Evaluation of the anesthetic effects of MS222 in the adult Mexican axolotl (Ambystoma mexicanum)

Investigation of Potassium Chloride for Euthanasia of Anesthetized African Clawed Frogs (Xenopus laevis)

Euthanasia is frequently performed in amphibians, but techniques are currently limited in number and variable in effectiveness. The current study examined the use of potassium chloride (KCl) for euthanasia of anesthetized African clawed frogs (Xenopus laevis). Twenty adult, female African clawed frogs were anesthetized by immersion in buffered tricaine methanesulfonate (MS-222) for 5 min beyond loss of righting reflex. Frogs were then randomly assigned to receive one of 4 treatments: KCl via intracardiac injection (10 mEq/kg; IC, n = 5), intracoelomic injection (100 mEq/kg; ICe, n = 5), immersion (4,500 mEq/L; IMS, n = 5), or no treatment (C, n = 5). After treatment, serial heart rate was measured via Doppler device until either the loss of Doppler sounds, a 60-min endpoint (IC, ICe, IMS), or recovery (C). Times to loss of righting reflex, loss of Doppler sounds, and/or recovery were recorded. Plasma potassium concentrations were measured immediately after Doppler sound cessation in frogs in IC (n = 1), ICe (n = 2), and IMS (n = 5). Injection failure occurred in 1 IC frog, and 1 Ice frog regained spontaneous movement 4 min after treatment administration. Data from these 2 frogs were not included in statistical analysis. Doppler sound cessation occurred in 4 of 4, 4 of 4, 0 of 5, and 0 of 5 frogs in IC, ICe, IMS, and C, respectively. Median (range) times to Doppler sound cessation in IC and ICe were 6 (0 to 16) s and 18 (10 to 25) min, respectively. Plasma potassium concentration was greater than 9.0 mmol/L in sampled frogs. Intracardiac KCl at 10 mEq/kg and intracoelomic KCl at 100 mEq/kg were effective for euthanasia of anesthetized African clawed frogs. Return to MS-222 solution after KCl administration may be warranted to prevent unintended, premature anesthetic recovery prior to death.

Establishing a New Research Axolotl Colony

The field of regenerative biology has taken a keen interest in the Mexican axolotl (Ambystoma mexicanum) over the past few decades, as this salamander successfully regenerates amputated limbs and injured body parts. Recent progress in research tool development has also made possible axolotl genetic manipulation and single-cell analysis, which will help understand the molecular mechanisms of complex tissue regeneration. To support the growing popularity of this model, we describe how to set up a new axolotl housing facility at a research laboratory. We also review husbandry practices for raising axolotls and using them in biological research, with a focus on diet, water quality, breeding, and anesthesia.

Anesthetic MS-222 eliminates nerve and muscle activity in frogs used for physiology teaching laboratories

Frogs are routinely used in physiology teaching laboratories to demonstrate important physiological processes. There have been recent directives that promote the use of the anesthetic MS-222 (tricaine methanesulfonate), rather than lowering body temperature with a cold water bath to prepare reptiles and amphibians for physiological experiments or euthanasia. Indeed, the most recent edition of the American Veterinary Medical Association (AVMA) Guidelines for the Euthanasia of Animals proclaims that chilling in water is not an appropriate method and advocates for the usage of MS-222 or other anesthetics. However, prominent researchers have responded to this position by highlighting evidence that cooling ectothermic vertebrates is, in fact, an effective and appropriate method. Furthermore, MS-222 is a known voltage-gated Na⁺ channel blocker, and this anesthetic's impact on the physiology of excitable tissues suggests that its use might be incompatible with experiments on nerve and muscle tissues. In the present study, I examined the effects of MS-222 at a concentration of 1.5 g/l on nerve, skeletal muscle, and cardiac muscle physiology of frogs. I found that immersion of frogs in this anesthetic blocked basic nerve and muscle physiology, making the frogs unsuitable for laboratory experiments. Applying MS-222 directly to the sciatic nerve dramatically blocked normal excitation-contraction coupling in skeletal muscle preparations, and direct application to the heart caused the organs to stop contracting. Based on these results, I conclude that MS-222 at the concentration studied may be incompatible with physiological preparations that rely on electrically excitable tissues for their normal function. Physiology educators who must use MS-222 with frogs should empirically determine an appropriate dosage and recovery time before using the anesthetic in the teaching laboratory.