In well trained animals approximately 55–80% of dopamine neurons discharge in synchrony during reward-based tasks (Schultz et al., 1997; Schultz, 2007). However, those studies did not consider VTA projection targets and as such may have provided information on only a subpopulation of VTA neurons. By directly measuring dopamine within the core and shell (as opposed to extrapolating release from VTA extracellular recordings) we revealed that although dopamine release is observed in both sub-regions, significant differences exist in the temporal properties of dopamine release across terminal regions. These differences may be related to a more potent dopamine uptake in the core than the shell and, thus, enabling dopamine to diffuse further from its release site in the shell (Jones et al., 1996). These temporal distinctions may contribute to the different functional roles of the core and shell in reward-seeking behaviors (Ito et al., 2000; Di Chiara, 2002; Cadoni & Di Chiara, 2007; Di Ciano et al., 2008).
