle, even if the only animal models available in nature are amphibians, like axolotl salamander (Ambystoma mexicanum) [7] and frogs (Xenopus laevis) [23,24], and reptiles.…”