Microdialysis Coupled with Electrochemical Detection - Drugs of Abuse: Neurological Reviews and Protocols - page 410

others prefer to use 2.2 m M [Ca 2+ ] because this condition has permitted the
validation of many pharmacological tools. A particular situation is encountered
when a neurotransmitter is present at so low a concentration that can be barely
detected. In this situation some authors prefer to increase [Ca 2+ ] to be able to
detect the neurotransmitter; others prefer to add an inhibitor of reuptake or of
degradation. We think the fi rst option should be tested fi rst because it should
produce minor pharmacological effects. The infl uence of other ions such as Mg 2+
has in a general minor infl uence but can be important in specifi c situations (1) .
4. Swivels: The swivel is small piece of equipment with an inlet and an outlet for
liquid. It is inserted between the probe and the perfusion syringe allowing the rat
to move freely in the half bowl, without twisting the polyethylene (PE) tubing
that delivers the Ringer. The use can be optional when testing drugs such as
sedatives or drugs that do not stimulate locomotion in general, but becomes
mandatory when drugs that stimulate locomotion such as psychostimulants are
used. When buying swivels it is advisable to purchase two-channel swivels
although they cost a little more than one-channel types, because they allow
connecting two probes implanted in the same animal. Swivel use may be a source
of leakage when the PE tubing does not fi t tightly to the metal probe inlet or
outlet. Leakage in turn can become a source of friction or complete free rotation
block, when the salts, contained in the PR, solidify in the ball bearing. In this
case, swivels can be washed with distilled water and dried with hot air.
3. Methods
3.1. Probe Construction and Implantation
3.1.1. Probe Geometry
Microdialysis probes can be inserted in brain tissue either transversally
or vertically. The fi rst method has the advantage of reduced tissue damage,
because its fl exible connection with the skull allows the fi ber to follow the brain
in its small movements in meningeal fl uids. Major disadvantages are a complex
and time-consuming surgery (11) . The second method has the advantage of
quick and simple surgery, but the presence of a rigid fi ber support produces a
tissue damage around the fi ber caused by brain movements within the skull.
We recently developed a vertical probe that combines some of the advantages
of both methods ( see Subheading 3.1.2. ).
3.1.2. Probe Construction
Concentric dialysis probes can be prepared with a 7-mm piece of AN 69
(sodium methallyl sulfate copolymer) dialysis fi ber (310 µm outer diameter
[o.d.] and 220 µm inner diameter [i.d.]; Hospal, Dasco, Italy), sealed at one
end with a drop of epoxy glue. The sealed end is gently sharpened with a thin
grain abrasive disk to reduce tissue damage during implant. Two 4-cm long
pieces of fused silica (Composite Metal Services, UK) tubing are introduced