EFFECT OF THE 5-HT1A AGONIST, 8-OH-DPAT ON INSTRUMENTAL PERFORMANCE IN RATS

These experiments assessed whether reported increases in food consumpt ion and food-reinforced instrumental performance in undeprived rats by the 5-HT1A agonist 8-hydroxy-2(di-n-propylamino)tetralin (8-OH-DPAT) are due to an increment in the incentive value of foods. Against this hypothesis, we found that when undeprived rats were trained to lever p ress for the food pellets and then allowed to consume the pellets unde r 8-OH-DPAT, this reexposure decreased subsequent instrumental extinct ion performance regardless of test drug condition relative to reexposu re under vehicle. Although both food consumption and reinforced lever press performance were incremented, 8-OH-DPAT was found generally to r educe instrumental extinction performance and lever pressing during a period when the reinforcer was delivered non-contingently, Rats inject ed with 8-OH-DPAT were, however, more sensitive to delay of reinforcem ent, and increased their lever press performance at a 3-s delay but de creased performance at 6-s and 12-s delays relative to animals injecte d with vehicle. These results are consistent with the hypothesis that 8-OH-DPAT modifies arousal processes in a manner similar to mild stres s, thereby acting both to elevate rewarded instrumental performance an d to increase sensitivity to the effects of non-reward.