Biomedical Engineering Reference
In-Depth Information
and the subsequent lack of dopaminergic inputs into the striatum. This causes an alte-
ration of the activity pattern in the basal ganglia [2]. Deep brain stimulation (DBS) is
a novel therapeutic option for PD as well as an increasing number of neuropsychiatric
disorders. Before DBS became a therapeutic intervention, electric stimulation of basal
ganglia had been used to guide neurosurgeons to the precise position for a surgical
lesion, the ultimate therapy of a late-stage PD. The main advantage of DBS over sur-
gical lesions is the reversibility and possibility to modulate stimulation parameters
[3]. The small volume of the target region for DBS in the human brain requires a
highly specific adaption of the electrodes which need to be thoroughly tested in ani-
mal models, including different materials and geometries. So far, DBS-data of animal
models of PD are scarce. During
in-vivo
stimulation, the properties of the DBS elec-
trodes are changing as a function of time caused by electrochemical processes at the
surface of the implant and the subsequent tissue response [5]. The tissue response is a
foreign substance reaction. Its intensity depends on the material [Grill and Mortimer,
1994] and is correlated with the thickness of the adventitia finally encapsulating the
implant [18]. Adventitia formation causes a steady change in the impedance of the
electrodes leading to changes in the attenuation of the stimulating signal. As a result,
the efficiency of the surrounding tissue stimulation is changing [12]; [13]; [7]. One
opportunity to minimize this problem is to choose an appropriate electrode material.
Previous investigations of our group [6]; [8] have shown that the use of stainless steel
electrodes is not appropriate because of the corrosion and erosion processes intensi-
fied by electrolytic electrode processes. Electrochemically induced alterations are
negligible for inert platinum electrodes, even though electrode processes may still
influence the surrounding tissue [5]. For an optimal adjustment of the DBS signal, the
kinetics of the electrode-impedance alterations caused by the adventitia formation
must be taken into account [12]; [13].
2
Materials and Methods
2.1
Animal Treatment
Forty, adult, male Wistar Han rats (240-260 g) were obtained from Charles River
Laboratory, Sulzfeld, Germany) and housed under temperature-controlled conditions
in a 12 h light-dark cycle with conventional rodent chow and water provided ad libi-
tum. The rats were subject to the following treatments:
•
anesthesia (40 rats)
•
6-OHDA-lesioning (40 rats, 2 rats died while surgery)
•
electrode implantation (38 rats (2 rats died while surgery): 15 unipolar electrodes,
21 bipolar electrodes)
•
chronical instrumentation (26 rats: 21 rats with bipolar electrodes, 5 rats with un-
ipolar electrodes)
•
impedance measurement without chronical instrumentation (10 rats with unipolar
electrodes)
The study was carried out in accordance with European Community Council directive
86/609/EEC for the care of laboratory animals and was approved by Rostock's Ani-
mal Care Committee (LALLF M-V/TSD/7221.3-1.2-043/06).
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