dopaminergic nerve terminals at nonphasic cells simply did not receive signals to cause release during lever-pressing perhaps due to presynaptic modulation of terminals (Howland et al., 2002; Britt & McGehee, 2008). Although this hetereogeneity in dopamine release is evident in both the core and shell, we have shown that transient frequency increases significantly in the shell compared to the core following cocaine administration (Aragona et al., 2008). However, during cocaine self-administration we observed spontaneous transients (i.e., dopamine release that occurred independent of ongoing behavior) equally at both phasic and nonphasic cell locations. Thus, dopamine can be released at nonphasic cell locations but is not apparent relative to goal-directed behaviors. Taken together these data suggest a complex and highly modifiable role for dopamine in modulating information processing in the NAc by both pharmacological agents and during cocaine-seeking behavior.
