Candidate: Thomas B. Morgan

Degree of: Doctor of Philosophy

Department: Psychology

Title: The Effects of Dextromethorphan on Response Acquisition with Delayed Reinforcement

Committee: Dr. Alan Poling, Chair
Dr. Lisa Baker
Dr. Steve Ragotzy
Dr. Cynthia Pietras

Date: Monday, May 16, 2005 9:00 a.m.-11:00 p.m.
3715 Wood Hall

Abstract: The current study examined in 2-hour sessions the effects of IP injections of dextromethorphan (DM) (0.0, 40.0, 60.0, and 80.0 mg/kg) on the acquisition of lever-press responding in rats that were exposed to a two-lever procedure in which responses on the reinforcement lever (RL) were reinforced with food after a 15-second resetting delay and responses on the cancellation lever cancelled a scheduled reinforcer. Response acquisition was observed at all drug doses. A decrease in RL responses, food deliveries, and the number of subjects that acquired responding was observed at the highest dose of DM. All doses of DM increased latency to respond relative to the control group. The results of the present study suggest that DM disrupts the acquisition of a novel response at high doses. Prior studies, using other procedures, have found DM-induced disruption of learning at lower doses. Although the two-lever response acquisition procedure is a tenable assay of drug effects on learning, the sensitivity of the procedure appears to be relatively low.

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