Is xenon a suitable euthanasia agent for mice?

Abstract

Objective: To compare behavioural and electrophysiological variables of mice undergoing gas euthanasia with either xenon (Xe) or carbon dioxide (CO₂).

Study design: Single animals chronically instrumented for electroencephalography (EEG) recording were randomized to undergo euthanasia with either CO₂ or Xe (n = 6 animals per group).

Animals: Twelve adult (>6 weeks old) male C57Bl6/n mice.

Methods: Mice were surgically instrumented with EEG and electromyogram electrodes. Following a 7-day recovery period, animals were placed individually in a sealed chamber and a 5-minute baseline recorded in 21% O₂. Gas [100% Xe (n = 6) or 100% CO₂ (n = 6)] was then added to the chamber at 30% chamber volume minute^-1 (2.8 L minute^-1) until cessation of breathing. EEG, behaviour (jumping and freezing) and locomotion speed were recorded throughout.

Results: Mice undergoing single gas euthanasia with Xe did not show jumping or freezing behaviours and had reduced locomotion speed compared to baseline, in contrast to CO₂, which resulted in increases in these variables. EEG recordings revealed sedative effects from Xe but heightened arousal from CO₂.

Conclusions: Our data suggest that Xe may be less aversive than CO₂ when using a 30% chamber volume minute^-1 fill rate and could improve the welfare of mice undergoing gas euthanasia.

Keywords: 3Rs; animal welfare; carbon dioxide; euthanasia; inert gases; mice.