Subthalamic nucleus deep brain stimulation suppresses neuroinflammation by Fractalkine pathway in Parkinson's disease rat model

Neuroinflammation-mediated white matter injury in Parkinson's disease and potential therapeutic strategies targeting NLRP3 inflammasome

Parkinson's disease (PD) is the second most common neurodegenerative disease in the world, severely affecting the quality of life of patients. Recent studies have shown that white matter (WM) plays a vital role in higher neurological functions such as behavior and cognition. In PD patients, neurodegeneration occurs not only in neuronal soma, but also in WM fiber bundles, which are composed of neural axons. The clinical symptoms of PD patients are related not only to the degeneration of neuronal soma, but also to the degeneration of WM. Most previous studies have focused on neuronal soma in substantia nigra (SN), while WM injury (WMI) in PD has been less studied. Moreover, most previous studies have focused on intracerebral lesions in PD, while less attention has been paid to the spinal cord distal to the brain. The above-mentioned factors may be one of the reasons for the poor treatment of previous drug outcomes. Neuroinflammation has been shown to exert a significant effect on the pathological process of brain and spinal cord neurodegeneration in PD. The NOD-like receptor family, pyrin domain-containing 3 (NLRP3) inflammasome has been shown to activate and mediate neuroinflammation and exacerbate neurodegeneration in PD. NLRP3 inflammasome inhibition may be a potential strategy for the treatment of WMI in PD. This review summarizes recent advances and future directions regarding neuroinflammation-mediated WMI in PD and potential therapeutic strategies for targeting NLRP3 inflammasome in the brain and spinal cord, providing new insights for researchers to develop more effective therapeutic approaches for PD patients.

Deep brain stimulation halts Parkinson's disease-related immune dysregulation in the brain and peripheral blood

Immune dysregulation in the brain and periphery is thought to contribute to the detrimental neurodegeneration that occurs in Parkinson's disease (PD). Identifying mechanisms to reverse this dysregulation is key to developing disease-altering therapeutics for this currently incurable disease. Here we utilized the longitudinal data from the Parkinson's Progression Marker Initiative to demonstrate that circulating lymphocytes progressively decline in PD and can be used to predict future motor symptom progression. Deep brain stimulation (DBS), which is used as a symptomatic treatment, could halt this progressive decline. By analyzing specific immune populations from a second cohort of patients, we could show that DBS causes a shift from the pro-inflammatory CD4+ T helper 17 cells driving neurodegeneration to anti-inflammatory CD4+ regulatory T cells. RNA-sequencing and immunohistochemistry in the brain of the A53T alpha-synuclein rat model of PD revealed that DBS also decreases neuroinflammation. These data suggest a potential disease-altering role for DBS by halting inflammatory processes.

Differentiation and regulation of CD4+ T cell subsets in Parkinson's disease

Parkinson's disease (PD) is the second most common neurodegenerative disease, and its hallmark pathological features are the loss of dopaminergic (DA) neurons in the midbrain substantia nigra pars compacta (SNpc) and the accumulation of alpha-synuclein (α-syn). It has been shown that the integrity of the blood-brain barrier (BBB) is damaged in PD patients, and a large number of infiltrating T cells and inflammatory cytokines have been detected in the cerebrospinal fluid (CSF) and brain parenchyma of PD patients and PD animal models, including significant change in the number and proportion of different CD4+ T cell subsets. This suggests that the neuroinflammatory response caused by CD4+ T cells is an important risk factor for the development of PD. Here, we systematically review the differentiation of CD4+ T cell subsets, and focus on describing the functions and mechanisms of different CD4+ T cell subsets and their secreted cytokines in PD. We also summarize the current immunotherapy targeting CD4+ T cells with a view to providing assistance in the diagnosis and treatment of PD.

Impact of subthalamic nucleus deep brain stimulation at different frequencies on neurogenesis in a rat model of Parkinson's disease

Neurogenesis, play a vital role in neuronal plasticity of adult mammalian brains, and its dysregulation is present in the pathophysiology of Parkinson's disease (PD). While subthalamic nucleus deep brain stimulation (STN-DBS) at various frequencies has been proven effective in alleviating PD symptoms, its influence on neurogenesis remains unclear. This study aimed to investigate the effects of 1-week electrical stimulation at frequencies of 60Hz, 130Hz, and 180Hz on neurogenesis in the subventricular zone (SVZ) of PD rats. A hemiparkinsonian rat model was established using 6-hydroxydopamine and categorized into six groups: control, PD, sham stimulation, 60Hz stimulation, 130Hz stimulation, and 180Hz stimulation. Motor function was assessed using the open field test and rotarod test after one week of STN-DBS at different frequencies. Tyrosine hydroxylase (TH) expression in brain tissue was analyzed via Western blot and immunohistochemistry. Immunofluorescence analysis was conducted to evaluate the expression of BrdU/Sox2, BrdU/GFAP, Ki67/GFAP, and BrdU/DCX in bilateral SVZ and the rostral migratory stream (RMS). Our findings revealed that high-frequency STN-DBS improved motor function. Specifically, stimulation at 130Hz increased dopaminergic neuron survival in the PD rat model, while significantly enhancing the proliferation of neural stem cells (NSCs) and neuroblasts in bilateral SVZ. Moreover, this stimulation effectively facilitated the generation of new NSCs in the ipsilateral RMS and triggered the emergence of fresh neuroblasts in bilateral RMS, with notable presence within the lesioned striatum. Conversely, electrical stimulation at 60Hz and 180Hz did not exhibit comparable effects. The observed promotion of neurogenesis in PD rats following STN-DBS provides valuable insights into the mechanistic basis of this therapeutic approach for PD.

Systematic review of rodent studies of deep brain stimulation for the treatment of neurological, developmental and neuropsychiatric disorders

Deep brain stimulation (DBS) modulates local and widespread connectivity in dysfunctional networks. Positive results are observed in several patient populations; however, the precise mechanisms underlying treatment remain unknown. Translational DBS studies aim to answer these questions and provide knowledge for advancing the field. Here, we systematically review the literature on DBS studies involving models of neurological, developmental and neuropsychiatric disorders to provide a synthesis of the current scientific landscape surrounding this topic. A systematic analysis of the literature was performed following PRISMA guidelines. 407 original articles were included. Data extraction focused on study characteristics, including stimulation protocol, behavioural outcomes, and mechanisms of action. The number of articles published increased over the years, including 16 rat models and 13 mouse models of transgenic or healthy animals exposed to external factors to induce symptoms. Most studies targeted telencephalic structures with varying stimulation settings. Positive behavioural outcomes were reported in 85.8% of the included studies. In models of psychiatric and neurodevelopmental disorders, DBS-induced effects were associated with changes in monoamines and neuronal activity along the mesocorticolimbic circuit. For movement disorders, DBS improves symptoms via modulation of the striatal dopaminergic system. In dementia and epilepsy models, changes to cellular and molecular aspects of the hippocampus were shown to underlie symptom improvement. Despite limitations in translating findings from preclinical to clinical settings, rodent studies have contributed substantially to our current knowledge of the pathophysiology of disease and DBS mechanisms. Direct inhibition/excitation of neural activity, whereby DBS modulates pathological oscillatory activity within brain networks, is among the major theories of its mechanism. However, there remain fundamental questions on mechanisms, optimal targets and parameters that need to be better understood to improve this therapy and provide more individualized treatment according to the patient's predominant symptoms.

Insights into neuroinflammatory mechanisms of deep brain stimulation in Parkinson's disease

Parkinson's disease, a progressive neurodegenerative disorder, involves gradual degeneration of the nigrostriatal dopaminergic pathway, leading to neuronal loss within the substantia nigra pars compacta and dopamine depletion. Molecular factors, including neuroinflammation, impaired protein homeostasis, and mitochondrial dysfunction, contribute to the neuronal loss. Deep brain stimulation, a form of neuromodulation, applies electric current through stereotactically implanted electrodes, effectively managing motor symptoms in advanced Parkinson's disease patients. Deep brain stimulation exerts intricate effects on neuronal systems, encompassing alterations in neurotransmitter dynamics, microenvironment restoration, neurogenesis, synaptogenesis, and neuroprotection. Contrary to initial concerns, deep brain stimulation demonstrates antiinflammatory effects, influencing cytokine release, glial activation, and neuronal survival. This review investigates the intricacies of deep brain stimulation mechanisms, including insertional effects, histological changes, and glial responses, and sheds light on the complex interplay between electrodes, stimulation, and the brain. This exploration delves into understanding the role of neuroinflammatory pathways and the effects of deep brain stimulation in the context of Parkinson's disease, providing insights into its neuroprotective capabilities.

Subthalamic nucleus deep brain stimulation alleviates oxidative stress via mitophagy in Parkinson's disease

Subthalamic nucleus deep brain stimulation (STN-DBS) has the potential to delay Parkinson's disease (PD) progression. Whether oxidative stress participates in the neuroprotective effects of DBS and related signaling pathways remains unknown. To address this, we applied STN-DBS to mice and monkey models of PD and collected brain tissue to evaluate mitophagy, oxidative stress, and related pathway. To confirm findings in animal experiments, a cohort of PD patients was recruited and oxidative stress was evaluated in cerebrospinal fluid. When PD mice received STN stimulation, the mTOR pathway was suppressed, accompanied by elevated LC3 II expression, increased mitophagosomes, and a decrease in p62 expression. The increase in mitophagy and balance of mitochondrial fission/fusion dynamics in the substantia nigra caused a marked enhancement of the antioxidant enzymes superoxide dismutase and glutathione levels. Subsequently, fewer mitochondrial apoptogenic factors were released to the cytoplasm, which resulted in a suppression of caspase activation and reservation of dopaminergic neurons. While interfaced with an mTOR activator, oxidative stress was no longer regulated by STN-DBS, with no neuroprotective effect. Similar results to those found in the rodent experiments were obtained in monkeys treated with chronic STN stimulation. Moreover, antioxidant enzymes in PD patients were increased after the operation, however, there was no relation between changes in antioxidant enzymes and motor impairment. Collectively, our study found that STN-DBS was able to increase mitophagy via an mTOR-dependent pathway, and oxidative stress was suppressed due to removal of damaged mitochondria, which was attributed to the dopaminergic neuroprotection of STN-DBS in PD.

A perspective on translating genomic discoveries into targets for brain-machine interface and deep brain stimulation devices

Mental illnesses have a huge impact on individuals, families, and society, so there is a growing need for more efficient treatments. In this context, brain-computer interface (BCI) technology has the potential to revolutionize the options for neuropsychiatric therapies. However, the development of BCI-based therapies faces enormous challenges, such as power dissipation constraints, lack of credible feedback mechanisms, uncertainty of which brain areas and frequencies to target, and even which patients to treat. Some of these setbacks are due to the large gap in our understanding of brain function. In recent years, large-scale genomic analyses uncovered an unprecedented amount of information regarding the biology of the altered brain function observed across the psychopathology spectrum. We believe findings from genetic studies can be useful to refine BCI technology to develop novel treatment options for mental illnesses. Here, we assess the latest advancements in both fields, the possibilities that can be generated from their intersection, and the challenges that these research areas will need to address to ensure that translational efforts can lead to effective and reliable interventions. Specifically, starting from highlighting the overlap between mechanisms uncovered by large-scale genetic studies and the current targets of deep brain stimulation treatments, we describe the steps that could help to translate genomic discoveries into BCI targets. Because these two research areas have not been previously presented together, the present article can provide a novel perspective for scientists with different research backgrounds. This article is categorized under: Neurological Diseases > Genetics/Genomics/Epigenetics Neurological Diseases > Biomedical Engineering.

Neuroplasticity in levodopa-induced dyskinesias: An overview on pathophysiology and therapeutic targets

Levodopa-induced dyskinesias (LIDs) are a common complication in patients with Parkinson's disease (PD). A complex cascade of electrophysiological and molecular events that induce aberrant plasticity in the cortico-basal ganglia system plays a key role in the pathophysiology of LIDs. In the striatum, multiple neurotransmitters regulate the different forms of physiological synaptic plasticity to provide it in a bidirectional and Hebbian manner. In PD, impairment of both long-term potentiation (LTP) and long-term depression (LTD) progresses with disease and dopaminergic denervation of striatum. The altered balance between LTP and LTD processes leads to unidirectional changes in plasticity that cause network dysregulation and the development of involuntary movements. These alterations have been documented, in both experimental models and PD patients, not only in deep brain structures but also at motor cortex. Invasive and non-invasive neuromodulation treatments, as deep brain stimulation, transcranial magnetic stimulation, or transcranial direct current stimulation, may provide strategies to modulate the aberrant plasticity in the cortico-basal ganglia network of patients affected by LIDs, thus restoring normal neurophysiological functioning and treating dyskinesias. In this review, we discuss the evidence for neuroplasticity impairment in experimental PD models and in patients affected by LIDs, and potential neuromodulation strategies that may modulate aberrant plasticity.

Immunomodulatory and endocrine effects of deep brain stimulation and spinal cord stimulation - A systematic review

INTRODUCTION

Deep Brain Stimulation (DBS) and Spinal Cord Stimulation (SCS) represent burgeoning treatments for diverse neurological disorders. This systematic review aims to consolidate findings on the immunological and endocrine effects of DBS and SCS, shedding light on the intricate mechanisms of neuromodulation.

MATERIALS AND METHODS

This systematic review, aligned with PRISMA protocols, synthesizes findings from 33 references-20 on DBS and 13 on SCS-to unravel the immunological and endocrine impacts of neuromodulation.

RESULTS

DBS interventions exhibited divergent effects on cytokines, with an increase in hepcidin levels and a variable impact on the IL-6/IL-10 ratio. While some studies reported elevated IL-6, animal studies consistently demonstrated a reduction in IL-1β and IL-6, with no significant changes in TNF-α and an increase in IL-10. Noteworthy hormonal changes included decreased corticosterone and ACTH concentrations and increased oxytocin levels following DBS of the hypothalamus. SCS mirrored similar effects on interleukins, indicating a reduction in IL-6 and IL-1β and an increase in IL-10 levels. Additionally, SCS led to reduced VEGF levels and elevated expression of neurotrophic factors such as BDNF and GDNF, particularly under burst stimulation.

CONCLUSIONS

Both DBS and SCS exert anti-inflammatory effects, manifesting as a decrease in pro-inflammatory cytokines alongside the stimulation of anti-inflammatory cytokine synthesis. These findings, observed in both animal and human models, imply that neurostimulation may modify the trajectory of neurological diseases by modulating local immune responses in an immunomodulatory and endocrine manner. This comprehensive exploration sets the stage for future research endeavors in this evolving domain.

Deep-Brain Subthalamic Nucleus Stimulation Enhances Food-Related Motivation by Influencing Neuroinflammation and Anxiety Levels in a Rat Model of Early-Stage Parkinson's Disease

Deep-brain subthalamic nucleus stimulation (DBS-STN) has become a well-established therapeutic option for advanced Parkinson's disease (PD). While the motor benefits of DBS-STN are widely acknowledged, the neuropsychiatric effects are still being investigated. Beyond its immediate effects on neuronal circuits, emerging research suggests that DBS-STN might also modulate the peripheral inflammation and neuroinflammation. In this work, we assessed the effects of DBS-STN on food-related motivation, food intake pattern, and the level of anxiety and compared them with markers of cellular and immune activation in nigrostriatal and mesolimbic areas in rats with the 6-OHDA model of early PD. To evaluate the potential mechanism of observed effects, we also measured corticosterone concentration in plasma and leukocyte distribution in peripheral blood. We found that DBS-STN applied during neurodegeneration has beneficial effects on food intake pattern and motivation and reduces anxiety. These behavioral effects occur with reduced percentages of IL-6-labeled cells in the ventral tegmental area and substantia nigra pars compacta in the stimulated brain hemisphere. At the same brain structures, the cFos cell activations were confirmed. Simultaneously, the corticosterone plasma concentration was elevated, and the peripheral blood lymphocytes were reduced after DBS-STN. We believe that comprehending the relationship between the effects of DBS-STN on inflammation and its therapeutic results is essential for optimizing DBS therapy in PD.

Subthalamic nucleus deep brain stimulation induces nigrostriatal dopaminergic plasticity in a stable rat model of Parkinson's disease

OBJECTIVE

Deep brain stimulation (DBS) of the subthalamic nucleus (STN) has been a highly effective treatment option for middle to late stage Parkinson's disease for decades. Though, the underlying mechanisms of action, particularly effects on the cellular level, remain in part unclear. In the context of identifying disease-modifying effects of STN-DBS by prompting cellular plasticity in midbrain dopaminergic systems, we analyzed neuronal tyrosine hydroxylase and c-Fos expression in the substantia nigra pars compacta (SNpc) and ventral tegmental area (VTA).

METHODS

We applied 1 week of continuous unilateral STN-DBS in a group of stable 6-hydroxydopamine (6-OHDA) hemiparkinsonian rats (STNSTIM) in comparison to a 6-OHDA control group (STNSHAM). Immunohistochemistry identified NeuN+, tyrosine hydroxylase+ and c-Fos+ cells within the SNpc and VTA.

RESULTS

After 1 week, rats in the STNSTIM group had 3.5-fold more tyrosine hydroxylase+ neurons within the SNpc (P = 0.010) but not in the VTA compared to sham controls. There was no difference in basal cell activity as indicated by c-Fos expression in both midbrain dopaminergic systems.

CONCLUSION

Our data support a neurorestorative effect of STN-DBS in the nigrostriatal dopaminergic system already after 7 days of continuous STN-DBS in the stable Parkinson's disease rat model without affecting basal cell activity.

Insular cortex stimulation alleviates neuropathic pain via ERK phosphorylation in neurons

AIMS

The clinical use of brain stimulation is attractive for patients who have side effects or tolerance. However, studies on insular cortex (IC) stimulation are lacking in neuropathic pain. The present study aimed to investigate the effects of IC stimulation (ICS) on neuropathic pain and to determine how ICS modulates pain.

METHODS

Changes in pain behaviors were observed following ICS with various parameters in neuropathic rats. Western blotting was performed to assess molecular changes in the expression levels of phosphorylated extracellular signal-regulated kinase (pERK), neurons, astrocytes, and microglia between experimental groups. Immunohistochemistry was performed to investigate the colocalization of pERK with different cell types.

RESULTS

The most effective pain-relieving effect was induced at 50 Hz-120 μA in single trial of ICS and it maintained 4 days longer after the termination of repetitive ICS. The expression levels of pERK, astrocytes, and microglia were increased in neuropathic rats. However, after ICS, the expression levels of pERK were decreased, and colocalization of pERK and neurons was reduced in layers 2-3 of the IC.

CONCLUSION

These results indicated that ICS attenuated neuropathic pain by the regulation of pERK in neurons located in layers 2-3 of the IC. This preclinical study may enhance the potential use of ICS and identify the therapeutic mechanisms of ICS in neuropathic pain.

Neuroinflammation mechanisms of neuromodulation therapies for anxiety and depression

Mood disorders are associated with elevated inflammation, and the reduction of symptoms after multiple treatments is often accompanied by pro-inflammation restoration. A variety of neuromodulation techniques that regulate regional brain activities have been used to treat refractory mood disorders. However, their efficacy varies from person to person and lack reliable indicator. This review summarizes clinical and animal studies on inflammation in neural circuits related to anxiety and depression and the evidence that neuromodulation therapies regulate neuroinflammation in the treatment of neurological diseases. Neuromodulation therapies, including transcranial magnetic stimulation (TMS), transcranial electrical stimulation (TES), electroconvulsive therapy (ECT), photobiomodulation (PBM), transcranial ultrasound stimulation (TUS), deep brain stimulation (DBS), and vagus nerve stimulation (VNS), all have been reported to attenuate neuroinflammation and reduce the release of pro-inflammatory factors, which may be one of the reasons for mood improvement. This review provides a better understanding of the effective mechanism of neuromodulation therapies and indicates that inflammatory biomarkers may serve as a reference for the assessment of pathological conditions and treatment options in anxiety and depression.

Low intensity focused ultrasound: a new prospect for the treatment of Parkinson's disease

Background: As a chronic and progressive neurodegenerative disease, Parkinson's disease (PD) still lacks effective and safe targeted drug therapy. Low-intensity focused ultrasound (LIFU), a new method to stimulate the brain and open the blood-brain barrier (BBB), has been widely concerned by PD researchers due to its non-invasive characteristics.Methods: PubMed was searched for the past 10 years using the terms 'focused ultrasound', 'transcranial ultrasound', 'pulse ultrasound', and 'Parkinson's disease'. Relevant citations were selected from the authors' references. After excluding articles describing high-intensity focused ultrasound or non-Parkinson's disease applications, we found more than 100 full-text analyses for pooled analysis.Results: Current preclinical studies have shown that LIFU could improve PD motor symptoms by regulating microglia activation, increasing neurotrophic factors, reducing oxidative stress, and promoting nerve repair and regeneration, while LIFU combined with microbubbles (MBs) can promote drugs to cross the BBB, which may become a new direction of PD treatment. Therefore, finding an efficient drug carrier system is the top priority of applying LIFU with MBs to deliver drugs.Conclusions: This article aims to review neuro-modulatory effect of LIFU and the possible biophysical mechanism in the treatment of PD, summarize the latest progress in delivering vehicles with MBs, and discuss its advantages and limitations.

Correlation of response to subthalamic deep brain stimulation in Parkinson’s disease patients with striatal dopamine transporter density on 99mtc-TRODAT-1 SPECT

BACKGROUND

Deep brain stimulation (DBS) is a surgical approach with electrical stimulation of certain parts of the brain, which reduce Parkinson's disease (PD) symptoms. Since the loss of dopaminergic neurons in the substantia nigra is the main pathophysiology of PD, we aimed to evaluate the association of response to DBS with preoperative dopamine transporter density (DAT) and its postoperative changes in PD patients who underwent the bilateral implantation of the electrodes in the subthalamic nucleus (STN).

METHOD

A prospective evaluation of Parkinson's disease patients who underwent STN-DBS for 2 years was done. 99mTc-TRODAT-1 single-photon emission computed tomography (SPECT) scan and assessment of PD using unified Parkinson's disease rating scale (UPDRS) III were performed in both pre- and post-operation states. The correlation of response to DBS after 6 months was assessed with baseline findings and postoperative changes of 99mTc-TRODAT-1 SPECT parameters.

RESULTS

Compared to the preoperative state, UPDRS III scores and Levodopa equivalent daily dose (LEDD) were significantly decreased after DBS. However, in 17 patients who underwent both pre-and post-operative 99mTc-TRODAT-1 SPECT, no significant change was seen in any quantitative parameters, including right and left striatal-binding ratio (SBR) as well as striatal asymmetry index (SAI). No significant correlation was also found between the percent of UPDRS III change after DBS and values of preoperative SBRs. The percentage of LEDD reduction also showed no significant correlation with the preoperative state of 99 m-TRODAT-1 SPECT.

CONCLUSION

Our results showed that the mechanism of DBS action is not accompanied by short-term compensation of DAT in basal ganglia in severely advanced PD.

Surgical Management of Synucleinopathies

Synucleinopathies represent a diverse set of pathologies with significant morbidity and mortality. In this review, we highlight the surgical management of three synucleinopathies: Parkinson’s disease (PD), dementia with Lewy bodies (DLB), and multiple system atrophy (MSA). After examining underlying molecular mechanisms and the medical management of these diseases, we explore the role of deep brain stimulation (DBS) in the treatment of synuclein pathophysiology. Further, we examine the utility of focused ultrasound (FUS) in the treatment of synucleinopathies such as PD, including its role in blood–brain barrier (BBB) opening for the delivery of novel drug therapeutics and gene therapy vectors. We also discuss other recent advances in the surgical management of MSA and DLB. Together, we give a diverse overview of current techniques in the neurosurgical management of these pathologies.

The role of neurotransmitter systems in mediating deep brain stimulation effects in Parkinson’s disease

Deep brain stimulation (DBS) is among the most successful paradigms in both translational and reverse translational neuroscience. DBS has developed into a standard treatment for movement disorders such as Parkinson’s disease (PD) in recent decades, however, specific mechanisms behind DBS’s efficacy and side effects remain unrevealed. Several hypotheses have been proposed, including neuronal firing rate and pattern theories that emphasize the impact of DBS on local circuitry but detail distant electrophysiological readouts to a lesser extent. Furthermore, ample preclinical and clinical evidence indicates that DBS influences neurotransmitter dynamics in PD, particularly the effects of subthalamic nucleus (STN) DBS on striatal dopaminergic and glutamatergic systems; pallidum DBS on striatal dopaminergic and GABAergic systems; pedunculopontine nucleus DBS on cholinergic systems; and STN-DBS on locus coeruleus (LC) noradrenergic system. DBS has additionally been associated with mood-related side effects within brainstem serotoninergic systems in response to STN-DBS. Still, addressing the mechanisms of DBS on neurotransmitters’ dynamics is commonly overlooked due to its practical difficulties in monitoring real-time changes in remote areas. Given that electrical stimulation alters neurotransmitter release in local and remote regions, it eventually exhibits changes in specific neuronal functions. Consequently, such changes lead to further modulation, synthesis, and release of neurotransmitters. This narrative review discusses the main neurotransmitter dynamics in PD and their role in mediating DBS effects from preclinical and clinical data.

The effects of electrical stimulation on glial cell behaviour

Neural interface devices interact with the central nervous system (CNS) to substitute for some sort of functional deficit and improve quality of life for persons with disabilities. Design of safe, biocompatible neural interface devices is a fast-emerging field of neuroscience research. Development of invasive implant materials designed to directly interface with brain or spinal cord tissue has focussed on mitigation of glial scar reactivity toward the implant itself, but little exists in the literature that directly documents the effects of electrical stimulation on glial cells. In this review, a survey of studies documenting such effects has been compiled and categorized based on the various types of stimulation paradigms used and their observed effects on glia. A hybrid neuroscience cell biology-engineering perspective is offered to highlight considerations that must be made in both disciplines in the development of a safe implant. To advance knowledge on how electrical stimulation affects glia, we also suggest experiments elucidating electrochemical reactions that may occur as a result of electrical stimulation and how such reactions may affect glia. Designing a biocompatible stimulation paradigm should be a forefront consideration in the development of a device with improved safety and longevity.

Mechanisms of electrical stimulation in eye diseases: A narrative review

Background

In the last two decades, electrical stimulation (ES) has been tested in patients with various eye diseases and shows great treatment potential in retinitis pigmentosa and optic neuropathy. However, the clinical application of ES in ophthalmology is currently limited. On the one hand, optimization and standardization of ES protocols is still an unmet need. On the other hand, poor understanding of the underlying mechanisms has hindered clinical exploitation.

Main Text

Numerous experimental studies have been conducted to identify the treatment potential of ES in eye diseases and to explore the related cellular and molecular mechanisms. In this review, we summarized the in vitro and in vivo evidence related to cellular and tissue response to ES in eye diseases. We highlighted several pathways that may be utilized by ES to impose its effects on the diseased retina.

Conclusions

Therapeutic effect of ES in retinal degenerative diseases might through preventing neuronal apoptosis, promoting neuronal regeneration, increasing neurotrophic factors production in Müller cells, inhibiting microglial activation, enhancing retinal blood flow, and modulating brain plasticity. Future studies are suggested to analyse changes in specific retinal cells for optimizing the treatment parameters and choosing the best fit ES delivery method in target diseases.

Deep Brain Stimulation of the Interposed Nucleus Reverses Motor Deficits and Stimulates Production of Anti-inflammatory Cytokines in Ataxia Mice

Cerebellum is one of the major targets of autoimmunity and cerebellar damage that leads to ataxia characterized by the loss of fine motor coordination and balance, with no treatment available. Deep brain stimulation (DBS) could be a promising treatment for ataxia but has not been extensively investigated. Here, our study aims to investigate the use of interposed nucleus of deep cerebellar nuclei (IN-DCN) for ataxia. We first characterized ataxia-related motor symptom of a Purkinje cell (PC)-specific LIM homeobox (Lhx)1 and Lhx5 conditional double knockout mice by motor coordination tests, and spontaneous electromyogram (EMG) recording. To validate IN-DCN as a target for DBS, in vivo local field potential (LFP) multielectrode array recording of IN-DCN revealed abnormal LFP amplitude surges in PCs. By synchronizing the EMG and IN-DCN recordings (neurospike and LFP) with high-speed video recordings, ataxia mice showed poorly coordinated movements associated with low EMG amplitude and aberrant IN-DCN neural firing. To optimize IN-DCN-DBS for ataxia, we tested DBS parameters from low (30 Hz) to high stimulation frequency (130 or 150 Hz), and systematically varied pulse width values (60 or 80 µs) to maximize motor symptom control in ataxia mice. The optimal IN-DCN-DBS parameter reversed motor deficits in ataxia mice as detected by animal behavioral tests and EMG recording. Mechanistically, cytokine array analysis revealed that anti-inflammatory cytokines such as interleukin (IL)-13 and IL-4 were upregulated after IN-DCN-DBS, which play key roles in neural excitability. As such, we show that IN-DCN-DBS is a promising treatment for ataxia and possibly other movement disorders alike.

Neuron derived fractalkine promotes microglia to absorb hematoma via CD163/HO-1 after intracerebral hemorrhage

BACKGROUND

Hematoma leads to progressive neurological deficits and poor outcomes after intracerebral hemorrhage (ICH). Early clearance of hematoma is widely recognized as an essential treatment to limit the damage and improve the clinical prognosis. CD163, alias hemoglobin (Hb) scavenger receptor on microglia, plays a pivotal role in hematoma absorption, but CD163 on neurons permits Hb uptake and results in neurotoxicity. In this study, we focus on how to specially promote microglial but not neuronal CD163 mediated-Hb uptake and hematoma absorption.

METHODS

RNA sequencing was used to explore the potential molecules involved in ICH progression, and hematoma was detected by magnetic resonance imaging (MRI). Western blot and immunofluorescence were used to evaluate the expression and location of fractalkine (FKN) after ICH. Erythrophagocytosis assay was performed to study the specific mechanism of action of FKN in hematoma clearance. Small interfering RNA (siRNA) transfection was used to explore the effect of peroxisome proliferator-activated receptor-γ (PPAR-γ) on hematoma absorption. Enzyme-linked immunosorbent assay (ELISA) was used to determine the serum FKN concentration in ICH patients.

RESULTS

FKN was found to be significantly increased around the hematoma in a mouse model after ICH. With its unique receptor CX3CR1 in microglia, FKN significantly decreased the hematoma size and Hb content, and improved neurological deficits in vivo. Further, FKN could enhance erythrophagocytosis of microglia in vitro via the CD163/ hemeoxygenase-1 (HO-1) axis, while AZD8797 (a specific CX3CR1 inhibitor) reversed this effect. Moreover, PPAR-γ was found to mediate the increase in the CD163/HO-1 axis expression and erythrophagocytosis induced by FKN in microglia. Of note, a higher serum FKN level was found to be associated with better hematoma resolution in ICH patients.

CONCLUSIONS

We systematically identified that FKN may be a potential therapeutic target to improve hematoma absorption and we shed light on ICH treatment.

Experimental deep brain stimulation in rodent models of movement disorders

Deep brain stimulation (DBS) is the preferred treatment for therapy-resistant movement disorders such as dystonia and Parkinson's disease (PD), mostly in advanced disease stages. Although DBS is already in clinical use for ~30 years and has improved patients' quality of life dramatically, there is still limited understanding of the underlying mechanisms of action. Rodent models of PD and dystonia are essential tools to elucidate the mode of action of DBS on behavioral and multiscale neurobiological levels. Advances have been made in identifying DBS effects on the central motor network, neuroprotection and neuroinflammation in DBS studies of PD rodent models. The phenotypic dt^sz mutant hamster and the transgenic DYT-TOR1A (ΔETorA) rat proved as valuable models of dystonia for preclinical DBS research. In addition, continuous refinements of rodent DBS technologies are ongoing and have contributed to improvement of experimental quality. We here review the currently existing literature on experimental DBS in PD and dystonia models regarding the choice of models, experimental design, neurobiological readouts, as well as methodological implications. Moreover, we provide an overview of the technical stage of existing DBS devices for use in rodent studies.

Role of the CX3CL1-CX3CR1 axis in renal disease

Excessive infiltration of immune cells into the kidney is a key feature of acute and chronic kidney diseases. The family of chemokines comprises key drivers of this process. Fractalkine [chemokine (C-X3-C motif) ligand 1 (CX3CL1)] is one of two unique chemokines synthesized as a transmembrane protein that undergoes proteolytic cleavage to generate a soluble species. Through interacting with its cognate receptor, chemokine (C-X3-C motif) receptor 1 (CX3CR1), CX3CL1 was originally shown to act as a conventional chemoattractant in the soluble form and as an adhesion molecule in the transmembrane form. Since then, other functions of CX3CL1 beyond leukocyte recruitment have been described, including cell survival, immunosurveillance, and cell-mediated cytotoxicity. This review summarizes diverse roles of CX3CL1 in kidney disease and potential uses as a therapeutic target and novel biomarker. As the CX3CL1-CX3CR1 axis has been shown to contribute to both detrimental and protective effects in various kidney diseases, a thorough understanding of how the expression and function of CX3CL1 are regulated is needed to unlock its therapeutic potential.

Influence of Simulated Deep Brain Stimulation on the Expression of Inflammatory Mediators by Human Central Nervous System Cells In Vitro

Deep brain stimulation (DBS) seems to modulate inflammatory processes. Whether this modulation leads to an induction or suppression of inflammatory mediators is still controversially discussed. Most studies of the influence of electrical stimulation on inflammation were conducted in rodent models with direct current stimulation and/or long impulses, both of which differ from the pattern in DBS. This makes comparisons with the clinical condition difficult. We established an in-vitro model that simulated clinical stimulation patterns to investigate the influence of electrical stimulation on proliferation and survival of human astroglial cells, microglia, and differentiated neurons. We also examined its influence on the expression of the inflammatory mediators C-X-C motif chemokine (CXCL)12, CXCL16, CC-chemokin-ligand-2 (CCL)2, CCL20, and interleukin (IL)-1β and IL-6 by these cells using quantitative polymerase chain reaction. In addition, protein expression was assessed by immunofluorescence double staining. In our model, electrical stimulation did not affect proliferation or survival of the examined cell lines. There was a significant upregulation of CXCL12 in the astrocyte cell line SVGA, and of IL-1β in differentiated SH-SY5Y neuronal cells at both messenger RNA and protein levels. Our model allowed a valid examination of chemokines and cytokines associated with inflammation in human brain cells. With it, we detected the induction of inflammatory mediators by electrical stimulation in astrocytes and neurons.

Subthalamic nucleus deep brain stimulation induces sustained neurorestoration in the mesolimbic dopaminergic system in a Parkinson's disease model

BACKGROUND

Deep brain stimulation (DBS) of the subthalamic nucleus (STN) is an established therapeutic principle in Parkinson's disease, but the underlying mechanisms, particularly mediating non-motor actions, remain largely enigmatic.

OBJECTIVE/HYPOTHESIS

The delayed onset of neuropsychiatric actions in conjunction with first experimental evidence that STN-DBS causes disease-modifying effects prompted our investigation on how cellular plasticity in midbrain dopaminergic systems is affected by STN-DBS.

METHODS

We applied unilateral or bilateral STN-DBS in two independent cohorts of 6-hydroxydopamine hemiparkinsonian rats four to eight weeks after dopaminergic lesioning to allow for the development of a stable dopaminergic dysfunction prior to DBS electrode implantation.

RESULTS

After 5 weeks of STN-DBS, stimulated animals had significantly more TH⁺ dopaminergic neurons and fibres in both the nigrostriatal and the mesolimbic systems compared to sham controls with large effect sizes of g_Hedges = 1.9-3.4. DBS of the entopeduncular nucleus as the homologue of the human Globus pallidus internus did not alter the dopaminergic systems. STN-DBS effects on mesolimbic dopaminergic neurons were largely confirmed in an independent animal cohort with unilateral STN stimulation for 6 weeks or for 3 weeks followed by a 3 weeks washout period. The latter subgroup even demonstrated persistent mesolimbic dopaminergic plasticity after washout. Pilot behavioural testing showed that augmentative dopaminergic effects on the mesolimbic system by STN-DBS might translate into improvement of sensorimotor neglect.

CONCLUSIONS

Our data support sustained neurorestorative effects of STN-DBS not only in the nigrostriatal but also in the mesolimbic system as a potential factor mediating long-latency neuropsychiatric effects of STN-DBS in Parkinson's disease.

Transcranial Ultrasound Stimulation Suppresses Neuroinflammation in a Chronic Mouse Model of Parkinson's Disease

OBJECTIVE

Neuroinflammation contributes to the development and progression of Parkinson's disease (PD). The aim of this study was to examine whether ultrasound (US) stimulation of the subthalamic nucleus (STN) could suppress the neuroinflammation in a chronic PD mouse model induced by 1-Methyl-4-phenyl-1, 2, 3, 6-tetrahydropyridine (MPTP).

METHODS

A chronic PD mouse model was built by injections of 20mg/kg MPTP and 250 mg/kg probenecid at 3.5-day intervals for 5 weeks. Mice were randomized into control+sham, MPTP+sham and MPTP+STN+US group. For MPTP+STN+US group, ultrasound wave (3.8 MHz, 50% duty cycle, 1 kHz pulse repetition frequency, 30 min/day) was delivered to the STN the day after MPTP and probenecid injection (the early stage of PD progression). The rotarod test and pole test were performed to evaluate the behavioral changes after ultrasound treatment. Then, the activity of microglia and astrocyte were measured to evaluate the inflammation level in the brain.

RESULTS

Ultrasound stimulation improved the latency to falls in the rotarod test (p = 0.033) and decreased the climbing time in the pole test (p = 0.016) compared with MPTP+sham group. Moreover, ultrasound stimulation reduced the chronic inflammation response as shown in microglia (p = 0.007) and astrocyte (p = 0.032) activation. In addition, HE, Nissl and Tunel staining showed that no brain tissue injury was induced by US.

CONCLUSION

These findings demonstrated that ultrasound stimulation could suppress neuroinflammation in PD mice.

SIGNIFICANCE

Transcranial ultrasound neuromodulation offers a novel approach for Parkinson's disease intervention, potentially through its anti-neuroinflammation functions.

Neuroimaging evaluation of deep brain stimulation in the treatment of representative neurodegenerative and neuropsychiatric disorders

Brain stimulation technology has become a viable modality of reversible interventions in the effective treatment of many neurological and psychiatric disorders. It is aimed to restore brain dysfunction by the targeted delivery of specific electronic signal within or outside the brain to modulate neural activity on local and circuit levels. Development of therapeutic approaches with brain stimulation goes in tandem with the use of neuroimaging methodology in every step of the way. Indeed, multimodality neuroimaging tools have played important roles in target identification, neurosurgical planning, placement of stimulators and post-operative confirmation. They have also been indispensable in pre-treatment screen to identify potential responders and in post-treatment to assess the modulation of brain circuitry in relation to clinical outcome measures. Studies in patients to date have elucidated novel neurobiological mechanisms underlying the neuropathogenesis, action of stimulations, brain responses and therapeutic efficacy. In this article, we review some applications of deep brain stimulation for the treatment of several diseases in the field of neurology and psychiatry. We highlight how the synergistic combination of brain stimulation and neuroimaging technology is posed to accelerate the development of symptomatic therapies and bring revolutionary advances in the domain of bioelectronic medicine.

Mesencephalic Electrical Stimulation Reduces Neuroinflammation after Photothrombotic Stroke in Rats by Targeting the Cholinergic Anti-Inflammatory Pathway

Inflammation is crucial in the pathophysiology of stroke and thus a promising therapeutic target. High-frequency stimulation (HFS) of the mesencephalic locomotor region (MLR) reduces perilesional inflammation after photothrombotic stroke (PTS). However, the underlying mechanism is not completely understood. Since distinct neural and immune cells respond to electrical stimulation by releasing acetylcholine, we hypothesize that HFS might trigger the cholinergic anti-inflammatory pathway via activation of the α7 nicotinic acetylcholine receptor (α7nAchR). To test this hypothesis, rats underwent PTS and implantation of a microelectrode into the MLR. Three hours after intervention, either HFS or sham-stimulation of the MLR was applied for 24 h. IFN-γ, TNF-α, and IL-1α were quantified by cytometric bead array. Choline acetyltransferase (ChAT)⁺ CD4⁺-cells and α7nAchR⁺-cells were quantified visually using immunohistochemistry. Phosphorylation of NFĸB, ERK1/2, Akt, and Stat3 was determined by Western blot analyses. IFN-γ, TNF-α, and IL-1α were decreased in the perilesional area of stimulated rats compared to controls. The number of ChAT⁺ CD4⁺-cells increased after MLR-HFS, whereas the amount of α7nAchR⁺-cells was similar in both groups. Phospho-ERK1/2 was reduced significantly in stimulated rats. The present study suggests that MLR-HFS may trigger anti-inflammatory processes within the perilesional area by modulating the cholinergic system, probably via activation of the α7nAchR.