CLASSIC CONDITIONING OF THE VENTILATORY RESPONSES IN RATS

Recent authors have stressed the role of conditioning in the control o f breathing, but experimental evidence of this role is still sparse an d contradictory. To establish that classic conditioning of the ventila tory responses can occur in rats, we performed a controlled experiment in which a 1-min tone [conditioned stimulus (CS)] was paired with a h ypercapnic stimulus [8.5% CO2, unconditioned stimulus (US)]. The exper imental group (n = 9) received five paired CS-US presentations, follow ed by one CS alone to test conditioning. This sequence was repeated si x times. The control group (n = 7) received the same number of CS and US, but each US was delivered 3 min after the CS. We observed that aft er the CS alone, breath duration was significantly longer in the exper imental than in the control group and mean ventilation was significant ly lower, thus showing inhibitory conditioning. This conditioning may have resulted from the association between the CS and the inhibitory a nd aversive effects of CO2. The present results confirmed the high sen sitivity of the respiratory controller to conditioning processes.