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 439

3.4.2. Stimulating Electrode Implantation

1. The stimulating electrode is prepared by separating the tips by 0.8-1.0 mm and
cutting (or fi ling) them to a uniform length. Dura mater is thoroughly cleared
from the stimulating electrode hole and the electrode is stereotaxically lowered
into the tissue oriented so that the tips of the electrode are splayed in the coronal
plane ( see Note 6 ). The electrode is lowered to 1 mm above the target, taking
care that it does not defl ect against bone at the side of the hole. The stylet is
now removed from the guide cannula and replaced with a micromanipulator
containing a carbon fi ber microelectrode. The carbon fi ber microelectrode is then
lowered to the target dopaminergic terminal region.

2. The stimulating electrode is connected to the stimulator and the carbon fi ber
and reference electrodes to the headstage. The voltammetric waveform is then
switched on. After allowing the carbon fi ber to stabilize for several minutes,
an electrical stimulation (60 biphasic pulses, 60 Hz, ±120 A, 2 ms/phase) is

applied through the stimulating electrode while dopamine is monitored at the
carbon fi ber microelectrode. The stimulating electrode is then lowered in 0.2-mm
increments until dopamine effl ux is detected following a stimulation. It is then
lowered further in 0.1-mm increments until dopamine release is maximal.

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3. Finally, cranioplastic cement is applied to the part of the cranium that is
still exposed, carefully covering the stimulating electrode and lower half of
its plastic hub.

3.5. Experiment
3.5.1. Connecting the Tether
On the experiment day ( see Note 7 ), all connectors are cleaned and the stylet
is removed and replaced with a micromanipulator containing a carbon fi ber
microelectrode. The stimulator cable (on which the headstage is mounted) is
connected and secured onto the stimulating electrode and the carbon fi ber and
reference electrodes are connected to the headstage ( Fig. 2 ).

3.5.2. Positioning the Carbon Fiber Microelectrode

1. The carbon fi ber microelectrode is slowly lowered into the brain and its output is
observed on an oscilloscope. When the carbon fi ber enters tissue the background
current will be seen. The electrode is slowly lowered to just above the target
tissue and allowed to stabilize for several minutes. If the electrode breaks, it will
be apparent by a sudden change in the shape of the background current to a more
resistive profi le (approximating a triangular wave), and it should be removed and
replaced with a fresh carbon fi ber microelectrode.

2. An electrical stimulation (24 biphasic pulses, 60 Hz, ±120 A, 2 ms/phase) is

applied to the stimulating electrode while dopamine is monitored at the carbon
fi ber microelectrode. The behavioral reaction to the stimulation is usually a head
turn to the ipsilateral side followed by sniffi ng. The carbon fi ber microelectrode

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