Date of Award:

12-2010

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Psychology

Advisor/Chair:

Timothy A. Shahan

Abstract

Psychological disorders such as autism, obsessive-compulsive disorder, drug addiction, and attention-deficit/hyperactivity disorder involve atypically persistent behavior and atypical activity of the neurotransmitter dopamine. Behavioral momentum theory states that the persistence of behavior in a context is determined by the reinforcement received previously in that context. Contexts previously associated with higher rates of reinforcement yield greater persistence of behavior than contexts previously associated with lower rates of reinforcement. According to a prominent hypothesis in behavioral neuroscience, dopamine mediates the incentive salience of a stimulus. A synthesis of behavioral momentum theory and the incentive salience hypothesis proposes similar roles for dopamine activity and reinforcement in determining the persistence of behavior in a context. The aim of this dissertation was to determine the extent to which a history of dopamine modulation in a context affects the subsequent persistence of behavior in extinction and relapse. Three groups of rats were trained to press a lever for food in two alternating contexts of a multiple schedule. Following a stable baseline, rats entered a treatment phase in which they received a drug or saline injection before and after sessions in each context. In the drug context, rats received the indirect dopamine agonist amphetamine, dopamine D1 antagonist SCH 23390, or a combination of amphetamine and SCH 23390 prior to the session and a saline injection following the session. The injection schedule was reversed for the saline context such that rats received a saline injection prior to each session in the saline context and a drug injection following the session. During an extinction phase, access to food was withheld. Response-independent food was then provided in each context to trigger reinstatement of responding. A history of dopamine agonism in a context increased the relative persistence of behavior, while a history of dopamine antagonism at D1 receptors and a combination of dopamine agonism and dopamine antagonism had little impact on the relative persistence of behavior. Likewise, reinstatement was relatively greater in a context previously associated with dopamine agonism. This effect was blocked when dopamine agonism was preceded by D1 antagonism. A history of D1 antagonism alone did not affect reinstatement. These results suggest that dopamine plays a role in the persistence of behavior in extinction and relapse, but that different dopamine receptors mediate these effects.

Comments

This work made publicly available electronically on October 1, 2010.

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