Fig. 2.

Interfacial dopamine concentration was transduced at a platinum microelectrode with the constant potential amperometry technique, which involved applying a +500 mV potential with respect to an AgCl electrode. Simultaneous calibration across four channels of the array was performed (A) prior to and (B) after implantation with dopamine solution concentrations ranging from 100 nM to 20 µM. (C) In vivo amperometric recordings were transformed into a dopamine concentration with the post-implant calibration fits. Although sites were sensitive to dopamine after probe explantation, the sensitivity was decreased (paired t-test, p=0.013, n=4). (D) To verify that the electrically-evoked in vivo electrochemical signals corresponded to changes in extra-synaptic dopamine concentrations, rats were injected i.p. with a dopamine uptake inhibitor (nomifensine, 12 mg/kg). Response curves represent an average of five trials with standard errors indicated by the gray fills. (E) MFB stimulation did not elicit detectable dopamine transients when a microelectrode site was positioned in the corpus callosum (CC), which contrasted with the large peaks observed simultaneously in the striatum (Str). Shown are three stimulation trials for 1-s long consecutive pulse trains using frequencies of 10, 50, and 100 Hz (150 µA, 2 ms duration biphasic waveforms). Subtraction of the two recordings decreased common noise between the two platinum microelectrodes.