Is xenon a suitable euthanasia agent for mice?

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

Study Design: Single animals chronically instrumented for electroencephalography (EEG) recording were randomized to undergo euthanasia with either CO 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% O. Gas [100% Xe (n = 6) or 100% CO (n = 6)] was then added to the chamber at 30% chamber volume minute (2.8 L minute) 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 CO, which resulted in increases in these variables. EEG recordings revealed sedative effects from Xe but heightened arousal from CO.

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