Different Temporal Gradients of Retrograde Amnesia Produced by Carbon Dioxide Anesthesia and Electroconvulsive Shock

Temporal gradients of amnesic effects from different doses of CO₂ were determined for rats and mice and compared with one obtained in a comparable previous study using electroconvulsive shock (ECS) as the amnesic agent. At 25-sec. exposure to CO₂, rats showed significant retrograde amnesia when treatment was delayed up to 4 min. after punishment, but not after 5, while ECS produced amnesia up to 30 sec. but not after 1 min. In the experimental groups three exposure durations to CO₂ were studied; 25, 15, and 10 sec. 25 sec. was used as the maximum exposure time since preliminary data indicated that this time produced maximum anesthesia with zero mortality. Using repeated learning trials followed by repeated exposures to CO₂, F. Leukel and E. Quinton found that CO₂ significantly impaired the acquisition of an active avoidance task in rats if the gas was administered within 5 min.