Cocaine abuse alters normal dopamine activity in the nucleus accumbens during associative learning (2013)

Undergraduates: Robert Edmiston, Michael Saddoris

Faculty Advisor: Regina Carelli
Department: Psychology & Neuroscience

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The nucleus accumbens (NAc) of the mesolimbic system plays an essential role in associative learning. Previous research has shown that phasic dopamine activity in the NAc correlates with the learning of associations between stimuli and natural rewards. However, it is unknown how previous cocaine exposure affects this activity. In order to test this, we used fast-scan cyclic voltammetry (FSCV) in the NAc to measure the release of dopamine in response to stimulus and reward presentation during first order conditioning. In first order conditioning, animals were repeatedly presented both with a stimulus that predicted a reward and with one that predicted no reward. We found that cocaine-exposed animals were able to behaviorally associate stimulus and reward to the same degree as water-administering controls. However, phasic dopamine released in the NAc in response to reward-predictive stimuli was significantly lower in cocaine-exposed animals with than in controls. Furthermore, there was differential dopamine release to the two types of stimuli in controls, but not in cocaine-exposed animals. These results suggest that abnormal dopamine signaling in animals with a history of cocaine abuse does not impair their ability to learn simple associations between stimulus and reward. In the future, FSCV might be used to determine if the activity of phasic dopamine in the NAc accounts for the inability of cocaine-exposed rats to learn more complex, higher order associations.