Daniel Kueh

Date of Award


Degree Name

Master of Arts



First Advisor

Dr. Lisa Baker

Second Advisor

Dr. Bradley Huitema

Third Advisor

Dr. Cynthia Pietras

Access Setting

Masters Thesis-Open Access


Drug discrimination is a model used to assess the subjective effects of different psychoactive drugs such as 3,4-methylenedioxymethamphetamine (MDMA) and cocaine. However, results from MDMA discrimination studies across different laboratories have not been consistent. Possible confounds for this inconsistency may include the use of different reinforcement schedules such as the fixed-ratio 20 (FR20) and the variable interval 15 seconds (VI15 s) during discrimination training. Studies examining the effects of these two schedules on the discriminative stimulus properties of MDMA and cocaine have not been conducted. Thus, the present study compared the FR20 and the VI15 s schedules to determine their influence on discrimination acquisition, response rates, frequency of reinforcements and stimulus generalization in rats trained to discriminate cocaine (10 mg/kg) or MDMA (1.5 mg/kg) from saline. Compared to the VI15 s schedule, the FR20 schedule facilitated rapid discrimination acquisition and established differential response rates and frequency of reinforcement under drug and vehicle conditions. MDMA (ED50 = 0.75 mg/kg) was also found to substitute for cocaine in rats trained to discriminate cocaine from saline.