Real-Time Measurements of Phasic Changes in Extracellular Dopamine Concentration in Freely Moving Rats by Fast-Scan Cyclic Voltammetry - Drugs of Abuse: Neurological Reviews and Protocols - page 433

3. Guide cannula: MD-2251 (locking, with stylet) (Bioanalytical Systems, West
Lafayette, IN).

4. Anchor screws: O-80 × 1/8 (stainless steel, 3.2 mm) (Plastics One, Roanoke, VA).

5. Cranioplastic cement: 675571/2 (Grip Cement) (DENTSPLY Caulk, Mil-
ford, DE).

6. Stimulating electrode: MS303/2 (stainless steel, 0.2 mm, bipolar) (Plastics One).

2.5. Experiment

1. Video character generator (UNC-CH Electronics Design Facility).

2.6. Electrode Calibration

1. Dopamine HCl (Sigma H6,025-5).

2. Flow injection apparatus (Rheodyne, Rohnert Park, CA).

3. Tris-HCl buffer solution: 12.0 m M Tris-HCl, 140 m M NaCl, 3.25 m M KCl,
1.20 m M CaCl 2 , 1.25 m M NaH 2 PO 4 , 1.20 m M MgCl 2 , 2.00 m M Na 2 SO 4 ,
pH 7.40. Store at room temperature.

2.7. Data Analysis

1. Software: Locally written in LabVIEW (National Instruments).

2.8. Verifi cation of Electrode Placement

1. Stainless steel electrode: 5725 (0.5 mm, 8° taper, 12 M ) (A-M Systems).

2. Stimulator: A360R/A362/PRO4 (World Precision Instruments, Sarasota, FL).

3. Paraformaldehyde: 4% Paraformaldehyde in phosphate buffer (80 m M Na 2 HPO 4 ,
20 m M NaH 2 PO 4 ), pH 7.4. Refrigerate.

4. Thionin stain: 1.75 m M Thionin acetate, 450 m M sodium acetate in 3.5% acetic
acid. Store at room temperature.

5. Potassium ferricyanide solution: 150 m M potassium ferricyanide in 10% HCl.
Make up fresh.

3. Methods
3.1. Electrochemistry
Using real-time electrochemical techniques, dopamine can be monitored
in brain tissue on the millisecond time scale ( see Note 1 ). It can be electro-
chemically detected at carbon fi ber microelectrodes because at physiological
temperature and pH it is oxidized by application of a relatively modest potential
to the electrode. This reaction converts dopamine to its o -quinone by oxidation
of the two hydroxyl groups of the catechol, thus liberating two electrons from
each dopamine molecule. These electrons are measured at the electrode as
(faradaic) current.
With fast-scan cyclic voltammetry, the carbon fi ber microelectrode ( see
Note 2 ) is held at a nonoxidizing potential and then periodically driven to an