Chronic high-frequency repetitive transcranial magnetic stimulation improves age-related cognitive impairment in parallel with alterations in neuronal excitability and the voltage-dependent Ca2+ current in female mice

Low-frequency rTMS modulated the excitability and high-frequency firing in hippocampal neurons of the Alzheimer's disease mouse model

Repetitive transcranial magnetic stimulation (rTMS), a non-invasive brain stimulation technique, holds potential for applications in the treatment of Alzheimer's disease (AD). This study aims to compare the therapeutic effects of rTMS at different frequencies on Alzheimer's disease and explore the alterations in neuronal electrophysiological properties throughout this process. APP/PS1 AD mice were subjected to two rTMS treatments at 0.5 Hz and 20 Hz, followed by assessments of therapeutic outcomes through the Novel Object Recognition (NOR) and Morris Water Maze (MWM) tests. Following this, whole-cell patch-clamp techniques were used to record action potential, voltage-gated sodium channel currents, and voltage-gated potassium channel currents in dentate gyrus granule neurons. The results show that AD mice exhibit significant cognitive decline compared to normal mice, along with a pronounced reduction in neuronal excitability and ion channel activity. Both frequencies of rTMS treatment partially reversed these changes, demonstrating similar therapeutic efficacy. Furthermore, the investigation indicates that low-frequency magnetic stimulation inhibited the concentrated firing of early action potentials in AD.

Magnetic Stimulation as a Therapeutic Approach for Brain Modulation and Repair: Underlying Molecular and Cellular Mechanisms

Neurological and psychiatric diseases generally have no cure, so innovative non-pharmacological treatments, including non-invasive brain stimulation, are interesting therapeutic tools as they aim to trigger intrinsic neural repair mechanisms. A common brain stimulation technique involves the application of pulsed magnetic fields to affected brain regions. However, investigations of magnetic brain stimulation are complicated by the use of many different stimulation parameters. Magnetic brain stimulation is usually divided into two poorly connected approaches: (1) clinically used high-intensity stimulation (0.5-2 Tesla, T) and (2) experimental or epidemiologically studied low-intensity stimulation (μT-mT). Human tests of both approaches are reported to have beneficial outcomes, but the underlying biology is unclear, and thus optimal stimulation parameters remain ill defined. Here, we aim to bring together what is known about the biology of magnetic brain stimulation from human, animal, and in vitro studies. We identify the common effects of different stimulation protocols; show how different types of pulsed magnetic fields interact with nervous tissue; and describe cellular mechanisms underlying their effects-from intracellular signalling cascades, through synaptic plasticity and the modulation of network activity, to long-term structural changes in neural circuits. Recent advances in magneto-biology show clear mechanisms that may explain low-intensity stimulation effects in the brain. With its large breadth of stimulation parameters, not available to high-intensity stimulation, low-intensity focal magnetic stimulation becomes a potentially powerful treatment tool for human application.

Repetitive transcranial magnetic stimulation enhances the neuronal excitability of mice by regulating dynamic characteristics of Granule cells' Ion channels

This study aims to explore the effects of acute high-frequency repetitive transcranial magnetic stimulation (hf-rTMS) on neuronal excitability of granule cells in the hippocampal dentate gyrus, as well as the underlying intrinsic mediating mechanisms by which rTMS regulates neuronal excitability. First, high-frequency single TMS was used to measure the motor threshold (MT) of mice. Then, rTMS with different intensities of 0 MT (control), 0.8 MT, and 1.2 MT were applied to acute mice brain slices. Next, patch-clamp technique was used to record the resting membrane potential and evoked nerve discharge of granule cells, as well as the voltage-gated sodium current (I Na) of voltage-gated sodium channels (VGSCs), transient outward potassium current (I A) and delayed rectifier potassium current (I K) of voltage-gated potassium channels (Kv). Results showed that acute hf-rTMS in both 0.8 MT and 1.2 MT groups significantly activated I Na and inhibited I A and I K compared with control group, due to the changes of dynamic characteristics of VGSCs and Kv. Acute hf-rTMS in both 0.8 MT and 1.2 MT groups significantly increased membrane potential and nerve discharge frequency. Therefore, changing dynamic characteristics of VGSCs and Kv, activating I Na and inhibiting I A and I K might be one of the intrinsic mediating mechanisms by which rTMS enhanced the neuronal excitability of granular cells, and this regulatory effect increased with the increase of stimulus intensity.

Double-target neural circuit-magnetic stimulation improves motor function in spinal cord injury by attenuating astrocyte activation

Multi-target neural circuit-magnetic stimulation has been clinically shown to improve rehabilitation of lower limb motor function after spinal cord injury. However, the precise underlying mechanism remains unclear. In this study, we performed double-target neural circuit-magnetic stimulation on the left motor cortex and bilateral L5 nerve root for 3 successive weeks in a rat model of incomplete spinal cord injury caused by compression at T10. Results showed that in the injured spinal cord, the expression of the astrocyte marker glial fibrillary acidic protein and inflammatory factors interleukin 1β, interleukin-6, and tumor necrosis factor-α had decreased, whereas that of neuronal survival marker microtubule-associated protein 2 and synaptic plasticity markers postsynaptic densification protein 95 and synaptophysin protein had increased. Additionally, neural signaling of the descending corticospinal tract was markedly improved and rat locomotor function recovered significantly. These findings suggest that double-target neural circuit-magnetic stimulation improves rat motor function by attenuating astrocyte activation, thus providing a theoretical basis for application of double-target neural circuit-magnetic stimulation in the clinical treatment of spinal cord injury.

Anesthesia inhibited corticospinal excitability and attenuated the modulation of repetitive transcranial magnetic stimulation

BACKGROUND

Lots of studies have measured motor evoked potential (MEP) induced by transcranial magnetic stimulation (TMS) in anesthetized animals. However, in awake animals, the measurement of TMS-induced MEP is scarce as lack of sufficient restraint. So far, the explicit study of anesthesia effects on corticospinal excitability and repetitive TMS (rTMS) induced modulation is still lacking. This study aimed to: (1) measure TMS-induced MEP in both awake restrained and anesthetized rats, (2) investigate the effect of anesthesia on corticospinal excitability, and (3) on rTMS-induced modulation.

METHODS

MEP of eighteen rats were measured under both wakefulness and anesthesia using flexible binding and surface electrodes. Peak-to-peak MEP amplitudes, resting motor threshold (RMT) and the slope of stimulus response (SR) were extracted to investigate anesthesia effects on corticospinal excitability. Thereafter, 5 or 10 Hz rTMS was applied with 600 pulses, and the increase in MEP amplitude and the decrease in RMT were used to quantify rTMS-induced modulation.

RESULTS

The RMT in the awake condition was 44.6 ± 1.2% maximum output (MO), the peak-to-peak MEP amplitude was 404.6 ± 48.8 μV at 60% MO. Under anesthesia, higher RMT (55.6 ± 2.9% MO), lower peak-to-peak MEP amplitudes (258.6 ± 32.7 μV) and lower slope of SR indicated that the corticospinal excitability was suppressed. Moreover, under anesthesia, high-frequency rTMS still showed significant modulation of corticospinal excitability, but the modulation of MEP peak-to-peak amplitudes was weaker than that under wakefulness.

CONCLUSIONS

This study measured TMS-induced MEP in both awake and anesthetized rats, and provided explicit evidence for the inhibitory effects of anesthesia on corticospinal excitability and on high-frequency rTMS-induced modulation of MEP.

Benefits from Repetitive Transcranial Magnetic Stimulation in Post-Stroke Rehabilitation

Stroke is an acute neurovascular central nervous system (CNS) injury and one of the main causes of long-term disability and mortality. Post-stroke rehabilitation as part of recovery is focused on relearning lost skills and regaining independence as much as possible. Many novel strategies in neurorehabilitation have been introduced. This review focuses on current evidence of the effectiveness of repetitive transcranial magnetic stimulation (rTMS), a noninvasive brain stimulation (NIBS), in post-stroke rehabilitation. Moreover, we present the effects of specific interventions, such as low-frequency or high-frequency rTMS therapy, on motor function, cognitive function, depression, and aphasia in post-stroke patients. Collected data suggest that high-frequency stimulation (5 Hz and beyond) produces an increase in cortical excitability, whereas low-frequency stimulation (≤1 Hz) decreases cortical excitability. Accumulated data suggest that rTMS is safe and can be used to modulate cortical excitability, which may improve overall performance. Side effects such as tingling sensation on the skin of the skull or headache are possible. Serious side effects such as epileptic seizures can be avoided by adhering to international safety guidelines. We reviewed clinical studies that present promising results in general recovery and stimulating neuroplasticity. This article is an overview of the current rTMS state of knowledge related to benefits in stroke, as well as its cellular and molecular mechanisms. In the stroke rehabilitation literature, there is a key methodological problem of creating double-blinding studies, which are very often impossible to conduct.

Repetitive Transcranial Magnetic Stimulation (rTMS) Modulates Thyroid Hormones Level and Cognition in the Recovery Stage of Stroke Patients with Cognitive Dysfunction

Background

This single-center study aimed to investigate the effects of repetitive transcranial magnetic stimulation (rTMS) on modulation of thyroid hormone levels and cognition in the recovery stage of patients with cognitive dysfunction following stroke.

Material/Methods

Seventy post-stroke patients who had cognitive impairment were randomly assigned to either the rTMS group or the control (sham) group. Both groups were administered basic treatment, with the rTMS group receiving rTMS (1 Hz, 90% MT, 1000 pulse/20 min, once a day for 5 days, for a total of 20 times), the stimulation site was the contralateral dorsolateral prefrontal cortex (DLPFC), and the sham group receiving sham stimulation which had the same stimulation parameters and site, except that the coil plane was placed perpendicular to the surface of the scalp. Cognitive function assessment and thyroid function tests were performed before and after 4 weeks of treatment.

Results

Serum levels of triiodothyronine (T3), free triiodothyronine (FT3), and thyroid stimulating hormone (TSH) showed a positive correlation with Montreal Cognitive Assessment (MoCA) scale score of stroke patients in the recovery phase. The post-treatment change in the scores of MoCA and Modified Barthel Index (MBI) and scores of 3 cognitive domains (visuospatial function, memory, and attention), as well as serum T3, FT3, and TSH levels, were improved more significantly in the rTMS group, and T3 and FT3 levels significantly affected the MoCA scores within the reference range.

Conclusions

Serum T3, FT3, and TSH levels of stroke patients in the recovery phase were positively correlated with MoCA score. rTMS increased T3, FT3, and TSH levels and also improved MoCA and MBI of patients in the recovery phase of stroke.

Effects of repetitive Transcranial Magnetic Stimulation in aged rats depend on pre-treatment cognitive status: Toward individualized intervention for successful cognitive aging

BACKGROUND

Repetitive Transcranial Magnetic Stimulation (rTMS) has shown initial promise in combating age-related cognitive decline and dementia. The nature and severity of cognitive aging, however, varies markedly between individuals.

OBJECTIVE/HYPOTHESIS

We hypothesized that the distinct constellation of brain changes responsible for individual differences in cognitive aging might influence the response to rTMS.

METHODS

Cognitive effects of rTMS were evaluated using a rat model of cognitive aging in which aged rats are classified as Aged-Impaired (AI) or -Unimpaired (AU) relative to young (Y) according to their performance in the Morris water maze. Several weeks later, following presentation of a sample odor in an olfactory recognition task, rats received either sham (Y, n = 9; AU, n = 8; AI, n = 9) or intermittent Theta Burst Stimulation (Y, n = 8; AU, n = 8; AI, n = 9). Memory was tested 24 h later.

RESULTS

Recognition memory in the sham and stimulated conditions depended on pre-treatment cognitive status in the aged rats. Y and AU sham rats displayed robust odor recognition, whereas sham-treated AI rats exhibited no retention. In contrast, rTMS treated AI rats showed robust retention, comparable in magnitude to Y, whereas the AU stimulated scored at chance.

CONCLUSION

Our results are consistent with a perspective that the unique neurobiology associated with variability in cognitive aging modulates the response to rTMS. Protocols with documented efficacy in young adults may have unexpected outcomes in aging or neurodegenerative conditions, requiring individualized approaches.

Immediate and cumulative effects of high-frequency repetitive transcranial magnetic stimulation on cognition and neuronal excitability in mice

This study primarily explored the potential effects of high-frequency (20 Hz) repetitive transcranial magnetic stimulation (rTMS) with different intervention protocols on cognition and neuronal excitability in mice. Mice were randomly divided into 4 groups: a control group that received sham stimulation, an rTMS in vitro group whose acute brain slices received high-frequency stimulation, an rTMS 1 d group that received high-frequency stimulation for only 1 d, and an rTMS 15 d group that received high-frequency stimulation for 15 d. The novel object recognition and step-down tests were used to assess cognitive ability. The patch-clamp technique was used to record the membrane potentials and neural discharges of dentate gyrus granule cells to evaluate neuronal excitability. Results revealed that cognition and neuronal excitability in the rTMS 15 d group were significantly increased than that in the control and rTMS 1 d groups. The neuronal excitability in the rTMS in vitro group was also significantly increased than that in the control and rTMS 1 d groups. No significant changes were observed between the control and rTMS 1 d groups. These results suggested that high-frequency rTMS applied to the acute brain slices of mice in vitro exerted an immediate effect on increasing neuronal excitability. Chronic high-frequency rTMS applied to the brain of mice in vivo exerted a cumulative effect in improving cognition and increasing neuronal excitability.

rTMS-Induced Changes in Glutamatergic and Dopaminergic Systems: Relevance to Cocaine and Methamphetamine Use Disorders

Cocaine use disorder and methamphetamine use disorder are chronic, relapsing disorders with no US Food and Drug Administration-approved interventions. Repetitive transcranial magnetic stimulation (rTMS) is a non-invasive brain stimulation tool that has been increasingly investigated as a possible therapeutic intervention for substance use disorders. rTMS may have the ability to induce beneficial neuroplasticity in abnormal circuits and networks in individuals with addiction. The aim of this review is to highlight the rationale and potential for rTMS to treat cocaine and methamphetamine dependence: we synthesize the outcomes of studies in healthy humans and animal models to identify and understand the neurobiological mechanisms of rTMS that seem most involved in addiction, focusing on the dopaminergic and glutamatergic systems. rTMS-induced changes to neurotransmitter systems include alterations to striatal dopamine release and metabolite levels, as well as to glutamate transporter and receptor expression, which may be relevant for ameliorating the aberrant plasticity observed in individuals with substance use disorders. We also discuss the clinical studies that have used rTMS in humans with cocaine and methamphetamine use disorders. Many such studies suggest changes in network connectivity following acute rTMS, which may underpin reduced craving following chronic rTMS. We suggest several possible future directions for research relating to the therapeutic potential of rTMS in addiction that would help fill current gaps in the literature. Such research would apply rTMS to animal models of addiction, developing a translational pipeline that would guide evidence-based rTMS treatment of cocaine and methamphetamine use disorder.

High Frequency Repetitive Transcranial Magnetic Stimulation Alleviates Cognitive Impairment and Modulates Hippocampal Synaptic Structural Plasticity in Aged Mice

Normal aging is accompanied by hippocampus-dependent cognitive impairment, which is a risk factor of Alzheimer’s disease. This study aims to investigate the effect of high frequency-repetitive transcranial magnetic stimulation (HF-rTMS) on hippocampus-dependent learning and memory in aged mice and explore its underlying mechanisms. Forty-five male Kunming mice (15 months old) were randomly divided into three groups: aged sham, 5 Hz rTMS, and 25 Hz rTMS. Two sessions of 5 Hz or 25 Hz rTMS comprising 1,000 pulses in 10 trains were delivered once a day for 14 consecutive days. The aged sham group was treated by the reverse side of the coil. In the adult sham group, 15 male Kunming mice (3 months old) were treated the same way as the aged sham group. A Morris water maze (MWM) was conducted following the stimulation, and synaptic ultrastructure was observed through a transmission electron microscope. HF-rTMS improved spatial learning and memory impairment in the aged mice, and 5 Hz was more significant than 25 Hz. Synaptic plasticity-associated gene profiles were modified by HF-rTMS, especially neurotrophin signaling pathways and cyclic adenosine monophosphate response element binding protein (CREB) cofactors. Compared to the aged sham group, synaptic plasticity-associated proteins, i.e., synaptophysin (SYN) and postsynaptic density (PSD)-95 were increased; brain-derived neurotrophic factor (BDNF) and phosphorylated CREB (pCREB) significantly increased after the 5 Hz HF-rTMS treatment. Collectively, our results suggest that HF-rTMS ameliorated cognitive deficits in naturally aged mice. The 5 Hz rTMS treatment significantly enhanced synaptic structural plasticity and activated the BDNF/CREB pathway in the hippocampus.

Age-related alterations of neuronal excitability and voltage-dependent Ca2+ current in a spontaneous mouse model of Alzheimer's disease

Alzheimer's disease (AD) is the most common age-dependent neurodegenerative disorder, characterized by a progressive dysfunction of central neurons, and senescence-accelerated mouse prone 8 (SAMP8), a spontaneous AD mouse model, appears to be an excellent model to investigate the process of AD. Previous studies have indicated that neuronal excitability is impaired in transgenic AD mice. In this study, the cognition of SAMP8 mice was tested using the passive avoidance task and Morris water maze; whole-cell current-clamp recordings were used to evaluate the neuronal excitability, including the resting membrane potential, the number of action potentials, and after-hyperpolarization; and the voltage-dependent Ca²⁺ current in hippocampal slices was measured using whole-cell voltage-clamp recordings. We found that compared to the young mice, the performance in the learning and memory behavior tasks was impaired in aged mice, and the hippocampal CA1 pyramidal neurons of the aged mice showed a significantly depolarized resting membrane potential, increased numbers of action potentials after injection of depolarizing current, and increased after-hyperpolarization after the action potentials. Consistent with the above changes, the voltage-dependent Ca²⁺ current was larger in aged mice than in young mice. These data suggested that the aged SAMP8 neurons were hyperexcitable, and the alterations in the voltage-dependent Ca²⁺ current of aged neurons occurred in parallel to the elevation in excitability.

Repetitive transcranial magnetic stimulation enhances spatial learning and synaptic plasticity via the VEGF and BDNF-NMDAR pathways in a rat model of vascular dementia

This study aimed to evaluate the effects of repetitive transcranial magnetic stimulation (rTMS) on learning and memory in a rat model of vascular dementia (VaD) and to analyze the associated mechanisms. Bilateral carotid artery occlusion (2-VO) was used to establish a rat model of VaD. High-frequency (5Hz) rTMS was performed on rats for four weeks. Spatial learning and memory abilities were evaluated using the Morris water maze (MWM), and synaptic plasticity in the hippocampus was assessed via long-term potentiation (LTP). Hippocampal expression of vascular endothelial growth factor (VEGF), brain-derived neurotrophic factor (BDNF) and three subunits of the N-methyl-D-aspartic acid receptor (NMDAR), NR1, NR2A and NR2B, was analyzed by Western blotting. Compared with the VaD group, escape latency was decreased (P<0.05) and the time spent in the target quadrant and the percentage of swimming distance within that quadrant were increased (P<0.05) in the rTMS group. LTP at hippocampal CA3-CA1 synapses was enhanced by rTMS (P<0.05). VEGF expression was up-regulated following 2-VO and was further increased by rTMS (P<0.05). BDNF, NR1 and NR2B expression was decreased in the VaD group and increased by rTMS (P<0.05). There were no significant differences in NR2A expression among the three groups. These results suggest that rTMS improved learning and memory in the VaD model rats via the up-regulation of VEGF, BDNF and NMDARs. In addition, NR2B may be more important than NR2A for LTP induction in the hippocampus during rTMS treatment of VaD.