Safety and efficacy of transcranial direct current stimulation in acute experimental ischemic stroke

The effects of transcranial direct current stimulation on upper-limb function post-stroke: A meta-analysis of multiple-session studies

OBJECTIVE

To systematically review how patient characteristics and/or transcranial direct current stimulation (tDCS) parameters influence tDCS effectiveness in respect to upper limb function post-stroke.

METHODS

Three electronic databases were searched for sham-controlled randomised trials using the Fugl-Meyer Assessment for upper extremity as outcome measure. A meta-analysis and nine subgroup-analyses were performed to identify which tDCS parameters yielded the greatest impact on upper limb function recovery in stroke patients.

RESULTS

Eighteen high-quality studies (507 patients) were included. tDCS applied in a chronic stage yields greater results than tDCS applied in a (sub)acute stage. Additionally, patients with low baseline upper limb impairments seem to benefit more from tDCS than those with high baseline impairments. Regarding tDCS configuration, all stimulation types led to a significant improvement, but only tDCS applied during therapy, and not before therapy, yielded significant results. A positive dose-response relationship was identified for current/charge density and stimulation duration, but not for number of sessions.

CONCLUSION

Our results demonstrate that tDCS improves upper limb function post-stroke. However, its effectiveness depends on numerous factors. Especially chronic stroke patients improved, which is promising as they are typically least amenable to recovery.

SIGNIFICANCE

The current work highlights the importance of several patient-related and protocol-related factors regarding tDCS effectiveness.

Cathodal Transcranial Direct Current Stimulation in Acute Ischemic Stroke: Pilot Randomized Controlled Trial

[Figure: see text].

Safety of Transcranial Direct Current Stimulation in Neurorehabilitation

Transcranial direct current stimulation (tDCS) has considerable potential as a useful method in the field of neurorehabilitation. However, the safety of tDCS for the human is primarily based on theoretical evidence related to electricity, and the safety information of applying tDCS to the human is only available from researcher's reporting. Based on tDCS studies with human and animal subjects and simulation-based studies of the safety of current stimulation in the past 20 years, this review investigated the safety of tDCS application to the human body. No severe complications have been reported in either adults or children for tDCS at an intensity of 4 mA or less, within a period of 60 minutes per day, using commonly applied 25 or 35 cm² electrodes. According to animal studies, the amount of electricity used for tDCS is less than 5% of the amount that permanently changes brain tissue, thereby ensuring safety to a certain extent. In order to increase the efficacy of tDCS for neurorehabilitation and to minimize even trivial complications in the human screening of exclusion criteria should be conducted with detailed observations of complications.

Development of a photochemical thrombosis investigation system to obtain a rabbit ischemic stroke model

Photochemical thrombosis is a method for the induction of ischemic stroke in the cerebral cortex. It can generate localized ischemic infarcts in the desired region; therefore, it has been actively employed in establishing an ischemic stroke animal model and in vivo assays of diagnostic and therapeutic techniques for stroke. To establish a rabbit ischemic stroke model and overcome the shortcoming of previous studies that were difficult to build a standardized photothrombotic rabbit model, we developed a photochemical thrombosis induction system that can produce consistent brain damage on a specific area. To verify the generation of photothrombotic brain damage using the system, longitudinal magnetic resonance imaging, 2,3,5-triphenyltetrazolium chloride staining, and histological staining were applied. These analytical methods have a high correlation for ischemic infarction and are appropriate for analyzing photothrombotic brain damage in the rabbit brain. The results indicated that the photothrombosis induction system has a main advantage of being accurately controlled a targeted region of photothrombosis and can produce cerebral hemisphere lesions on the target region of the rabbit brain. In conjugation with brain atlas, it can induce photochemical ischemic stroke locally in the part of the brain that is responsible for a particular brain function and the system can be used to develop animal models with degraded specific functions. Also, the photochemical thrombosis induction system and a standardized rabbit ischemic stroke model that uses this system have the potential to be used for verifications of biomedical techniques for ischemic stroke at a preclinical stage in parallel with further performance improvements.

Neurovascular Coupling Impairment in Acute Ischemic Stroke by Optogenetics and Optical Brain Imaging

The coupling between neuronal activity and cerebral blood flow (CBF), known as neurovascular coupling, has been reported to be impaired after stroke. This study aims to investigate the neurovascular coupling impairment at the acute stage after ischemic stroke. Laser speckle contrast imaging (LSCI) was applied to measure the hemodynamic response to optogenetic excitation of sensorimotor neurons in healthy and ischemic brain. The results showed that the hemodynamic response to optogenetic stimulation decreased and the regional CBF response was correlated with the distance from the ischemic core at the acute stage, regardless of the change in resting CBF. Our results also demonstrated that excitatory neuronal stimulation of intact area could promote the recovery of neurovascular coupling, whereas peri-infarct neuronal excitation failed to restore neurovascular function 24 hrs after ischemia. These results suggested the intact periphery of penumbra as the target for excitatory stimulation in aspect of restoring the perfusion after ischemic stroke.

Intracranial alternating current stimulation facilitates neurogenesis in a mouse model of Alzheimer's disease

BACKGROUND

Neurogenesis is significantly impaired in the brains of both human patients and experimental animal models of Alzheimer's disease (AD). Although deep brain stimulation promotes neurogenesis, it is an invasive technique that may damage neural circuitry along the path of the electrode. To circumvent this problem, we assessed whether intracranial electrical stimulation to the brain affects neurogenesis in a mouse model of Alzheimer's disease (5xFAD).

METHODS AND RESULTS

We used Ki67, Nestin, and doublecortin (DCX) as markers and determined that neurogenesis in both the subventricular zone (SVZ) and hippocampus were significantly reduced in the brains of 4-month-old 5xFAD mice. Guided by a finite element method (FEM) computer simulation to approximately estimate current and electric field in the mouse brain, electrodes were positioned on the skull that were likely to deliver stimulation to the SVZ and hippocampus. After a 4-week program of 40-Hz intracranial alternating current stimulation (iACS), neurogenesis indicated by expression of Ki67, Nestin, and DCX in both the SVZ and hippocampus were significantly increased compared to 5xFAD mice who received sham stimulation. The magnitude of neurogenesis was close to the wild-type (WT) age-matched unmanipulated controls.

CONCLUSION

Our results suggest that iACS is a promising, less invasive technique capable of effectively stimulating the SVZ and hippocampus regions in the mouse brain. Importantly, iACS can significantly boost neurogenesis in the brain and offers a potential treatment for AD.

tDCS Accelerates the Rehabilitation of MCAO-Induced Motor Function Deficits via Neurogenesis Modulated by the Notch1 Signaling Pathway

Background. Ischemic stroke carries a high mortality rate and is a leading cause of severe neurological disability. However, the efficacy of current therapeutic options remains limited. Objective. We aimed to investigate the treatment efficacy of transcranial direct current stimulation (tDCS) in motor function rehabilitation after ischemic stroke and explore the underlying mechanisms. Methods. Male Sprague-Dawley rats with epicranial electrodes were used to establish pathogenetic model through temporary right middle cerebral artery occlusion (MCAO). Subsequently, animals were randomly divided into 4 groups: MCAO + tDCS/sham tDCS, Control + tDCS/sham tDCS. Animals in the groups with tDCS underwent 10 days of cathodal tDCS totally (500 µA, 15 minutes, once a day). During and after tDCS treatment, the motor functions of the animals, ischemic damage area, proliferation and differentiation of neural stem cells (NSCs), and distribution, and protein expression of Notch1 signaling molecules were detected. Results. The rehabilitation of MCAO-induced motor function deficits was dramatically accelerated by tDCS treatment. NSC proliferation in the subventricular zone (SVZ) was significantly increased after MCAO surgery, and tDCS treatment promoted this process. Additionally, NSCs probably migrated from the SVZ to the ischemic striatum and then differentiated into neurons and oligodendrocytes after MCAO surgery, both of which processes were accelerated by tDCS treatment. Finally, tDCS treatment inhibited the activation of Notch1 signaling in NSCs in the ischemic striatum, which may be involved in NSC differentiation in the MCAO model. Conclusion. Our results suggest that tDCS may exert therapeutic efficacy after ischemic stroke in a regenerative medical perspective.

Contralesional Application of Transcranial Direct Current Stimulation on Functional Improvement in Ischemic Stroke Mice

BACKGROUND AND PURPOSE

The therapeutic use of transcranial direct current stimulation (tDCS), an adjuvant tool for stroke, induces long-term changes in cortical excitability, for example, the secretion of activity-dependent growth factors. We assessed the proper therapeutic configuration of high-definition tDCS (HD-tDCS) in the subacute stage of ischemic stroke and its underlying expression profiling of growth factors to propose a new method for ensuring better therapeutic effects.

METHODS

Male C57BL/6J mice were subjected to middle cerebral artery occlusion, after which repetitive HD-tDCS (20 minutes, 55 µA/mm², charge density 66 000 C/m²) was applied from subacute phases of their ischemic insult. Behavioral tests assessing motor and cognitive functions were used to determine suitable conditions and HD-tDCS stimulation sites. Gene expression profiling of growth factors and their secretion and activation were analyzed to shed light on the underlying mechanisms.

RESULTS

Anodal HD-tDCS application over the contralesional cortex, especially the motor cortex, was more effective than ipsilesional stimulation in attenuating motor and cognitive deficits. In the HD-tDCS application over the contralesional motor cortex, positive changes in Bmp8b, Gdf5, Il4, Pdgfa, Pgf, and Vegfb were observed in the ipsilesional site. The expression of GDF5 (growth/differentiation factor 5) and PDGFA (platelet-derived growth factor subunit A) tended to similarly increase in both ipsi- and contralesional striata. However, higher expression levels of GDF5 and PDGFA and their receptors were observed in the peri-infarct regions of the striatum after HD-tDCS, especially in PDGFA expression. A higher number of proliferating or newly formed neuronal cells was detected in ipsilesional sites such as the subventricular zone.

CONCLUSIONS

Application of anodal HD-tDCS over the contralesional cortex may enhance beneficial recovery through the expression of growth factors, such as GDF5 and PDGFA, in the ipsilesional site. Therefore, this therapeutic configuration may be applied in the subacute stage of ischemic stroke to ameliorate neurological impairments.

Cathodal tDCS exerts neuroprotective effect in rat brain after acute ischemic stroke

BACKGROUND

Transcranial direct current stimulation (tDCS) is a non-invasive brain modulation technique that has been proved to exert beneficial effects in the acute phase of stroke. To explore the underlying mechanism, we investigated the neuroprotective effects of cathodal tDCS on brain injury caused by middle cerebral artery occlusion (MCAO).

RESULTS

We established the MCAO model and sham MCAO model with an epicranial electrode implanted adult male Sprague-Dawley rats, and then they were randomly divided into four groups (MCAO + tDCS, MCAO + sham tDCS (Sham), Control + tDCS and Control + Sham group). In this study, the severity degree of neurological deficit, the morphology of brain damage, the apoptosis, the level of neuron-specific enolase and inflammatory factors, the activation of glial cells was detected. The results showed that cathodal tDCS significantly improved the level of neurological deficit and the brain morphology, reduced the brain damage area and apoptotic index, and increased the number of Nissl body in MCAO rats, compared with MCAO + Sham group. Meanwhile, the high level of NSE, inflammatory factors, Caspase 3 and Bax/Bcl2 ratio in MCAO rats was reduced by cathodal tDCS. Additionally, cathodal tDCS inhibited the activation of astrocyte and microglia induced by MCAO. No difference was found in two Control groups.

CONCLUSION

Our results suggested that cathodal tDCS could accelerate the recovery of neurologic deficit and brain damage caused by MCAO. The inhibition of neuroinflammation and apoptosis resulted from cathodal tDCS may be involved in the neuroprotective process.

Regenerative Rehabilitation for Stroke Recovery by Inducing Synergistic Effects of Cell Therapy and Neurorehabilitation on Motor Function: A Narrative Review of Pre-Clinical Studies

Neurological diseases severely affect the quality of life of patients. Although existing treatments including rehabilitative therapy aim to facilitate the recovery of motor function, achieving complete recovery remains a challenge. In recent years, regenerative therapy has been considered as a potential candidate that could yield complete functional recovery. However, to achieve desirable results, integration of transplanted cells into neural networks and generation of appropriate microenvironments are essential. Furthermore, considering the nascent state of research in this area, we must understand certain aspects about regenerative therapy, including specific effects, nature of interaction when administered in combination with rehabilitative therapy (regenerative rehabilitation), and optimal conditions. Herein, we review the current status of research in the field of regenerative therapy, discuss the findings that could hold the key to resolving the challenges associated with regenerative rehabilitation, and outline the challenges to be addressed with future studies. The current state of research emphasizes the importance of determining the independent effect of regenerative and rehabilitative therapies before exploring their combined effects. Furthermore, the current review highlights the progression in the treatment perspective from a state of compensation of lost function to that of a possibility of complete functional recovery.

Resilience to Injury: A New Approach to Neuroprotection?

Despite thousands of neuroprotectants demonstrating promise in preclinical trials, a neuroprotective therapeutic has yet to be approved for the treatment of acute brain injuries such as stroke or traumatic brain injury. Developing a more detailed understanding of models and populations demonstrating "neurological resilience" in spite of brain injury can give us important insights into new translational therapies. Resilience is the process of active adaptation to a stressor. In the context of neuroprotection, models of preconditioning and unique animal models of extreme physiology (such as hibernating species) reliably demonstrate resilience in the laboratory setting. In the clinical setting, resilience is observed in young patients and can be found in those with specific genetic polymorphisms. These important examples of resilience can help transform and extend the current neuroprotective framework from simply countering the injurious cascade into one that anticipates, monitors, and optimizes patients' physiological responses from the time of injury throughout the process of recovery. This review summarizes the underpinnings of key adaptations common to models of resilience and how this understanding can be applied to new neuroprotective approaches.

Optogenetic translocation of protons out of penumbral neurons is protective in a rodent model of focal cerebral ischemia

BACKGROUND

Intracellular acidosis in the ischemic penumbra can contribute to further cell death, effectively enlarging the infarct core. Restoring the acid-base balance may enhance tissue survivability after cerebral ischemia.

OBJECTIVE

This study investigated whether translocating protons out of penumbral neurons could mitigate tissue acidification and induce neuroprotection in a rodent model of acute cerebral ischemia.

METHODS

We modulated the penumbral neurons via a light-driven pump to translocate protons out (i.e., archaerhodopsin/ArchT group) or into (i.e., channelrhodopsin-2/ChR2 group) neurons after focal cerebral ischemia in rats. Intracellular pH values were imaged via neutral red (NR) fluorescence and cerebral blood flow (CBF) was monitored through laser speckle contrast imaging (LSCI). Global CBF responses to electrical stimulation of the hindlimbs were obtained 24 h and 48 h after ischemia to assess neurological function. Behavioral and histological outcomes were evaluated 48 h after ischemia. A control group without gene modification was included.

RESULTS

The reduction of relative pH (R_pH), the amplitude of negative peak of hypoemic response (R_NP) and the hemispheric lateralization index (LI) in ArchT group were significantly less than those of the ChR2 or control group. Moreover, R_pH was strongly correlated with R_NP (r = 0.60) and LI (r_24h = 0.80, r_48h = 0.59). In addition, behavioral and histological results supported a neuroprotective effect of countering neuronal acidosis in penumbra through optogenetic stimulation.

CONCLUSION(S)

These results indicate that countering intracellular acidosis by optogenetically translocating protons out of penumbral neurons during the acute ischemic stage could induce protection after ischemic brain injury.

Memory and Cognition-Related Neuroplasticity Enhancement by Transcranial Direct Current Stimulation in Rodents: A Systematic Review

Brain stimulation techniques, including transcranial direct current stimulation (tDCS), were identified as promising therapeutic tools to modulate synaptic plasticity abnormalities and minimize memory and learning deficits in many neuropsychiatric diseases. Here, we revised the effect of tDCS on the modulation of neuroplasticity and cognition in several animal disease models of brain diseases affecting plasticity and cognition. Studies included in this review were searched following the terms (“transcranial direct current stimulation”) AND (mice OR mouse OR animal) and according to the PRISMA statement requirements. Overall, the studies collected suggest that tDCS was able to modulate brain plasticity due to synaptic modifications within the stimulated area. Changes in plasticity-related mechanisms were achieved through induction of long-term potentiation (LTP) and upregulation of neuroplasticity-related proteins, such as c-fos, brain-derived neurotrophic factor (BDNF), or N-methyl-D-aspartate receptors (NMDARs). Taken into account all revised studies, tDCS is a safe, easy, and noninvasive brain stimulation technique, therapeutically reliable, and with promising potential to promote cognitive enhancement and neuroplasticity. Since the use of tDCS has increased as a novel therapeutic approach in humans, animal studies are important to better understand its mechanisms as well as to help improve the stimulation protocols and their potential role in different neuropathologies.

Transcranial direct current stimulation associated with physical-therapy in acute stroke patients - A randomized, triple blind, sham-controlled study

BACKGROUND

Transcranial Direct Current Stimulation has been increasing in popularity in the last few years. Despite vast amounts of articles on the use of tDCS on stroke patients, very little has been done during the acute phase.

OBJECTIVES

Measure the effects of tDCS on functional and sensory outcomes throughout the first year post onset of stroke.

METHODS

50 acute stroke patients were randomized and placed into either the treatment or sham group. Anodal tDCS was applied (2 mA, 20 min) 5 times a week during the first month post stroke. Patients were evaluated with the Wolf Motor Function Test, the Semmes Weinstein Monofilament Test, the Upper Extremity section (UEFM), the Lower Extremity section (LEFM) and the Somatosensory section of the Fugl Meyer Test, the Tardieu Spasticity Scale, the Stroke Impact Scale (SIS), the Hospital Anxiety and Depression Scale (HADS) and the Barthel Index. Evaluations were held at 48 h post stroke, week 1, 2, 3, 4, 3 months, 6 months and 1 year.

RESULTS

There were statistically and clinically significant improvements after tDCS in all functional motor outcomes, and somatosensory functions. Differences between both groups for the main outcome (WMFT time) were 51% (p = 0.04) at one month, and 57% (p = 0.02) at one year.

CONCLUSION

tDCS seems to be an effective adjuvant to conventional rehabilitation techniques. If applied in the acute stages of stroke, functional recovery is not only accelerated, but improved, and results are maintained up to one-year post stroke.

Transcranial Current Stimulation Alters the Expression of Immune-Mediating Genes

Despite its extensive use in clinical studies, the molecular mechanisms underlying the effects of transcranial direct current stimulation (tDCS) remain to be elucidated. We previously described subacute effects of tDCS on immune- and stem cells in the rat brain. To investigate the more immediate effects of tDCS regulating those cellular responses, we treated rats with a single session of either anodal or cathodal tDCS, and analyzed the gene expression by microarray; sham-stimulated rats served as control. Anodal tDCS increased expression of several genes coding for the major histocompatibility complex I (MHC I), while cathodal tDCS increased the expression of the immunoregulatory protein osteopontin (OPN). We confirmed the effects of gene upregulation by immunohistochemistry at the protein level. Thus, our data show a novel mechanism for the actions of tDCS on immune- and inflammatory processes, providing a target for future therapeutic studies.

Central Nervous System Electrical Stimulation for Neuroprotection in Acute Cerebral Ischemia: Meta-Analysis of Preclinical Studies

Background and Purpose- Brain electrical stimulation, widely studied to facilitate recovery from stroke, has also been reported to confer direct neuroprotection in preclinical models of acute cerebral ischemia. Systematic review of controlled preclinical acute cerebral ischemia studies would aid in planning for initial human clinical trials. Methods- A systematic Medline search identified controlled, preclinical studies of central nervous system electrical stimulation in acute cerebral ischemia. Studies were categorized among 6 stimulation strategies. Three strategies applied different stimulation types to tissues within the ischemic zone (cathodal hemispheric stimulation [CHS], anodal hemispheric stimulation, and pulsed hemispheric stimulation), and 3 strategies applied deep brain stimulation to different neuronal targets remote from the ischemic zone (fastigial nucleus stimulation, subthalamic vasodilator area stimulation, and dorsal periaqueductal gray stimulation). Random-effects meta-analysis assessed electrical stimulation modification of final infarct volume. Study-level risk of bias and intervention-level readiness-for-translation were assessed using formal rating scales. Results- Systematic search identified 28 experiments in 21 studies, including a total of 350 animals, of electrical stimulation in preclinical acute cerebral ischemia. Overall, in animals undergoing electrical stimulation, final infarct volumes were reduced by 37% (95% CI, 34%-40%; P<0.001), compared with control. There was evidence of heterogeneity of efficacy among stimulation strategies (I²=93.1%, P_{heterogeneity}<0.001). Among the within-ischemic zone stimulation strategies, only CHS significantly reduced the infarct volume (27 %; 95% CI, 22%-33%; P<0.001); among the remote-from ischemic zone approaches, all (fastigial nucleus stimulation, subthalamic vasodilator area stimulation, and dorsal periaqueductal gray stimulation) reduced infarct volumes by approximately half. On formal rating scales, CHS studies had the lowest risk of bias, and CHS had the highest overall quality of intervention-level evidence supporting readiness to proceed to clinical testing. Conclusions- Electrical stimulation reduces final infarct volume across preclinical studies. CHS shows the most robust evidence and is potentially appropriate for progression to early-stage human clinical trial testing as a promising neuroprotective intervention.

Protecting the ischaemic penumbra as an adjunct to thrombectomy for acute stroke

After ischaemic stroke, brain damage can be curtailed by rescuing the 'ischaemic penumbra' - that is, the severely hypoperfused, at-risk but not yet infarcted tissue. Current evidence-based treatments involve restoration of blood flow so as to salvage the penumbra before it evolves into irreversibly damaged tissue, termed the 'core'. Intravenous thrombolysis (IVT) can salvage the penumbra if given within 4.5 h after stroke onset; however, the early recanalization rate is only ~30%. Direct removal of the occluding clot by mechanical thrombectomy considerably improves outcomes over IVT alone, but despite early recanalization in > 80% of cases, ~50% of patients who receive this treatment do not enjoy functional independence, usually because the core is already too large at the time of recanalization. Novel therapies aiming to 'freeze' the penumbra - that is, prevent core growth until recanalization is complete - hold potential as adjuncts to mechanical thrombectomy. This Review focuses on nonpharmacological approaches that aim to restore the physiological balance between oxygen delivery to and oxygen demand of the penumbra. Particular emphasis is placed on normobaric oxygen therapy, hypothermia and sensory stimulation. Preclinical evidence and early pilot clinical trials are critically reviewed, and future directions, including clinical translation and trial design issues, are discussed.

A safety study of 500 μA cathodal transcranial direct current stimulation in rat

Background

Transcranial direct current stimulation (tDCS) is a noninvasive neural control technology that has become a research hotspot. To facilitate further research of tDCS, the biosafety of 500 μA cathodal tDCS, a controversial parameter in rats was evaluated.

Results

24 animals were randomly divided into two groups: a cathodal tDCS group (tDCS, n = 12) and control group (control, n = 12). Animals in the tDCS group received 5 consecutive days of cathodal tDCS (500 μA, 15 min, once per day) followed by a tDCS-free interval of 2 days and 5 additional days of stimulation, totally two treatments of tDCS for a total of 10 days. Computational 3D rat model was adopted to calculate the current density distributions in brain during tDCS treatment. Essential brain functions including motor function and learning and memory ability were evaluated. Additionally, to estimate the neurotoxicity of tDCS, the brain morphology, neurotransmitter levels and cerebral temperature were investigated. Our results showed that the current density inside the brain was less than 20 A/m² during tDCS treatment in computational model. tDCS did not affect motor functions and learning and memory ability after tDCS treatment. In addition, no significant differences were found for the tDCS group in hematology, serum biochemical markers or the morphology of major organs. Moreover, tDCS treatment had no effect on the brain morphology, neural structures, neurotransmitter levels or cerebral temperature.

Conclusion

500 μA cathodal tDCS as performed in the present study was safe for rodents.

Electronic supplementary material

The online version of this article (10.1186/s12868-019-0523-7) contains supplementary material, which is available to authorized users.

Electrical Stimulation of the Mesencephalic Locomotor Region Attenuates Neuronal Loss and Cytokine Expression in the Perifocal Region of Photothrombotic Stroke in Rats

Deep brain stimulation of the mesencephalic locomotor region (MLR) improves the motor symptoms in Parkinson’s disease and experimental stroke by intervening in the motor cerebral network. Whether high-frequency stimulation (HFS) of the MLR is involved in non-motor processes, such as neuroprotection and inflammation in the area surrounding the photothrombotic lesion, has not been elucidated. This study evaluates whether MLR-HFS exerts an anti-apoptotic and anti-inflammatory effect on the border zone of cerebral photothrombotic stroke. Rats underwent photothrombotic stroke of the right sensorimotor cortex and the implantation of a microelectrode into the ipsilesional MLR. After intervention, either HFS or sham stimulation of the MLR was applied for 24 h. The infarct volumes were calculated from consecutive brain sections. Neuronal apoptosis was analyzed by TUNEL staining. Flow cytometry and immunohistochemistry determined the perilesional inflammatory response. Neuronal apoptosis was significantly reduced in the ischemic penumbra after MLR-HFS, whereas the infarct volumes did not differ between the groups. MLR-HFS significantly reduced the release of cytokines and chemokines within the ischemic penumbra. MLR-HFS is neuroprotective and it reduces pro-inflammatory mediators in the area that surrounds the photothrombotic stroke without changing the number of immune cells, which indicates that MLR-HFS enables the function of inflammatory cells to be altered on a molecular level.

Noninvasive Brain Stimulation to Enhance Functional Recovery After Stroke: Studies in Animal Models

Background. Stroke is the leading cause of adult disability, but treatment options remain limited, leaving most patients with incomplete recovery. Patient and animal studies have shown potential of noninvasive brain stimulation (NIBS) strategies to improve function after stroke. However, mechanisms underlying therapeutic effects of NIBS are unclear and there is no consensus on which NIBS protocols are most effective. Objective. Provide a review of articles that assessed effects and mechanisms of repetitive transcranial magnetic stimulation (rTMS) and transcranial direct current stimulation (tDCS) in animal stroke models. Methods. Articles were searched in PubMed, including cross-references. Results. Nineteen eligible studies reporting effects of rTMS or tDCS after stroke in small rodents were identified. Seventeen of those described improved functional recovery or neuroprotection compared with untreated control or sham-stimulated groups. The effects of rTMS could be related to molecular mechanisms associated with ischemic tolerance, neuroprotection, anti-apoptosis, neurogenesis, angiogenesis, or neuroplasticity. Favorable outcome appeared most effectively when using high-frequency (>5 Hz) rTMS or intermittent theta burst stimulation of the ipsilesional hemisphere. tDCS effects were strongly dependent on stimulation polarity and onset time. Although these findings are promising, most studies did not meet Good Laboratory Practice assessment criteria. Conclusions. Despite limited data availability, animal stroke model studies demonstrate potential of NIBS to promote stroke recovery through different working mechanisms. Future studies in animal stroke models should adhere to Good Laboratory Practice guidelines and aim to further develop clinically applicable treatment protocols by identifying most favorable stimulation parameters, treatment onset, adjuvant therapies, and underlying modes of action.

Anodal transcranial direct current stimulation prevents methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced neurotoxicity by modulating autophagy in an in vivo mouse model of Parkinson's disease

Parkinson's disease (PD) is a neurodegenerative disorder characterized by the accumulation of protein inclusions and the loss of dopaminergic neurons. Transcranial direct current stimulation (tDCS) is a non-invasive brain-stimulating technique that has demonstrated promising results in clinical studies of PD. Despite accumulating evidence indicating that tDCS exerts a protective effect, the mechanism underlying its activity remains unknown. In the present study, we first investigated the neuroprotective effect of tDCS in a 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced PD mouse model and then evaluated the effect of tDCS on the autophagy pathway. tDCS improved behavioral alterations, increased tyrosine hydroxylase protein levels and suppressed α-synuclein protein levels in MPTP-treated mice. MPTP-treated mice subjected to tDCS also had lower levels of autophagy-related proteins, such as microtubule-associated protein 1 light chain 3 and AMP-activated protein kinase, and higher levels of mechanistic target of rapamycin and p62. In addition, the protein levels of phosphoinositide 3-kinase and brain-derived neurotrophic factor were higher, and the levels of unc-51-like kinase 1 were lower in MPTP-treated mice subjected to tDCS. Our findings suggest that tDCS protected against MPTP-induced PD in a mouse model by modulating autophagy.

Design and Methodology of a Pilot Randomized Controlled Trial of Transcranial Direct Current Stimulation in Acute Middle Cerebral Artery Stroke (STICA)

Background: Stroke is a major cause of death and disability worldwide. The related burden is expected to further increase due to aging populations, calling for more efficient treatment. Ischemic stroke results from a focal reduction in cerebral blood flow due to the sudden occlusion of a brain artery. Ischemic brain injury results from a sequence of pathophysiological events that evolve over time and space. This cascade includes excitotoxicity and peri-infarct depolarizations (PIDs). Focal impairment of cerebral blood flow restricts the delivery of energetics substrates and impairs ionic gradients. Membrane potential is eventually lost, and neurons depolarize. Although recanalization therapies target the ischemic penumbra, they can only rescue the penumbra still present at the time of reperfusion. A promising novel approach is to "freeze" the penumbra until reperfusion occurs. Transcranial direct current stimulation (tDCS) is a non-invasive method of neuromodulation. Based on preclinical evidence, we propose to test the penumbra freezing concept in a clinical phase IIa trial assessing whether cathodal tDCS-shown in rodents to reduce infarction volume-prevents early infarct growth in human acute Middle Cerebral Artery (MCA) stroke, in adjunction to conventional revascularization methods. Methods: This is a monocentric randomized, double-blind, and placebo-controlled trial performed in patients with acute MCA stroke eligible to revascularization procedures. Primary outcome is infarct volume growth on diffusion weighted imaging (DWI) at day 1 relative to baseline. Secondary outcomes include safety and clinical efficacy. Significance: Results from this clinical trial are expected to provide rationale for a phase III study. Clinical trial registration-EUDRACT: 2016-A00160-51.

Using animal models to improve the design and application of transcranial electrical stimulation in humans

Purpose of Review

Transcranial electrical stimulation (tES) is a non-invasive stimulation technique used for modulating brain function in humans. To help tES reach its full therapeutic potential, it is necessary to address a number of critical gaps in our knowledge. Here, we review studies that have taken advantage of animal models to provide invaluable insight about the basic science behind tES.

Recent Findings

Animal studies are playing a key role in elucidating the mechanisms implicated in tES, defining safety limits, validating computational models, inspiring new stimulation protocols, enhancing brain function and exploring new therapeutic applications.

Summary

Animal models provide a wealth of information that can facilitate the successful utilization of tES for clinical interventions in human subjects. To this end, tES experiments in animals should be carefully designed to maximize opportunities for applying discoveries to the treatment of human disease.

Molecular and elemental effects underlying the biochemical action of transcranial direct current stimulation (tDCS) in appetite control

Recent studies highlight that obesity may alter the electric activity in brain areas triggering appetite and craving. Transcranial direct current brain stimulation (tDCS) has recently emerged as a safe alternative for treating food addiction via modulating cortical excitability without any high-risk surgical procedure to be utilized. As for anodal-type tDCS (atDCS), we observe increased excitability and spontaneous firing of the cortical neurons, whilst for the cathodal-type tDCS (ctDCS) a significant decrease is induced. Unfortunately, for the method to be fully used in a clinical setting, its biochemical action mechanism must be precisely defined, although it is proposed that molecular remodelling processes play in concert with brain activity changes involving the ions of: Na, Cl, K and Ca. Herein, we proposed for the first time Fourier transform infrared (FTIR) and synchrotron X-ray fluorescence (SRXRF) microprobes for a combined molecular and elemental analysis in the brain areas implicated appetite control, upon experimental treatment by either atDCS or ctDCS. The study, although preliminary, shows that by stimulating the prefrontal cortex in the rats fed high-caloric nutrients, the feeding behavior can be significantly changed, resulting in significantly inhibited appetite. Both, atDCS and ctDCS produced significant molecular changes involving qualitative and structural properties of lipids, whereas atDCS was found with a somewhat more significant effect on protein secondary structure in all the brain areas investigated. Also, tDCS was reported to reduce surface masses of Na, Cl, K, and Ca in almost all brain areas investigated, although the atDCS deemed to have a stronger neuro-modulating effect. Taken together, one can report that tDCS is an effective treatment technique, and its action mechanism in the appetite control seems to involve a variety of lipid-, protein- and metal/non-metal-ion-driven biochemical changes, regardless the current polarization.

Relationships between muscle mass, intramuscular adipose and fibrous tissues of the quadriceps, and gait independence in chronic stroke survivors: a cross-sectional study

OBJECTIVE

To examine the relationships between muscle mass, intramuscular adipose and fibrous tissues of the quadriceps, and gait independence in chronic stroke survivors.

DESIGN

Cross-sectional study.

SETTING

Hospital-based research.

PARTICIPANTS

Seventeen chronic stroke survivors who were unable to walk independently (non-independent walker group) and 11 chronic stroke survivors who were able to walk independently (independent walker group) participated in this study. In addition, 25 healthy older adults (healthy group) were enrolled.

INTERVENTIONS

None.

MAIN OUTCOME MEASURES

The muscle mass and intramuscular adipose and fibrous tissues of the rectus femoris and vastus intermedius were assessed based on muscle thickness and echo intensity of ultrasound images, respectively.

RESULTS

The thicknesses of the rectus femoris and vastus intermedius on the paretic and non-paretic sides in the non-independent walker group were significantly lower than those in the healthy group (mean difference -0.5 to -0.2cm; P<0.001-0.037). The paretic side in the non-independent walker group had significantly higher rectus femoris and vastus intermedius echo intensity compared with the healthy group (mean difference 15.8-17.4; P=0.007-0.025). The thickness of the rectus femoris on the non-paretic side was significantly lower in the independent walker group than in the healthy group (mean difference -0.3cm; P=0.001).

CONCLUSIONS

These results suggest that chronic stroke survivors who are unable to walk independently are likely to experience secondary changes in skeletal muscle on both the paretic and non-paretic sides.

Glial responses to implanted electrodes in the brain

The use of implants that can electrically stimulate or record electrophysiological or neurochemical activity in nervous tissue is rapidly expanding. Despite remarkable results in clinical studies and increasing market approvals, the mechanisms underlying the therapeutic effects of neuroprosthetic and neuromodulation devices, as well as their side effects and reasons for their failure, remain poorly understood. A major assumption has been that the signal-generating neurons are the only important target cells of neural-interface technologies. However, recent evidence indicates that the supporting glial cells remodel the structure and function of neuronal networks and are an effector of stimulation-based therapy. Here, we reframe the traditional view of glia as a passive barrier, and discuss their role as an active determinant of the outcomes of device implantation. We also discuss the implications that this has on the development of bioelectronic medical devices.

Integrated treatment modality of cathodal-transcranial direct current stimulation with peripheral sensory stimulation affords neuroprotection in a rat stroke model

Cathodal-transcranial direct current stimulation induces therapeutic effects in animal ischemia models by preventing the expansion of ischemic injury during the hyperacute phase of ischemia. However, its efficacy is limited by an accompanying decrease in cerebral blood flow. On the other hand, peripheral sensory stimulation can increase blood flow to specific brain areas resulting in rescue of neurovascular functions from ischemic damage. Therefore, the two modalities appear to complement each other to form an integrated treatment modality. Our results showed that hemodynamics was improved in a photothrombotic ischemia model, as cerebral blood volume and hemoglobin oxygen saturation ([Formula: see text]) recovered to 71% and 76% of the baseline values, respectively. Furthermore, neural activities, including somatosensory-evoked potentials (110% increase), the alpha-to-delta ratio (27% increase), and the [Formula: see text] ratio (27% decrease), were also restored. Infarct volume was reduced by 50% with a 2-fold preservation in the number of neurons and a 6-fold reduction in the number of active microglia in the infarct region compared with the untreated group. Grip strength was also better preserved (28% higher) compared with the untreated group. Overall, this nonpharmacological, nonintrusive approach could be prospectively developed into a clinical treatment modality.

Low intensity transcranial electric stimulation: Safety, ethical, legal regulatory and application guidelines

Low intensity transcranial electrical stimulation (TES) in humans, encompassing transcranial direct current (tDCS), transcutaneous spinal Direct Current Stimulation (tsDCS), transcranial alternating current (tACS), and transcranial random noise (tRNS) stimulation or their combinations, appears to be safe. No serious adverse events (SAEs) have been reported so far in over 18,000 sessions administered to healthy subjects, neurological and psychiatric patients, as summarized here. Moderate adverse events (AEs), as defined by the necessity to intervene, are rare, and include skin burns with tDCS due to suboptimal electrode-skin contact. Very rarely mania or hypomania was induced in patients with depression (11 documented cases), yet a causal relationship is difficult to prove because of the low incidence rate and limited numbers of subjects in controlled trials. Mild AEs (MAEs) include headache and fatigue following stimulation as well as prickling and burning sensations occurring during tDCS at peak-to-baseline intensities of 1-2mA and during tACS at higher peak-to-peak intensities above 2mA. The prevalence of published AEs is different in studies specifically assessing AEs vs. those not assessing them, being higher in the former. AEs are frequently reported by individuals receiving placebo stimulation. The profile of AEs in terms of frequency, magnitude and type is comparable in healthy and clinical populations, and this is also the case for more vulnerable populations, such as children, elderly persons, or pregnant women. Combined interventions (e.g., co-application of drugs, electrophysiological measurements, neuroimaging) were not associated with further safety issues. Safety is established for low-intensity 'conventional' TES defined as <4mA, up to 60min duration per day. Animal studies and modeling evidence indicate that brain injury could occur at predicted current densities in the brain of 6.3-13A/m2 that are over an order of magnitude above those produced by tDCS in humans. Using AC stimulation fewer AEs were reported compared to DC. In specific paradigms with amplitudes of up to 10mA, frequencies in the kHz range appear to be safe. In this paper we provide structured interviews and recommend their use in future controlled studies, in particular when trying to extend the parameters applied. We also discuss recent regulatory issues, reporting practices and ethical issues. These recommendations achieved consensus in a meeting, which took place in Göttingen, Germany, on September 6-7, 2016 and were refined thereafter by email correspondence.

Adverse events of tDCS and tACS: A review

Transcranial direct current stimulation (tDCS) and transcranial alternating current stimulation (tACS) have been applied to many research issues because these stimulation techniques can modulate neural activity in the human brain painlessly and non-invasively with weak electrical currents. However, there are no formal safety guidelines for the selection of stimulus parameters in either tDCS or tACS. As a means of gathering the information that is needed to produce safety guidelines, in this article, we summarize the adverse events of tDCS and tACS. In both stimulation techniques, most adverse effects are mild and disappear soon after stimulation. Nevertheless, several papers have reported that, in tDCS, some adverse events persist even after stimulation. The persistent events consist of skin lesions similar to burns, which can arise even in healthy subjects, and mania or hypomania in patients with depression. Recently, one paper reported a pediatric patient presenting with seizure after tDCS, although the causal relationship between stimulation and seizure is not clear. As this seizure is the only serious adverse events yet reported in connection with tDCS, tDCS is considered safe. In tACS, meanwhile, no persistent adverse events have been reported, but considerably fewer reports are available on the safety of tACS than on the safety of tDCS. Therefore, to establish the safety of tDCS and tACS, we need to scan the literature continuously for information on the adverse events of both stimulation techniques. Further safety investigations are also required.

Safety of Transcranial Direct Current Stimulation: Evidence Based Update 2016

This review updates and consolidates evidence on the safety of transcranial Direct Current Stimulation (tDCS). Safety is here operationally defined by, and limited to, the absence of evidence for a Serious Adverse Effect, the criteria for which are rigorously defined. This review adopts an evidence-based approach, based on an aggregation of experience from human trials, taking care not to confuse speculation on potential hazards or lack of data to refute such speculation with evidence for risk. Safety data from animal tests for tissue damage are reviewed with systematic consideration of translation to humans. Arbitrary safety considerations are avoided. Computational models are used to relate dose to brain exposure in humans and animals. We review relevant dose-response curves and dose metrics (e.g. current, duration, current density, charge, charge density) for meaningful safety standards. Special consideration is given to theoretically vulnerable populations including children and the elderly, subjects with mood disorders, epilepsy, stroke, implants, and home users. Evidence from relevant animal models indicates that brain injury by Direct Current Stimulation (DCS) occurs at predicted brain current densities (6.3-13 A/m(2)) that are over an order of magnitude above those produced by conventional tDCS. To date, the use of conventional tDCS protocols in human trials (≤40 min, ≤4 milliamperes, ≤7.2 Coulombs) has not produced any reports of a Serious Adverse Effect or irreversible injury across over 33,200 sessions and 1000 subjects with repeated sessions. This includes a wide variety of subjects, including persons from potentially vulnerable populations.

Glia: A Neglected Player in Non-invasive Direct Current Brain Stimulation

Non-invasive electrical brain stimulation by application of direct current (DCS) promotes plasticity in neuronal networks in vitro and in in vivo. This effect has been mainly attributed to the direct modulation of neurons. Glia represents approximately 50% of cells in the brain. Glial cells are electrically active and participate in synaptic plasticity. Despite of that, effects of DCS on glial structures and on interaction with neurons are only sparsely investigated. In this perspectives article we review the current literature, present own dose response data and provide a framework for future research from two points of view: first, the direct effects of DCS on glia and second, the contribution of glia to DCS related neuronal plasticity.

An integrated neuroprotective intervention for brain ischemia validated by ECoG-fPAM

Brain ischemia is a neurological deficit caused by a reduction in the blood supply to tissue, and one of the leading causes of disability in the world. Currently, the most well-known therapeutic agent for ischemia recovery is recombinant tissue plasminogen activator (rtPA), but it is viable for only a small portion (approximately 3.6%) of ischemic patients and may cause side effects such as tissue damage. Thus, introducing a new therapeutic concept for ischemia, we proposed an integrated intervention combining global and focal stimulations in this article. To investigate the potential therapeutic effect of cathodal-transcranial direct current stimulation (C-tDCS) with peripheral sensory stimulation (PSS) during the hyperacute phase of stroke, the present study evaluated neurovascular and neuroprotective responses of the rat cortex following ischemic insult. A hybrid, dual-modality system, including electrocorticography (ECoG) and functional photoacoustic microscopy (fPAM), termed ECoG-fPAM, was used to image cortical functional responses pre- and post-ischemia. Using ECoG-fPAM, results showed that cerebral blood volume (CBV) was able to be recovered during the intervention. In addition, neural activity including somatosensory evoked potentials (SSEPs) and alpha-to-delta ratio (ADR) were restored and greater than the baseline value when the integrated intervention was administered. The results of NeuN/ED-1 immunohistochemical staining and TTC staining also supported the neuroprotective effect of this intervention, protecting more neurons and decreasing the infarct size. Overall, the results acquired from the ECoG-fPAM system demonstrated that C-tDCS + PSS administered immediately following ischemia induction can significantly promote neuroprotection via inhibition of ischemia expansion and reversed cortical neurovascular functions, suggesting effective recovery.

Transcranial Direct Current Stimulation Modulates Neurogenesis and Microglia Activation in the Mouse Brain

Transcranial direct current stimulation (tDCS) has been suggested as an adjuvant tool to promote recovery of function after stroke, but the mechanisms of its action to date remain poorly understood. Moreover, studies aimed at unraveling those mechanisms have essentially been limited to the rat, where tDCS activates resident microglia as well as endogenous neural stem cells. Here we studied the effects of tDCS on microglia activation and neurogenesis in the mouse brain. Male wild-type mice were subjected to multisession tDCS of either anodal or cathodal polarity; sham-stimulated mice served as control. Activated microglia in the cerebral cortex and neuroblasts generated in the subventricular zone as the major neural stem cell niche were assessed immunohistochemically. Multisession tDCS at a sublesional charge density led to a polarity-dependent downregulation of the constitutive expression of Iba1 by microglia in the mouse cortex. In contrast, both anodal and, to an even greater extent, cathodal tDCS induced neurogenesis from the subventricular zone. Data suggest that tDCS elicits its action through multifacetted mechanisms, including immunomodulation and neurogenesis, and thus support the idea of using tDCS to induce regeneration and to promote recovery of function. Furthermore, data suggest that the effects of tDCS may be animal- and polarity-specific.

Transcranial direct current stimulation accelerates recovery of function, induces neurogenesis and recruits oligodendrocyte precursors in a rat model of stroke

BACKGROUND

Clinical data suggest that transcranial direct current stimulation (tDCS) may be used to facilitate rehabilitation after stroke. However, data are inconsistent and the neurobiological mechanisms underlying tDCS remain poorly explored, impeding its implementation into clinical routine. In the healthy rat brain, tDCS affects neural stem cells (NSC) and microglia. We here investigated whether tDCS applied after stroke also beneficially affects these cells, which are known to be involved in regeneration and repair.

METHODS

Focal cerebral ischemia was induced in rats by transient occlusion of the middle cerebral artery. Twenty-eight animals with comparable infarcts, as judged by magnetic resonance imaging, were randomized to receive a multi-session paradigm of either cathodal, anodal, or sham tDCS. Behaviorally, recovery of motor function was assessed by Catwalk. Proliferation in the NSC niches was monitored by Positron-Emission-Tomography (PET) employing the radiotracer 3'-deoxy-3'-[(18)F]fluoro-l-thymidine ([(18)F]FLT). Microglia activation was depicted with [(11)C]PK11195-PET. In addition, immunohistochemical analyses were used to quantify neuroblasts, oligodendrocyte precursors, and activation and polarization of microglia.

RESULTS

Anodal and cathodal tDCS both accelerated functional recovery, though affecting different aspects of motor function. Likewise, tDCS induced neurogenesis independently of polarity, while only cathodal tDCS recruited oligodendrocyte precursors towards the lesion. Moreover, cathodal stimulation preferably supported M1-polarization of microglia.

CONCLUSIONS

TDCS acts through multifaceted mechanisms that far exceed its primary neurophysiological effects, encompassing proliferation and migration of stem cells, their neuronal differentiation, and modulation of microglia responses.

Pulsed Transcranial Ultrasound Stimulation Immediately After The Ischemic Brain Injury is Neuroprotective

GOAL

We applied a low-intensity pulsed transcranial ultrasound stimulation (pTUS) to the ischemic cortex after a distal middle cerebral artery occlusion (dMCAO) to study whether pTUS is capable of protecting brain from ischemic injury.

METHODS

Rats were randomly assigned to Sham (n = 6), Control (n = 16), and pTUS (n = 16) groups. The pTUS-treated rats were subjected to 60-min ultrasonic stimulation immediately after the ischemia. After 48 h, the sensorimotor-related behavioral outcomes were assessed by a neurological severity score (NSS), and the permanent brain injury was assessed by the histologic analysis of TTC staining of brain slices.

RESULTS

pTUS group showed significantly lower NSS (n = 10, 5.5 ± 2.5) than the Control group ( n = 10, 10.5 ±1.4) (p < 0.01). Concordantly, the ischemic lesion was significantly reduced after receiving pTUS immediately after dMCAO. The cortical infarct volume in the control group was more than threefold of the pTUS group (43.39% ± 2.33%, n = 16 versus 13.78% ± 8.18%, n = 16, p < 0.01). Immunohistochemical staining indicated reduction of neutrophils in the affected area, and laser speckle imaging showed significant increase of a cerebral blood flow after pTUS, which consistently supported the neuroprotection of pTUS in ischemic brain injury.

CONCLUSION

Both behavior and histological results suggested that pTUS on ischemic core immediately after ischemic stroke could be neuroprotective.

SIGNIFICANCE

The noninvasiveness and high spatiotemporal resolution of pTUS makes it a unique neuromodulation technique in comparison with the current TMS and tDCS.

The morphological and molecular changes of brain cells exposed to direct current electric field stimulation

BACKGROUND

The application of low-intensity direct current electric fields has been experimentally used in the clinic to treat a number of brain disorders, predominantly using transcranial direct current stimulation approaches. However, the cellular and molecular changes induced by such treatment remain largely unknown.

METHODS

Here, we tested various intensities of direct current electric fields (0, 25, 50, and 100V/m) in a well-controlled in vitro environment in order to investigate the responses of neurons, microglia, and astrocytes to this type of stimulation. This included morphological assessments of the cells, viability, as well as shape and fiber outgrowth relative to the orientation of the direct current electric field. We also undertook enzyme-linked immunosorbent assays and western immunoblotting to identify which molecular pathways were affected by direct current electric fields.

RESULTS

In response to direct current electric field, neurons developed an elongated cell body shape with neurite outgrowth that was associated with a significant increase in growth associated protein-43. Fetal midbrain dopaminergic explants grown in a collagen gel matrix also showed a reorientation of their neurites towards the cathode. BV2 microglial cells adopted distinct morphological changes with an increase in cyclooxygenase-2 expression, but these were dependent on whether they had already been activated with lipopolysaccharide. Finally, astrocytes displayed elongated cell bodies with cellular filopodia that were oriented perpendicularly to the direct current electric field.

CONCLUSION

We show that cells of the central nervous system can respond to direct current electric fields both in terms of their morphological shape and molecular expression of certain proteins, and this in turn can help us to begin understand the mechanisms underlying the clinical benefits of direct current electric field.

Transcranial direct current stimulation promotes the mobility of engrafted NSCs in the rat brain

Transcranial direct current stimulation (tDCS) is used in numerous clinical studies and considered an effective and versatile add-on therapy in neurorehabilitation. To date, however, the underlying neurobiological mechanisms remain elusive. In a rat model of tDCS, we recently observed a polarity-dependent accumulation of endogenous neural stem cells (NSCs) in the stimulated cortex. Based upon these findings, we hypothesized that tDCS may exert a direct migratory effect on endogenous NSCs towards the stimulated cortex. Using noninvasive imaging, we here investigated whether tDCS may also cause a directed migration of engrafted NSCs. Murine NSCs were labeled with superparamagnetic particles of iron oxide (SPIOs) and implanted into rat striatum and corpus callosum. MRI was performed (i) immediately after implantation and (ii) after 10 tDCS sessions of anodal or cathodal polarity. Sham-stimulated rats served as control. Imaging results were validated ex vivo using immunohistochemistry. Overall migratory activity of NSCs almost doubled after anodal tDCS. However, no directed migration within the electric field (i.e. towards or away from the electrode) could be observed. Rather, an undirected outward migration from the center of the graft was detected. Xenograft transplantation induced a neuroinflammatory response that was significantly enhanced following cathodal tDCS. This inflammatory response did not impact negatively on the survival of implanted NSCs. Data suggest that anodal tDCS increases the undirected migratory activity of implanted NSCs. Since the electric field did not guide implanted NSCs over large distances, previously observed polarity-dependent accumulation of endogenous NSCs in the cortex might have originated from local proliferation. Results enhance our understanding of the neurobiological mechanisms underlying tDCS, and may thereby help to develop a targeted and sustainable application of tDCS in clinical practice.

Cellular and molecular mechanisms of action of transcranial direct current stimulation: evidence from in vitro and in vivo models

Transcranial direct current stimulation is a noninvasive technique that has been experimentally tested for a number of psychiatric and neurological conditions. Preliminary observations suggest that this approach can indeed influence a number of cellular and molecular pathways that may be disease relevant. However, the mechanisms of action underlying its beneficial effects are largely unknown and need to be better understood to allow this therapy to be used optimally. In this review, we summarize the physiological responses observed in vitro and in vivo, with a particular emphasis on cellular and molecular cascades associated with inflammation, angiogenesis, neurogenesis, and neuroplasticity recruited by direct current stimulation, a topic that has been largely neglected in the literature. A better understanding of the neural responses to transcranial direct current stimulation is critical if this therapy is to be used in large-scale clinical trials with a view of being routinely offered to patients suffering from various conditions affecting the central nervous system.

Fractal dimension of EEG activity senses neuronal impairment in acute stroke

The brain is a self-organizing system which displays self-similarities at different spatial and temporal scales. Thus, the complexity of its dynamics, associated to efficient processing and functional advantages, is expected to be captured by a measure of its scale-free (fractal) properties. Under the hypothesis that the fractal dimension (FD) of the electroencephalographic signal (EEG) is optimally sensitive to the neuronal dysfunction secondary to a brain lesion, we tested the FD's ability in assessing two key processes in acute stroke: the clinical impairment and the recovery prognosis. Resting EEG was collected in 36 patients 4-10 days after a unilateral ischemic stroke in the middle cerebral artery territory and 19 healthy controls. National Health Institute Stroke Scale (NIHss) was collected at T0 and 6 months later. Highuchi FD, its inter-hemispheric asymmetry (FDasy) and spectral band powers were calculated for EEG signals. FD was smaller in patients than in controls (1.447±0.092 vs 1.525±0.105) and its reduction was paired to a worse acute clinical status. FD decrease was associated to alpha increase and beta decrease of oscillatory activity power. Larger FDasy in acute phase was paired to a worse clinical recovery at six months. FD in our patients captured the loss of complexity reflecting the global system dysfunction resulting from the structural damage. This decrease seems to reveal the intimate nature of structure-function unity, where the regional neural multi-scale self-similar activity is impaired by the anatomical lesion. This picture is coherent with neuronal activity complexity decrease paired to a reduced repertoire of functional abilities. FDasy result highlights the functional relevance of the balance between homologous brain structures' activities in stroke recovery.

Fractal dimension of EEG activity senses neuronal impairment in acute stroke

The brain is a self-organizing system which displays self-similarities at different spatial and temporal scales. Thus, the complexity of its dynamics, associated to efficient processing and functional advantages, is expected to be captured by a measure of its scale-free (fractal) properties. Under the hypothesis that the fractal dimension (FD) of the electroencephalographic signal (EEG) is optimally sensitive to the neuronal dysfunction secondary to a brain lesion, we tested the FD's ability in assessing two key processes in acute stroke: the clinical impairment and the recovery prognosis. Resting EEG was collected in 36 patients 4-10 days after a unilateral ischemic stroke in the middle cerebral artery territory and 19 healthy controls. National Health Institute Stroke Scale (NIHss) was collected at T0 and 6 months later. Highuchi FD, its inter-hemispheric asymmetry (FDasy) and spectral band powers were calculated for EEG signals. FD was smaller in patients than in controls (1.447±0.092 vs 1.525±0.105) and its reduction was paired to a worse acute clinical status. FD decrease was associated to alpha increase and beta decrease of oscillatory activity power. Larger FDasy in acute phase was paired to a worse clinical recovery at six months. FD in our patients captured the loss of complexity reflecting the global system dysfunction resulting from the structural damage. This decrease seems to reveal the intimate nature of structure-function unity, where the regional neural multi-scale self-similar activity is impaired by the anatomical lesion. This picture is coherent with neuronal activity complexity decrease paired to a reduced repertoire of functional abilities. FDasy result highlights the functional relevance of the balance between homologous brain structures' activities in stroke recovery.

Neuroprotective effect of cathodal transcranial direct current stimulation in a rat stroke model

Experimental focal brain ischemia generates in the penumbra recurrent depolarizations which spread across the injured cortex inducing infarct growth. Transcranial direct current stimulation can induce a lasting, polarity-specific, modulation of cortical excitability. To verify whether cathodal transcranial direct current stimulation could reduce the infarct size and the number of depolarizations, focal ischemia was induced in the rat by the 3 vessels occlusion technique. In the first experiment 12 ischemic rats received cathodal stimulation (alternating 15 min on and 15 min off) starting 45 min after middle cerebral artery occlusion and lasting 4 h. In the second experiment 12 ischemic rats received cathodal transcranial direct current stimulation with the same protocol but starting soon after middle cerebral artery occlusion and lasting 6 h. In both experiments controls were 12 ischemic rats not receiving stimulation. Cathodal stimulation reduced the infarct volume in the first experiment by 20% (p=0.002) and in the second by 30% (p=0.003). The area of cerebral infarction was smaller in animals receiving cathodal stimulation in both experiments (p=0.005). Cathodal stimulation reduced the number of depolarizations (p=0.023) and infarct volume correlated with the number of depolarizations (p=0.048). Our findings indicate that cathodal transcranial direct current stimulation exert a neuroprotective effect in the acute phase of stroke possibly decreasing the number of spreading depolarizations. These findings may have translational relevance and open a new avenue in neuroprotection of stroke in humans.

The role of the immune system in central nervous system plasticity after acute injury

Acute brain injuries cause rapid cell death that activates bidirectional crosstalk between the injured brain and the immune system. In the acute phase, the damaged CNS activates resident and circulating immune cells via the local and systemic release of soluble mediators. This early immune activation is necessary to confine the injured tissue and foster the clearance of cellular debris, thus bringing the inflammatory reaction to a close. In the chronic phase, a sustained immune activation has been described in many CNS disorders, and the degree of this prolonged response has variable effects on spontaneous brain regenerative processes. The challenge for treating acute CNS damage is to understand how to optimally engage and modify these immune responses, thus providing new strategies that will compensate for tissue lost to injury. Herein we have reviewed the available information regarding the role and function of the innate and adaptive immune responses in influencing CNS plasticity during the acute and chronic phases of after injury. We have examined how CNS damage evolves along the activation of main cellular and molecular pathways that are associated with intrinsic repair, neuronal functional plasticity and facilitation of tissue reorganization.