Microdialysis Coupled with Electrochemical Detection - Drugs of Abuse: Neurological Reviews and Protocols - page 411

in the dialysis fi ber, taking care to have the inlet reach the lower end and the
outlet reach the higher end of the dialyzing portion (1.0 mm) of the fi ber. The
inlet and the outlet are then sealed to the fi ber and to a 18-mm piece of stainless
steel (obtained from a 24-gauge needle) that were then inserted into a piece of
200- L micropipet tip 6 mm long and glued to it. The fi ber is fi nally covered

with a thin layer of epoxy glue except for the dialyzing part. The probe is left
to dry for 24 h (1 , 5) . Among the wide spectrum of dialysis probes used, this
type offers the distinction of being rigid enough to be implanted properly in
brain, but at the same time is fl exible enough to follow brain movements within
the skull, preventing related tissue damage. We noticed that implanting probes
with metal parts in contact with the brain resulted, at histological examination,
in an increased space between the fi ber and the tissue and in a reduced recovery
of the probe. Probes have to be checked before use. At the beginning of surgery
they can be connected to a perfusion pump delivering saline and left to dialyze
until the end of surgery. There are three reasons for this: (1) checking that the
fi ber is not clogged; (2) the liquid pressure makes the fi ber more rigid during
implant, allowing a more precise positioning in deep areas; (3) removal of Ca 2+
most likely reduces tissue damages due to calcium-dependent processes.

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3.1.3. Time After Implant
The microdialysis technique was fi rst developed in anesthetized rats (7 , 12)
and later used in freely moving rats (13) . It was soon understood that a recovery
period was necessary to clean up the excess of transmitter due to leakage from
terminals damaged by the probe insertion. In the majority of studies a period of
recovery of about 24 h is used although depending on the probe 6-8 h might be
suffi cient to get Ca 2+ dependent tetrodotoxin (TTX)-sensitive neurotransmitter
release. When the microdialysis probe is implanted in mice we noticed that
48-h recovery determines a more stable baseline of extracellular concentration
of DA (14) .

3.1.4. Chronic Implants
Microdialysis can also be performed by implanting a guide cannula 1-2 mm
above the brain area of interest, well in advance, to allow the animal to recover
from the surgery. On the test day a fi ber is implanted and the neurotransmitter is
assayed. Drawbacks of this method are due to (1) the presence of a rigid metal
guide that produces tissue damage above the area investigated and (2) probe
insertion that produces an acute trauma in the area investigated. Infl ammation
of tissue at the site of repeated insertion may reduce the recovery of the probe
(1 , 15) . The advantage of this method is that a different probe can be implanted
in the same animal at long time interval to assess changes in the extracellular
concentration of a neurotransmitter (e.g., due to a chronic treatment). Repeated