Fast scan cyclic voltammetry

Suction a single carbon fiber (7μm diameter, Goodfellow) into a capillary tube (Sutter).

Load the carbon fiber/capillary tube into a puller (Narishinge), and under the microscope, hand-cut (scalpel blade) fiber tips 30-100μm past the capillary tip.

Anesthetize mice at postnatal day 90–110 with a ketamine-xylazine mixture.

Perfuse the mice transcardially with ice-cold artificial cerebrospinal fluid (aCSF )containing the following (in mM): 125 NaCl, 2.5 KCl, 1.25 NaH₂PO₄, 2.0 CaCl₂, 1.0 MgCl₂, 25 NaHCO₃, and 12.5 glucose, bubbled continuously with carbogen (95% O₂ and 5% CO₂).

Expose the skull by a caudal to rostral midline incision and gentle remove the brain with a spatula

Glue the brain to the stage of a vibrating microtome (Leica Instrument) and immerse it in ice cold aCSF.

Cut parasagittal slices containing the dorsal striatum at a thickness of 240 μm

Transfer the slices to a holding chamber where there are submerged in aCSF at 37 ºC

Recording dish with cover stimulating electrode and carbon fiber electrode, Amplifier (Molecular Devices), a digitizer (Molecular Devices), and pClamp (Molecular Devices)

Before recording, condition the electrodes by running the ramp at 60 Hz for 15 min and 10 Hz for another 15 min.

Deliver a voltage ramp to and from 1.2 V (400 V/s) every 100 ms (10 Hz) to detect the oxidation and redox peak for DA.

Before recording, calibrate the carbon fiber electrode by applying a flow of dopamine diluted in aSCF in known concentrations until dopamine signals are stable

Dopamine transients are evoked by electrical stimulation delivered through a concentric, bipolar electrode (FHC) placed in the rostrodorsal striatum.

Use a single electrical pulse ( 300 MA , 0.2 ms ).

Perforvoltammetricic measurements by sampling at dorsostriatal sites ~200–400 µm ventral and posterior from the forceps minor corpus callosum.

Take four recordings each site with two-minute intervals between recordings and then averaged as a reported measure.

The voltammogram and peak oxidative current amplitudes of the dopamine transient are measured.

Note: Experiments were rejected when the evoked current did not have the characteristic electrochemical signature of dopamine.

-Four recordings taken at each site with two-minute intervals between recordings and then averaged as a reported measure.

-Considering the slice where the GPe was first evidenced as the most lateral slice.

• consecutive slices 480 µm apart and medial of this lateral slice should be considered intermediate and medial ones. -The recording order of the slices is randomized to reduce potential recording biases and mitigate possible electrode sensitivity issues.

-Electrode sensitivity is to be retested at the end of recordings with a freshly made dopamine stock used for calibration.

-Recordings from electrodes with a larger than 10% change from calibrated dopamine solution are subtracted.