The dopamine-depleting agent tetrabenazine alters effort-based choice, suppressing food-reinforced behaviors with high response requirements, while increasing selection of low-cost options. In the present experiments, rats were tested on a concurrent fixed ratio 5/chow feeding choice task, in which high-carbohydrate Bio-serv pellets reinforced lever pressing and lab chow was concurrently available. Detailed timing of lever pressing was monitored with an event recording system, and the temporal characteristics of operant behavior seen after 1.0 mg/kg tetrabenazine or vehicle injections were analyzed. Tetrabenazine shifted choice, decreasing lever pressing but increasing chow intake. There was a small effect on the interresponse-time distribution within ratios, but marked increases in the total duration of pauses in responding. The postreinforcement-pause (PRP) distribution was bimodal, but tetrabenazine did not increase the duration of PRPs. Tetrabenazine increased time feeding and duration and number of feeding bouts, but did not affect feeding rate or total time spent lever pressing for pellets and consuming chow. Thus, TBZ appears to predominantly affect the relative allocation of lever pressing versus chow, with little alteration in consummatory motor acts involved in chow intake. Tetrabenazine is used to model motivational symptoms in psychopathology, and these effects in rats could have implications for psychiatric research.
Keywords: behavioral economics; dopamine; effort; reinforcement; work.
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