Name: controlling parkinson's disease with adaptive deep brain stimulation
Uploaded: 2014-07-16T13:00:00
Duration: 11 min 12 s
Description: Watch this Scientific Journal Video about Controlling Parkinson's Disease With Adaptive Deep Brain Stimulation at JoVE.com

This method was developed using funding from the Wellcome Trust, Medical Research Council, National Institute for Health Research Oxford Biomedical Research Centre, and Rosetrees Trust. The UCL Unit of Functional Neurosurgery is supported by the UK Parkinson Appeal and the Monument Trust.

1. Consent and Biomarker Identification
This protocol has been reviewed and approved by the National Research Ethics Service Committee South Central - Oxford A.
<ol>
	<li>Identify appropriate subjects for study: subjects are those who are clinically identified as being suitable for deep brain stimulation (medically refractory Parkinson&#39;s disease). Note: Perform experiment after electrode implantation (day 1) and before battery/stimulator placement (day 7) whilst wires are externalized.</li>
	<li>Consent patient for stimulation testing and overnight&#160;Parkinsonian medication withdrawal.</li>
	<li>Following 12 hr&#160;withdrawal of Parkinsonian medication, connect externalized DBS electrodes to appropriate amplifier (amplifier must be designed, safety tested &#38; validated for intracranial neurophysiological use in humans)16.</li>
	<li>Record local field potential (LFP) at rest from all contacts bilaterally (L 0-3 &#38; R 0-3.)</li>
	<li>Create bipolar montages (0,2 and 1,3) by subtraction of recordings from adjacent contacts.</li>
	<li>Perform power spectral analysis to identify patient specific beta peak frequency and bipolar contact pair with highest beta amplitude for stimulation testing. Note: majority of PD patients off medication have a beta peak2. If no beta peak is discernible off medication, the patient should be excluded from further analysis as this may represent DBS targeting complications.</li>
	<li>Select contact for monopolar stimulation that is bridged by bipolar contact pair (0,2 or 1,3) with highest beta amplitude.</li>
</ol>
2. Connection of Patient to aDBS Setup
<ol>
	<li>Connect the DBS electrode to the analogue amplifier and filter. Note: band pass filter between 3 - 37 Hz with x 9,100 gain.</li>
	<li>Connect reference to patient. Note: Reference should be 5 cm x 5 cm neurostimulator gel electrode pad connected by a standard 2 mm monopolar electrode wire. Place the electrode over the left clavicle.</li>
	<li>Connect analogue amplifier to A/D converter and portable computer running signal analysis software. Second stage digitally filter the signal around the patient specific beta peak with a 4 Hz pass band. Monitor beta amplitude and use this to control stimulation with a pre-set threshold. Smooth beta amplitude with a smoothing window (400 msec was heuristically effective in this setup.)</li>
	<li>Connect D/A trigger to stimulator.</li>
	<li>Connect stimulator to patient through amplifier. Note: For safety, ensure charge densities are limited to &#60;30 &#956;Q/cm2 and stimulator has linear input - output function. Optically isolate all connections to patient. Stimulator should be designed and tested with EN60601-1 medical safety standard as reference.</li>
</ol>
3. Testing of Conventional Continuous Stimulation
<ol>
	<li>Turn on conventional high frequency stimulation, but initially at zero voltage (100 msec, 130 Hz, 0 V). Apply monopolar stimulation at contact bridged by bipolar contact pair with highest beta amplitude. Monitor stimulator readout continuously throughout experiment to ensure that stimulation delivered is as expected.</li>
	<li>Slowly increase stimulation voltage by 0.5 V increments every few minutes, looking for clinical effect threshold. Establish clinically useful stimulation voltage (generally 1.5-3.0 V) accompanied by minimal or no side-effects such as paresthesia.</li>
</ol>
4. Testing of Threshold with on/off Switching and Trigger Setting
<ol>
	<li>With the stimulation at the clinically effective voltage, switch the stimulator off with 250 msec ramping down.</li>
	<li>With the stimulation at the clinically effective voltage, switch the stimulator on with 250 msec ramping up.</li>
	<li>Enquire about paresthesia and any other possible side-effects experienced upon switching stimulation on and off.</li>
	<li>If side effects are present, reduce the voltage by 0.25 V and repeat steps 4.1 to 4.3 until below paresthesia upon on/off switching threshold.</li>
	<li>By titration find the threshold for paresthesia with on/off switching again and set the voltage just below (0.1 V) this threshold for further testing. If this is clinically ineffective then try other contact (choose contact 1 or 2). Note: switching stimulator on and off may also in some patients cause a spike artifact, possibly related to capacitance charging at the tissue electrode interface. As the signal was pass-band filtered in the beta band, before setting a trigger level, this artifact was greatly attenuated. Nevertheless, in a few instances this artifact was sufficient to cause self-triggering. To address this in these cases, we reduced the voltage of stimulation, and increased trigger threshold to escape self-triggering. Another way that this could be tackled in the future if necessary is through the incorporation of a lock out period after each trigger onset to avoid self-triggering.</li>
	<li>Turn on stimulation at voltage just under the on/off switching paresthesia threshold determined above.</li>
	<li>Increase beta amplitude trigger threshold to a level that results in the minimum time on stimulation whilst maintaining clinical effect. Aim for at least 50% reduction in time on stimulation.</li>
	<li>Turn off stimulation and leave patient without stimulation (following set up and between test blocks) for 10 min&#160;to washout stimulation effect.</li>
</ol>
5. Testing of Patient Across Different Stimulation Conditions
<ol>
	<li>Ensure blinding of patients to test conditions (adaptive DBS, conventional &#38; off).</li>
	<li>Apply each test condition for a minimum of a 5 min&#160;stabilization period with the condition running before clinical testing begins. Counterbalance test condition order across subjects. Fix the voltage, pulse width and stimulation frequency identically across test conditions so that the only difference relates to the timing of stimulation with regard to beta amplitude.</li>
	<li>At a predetermined fixed point after commencement of stimulation (e.g., as a minimum 300 sec), assess the patient clinically for effect through the UPDRS rating scale.</li>
	<li>Video record assessment and then blind&#160;rate by independent experts offline (excluding rigidity.)</li>
	<li>Perform clinical assessment using objective measures (accelerometry or actigraphy).</li>
</ol>

<ol>
	<li>Schrag, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Dyskinesias+and+motor+fluctuations+in+Parkinson's+disease:+A+community-based+study.">Dyskinesias and motor fluctuations in Parkinson's disease: A community-based study.</a> Brain. 123 (11), 2297-2305 (2000).</li><li>Little, S., Brown, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=What+brain+signals+are+suitable+for+feedback+control+of+deep+brain+stimulation+in+Parkinson's+disease.">What brain signals are suitable for feedback control of deep brain stimulation in Parkinson's disease.</a> Annals of the New York Academy of Sciences. 1265 (1), 9-24 (2012).</li><li>Chen, C. C., Br&#252;cke, C., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Deep+brain+stimulation+of+the+subthalamic+nucleus:+a+two-edged+sword.">Deep brain stimulation of the subthalamic nucleus: a two-edged sword.</a> Current biology. 16 (22), 952-953 (2006).</li><li>Modolo, J., Legros, A., Thomas, A. W., Beuter, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Model-driven+therapeutic+treatment+of+neurological+disorders:+reshaping+brain+rhythms+with+neuromodulation.">Model-driven therapeutic treatment of neurological disorders: reshaping brain rhythms with neuromodulation.</a> Interface Focus. (1), 61-74 (2011).</li><li>Priori, A., Foffani, G., Rossi, L., Marceglia, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Adaptive+deep+brain+stimulation+(aDBS)+controlled+by+local+field+potential+oscillations.">Adaptive deep brain stimulation (aDBS) controlled by local field potential oscillations.</a> Experimental neurology. 245, 77-86 (2012).</li><li>K&#252;hn, A. A., Kupsch, A., Schneider, G., Brown, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Reduction+in+subthalamic+8-35+Hz+oscillatory+activity+correlates+with+clinical+improvement+in+Parkinson's+disease.">Reduction in subthalamic 8-35 Hz oscillatory activity correlates with clinical improvement in Parkinson's disease.</a> The European journal of neuroscience. 23 (7), 1956-1960 (2006).</li><li>Eusebio, A., Cagnan, H., Brown, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Does+suppression+of+oscillatory+synchronisation+mediate+some+of+the+therapeutic+effects+of+DBS+in+patients+with+Parkinson's+disease.">Does suppression of oscillatory synchronisation mediate some of the therapeutic effects of DBS in patients with Parkinson's disease.</a> Frontiers in integrative neuroscience. 6, (2012).</li><li>Giannicola, G., Rosa, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Subthalamic+local+field+potentials+after+seven-year+deep+brain+stimulation+in+Parkinson's+disease.">Subthalamic local field potentials after seven-year deep brain stimulation in Parkinson's disease.</a> Experimental neurology. 237 (2), 312-317 (2012).</li><li>L&#243;pez-Azc&#225;rate, J., Tainta, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Coupling+between+beta+and+high-frequency+activity+in+the+human+subthalamic+nucleus+may+be+a+pathophysiological+mechanism+in+Parkinson's+disease.">Coupling between beta and high-frequency activity in the human subthalamic nucleus may be a pathophysiological mechanism in Parkinson's disease.</a> The Journal of Neuroscience. 30 (19), 6667-6677 (2010).</li><li>Ozkurt, T. E., Butz, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=High+frequency+oscillations+in+the+subthalamic+nucleus:+A+neurophysiological+marker+of+the+motor+state+in+Parkinson's+disease.">High frequency oscillations in the subthalamic nucleus: A neurophysiological marker of the motor state in Parkinson's disease.</a> Experimental neurology. 229 (2), 324-331 (2011).</li><li>Pogosyan, A., Yoshida, F., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Parkinsonian+impairment+correlates+with+spatially+extensive+subthalamic+oscillatory+synchronization.">Parkinsonian impairment correlates with spatially extensive subthalamic oscillatory synchronization.</a> Neuroscience. 171 (1), 245-257 (2010).</li><li>Chen, C. C., Hsu, Y. T., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Complexity+of+subthalamic+13-35+Hz+oscillatory+activity+directly+correlates+with+clinical+impairment+in+patients+with+Parkinson's+disease.">Complexity of subthalamic 13-35 Hz oscillatory activity directly correlates with clinical impairment in patients with Parkinson's disease.</a> Experimental neurology. 224 (1), 234-240 (2010).</li><li>Rosin, B., Slovik, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Closed-loop+deep+brain+stimulation+is+superior+in+ameliorating+parkinsonism.">Closed-loop deep brain stimulation is superior in ameliorating parkinsonism.</a> Neuron. 72 (2), 370-384 (2011).</li><li>Little, S., Pogosyan, A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Adaptive+Deep+Brain+Stimulation+in+Advanced+Parkinson+Disease.">Adaptive Deep Brain Stimulation in Advanced Parkinson Disease.</a> Annals of neurology. 74 (3), 449-457 (2013).</li><li>Afshar, P., Khambhati, A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+translational+platform+for+prototyping+closed-loop+neuromodulation+systems.+Frontiers+in+neural+circuits.">A translational platform for prototyping closed-loop neuromodulation systems. Frontiers in neural circuits.</a> 6, (2012).</li><li>Eusebio, A., Thevathasan, W., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Deep+brain+stimulation+can+suppress+pathological+synchronisation+in+parkinsonian+patients.">Deep brain stimulation can suppress pathological synchronisation in parkinsonian patients.</a> Journal of neurology, neurosurgery, and psychiatry. 82 (5), 569-573 (2011).</li><li>Little, S., Pogosyan, A., Kuhn, A. A., Brown, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Beta+band+stability+over+time+correlates+with+Parkinsonian+rigidity+and+bradykinesia.">Beta band stability over time correlates with Parkinsonian rigidity and bradykinesia.</a> Experimental neurology. 236 (2), 383-388 (2012).</li></ol>

L.Z., M.H.: consultancy, travel support, speaking fees, Medtronic, St Jude. T.F.: consultancy, AbbVie Pharmaceuticals, St Jude, Medtronic; P.L.: consultancy, speaking fees, Medtronic, St Jude. P.B.: consultancy, Medtronic, Sapiens.

This article outlines a new method for the study and validation of adaptive deep brain stimulation in post-operative patients. DBS treatment is part of standard treatment for PD, essential tremor and dystonia and is being introduced and tested in a range of other conditions including cluster headache, epilepsy, Gilles de la Tourette syndrome, obsessive compulsive disorder and depression. At present, all clinical stimulation paradigms employ continuous, open-loop stimulation and although these simple stimulation paradigms are often effective, it is hoped that they can be significantly improved by making them responsive to disease appropriate biomarkers and thereby optimizing stimulation in an informed, patient specific manner. The method, outlined here, allows the testing of aDBS in patients externalized after their first surgery (electrode implantation), prior to internalization and implantation of the battery and stimulator. Using this method, it is hoped therefore that researchers can investigate the efficacy of aDBS using a range of biomarkers across the spectrum of disorders for which DBS is used. This may then lead to trials in the chronically implanted clinical setting.
The protocol that we have used and found to be successful is outlined above. We discerned a number of critical steps for fine-tuning the process in order to achieve successful aDBS. Parameters that can be controlled in this simple aDBS setup include voltage, trigger threshold, stimulation contact and ramping duration. These must all be balanced against the side effects of switching stimulation on and off (paresthesia), technical problems (recurrent &#8216;self&#39; triggering) and clinical efficacy. Switching stimulation on and off causes a voltage dependent artifact in the LFP that, despite filtering, can potentially leak into the frequency range of interest. If this is severe, it can cause the system to self-trigger even in the absence of an elevation in the biomarker signal, -here beta activity in the local field potential. This does not represent a safety issue as it effectively results in the aDBS being on all the time and therefore mimicking cDBS which is known to be safe. However, it does result in a lack of reactivity to beta amplitude and the loss therefore of any potential benefit of aDBS over cDBS. We found that, if necessary, self-triggering could be avoided by reducing the stimulation voltage, raising the threshold or changing the stimulation contact. The 250 msec ramping of stimulation on and off was found to be satisfactory compromise with regard to preventing paresthesias whilst maintaining responsiveness of aDBS. At present parameters have to be adjusted heuristically in order to achieve the best response profile in individual patients and we have not yet identified consistent rules that are applicable at the group level to achieve this reliably. Nevertheless, in all patients studied thus far, we have found that heuristic adjustment of voltage, trigger threshold and stimulation contact enabled efficacious aDBS, and optimal parameters were identified in less than 30 min. It is hoped that the management of side effects (paresthesias from on/off switching) and artifact contamination (possibly related to tissue-electrode capacitance) can be further investigated and better understood to derive more generalized rules regarding their minimization.
The potential parameter space for exploration will also become larger and more complicated as the complexity of biomarkers and stimulation algorithms grow. For instance, high frequency power ratios, phase amplitude coupling and beta variability have all been shown to relate to Parkinsonian state9,10,12,17. The method described in this paper should enable the systematic investigation of such parameters and their effect on the clinical efficacy of stimulation in addition to their side effect profile. However, the thorough optimization of all parameters in the future is likely to be facilitated once DBS models and algorithmic optimization routines that focus on the response of the biomarker rather than clinical effects allow limitation of the parameter ranges to be searched empirically.
This method has demonstrated improved power consumption and clinical efficacy when compared to conventional DBS and has the potential to be further improved in PD with advancement in our understanding regarding biomarkers and stimulation patterning. In other conditions where DBS is used, much less is known regarding underlying pathophysiology and therefore corresponding biomarkers are yet to be fully determined. Significant further research is required to fully harness the potential of aDBS in Parkinsonism, and to explore its feasibility in a number of other potential neurological and neuropsychiatric conditions in which severity and impairment fluctuate over time.

Parkinson&#39;s disease is a common severely disabling degenerative movement disorder for which long term medical treatment is unsatisfactory1. DBS is effective for advanced medically refractory PD but is limited in terms of efficacy, side effects and cost2. Conventional stimulation is set heuristically by a movement disorders specialist and left running continuously without change until the next clinic visit. Typical stimulation parameters are 60 msec pulse width, 3 V intensity, and 130 Hz repetition. However, this continuous high voltage stimulation may interfere with normal motor functioning3. Much as cardiac pacing has successfully transitioned from simple open loop systems to complex responsive closed loop systems, with an associated improvement in outcome, it is hoped that DBS can similarly be improved by making it responsive to underlying brain rhythms - adaptive DBS (aDBS)4,5.
In order to realize aDBS, it is firstly critical to identify reliable biomarkers of disease. Parkinson&#39;s disease is characterized by prominent beta (13-33 Hz) oscillations recorded throughout the basal ganglia circuit2. These beta oscillations are suppressed by levodopa and DBS in proportion to improvement in clinical state6,7. They are stable and robust in the long term and can be recorded from the same electrodes used for clinical DBS making them attractive targets for biomarkers8. In addition to beta oscillations, a range of other, more complex, potential biomarkers have been identified that have been shown to relate to severity of symptoms2,9-12.
Proof of principle of aDBS has now been demonstrated in a non - human primate model of PD13. This used a single cortical motor neuron to control stimulation with firing of the neuron triggering DBS stimulation after a fixed delay. The study reported that adaptive stimulation was more efficacious than conventional DBS. Recent work has since successfully extended aDBS to humans, the method for which is presented in this JoVE article14. This study investigated patients with PD in the immediate post-operative period prior to internalization of their wires and connection to their battery pack / stimulator. Beta oscillations were monitored in real time online and used to control the timing of high frequency stimulation. This led to a &#62;50% reduction in power consumption and a 25% improvement in motor impairment compared to standard stimulation. These results will need to be replicated in the chronically implanted state where thresholds and effective stimulation parameters can change as well as drug levels. As such, biomarkers and control algorithms may need to be adjusted and matched accordingly and indeed may well require further complexity to adapt to this different parameter landscape. Devices that are equipped for longer term stimulation and recording are currently being developed and trialed in a research setting15. Meanwhile there is a need for a platform that will allow the possible benefits of adaptive DBS and the algorithms that underpin its performance to be further evaluated and refined. This is an important step, as errors and sub-optimal approaches are more difficult to reverse once systems are internalized for chronic use. Moreover, acute studies are necessary to motivate efforts in overcoming the challenges implicit in developing chronic internalized adaptive DBS system.
The goal of this methods report is to enable researchers to explore a range of different biomarkers and stimulation paradigms in DBS patients and to optimize parameters so as to maximize efficacy and minimize side effects / power consumption. It is the first method of its kind to be effective in patients with Parkinsonism and yet is relatively simple and easy to apply. The method is designed to investigate any DBS patient for whom there is a known LFP biomarker and who has a period of externalization post-operatively (up to 1 week period when electrode wires are extra-cranial and available for experimentation prior to battery/stimulator insertion).

<table border="0" cellpadding="0" cellspacing="0" width="573">
	<colgroup>
		<col />
		<col />
		<col />
		<col />
	</colgroup>
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">StimRecord Amplifier (3-37 Hz)</td>
			<td style="width:71px;">In house</td>
			<td style="width:119px;">NA</td>
			<td style="width:167px;">Common mode rejection, 3-37Hz (bandpass), x9500 amplifier. See - Eusebio, A et al. Deep brain stimulation can suppress pathological synchronisation in parkinsonian patients. JNNP (5), 569&#8211;573 (2011)</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">1401 Digital acquisition unit</td>
			<td style="width:71px;">CED</td>
			<td style="width:119px;">Micro 1401-3</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Spike 2 software</td>
			<td style="width:71px;">CED</td>
			<td style="width:119px;">NA</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Stimulator</td>
			<td style="width:71px;">In house</td>
			<td style="width:119px;">NA</td>
			<td>Biphase, variable, ramped stimulator. See - Little et al. Adaptive deep brain stimulation in advanced Parkinson&#39;s disease. Annals of Neurology 2013.</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Gel electrode reference pad</td>
			<td style="width:71px;">Axelgaard</td>
			<td style="width:119px;">895220</td>
			<td>5x5 cm PALS platinum gel electrode pad</td>
		</tr>
	</tbody>
</table>

controlling parkinson's disease with adaptive deep brain stimulation

Adaptive deep brain stimulation (aDBS) has the potential to improve the treatment of Parkinson&#39;s disease by optimizing stimulation in real time according to fluctuating disease and medication state. In the present realization of adaptive DBS we record and stimulate from the DBS electrodes implanted in the subthalamic nucleus of patients with Parkinson&#39;s disease in the early post-operative period. Local field potentials are analogue filtered between 3 and 47 Hz before being passed to a data acquisition unit where they are digitally filtered again around the patient specific beta peak, rectified and smoothed to give an online reading of the beta amplitude. A threshold for beta amplitude is set heuristically, which, if crossed, passes a trigger signal to the stimulator. The stimulator then ramps up stimulation to a pre-determined clinically effective voltage over 250 msec and continues to stimulate until the beta amplitude again falls down below threshold. Stimulation continues in this manner with brief episodes of ramped DBS during periods of heightened beta power.
Clinical efficacy is assessed after a minimum period of stabilization (5 min) through the unblinded and blinded video assessment of motor function using a selection of scores from the Unified Parkinson&#39;s Rating Scale (UPDRS). Recent work has demonstrated a reduction in power consumption with aDBS as well as an improvement in clinical scores compared to conventional DBS. Chronic aDBS could now be trialed in Parkinsonism.

Results using this method have recently been published using this protocol for beta amplitude (Figure 1)14. This study showed that clinically efficacious stimulation can be achieved despite a &#62;50% reduction in time on stimulation (p &#60; 0.001). It was also noted that time on stimulation tended to progressively drop despite a constant trigger threshold (2-tailed, 1-sample t test, t7 = 3.2, p = 0.01). Motor scores were improved by 66% and 50% during aDBS in the unblinded and blinded conditions, respectively. Despite the reduced amount of total stimulation - clinical outcome was 29% (p=0.03) and 27% (p=0.005) better in the aDBS group compared with the conventional DBS group (unblinded and blinded respectively, Figure&#160;2).
<img alt="Figure 1" fo:content-width="5in" fo:src="/files/ftp_upload/51403/51403fig1highres.jpg" src="/files/ftp_upload/51403/51403fig1.jpg" /> 
Figure 1. Experimental setup.&#160;Experimental setup for adaptive deep brain stimulation in externalized subjects. Bipolar local field potential (LFP) is passed through a custom built StimRecord amplifier that filters (3-37 Hz) and amplifies (x9,100). The analogue (A) output is passed to a data acquisition unit, which converts it to a digital (D) signal that is displayed on a portable computer. The signal is digitally filtered around the beta peak in real time and converted to beta amplitude by rectifying and smoothing. A threshold is set that triggers stimulation in a monopolar montage between the 2 bipolar recording electrodes when beta power crosses the threshold. Stimulation terminates when beta power drops again below threshold. (Reprinted with permission from Annals of Neurology.) <a href="https://www.jove.com/files/ftp_upload/51403/51403fig1highres.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" fo:content-width="5in" fo:src="/files/ftp_upload/51403/51403fig2highres.jpg" src="/files/ftp_upload/51403/51403fig2.jpg" /> 
Figure 2. Clinical improvements. Mean &#177; SEM % change in hemibody UPDRS scores (items 20, 22, and 23) with different stimulation conditions as assessed unblinded during the experimental sessions (A)&#160;or from video recordings by blinded experts (B). Asterixes denote significant differences following correction for multiple comparisons by the false discovery rate procedure. All changes were significant from the unstimulated state, with the exception of the blinded score for random stimulation (Reprinted with permission from Annals of Neurology.) <a href="https://www.jove.com/files/ftp_upload/51403/51403fig2highres.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

Watch this Scientific Journal Video about Controlling Parkinson's Disease With Adaptive Deep Brain Stimulation at JoVE.com

Controlling Parkinson&#039;s Disease With Adaptive Deep Brain Stimulation

Adaptive deep brain stimulation (aDBS) is effective for Parkinson&#8217;s disease, improving symptoms and reducing power consumption compared to conventional deep brain stimulation (cDBS). In aDBS we track a local field potential biomarker (beta oscillatory amplitude) in real time and use this to control the timing of stimulation.

Controlling Parkinson's Disease With Adaptive Deep Brain Stimulation

Adaptive deep brain stimulation (aDBS) has the potential to improve the treatment of Parkinson&#39;s disease by optimizing stimulation in real time ...

controlling-parkinson-s-disease-with-adaptive-deep-brain-stimulation

Research

JoVE Journal

Medicine

Intra-Operative Behavioral Tasks in Awake Humans Undergoing Deep Brain Stimulation Surgery

Deep brain stimulation (DBS) is a surgical procedure that directs chronic, high frequency electrical stimulation to specific targets in the brain through implanted electrodes. Deep brain stimulation was first implemented as a therapeutic modality by Benabid et al. in the late 1980s, when he used this technique to stimulate the ventral intermediate nucleus of the thalamus for the treatment of tremor 1. Currently, the procedure is used to treat patients who fail to respond adequately to medical management for diseases such as Parkinson's, dystonia, and essential tremor. The efficacy of this procedure for the treatment of Parkinson's disease has been demonstrated in well-powered, randomized controlled trials 2. Presently, the U.S. Food and Drug Administration has approved DBS as a treatment for patients with medically refractory essential tremor, Parkinson's disease, and dystonia. Additionally, DBS is currently being evaluated for the treatment of other psychiatric and neurological disorders, such as obsessive compulsive disorder, major depressive disorder, and epilepsy. 
DBS has not only been shown to help people by improving their quality of life, it also provides researchers with the unique opportunity to study and understand the human brain. Microelectrode recordings are routinely performed during DBS surgery in order to enhance the precision of anatomical targeting. Firing patterns of individual neurons can therefore be recorded while the subject performs a behavioral task. Early studies using these data focused on descriptive aspects, including firing and burst rates, and frequency modulation 3. More recent studies have focused on cognitive aspects of behavior in relation to neuronal activity 4,5. This article will provide a description of the intra-operative methods used to perform behavioral tasks and record neuronal data with awake patients during DBS cases. Our exposition of the process of acquiring electrophysiological data will illuminate the current scope and limitations of intra-operative human experiments.

Deep brain stimulation surgery offers a unique opportunity to examine information encoding in the awake human brain. This article will describe intra-operative methods used to perform cognitive and behavioral tasks while simultaneously acquiring physiological data such as EMG, single-unit neuronal activity and/or local field potentials.

Deep brain stimulation (DBS) is a surgical procedure that directs chronic, high frequency electrical stimulation to specific targets in the brain through ...

Development of a Unilaterally-lesioned 6-OHDA Mouse Model of Parkinson's Disease

The unilaterally lesioned 6-hyroxydopamine (6-OHDA)-lesioned rat model of Parkinson's disease (PD) has proved to be invaluable in advancing our understanding of the mechanisms underlying parkinsonian symptoms, since it recapitulates the changes in basal ganglia circuitry and pharmacology observed in parkinsonian patients1-4. However, the precise cellular and molecular changes occurring at cortico-striatal synapses of the output pathways within the striatum, which is the major input region of the basal ganglia remain elusive, and this is believed to be site where pathological abnormalities underlying parkinsonian symptoms arise3,5.
In PD, understanding the mechanisms underlying changes in basal ganglia circuitry following degeneration of the nigro-striatal pathway has been greatly advanced by the development of bacterial artificial chromosome (BAC) mice over-expressing green fluorescent proteins driven by promoters specific for the two striatal output pathways (direct pathway: eGFP-D1; indirect pathway: eGFP-D2 and eGFP-A2a)8, allowing them to be studied in isolation. For example, recent studies have suggested that there are pathological changes in synaptic plasticity in parkinsonian mice9,10. However, these studies utilised juvenile mice and acute models of parkinsonism. It is unclear whether the changes described in adult rats with stable 6-OHDA lesions also occur in these models. Other groups have attempted to generate a stable unilaterally-lesioned 6-OHDA adult mouse model of PD by lesioning the medial forebrain bundle (MFB), unfortunately, the mortality rate in this study was extremely high, with only 14% surviving the surgery for 21 days or longer11. More recent studies have generated intra-nigral lesions with both a low mortality rate &gt;80% loss of dopaminergic neurons, however expression of L-DOPA induced dyskinesia11,12,13,14 was variable in these studies. Another well established mouse model of PD is the MPTP-lesioned mouse15. Whilst this model has proven useful in the assessment of potential neuroprotective agents16, it is less suitable for understanding mechanisms underlying symptoms of PD, as this model often fails to induce motor deficits, and shows a wide variability in the extent of lesion17, 18.
Here we have developed a stable unilateral 6-OHDA-lesioned mouse model of PD by direct administration of 6-OHDA into the MFB, which consistently causes &gt;95% loss of striatal dopamine (as measured by HPLC), as well as producing the behavioural imbalances observed in the well characterised unilateral 6-OHDA-lesioned rat model of PD. This newly developed mouse model of PD will prove a valuable tool in understanding the mechanisms underlying generation of parkinsonian symptoms.

Development of a Unilaterally-lesioned 6-OHDA Mouse Model of Parkinson&#039;s Disease

A protocol for performing unilateral 6-OHDA lesions of the medial forebrain bundle in mice is described. This method has a low mortality rate (13.3 %) with 89% of the surviving animals showing &#62;95% loss of striatal dopamine and 90.63&#177;-4.02 % ipsiversive rotational bias towards the side of the lesion.

The unilaterally lesioned 6-hyroxydopamine (6-OHDA)-lesioned rat model of Parkinson's disease (PD) has proved to be invaluable in advancing our ...

MALDI Imaging Mass Spectrometry of Neuropeptides in Parkinson's Disease

MALDI imaging mass spectrometry (IMS) is a powerful approach that facilitates the spatial analysis of molecular species in biological tissue samples2 (Fig.1). A 12 &mu;m thin tissue section is covered with a MALDI matrix, which facilitates desorption and ionization of intact peptides and proteins that can be detected with a mass analyzer, typically using a MALDI TOF/TOF mass spectrometer. Generally hundreds of peaks can be assessed in a single rat brain tissue section. In contrast to commonly used imaging techniques, this approach does not require prior knowledge of the molecules of interest and allows for unsupervised and comprehensive analysis of multiple molecular species while maintaining high molecular specificity and sensitivity2. Here we describe a MALDI IMS based approach for elucidating region-specific distribution profiles of neuropeptides in the rat brain of an animal model Parkinson's disease (PD). 
PD is a common neurodegenerative disease with a prevalence of 1% for people over 65 of age3,4. The most common symptomatic treatment is based on dopamine replacement using L-DOPA5. However this is accompanied by severe side effects including involuntary abnormal movements, termed L-DOPA-induced dyskinesias (LID)1,3,6. One of the most prominent molecular change in LID is an upregulation of the opioid precursor prodynorphin mRNA7. The dynorphin peptides modulate neurotransmission in brain areas that are essentially involved in movement control7,8. However, to date the exact opioid peptides that originate from processing of the neuropeptide precursor have not been characterized. Therefore, we utilized MALDI IMS in an animal model of experimental Parkinson's disease and L-DOPA induced dyskinesia. 
MALDI imaging mass spectrometry proved to be particularly advantageous with respect to neuropeptide characterization, since commonly used antibody based approaches targets known peptide sequences and previously observed post-translational modifications. By contrast MALDI IMS can unravel novel peptide processing products and thus reveal new molecular mechanisms of neuropeptide modulation of neuronal transmission. While the absolute amount of neuropeptides cannot be determined by MALDI IMS, the relative abundance of peptide ions can be delineated from the mass spectra, giving insights about changing levels in health and disease. In the examples presented here, the peak intensities of dynorphin B, alpha-neoendorphin and substance P were found to be significantly increased in the dorsolateral, but not the dorsomedial, striatum of animals with severe dyskinesia involving facial, trunk and orolingual muscles (Fig. 5). Furthermore, MALDI IMS revealed a correlation between dyskinesia severity and levels of des-tyrosine alpha-neoendorphin, representing a previously unknown mechanism of functional inactivation of dynorphins in the striatum as the removal of N-terminal tyrosine reduces the dynorphin's opioid-receptor binding capacity9. This is the first study on neuropeptide characterization in LID using MALDI IMS and the results highlight the potential of the technique for application in all fields of biomedical research.

MALDI Imaging Mass Spectrometry of Neuropeptides in Parkinson&#039;s Disease

Dopamine replacement pharmacotherapy using L-DOPA is the most commonly used symptomatic treatment of Parkinson&#x2019;s disease, but is accompanied by side effects including involuntary abnormal movements, termed dyskinesia 1. Here, a protocol for MALDI imaging mass spectrometry is presented that detects changes in rat brain neuropeptide levels related to dyskinesia.

MALDI imaging mass spectrometry (IMS) is a powerful approach that facilitates the spatial analysis of molecular species in biological tissue samples2 ...

Skin Punch Biopsy Explant Culture for Derivation of Primary Human Fibroblasts

Tissues and cell lines derived from an individual with disease are ideal sources to study disease-related cellular phenotypes. Patient-derived fibroblasts in this protocol have been successfully used in the derivation of induced pluripotent stem cells to model disease1. Early passages of these fibroblasts can also be used for cell-based functional assays to study specific disease pathways, mechanisms2 and subsequent drug screening approaches. The advantage of the presented protocol over enzymatic procedures are 1) the reproducibility of the technique from small amounts of tissue derived from older patients, e.g. patients affected with Parkinson's disease, 2) the technically simple approach over more challenging methodologies using enzymatic treatments, and 3) the time consideration: this protocol takes 15-20 min and can be performed immediately after biopsy arrival. Enzymatic treatments can take up to 4 hr and have the problems of overdigestion, reduction of cell viability and subsequent attachment of cells when not handled properly. This protocol describes the dissection and preparation of a 4-mm human skin biopsy for derivation of a fibroblast culture and has a very high success rate which is important when dealing with patient-derived tissue samples. In this culture, keratinocytes migrate out of the biopsy tissue within the first week after preparation. Fibroblasts appear 7-10 days after the first outgrowth of keratinocytes. DMEM high glucose media supplemented with 20% FBS favors the growth of fibroblasts over keratinocytes and fibroblasts will overgrow the keratinocytes. After 2 passages keratinocytes have been diluted out resulting in relatively homogenous fibroblast cultures which expresses the fibroblast marker SERPINH1 (HSP-47). Using this approach, 15-20 million fibroblasts can be derived in 4-8 weeks for cell banking. The skin dissection takes about 15-20 min, cells are then monitored once a day under the microscope, and media is changed every 2-3 days after attachment and outgrowth of cells.

The fibroblast explant culture protocol from human skin punch biopsies is a technically robust and simple way to derive skin cells within 4-8 weeks for banking of about 15-20 million cells at a low passage number.

Tissues and cell lines derived from an individual with disease are ideal sources to study disease-related cellular phenotypes. Patient-derived fibroblasts ...

Isolation of Soluble and Insoluble PrP Oligomers in the Normal Human Brain

The central event in the pathogenesis of prion diseases involves a conversion of the host-encoded cellular prion protein PrPC into its pathogenic isoform PrPSc 1. PrPC is detergent-soluble and sensitive to proteinase K (PK)-digestion, whereas PrPSc forms detergent-insoluble aggregates and is partially resistant to PK2-6. The conversion of PrPC to PrPSc is known to involve a conformational transition of &alpha;-helical to &beta;-sheet structures of the protein. However, the in vivo pathway is still poorly understood. A tentative endogenous PrPSc, intermediate PrP* or "silent prion", has yet to be identified in the uninfected brain7.
Using a combination of biophysical and biochemical approaches, we identified insoluble PrPC aggregates (designated iPrPC) from uninfected mammalian brains and cultured neuronal cells8, 9. Here, we describe detailed procedures of these methods, including ultracentrifugation in detergent buffer, sucrose step gradient sedimentation, size exclusion chromatography, iPrP enrichment by gene 5 protein (g5p) that specifically bind to structurally altered PrP forms10, and PK-treatment. The combination of these approaches isolates not only insoluble PrPSc and PrPC aggregates but also soluble PrPC oligomers from the normal human brain. Since the protocols described here have been used to isolate both PrPSc from infected brains and iPrPC from uninfected brains, they provide us with an opportunity to compare differences in physicochemical features, neurotoxicity, and infectivity between the two isoforms. Such a study will greatly improve our understanding of the infectious proteinaceous pathogens. The physiology and pathophysiology of iPrPC are unclear at present. Notably, in a newly-identified human prion disease termed variably protease-sensitive prionopathy, we found a new PrPSc that shares the immunoreactive behavior and fragmentation with iPrPC 11, 12. Moreover, we recently demonstrated that iPrPC is the main species that interacts with amyloid-&beta; protein in Alzheimer disease13. In the same study, these methods were used to isolate Abeta aggregates and oligomers in Alzheimer's disease13, suggesting their application to non-prion protein aggregates involved in other neurodegenerative disorders.

A new species of cellular prion protein (PrPC) has recently been identified in uninfected human brains using the methods described here. These methods can be used to isolate various PrP species, while some of them are also useful in isolating other misfolded protein aggregates from human brains.

The central event in the pathogenesis of prion diseases involves a conversion of the host-encoded cellular prion protein PrPC into its pathogenic isoform ...

The Use of Primary Human Fibroblasts for Monitoring Mitochondrial Phenotypes in the Field of Parkinson's Disease

Parkinson's disease (PD) is the second most common movement disorder and affects 1% of people over the age of 60 1. Because ageing is the most important risk factor, cases of PD will increase during the next decades 2. Next to pathological protein folding and impaired protein degradation pathways, alterations of mitochondrial function and morphology were pointed out as further hallmark of neurodegeneration in PD 3-11.
After years of research in murine and human cancer cells as in vitro models to dissect molecular pathways of Parkinsonism, the use of human fibroblasts from patients and appropriate controls as ex vivo models has become a valuable research tool, if potential caveats are considered. Other than immortalized, rather artificial cell models, primary fibroblasts from patients carrying disease-associated mutations apparently reflect important pathological features of the human disease.
Here we delineate the procedure of taking skin biopsies, culturing human fibroblasts and using detailed protocols for essential microscopic techniques to define mitochondrial phenotypes. These were used to investigate different features associated with PD that are relevant to mitochondrial function and dynamics. Ex vivo, mitochondria can be analyzed in terms of their function, morphology, colocalization with lysosomes (the organelles degrading dysfunctional mitochondria) and degradation via the lysosomal pathway. These phenotypes are highly relevant for the identification of early signs of PD and may precede clinical motor symptoms in human disease-gene carriers. Hence, the assays presented here can be utilized as valuable tools to identify pathological features of neurodegeneration and help to define new therapeutic strategies in PD.

The Use of Primary Human Fibroblasts for Monitoring Mitochondrial Phenotypes in the Field of Parkinson&#039;s Disease

Fibroblasts from patients carrying mutations in Parkinson's disease-causing genes represent an easily accessible ex vivo model to study disease-associated phenotypes. Live cell imaging gives the opportunity to study morphological and functional parameters in living cells. Here we describe the preparation of human fibroblasts and subsequent monitoring of mitochondrial phenotypes.

Parkinson's disease (PD) is the second most  common movement disorder and affects 1% of people over the age of 60 1. Because ageing is  the most important ...

Gene-environment Interaction Models to Unmask Susceptibility Mechanisms in Parkinson's Disease

Lipoxygenase (LOX) activity has been implicated in neurodegenerative disorders such as Alzheimer&#39;s disease, but its effects in Parkinson&#39;s disease (PD) pathogenesis are less understood. Gene-environment interaction models have utility in unmasking the impact of specific cellular pathways in toxicity that may not be observed using a solely genetic or toxicant disease model alone.&#160;To evaluate if distinct LOX isozymes selectively contribute to PD-related neurodegeneration, transgenic (i.e. 5-LOX and 12/15-LOX deficient) mice can be challenged with a toxin that mimics cell injury and death in the disorder.&#160;Here we describe the use of a neurotoxin, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), which produces a nigrostriatal lesion to elucidate the distinct contributions of LOX isozymes to neurodegeneration related to PD. The use of MPTP in mouse, and nonhuman primate, is well-established to recapitulate the nigrostriatal damage in PD.&#160;The extent of MPTP-induced lesioning is measured by HPLC analysis of dopamine and its metabolites and semi-quantitative Western blot analysis of striatum for tyrosine hydroxylase (TH), the rate-limiting enzyme for the synthesis of dopamine. To assess inflammatory markers, which may demonstrate LOX isozyme-selective sensitivity, glial fibrillary acidic protein (GFAP) and Iba-1 immunohistochemistry are performed on brain sections containing substantia nigra, and GFAP Western blot analysis is performed on striatal homogenates.&#160;This experimental approach can provide novel insights into gene-environment interactions underlying nigrostriatal degeneration and PD.

Gene-environment Interaction Models to Unmask Susceptibility Mechanisms in Parkinson&#039;s Disease

Lipoxygenase (LOX) isozymes can generate products that may increase or decrease neuroinflammation and neurodegeneration.&#160;A gene-environment interaction study could identify LOX isozyme-specific effects. Using the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) model of nigrostriatal damage in two LOX isozyme-deficient transgenic lines allows for comparison of the contribution of LOX isozymes on dopaminergic integrity and inflammation.

Lipoxygenase (LOX) activity has been implicated in neurodegenerative disorders such as Alzheimer&#39;s disease, but its effects in Parkinson&#39;s disease ...

Excitotoxic Stimulation of Brain Microslices as an In vitro Model of Stroke

Examining molecular mechanisms involved in neuropathological conditions, such as ischemic stroke, can be difficult when using whole animal systems. As such, primary or &#39;neuronal-like&#39; cell culture systems are commonly utilized. While&#160;these systems are relatively easy to work with, and are useful model systems in which various functional outcomes (such as cell death) can be readily quantified, the examined outcomes and pathways in cultured immature neurons (such as excitotoxicity-mediated cell death pathways) are not necessarily the same as those observed in mature brain, or in intact tissue. Therefore, there is the need to develop models in which cellular mechanisms in mature neural tissue can be examined. We have developed an in vitro technique that can be used to investigate a variety of molecular pathways in intact nervous tissue. The technique described herein utilizes rat cortical tissue, but this technique can be adapted to use tissue from a variety of species (such as mouse, rabbit, guinea pig, and chicken) or brain regions (for example, hippocampus, striatum, etc.). Additionally, a variety of stimulations/treatments can be used (for example, excitotoxic, administration of inhibitors, etc.). In conclusion, the brain slice model described herein can be used to examine a variety of molecular mechanisms involved in excitotoxicity-mediated brain injury.

Excitotoxic Stimulation of Brain Microslices as an In vitro Model of Stroke

We have developed a brain slice model which can be used to examine molecular mechanisms involved in excitotoxicity-mediated brain injury.&#160;This technique generates viable mature brain tissue and reduces animal numbers required for experimentation, whilst keeping the neuronal circuitry, cellular interactions, and postsynaptic compartments partly intact.

Examining molecular mechanisms involved in neuropathological conditions, such as ischemic stroke, can be difficult when using whole animal systems. As ...

Using Saccadometry with Deep Brain Stimulation to Study Normal and Pathological Brain Function

The oculomotor system involves a large number of brain areas including parts of the basal ganglia, and various neurodegenerative diseases including Parkinson's and Huntington's can disrupt it. People with Parkinson's disease, for example, tend to have increased saccadic latencies. Consequently, the quantitative measurement of saccadic eye movements has received considerable attention as a potential biomarker for neurodegenerative conditions. A lot more can be learned about the brain in both health and disease by observing what happens to eye movements when the function of specific brain areas is perturbed. Deep brain stimulation is a surgical intervention used for the management of a range of neurological conditions including Parkinson's disease, in which stimulating electrodes are placed in specific brain areas including several sites in the basal ganglia. Eye movement measurements can then be made with the stimulator systems both off and on and the results compared. With suitable experimental design, this approach can be used to study the pathophysiology of the disease being treated, the mechanism by which DBS exerts it beneficial effects, and even aspects of normal neurophysiology.

This paper describes the use of quantitative measurement of eye movements in conjunction with stimulation of focal areas of the deep brain in order to study physiology, pathophysiology, and the mechanisms of deep brain stimulation.

The oculomotor system involves a large number of brain areas including parts of the basal ganglia, and various neurodegenerative diseases including ...

Development of an Alpha-synuclein Based Rat Model for Parkinson's Disease via Stereotactic Injection of a Recombinant Adeno-associated Viral Vector

In order to study the molecular pathways of Parkinson&#39;s disease (PD) and to develop novel therapeutic strategies, scientific investigators rely on animal models. The identification of PD-associated genes has led to the development of genetic PD models. Most transgenic &#945;-SYN mouse models develop gradual &#945;-SYN pathology but fail to display clear dopaminergic cell loss and dopamine-dependent behavioral deficits. This hurdle was overcome by direct targeting of the substantia nigra with viral vectors overexpressing PD-associated genes. Local gene delivery using viral vectors provides an attractive way to express transgenes in the central nervous system. Specific brain regions can be targeted (e.g. the substantia nigra), expression can be induced in the adult setting and high expression levels can be achieved. Further, different vector systems based on various viruses can be used. The protocol outlines all crucial steps to perform a viral vector injection in the substantia nigra of the rat to develop a viral vector-based alpha-synuclein animal model for Parkinson&#39;s disease.

Development of an Alpha-synuclein Based Rat Model for Parkinson&#039;s Disease via Stereotactic Injection of a Recombinant Adeno-associated Viral Vector

This manuscript describes how viral vector-mediated local gene delivery provides an attractive way to express transgenes in the central nervous system. The protocol outlines all crucial steps to perform a viral vector injection in the substantia nigra of the rat to develop a viral vector-based animal model for Parkinson's disease.

In order to study the molecular pathways of Parkinson&#39;s disease (PD) and to develop novel therapeutic strategies, scientific investigators rely on ...