Implication of the subthalamic nucleus in the pathophysiology and pathogenesis of Parkinson's disease

Architecture of the subthalamic nucleus

The subthalamic nucleus (STN) is a major neuromodulation target for the alleviation of neurological and neuropsychiatric symptoms using deep brain stimulation (DBS). STN-DBS is today applied as treatment in Parkinson´s disease, dystonia, essential tremor, and obsessive-compulsive disorder (OCD). STN-DBS also shows promise as a treatment for refractory Tourette syndrome. However, the internal organization of the STN has remained elusive and challenges researchers and clinicians: How can this small brain structure engage in the multitude of functions that renders it a key hub for therapeutic intervention of a variety of brain disorders ranging from motor to affective to cognitive? Based on recent gene expression studies of the STN, a comprehensive view of the anatomical and cellular organization, including revelations of spatio-molecular heterogeneity, is now possible to outline. In this review, we focus attention to the neurobiological architecture of the STN with specific emphasis on molecular patterns discovered within this complex brain area. Studies from human, non-human primate, and rodent brains now reveal anatomically defined distribution of specific molecular markers. Together their spatial patterns indicate a heterogeneous molecular architecture within the STN. Considering the translational capacity of targeting the STN in severe brain disorders, the addition of molecular profiling of the STN will allow for advancement in precision of clinical STN-based interventions.

Long-Term Outcomes of Bilateral Subthalamic Nucleus Deep Brain Stimulation for Patients With Parkinson's Disease: 10 Years and Beyond

BACKGROUND

Deep brain stimulation (DBS) of the subthalamic nucleus (STN) represents an effective treatment for severe Parkinson's disease (PD), but little is known about the long-term benefit.

OBJECTIVE

To investigate the survival rate and long-term outcome of DBS.

METHODS

We investigated all 81 patients including 37 males and 44 females who underwent bilateral STN DBS from March 2005 to March 2008 at a single institution. The current survival status of the patients was investigated. Preoperative and postoperative follow-up assessments were analyzed.

RESULTS

The mean age at the time of surgery was 62 (range 27-82) years, and the median clinical follow-up duration was 145 months. Thirty-five patients (43%) died during the follow-up period. The mean duration from DBS surgery to death was 110.46 ± 40.8 (range 0-155) months. The cumulative survival rate is as follows: 98.8 ± 1.2% (1 year), 95.1 ± 2.4% (5 years), and 79.0 ± 4.5% (10 years). Of the 81 patients, 33 (40%) were ambulatory up to more than 11 years. The Unified Parkinson's Disease Rating Scale (UPDRS) score was significantly improved until 5 years after surgery although it showed a tendency to increase again after 10 years. The patient group with both electrodes located within the STN showed a higher rate of survival and maintained ambulation.

CONCLUSION

STN DBS is a safe and effective treatment for patients with advanced PD. This study based on the long-term follow-up of large patient populations can be used to elucidate the long-term fate of patients who underwent bilateral STN DBS for PD.

Bidirectional Optogenetic Modulation of the Subthalamic Nucleus in a Rodent Model of Parkinson's Disease

Parkinson's disease (PD) is a neurodegenerative disorder characterized by a range of motor symptoms. Treatments are focused on dopamine replacement therapy or deep brain stimulation (DBS). The subthalamic nucleus (STN) is a common target for DBS treatment of PD. However, the function of the STN in normal conditions and pathology is poorly understood. Here, we show in rats that optogenetic modulation of STN neuronal activity exerts bidirectional control of motor function, where inhibition of the STN increases movement and STN activation decreases movement. We also examined the effect of bidirectional optogenetic manipulation STN neuronal activity under dopamine depleted condition using the bilateral rodent 6-hydroxydopamine (6-OHDA) model of Parkinson's disease. Optogenetic inhibition of the STN in the absence of dopamine had no impact on motor control yet STN excitation led to pronounced abnormal involuntary movement. Administration of levodopa rescued the abnormal involuntary movements induced by STN excitation. Although dopamine and STN dysfunction are well established in PD pathology, here we demonstrate simultaneous STN over activity and loss of dopamine lead to motor deficits. Moreover, we show the dysfunction of the STN is dependent on dopamine. This study provides evidence that the loss of dopamine and the over activity of the STN are key features of PD motor deficits. These results provide insight into the STN pathology in PD and therapeutic mechanism of targeting the STN for the treatment for PD.

Modulation of sensory cortical activity by deep brain stimulation in advanced Parkinson's Disease

Despite optimal oral drug treatment, about 90% of patients with Parkinson's disease develop motor fluctuation and dyskinesia within 5-10 years from the diagnosis. Moreover, the patients show non-motor symptoms in different sensory domains. Bilateral deep brain stimulation applied to the subthalamic nucleus is considered the most effective treatment in advanced Parkinson's disease and it has been suggested to affect sensorimotor modulation and relate to motor improvement in patients. However, observations on the relationship between sensorimotor activity and clinical improvement have remained sparse. Here we studied the somatosensory evoked magnetic fields in thirteen right-handed patients with advanced Parkinson's disease before and 7 months after stimulator implantation. Somatosensory processing was addressed with magnetoencephalography during alternated median nerve stimulation at both wrists. The strengths and the latencies of the ~60-ms responses at the contralateral primary somatosensory cortices were highly variable but detectable and reliably localized in all patients. The response strengths did not differ between preoperative and postoperative DBS_ON measurements. The change in the response strength between pre- and postoperative condition in the dominant left hemisphere of our right-handed patients correlated with the alleviation of their motor symptoms (p = 0.04). However, the result did not survive correction for multiple comparisons. Magnetoencephalography appears an effective tool to explore non-motor effects in patients with Parkinson's disease, and it may help in understanding the neurophysiological basis of deep brain stimulation. However, the high interindividual variability in the somatosensory responses and poor tolerability of DBS_OFF condition warrants larger patient groups and measurements also in non-medicated patients.

Striatal dopamine transporter availability and individual clinical course within the 1-year follow-up of deep brain stimulation of the subthalamic nucleus in patients with Parkinson's disease

OBJECTIVE

Degeneration of dopaminergic neurons in the substantia nigra projecting to the striatum is responsible for the motor symptoms in Parkinson's disease (PD). Deep brain stimulation (DBS) of the subthalamic nucleus (STN) is a well-established procedure to alleviate these symptoms in advanced PD. Yet the mechanism of action, especially the effects of STN-DBS on the availability of striatal dopamine transporter (DAT) as a marker of nigrostriatal nerve cell function, remains largely unknown. The aim of this study was therefore to evaluate whether 1) DAT availability changes within 1 year of STN-DBS and 2) the clinical outcome can be predicted based on preoperative DAT availability.

METHODS

Twenty-seven PD patients (mean age 62.7 ± 8.9 years; mean duration of illness 13.0 ± 4.9 years; PD subtypes: akinetic-rigid, n = 11; equivalence, n = 13; and tremor-dominant, n = 3) underwent [123I]FP-CIT SPECT preoperatively and after 1 year of STN-DBS. DAT availability as determined by the specific binding ratio (SBR) was assessed by volume of interest (VOI) analysis of the caudate nucleus and the putamen ipsilateral and contralateral to the clinically more affected side.

RESULTS

Unified Parkinson's Disease Rating Scale (UPDRS) III scores improved significantly (mean preoperative on medication 25.6 ± 12.3, preoperative off medication 42.3 ± 15.2, postoperative on medication/off stimulation 41.4 ± 13.2, and postoperative on medication/on stimulation 16.1 ± 9.4; preoperative on medication vs postoperative on medication/on stimulation, p = 0.006), while the levodopa-equivalent daily dose was reduced (mean preoperative 957 ± 440 mg vs postoperative 313 ± 189 mg, p < 0.001). The SBR did not differ significantly before and 1 year after DBS, regardless of PD subtype. Preoperative DAT availability was not related to the change in UPDRS III score, but the change in DAT availability was significantly correlated with the change in UPDRS III score (contralateral head of the caudate VOI, p = 0.014; contralateral putamen VOI, p = 0.018).

CONCLUSIONS

Overall, DAT availability did not change significantly after 1 year of STN-DBS. However, on an individual basis, the improvement in UPDRS III score was associated with an increase in DAT availability, whereas DAT availability before STN-DBS surgery did not predict the clinical outcome. Whether a subtype-specific pattern of preoperative DAT availability can become a reliable predictor of successful STN-DBS must be evaluated in larger study cohorts.

Volumetric analysis of subthalamic nucleus and red nucleus in patients of advanced Parkinson's disease using SWI sequences

Background:

Parkinson’s disease is associated with significant changes in morphometry of subthalamic nucleus (STN); however, not much is known as the disease progresses. The aim of present study was to investigate the volume of STN and Red nucleus (RN) on 3T-magnetic resonance imaging (MRI) and its possible correlation with disease progression in advanced Parkinson’s disease patients.

Methods:

Patients of advanced Parkinson’s disease were prospectively followed for clinical details, motor severity scores, and radiological evaluation. Volumes of the STN and RN were measured on susceptibility weighted imaging, coronal sections in 3T MRI and were correlated with demographic and clinical features.

Results:

A total of 52 patients were included in our study. There were 42 (80.77%) males and 10 (19.23%) females. Mean age of onset of Parkinson’s disease was 49.48 + 10.90 years. Average duration of disease in the present cohort was 7.65 + 4.31 years. Average STN and RN volume were 103.46 + 21.17 mm³ and 321.73 + 67.66 mm³. Age of onset, disease duration and Unified Parkinson’s Disease Rating Scale Part III scores were not found to be associated with changes in STN Volumes. Weak positive trend was noted between RN volume and disease duration (Pearson cor. 0.204, P = 0.14). Patients in early-onset Parkinson’s disease group had significantly more volume of RN than patients in late-onset Parkinson’s disease group (P = 0.014).

Conclusion:

Disease duration and early age of onset in Parkinson’s disease can be associated with increased RN volume. Volume of STN shows relatively no change even with disease progression.

Deep Brain Stimulation of the Subthalamic Nucleus Modulates Reward-Related Behavior: A Systematic Review

Deep brain stimulation of the subthalamic nucleus (STN-DBS) is an effective treatment for the motor symptoms of movement disorders including Parkinson's Disease (PD). Despite its therapeutic benefits, STN-DBS has been associated with adverse effects on mood and cognition. Specifically, apathy, which is defined as a loss of motivation, has been reported to emerge or to worsen following STN-DBS. However, it is often challenging to disentangle the effects of STN-DBS per se from concurrent reduction of dopamine replacement therapy, from underlying PD pathology or from disease progression. To this end, pre-clinical models allow for the dissociation of each of these factors, and to establish neural substrates underlying the emergence of motivational symptoms following STN-DBS. Here, we performed a systematic analysis of rodent studies assessing the effects of STN-DBS on reward seeking, reward motivation and reward consumption across a variety of behavioral paradigms. We find that STN-DBS decreases reward seeking in the majority of experiments, and we outline how design of the behavioral task and DBS parameters can influence experimental outcomes. While an early hypothesis posited that DBS acts as a "functional lesion," an analysis of lesions and inhibition of the STN revealed no consistent pattern on reward-related behavior. Thus, we discuss alternative mechanisms that could contribute to the amotivational effects of STN-DBS. We also argue that optogenetic-assisted circuit dissection could yield important insight into the effects of the STN on motivated behavior in health and disease. Understanding the mechanisms underlying the effects of STN-DBS on motivated behavior-will be critical for optimizing the clinical application of STN-DBS.

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.

Determinants of dopaminergic neuron loss in Parkinson's disease

The cardinal motor symptoms of Parkinson's disease (PD) are caused by the death of dopaminergic neurons in the substantia nigra pars compacta (SNc). Alpha-synuclein (aSYN) pathology and mitochondrial dysfunction have been implicated in PD pathogenesis, but until recently it was unclear why SNc dopaminergic neurons should be particularly vulnerable to these two types of insult. In this brief review, the evidence that SNc dopaminergic neurons have an anatomical, physiological, and biochemical phenotype that predisposes them to mitochondrial dysfunction and synuclein pathology is summarized. The recognition that certain traits may predispose neurons to PD-linked pathology creates translational opportunities for slowing or stopping disease progression.

Mechanisms of deep brain stimulation

Deep brain stimulation (DBS) is widely used for the treatment of movement disorders including Parkinson's disease, essential tremor, and dystonia and, to a lesser extent, certain treatment-resistant neuropsychiatric disorders including obsessive-compulsive disorder. Rather than a single unifying mechanism, DBS likely acts via several, nonexclusive mechanisms including local and network-wide electrical and neurochemical effects of stimulation, modulation of oscillatory activity, synaptic plasticity, and, potentially, neuroprotection and neurogenesis. These different mechanisms vary in importance depending on the condition being treated and the target being stimulated. Here we review each of these in turn and illustrate how an understanding of these mechanisms is inspiring next-generation approaches to DBS.

Progression and survival in Parkinson's disease with subthalamic nucleus stimulation

BACKGROUND

Treatment for Parkinson's disease (PD) is symptomatic. Surgical treatment with continuous high-frequency stimulation of the subthalamic nucleus (STN-DBS) is established as a safe symptomatic treatment with long-term beneficial effects. It has been postulated that STN-DBS could halt the progression of PD through a disease modifying or neuroprotective effect.

OBJECTIVE

To investigate the postulated disease modifying or neuroprotective effect of STN-DBS by comparing the rate of deterioration of parkinsonism and mortality over time in two selected and matched groups of patients with PD with and without surgery.

METHODS

Group A was derived from all patients who received STN-DSB surgery at Oslo University Hospital, from January 2001 to December 2007. Group B was derived from a prevalence study of PD in the Stavanger area of Western Norway in 1993. The two groups were individually matched and the disease progression measured by Unified Parkinson's Disease Rating Scale-motor scores, and the mortality was compared.

RESULTS

The mean annual change based on baseline and last observation scores in individually matched groups was 0.97 (SD = 3.57) for the surgery group and 1.04 (SD = 3.33) for the controls and thus not significantly different, F(1, 104) = .21, P = 0.89. The long-term mortality was also similar in the two groups during long-term follow-up, hazard ratio = 1.76, CL 0.91-3.40, P = 0.091.

CONCLUSION

This study gives no support to a postulated disease modifying or neuroprotective effect of STN-DBS in patients with PD.

Hypothalamic attack: a wonderful artifact or a useful perspective on escalation and pathology in aggression? A viewpoint

W.R. Hess' early demonstration of aggressive responses evoked by electrical stimulation in the cat's hypothalamus had a significant impact on the development of psychological and behavioral concepts. Many ideas on behavioral routines, allegedly organized in the brainstem, derive from his observation. Similar responses have since been evoked from the hypothalamus of many different species, suggesting that the mechanism mediating these responses is evolutionarily well preserved. However, these effects have also been portrayed as artificial responses to an artificial stimulus in an artificial environment. True enough; after many years of research, crucial questions on the underlying mechanism remain unanswered. Questions such as: How do they emerge in the first place? What neuronal elements mediate these responses? What is their role in "spontaneous" aggression? In the first part of this chapter we show methodology to study such questions in a consistent way using behavioral, physiological, anatomical, and pharmacological findings on hypothalamic attack in rats. In the second part we suggest that one important function of the underlying mechanism is to match the dynamics of the endocrine stress response with the dynamics of the behavioral and physiological requirements of coping with conflicts. This neuroendocrine-behavioral matching seems crucial right from the first emergence of the aggressive response in inexperienced animals, up to the full-blown violent responding in fully experienced animals. Impeding these essential functions results in inadequate coping with conflicts. The stress response during a first conflict in an inexperienced individual in an unfamiliar environment seems to rapidly initialize a crucial change in a mechanism involved in the appraisal of social signals during conflict. That change has enduring consequences for future conflict strategies. This concept opens another perspective on "escalated" or "pathological" aggression, especially so in individuals with a dysfunctional stress response.

Subthalamic lesion or levodopa treatment rescues giant GABAergic currents of PINK1-deficient striatum

Cellular electrophysiological signatures of Parkinson's disease described in the pharmacological 6-hydroxydopamine (6-OHDA) animal models of Parkinson's disease include spontaneous repetitive giant GABAergic currents in a subpopulation of striatal medium spiny neurons (MSNs), and spontaneous rhythmic bursts of spikes generated by subthalamic nucleus (STN) neurons. We investigated whether similar signatures are present in Pink1(-/-) mice, a genetic rodent model of the PARK6 variant of Parkinson's disease. Although 9- to 24-month-old Pink1(-/-) mice show reduced striatal dopamine content and release, and impaired spontaneous locomotion, the relevance of this model to Parkinson's disease has been questioned because mesencephalic dopaminergic neurons do not degenerate during the mouse lifespan. We show that 75% of the MSNs of 5- to 7-month-old Pink1(-/-) mice exhibit giant GABAergic currents, occurring either singly or in bursts (at 40 Hz), rather than the low-frequency (2 Hz), low-amplitude, tonic GABAergic drive common to wild-type MSNs of the same age. STN neurons from 5- to 7-month-old Pink1(-/-) mice spontaneously generated bursts of spikes instead of the control tonic drive. Chronic kainic acid lesion of the STN or chronic levodopa treatment reliably suppressed the giant GABAergic currents of MSNs after 1 month and replaced them with the control tonic activity. The similarity between the in vitro resting states of Pink1 MSNs and those of fully dopamine (DA)-depleted MSNs of 6-OHDA-treated mice, together with the beneficial effect of levodopa treatment, strongly suggest that dysfunction of mesencephalic dopaminergic neurons in Pink1(-/-) mice is more severe than expected. The beneficial effect of the STN lesion also suggests that pathological STN activity strongly influences striatal networks in Pink1(-/-) mice.

Nigrostriatal denervation changes the effect of cannabinoids on subthalamic neuronal activity in rats

RATIONALE

It is known that dopaminergic cell loss leads to increased endogenous cannabinoid levels and CB1 receptor density.

OBJECTIVE

The aim of this study was to evaluate the influence of dopaminergic cell loss, induced by injection of 6-hydroxydopamine, on the effects exerted by cannabinoid agonists on neuron activity in the subthalamic nucleus (STN) of anesthetized rats.

RESULTS

We have previously shown that Δ(9)-tetrahydrocannabinol (Δ(9)-THC) and anandamide induce both stimulation and inhibition of STN neuron activity and that endocannabinoids mediate tonic control of STN activity. Here, we show that in intact rats, the cannabinoid agonist WIN 55,212-2 stimulated all recorded STN neurons. Conversely, after dopaminergic depletion, WIN 55,212-2, Δ(9)-THC, or anandamide inhibited the STN firing rate without altering its discharge pattern, and stimulatory effects were not observed. Moreover, anandamide exerted a more intense inhibitory effect in lesioned rats in comparison to control rats.

CONCLUSIONS

Cannabinoids induce different effects on the STN depending on the integrity of the nigrostriatal pathway. These findings advance our understanding of the role of cannabinoids in diseases involving dopamine deficits.

Role of glial cells in neurotoxin-induced animal models of Parkinson's disease

Dopaminergic neurons are selectively vulnerable to oxidative stress and inflammatory attack. The neuronal cell loss in the substantia nigra is associated with a glial response composed markedly of activated microglia and, to a lesser extent, of reactive astrocytes although these glial responses may be the source of neurotrophic factors and can protect against oxidative stress such as reactive oxygen species and reactive nitrogen species. However, the glial response can also mediate a variety of deleterious events related to the production of pro-inflammatory, pro-oxidant reactive species, prostaglandins, cytokines, and so on. In this review, we discuss the possible protective and deleterious effects of glial cells in the neurodegenerative diseases and examine how these factors may contribute to the pathogenesis of Parkinson's disease. This review suggests that further investigation concerning glial reaction in Parkinson's disease may lead to disease-modifying therapeutic approaches and may contribute to the pathogenesis of this disease.

Investigating the depth electrode-brain interface in deep brain stimulation using finite element models with graded complexity in structure and solution

Deep brain stimulation (DBS) is an increasingly used surgical therapy for a range of neurological disorders involving the long-term electrical stimulation of various regions of the human brain in a disorder specific manner. Despite being used for the last 20 years, the underlying mechanisms are still not known, and disputed. In particular, when the electrodes are implanted into the human brain, an interface is created with changing biophysical properties which may impact on stimulation. We previously defined the electrode-brain interface (EBI) as consisting of three structural elements: the quadripolar DBS electrode, the peri-electrode space and the surrounding brain tissue. In order to understand more about the nature of this EBI, we used structural computational models of this interface, and estimated the effects of stimulation using coupled axon models. These finite element models differ in complexity, each highlighting a different feature of the EBI's effect on the DBS-induced electric field. We show that the quasi-static models are sufficient to demonstrate the difference between the acute and chronic clinical stages post-implantation. However, the frequency-dependent models are necessary as the waveform shaping has a major influence on the activation of neuronal fibres. We also investigate anatomical effects on the electric field, by taking specific account of the ventricular system in the human brain. Taken together, these models allow us to visualise the static, dynamic and target specific properties of the DBS-induced field in the surrounding brain regions.

Deep brain stimulation of the subthalamic nucleus in Parkinson's Disease 1993 – 2003: where are we 10 years on?

Since its advent in 1993, high frequency stimulation (HFS) of the subthalamic nucleus (STN) has rapidly developed into the most commonly practiced surgical procedure for the treatment of Parkinson's Disease (PD). Although its exact mechanism of action, be it through an inhibitory depolarization block, desynchronization of neuronal circuits or other means, is not clear, the efficacy and safety of the technique are now well established. HFS of the STN improves the motor function by at least 60%, drastically reduces the levodopa requirement and significantly improves the quality of life in PD. This review updates the recent concepts on the pathophysiology of PD and analyses the basic science principles underlying the clinical practice of the STN HFS. The evolution of the surgical technique and long-term patients' outcome are further discussed.

Evolution of Deep Brain Stimulation: Human Electrometer and Smart Devices Supporting the Next Generation of Therapy

Deep Brain Stimulation (DBS) provides therapeutic benefit for several neuropathologies including Parkinson's disease (PD), epilepsy, chronic pain, and depression. Despite well established clinical efficacy, the mechanism(s) of DBS remains poorly understood. In this review we begin by summarizing the current understanding of the DBS mechanism. Using this knowledge as a framework, we then explore a specific hypothesis regarding DBS of the subthalamic nucleus (STN) for the treatment of PD. This hypothesis states that therapeutic benefit is provided, at least in part, by activation of surviving nigrostriatal dopaminergic neurons, subsequent striatal dopamine release, and resumption of striatal target cell control by dopamine. While highly controversial, we present preliminary data that are consistent with specific predications testing this hypothesis. We additionally propose that developing new technologies, e.g., human electrometer and closed-loop smart devices, for monitoring dopaminergic neurotransmission during STN DBS will further advance this treatment approach.

Surgery for movement disorders

Movement disorders, such as Parkinson's disease, tremor, and dystonia, are among the most common neurological conditions and affect millions of patients. Although medications are the mainstay of therapy for movement disorders, neurosurgery has played an important role in their management for the past 50 years. Surgery is now a viable and safe option for patients with medically intractable Parkinson's disease, essential tremor, and dystonia. In this article, we provide a review of the history, neurocircuitry, indication, technical aspects, outcomes, complications, and emerging neurosurgical approaches for the treatment of movement disorders.

Immunohistochemical study on the distribution of canonical transient receptor potential channels in rat basal ganglia

In the present study, we examined the localizations of canonical transient receptor potential channels (TRPCs) in rat basal ganglia. The dot-like staining pattern of TRPC5 was observed through the globus pallidus (GP) and caudate-putamen. TRPC7 had a strikingly high level of expression in the neuropil in the GP. In the subthalamic nucleus, strong staining for TRPC5 was observed in the cell bodies, while moderate to high immunoreactivies for TRPC1, TRPC3, TRPC4 and TRPC7 were found in the cell bodies and surrounding neuropil. In the substantia nigra, immunoreactivities for TRPC3 and TRPC7 were prominent in the cell bodies and several processes in the pars compacta and pars reticulata. TRPC6 was expressed in the neuropil, not in the cell bodies. This study may provide useful data for the future investigations on the structural and functional properties of TRPCs.

Balance of monosynaptic excitatory and disynaptic inhibitory responses of the globus pallidus induced after stimulation of the subthalamic nucleus in the monkey

The subthalamic nucleus (STN) plays a pivotal role in controlling the activity of both the external and internal segments of the globus pallidus (GPe and GPi, respectively). Both nuclei receive monosynaptic excitatory and disynaptic GPe-mediated inhibitory inputs from the STN. Thus, we investigated the balance of these antagonistic inputs that may determine the overall response of pallidum to STN activation in monkeys. Single stimulation of the STN evoked a short-latency excitation followed by a weak inhibition in GPe neurons and a short-latency, very short-duration excitation followed by a strong inhibition in GPi neurons. Burst high-frequency stimulation (BHFS) (10 stimuli with 100 Hz) of the STN (STN-BHFS) evoked powerful excitatory responses in GPe neurons. Local injection of a mixture of 1, 2, 3, 4-tetrahydro-6-nitro-2, 3-dioxobenzo[f]quinoxaline-7-sulfonamide (NBQX; AMPA/kainate receptor blocker) and 3-(2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid (CPP; NMDA receptor blocker) greatly diminished or abolished excitatory responses to the STN stimulation. In contrast to the GPe, STN-BHFS evoked a predominantly inhibitory response in GPi neurons. The inhibition could be blocked either by a local application of the GABAA receptor antagonist gabazine or by an injection of an NBQX/CPP/gabazine mixture into the GPe. STN-BHFS induced weak excitatory or inhibitory responses in a small number of phasically active putamen neurons. These data suggest that with single stimulation and during STN-BHFS, the STN-GPe excitatory response dominates over the STN-GPe-GPe recurrent inhibition in the GPe, whereas the STN-GPe-GPi inhibitory response dominates over the STN-GPi excitatory response in the GPi.

Disease progression continues in patients with advanced Parkinson's disease and effective subthalamic nucleus stimulation

OBJECTIVES

Glutamate mediated excitotoxicity of the hyperactive subthalamic nucleus (STN) has been reported to contribute to nigral degeneration in Parkinson's disease (PD). Deep brain stimulation of the STN (STN DBS), in its role as a highly effective treatment of severe PD motor complications, has been thought to inhibit STN hyperactivity and therefore decrease progression of PD.

METHODS

In a prospective two centre study, disease progression was determined by means of serial (18)F-fluorodopa (F-dopa) positron emission tomography (PET) in 30 patients with successful STN DBS over the first 16 (SD 6) months after surgery.

RESULTS

Depending on the method of PET data analysis used in the two centres, annual progression rates relative to baseline were 9.5-12.4% in the caudate and 10.7-12.9% in the putamen.

CONCLUSIONS

This functional imaging study is the first to demonstrate a continuous decline of dopaminergic function in patients with advanced PD under clinically effective bilateral STN stimulation. The rates of progression in patients with STN DBS were within the range of previously reported data from longitudinal imaging studies in PD. Therefore this study could not confirm the neuroprotective properties of DBS in the STN target.

Cellular pathology of Parkinson?s disease: astrocytes, microglia and inflammation

Parkinson's disease (PD) is a frequent neurological disorder of the basal ganglia, which is characterized by the progressive loss of dopaminergic neurons mainly in the substantia nigra pars compacta (SNpc). Inflammatory processes have been shown to be associated with the pathogenesis of PD. Activated microglia, as well as to a lesser extent reactive astrocytes, are found in the area associated with cell loss, possibly contributing to the inflammatory process by the release of pro-inflammatory prostaglandins or cytokines. Further deleterious factors released by activated microglia or astrocytes are reactive oxygen species. On the other hand, they may mediate neuroprotective properties by the release of trophic factors or the uptake of glutamate. In this review, we will discuss the different aspects of activated glial cells and potential mechanisms that mediate or protect against cell loss in PD.

Pathogenic role of glial cells in Parkinson's disease

Parkinson's disease (PD) is a common neurodegenerative disorder characterized by the progressive loss of the dopaminergic neurons in the substantia nigra pars compacta (SNpc). The loss of these neurons is associated with a glial response composed mainly of activated microglial cells and, to a lesser extent, of reactive astrocytes. This glial response may be the source of trophic factors and can protect against reactive oxygen species and glutamate. Alternatively, this glial response can also mediate a variety of deleterious events related to the production of pro-oxidant reactive species, and pro-inflammatory prostaglandin and cytokines. We discuss the potential protective and deleterious effects of glial cells in the SNpc of PD and examine how those factors may contribute to the pathogenesis of this disease.

Glial cell response: A pathogenic factor in Parkinson's disease

Parkinson's disease (PD) is a common neurodegenerative disorder characterized by the progressive loss of dopaminergic neurons in the substantia nigra pars compacta (SNpc). The loss of these neurons is associated with a glial response composed mainly of activated microglial cells and, to a lesser extent, of reactive astrocytes. This glial response may be the source of trophic factors and can protect against reactive oxygen species and glutamate. Alternatively, this glial response can also mediate a variety of deleterious events related to the production of pro-oxidant reactive species, proinflammatory prostaglandin, and cytokines. In this review, the authors discuss the potential protective and deleterious effects of glial cells in the SNpc of PD and examine how these factors may contribute to the pathogenesis of this disease.

Excitatory effects of dopamine on subthalamic nucleus neurons: in vitro study of rats pretreated with 6-hydroxydopamine and levodopa

Increased output from the subthalamic nucleus (STN) following chronic dopamine depletion has been linked to the rigidity and tremor seen in Parkinson's disease (PD). We used extracellular microelectrode recordings from rat brain slices to investigate effects of dopamine on STN neurons. In brain slices prepared from rats that received unilateral 6-hydroxydopamine (6-OHDA) treatment, the spontaneous firing rate of STN neurons was reduced by 63%, and the firing pattern was more irregular, compared to STN neurons from normal rats. However, treatment with levodopa (50 mg/kg, i.p., daily) for 4 weeks normalized the firing rate and pattern of STN neurons in the 6-OHDA-treated rats. Dopamine (3-300 microM), added to the superfusate, significantly increased the firing rates of STN neurons in a concentration-dependent fashion, and also produced a more regular firing pattern in 6-OHDA-lesioned tissue. This excitatory effect of dopamine was mimicked by a D2 receptor agonist (quinpirole), and was reduced by the D2 antagonists haloperidol, clozapine and sulpiride. Antagonists of the D1 receptor (SCH-23390) and ionotropic glutamatergic receptors (CNQX and AP5) could not block the effect of dopamine on firing rate. These results suggest that dopamine exerts a direct excitatory influence on STN neurons via the activation of D2-like receptors.

Neurophysiological correlate of clinical signs in Parkinson's disease

Clinical diagnosis of Parkinson's disease (PD) is not always coincident with pathological findings. A better characterization of the disease from the results of studies in various areas of neuroscience can help in improving the rate of diagnostic certainty. Neurophysiology is among the techniques with better chances to furnish specific diagnostic cues on motor aspects of the disease. Neurophysiology provides quantifiable data using non-invasive, relatively inexpensive, methods. Neurophysiological tests can be applied with no previous preparation, and repeated many times without dangerous consequences. To be rewarding, however, neurophysiological examination should be done in close cooperation between the clinician who detects relevant specific signs, and the neurophysiologist who devises the most demonstrative methods to document those signs. In this review, we describe the neurophysiological correlate of symptoms and signs in patients with PD, and particularly their pathophysiological meaning, with special focus on those that could be more helpful to the neurologists in establishing differences with respect to other diseases presenting with parkinsonism.

Treatment results: Parkinson's disease

Deep brain stimulation (DBS) is a neurosurgical treatment of Parkinson's disease that is applied to three targets: the ventral intermediate nucleus of the thalamus (Vim), the globus pallidus internas (GPi) and the subthalamic nucleus (STN). Vim DBS mainly improves contralateral tremor and, therefore, is being supplanted by DBS of the two other targets, even in patients with tremor dominant disease. STN and GPi DBS improve off-motor phases and dyskinesias. There is little comparative data between these procedures. The magnitude of the motor improvement seems more constant with STN than GPi DBS. STN DBS allows a decrease in antiparkinsonian drug doses and consumes moderate current. These advantages of STN over GPi DBS are offset by the need for more intensive postoperative management. The DBS procedure has the unique advantage of reversibility and adjustability over time. Patients with young-onset Parkinson's disease suffering from levodopa-induced motor complications but still responding well to levodopa and who exhibit no behavioral, mood, or cognitive impairment benefit the most from STN DBS. Adverse effects more specific of the DBS procedure are infection, cutaneous erosion, and lead breaking or disconnection. Intracranial electrode implantation can induce a hematoma or contusion. Most authors agree that the benefit to risk ratio of DBS is favorable.

Pharmacological identification of inward current evoked by dopamine in rat subthalamic neurons in vitro

Dopaminergic mechanisms in the subthalamic nucleus (STN) are implicated in the pathophysiology of Parkinson's disease. Here, electrophysiological responses of STN neurons to dopamine (DA) were investigated by using whole-cell patch-clamp recordings in the rat brain slice preparation. Under current-clamp, DA depolarized membrane potential and increased the frequency of spontaneous action potentials of STN neurons. Under voltage-clamp, DA (3-300 microM) produced a reversible concentration-dependent inward current (I(DA); 6-40 pA) with an EC(50) of 13 microM. This DA-induced current had a negative slope conductance which reversed at -102 mV. It was partially reduced by barium and by superfusion with an elevated concentration of extracellular K(+). Moreover, TTX and glutamate receptor antagonists (CNQX and AP5) did not significantly affect the DA responses, indicating that I(DA) is not dependent upon afferent synaptic activity in the STN. Quinpirole, a D(2) receptor agonist, mimicked the DA action more effectively than did the D(1) agonist SKF-38393. The D(2) antagonist sulpiride, but not the D(1) antagonist SCH-23390, blocked responses induced by DA. Intracellular application of G-protein inhibitor GDP-beta-S also suppressed I(DA). GTP-gamma-S, added to the pipette solution, evoked a sustained inward shift in the absence of DA. These results suggest that DA increases the activity of STN neurons via activation of G-protein-coupled D(2)-like receptors which reduce a K(+) conductance.

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

Inactivation of the subthalamic nucleus (STN) by deep brain stimulation or lesioning can ameliorate symptoms in Parkinson' disease (PD) and may alter the underlying progressive degenerative process. We evaluated the effects of STN lesions in a terminal lesion model of PD in rats. Multiple intrastriatal 6-OHDA injections (4 x 7 microg) resulted in a partial loss of striatal TH-positive innervation (-30 to -40%) and nigral dopaminergic neurons (-60%), which was associated with behavioral deficits as observed in drug-induced rotational asymmetry, side-stepping, and postural balancing reactions. Unilateral ibotenic acid lesions of the STN did produce a 50-60% loss of STN neurons based on stereological analysis, which did not induce a functional impairment in rotational asymmetry or spontaneous sensorimotor behaviors. When STN lesions were performed 1 week prior to the 6-OHDA terminal striatal lesions, a significant rescue effect (+23%) on nigral dopaminergic neurons against terminal 6-OHDA neurotoxicity could be demonstrated, whereas striatal TH-positive fiber loss was not attenuated in these animals. In addition, animals with combined STN and striatal lesions exhibited a significant recovery in postural balancing reactions induced by 6-OHDA terminal lesions and did not show a significant impairment in any of the other behavioral parameters examined. Taken together, STN lesions can exert neuroprotective effects on nigral dopamine neurons in a partial lesion model of PD which result in recovery of spontaneous sensorimotor behavior. These findings may therefore provide new insights into the functional interaction between the glutamatergic and the dopaminergic neurotransmitter systems and foster novel therapeutic concepts for the early and middle phases of Parkinson's disease.

The role of glial cells in Parkinson's disease

Parkinson's disease is a common neurodegenerative disorder characterized by the progressive loss of the dopaminergic neurons in the substantia nigra pars compacta. The loss of these neurons is associated with a glial response composed mainly of activated microglial cells and, to a lesser extent, of reactive astrocytes. This glial response may be the source of trophic factors and can protect against reactive oxygen species and glutamate. Aside from these beneficial effects, the glial response can mediate a variety of deleterious events related to the production of reactive species, and pro-inflammatory prostaglandin and cytokines. This article reviews the potential protective and deleterious effects of glial cells in the substantia nigra pars compacta of Parkinson's disease.

Effect of bilateral subthalamic electrical stimulation in Parkinson's disease

BACKGROUND

Bilateral high frequency subthalamic stimulation has been reported to be effective in the treatment of Parkinson's disease and levodopa-induced dyskinesias. To analyze the results of this surgical procedure we critically reviewed 17 parkinsonian patients with advanced disease complicated by motor fluctuations and dyskinesias.

METHODS

Between January 1998 and June 1999 these 17 consecutive patients (age 48-68 years; illness duration 8-27 years) underwent bilateral stereotactically guided implantation of electrodes into the subthalamic nucleus in the Department of Neurosurgery of the Istituto Nazionale Neurologico "C. Besta." Parameters used for continuous high-frequency stimulation were: frequency 160 Hz, pulse width 90 microsec, mean amplitude 2.05 +/- 0.45 V. Parts II and III of the UPDRS were used to assess motor performance before and after operation by the neurologic team. The follow-up ranged between 6 and 18 months.

RESULTS

At latest examination, mean UPDRS II and III scores had improved by 30% (on stimulation, off therapy) with mean 50% reduction in daily off time. Peak dyskinesias and early morning dystonias also improved in relation to therapy reduction. Side effects were persistent postoperative supranuclear oculomotor palsy and postural instability in one case, worsened off-medication hypophonia in three, and temporary nocturnal confusion episodes in three. Postoperative MRI revealed a clinically silent intracerebral haematoma in one case. One electrode required repositioning.

CONCLUSIONS

Continuous high frequency STN stimulation is an effective treatment for advanced PD. A functionally useful and safe electrode placement can be performed without microrecording.