Abstract: Organisms constantly assess the cost and benefit of the possible future outcomes of their behavior and use the information to guide the future behavior, a process called cost-benefit decision making. The current study used a T-maze delayed reward procedure to examine the effects of the non-selective dopamine receptor antagonist haloperidol and the norepinephrine/serotonin reuptake inhibitor imipramine on decision making (choice between a delayed high reward [HR] and an immediate low reward), and how delay on access to the HR alters the decision making. Six groups of rats (n=8 per group) were treated with saline, haloperidol, imipramine (3, 8 or 10 mg/kg), or a combination of haloperidol (0.2mg/kg) and imipramine (8mg/kg). The experiment comprised three periods: initial training period during which animals had free access to the rewards located in both arms of the T-maze for each of the 10 daily trials; forced training period during which animals were allowed to have access to each of the two arms for the first two forced trials followed by 10 choice trials (access to both arms) with a delay imposed on the HR; and test period which was similar with the forced training period except that animals received drug treatment before the test session. Haloperidol decreased choice to HR when 15 or 30 s delay was applied to HR. In contrast, imipramine increased choice to HR. The decreased HR choice induced by haloperidol was reversed by imipramine. Increasing delay to HR decreased choice to HR. In conclusion, these data suggest that delay is an important factor for determining choice behavior, and that haloperidol and imipramine have opposing effects on decision making.

Key words: haloperidol, imipramine, cost-benefit, decision making, delay reward