Subthalamic nucleus lesions are neuroprotective against terminal 6-OHDA-induced striatal lesions and restore postural balancing reactions

A Computational Model of Loss of Dopaminergic Cells in Parkinson's Disease Due to Glutamate-Induced Excitotoxicity

Parkinson's disease (PD) is a neurodegenerative disease associated with progressive and inexorable loss of dopaminergic cells in Substantia Nigra pars compacta (SNc). Although many mechanisms have been suggested, a decisive root cause of this cell loss is unknown. A couple of the proposed mechanisms, however, show potential for the development of a novel line of PD therapeutics. One of these mechanisms is the peculiar metabolic vulnerability of SNc cells compared to other dopaminergic clusters; the other is the SubThalamic Nucleus (STN)-induced excitotoxicity in SNc. To investigate the latter hypothesis computationally, we developed a spiking neuron network-model of SNc-STN-GPe system. In the model, prolonged stimulation of SNc cells by an overactive STN leads to an increase in ‘stress' variable; when the stress in a SNc neuron exceeds a stress threshold, the neuron dies. The model shows that the interaction between SNc and STN involves a positive-feedback due to which, an initial loss of SNc cells that crosses a threshold causes a runaway-effect, leading to an inexorable loss of SNc cells, strongly resembling the process of neurodegeneration. The model further suggests a link between the two aforementioned mechanisms of SNc cell loss. Our simulation results show that the excitotoxic cause of SNc cell loss might initiate by weak-excitotoxicity mediated by energy deficit, followed by strong-excitotoxicity, mediated by a disinhibited STN. A variety of conventional therapies were simulated to test their efficacy in slowing down SNc cell loss. Among them, glutamate inhibition, dopamine restoration, subthalamotomy and deep brain stimulation showed superior neuroprotective-effects in the proposed model.

Subthalamic Nucleus Deep Brain Stimulation: Basic Concepts and Novel Perspectives

Over the last decades, extensive basic and clinical knowledge has been acquired on the use of subthalamic nucleus (STN) deep brain stimulation (DBS) for Parkinson's disease (PD). It is now clear that mechanisms involved in the effects of this therapy are far more complex than previously anticipated. At frequencies commonly used in clinical practice, neural elements may be excited or inhibited and novel dynamic states of equilibrium are reached. Electrode contacts used for chronic DBS in PD are placed near the dorsal border of the nucleus, a highly cellular region. DBS may thus exert its effects by modulating these cells, hyperdirect projections from motor cortical areas, afferent and efferent fibers to the motor STN. Advancements in neuroimaging techniques may allow us to identify these structures optimizing surgical targeting. In this review, we provide an update on mechanisms and the neural elements modulated by STN DBS.

Basal ganglia, movement disorders and deep brain stimulation: advances made through non-human primate research

Studies in non-human primates (NHPs) have led to major advances in our understanding of the function of the basal ganglia and of the pathophysiologic mechanisms of hypokinetic movement disorders such as Parkinson's disease and hyperkinetic disorders such as chorea and dystonia. Since the brains of NHPs are anatomically very close to those of humans, disease states and the effects of medical and surgical approaches, such as deep brain stimulation (DBS), can be more faithfully modeled in NHPs than in other species. According to the current model of the basal ganglia circuitry, which was strongly influenced by studies in NHPs, the basal ganglia are viewed as components of segregated networks that emanate from specific cortical areas, traverse the basal ganglia, and ventral thalamus, and return to the frontal cortex. Based on the presumed functional domains of the different cortical areas involved, these networks are designated as 'motor', 'oculomotor', 'associative' and 'limbic' circuits. The functions of these networks are strongly modulated by the release of dopamine in the striatum. Striatal dopamine release alters the activity of striatal projection neurons which, in turn, influences the (inhibitory) basal ganglia output. In parkinsonism, the loss of striatal dopamine results in the emergence of oscillatory burst patterns of firing of basal ganglia output neurons, increased synchrony of the discharge of neighboring basal ganglia neurons, and an overall increase in basal ganglia output. The relevance of these findings is supported by the demonstration, in NHP models of parkinsonism, of the antiparkinsonian effects of inactivation of the motor circuit at the level of the subthalamic nucleus, one of the major components of the basal ganglia. This finding also contributed strongly to the revival of the use of surgical interventions to treat patients with Parkinson's disease. While ablative procedures were first used for this purpose, they have now been largely replaced by DBS of the subthalamic nucleus or internal pallidal segment. These procedures are not only effective in the treatment of parkinsonism, but also in the treatment of hyperkinetic conditions (such as chorea or dystonia) which result from pathophysiologic changes different from those underlying Parkinson's disease. Thus, these interventions probably do not counteract specific aspects of the pathophysiology of movement disorders, but non-specifically remove the influence of the different types of disruptive basal ganglia output from the relatively intact portions of the motor circuitry downstream from the basal ganglia. Knowledge gained from studies in NHPs remains critical for our understanding of the pathophysiology of movement disorders, of the effects of DBS on brain network activity, and the development of better treatments for patients with movement disorders and other neurologic or psychiatric conditions.

Subthalamic nucleus deep brain stimulation is neuroprotective in the A53T α-synuclein Parkinson's disease rat model

Objective

Deep brain stimulation (DBS) of the subthalamic nucleus (STN) is a highly effective symptomatic therapy for motor deficits in Parkinson's disease (PD). An additional, disease‐modifying effect has been suspected from studies in toxin‐based PD animal models, but these models do not reflect the molecular pathology and progressive nature of PD that would be required to evaluate a disease‐modifying action. Defining a disease‐modifying effect could radically change the way in which DBS is used in PD.

Methods

We applied STN‐DBS in an adeno‐associated virus (AAV) 1/2‐driven human mutated A53T α‐synuclein (aSyn)‐overexpressing PD rat model (AAV1/2‐A53T‐aSyn). Rats were injected unilaterally, in the substantia nigra (SN), with AAV1/2‐A53T‐aSyn or control vector. Three weeks later, after behavioral and nigrostriatal dopaminergic deficits had developed, rats underwent STN‐DBS electrode implantation ipsilateral to the vector‐injected SN. Stimulation lasted for 3 weeks. Control groups remained OFF stimulation. Animals were sacrificed at 6 weeks.

Results

Motor performance in the single pellet reaching task was impaired in the AAV1/2‐A53T‐aSyn–injected stim‐OFF group, 6 weeks after AAV1/2‐A53T‐aSyn injection, compared to preoperative levels (–82%; p < 0.01). Deficits were reversed in AAV1/2‐A53T‐aSyn, stim‐ON rats after 3 weeks of active stimulation, compared to the AAV1/2‐A53T‐aSyn stim‐OFF rats (an increase of ∼400%; p < 0.05), demonstrating a beneficial effect of DBS. This motor improvement was maintained when the stimulation was turned off and was accompanied by a higher number of tyrosine hydroxylase⁺ SN neurons (increase of ∼29%), compared to AAV1/2‐A53T‐aSyn stim‐OFF rats (p < 0.05).

Interpretation

Our data support the putative neuroprotective and disease‐modifying effect of STN‐DBS in a mechanistically relevant model of PD. Ann Neurol 2017;81:825–836

Continuous High-Frequency Stimulation of the Subthalamic Nucleus Improves Cell Survival and Functional Recovery Following Dopaminergic Cell Transplantation in Rodents

Subthalamic nucleus (STN) high-frequency stimulation (HFS) is a routine treatment in Parkinson's disease (PD), with confirmed long-term benefits. An alternative, but still experimental, treatment is cell replacement and restorative therapy based on transplanted dopaminergic neurons. The current experiment evaluated the potential synergy between neuromodulation and grafting by studying the effect of continuous STN-HFS on the survival, integration, and functional efficacy of ventral mesencephalic dopaminergic precursors transplanted into a unilateral 6-hydroxydopamine medial forebrain bundle lesioned rodent PD model. One group received continuous HFS of the ipsilateral STN starting a week prior to intrastriatal dopaminergic neuron transplantation, whereas the sham-stimulated group did not receive STN-HFS but only dopaminergic grafts. A control group was neither lesioned nor transplanted. Over the following 7 weeks, the animals were probed on a series of behavioral tasks to evaluate possible graft and/or stimulation-induced functional effects. Behavioral and histological data suggest that STN-HFS significantly increased graft cell survival, graft-host integration, and functional recovery. These findings might open an unexplored road toward combining neuromodulative and neuroregenerative strategies to treat severe neurologic conditions.

Subthalamotomy in the treatment of Parkinson's disease: clinical aspects and mechanisms of action

Parkinson's disease (PD) is a neurodegenerative condition that can be pharmacologically treated with levodopa. However, important motor and nonmotor symptoms appear with its long-term use. The subthalamic nucleus (STN) is known to be involved in the pathophysiology of PD and to contribute to levodopa-induced complications. Surgery is considered in patients who have advanced PD that is refractory to pharmacotherapy and who display disabling dyskinesia. Deep brain stimulation of the STN is currently the main surgical procedure for PD, but lesioning is still performed. This review covers the clinical aspects and complications of subthalamotomy as one of the lesion-based options for PD patients with levodopa-induced dyskinesias. Moreover, the authors discuss the possible effects of subthalamic lesioning.

Subthalamic neurostimulation for Parkinson's disease with early fluctuations: balancing the risks and benefits

Electrical stimulation of the subthalamic nucleus is an established treatment for patients with advanced Parkinson's disease with pharmacologically unresponsive fluctuations. Compared with pharmacological treatment, subthalamic neurostimulation significantly improves motor symptoms, particularly during the phases of poor response to drug treatment, and reduces the severity of dyskinesias. Importantly, it also significantly improves quality of life and other integral measures of disease severity. The treatment response can last for more than 10 years, although there is no evidence that levodopa-resistant symptoms are delayed by subthalamic neurostimulation. At present, the mean disease duration for patients at the time of implantation is 12 years. In a recent study (EARLYSTIM) in patients with a disease duration of 7·5 years and fluctuations for 1·5 years, similar improvements in clinical outcomes were reported. These findings suggest that neurostimulation of the subthalamic nucleus could be used earlier in the disease course for carefully selected patients if the benefits of the treatment are weighed against the surgical risks and the lifelong need for specialised care by an experienced team. As mobility is consistently improved during the times with poor mobility by reducing fluctuations and delaying levodopa-sensitive complications, we propose that this treatment changes the disease course.

Timing of deep brain stimulation in Parkinson disease: a need for reappraisal?

We review the current application of deep brain stimulation (DBS) in Parkinson disease (PD) and consider the evidence that earlier use of DBS confers long-term symptomatic benefit for patients compared to best medical therapy. Electronic searches were performed of PubMed, Web of Knowledge, Embase, Cochrane Database of Systematic Reviews, and Cochrane Central Register of Controlled Trials to identify all article types relating to the timing of DBS in PD. Current evidence suggests that DBS is typically performed in late stage PD, a mean of 14 to 15 years after diagnosis. Current guidelines recommend that PD patients who are resistant to medical therapies, have significant medication side effects and lengthening off periods, but are otherwise cognitively intact and medically fit for surgery be considered for DBS. If these criteria are rigidly interpreted, it may be that, by the time medical treatment options have been exhausted, the disease has progressed to the point that the patient may no longer be fit for neurosurgical intervention. From the evidence available, we conclude that surgical management of PD alone or in combination with medical therapy results in greater improvement of motor symptoms and quality of life than medical treatment alone. There is evidence to support the use of DBS in less advanced PD and that it may be appropriate for earlier stages of the disease than for which it is currently used. The improving short and long-term safety profile of DBS makes early application a realistic possibility.

Subthalamic nucleus deep brain stimulation for Parkinson's disease: 8 years of follow-up

Objective

The short-term benefits of bilateral stimulation of the subthalamic nucleus (STN) in patients with advanced Parkinson’s disease (PD) are well documented, but long-term benefits are still uncertain. The aim of this study is to evaluate the outcome of 8 years of bilateral STN stimulation to PD patients.

Methods

In this study, 31 consecutive PD patients were treated with bilateral STN stimulation. Their functional status was measured using the Activities of Daily Living section of the Unified Parkinson’s Disease Rating Scale (UPDRS-ADL) at drug on (with medication) and drug off (without medication) states preoperatively and at 1, 5, and 8 years postoperatively. In addition, Levodopa equivalent doses and stimulation parameters were also assessed.

Results

After 8 years of STN stimulation, the UPDRS-ADL scores were improved by 4% at drug off status (P > 0.05) and 22% at drug on status (P < 0.05) compared with baseline; the levodopa daily doses were reduced by 28% (P < 0.05) compared with baseline; the stimulation voltage and pulse width were not changed, but the stimulation frequency was decreased remarkably compared with the 5 years of follow-up. Adverse events were observed in 6 patients, including misplacement of the electrode and skin erosion requiring further surgery. All events were resolved without permanent sequelae. 2 patients died of aspiration pneumonia 6 and 7 years after surgery.

Conclusions

The marked improvement in UPDRS-ADL scores were still observed after 8 years of bilateral STN stimulation with medication.

Altered nucleolar morphology in substantia nigra dopamine neurons following 6-hydroxydopamine lesion in rats

The nucleolus, the site of ribosomal ribonucleic acid (rRNA) transcription and assembly, is an important player in the cellular response to stress. Altered nucleolar function and morphology, including decreased nucleolar volume, has been observed in Parkinson's disease; thus the nucleolus represents a potential indicator of neurodegeneration in the disease. This study determined the effects of a partial unilateral intrastriatal 6-hydroxydopamine (6-OHDA) lesion, which models the dopaminergic loss found in Parkinson's disease, on the nucleoli of dopaminergic cells in the substantia nigra pars compacta (SNpc). Adult male Long-Evans rats underwent unilateral intrastriatal infusion of 6-OHDA (12.5μg). Lesions were verified by amphetamine-stimulated rotation 7 days later, and rats were euthanized 14 days after infusion. Coronal sections (50μm) were stained for tyrosine hydroxylase-silver nucleolar (TH-AgNOR) stain using MultiBrain Technology (NeuroScience Associates), which resulted in clearly defined nucleoli and neuronal outlines. Stereological methods were used to compare dopaminergic morphology between lesioned and intact hemispheres in each rat. In cells exhibiting a definable nucleolus, nucleolar volume was decreased by 16% on the ipsilateral side. The ipsilateral SNpc also exhibited an 18% decrease in SNpc planimetric volume, a 46% decrease in total TH-positive neuron number, and an 11% decrease in neuronal body volume (all P<0.05 by paired t-test). These findings suggest that the 6-OHDA lesion alters nucleolar morphology and that these changes are similar to those occurring in Parkinson's disease.

Restorative strategies for the dopaminergic nigrostriatal projection pathway

New insights into the mechanism of dopaminergic (DA) nigrostriatal neuron degeneration and regeneration in experimental studies in animal models of Parkinson's disease (PD) have opened up the discussion about novel therapeutic strategies such as cell-based therapies and neuroprotection of DA neurons. These cellular and molecular approaches aim at preventing or slowing down the progressive degeneration of DA neurons and/or replacing the lost ones. Here, a brief overview of basic principles and current strategies of these novel restorative approaches is discussed in light of experimental results and possible clinical applications.

The impact of subthalamic deep brain stimulation on nigral neuroprotection-myth or reality?

OBJECTIVE

  In the present review article we summarize available clinical and preclinical evidence, if modulation of the subthalamic nucleus (STN) could be a target for neuroprotection in Parkinson's disease (PD).

BACKGROUND

  Chronic deep brain stimulation (DBS) of the STN has emerged as a powerful therapeutic alternative for the treatment of PD, ensuring stable symptom control for up to five years despite the progressive nature PD.

MATERIALS AND METHODS

  Comparative review of literature in PuBMed available up to December 2008.

RESULTS

  The assessment of neuroprotection has been proven difficult in the clinical situation, as medical or surgical therapeutic options that improve PD symptoms could be erroneously considered to be neuroprotective because of the difficulty of differentiating between symptomatic effects and potential neuromodulative disease-related effects of various treatment options applied in PD. The methodological limitations of clinical trials underline the importance of putative neuroprotective compounds to be tested in clinically driven preclinical studies. Thus, animal models, mimicking progressive nigrostriatal cell death, are indispensable to further advance the important issue of neuroprotection or neuromodulation following DBS.

CONCLUSION

  Clear clinical evidence for STN-DBS-related neuroprotection in PD is missing. However, numerous preclinical studies show (and are discussed) that silencing of the STN via lesion or DBS may exert neuromodulative effects on nigral dopamine neurons.

A novel use of combined tyrosine hydroxylase and silver nucleolar staining to determine the effects of a unilateral intrastriatal 6-hydroxydopamine lesion in the substantia nigra: a stereological study

Neurotoxic lesions of the nigrostriatal pathway model the deficits found in Parkinson's disease. This study used stereology and a novel staining method to examine the effects of a partial unilateral striatal 6-hydroxydopamine (6-OHDA) lesion on substantia nigra pars compacta (SNpc) dopamine neuron number and morphology in rats. Adult male Long-Evans rats were subjected to unilateral lesion of the SNpc by intrastriatal microinjection of 6-OHDA (12.5 μg). Lesions were verified by d-amphetamine-stimulated rotation (2.5 mg/kg, sc) by force-plate rotometry 7 days post-surgery. Seven days after rotation testing, rats were euthanized, and brains were prepared for either histology (n=12) or determination of striatal dopamine content by HPLC-EC (n=20). Brains prepared for histology were stained for tyrosine hydroxylase (TH) combined with a silver nucleolar (AgNOR) stain using a modified protocol developed for stereological assessment. The AgNOR counterstain allowed for precise definition of the nucleolus of the cells, facilitating both counting and qualitative morphometry of TH-positive neurons. Stereological quantitation determined a 54% decrease in TH-positive neuron number (P<0.01), and a 14% decrease in neuron volume (P<0.05) on the lesioned side. Striatal dopamine concentration was decreased by 92% (P<0.01), suggesting that striatal dopamine analysis may overestimate the numbers of SNpc neurons lost. These findings demonstrate that combined use of TH and AgNOR staining provides improved characterization of 6-OHDA-induced pathology. Furthermore, the data suggest that decreased neuronal volume as well as number contributes to the functional deficits observed after unilateral intrastriatal 6-OHDA lesion.

Glutamate receptors as therapeutic targets for Parkinson's disease

Parkinson's disease (PD) is a neurodegenerative disorder characterized by motor symptoms including tremor and bradykinesia. The primary pathophysiology underlying PD is the degeneration of dopaminergic neurons of the substantia nigra pars compacta. Loss of these neurons causes pathological changes in neurotransmission in the basal ganglia motor circuit. The ability of ionotropic and metabotropic glutamate receptors to modulate neurotransmission throughout the basal ganglia suggests that these receptors may be targets for reversing the effects of altered neurotransmission in PD. Studies in animal models suggest that modulating the activity of these receptors may alleviate the primary motor symptoms of PD as well as side effects induced by dopamine replacement therapy. Moreover, glutamate receptor ligands may slow disease progression by delaying progressive dopamine neuron degeneration. Antagonists of NMDA receptors have shown promise in reversing motor symptoms, levodopa-induced dyskinesias, and neurodegeneration in preclinical PD models. The effects of drugs targeting AMPA receptors are more complex; while antagonists of these receptors exhibit utility in the treatment of levodopa-induced dyskinesias, AMPA receptor potentiators show promise for neuroprotection. Pharmacological modulation of metabotropic glutamate receptors (mGluRs) may hold even more promise for PD treatment due to the ability of mGluRs to fine-tune neurotransmission. Antagonists of mGluR5, as well as activators of group II mGluRs and mGluR4, have shown promise in several animal models of PD. These drugs reverse motor deficits in addition to providing protection against neurodegeneration. Glutamate receptors therefore represent exciting targets for the development of novel pharmacological therapies for PD.

Amphetamine-evoked rotation requires newly synthesized dopamine at 14 days but not 1 day after intranigral 6-OHDA and is consistently dissociated from sensorimotor behavior

Immediately after unilateral, intranigral 6-hydroxydopamine (6-OHDA), amphetamine (AMPH) evokes "paradoxical" contraversive rotation, whereas 14 days later, AMPH evokes the traditional ipsiversive rotation used to model the chronic Parkinsonian state. In this study, the hypothesis was that accelerated dopamine (DA) synthesis ipsilateral to the lesion augments cytoplasmic DA to produce paradoxical rotation. Therefore, the sensitivity to synthesis inhibition of AMPH-evoked rotation at 1 or 14 days after 6-OHDA was assessed. To determine the functional status that might be reflected by paradoxical rotation, sensorimotor abilities were examined at 1 and 14 days following unilateral 6-OHDA using the elevated swing, paw placement, grip strength, ladder walking, somatosensory neglect, and cylinder tests. At 14 days after 6-OHDA when AMPH-evoked ipsiversive rotation is mediated by the intact hemisphere, rotation was dose-dependently reduced by tyrosine hydroxylase (TH) inhibition with alpha-methyl-p-tyrosine (alpha-MPT) or dopa decarboxylase (DDC) inhibition with 3-hydroxybenzyl hydrazine (NSD-1015), indicating dependence upon newly synthesized DA. Conversely, at 1 day after 6-OHDA, paradoxical rotation, presumably mediated by the treated hemisphere, was completely resistant to synthesis blockade, indicating an abundant supply of intracellular DA that is independent from synthesis rates. Sensorimotor behaviors were not correlated with AMPH-evoked rotation. The present data do not support the hypothesis that enhanced DA synthesis is required to express paradoxical rotation. Therefore, alternative mechanisms that may enhance cytoplasmic DA to produce paradoxical rotation are discussed.

Neuronal activity in the subthalamic nucleus modulates the release of dopamine in the monkey striatum

The primate subthalamic nucleus (STN) is commonly seen as a relay nucleus between the external and internal pallidal segments, and as an input station for cortical and thalamic information into the basal ganglia. In rodents, STN activity is also known to influence neuronal activity in the dopaminergic substantia nigra pars compacta (SNc) through inhibitory and excitatory mono- and polysynaptic pathways. Although the anatomical connections between STN and SNc are not entirely the same in primates as in rodents, the electrophysiologic and microdialysis experiments presented here show directly that this functional interaction can also be demonstrated in primates. In three Rhesus monkeys, extracellular recordings from SNc during microinjections into the STN revealed that transient pharmacologic activation of the STN by the acetylcholine receptor agonist carbachol substantially increased burst firing of single nigral neurons. Transient inactivation of the STN with microinjections of the GABA-A receptor agonist muscimol had the opposite effect. While the firing rates of individual SNc neurons changed in response to the activation or inactivation of the STN, these changes were not consistent across the entire population of SNc cells. Permanent lesions of the STN, produced in two animals with the fiber-sparing neurotoxin ibotenic acid, reduced burst firing and firing rates of SNc neurons, and substantially decreased dopamine levels in the primary recipient area of SNc projections, the striatum, as measured with microdialysis. These results suggest that activity in the primate SNc is prominently influenced by neuronal discharge in the STN, which may thus alter dopamine release in the striatum.

Frontiers in the surgical treatment of Parkinson's disease

Despite the continued refinement of medical and surgical therapies, the treatment of Parkinson's disease (PD) remains challenging. Current treatment strategies are largely focused on managing the motor symptoms of the disease, either by dopamine-based medications or, in advanced stages, by the application of deep brain stimulation to more stably alter the function of the basal ganglia. Important advances have been made in the last decade, but unfortunately a number of the motor symptoms of late-stage PD remain poorly treated, and while currently available therapies address the symptoms of the disease, they fail to alter the course of the disease itself. This has spurred basic and clinical exploration on a number of fronts. Several centers have examined novel stimulation targets to treat refractory symptoms of gait difficulty and axial imbalance. Basic and clinical researchers are examining whether the use of deep brain stimulation might slow the progress of the disease and thus be a useful neuroprotective therapy if initiated earlier in the progression of the disease. An expanded understanding of the genetic and cellular events that underlie PD has led some researchers to explore the use of neurotrophic factors or genetic restoration to preserve threatened neuronal populations. Finally, there has been much research on the use of fetal mesencephalic or stem cell populations to restore dopaminergic function. In this report, we will examine each of these potential new surgical therapies and the promise they may hold for the future treatment of PD.

Human neural progenitor cell transplants into the subthalamic nucleus lead to functional recovery in a rat model of Parkinson’s disease

Despite the success of foetal nigral transplantation for the treatment of Parkinson's disease, supply limitations of tissue means that alternative sources must be found. Transplantation of human neural progenitor cells (HNPCs) may offer a solution, however few studies have shown functional recovery in animal models of PD without cell modification. Here we show that unmodified HNPC grafted into the subthalamic nucleus (STN) show excellent survival of up to 5 months and induce significant functional recovery following amphetamine-induced rotations within 4 weeks. For the first time we also show that HNPCs, which remain in an immature nestin-positive state, produce VEGF in vivo allowing further modification of the host brain. This suggests that even in the absence of cell replacement strategies utilising immature progenitor cells could be of real therapeutic value.

Subthalamic nucleus deep brain stimulation in elderly patients--analysis of outcome and complications

Background

There is an ongoing discussion about age limits for deep brain stimulation (DBS). Current indications for DBS are tremor-dominant disorders, Parkinson's disease, and dystonia. Electrode implantation for DBS with analgesia and sedation makes surgery more comfortable, especially for elderly patients. However, the value of DBS in terms of benefit-risk ratio in this patient population is still uncertain.

Methods

Bilateral electrode implantation into the subthalamic nucleus (STN) was performed in a total of 73 patients suffering from Parkinson's disease. Patients were analyzed retrospectively. For this study they were divided into two age groups: group I (age <65 years, n = 37) and group II (age ≥ 65 years, n = 36). Examinations were performed preoperatively and at 6-month follow-up intervals for 24 months postoperatively. Age, UPDRS motor score (part III) on/off, Hoehn & Yahr score, Activity of Daily Living (ADL), L-dopa medication, and complications were determined.

Results

Significant differences were found in overall performance determined as ADL scores (group I: 48/71 points, group II: 41/62 points [preoperatively/6-month postoperatively]) and in the rate of complications (group I: 4 transient psychosis, 4 infections in a total of 8 patients, group II: 2 deaths [unrelated to surgery], 1 intracerebral hemorrhage, 7 transient psychosis, 3 infections, 2 pneumonia in a total of 13 patients), (p < 0.05). Interestingly, changes in UPDRS scores, Hoehn & Yahr scores, and L-dopa medication were not statistically different between the two groups.

Conclusion

DBS of the STN is clinically as effective in elderly patients as it is in younger ones. However, a more careful selection and follow-up of the elderly patients are required because elderly patients have a higher risk of surgery-related complications and a higher morbidity rate.

Dopamine transporter imaging and the effects of deep brain stimulation in patients with Parkinson’s disease

PURPOSE

Single-photon emission computed tomography (SPECT) with [123I]FP-CIT is a marker for loss of presynaptic dopamine transporters in the striatum in Parkinson's disease (PD). We used [123I]FP-CIT SPECT in order to evaluate binding to the dopamine transporter before and after neurosurgical treatment with bilateral stimulation in the subthalamic nucleus (STN).

METHODS

Thirty-five patients with levodopa-responsive PD were examined with [123I]FP-CIT SPECT pre-operatively (baseline scan: mean 3 months before surgery), and 3 and 12 months after surgery.

RESULTS

Pre-operatively, all patients already had substantial signs of severe nigrostriatal neuronal loss as determined from the [123I]FP-CIT SPECT scans. One year after surgery the specific [123I]FP-CIT binding to the striatum was significantly reduced by 10.3% compared with the pre-operative baseline scan. The mean time span from the baseline scan before surgery to the follow-up scan 1 year after surgery was 16.2 months. Hence, the rate of reduction equals a mean annual reduction of 7.7%. A comparable control group of patients with PD who did not undergo surgery was also examined longitudinally. In this group the specific binding of [123I]FP-CIT was reduced by 6.7% per year.

CONCLUSION

The specific binding of [123I]FP-CIT was reduced equally in the STN-stimulated patients and a group of non-operated PD patients with advanced disease. Our study does not support the notion that electrode implantation and STN stimulation exert a neuroprotective effect by themselves.

Protection of nigral cell death by bilateral subthalamic nucleus stimulation

In Parkinson disease (PD), the subthalamic nucleus (STN) becomes hyperactive (disinhibited), which is reported to cause excitotoxic damage to midbrain dopaminergic neurons. Here, we examined whether silencing of the hyperactive STN by chronic bilateral deep brain stimulation (DBS) increased the survival of midbrain dopaminergic neurons in a rat model of PD. High-precision design-based stereologic examination of the total number of neurons and tyrosine tydroxylase (TH) immunoreactive neurons in the substantia nigra pars compacta revealed that STN DBS resulted in a significant survival of these neurons. These data provide the first evidence in vivo that bilateral STN DBS is useful for protecting midbrain dopaminergic neurons from cell death in PD.

Evolution of Parkinson's disease during 4 years of bilateral deep brain stimulation of the subthalamic nucleus

Patients with advanced Parkinson's disease (PD) and motor complications can obtain significant symptom improvement by deep brain stimulation (DBS) of the subthalamic nucleus (STN). Very little is published, however, about long-term effect and disease evolution during DBS. We performed a 4-year prospective study of the first 22 consecutive patients treated with STN DBS. The patients were evaluated with Unified Parkinson's Disease Rating Scale Part II to VI and a patient diary concerning on-off periods and dyskinesia. Patients were scored before surgery on medication and off medication for 10 to 12 hours and in four conditions 1 and 4 years after surgery: off medication+/-stimulation and on medication+/-stimulation. In advanced PD, a significant reduction of dyskinesia and off periods was present 4 years (90%/67%) after the operation. Total motor function on stimulation alone improved 55% at 4 years, compared with baseline and activities of daily living (42%). On stimulation, significant worsening of axial symptoms and speech was present from 1 to 4 years. To evaluate disease evolution, motor symptoms were assessed off stimulation and medication for 12 hours and were found not to worsen compared with baseline, which is remarkable in an otherwise progressive disorder. Five patients developed dementia. Severe adverse events were not observed.

Subthalamic nucleus lesioning inhibits expression and phosphorylation of c-Jun in nigral neurons in the rat's 6-OHDA model of Parkinson's disease

Parkinson's Disease (PD) is characterized by a loss of nigral dopamine (DA) neurons, followed by a striatal DA deficit. Inhibition of the subthalamic nucleus (STN) reverses L-DOPA sensitive motor symptoms and improves efficacy of pharmacotherapy in PD-patients. The underlying mechanism of these effects, however, remains largely unknown. Previously, we could show in the rat's 6-hydroxyDA (6-OHDA) model of PD that ablative STN-lesioning exerts functionally neuroprotective effects on the DAergic nigrostriatal pathway against 6-OHDA toxicity, in terms of elevating the number of tyrosine hydroxylase (TH)-expressing neurons rather than enhancing the total number of cells surviving 2 and 6 weeks post lesioning, as assessed via fluorogold staining. These data were correlated with increased functional recovery of 6-OHDA-lesioned rats with preceding STN-lesioning. Here, we extend the previous study design to observation periods of up to 12 weeks to assess long-term effects. Furthermore, to elucidate cellular mechanisms underlying potential neuroprotective effects, we explore the regulation of cellular markers involved in neurodegenerative cascades via immunocytochemistry. We show that preceding STN-lesioning significantly inhibits 6-OHDA induced expression/phosphorylation of the transcription factor c-Jun in surviving nigral neurons in comparison with controls. However, we also demonstrate that functionally neuroprotective effects of preceding STN-lesioning subside after 12 weeks, as assessed with TH immunostaining. We therefore conclude that c-Jun induction/phosphorylation is involved in 6-OHDA toxicity and that STN-lesioning transiently preserves of dopaminergic phenotype of nigral neurons partially via delaying the induction and attenuating the expression and phosphorylation of c-Jun.

Cell survival patterns in the pedunculopontine tegmental nucleus of methyl-4-phenyl-1,2,3,6-tetrahydropyridine-treated monkeys and 6OHDA-lesioned rats: evidence for differences to idiopathic Parkinson disease patients?

We explore the patterns of cell loss in the pedunculopontine tegmental nucleus (PpT), a major locomotor and muscle tone suppression centre of the brainstem, in two animal models of Parkinson disease, namely MPTP (methyl-4-phenyl-1,2,3,6-tetrahydropyridine)-treated monkeys and 6-hydroxydopamine(6OHDA)-lesioned rats. Although there have been many studies documenting the loss of dopaminergic cells from the substantia nigra in these animal models, there has been little, if any, documentation of a loss of cells in the PpT. Results were obtained from macaque monkeys (Macaca fascicularis) and Sprague-Dawley rats. For the monkey series, animals were injected intramuscularly with MPTP (0.2 mg/kg) for 8 days consecutively and then allowed to survive for 21 days thereafter. Each monkey underwent behavioural assessment for parkinsonian symptoms. For the rat series, 6OHDA was injected into the midbrain using stereotactic coordinates. Rats were then allowed to survive for either 7, 14, 28, or 84 days thereafter. Monkey and rat brains were aldehyde-fixed and processed for routine tyrosine hydroxylase (TH; to label nigral dopaminergic cells) and nitric oxide synthase (NOs; to label PpT cholinergic cells) immunocytochemistry. In monkeys, the morphology, distribution and number of NOs(+) cells in the controls and MPTP-treated cases were very similar. In fact, in terms of number, there was only a 1% difference in the mean cell number between the controls and MPTP-treated cases. A comparable pattern was evident in 6OHDA-lesioned rats; there was no substantial difference in morphology, distribution and number of NOs(+) cells on the 6OHDA-lesioned cases when compared to the controls at each of the survival periods post-surgery. In summary, we show no loss of the large cholinergic/NOs(+) cells in the PpT in two animal models of Parkinson disease. This is in contrast to the heavy loss of these cells reported by previous findings in idiopathic Parkinson disease in patients.

Acute and separate modulation of motor and cognitive performance in parkinsonian rats by bilateral stimulation of the subthalamic nucleus

The subthalamic nucleus (STN) is involved in motor and cognitive performance through its key role in the basal ganglia-thalamocortical circuits, but how these different modalities (motor and cognition) are controlled (similar vs. dissimilar) has not yet been elucidated. In the present study, the effects of bilateral STN deep brain stimulation (DBS) on motor and cognitive performance were investigated in a rat model of Parkinson disease (PD). After being trained in a choice reaction time (CRT) task, rats received bilateral injections of 6-hydroxydopamine (6-OHDA) into the striatum. One group of 6-OHDA animals was implanted bilaterally with stimulation electrodes at the level of the STN. Stimulations were performed at 130 Hz (frequency), 60 micros (pulse width), and varying amplitudes of 1, 3, 30, and 150 microA during the CRT task. Finally, rats were sacrificed and the brains processed for staining to determine the dopaminergic lesion (TH immunohistochemistry) and localization of the electrode tip (HE histochemistry). Bilateral 6-OHDA infusion significantly decreased (70%) the number of dopaminergic cells in the substantia nigra pars compacta (SNc) and increased motor time (MT), proportion of premature responding (PR), and reaction time (RT). Bilateral STN stimulation with an amplitude of 3 microA normalized 6-OHDA-induced deficits in PR and RT. Simulation with an amplitude of 30 microA reversed the lesion-induced deficits in MT and RT. Our data show for the first time that bilateral STN stimulation differentially affected the 6-OHDA-induced motor and cognitive deficits. This means that basal ganglia-thalamocortical motor and associative circuits responsible for specific motor and cognitive performance, which are processed through the STN, have unique physiological properties that can acutely and separately be modulated by specific electrical stimuli.

Rationale for and use of NMDA receptor antagonists in Parkinson's disease

N-Methyl-d-aspartate (NMDA) glutamate receptors are a class of excitatory amino acid receptors, which have several important functions in the motor circuits of the basal ganglia, and are viewed as important targets for the development of new drugs to prevent or treat Parkinson's disease (PD). NMDA receptors are ligand-gated ion channels composed of multiple subunits, each of which has distinct cellular and regional patterns of expression. They have complex regulatory properties, with both agonist and co-agonist binding sites and regulation by phosphorylation and protein-protein interactions. They are found in all of the structures of the basal ganglia, although the subunit composition in the various structures is different. NMDA receptors present in the striatum are crucial for dopamine-glutamate interactions. The abundance, structure, and function of striatal receptors are altered by the dopamine depletion and further modified by the pharmacological treatments used in PD. In animal models, NMDA receptor antagonists are effective antiparkinsonian agents and can reduce the complications of chronic dopaminergic therapy (wearing off and dyskinesias). Use of these agents in humans has been limited because of the adverse effects associated with nonselective blockade of NMDA receptor function, but the development of more potent and selective pharmaceuticals holds the promise of an important new therapeutic approach for PD.

Long-term stimulation of the subthalamic nucleus in hemiparkinsonian rats: neuroprotection of dopaminergic neurons

OBJECT

The goal of this study was to evaluate the neuroprotective effects conferred by long-term electrical stimulation of the subthalamic nucleus (STN) against degeneration of dopaminergic neurons by assessing motor functional and immunohistological findings in hemiparkinsonian rats.

METHODS

In 13 of 25 rats, a concentric microelectrode was stereotactically implanted into the right STN under the guidance of extracellular microelectrode recording. After this had been done the animals were given an injection of 6-hydroxydopamine (6-OHDA) into the right striatum. Seven of the rats received continuous stimulation (frequency 130 Hz, intensity 80-100 microA) for 2 weeks (Group A); the other six did not receive any stimulation during this period (Group B). Twelve rats did not receive electrode implantation and underwent 6-OHDA injection only; these animals served as a control group (Group C). After 2 weeks, motor function in the rats was evaluated by conducting an amphetamine-induced rotation test. Finally, tyrosine hydroxylase-immunoreactive neurons in the pars compacta of the substantia nigra (SNc) were counted to evaluate the extent of degeneration of dopaminergic neurons. Ipsilateral rotation was significantly decreased in Group A, regardless of the effects of stimulation delivered during the test (p < 0.05). Rats in Group B demonstrated typical circling as did those in Group C, except that on stimulation Group B rats immediately stopped circling or changed direction. Tyrosine hydroxylase-immunoreactive neurons in the SNc were significantly preserved in the animals in Group A, whereas neurons in animals in Groups B and C were moderately depleted (p < 0.01).

CONCLUSIONS

Acutely, STN stimulation improved rotation symmetry in rats with moderate SNc degeneration. When STN stimulation had been applied for the preceding 2 weeks, motor function was better and SNc neural degeneration was significantly milder. Subthalamic nucleus stimulation thus appears to protect dopaminergic neurons in this hemiparkinsonian model, in addition to improving motor function in these animals.

Ablation of the subthalamic nucleus protects dopaminergic phenotype but not cell survival in a rat model of Parkinson's disease

Inhibition or ablation of the hyperactive subthalamic nucleus (STN) in Parkinson's disease (PD) does not only reverse motor deficits, silencing the glutamatergic output of the subthalamic nucleus, but has also been implicated to have neuroprotective effects on nigral neurons in animal models of Parkinson's disease. Ablation of the subthalamic nucleus has been shown to increase the number of tyrosinhydroxylase-immunopositive cells and partially restores behavioral deficits in animal models of Parkinson's disease. However, it is unclear whether subthalamic nucleus ablation indeed prevents cell death or whether the effect is due to the rescue of the dopaminergic (DA) phenotype of impaired cells by upregulating tyrosine hydroxylase (TH). We therefore investigated the potential neuroprotective effects of a preceding subthalamic nucleus lesion on 6-hydroxydopamine (6-OHDA)-induced nigral cell death and compared the retrograde tracer fluorogold (FG) as a marker of cell survival with tyrosinhydroxylase immunoreactivity as a marker of the dopaminergic phenotype. In the present study, we show that ablation of the subthalamic nucleus does not affect the number of fluorogold-labeled cells but increases the number of tyrosinhydroxylase-positive neurons in subthalamic nucleus-lesioned hemiparkinsonian animals and leads to partial behavioral recovery of the rats. We conclude that subthalamic nucleus ablation exerts neuroprotective properties on the dopaminergic nigrostriatal pathway against 6-hydroxydopamine toxicity in terms of rescuing the neurotransmitter phenotype in the remaining neurons rather than enhancing the total number of nigral cells.

Subthalamic GAD gene therapy in a Parkinson's disease rat model

The motor abnormalities of Parkinson's disease (PD) are caused by alterations in basal ganglia network activity, including disinhibition of the subthalamic nucleus (STN), and excessive activity of the major output nuclei. Using adeno-associated viral vector-mediated somatic cell gene transfer, we expressed glutamic acid decarboxylase (GAD), the enzyme that catalyzes synthesis of the neurotransmitter GABA, in excitatory glutamatergic neurons of the STN in rats. The transduced neurons, when driven by electrical stimulation, produced mixed inhibitory responses associated with GABA release. This phenotypic shift resulted in strong neuroprotection of nigral dopamine neurons and rescue of the parkinsonian behavioral phenotype. This strategy suggests that there is plasticity between excitatory and inhibitory neurotransmission in the mammalian brain that could be exploited for therapeutic benefit.