Effects of carbon monoxide on responding under a progressive ratio schedule in rats

Under a progressive ratio schedule the response requirement increases arithmetically with each reinforcement, and the session is terminated when responding ceases for 15 min. Four rats, responding for food on this schedule, were exposed to 4 levels of carbon monoxide, ranging from 155 to 700 ppm, beginning 30 min before the test session and continuing throughout the session. The size of the last completed ratio and the local rate of responding decreased during exposure to the higher levels of carbon monoxide. Post reinforcement pause time was slightly increased for 3 of 4 rats during exposure to the highest level of CO.