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 443

4.4. Surgery
6. To provide adequate space between the stimulating electrode and the guide
cannula, the stimulating electrode wires should be bent at a 90° angle from the
plastic hub and then bent back down at another 90° angle, to give a horizontal
distance of ~2 mm between the hub and the main axis of the wires. Following
surgery, the animal should be monitored daily and gently handled to facilitate
experimental procedures. While handling, the stylet should be removed from the
guide cannula, cleaned with an alcohol wipe, and reinserted.
4.5. Experiment
7. Experiments should be conducted 2-10 d after surgery. The earliest post-surgical
day that experiments can be carried out on is dependent on the rat's well being.
Full recovery usually takes 2 d, but it can be as many as 5. The latest day that
experiments can be carried out is dependent on a number of factors concerning
the integrity of each of the electrodes. After a period of time in the brain,
reference electrodes can drop their holding potential by approx 0.20 V. This
is most likely due to dechlorination of the silver wire. After this occurs, all
applied potentials will be 0.20 V lower than anticipated. This problem is easily
identifi able to the trained eye by the shifted appearance of the background current
on the oscilloscope. The occurrence of this problem potentially could be avoided
with the use of removable reference electrodes. The stimulating electrode may
also lose its functionality after several days implanted in the brain, resulting in
both a lack of behavioral and neurochemical response to stimulation. Lastly, an
accumulation of dried blood or perhaps gliosis at the tip of the guide cannula can
cause carbon fi ber microelectrodes to break as they are lowered into the brain.
This problem can sometimes be resolved by inserting a stylet cut to extend past
the tip of the guide cannula, but not as far as the target tissue to clear a path for
the electrode. However, the problem becomes more prolifi c and the remedy less
effective as post-surgical time increases.
8. During the initial period that voltammetric scans are applied to a fresh carbon
fi ber microelectrode, the background current tends to drift. This may be due
to adsorption of brain material to the electrode surface ( see notes on electrode
calibration) and other surface changes. Therefore the electrode should be left
to equilibrate (while applying voltammetric scans) for about 30 min before the
start of the experiment. This time can also be used to habituate the rat to the
environment.
9. Although fast-scan cyclic voltammetry has the best chemical selectivity of the
real-time electrochemical techniques, it is not defi nitive. Therefore, in addition
to confi rming that cyclic voltammograms obtained in vivo correlate well with
those from in vitro calibrations of dopamine, a set of identifi cation criteria is
used (13) . First, the anatomy should support the presence of the analyte, that is,
the electrode must be in a dopamine-rich region. This is readily evaluated with
common histological techniques. Next, the physiology should be consistent with