Degrees of aversion shown by rats and mice to different concentrations of inhalational anaesthetics

Study of effects of inhalational anaesthetics used on small rodents

source: M.C. Leach et al
Veterinary Record vol 150 no26, June 29 2002
starts p808, 8 pages long

It is important to assess how humane anaesthetics are that are used with rodents, since many procedures require a general anaesthetic. Little work has been carried out on distress suffered by animals and how they initially react to anaesthetics. This research was carried out at Birmingham University, England, using 60 mice and 60 rats. Their levels of aversion were measured using different agents at high, medium and low concentrations in test chambers. The animals were able to enter and leave the test chambers when they wanted to. The rodents' aversion levels were measured by how long they spent in these chambers, and their initial withdrawal.

Both mice and rats showed most aversion to carbon dioxide. Rats showed least aversion to halothane, and mice showed least aversion to enflurane and halothane. Their reactions to isoflurane were also tested, and they were less aversive to this agent than to carbon dioxide. Rats showed greater levels of aversion the higher the concentrations, though mice tended not to show more aversion to agents at high than at medium concentrations.

Some aversion was found for all four agents. Medium concentrations of halothane (rats) or halothane or enflurane (mice) appear to provide the best balance in terms of minimizing distress, and rapid induction.