(a) Schematic diagram of using an OECT-array to map dopamine release around NAc region in response to neural stimulation of VTA. (b) Immunostaining of brain tissues in NAc (upper) or VTA (lower) after the electrochemical measurements. The NAc brain slices were stained for dopaminergic axon terminals (TH+, red) and cell nuclei (DAPI, cyan); the VTA brain slices were stained for dopaminergic neurons (TH+, red) and neural activation marker (c-Fos+, green). The implantation track of the OECT-array (in NAc) and the stimulation electrode (in VTA) were indicated by the dashed lines. Scale bar, 100 μm. (c) The IDS recorded from the OECT-unit placed in NAc in response to electrical stimulation of VTA (2 ms pulse width, 50 Hz, 50 pulses; VDS = 0.05V; VGS = 0.65V). The gray curves are the raw IDS recording from multiple VTA-stimulation trials, the solid red curve shows the average of all 34 trials, and the red shade indicates the range of standard error. (d) Quantitative measurements of dopamine release in NAc in response to VTA-stimulation, n = 3, * indicates p<0.05 by student t-test. (e) Frequency-dependent dopamine release in the NAc as evoked by VTA stimulation (2 ms pulse width, 1 s duration, 30, 50, or 100 Hz), n = 3. (f) Comparison of dopamine release simultaneously measured by the 1st (inside NAc) and the 2nd (outside NAc) OECT-unit in response to VTA-stimulation (2 ms pulse width, 50 Hz, 1 s duration), n = 8, ** indicates p<0.005 by student t-test. For panel d-f, error bars indicate standard error.