Mice/rats are different than people in their gas sensing abilities. They do not react to a buildup of CO2, but to a lack of oxygen. That is why slowly cranking up the gas makes them freak out; they can feel the oxygen level decreasing, so they try and run.
People on the other hand are wired to detect CO2 levels. We begin to "freak out" when the CO3 levels are too high, not when the oxygen levels drop.
Moral of the story: slowly turning the gas up is actually more traumatic for the rodent than it may appear. The BEST way to administer the gas (and this is from actual experience with research animals, who MUST be killed 100% humanely) is to pre charge the container with CO2, then drop the mouse in. That way it goes from pure room air to pure CO2 instantly...thy are unconscious before they even hit the bottom of the container. The gasping breaths they take are stimulated by the brainstem AFTER they are unconscious; thus they are not feeling pain or suffering in any way.
Reply With Quote