Classical conditioning to hypoxia using odors as conditioned stimuli in rats

The authors performed a differential conditioning experiment in 30 rats, us ing 2 odors as the conditioned stimuli (CS+ and CS-) and hypoxia (8% O-2) a s the unconditioned stimulus. Vanillin was the CS+ and rose the CS- in half of the rats, and vice versa in the other half. Fifteen paired CS+/hypoxia trials and 15 CS- only trials were performed in random order, followed by 3 CS+ only and 3 CS- only trials to test for conditioning. The increase in v entilation from prestimulus levels averaged 116 +/- 85% in response to CSS versus 55 +/- 36% in response to CS-. This effect was supported by the sign ificant Pre-Post Stimulus X CS Type interaction for this variable (p <.003) . The data confirm the sensitivity of breathing to conditioning processes a nd also indirectly support the hypothesis that feedforward responses may co mplement feedback reflex pathways in respiratory homeostasis.