Pros and Cons of Ablation for Functional Neurosurgery in the Neurostimulation Age

Should one recommend stereotactic ablation for Parkinson disease, tremor, dystonia, and obsessive compulsive disorder, in this era of DBS? The answer depends on several variables such as the symptoms to treat, the patient's preferences and expectations, the surgeons' competence and preference, the availability of financial means (by government health care, by private insurance), the geographical issues, and not least the current and dominating fashion at that particular time. Both ablation and stimulation can be either used alone or even combined (provided expertise in both of them) to treat various symptoms of movement and mind disorders.

Serotonergic control of the glutamatergic neurons of the subthalamic nucleus

The subthalamic nucleus (STN) houses a dense cluster of glutamatergic neurons that play a central role in the functional dynamics of the basal ganglia, a group of subcortical structures involved in the control of motor behaviors. Numerous anatomical, electrophysiological, neurochemical and behavioral studies have reported that serotonergic neurons from the midbrain raphe nuclei modulate the activity of STN neurons. Here, we describe this serotonergic innervation and the nature of the regulation exerted by serotonin (5-hydroxytryptamine, 5-HT) on STN neuron activity. This regulation can occur either directly within the STN or at distal sites, including other structures of the basal ganglia or cortex. The effect of 5-HT on STN neuronal activity involves several 5-HT receptor subtypes, including 5-HT_1A, 5-HT_1B, 5-HT_2C and 5-HT₄ receptors, which have garnered the highest attention on this topic. The multiple regulatory effects exerted by 5-HT are thought to be modified under pathological conditions, altering the activity of the STN, or due to the benefits and side effects of treatments used for Parkinson's disease, notably the dopamine precursor l-DOPA and high-frequency STN stimulation. Originally understood as a motor center, the STN is also associated with decision making and participates in mood regulation and cognitive performance, two domains of personality that are also regulated by 5-HT. The literature concerning the link between 5-HT and STN is already important, and the functional overlap is evident, but this link is still not entirely understood. The understanding of this link between 5-HT and STN should be increased due to the possible importance of this regulation in the control of fronto-STN loops and inherent motor and non-motor behaviors.

Revisiting Forel Field Surgery

BACKGROUND

Lesioning the Forel field or the subthalamic region is considered a possible treatment for tremoric patients with Parkinson disease, essential tremor, and other diseases. This surgical treatment was performed in the 1960s to 1970s and was an alternative to thalamotomy. Recently, there has been increasing interest in the reappraisal of stimulating and/or lesioning these targets, partly as a result of innovations in imaging and noninvasive ablative technologies, such as magnetic resonance-guided focused ultrasonography.

OBJECTIVE

We wanted to perform a thorough review of the subthalamic region, both from an anatomic and a surgical standpoint, to offer a comprehensive and updated analysis of the techniques and results reported for patients with tremor treated with different techniques.

METHODS

We performed a systematic review of the literature, gathering articles that included patients who underwent ablative or stimulation surgical techniques, targeting the pallidothalamic pathways (pallidothalamic tractotomy), cerebellothalamic pathway (cerebellothalamic tractotomy), or subthalamic area.

RESULTS

Pallidothalamic tractotomy consists of a reduced area that includes pallidofugal pathways. It may be considered an interesting target, given the benefit/risk ratio and the clinical effect, which, compared with pallidotomy, involves a lower risk of injury or involvement of vital structures such as the internal capsule or optic tract. Cerebellothalamic tractotomy and/or posterior subthalamic area are other alternative targets to thalamic stimulation or ablative surgery.

CONCLUSIONS

Based on the significant breakthrough that magnetic resonance-guided focused ultrasonography has meant in the neurosurgical world, some classic targets such as the pallidothalamic tract, Forel field, and posterior subthalamic area may be reconsidered as surgical alternatives for patients with movement disorders.

The Effect of Pain Reduction during Headframe Fixation for Stereotactic Radiosurgery by the Preceded Local Anesthesia under the Needle Cap Guidance

Background

Gamma knife radiosurgery (GKRS) has become a major alternative in the neurosurgical field. However, many patients complained of considerable discomfort during the fixation of rigid headframe. This study investigated whether our modified procedure could reduce fixation-related pain.

Methods

Sixty-six patients who underwent GKRS were enrolled in this study. Thirty-one patients (Group A) underwent the conventional subcutaneous infiltration technique, and 35 patients (Group B) did the modified procedure. In group A, the headframe was held in position by an assistant, and local anesthetics were injected subcutaneously using a 23-gauge spinal needle at pinning sites. Subsequently, pins were applied according to measurements based on spinal needle depth. In group B, with the frame held in position by an assistant, pin sites were marked with a surgical pen under the guidance of needle cap placed on the pin holes. The head frame was then removed, and local anesthetics were injected subcutaneously and periosteally at each marked pin site using a 26-gauge needle. The headframe was then repositioned 5 minutes after local infiltration, and pins were applied according to measurements based on spinal needle depth. To evaluate pain severity during procedures, visual analogue scale (VAS) scores were recorded during local infiltration and frame placement with pins. The pain scores of the two groups were analyzed statistically.

Results

Group B had a significantly lower VAS score during frame placement than group A (7.26 vs. 3.61; p<0.001), and mean VAS score at local infiltration was also significantly lower in group B (4.74 vs. 3.74; p=0.008).

Conclusion

Patients in group B experienced significantly less pain than those in group A during pin placement. Pre-fixation time advanced local anesthesia might reduce pain during stereotactic procedures, and the use of a 26-gauge needle appeared in less pain during local infiltration.

Post mortem examination of Parkinson's disease brains suggests decline in mitochondrial biomass, reversed by deep brain stimulation of subthalamic nucleus

Deep brain stimulation (DBS) of the subthalamic nucleus (STN) is the most commonly used surgical treatment for Parkinson's disease (PD). The disease-modifying aspects of DBS at a cellular level are not fully understood, and the key question of the effect of DBS on the degeneration of the dopaminergic (DA) neurons in the substantia nigra pars compacta (SNpc) remains to be answered. A major technical hurdle in determining any neuroprotective effect by DBS is its use in mid- to late-stage patients with PD when a majority of the DA neurons have been lost. In this work, we hypothesized that the long-term clinical benefits of DBS are, at least in part, due to a neuromodulatory effect on the SNpc neurons. These changes would affect cellular energetics and mitochondrial metabolism. We examined the number and volume of mitochondria as well as their vicinity to the DA presynaptic terminals postmortem caudate and putamen of 3 healthy individuals, 4 PD cases, and 3 DBS-treated patients. PD seems to have caused an increase in the mean distance between mitochondria and presynaptic terminals as well as a decrease in mean mitochondrial volume and numbers in DA projections. Although there was no difference in distance between mitochondria and presynaptic terminals of SNpc neurons in PD brains vs. DBS-treated brains, DBS treatment seemed to have inhibited or reversed the reduction in mitochondrial volume and numbers caused by PD. These results suggest enhanced metabolic plasticity leading to neuroprotection in the SNpc as a result of STN-DBS.-Mallach, A., Weinert, M., Arthur, J., Gveric, D., Tierney, T. S., Alavian, K. N. Post mortem examination of Parkinson's disease brains suggests decline in mitochondrial biomass, reversed by deep brain stimulation of subthalamic nucleus.

Subthalamotomy for Parkinson's disease: clinical outcome and topography of lesions

OBJECTIVE

Subthalamotomy is an effective alternative for the treatment of Parkinson's disease (PD). However, uncertainty about the optimal target location and the possibility of inducing haemichorea-ballism have limited its application. We assessed the correlation between the topography of radiofrequency-based lesions of the subthalamic nucleus (STN) with motor improvement and the emergence of haemichorea-ballism.

METHODS

Sixty-four patients with PD treated with subthalamotomy were evaluated preoperatively and postoperatively using the Unified Parkinson's Disease Rating Scale motor score (UPDRSm), MRI and tractography. Patients were classified according to the degree of clinical motor improvement and dyskinesia scale. Lesions were segmented on MRI and averaged in a standard space. We examined the relationship between the extent of lesion-induced disruption of fibres surrounding the STN and the development of haemichorea-ballism.

RESULTS

Maximum antiparkinsonian effect was obtained with lesions located within the dorsolateral motor region of the STN as compared with those centre-placed in the dorsal border of the STN and the zona incerta (71.3%, 53.5% and 20.8% UPDRSm reduction, respectively). However, lesions that extended dorsally beyond the STN showed lower probability of causing haemichorea-ballism than those placed entirely within the nucleus. Tractography findings indicate that interruption of pallidothalamic fibres probably determines a low probability of haemichorea-ballism postoperatively.

CONCLUSIONS

The topography of the lesion is a major factor in the antiparkinsonian effect of subthalamotomy in patients with PD. Lesions involving the motor STN and pallidothalamic fibres induced significant motor improvement and were associated with a low incidence of haemichorea-ballism.

On the neuronal circuitry mediating L-DOPA-induced dyskinesia

With the advent of rodent models of l-DOPA-induced dyskinesia (LID), a growing literature has linked molecular changes in the striatum to the development and expression of abnormal involuntary movements. Changes in information processing at the striatal level are assumed to impact on the activity of downstream basal ganglia nuclei, which in turn influence brain-wide networks, but very little is actually known about systems-level mechanisms of dyskinesia. As an aid to approach this topic, we here review the anatomical and physiological organisation of cortico-basal ganglia-thalamocortical circuits, and the changes affecting these circuits in animal models of parkinsonism and LID. We then review recent findings indicating that an abnormal cerebellar compensation plays a causal role in LID, and that structures outside of the classical motor circuits are implicated too. In summarizing the available data, we also propose hypotheses and identify important knowledge gaps worthy of further investigation. In addition to informing novel therapeutic approaches, the study of LID can provide new clues about the interplay between different brain circuits in the control of movement.

Early effect of thalamotomy on cognitive function in patients with Parkinson’s disease

Thalamotomy is a neurosurgical procedure used in the treatment of advanced Parkinson’s disease (PD). The aim of our research is to evaluate the early impact of a lesion in the ventrointermedial nucleus (VIM) of the thalamus on cognitive and motor function in people with PD. Sixty patients who qualified for right- or left-sided VIM thalamotomy were involved in the study. The cognitive and motor functions of each patient were assessed both prior to and following the surgical procedure. Twenty-nine PD patients without ablative treatment were qualified for the comparison group, and 57 neurologically healthy individuals were assigned to the control group. The following tests were carried out: Mini Mental State Examination, Benton Visual Retention Test, Stroop Color and Word Test, Trail Making Test A&B, and Rey Auditory Verbal Learning Test. Statistically significant differences were found in reaction time, visual-spatial working memory, auditory-verbal memory, and overall level of cognitive function when comparing the results of tests carried out before and after thalamotomy and when comparing patients who had undergone surgery with untreated or healthy individuals. In patients with right-sided and left-sided thalamotomy differences were also found in the mean number of perseverative errors and recalled words.

Subthalamic oscillatory activity in parkinsonian patients with off-period dystonia

OBJECTIVES

The study was aimed to explore oscillatory activity in the subthalamic nucleus (STN) in Parkinson's disease (PD) with off-period dystonia, a type of levodopa-induced dyskinesias (LID).

METHODS

Eighteen patients with PD who underwent STN DBS were studied. Nine patients had dyskinesia defined as the LID group and nine patients who did not present any sign of dyskinesia were defined as the control group. Microelectrode recordings in the STN together with electromyogram (EMG) were recorded. Spectral and coherence analyses were performed to study the neuronal oscillations in relation to limb muscles.

RESULTS

Two hundred and fifteen neurons were identified. There were 39 neurons with tremor-frequency band (4-7 Hz) oscillation, 57 neurons with β-frequency band (12-30 Hz, β-FB) oscillation and 100 neurons without oscillation, and 19 neurons with very low-frequency band oscillation at a mean peak power of 1.2 ± 0.5 Hz (LFB). These LFB oscillatory neurons (n = 15) were frequently significantly coherent with EMG of off-period dystonia. Notably, 89% (n = 17) neurons with LFB oscillation were found in the patients in the off-dystonia group. The age at onset of PD, duration of PD, and levodopa equivalent dose daily consumption were statistically different between two groups (P < 0.05).

CONCLUSIONS

Subthalamic LFB oscillatory neurons seem to play an important role in the genesis of off-period dystonia in advanced PD. Clinical and demographic analyses confirmed that the earlier age at onset of PD, longer duration of PD, and levodopa exposure are important risk factors in the development of the type of LID.

Oscillatory activity in the basal ganglia and deep brain stimulation

Over the past 10 years, research into the neurophysiology of the basal ganglia has provided new insights into the pathophysiology of movement disorders. The presence of pathological oscillations at specific frequencies has been linked to different signs and symptoms in PD and dystonia, suggesting a new model to explain basal ganglia dysfunction. These advances occurred in parallel with improvements in imaging and neurosurgical techniques, both of which having facilitated the more widespread use of DBS to modulate dysfunctional circuits. High-frequency stimulation is thought to disrupt pathological activity in the motor cortex/basal ganglia network; however, it is not easy to explain all of its effects based only on changes in network oscillations. In this viewpoint, we suggest that a return to classic anatomical concepts might help to understand some apparently paradoxical findings. © 2016 International Parkinson and Movement Disorder Society.

Deep Brain Stimulation for Tourette-Syndrome: A Systematic Review and Meta-Analysis

BACKGROUND

A significant proportion of patients with Tourette syndrome (TS) continue to experience symptoms across adulthood that in severe cases fail to respond to standard therapies. For these cases, deep brain stimulation (DBS) is emerging as a promising treatment option.

OBJECTIVE

We conducted a systematic literature review to evaluate the efficacy of DBS for GTS.

METHODS

Individual data of case reports and series were pooled; the Yale Global Tic Severity Scale (YGTSS) was chosen as primary outcome parameter.

RESULTS

In total, 57 studies were eligible, including 156 cases. Overall, DBS resulted in a significant improvement of 52.68% (IQR = 40.74, p < 0.001) in the YGTSS. Analysis of controlled studies significantly favored stimulation versus off stimulation with a standardized mean difference of 0.96 (95% CI: 0.36-1.56). Disentangling different target points revealed significant YGTSS reductions after stimulation of the thalamus, the posteroventrolateral part and the anteromedial part of the globus pallidus internus, the anterior limb of the internal capsule and nucleus accumbens with no significant difference between these targets. A significant negative correlation of preoperative tic scores with the outcome of thalamic stimulation was found.

CONCLUSIONS

Despite small patient numbers, we conclude that DBS for GTS is a valid option for medically intractable patients. Different brain targets resulted in comparable improvement rates, indicating a modulation of a common network. Future studies might focus on a better characterization of the clinical effects of distinct regions, rather than searching for a unique target.

Altered Neuronal Firing Pattern of the Basal Ganglia Nucleus Plays a Role in Levodopa-Induced Dyskinesia in Patients with Parkinson's Disease

BACKGROUND

Levodopa therapy alleviates the symptoms of Parkinson's disease (PD), but long-term treatment often leads to motor complications such as levodopa-induced dyskinesia (LID).

AIM

To explore the neuronal activity in the basal ganglia nuclei in patients with PD and LID.

METHODS

Thirty patients with idiopathic PD (age, 55.1 ± 11.0 years; disease duration, 8.7 ± 5.6 years) were enrolled between August 2006 and August 2013 at the Xuanwu Hospital, Capital Medical University, China. Their Hoehn and Yahr (1967) scores ranged from 2-4 and their UPDRS III scores were 28.5 ± 5.2. Fifteen of them had severe LID (UPDRS IV scores of 6.7 ± 1.6). Microelectrode recording was performed in the globus pallidus internus (GPi) and subthalamic nucleus (STN) during pallidotomy (n = 12) or STN deep brain stimulation (DBS; bilateral, n = 12; unilateral, n = 6). The firing patterns and frequencies of various cell types were analyzed by assessing single cell interspike intervals (ISIs) and the corresponding coefficient of variation (CV).

RESULTS

A total of 295 neurons were identified from the GPi (n = 12) and STN (n = 18). These included 26 (8.8%) highly grouped discharge, 30 (10.2%) low frequency firing, 78 (26.4%) rapid tonic discharge, 103 (34.9%) irregular activity, and 58 (19.7%) tremor-related activity. There were significant differences between the two groups (p < 0.05) for neurons with irregular firing, highly irregular cluster-like firing, and low-frequency firing.

CONCLUSION

Altered neuronal activity was observed in the basal ganglia nucleus of GPi and STN, and may play important roles in the pathophysiology of PD and LID.

Effect of Subthalamic Deep Brain Stimulation on Levodopa-Induced Dyskinesia in Parkinson's Disease

PURPOSE

To evaluate the effect of bilateral subthalamic nucleus (STN) deep brain stimulation (DBS) on levodopa-induced peak-dose dyskinesia in patients with Parkinson's disease (PD).

MATERIALS AND METHODS

A retrospective review was conducted on patients who underwent STN DBS for PD from May 2000 to July 2012. Only patients with levodopa-induced dyskinesia prior to surgery and more than 1 year of available follow-up data after DBS were included. The outcome measures included the dyskinesia subscore of the Unified Parkinson's Disease Rating Scale (UPDRS) part IV (items 32 to 34 of UPDRS part IV) and the levodopa equivalent daily dose (LEDD). The patients were divided into two groups based on preoperative to postoperative LEDD change at 12 months after the surgery: Group 1, LEDD decrease >15%; Group 2, all other patients. Group 2 was further divided by the location of DBS leads.

RESULTS

Of the 100 patients enrolled, 67 were in Group 1, while those remaining were in Group 2. Twelve months after STN DBS, Groups 1 and 2 showed improvements of 61.90% and 57.14%, respectively, in the dyskinesia subscore. Group 1 was more likely to experience dyskinesia suppression; however, the association between the groups and dyskinesia suppression was not statistically significant (p=0.619). In Group 2, dyskinesia was significantly decreased by stimulation of the area above the STN in 18 patients compared to stimulation of the STN in 15 patients (p=0.048).

CONCLUSION

Levodopa-induced dyskinesia is attenuated by STN DBS without reducing the levodopa dosage.

Dopamine heteroreceptor complexes as therapeutic targets in Parkinson's disease

INTRODUCTION

Several types of D2R and D1R heteroreceptor complexes were discovered in the indirect and direct pathways of the striatum, respectively. The hypothesis is given that changes in the function of the dopamine heteroreceptor complexes may help us understand the molecular mechanisms underlying the motor complications of long-term therapy in Parkinson's disease (PD) with l-DOPA and dopamine receptor agonists.

AREAS COVERED

In the indirect pathway, the potential role of the A2AR-D2R, A2AR-D2R-mGluR5 and D2R-NMDAR heteroreceptor complexes in PD are covered and in the direct pathway, the D1R-D3R, A1R-D1R, D1R-NMDAR and putative A1R-D1R-D3R heteroreceptor complexes.

EXPERT OPINION

One explanation for the more powerful ability of l-DOPA treatment versus treatment with the partial dopamine receptor agonist/antagonist activity to induce dyskinesias, may be that dopamine formed from l-DOPA acts as a full agonist. The field of D1R and D2R heteroreceptor complexes in the CNS opens up a new understanding of the wearing off of the antiparkinson actions of l-DOPA and dopamine receptor agonists and the production of l-DOPA-induced dyskinesias. It can involve a reorganization of the D1R and D2R heteroreceptor complexes and a disbalance of the D1R and D2R homomers versus non-dopamine receptor homomers in the direct and indirect pathways.

80 Hz versus 130 Hz subthalamic nucleus deep brain stimulation: effects on involuntary movements

BACKGROUND

Subthalamic Nucleus Deep Brain Stimulation (STN-DBS) represents a valid therapeutic option for advanced Parkinson's disease (PD), leading to a significant amelioration of motor fluctuations and levodopa-induced involuntary movements (IM). This study address the issue of whether stimulation frequency may influence the control of IM in STN-DBS treated patients, comparing the effects of 80 Hz and 130 Hz STN-DBS frequencies in 10 parkinsonian patients with residual IM (dyskinesia in 6 cases and dystonia in 4 cases).

METHODS

Patients were evaluated by means of the Rush Dyskinesias Rating Scale (blinded-video analysis) and Unified Parkinson's Disease Rating Scale at 4 different time-points: baseline, shortly after the switch of stimulation frequency from 130 Hz to 80 Hz, after 1 month and 12 months of chronic 80 Hz stimulation.

RESULTS

IM improved in most subjects after the switch of stimulation frequency: dyskinesias improved in 6/6 subjects and dystonic features in 3/4 subjects after one month of 80 Hz stimulation. However, the 130 Hz STN stimulation was restored in 4 subjects during the following months, because of a gradual worsening of parkinsonian symptoms. A sustained efficacy on motor features and IM was observed with 80 Hz stimulation frequency in the remaining patients.

CONCLUSIONS

In this limited cohort of STN-DBS patients, we observed an improvement of residual IM after the switch of stimulation frequency from 130 Hz to 80 Hz. However, a moderate worsening of parkinsonian symptoms was observed in a portion of patients, requiring to return at 130 Hz STN-DBS.

Therapeutic stimulation versus ablation

The renaissance of functional stereotactic neurosurgery was pioneered in the mid 1980s by Laitinen's introduction of Leksell's posteroventral pallidotomy for Parkinson´s disease (PD). This ablative procedure experienced a worldwide spread in the 1990s, owing to its excellent effect on dyskinesias and other symptoms of post-l-dopa PD. Modern deep brain stimulation (DBS), pioneered by Benabid and Pollak in 1987 for the treatment of tremor, first became popular when it was applied to the subthalamic nucleus (STN) in the mid 1990s, where it demonstrated a striking effect on all cardinal symptoms of advanced PD, and permitted reduced dosages of medication. DBS, as a nondestructive, adaptable, and reversible procedure that is proving safe in bilateral surgery on basal ganglia, has great appeal to clinicians and patients alike, despite the fact that it is expensive, laborious, and relies on very strict patient selection criteria, especially for STN DBS. Psychiatric surgery has experienced the same phenomenon, with DBS supplanting completely stereotactic ablative procedures. This chapter discusses the pros and cons of ablation versus stimulation and investigates the reasons why DBS has overshadowed proven efficient ablative procedures such as pallidotomy for PD, and capsulotomy and cingulotomy for obsessive-compulsive disorder and depression.

Topography of dyskinesias and torticollis evoked by inhibition of substantia nigra pars reticulata

GABAergic neurons of the substantia nigra pars reticulata (SNpr) and globus pallidus pars interna (GPi) constitute the output pathways of the basal ganglia. In monkeys, choreiform limb dyskinesias have been described after inhibition of the GPi, but not the SNpr. Given the anatomical and functional similarities between these structures, we hypothesized that choreiform dyskinesias could be evoked by inhibition of an appropriate region within the SNpr. The GABAA receptor agonist, muscimol, was infused into various sites within the SNpr and the adjacent STN of freely moving macaques. The effect of the GABAA antagonist, bicuculline (BIC), was also examined. Muscimol (MUS) in SNpr evoked the following: (1) choreiform dyskinesias of the contralateral arm and/or leg from central and lateral sites; (2) contralaterally directed torticollis from central and posterior sites; and (3) contraversive quadrupedal rotation from anterior and lateral sites. MUS infusions into the adjacent SN pars compacta or STN were without effect, ruling out a contribution of drug spread to adjacent structures. BIC in SNpr induced ipsiversive postures without choreiform dyskinesia or torticollis, whereas in the STN, it evoked ballistic movements. This is the first report of choreiform dyskinesia evoked by inhibition of the SNpr. This highly site-specific effect was obtained from a restricted region within the SNpr distinct from that responsible for inducing torticollis. These results suggest that overactivity of different SNpr outputs mediates choreiform dyskinesia and torticollis. These abnormalities are symptoms of dystonia, Huntington's disease, and iatrogenic dyskinesias, suggesting that these conditions may result, in part, from a loss of function in SNpr efferent projections.

Clinical features, pathophysiology, and treatment of levodopa-induced dyskinesias in Parkinson's disease

Dyskinetic disorders are characterized by excess of motor activity that may interfere with normal movement control. In patients with Parkinson's disease, the chronic levodopa treatment induces dyskinetic movements known as levodopa-induced dyskinesias (LID). This paper analyzed the pathophysiology, clinical manifestations, pharmacological treatments, and surgical procedures to treat hyperkinetic disorders. Surgery is currently the only treatment available for Parkinson's disease that may improve both parkinsonian motor syndrome and LID. However, this paper shows the different mechanisms involved are not well understood.

Contrasting connectivity of the ventralis intermedius and ventralis oralis posterior nuclei of the motor thalamus demonstrated by probabilistic tractography

BACKGROUND

Targeting of the motor thalamus for the treatment of tremor has traditionally been achieved by a combination of anatomical atlases and neuroimaging, intraoperative clinical assessment, and physiological recordings.

OBJECTIVE

To evaluate whether thalamic nuclei targeted in tremor surgery could be identified by virtue of their differing connections with noninvasive neuroimaging, thereby providing an extra factor to aid successful targeting.

METHODS

Diffusion tensor tractography was performed in 17 healthy control subjects using diffusion data acquired at 1.5-T magnetic resonance imaging (60 directions, b value = 1000 s/mm, 2 × 2 × 2-mm³ voxels). The ventralis intermedius (Vim) and ventralis oralis posterior (Vop) nuclei were identified by a stereotactic neurosurgeon, and these sites were used as seeds for probabilistic tractography. The expected cortical connections of these nuclei, namely the primary motor cortex (M1) and contralateral cerebellum for the Vim and M1, the supplementary motor area, and dorsolateral prefrontal cortex for the Vop, were determined a priori from the literature.

RESULTS

Tractogram signal intensity was highest in the dorsolateral prefrontal cortex and supplementary motor area after Vop seeding (P < .001, Wilcoxon signed-rank tests). High intensity was seen in M1 after seeding of both nuclei but was greater with Vim seeding (P < .001). Contralateral cerebellar signal was highest with Vim seeding (P < .001).

CONCLUSION

Probabilistic tractography can depict differences in connectivity between intimate nuclei within the motor thalamus. These connections are consistent with published anatomical studies; therefore, tractography may provide an important adjunct in future targeting in tremor surgery.

The role of the subthalamic nucleus in L-DOPA induced dyskinesia in 6-hydroxydopamine lesioned rats

L-DOPA is the most effective treatment for Parkinson's disease (PD), but prolonged use leads to disabling motor complications including dyskinesia. Strong evidence supports a role of the subthalamic nucleus (STN) in the pathophysiology of PD whereas its role in dyskinesia is a matter of controversy. Here, we investigated the involvement of STN in dyskinesia, using single-unit extracellular recording, behavioural and molecular approaches in hemi-parkinsonian rats rendered dyskinetic by chronic L-DOPA administration. Our results show that chronic L-DOPA treatment does not modify the abnormal STN activity induced by the 6-hydroxydopamine lesion of the nigrostriatal pathway in this model. Likewise, we observed a loss of STN responsiveness to a single L-DOPA dose both in lesioned and sham animals that received daily L-DOPA treatment. We did not find any correlation between the abnormal involuntary movement (AIM) scores and the electrophysiological parameters of STN neurons recorded 24 h or 20–120 min after the last L-DOPA injection, except for the axial subscores. Nonetheless, unilateral chemical ablation of the STN with ibotenic acid resulted in a reduction in global AIM scores and peak-severity of dyskinesia. In addition, STN lesion decreased the anti-dyskinetogenic effect of buspirone in a reciprocal manner. Striatal protein expression was altered in dyskinetic animals with increases in ΔFosB, phosphoDARPP-32, dopamine receptor (DR) D3 and DRD2/DRD1 ratio. The STN lesion attenuated the striatal molecular changes and normalized the DRD2/DRD1 ratio. Taken together, our results show that the STN plays a role, if modest, in the physiopathology of dyskinesias.

Novel applications of deep brain stimulation

The success of deep brain stimulation (DBS) surgery in treating medically refractory symptoms of some movement disorders has inspired further investigation into a wide variety of other treatment-resistant conditions. These range from disorders of gait, mood, and memory to problems as diverse as obesity, consciousness, and addiction. We review the emerging indications, rationale, and outcomes for some of the most promising new applications of DBS in the treatment of postural instability associated with Parkinson's disease, depression, obsessive–compulsive disorder, obesity, substance abuse, epilepsy, Alzheimer′s-type dementia, and traumatic brain injury. These studies reveal some of the excitement in a field at the edge of a rapidly expanding frontier. Much work still remains to be done on basic mechanism of DBS, optimal target and patient selection, and long-term durability of this technology in treating new indications.

Deep brain stimulation emerging indications

There are a number of emerging surgical indications for deep brain stimulation. We have shown that modulation of activity within motor, mood, and cognitive circuits has beneficial effects in patients with Parkinson's disease, treatment-resistant depression, and perhaps Alzheimer's type dementia. We review the rationale, safety, and efficacy for each of these indications, focusing on disease mechanisms and relevant data that are necessary to document therapeutic value in each case. The review closes with some thoughts on possible future directions for deep brain stimulation. It is likely that applications for deep brain stimulation will continue to expand as accumulating data establish its safety and efficacy profile in these and other conditions.

Surgical approach to l-dopa-induced dyskinesias

Many patients treated chronically with l-dopa for Parkinson disease (PD) become functionally disabled by l-dopa-induced dyskinesias (LID). Evolved from early empirical procedures, modern stereotactic surgical lesioning techniques and deep brain stimulation (DBS) can effectively treat LID while simultaneously improving the cardinal motor symptoms of PD. Here we review the common surgical targets used to treat LID, and compare their relative efficacy. We explain the anti-dyskinetic action of surgery at each of these targets based on evolving models of basal ganglia function. Finally, we discuss the appropriate selection of patients with LID for surgery and address relevant technical and management issues in these patients.

Deep brain stimulation of pedunculopontine tegmental nucleus (PPTg) promotes cognitive and metabolic changes: a target-specific effect or response to a low-frequency pattern of stimulation?

Deep brain stimulation (DBS) is a reliable treatment for advanced Parkinson's disease (PD) patients, but a possible risk of worsening cognitive functions, although modest, may postpone or halt DBS clinical indication. In a small cohort of PD patients we have pioneered the simultaneous implantation of both the subthalamic nucleus (STN) and the pedunculopontine tegmental nucleus (PPTg). Here we describe the cognitive test performance and the corresponding cortical metabolic activity, as assessed through 18-fluorodeoxyglucose (FDG)-positron emission tomography (PET), of these six PD patients tested in PPTg-ON vs- PPTg-OFF condition. PPTg-ON condition (at low frequency, 25 Hz) induced better performance in tests exploring both executive and attentive domains, which were coupled with an increased glucose utilization in prefrontal and frontal bilateral cortical areas, including both lateral (i.e., BA9) and more antero-medial cortices (BA 25-32). Moreover, during PPTg-ON, a surprising increase of FDG consumption was also observed in the left ventral striatum. These data are consistent with the hypothesis of a positive effect of 25 Hz PPTg-DBS on PD patients' cognitive profile, probably due to a facilitatory effect exerted by PPTg on both associative and limbic pathways.

Therapy for dyskinesias in Parkinson’s disease patients

Dyskinesia hampers the quality of life for most Parkinson’s disease patients following several years of therapy. However, the severity of L-Dopa-induced dyskinesia (LID) varies between patients, being quite tolerable in late-onset patients. Understanding the pathogenesis of LID has contributed to the development of a set of therapeutic strategies, including the choice, in early stages, of the least pulsatile regimen of dopamine-receptor activation. In cases where LIDs are already disabling, there is only a limited number of options: the optimization of ongoing DOPA-centered treatment, the utilization of glutamate antagonists and the exploration of the benefits of antipsychotic agents. More radical solutions are provided by deep brain stimulation in the subthalamic nucleus (or internal pallidus). This approach has proved efficacious in reducing LID, largely because it allows a reduction in dopaminergic daily doses. Stereotactic neurosurgery has fuelled several lines of investigation regarding the crosstalk between the basal ganglia and motor cortex. Here, we will present interesting evidence highlighting the potential for repetitive transcranial stimulation in reducing the occurrence of LID. The future may disclose important new avenues for the treatment of LIDs, given the current development of promising agents that might target different facets of dyskinesia, such as the impairment of striatal plasticity and non-Dopaminergic contributors such as adenosine, nitric oxide and the nucleotide cascade.

Gene therapy in Parkinson's disease: rationale and current status

Parkinson's disease is the second most common age-related neurodegenerative disorder, typified by the progressive loss of substantia nigra pars compacta dopamine neurons and the consequent decrease in the neurotransmitter dopamine. Patients exhibit a range of clinical symptoms, with the most common affecting motor function and including resting tremor, rigidity, akinesia, bradykinesia and postural instability. Current pharmacological interventions are palliative and largely aimed at increasing dopamine levels through increased production and/or inhibition of metabolism of this key neurotransmitter. The gold standard for treatment of both familial and sporadic Parkinson's disease is the peripheral administration of the dopamine precursor, levodopa. However, many patients gradually develop levodopa-induced dyskinesias and motor fluctuations. In addition, dopamine enhancement therapies are most useful when a portion of the nigrostriatal pathway is intact. Consequently, as the number of substantia nigra dopamine neurons and striatal projections decrease, these treatments become less efficacious. Current translational research is focused on the development of novel disease-modifying therapies, including those utilizing gene therapeutic approaches. Herein we present an overview of current gene therapy clinical trials for Parkinson's disease. Employing either recombinant adeno-associated virus type 2 (rAAV2) or lentivirus vectors, these clinical trials are focused on three overarching approaches: augmentation of dopamine levels via increased neurotransmitter production; modulation of the neuronal phenotype; and neuroprotection. The first two therapies discussed in this article focus on increasing dopamine production via direct delivery of genes involved in neurotransmitter synthesis (amino acid decarboxylase, tyrosine hydroxylase and GTP [guanosine triphosphate] cyclohydrolase 1). In an attempt to bypass the degenerating nigrostriatal pathway, a third clinical trial utilizes rAAV2 to deliver glutamic acid decarboxylase to the subthalamic nucleus, converting a subset of excitatory neurons to GABA-producing cells. In contrast, the final clinical trial is aimed at protecting the degenerating nigrostriatum by striatal delivery of rAAV2 harbouring the neuroprotective gene, neurturin. Based on preclinical studies, this gene therapeutic approach is posited to slow disease progression by enhancing neuronal survival. In addition, we discuss the outcome of each clinical trial and discuss the potential rationale for the marginal yet incremental clinical advancements that have thus far been realized for Parkinson's disease gene therapy.

Adenosine A2A receptors and Parkinson's disease

The drug treatment of Parkinson's disease (PD) is accompanied by a loss of drug efficacy, the onset of motor complications, lack of effect on non-motor symptoms, and a failure to modify disease progression. As a consequence, novel approaches to therapy are sought, and adenosine A(2A) receptors (A(2A)ARs) provide a viable target. A(2A)ARs are highly localized to the basal ganglia and specifically to the indirect output pathway, which is highly important in the control of voluntary movement. A(2A)AR antagonists can modulate gamma-aminobutyric acid (GABA) and glutamate release in basal ganglia and other key neurotransmitters that modulate motor activity. In both rodent and primate models of PD, A(2A)AR antagonists produce alterations in motor behavior, either alone or in combination with dopaminergic drugs, which suggest that they will be effective in the symptomatic treatment of PD. In clinical trials, the A(2A)AR antagonist istradefylline reduces "off" time in patients with PD receiving optimal dopaminergic therapy. However, these effects have proven difficult to demonstrate on a consistent basis, and further clinical trials are required to establish the clinical utility of this drug class. Based on preclinical studies, A(2A)AR antagonists may also be neuroprotective and have utility in the treatment of neuropsychiatric disorders. We are only now starting to explore the range of potential uses of A(2A)AR antagonists in central nervous system disorders, and their full utility is still to be uncovered.

alpha-Synuclein: a therapeutic target for Parkinson's disease?

Parkinson's disease is a progressive age-related neurodegenerative disease with invariant loss of substantia nigra dopamine neurons and striatal projections. This disorder is well known for the associated motoric symptoms including resting tremor and the inability to initiate movement. However, it is now apparent that Parkinson's disease is a multisystem disorder with patients exhibiting symptoms derived from peripheral nervous system and extra-nigral dysfunctions in addition to the prototypical nigrostriatal damage. Although the etiology for sporadic Parkinson's disease is unknown, information gleaned from both familial forms of the disease and animal models places misfolded alpha-synuclein at the forefront. The disease is currently without a cure and most therapies target the motoric symptoms relying on increasing dopamine tone. In this review, the role of alpha-synuclein in disease pathogenesis and as a potential therapeutic target focusing on toxic conformers of this protein is considered. The addition of protofibrillar/oligomer-directed neurotherapeutics to the existing armamentarium may extend the symptom-free stage of Parkinson's disease as well as alleviate pathogenesis.