Effects of carbon monoxide on fixed-consecutive-number performance in rats

Four rats were trained under a fixed-consecutive-number (FCN) schedule to make sequences of 20 or more consecutive responses on one lever followed by a single response on a second lever. When performance was stable, they were exposed to 200, 400, and 600 parts-per-million (PPM) carbon monoxide (CO) for either 30 or 60 min before and during a 45-min session. Decreases in response rate at CO levels as low as 200 ppm were due to both decreased local response rate and extended pauses. A lowered percentage of reinforcement, due to decreases in response sequence length, was also found at CO levels as low as 200 ppm. This decreased sequence length may reflect effects of CO on response rate, or a disruption of discriminative aspects of FCN schedule performance.