Modulation of the behavioral effects of carbon monoxide by reinforcement contingencies

Behavioral effects of carbon monoxide (CO) were studied in rats during 75-minute exposures in which food reinforcement depended either on 30 lever presses (fixed ratio, FR, 30) or on the first lever press after 3 min (fixed interval, FI, 3 min). Concentrations of 500, 700, and 900 ppm were studied for each rat under at least one of the reinforcement schedules presented singly and under one or more compound schedules (multiple (MULT) FR FI, MULT FR FR, MULT FI FI). Response rates decreased as a function of CO concentrations under all conditions, but overall rate decreases were greater at lower concentrations under the FR schedule than under the FI schedule. Differential effects of CO on the schedule-generated patterns of FR and FI responding were responsible for the differences in rate decreases under those schedules. In some cases, the multiple schedule context attenuated the rate-decreasing effect of CO on FR responding. Differences in magnitude of CO effects were not attributable to previous CO exposures, control response rates, or reinforcement frequency. The extent to which CO disrupts behavior can be a function of the prevailing behavioral contingencies.