Rapid dopamine release in the NAc core is consistent with prior studies showing an increase in [DA]s within seconds before and immediately following the response for intravenous cocaine (Phillips et al., 2003b; Stuber et al., 2005a; Stuber et al., 2005b). We previously showed that electrical stimulation of the VTA and consequent dopamine release in the core evokes cocaine self-administration, indicating that phasic dopamine transients preceding the response may function to promote reward-seeking (Phillips et al., 2003b). Additionally, rapid dopamine release in the core within seconds following the cocaine-reinforced response appears to be related to external cues (i.e., tone-houselight) paired with drug infusion during self-administration (Phillips et al., 2003b). The finding that these chemical signals are significantly attenuated during extinction (Stuber et al., 2005b) supports the notion that the changes in dopamine at the time of the lever press are not related to a direct pharmacological action of cocaine, but instead reflect learned associations between response completion, cue onset and cocaine reward.
