To examine the relationship between rapid dopamine release and NAc cell firing, Experiment 2 employed a combined electrochemistry and electrophysiology technique (Cheer et al., 2005). This powerful method allowed for the simultaneous recording of NAc cell firing and dopamine release from the same electrode during behavior. This study revealed that dopamine changes that occur within seconds of lever pressing for intravenous cocaine are accompanied by changes in unit activity of some NAc neurons. We previously established several patterns of cell firing during cocaine self-administration using multiple electrode arrays (Carelli, 2000; Hollander et al., 2002) and also demonstrated equal distribution of cell types across the core and shell (Carelli & Wondolowski, 2006). These distinct firing patterns were maintained when collecting with a single carbon fiber-electrode. Remarkably, at the majority of the sites where cells responded to the lever press with a phasic change in activity, dynamic increases in the extracellular concentration of dopamine were found. At those same locations significantly larger increases in stimulated dopamine release were measured indicating stronger dopaminergic influences compared to sites at which nonphasic neurons were recorded.
