Figure 3.

Cue presentation elicits a phasic surge in dopamine. A, The rise in signal evoked by a representative cue presentation (denoted by black triangle). The peak in dopamine concentration occurred just before the operant response for intra-oral sucrose (denoted by vertical dashed line) and fell to baseline levels during the duration of the intra-oral infusion (black bar) and tone-light stimulus (open bar). B, Dopamine was identified from its peaks at 0.66 and -0.22 V and in the cyclic voltammogram (C, left). As can be seen in the color plot, the oxidation peak (green) is accompanied by its reduction peak (yellow). A statistical comparison of this cyclic voltammogram with one from electrically evoked dopamine release (normalized and shown in red) reveals a close correlation (r² = 0.77). The events that take place in the later part of the color plot, and shown in the right-hand cyclic voltammogram (C, right), are clearly not changes in dopamine concentration. This cyclic voltammogram was not correlated with the one from electrically evoked dopamine release (r² = 0.16). Rather, the events in the latter part of the color plot are more likely caused by a basic pH change in the extracellular space. This interference was removed from the signal trace in the same manner as described for removing interference from electrically evoked dopamine release (Fig. 2).