Fluvoxamine and desipramine on fixed-ratio responding: effects of reinforcement magnitude.

Fluvoxamine, a serotonin reuptake blocker, was previously shown to decrease ethanol-maintained behavior at doses lower than those needed to decrease food-maintained behavior. While these effects could have been due to different response rates and histories of the two groups being compared, a subsequent study found differential effects using a within-subjects design, in which rates of responding were well equated. Another explanation for such differential effects is that food and ethanol reinforcement differ in a quantitative fashion. This is difficult to resolve when comparing between behaviors maintained by different events. To examine how such quantitative differences in reinforcement magnitude might influence the effects of fluvoxamine, we used a multiple schedule of fixed-ratio 30 responding in the pigeon. In each of the three fixed-ratio 30 components, behavior was maintained by a different duration of grain presentation (2, 4, and 8 s). The effects of fluvoxamine and also desipramine were examined. Both dose-dependently decreased fixed-ratio responding. Their effects were independent of the duration of grain presentation maintaining responding. These results do not support the idea that the differential effects of fluvoxamine on ethanol-maintained behavior, as compared with food-maintained behavior, are a result of quantitative differences in reinforcement magnitude.