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 438

3. The exposed carbon fi ber then needs to be cut with a sharp scalpel under a light
microscope (~400 m. The electrode

should also be inspected under the microscope for visible cracks or abnormalities
in the fi ber or glass seal, and discarded if any are present.

× magnifi cation) to a length of 75-150 µ

4. Trimmed carbon fi ber microelectrodes are loaded into micromanipulators that
can interface with the guide cannula implanted in the rat brain ( Fig. 2 ). The
electrode is inserted into the manipulator and a small diameter stainless steel
wire, dipped in silver paint, is fed into the back of the capillary to make an
electrical connection with the carbon fi ber. The wire and capillary are then
secured to the micromanipulator with heat shrink tubing.

5. The microelectrode is soaked in isopropanol for at least ten minutes, and then
before use, the fi delity of the glass seal and the carbon fi ber should be inspected
once again under a light microscope.

3.3.2. Ag/AgCl Reference Electrodes

1. A piece of silver wire is cut to ~10 mm, inserted into the socket of a gold
connector, and fi xed with epoxy.

2. Once this has cured, the positive terminal of a 1.5-V battery is connected to the
gold pin on the silver wire (anode) and the negative terminal to a stainless steel wire
(cathode) immersed in a concentrated solution of hydrochloric acid (37%).

3. The silver wire is dipped into the hydrochloric acid for about 30 s until its
surface becomes dark gray (bubbles should appear as gas is evolved during
this process).

3.4. Surgery
3.4.1. Guide Cannula and Reference Electrode Implantations

1. The rat is anesthetized with intramuscular ketamine (80 mg/kg) and xylazine
(12 mg/kg) and placed in a stereotaxic frame. The scalp is incised and retracted to
reveal a 15-20 mm (longitudinal) and 10-15 mm (lateral) area of cranium.

2. Holes are drilled for the guide cannula, stimulating and reference electrodes
and three anchor screws. The stimulating electrode can be positioned either in
the dopaminergic cell bodies region (substantia nigra/ventral tegmental area;
1.0 mm lateral and 5.2 mm caudal from bregma, ~8.5 mm ventral from dura
mater) or the ascending fi bers in the medial forebrain bundle (1.4 mm lateral
and 4.6 mm caudal from bregma, ~8.5 mm ventral from dura mater). The guide
cannula and stylet are trimmed to 2.5 mm past the plastic hub and positioned
above the target area (e.g., 1.3 mm lateral and 1.3 mm rostral from bregma
would be above the caudate-putamen and the core of the nucleus accumbens).
The reference electrode is placed in the contralateral hemisphere opposite the
guide cannula.

3. Once the guide cannula, reference electrodes and anchor screws are in place,
they are secured with cranioplastic cement, leaving the stimulating electrode
hole exposed.