Focused ultrasound excites cortical neurons via mechanosensitive calcium accumulation and ion channel amplification

Transcranial ultrasound neuromodulation facilitates isoflurane-induced general anesthesia recovery and improves cognition in mice

Delayed arousal and cognitive dysfunction are common, especially in older patients after general anesthesia (GA). Elevating central nervous system serotonin (5-HT) levels can promote recovery from GA and increase synaptic plasticity to improve cognition. Ultrasound neuromodulation has become a noninvasive physical intervention therapy with high spatial resolution and penetration depth, which can modulate neuronal excitability to treat psychiatric and neurodegenerative diseases. This study aims to use ultrasound to noninvasively modulate the brain 5-HT levels of mice to promote recovery from GA and improve cognition in mice. The dorsal raphe nucleus (DRN) of mice during GA was stimulated by the 1.1 MHz ultrasound with a negative pressure of 356 kPa, and the liquid chromatography coupled tandem mass spectrometry (LC-MS/MS) method was used to measure the DRN 5-HT concentrations. The mice's recovery time from GA was assessed, and the cognition was evaluated through spontaneous alternation Y-maze and novel object recognition (NOR) tests. After ultrasound stimulation, the mice's DRN 5-HT levels were significantly increased (control: 554.0 ± 103.2 ng/g, anesthesia + US: 664.2 ± 84.1 ng/g, *p = 0.0389); the GA recovery time (return of the righting reflex (RORR) emergence latency time) of mice was significantly reduced (anesthesia: 331.6 ± 70 s, anesthesia + US: 223.2 ± 67.7 s, *p = 0.0215); the spontaneous rotation behavior score of mice was significantly increased (anesthesia: 59.46 ± 5.26 %, anesthesia + US: 68.55 ± 5.24 %; *p = 0.0126); the recognition index was significantly increased (anesthesia: 55.02 ± 6.23 %, anesthesia + US: 78.52 ± 12.21 %; ***p = 0.0009). This study indicates that ultrasound stimulation of DRN increases serotonin levels, accelerates recovery from anesthesia, and improves cognition, which could be an important strategy for treating delayed arousal, postoperative delirium, or even lasting cognitive dysfunction after GA.

Modeling ultrasound modulation of neural function in a single cell

Background

Low intensity ultrasound stimulation has been shown to non-invasively modulate neural function in the central nervous system (CNS) and peripheral nervous system (PNS) with high precision. Ultrasound sonication is capable of either excitation or inhibition, depending on the ultrasound parameters used. On the other hand, the mode of interaction of ultrasonic waves with the neural tissue for effective neuromodulation remains ambiguous.

New method

Here within we propose a numerical model that incorporates the mechanical effects of ultrasound stimulation on the Hodgkin-Huxley (HH) neuron by incorporating the relation between increased external pressure and the membrane induced tension, with a stress on the flexoelectric effect on the neural membrane. The external pressure causes an increase in the total tension of the membrane thus affecting the probability of the ion channels being open after the conformational changes that those channels undergo.

Results

The interplay between varying the acoustic intensities and frequencies depicts different action potential suppression rates, whereby a combination of low intensity and low frequency ultrasound sonication proved to be the most effective in modulating neural function.Comparison with Existing Methods: Our method solely depends on the HH model of a single neuron and the linear flexoelectric effect of the dielectric neural membrane, when under an ultrasound-induced mechanical strain, while varying the ion-channels conductances based on different sonication frequencies and intensities. We study the effect of ultrasound parameters on the firing rate, latency, and action potential amplitude of a HH neuron for a better understanding of the neuromodulation modality of ultrasound stimulation (in the continuous and pulsed modes).

Conclusions

This simulation work confirms the published experimental data that low intensity and low frequency ultrasound sonication has a higher success rate of modulating neural firing.

No ultrasounds detected from fungi when dehydrated

Many organisms (including certain plant species) can be observed to emit sounds, potentially signifying threat alerts. Sensitivity to such sounds and vibrations may also play an important role in the lives of fungi. In this work, we explore the potential of ultrasound activity in dehydrating fungi, and discover that several species of fungi do not emit sounds (detectable with conventional instrumentation) in the frequency range of 10kHz to 210kHz upon dehydration. Over 5 terabytes of ultrasound recordings were collected and analysed. We conjecture that fungi interact via non-sound means, such as electrical or chemical.

Transcranial ultrasound stimulation at the peak-phase of theta-cycles in the hippocampus improve memory performance

The present study aimed to investigate the effectiveness of closed-loop transcranial ultrasound stimulation (closed-loop TUS) as a non-invasive, high temporal-spatial resolution method for modulating brain function to enhance memory. For this purpose, we applied closed-loop TUS to the CA1 region of the rat hippocampus for 7 consecutive days at different phases of theta cycles. Following the intervention, we evaluated memory performance through behavioral testing and recorded the neural activity. Our results indicated that closed-loop TUS applied at the peak phase of theta cycles significantly improves the memory performance in rats, as evidenced by behavioral testing. Furthermore, we observed that closed-loop TUS modifies the power and cross-frequency coupling strength of local field potentials (LFPs) during memory task, as well as modulates neuronal activity patterns and synaptic transmission, depending on phase of stimulation relative to theta rhythm. We demonstrated that closed-loop TUS can modulate neural activity and memory performance in a phase-dependent manner. Specifically, we observed that effectiveness of closed-loop TUS in regulating neural activity and memory is dependent on the timing of stimulation in relation to different theta phase. The findings implied that closed-loop TUS may have the capability to alter neural activity and memory performance in a phase-sensitive manner, and suggested that the efficacy of closed-loop TUS in modifying neural activity and memory was contingent on timing of stimulation with respect to the theta rhythm. Moreover, the improvement in memory performance after closed-loop TUS was found to be persistent.

Single-neuron mechanical perturbation evokes calcium plateaus that excite and modulate the network

Mechanical stimulation is a promising means to non-invasively excite and modulate neuronal networks with a high spatial resolution. Despite the thorough characterization of the initiation mechanism, whether or how mechanical responses disperse into non-target areas remains to be discovered. Our in vitro study demonstrates that a single-neuron deformation evokes responses that propagate to about a third of the untouched neighbors. The responses develop via calcium influx through mechanosensitive channels and regeneratively propagate through the neuronal ensemble via gap junctions. Although independent of action potentials and synapses, mechanical responses reliably evoke membrane depolarizations capable of inducing action potentials both in the target and neighbors. Finally, we show that mechanical stimulation transiently potentiates the responding assembly for further inputs, as both gain and excitability are transiently increased exclusively in neurons that respond to a neighbor's mechanical stimulation. The findings indicate a biological component affecting the spatial resolution of mechanostimulation and point to a cross-talk in broad-network mechanical stimulations. Since giga-seal formation in patch-clamp produces a similar mechanical stimulus on the neuron, our findings inform which neuroscientific questions could be reliably tackled with patch-clamp and what recovery post-gigaseal formation is necessary.

Lentiviral Transduction-based CRISPR/Cas9 Editing of Schistosoma mansoni Acetylcholinesterase

Background

Recent studies on CRISPR/Cas9-mediated gene editing in Schistosoma mansoni have shed new light on the study and control of this parasitic helminth. However, the gene editing efficiency in this parasite is modest.

Methods

To improve the efficiency of CRISPR/Cas9 genome editing in schistosomes, we used lentivirus, which has been effectively used for gene editing in mammalian cells, to deliver plasmid DNA encoding Cas9 nuclease, a sgRNA targeting acetylcholinesterase (SmAChE) and a mCherry fluorescence marker into schistosomes.

Results

MCherry fluorescence was observed in transduced eggs, schistosomula, and adult worms, indicating that the CRISPR components had been delivered into these parasite stages by lentivirus. In addition, clearly changed phenotypes were observed in SmAChE-edited parasites, including decreased SmAChE activity, reduced hatching ability of edited eggs, and altered behavior of miracidia hatched from edited eggs. Next-generation sequencing analysis demonstrated that the lentiviral transduction-based CRISPR/Cas9 gene modifications in SmAChE-edited schistosomes were homology-directed repair predominant but with much lower efficiency than that obtained using electroporation (data previously published by our laboratory) for the delivery of CRISPR components.

Conclusion

Taken together, electroporation is more efficient than lentiviral transduction in the delivery of CRISPR/Cas9 into schistosomes for programmed genome editing. The exploration of tactics for enhancing CRISPR/Cas9 gene editing provides the basis for the future improvement of programmed genome editing in S. mansoni.

Rib detection using pitch-catch ultrasound and classification algorithms for a novel ultrasound therapy device

BACKGROUND

Noninvasive ultrasound (US) has been used therapeutically for decades, with applications in tissue ablation, lithotripsy, and physical therapy. There is increasing evidence that low intensity US stimulation of organs can alter physiological and clinical outcomes for treatment of health disorders including rheumatoid arthritis and diabetes. One major translational challenge is designing portable and reliable US devices that can be used by patients in their homes, with automated features to detect rib location and aid in efficient transmission of energy to organs of interest. This feasibility study aimed to assess efficacy in rib bone detection without conventional imaging, using a single channel US pitch-catch technique integrated into an US therapy device to detect pulsed US reflections from ribs.

METHODS

In 20 healthy volunteers, the location of the ribs and spleen were identified using a diagnostic US imaging system. Reflected ultrasound signals were recorded at five positions over the spleen and adjacent ribs using the therapy device. Signals were classified as between ribs (intercostal), partially over a rib, or fully over a rib using four models: threshold-based time domain classification, threshold-based frequency domain classification, logistic regression, and support vector machine (SVM).

RESULTS

SVM performed best overall on the All Participants cohort with accuracy up to 96.25%. All models' accuracies were improved by separating participants into two cohorts based on Body Mass Index (BMI) and re-fitting each model. After separation into Low BMI and High BMI cohorts, a simple time-thresholding approach achieved accuracies up to 100% and 93.75%, respectively.

CONCLUSION

These results demonstrate that US reflection signal classification can accurately provide low complexity, real-time automated onboard rib detection and user feedback to advance at-home therapeutic US delivery.

Increased intracellular diffusivity of macromolecules within a mammalian cell by low-intensity pulsed ultrasound

Whilst a number of studies have demonstrated that low-intensity pulsed ultrasound (LIPUS) is a promising therapeutic ultrasound technique that can be used for delivering mild mechanical stimuli to target tissue non-invasively, the underlying biophysical mechanisms still remain unclear. Most mechanism studies have focused explicitly on the effects of LIPUS on the cell membrane and mechanosensitive receptors. In the present study, we propose an additional mechanism by which LIPUS propagation through living cells may directly impact intracellular dynamics, particularly the diffusion transport of biomolecules. To support our hypothesis, human epithelial-like cells (SaOS-2 and HeLa) seeded on a confocal dish placed on a microscope stage were exposed to LIPUS with various exposure conditions (ultrasound frequencies of 0.5, 1 and 3 MHz, peak acoustic pressure of 200 and 400 kPa, a pulse repetition frequency of 1 kHz and a 20 % duty cycle), and the diffusivities of various sizes of biomolecules in the cytoplasm area were measured using fluorescence recovery after photobleaching (FRAP). Furthermore, giant unilamellar vesicles (GUVs) filled with macromolecules were used to examine the physical causal relationship between LIPUS and molecular diffusion changes. Nucleocytoplasmic transport coefficients were also measured by modified FRAP that bleaches the whole cell nuclear region. Extracellular signal-regulated kinases (ERK) activity (the phosphorylation dynamics) was monitored using fluorescence resonance energy transfer (FRET) microscopy. All the measurements were taken during, before and after the LIPUS exposure. Our experimental results clearly showed that the diffusion coefficients of macromolecules within the cell increased with acoustic pressure by 12.1 to 33.5 % during the sonication, and the increments were proportional to their molecular sizes regardless of the ultrasound frequency used. This observation in living cells was consistent with the GUVs exposed to the LIPUS, which indicated that the diffusivity increase was a passive physical response to the acoustic energy of LIPUS. Under the 1 MHz LIPUS exposure with 400 kPa, the passive nucleocytoplasmic transport of enhanced green fluorescent protein (EGFP) was accelerated by 21.4 %. With the same LIPUS exposure condition, both the diffusivity and phosphorylation of ERK induced by EGF treatment were significantly elevated simultaneously, which implied that LIPUS could also modify the kinase kinetics in the signal transduction process. Taken together, this study is the first attempt to uncover the physical link between LIPUS and the dynamics of intracellular macromolecules and related biological processes that LIPUS can possibly increase the diffusivity of intracellular macromolecules, leading to the changes in the basic cellular processes: passive nucleocytoplasmic transport and ERK. Our findings can provide a novel perspective that the mechanotransduction process that the intracellular region, in addition to the cell membrane, can convert the acoustic stimuli of LIPUS to biochemical signals.

A Miniature Ultrasound Source for Neural Modulation

This work describes a unique ultrasound (US) exposure system designed to create very localized ( [Formula: see text]) sound fields at operating frequencies that are currently being used for preclinical US neuromodulation. This system can expose small clusters of neuronal tissue, such as cell cultures or intact brain structures in target animal models, opening up opportunities to examine possible mechanisms of action. We modified a dental descaler and drove it at a resonance frequency of 96 kHz, well above its nominal operating point of 28 kHz. A ceramic microtip from an ultrasonic wire bonder was attached to the end of the applicator, creating a 100- [Formula: see text] point source. The device was calibrated with a polyvinylidene difluoride (PVDF) membrane hydrophone, in a novel, air-backed, configuration. The experimental results were confirmed by simulation using a monopole model. The results show a consistent decaying sound field from the tip, well-suited to neural stimulation. The system was tested on an existing neurological model, Drosophila melanogaster, which has not previously been used for US neuromodulation experiments. The results show brain-directed US stimulation induces or suppresses motor actions, demonstrated through synchronized tracking of fly limb movements. These results provide the basis for ongoing and future studies of US interaction with neuronal tissue, both at the level of single neurons and intact organisms.

High-throughput ultrasound neuromodulation in awake and freely behaving rats

Transcranial ultrasound neuromodulation is a promising potential therapeutic tool for the noninvasive treatment of neuropsychiatric disorders. However, the expansive parameter space and difficulties in controlling for peripheral auditory effects make it challenging to identify ultrasound sequences and brain targets that may provide therapeutic efficacy. Careful preclinical investigations in clinically relevant behavioral models are critically needed to identify suitable brain targets and acoustic parameters. However, there is a lack of ultrasound devices allowing for multi-target experimental investigations in awake and unrestrained rodents. We developed a miniaturized 64-element ultrasound array that enables neurointerventional investigations with within-trial active control targets in freely behaving rats. We first characterized the acoustic field with measurements in free water and with transcranial propagation. We then confirmed in vivo that the array can target multiple brain regions via electronic steering, and verified that wearing the device does not cause significant impairments to animal motility. Finally, we demonstrated the performance of our system in a high-throughput neuromodulation experiment, where we found that ultrasound stimulation of the rat central medial thalamus, but not an active control target, promotes arousal and increases locomotor activity.

Desynchronization of neuronal firing in multiparameter ultrasound stimulation

Low-intensity transcranial ultrasound stimulation, a novel neuromodulation technique, that possesses the advantages of non-invasiveness, high penetration depth, and high spatial resolution, has achieved positive neuromodulation effects in animal studies. But the regulatory mechanism remains controversial. The intramembrane cavitation effect is considered one of the mechanisms for ultrasound neuromodulation. In this study, the modified equations of ultrasonic cavitation bubble dynamics were coupled with the dual-coupled neuron Hindmarsh-Rose model, small-world neural network model, and the Jansen-Rit neural mass model, which simulate simple coupled neurons, complex neuronal networks, and discharge signals in epileptic disorders respectively. The results demonstrated that ultrasound stimulation has an appreciable modulatory effect on neuronal firing desynchronization in Hindmarsh-Rose model and small-world neural network model. The desynchronization effect is related to the stimulation frequency and intensity. Furthermore, ultrasound stimulation has an inhibitory effect on epileptic seizures, and the effect is enhanced by increasing ultrasound frequency from 0.1-1.0 MHz. This is the first combination of ultrasonic intramembrane cavitation effect theory with neurons and neural network firing desynchronization, which can provide guidance of parametric and theories support for the studies of neurological diseases such as epilepsy and Parkinson's disease.

Functional material-mediated wireless physical stimulation for neuro-modulation and regeneration

Nerve injuries and neurological diseases remain intractable clinical challenges. Despite the advantages of stem cell therapy in treating neurological disorders, uncontrollable cell fates and loss of cell function in vivo are still challenging. Recently, increasing attention has been given to the roles of external physical signals, such as electricity and ultrasound, in regulating stem cell fate as well as activating or inhibiting neuronal activity, which provides new insights for the treatment of neurological disorders. However, direct physical stimulations in vivo are short in accuracy and safety. Functional materials that can absorb energy from a specific physical field exerted in a wireless way and then release another localized physical signal hold great advantages in mediating noninvasive or minimally invasive accurate indirect physical stimulations to promote the therapeutic effect on neurological disorders. In this review, the mechanism by which various physical signals regulate stem cell fate and neuronal activity is summarized. Based on these concepts, the approaches of using functional materials to mediate indirect wireless physical stimulation for neuro-modulation and regeneration are systematically reviewed. We expect that this review will contribute to developing wireless platforms for neural stimulation as an assistance for the treatment of neurological diseases and injuries.

Multifunctional Fiber-Based Optoacoustic Emitter as a Bidirectional Brain Interface

A bidirectional brain interface with both "write" and "read" functions can be an important tool for fundamental studies and potential clinical treatments for neurological diseases. Herein, a miniaturized multifunctional fiber-based optoacoustic emitter (mFOE) is reported thatintegrates simultaneous optoacoustic stimulation for "write" and electrophysiology recording of neural circuits for "read". Because of the intrinsic ability of neurons to respond to acoustic wave, there is no requirement of the viral transfection. The orthogonality between optoacoustic waves and electrical field provides a solution to avoid the interference between electrical stimulation and recording. The stimulation function of the mFOE is first validated in cultured ratcortical neurons using calcium imaging. In vivo application of mFOE for successful simultaneous optoacoustic stimulation and electrical recording of brain activities is confirmed in mouse hippocampus in both acute and chronical applications up to 1 month. Minor brain tissue damage is confirmed after these applications. The capability of simultaneous neural stimulation and recording enabled by mFOE opens up new possibilities for the investigation of neural circuits and brings new insights into the study of ultrasound neurostimulation.

A Review of Ultrasound Neuromodulation Technologies

The invasiveness of neuromodulation technologies that require surgical implantation (e.g., electrical and optical stimulation) may limit their clinical application. Thus, alternative technologies that offer similar benefits without surgery are of paramount importance in the field of neuromodulation. Low-intensity ultrasound is an emerging modality for neural stimulation as ultrasound can be focused in deep tissues with millimeter resolution. Transcranial focused ultrasound stimulation (tFUS) has already been demonstrated in a wide range of animals and even humans at different sonication frequencies (mostly in the sub-MHz range due to the presence of the skull). This article first provides some fundamental knowledge in ultrasound, and then reviews various examples of successful tFUS experiments in animals and humans using different stimulation patterns, as well as available tFUS technologies for generating, focusing, and steering ultrasound beams in neural tissues. In particular, phased array technologies for the ultrasound stimulation application are discussed with an emphasis on the design, fabrication, and integration of ultrasound transducer arrays as well as the design and development of phased array electronics with beamformer and high-voltage driver circuitry. The challenges in tFUS, such as its underlying mechanism, indirect auditory response, and skull aberration effects, are also discussed.

Wireless agents for brain recording and stimulation modalities

New sensors and modulators that interact wirelessly with medical modalities unlock uncharted avenues for in situ brain recording and stimulation. Ongoing miniaturization, material refinement, and sensitization to specific neurophysiological and neurochemical processes are spurring new capabilities that begin to transcend the constraints of traditional bulky and invasive wired probes. Here we survey current state-of-the-art agents across diverse realms of operation and evaluate possibilities depending on size, delivery, specificity and spatiotemporal resolution. We begin by describing implantable and injectable micro- and nano-scale electronic devices operating at or below the radio frequency (RF) regime with simple near field transmission, and continue with more sophisticated devices, nanoparticles and biochemical molecular conjugates acting as dynamic contrast agents in magnetic resonance imaging (MRI), ultrasound (US) transduction and other functional tomographic modalities. We assess the ability of some of these technologies to deliver stimulation and neuromodulation with emerging probes and materials that provide minimally invasive magnetic, electrical, thermal and optogenetic stimulation. These methodologies are transforming the repertoire of readily available technologies paired with compatible imaging systems and hold promise toward broadening the expanse of neurological and neuroscientific diagnostics and therapeutics.

Investigation of liver-targeted peripheral focused ultrasound stimulation (pFUS) and its effect on glucose homeostasis and insulin resistance in type 2 diabetes mellitus: a proof of concept, phase 1 trial

BACKGROUND

Mechanical waves produced by ultrasound pulses have been shown to activate mechanosensitive ion channels and modulate peripheral nerves. However, while peripheral ultrasound neuromodulation has been demonstrated in vitro and in pre-clinical models, there have been few reports of clinical tests.

AIM

We modified a diagnostic imaging system for ultrasound neuromodulation in human subjects. We report the first safety and feasibility outcomes in subjects with type 2 diabetes (T2D) mellitus and discuss these outcomes in relation to previous pre-clinical results.

DESIGN

The study was performed as an open label feasibility study to assess the effects of hepatic ultrasound (targeted to the porta hepatis) on glucometabolic parameters in subjects with T2D. Stimulation (peripheral focused ultrasound stimulation treatment) was performed for 3 days (i.e. 15 min per day), preceded by a baseline examination and followed by a 2-week observation period.

METHODS

Multiple metabolic assays were employed including measures of fasting glucose and insulin, insulin resistance and glucose metabolism. The safety and tolerability were also assessed by monitoring adverse events, changes in vital signs, electrocardiogram parameters and clinical laboratory measures.

RESULTS AND CONCLUSION

We report post-pFUS trends in several outcomes that were consistent with previous pre-clinical findings. Fasting insulin was lowered, resulting in a reduction of HOMA-IR scores (P-value 0.01; corrected Wilcoxon signed-rank test). Additional safety and exploratory markers demonstrated no device-related adverse impact of pFUS. Our findings demonstrate that pFUS represents a promising new treatment modality that could be used as a non-pharmaceutical adjunct or even alternative to current drug treatments in diabetes.

Functional nanoparticle-enabled non-genetic neuromodulation

Stimulating ion channels targeting in neuromodulation by external signals with the help of functionalized nanoparticles, which integrates the pioneering achievements in the fields of neurosciences and nanomaterials, has involved into a novel interdisciplinary field. The emerging technique developed in this field enable simple, remote, non-invasive, and spatiotemporally precise nerve regulations and disease therapeutics, beyond traditional treatment methods. In this paper, we define this emerging field as nano-neuromodulation and summarize the most recent developments of non-genetic nano-neuromodulation (non-genetic NNM) over the past decade based on the innovative design concepts of neuromodulation nanoparticle systems. These nanosystems, which feature diverse compositions, structures and synthesis approaches, could absorb certain exogenous stimuli like light, sound, electric or magnetic signals, and subsequently mediate mutual transformations between above signals, or chemical reactions, to regulate stimuli-sensitive ion channels and ion migrations which play vital roles in the nervous system. We will also discuss the obstacles and challenges in the future development of non-genetic NNM, and propose its future developments, to add the further progress of this promising field.

Functional nanoparticle-enabled non-genetic neuromodulation

Stimulating ion channels targeting in neuromodulation by external signals with the help of functionalized nanoparticles, which integrates the pioneering achievements in the fields of neurosciences and nanomaterials, has involved into a novel interdisciplinary field. The emerging technique developed in this field enable simple, remote, non-invasive, and spatiotemporally precise nerve regulations and disease therapeutics, beyond traditional treatment methods. In this paper, we define this emerging field as nano-neuromodulation and summarize the most recent developments of non-genetic nano-neuromodulation (non-genetic NNM) over the past decade based on the innovative design concepts of neuromodulation nanoparticle systems. These nanosystems, which feature diverse compositions, structures and synthesis approaches, could absorb certain exogenous stimuli like light, sound, electric or magnetic signals, and subsequently mediate mutual transformations between above signals, or chemical reactions, to regulate stimuli-sensitive ion channels and ion migrations which play vital roles in the nervous system. We will also discuss the obstacles and challenges in the future development of non-genetic NNM, and propose its future developments, to add the further progress of this promising field.

Graphical Abstract

Ultrasonocoverslip: In-vitro platform for high-throughput assay of cell type-specific neuromodulation with ultra-low-intensity ultrasound stimulation

Brain stimulation with ultra-low-intensity ultrasound has rarely been investigated due to the lack of a reliable device to measure small neuronal signal changes made by the ultra-low intensity range. We propose Ultrasonocoverslip, an ultrasound-transducer-integrated-glass-coverslip that determines the minimum intensity for brain cell activation. Brain cells can be cultured directly on Ultrasonocoverslip to simultaneously deliver uniform ultrasonic pressure to hundreds of cells with real-time monitoring of cellular responses using fluorescence microscopy and single-cell electrophysiology. The sensitivity for detecting small responses to ultra-low-intensity ultrasound can be improved by averaging simultaneously obtained responses. Acoustic absorbers can be placed under Ultrasonocoverslip, and stimuli distortions are substantially reduced to precisely deliver user-intended acoustic stimulations. With the proposed device, we discover the lowest acoustic threshold to induce reliable neuronal excitation releasing glutamate. Furthermore, mechanistic studies on the device show that the ultra-low-intensity ultrasound stimulation induces cell type-specific neuromodulation by activating astrocyte-mediated neuronal excitation without direct neuronal involvement. The performance of ultra-low-intensity stimulation is validated by in vivo experiments demonstrating improved safety and specificity in motor modulation of tail movement compared to that with supra-watt-intensity.

Transcranial focused ultrasound-mediated neurochemical and functional connectivity changes in deep cortical regions in humans

Low-intensity transcranial ultrasound stimulation (TUS) is an emerging non-invasive technique for focally modulating human brain function. The mechanisms and neurochemical substrates underlying TUS neuromodulation in humans and how these relate to excitation and inhibition are still poorly understood. In 24 healthy controls, we separately stimulated two deep cortical regions and investigated the effects of theta-burst TUS, a protocol shown to increase corticospinal excitability, on the inhibitory neurotransmitter gamma-aminobutyric acid (GABA) and functional connectivity. We show that theta-burst TUS in humans selectively reduces GABA levels in the posterior cingulate, but not the dorsal anterior cingulate cortex. Functional connectivity increased following TUS in both regions. Our findings suggest that TUS changes overall excitability by reducing GABAergic inhibition and that changes in TUS-mediated neuroplasticity last at least 50 mins after stimulation. The difference in TUS effects on the posterior and anterior cingulate could suggest state- or location-dependency of the TUS effect-both mechanisms increasingly recognized to influence the brain's response to neuromodulation.

Low-intensity transcranial ultrasound stimulation modulates neural activities in mice under propofol anaesthesia

BACKGROUND

Previous studies have reported that transcranial focused ultrasound stimulation can significantly decrease the time to emergence from intraperitoneal ketamine-xylazine anaesthesia in rats. However, how transcranial focused ultrasound stimulation modulates neural activity in anaesthetized rats is unclear.

METHODS

In this study, to answer this question, we used low-intensity transcranial ultrasound stimulation (TUS) to stimulate the brain tissue of propofol-anaesthetized mice, recorded local field potentials (LFPs) in the mouse motor cortex and electromyography (EMG) signals from the mouse neck, and analysed the emergence and recovery time, mean absolute power, relative power and entropy of local field potentials.

RESULTS

We found that the time to emergence from anaesthesia in the TUS group (20.3 ± 1.7 min) was significantly less than that in the Sham group (32 ± 2.6 min). We also found that compared with the Sham group, 20 min after low-intensity TUS during recovery from anaesthesia, (1) the absolute power of local field potentials in mice was significantly reduced in the [1-4 Hz] and [13-30 Hz] frequency bands and significantly increased in the [55-100 Hz], [100-140 Hz] and [140-200 Hz] frequency bands; (2) the relative power of local field potentials in mice was enhanced at [30-45 Hz], [100-140 Hz] and [140-200 Hz] frequency bands; (3) the entropy of local field potentials ([1-200 Hz]) was increased.

CONCLUSION

These results demonstrate that low-intensity TUS can effectively modulate neural activities in both awake and anaesthetized mice and has a positive effect on recovery from propofol anaesthesia in mice.

Force-induced motions of the PIEZO1 blade probed with fluorimetry

Mechanical forces are thought to activate mechanosensitive PIEZO channels by changing the conformation of a large transmembrane blade domain. Yet, whether different stimuli induce identical conformational changes in this domain remains unclear. Here, we repurpose a cyclic permuted green fluorescent protein as a conformation-sensitive probe to track local rearrangements along the PIEZO1 blade. Two independent probes, one inserted in an extracellular site distal to the pore and the other in a distant intracellular proximal position, elicit sizable fluorescence signals when the tagged channels activate in response to fluid shear stress of low intensity. Neither cellular indentations nor osmotic swelling of the cell elicit detectable fluorescence signals from either probe, despite the ability of these stimuli to activate the tagged channels. High-intensity flow stimuli are ineffective at eliciting fluorescence signals from either probe. Together, these findings suggest that low-intensity fluid shear stress causes a distinct form of mechanical stress to the cell.

Ultrasound meets the cell membrane: for enhanced endocytosis and drug delivery

Endocytosis plays a crucial role in drug delivery for precision therapy. As a non-invasive and spatiotemporal-controllable stimulus, ultrasound (US) has been utilized for improving drug delivery efficiency due to its ability to enhance cell membrane permeability. When US meets the cell membrane, the well-known cavitation effect generated by US can cause various biophysical effects, facilitating the delivery of various cargoes, especially nanocarriers. The comprehension of recent progress in the biophysical mechanism governing the interaction between ultrasound and cell membranes holds significant implications for the broader scientific community, particularly in drug delivery and nanomedicine. This review will summarize the latest research results on the biological effects and mechanisms of US-enhanced cellular endocytosis. Moreover, the latest achievements in US-related biomedical applications will be discussed. Finally, challenges and opportunities of US-enhanced endocytosis for biomedical applications will be provided.

The Emergence of Functional Ultrasound for Noninvasive Brain-Computer Interface

A noninvasive brain-computer interface is a central task in the comprehensive analysis and understanding of the brain and is an important challenge in international brain-science research. Current implanted brain-computer interfaces are cranial and invasive, which considerably limits their applications. The development of new noninvasive reading and writing technologies will advance substantial innovations and breakthroughs in the field of brain-computer interfaces. Here, we review the theory and development of the ultrasound brain functional imaging and its applications. Furthermore, we introduce latest advancements in ultrasound brain modulation and its applications in rodents, primates, and human; its mechanism and closed-loop ultrasound neuromodulation based on electroencephalograph are also presented. Finally, high-frequency acoustic noninvasive brain-computer interface is prospected based on ultrasound super-resolution imaging and acoustic tweezers.

Elucidating Mechanotransduction Processes During Magnetomechanical Neuromodulation Mediated by Magnetic Nanodiscs

Purpose

Noninvasive cell-type-specific manipulation of neural signaling is critical in basic neuroscience research and in developing therapies for neurological disorders. Magnetic nanotechnologies have emerged as non-invasive neuromodulation approaches with high spatiotemporal control. We recently developed a wireless force-induced neurostimulation platform utilizing micro-sized magnetic discs (MDs) and low-intensity alternating magnetic fields (AMFs). When targeted to the cell membrane, MDs AMFs-triggered mechanoactuation enhances specific cell membrane receptors resulting in cell depolarization. Although promising, it is critical to understand the role of mechanical forces in magnetomechanical neuromodulation and their transduction to molecular signals for its optimization and future translation.

Methods

MDs are fabricated using top-down lithography techniques, functionalized with polymers and antibodies, and characterized for their physical properties. Primary cortical neurons co-cultured with MDs and transmembrane protein chemical inhibitors are subjected to 20 s pulses of weak AMFs (18 mT, 6 Hz). Calcium cell activity is recorded during AMFs stimulation.

Results

Neuronal activity in primary rat cortical neurons is evoked by the AMFs-triggered actuation of targeted MDs. Ion channel chemical inhibition suggests that magnetomechanical neuromodulation results from MDs actuation on Piezo1 and TRPC1 mechanosensitive ion channels. The actuation mechanisms depend on MDs size, with cell membrane stretch and stress caused by the MDs torque being the most dominant.

Conclusions

Magnetomechanical neuromodulation represents a tremendous potential since it fulfills the requirements of negligible heating (ΔT < 0.1 °C) and weak AMFs (< 100 Hz), which are limiting factors in the development of therapies and the design of clinical equipment.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12195-023-00786-8.

Ultrasonic neuromodulation mediated by mechanosensitive ion channels: current and future

Ultrasound neuromodulation technology is a promising neuromodulation approach, with the advantages of noninvasiveness, high-resolution, deep penetration and good targeting, which aid in circumventing the side effects of drugs and invasive therapeutic interventions. Ultrasound can cause mechanical effects, activate mechanosensitive ion channels and alter neuronal excitability, producing biological effects. The structural determination of mechanosensitive ion channels will greatly contribute to our understanding of the molecular mechanisms underlying mechanosensory transduction. However, the underlying biological mechanism of ultrasonic neuromodulation remains poorly understood. Hence, this review aims to provide an outline of the properties of ultrasound, the structures of specific mechanosensitive ion channels, and their role in ultrasound neuromodulation.

A scoping review of current and emerging techniques for evaluation of peripheral nerve health, degeneration, and regeneration: part 1, neurophysiology

Peripheral neuroregeneration research and therapeutic options are expanding exponentially. With this expansion comes an increasing need to reliably evaluate and quantify nerve health. Valid and responsive measures that can serve as biomarkers of the nerve status are essential for both clinical and research purposes for diagnosis, longitudinal follow-up, and monitoring the impact of any intervention. Furthermore, such biomarkers can elucidate regeneration mechanisms and open new avenues for research. Without these measures, clinical decision-making falls short, and research becomes more costly, time-consuming, and sometimes infeasible. As a companion to Part 2, which is focused on non-invasive imaging, Part 1 of this two-part scoping review systematically identifies and critically examines many current and emerging neurophysiological techniques that have the potential to evaluate peripheral nerve health, particularly from the perspective of regenerative therapies and research.

Modeling of Calcium-dependent Low Intensity Low Frequency Ultrasound Modulation of a Hodgkin-Huxley Neuron

Non-invasive low intensity, low frequency ultrasound is a progressive neuromodulation approach that can reach deep brain areas with peak spatial and temporal resolution for highly-targeted diagnostic and therapeutic purposes. Coupling the ultrasound mechanical effects to the neural membrane comprises different mechanisms that are, to-date, still a topic of debate. The availability of calcium ions in the extracellular medium is of high significance when it comes to the effect of ultrasound on the neural tissue. Whereby the generated calcium influx can directly affect the voltage-gated ion channels, amplifying their action. We modeled the flexoelectric-induced effects of ultrasound to a single firing neuron, taking into consideration the effect of calcium channel embedding into the neural membrane on the neuron's firing rate, latency response, peak-to-peak voltage, and general shape of the action potential.Clinical Relevance- Upon Ultrasound sonication, the mechanical waves interact with the neural membrane and alter the kinetics of the calcium channels, thus changing the neural response.

Essential Tremor - Deep Brain Stimulation vs. Focused Ultrasound

INTRODUCTION

Essential Tremor (ET) is one of the most common tremor syndromes typically presented as action tremor, affecting mainly the upper limbs. In at least 30-50% of patients, tremor interferes with quality of life, does not respond to first-line therapies and/or intolerable adverse effects may occur. Therefore, surgery may be considered.

AREAS COVERED

In this review, the authors discuss and compare unilateral ventral intermedius nucleus deep brain stimulation (VIM DBS) and bilateral DBS with Magnetic Resonance-guided Focused Ultrasound (MRgFUS) thalamotomy, which comprises focused acoustic energy generating ablation under real-time MRI guidance. Discussion includes their impact on tremor reduction and their potential complications. Finally, the authors provide their expert opinion.

EXPERT OPINION

DBS is adjustable, potentially reversible and allows bilateral treatments; however, it is invasive requires hardware implantation, and has higher surgical risks. Instead, MRgFUS is less invasive, less expensive, and requires no hardware maintenance. Beyond these technical differences, the decision should also involve the patient, family, and caregivers.

Acoustic radiation force for analyzing the mechanical stress in ultrasound neuromodulation

Objective. Although recent studies have shown that mechanical stress plays an important role in ultrasound neuromodulation, the magnitude and distribution of the mechanical stress generated in tissues by focused ultrasound transducers have not been adequately examined. Various acoustic radiation force (ARF) equations used in previous studies have been evaluated based on the tissue displacement results and are suitable for estimating the displacement. However, it is unclear whether mechanical stress can be accurately determined. This study evaluates the mechanical stress predicted by various AFR equations and suggests the optimal equation for estimating the mechanical stress in the brain tissue.Approach. In this paper, brain tissue responses are compared through numerical finite element simulations by applying the three most used ARF equations-Reynolds stress force ((RSF)), momentum flux density tensor force, and attenuation force. Three ARF fields obtained from the same pressure field were applied to the linear elastic model to calculate the displacement, mechanical stress, and mean pressure generated inside the tissue. Both the simple pressure field using a single transducer and the complex standing wave pressure field using two transducers were simulated.Main results. For the case using a single transducer, all three ARFs showed similar displacement. However, when comparing the mechanical stress results, only the results using the RSF showed a strong stress tensor at the focal point. For the case of using two transducers, the displacement and stress tensor field of the pattern related to the standing wave were calculated only from the results using the RSF.Significance. The model using RSF equation allows accurate analysis on stress tensor inside the tissue for ultrasound neuromodulation.

Spinal cord injury: molecular mechanisms and therapeutic interventions

Spinal cord injury (SCI) remains a severe condition with an extremely high disability rate. The challenges of SCI repair include its complex pathological mechanisms and the difficulties of neural regeneration in the central nervous system. In the past few decades, researchers have attempted to completely elucidate the pathological mechanism of SCI and identify effective strategies to promote axon regeneration and neural circuit remodeling, but the results have not been ideal. Recently, new pathological mechanisms of SCI, especially the interactions between immune and neural cell responses, have been revealed by single-cell sequencing and spatial transcriptome analysis. With the development of bioactive materials and stem cells, more attention has been focused on forming intermediate neural networks to promote neural regeneration and neural circuit reconstruction than on promoting axonal regeneration in the corticospinal tract. Furthermore, technologies to control physical parameters such as electricity, magnetism and ultrasound have been constantly innovated and applied in neural cell fate regulation. Among these advanced novel strategies and technologies, stem cell therapy, biomaterial transplantation, and electromagnetic stimulation have entered into the stage of clinical trials, and some of them have already been applied in clinical treatment. In this review, we outline the overall epidemiology and pathophysiology of SCI, expound on the latest research progress related to neural regeneration and circuit reconstruction in detail, and propose future directions for SCI repair and clinical applications.

Improving the quality of ultrasound images acquired using a therapeutic transducer

To enhance the effectiveness and safety of focused ultrasound (FUS) therapy, ultrasound image-based guidance and treatment monitoring are crucial. However, the use of FUS transducers for both therapy and imaging is impractical due to their low spatial resolution, signal-to-noise ratio (SNR), and contrast-to-noise ratio (CNR). To address this issue, we propose a new method that significantly improve the quality of images obtained by a FUS transducer. The proposed method employs coded excitation to enhance SNR and Wiener deconvolution to solve the problem of low axial resolution resulting from the narrow spectral bandwidth of FUS transducers. Specifically, the method eliminates the impulse response of a FUS transducer from received ultrasound signals using Wiener deconvolution, and pulse compression is performed using a mismatched filter. Simulation and commercial phantom experiments confirmed that the proposed method significantly improves the quality of images acquired by the FUS transducer. The -6 dB axial resolution was improved 1.27 mm to 0.37 mm that was similar to the resolution achieved by the imaging transducer, i.e., 0.33 mm. SNR and CNR also increased from 16.5 dB and 0.69 to 29.1 dB and 3.03, respectively, that were also similar to those by the imaging transducer (27.8 dB and 3.16). Based on the results, we believe that the proposed method has great potential to enhance the clinical utility of FUS transducers in ultrasound image-guided therapy.

Evaluation of a Novel Acoustic Coupling Medium for Human Low-Intensity Focused Ultrasound Neuromodulation Applications

OBJECTIVE

Single-element low-intensity focused ultrasound (LIFU) is an emerging form of human neuromodulation. Current coupling methods are impractical for clinical bedside use. Here, we evaluate commercially available high-viscosity gel polymer matrices as couplants for human LIFU neuromodulation applications.

METHODS

We first empirically tested the acoustic transmission of three densities at 500 kHz and then subjected the gel with the least acoustic attenuation to further tests of the effect of thickness, frequency, de-gassing and production variability.

RESULTS

The highest-density gel had the lowest acoustic attenuation (3.3%) with low lateral (<0.5 mm) and axial (<2 mm) beam distortion. Different thicknesses of the gel up to 10 mm did not appreciably affect results. The gel polymers exhibited frequency-dependent attenuation at 1 and 3 MHz up to 86.6%, as well as significant beam distortion >4 mm. Poor de-gassing methods also increased pressure attenuation at 500 kHz up to 59.6%. Standardized methods of making these gels should be established to reduce variability.

CONCLUSION

Commercially available de-gassed, high-density gel matrices are a low-cost, easily malleable, low-attenuation and distortion medium for the coupling of single-element LIFU transducers for human neuromodulation applications at 500 kHz.

Effects of focused ultrasound in a "clean" mouse model of ultrasonic neuromodulation

Recent studies on ultrasonic neuromodulation (UNM) in rodents have shown that focused ultrasound (FUS) can activate peripheral auditory pathways, leading to off-target and brain-wide excitation, which obscures the direct activation of the target area by FUS. To address this issue, we developed a new mouse model, the double transgenic Pou4f3+/DTR × Thy1-GCaMP6s, which allows for inducible deafening using diphtheria toxin and minimizes off-target effects of UNM while allowing effects on neural activity to be visualized with fluorescent calcium imaging. Using this model, we found that the auditory confounds caused by FUS can be significantly reduced or eliminated within a certain pressure range. At higher pressures, FUS can result in focal fluorescence dips at the target, elicit non-auditory sensory confounds, and damage tissue, leading to spreading depolarization. Under the acoustic conditions we tested, we did not observe direct calcium responses in the mouse cortex. Our findings provide a cleaner animal model for UNM and sonogenetics research, establish a parameter range within which off-target effects are confidently avoided, and reveal the non-auditory side effects of higher-pressure stimulation.

Non-Invasive Hybrid Ultrasound Stimulation of Visual Cortex In Vivo

The optic nerve is the second cranial nerve (CN II) that connects and transmits visual information between the retina and the brain. Severe damage to the optic nerve often leads to distorted vision, vision loss, and even blindness. Such damage can be caused by various types of degenerative diseases, such as glaucoma and traumatic optic neuropathy, and result in an impaired visual pathway. To date, researchers have not found a viable therapeutic method to restore the impaired visual pathway; however, in this paper, a newly synthesized model is proposed to bypass the damaged portion of the visual pathway and set up a direct connection between a stimulated visual input and the visual cortex (VC) using Low-frequency Ring-transducer Ultrasound Stimulation (LRUS). In this study, by utilizing and integrating various advanced ultrasonic and neurological technologies, the following advantages are achieved by the proposed LRUS model: 1. This is a non-invasive procedure that uses enhanced sound field intensity to overcome the loss of ultrasound signal due to the blockage of the skull. 2. The simulated visual signal generated by LRUS in the visual-cortex-elicited neuronal response in the visual cortex is comparable to light stimulation of the retina. The result was confirmed by a combination of real-time electrophysiology and fiber photometry. 3. VC showed a faster response rate under LRUS than light stimulation through the retina. These results suggest a potential non-invasive therapeutic method for restoring vision in optic-nerve-impaired patients using ultrasound stimulation (US).

Induction of a torpor-like hypothermic and hypometabolic state in rodents by ultrasound

Torpor is an energy-conserving state in which animals dramatically decrease their metabolic rate and body temperature to survive harsh environmental conditions. Here, we report the noninvasive, precise and safe induction of a torpor-like hypothermic and hypometabolic state in rodents by remote transcranial ultrasound stimulation at the hypothalamus preoptic area (POA). We achieve a long-lasting (>24 h) torpor-like state in mice via closed-loop feedback control of ultrasound stimulation with automated detection of body temperature. Ultrasound-induced hypothermia and hypometabolism (UIH) is triggered by activation of POA neurons, involves the dorsomedial hypothalamus as a downstream brain region and subsequent inhibition of thermogenic brown adipose tissue. Single-nucleus RNA-sequencing of POA neurons reveals TRPM2 as an ultrasound-sensitive ion channel, the knockdown of which suppresses UIH. We also demonstrate that UIH is feasible in a non-torpid animal, the rat. Our findings establish UIH as a promising technology for the noninvasive and safe induction of a torpor-like state.

Low-intensity ultrasound directly modulates neural activity of the cerebellar cortex

BACKGROUND

Low-intensity ultrasound is a noninvasive neuromodulation technique with the potential to focally manipulate deep brain activity at millimeter-scale resolution. However, there have been controversies over the direct influence of ultrasound on neurons, due to an indirect auditory activation. Besides, the capacity of ultrasound to stimulate the cerebellum remains underestimated.

OBJECTIVE

To validate the direct neuromodulation effects of ultrasound on the cerebellar cortex from both cellular and behavioral levels.

METHODS

Two-photon calcium imaging were used to measure the neuronal responses of cerebellar granule cells (GrCs) and Purkinje cells (PCs) to ultrasound application in awake mice. And a mouse model of paroxysmal kinesigenic dyskinesia (PKD), in which direct activation of the cerebellar cortex leads to dyskinetic movements, was used to assess the ultrasound-induced behavioral responses.

RESULTS

Low-intensity ultrasound stimulus (0.1 W/cm2) evoked rapidly increased and sustained neural activity in GrCs and PCs at targeted region, while no significant changes in calcium signals were observed responding to off-target stimulus. The efficacy of ultrasonic neuromodulation relies on acoustic dose modified by ultrasonic duration and intensity. In addition, transcranial ultrasound reliably triggered dyskinesia attacks in proline-rich transmembrane protein 2 (Prrt2) mutant mice, suggesting that the intact cerebellar cortex were activated by ultrasound.

CONCLUSION

Low-intensity ultrasound directly activates the cerebellar cortex in a dose-dependent manner, and thus serves as a promising tool for cerebellar manipulation.

Focused ultrasound neuromodulation of the spleen activates an anti-inflammatory response in humans

Focused ultrasound stimulation (FUS) activates mechanosensitive ion channels and is emerging as a method of noninvasive neuromodulation. In preclinical studies, FUS of the spleen (sFUS) activates an anti-inflammatory neural pathway which suppresses acute and chronic inflammation. However, the relevance of sFUS for regulating inflammatory responses in humans is unknown. Here, we used a modified diagnostic ultrasound imaging system to target the spleen of healthy human subjects with 3 min of continuously swept or stationary focused pulsed ultrasound, delivered at three different energy levels within allowable safety exposure limits. Potential anti-inflammatory effects of sFUS were assessed by measuring sFUS-elicited changes in endotoxin-induced tumor necrosis factor (TNF) production in whole blood samples from insonified subjects. We found that stimulation with either continuously swept or focused pulsed ultrasound has an anti-inflammatory effect: sFUS lowers TNF production for >2 h, with TNF returning to baseline by 24 h following sFUS. This response is independent of anatomical target (i.e., spleen hilum or parenchyma) or ultrasound energy level. No clinical, biochemical, or hematological parameters are adversely impacted. This is the first demonstration that sFUS suppresses the normal inflammatory response in humans, with potential implications for noninvasive bioelectronic therapy of inflammatory disorders.

Induction of a torpor-like hypothermic and hypometabolic state in rodents by ultrasound

Torpor is an energy-conserving state in which animals dramatically decrease their metabolic rate and body temperature to survive harsh environmental conditions. Here, we report the noninvasive, precise and safe induction of a torpor-like hypothermic and hypometabolic state in rodents by remote transcranial ultrasound stimulation at the hypothalamus preoptic area (POA). We achieve a long-lasting (>24 h) torpor-like state in mice via closed-loop feedback control of ultrasound stimulation with automated detection of body temperature. Ultrasound-induced hypothermia and hypometabolism (UIH) is triggered by activation of POA neurons, involves the dorsomedial hypothalamus as a downstream brain region and subsequent inhibition of thermogenic brown adipose tissue. Single-nucleus RNA-sequencing of POA neurons reveals TRPM2 as an ultrasound-sensitive ion channel, the knockdown of which suppresses UIH. We also demonstrate that UIH is feasible in a non-torpid animal, the rat. Our findings establish UIH as a promising technology for the noninvasive and safe induction of a torpor-like state.

Noninvasive ultrasound stimulation to treat myocarditis through splenic neuro-immune regulation

BACKGROUND

The cholinergic anti-inflammatory pathway (CAP) has been widely studied to modulate the immune response. Current stimulating strategies are invasive or imprecise. Noninvasive low-intensity pulsed ultrasound (LIPUS) has become increasingly appreciated for targeted neuronal modulation. However, its mechanisms and physiological role on myocarditis remain poorly defined.

METHODS

The mouse model of experimental autoimmune myocarditis was established. Low-intensity pulsed ultrasound was targeted at the spleen to stimulate the spleen nerve. Under different ultrasound parameters, histological tests and molecular biology were performed to observe inflammatory lesions and changes in immune cell subsets in the spleen and heart. In addition, we evaluated the dependence of the spleen nerve and cholinergic anti-inflammatory pathway of low-intensity pulsed ultrasound in treating autoimmune myocarditis in mice through different control groups.

RESULTS

The echocardiography and flow cytometry of splenic or heart infiltrating immune cells revealed that splenic ultrasound could alleviate the immune response, regulate the proportion and function of CD4+ Treg and macrophages by activating cholinergic anti-inflammatory pathway, and finally reduce heart inflammatory injury and improve cardiac remodeling, which is as effective as an acetylcholine receptor agonists GTS-21. Transcriptome sequencing showed significant differential expressed genes due to ultrasound modulation.

CONCLUSIONS

It is worth noting that the ultrasound therapeutic efficacy depends greatly on acoustic pressure and exposure duration, and the effective targeting organ was the spleen but not the heart. This study provides novel insight into the therapeutic potentials of LIPUS, which are essential for its future application.

Modulation effects of low-intensity transcranial ultrasound stimulation on the neuronal firing activity and synaptic plasticity of mice

Low-intensity transcranial ultrasound stimulation (TUS) has been effective in modulating several neurological and psychiatric disorders. However, how TUS modulates neuronal firing activity and synaptic plasticity remains unclear. Thus, we behaviorally tested the whisker-dependent novel object discrimination ability in mice after ultrasound stimulation and examined the cortical neuronal firing activity and synaptic plasticity in awake mice after ultrasound stimulation by two-photon fluorescence imaging. The current study presented the following results: (1) TUS could significantly improve the whisker-dependent new object discrimination ability of mice, suggesting that their learning and memory abilities were significantly enhanced; (2) TUS significantly enhanced neuronal firing activity; and (3) TUS increased the growth rate of dendritic spines in the barrel cortex, but did not promote the extinction of dendritic spines, resulting in enhanced synaptic plasticity. The above results indicate that TUS can improve the learning and memory ability of mice and enhance the neuronal firing activity and synaptic plasticity that are closely related to it. This study provides a research basis for the application of ultrasound stimulation in the treatment of learning- and memory-related diseases.

Low-Intensity Focused Ultrasound Neuromodulation for Stroke Recovery: A Novel Deep Brain Stimulation Approach for Neurorehabilitation?

Stroke as the leading cause of adult long-term disability and has a significant impact on patients, society and socio-economics. Non-invasive brain stimulation (NIBS) approaches such as transcranial magnetic stimulation (TMS) or transcranial electrical stimulation (tES) are considered as potential therapeutic options to enhance functional reorganization and augment the effects of neurorehabilitation. However, non-invasive electrical and magnetic stimulation paradigms are limited by their depth focality trade-off function that does not allow to target deep key brain structures critically important for recovery processes. Transcranial ultrasound stimulation (TUS) is an emerging approach for non-invasive deep brain neuromodulation. Using non-ionizing, ultrasonic waves with millimeter-accuracy spatial resolution, excellent steering capacity and long penetration depth, TUS has the potential to serve as a novel non-invasive deep brain stimulation method to establish unprecedented neuromodulation and novel neurorehabilitation protocols. The purpose of the present review is to provide an overview on the current knowledge about the neuromodulatory effects of TUS while discussing the potential of TUS in the field of stroke recovery, with respect to existing NIBS methods. We will address and discuss critically crucial open questions and remaining challenges that need to be addressed before establishing TUS as a new clinical neurorehabilitation approach for motor stroke recovery.

Ultrasound as a versatile tool for short- and long-term improvement and monitoring of brain function

Treating the brain with focused ultrasound (FUS) at low intensities elicits diverse responses in neurons, astroglia, and the extracellular matrix. In combination with intravenously injected microbubbles, FUS also opens the blood-brain barrier (BBB) and facilitates focal drug delivery. However, an incompletely understood cellular specificity and a wide parameter space currently limit the optimal application of FUS in preclinical and human studies. In this perspective, we discuss how different FUS modalities can be utilized to achieve short- and long-term improvements, thereby potentially treating brain disorders. We review the ongoing efforts to determine which parameters induce neuronal inhibition versus activation and how mechanoreceptors and signaling cascades are activated to induce long-term changes, including memory improvements. We suggest that optimal FUS treatments may require different FUS modalities and devices, depending on the targeted brain area or local pathology, and will be greatly enhanced by new techniques for monitoring FUS efficacy.

Principles and applications of sono-optogenetics

Optogenetics has revolutionized neuroscience research through its spatiotemporally precise activation of specific neurons by illuminating light on opsin-expressing neurons. A long-standing challenge of in vivo optogenetics arises from the limited penetration depth of visible light in the neural tissue due to scattering and absorption of photons. To address this challenge, sono-optogenetics has been developed to enable spatiotemporally precise light production in a three-dimensional volume of neural tissue by leveraging the deep tissue penetration and focusing ability of ultrasound as well as circulation-delivered mechanoluminescent nanotransducers. Here, we present a comprehensive review of the sono-optogenetics method from the physical principles of ultrasound and mechanoluminescence to its emerging applications for unique neuroscience studies. We also discuss a few promising directions in which sono-optogenetics can make a lasting transformative impact on neuroscience research from the perspectives of mechanoluminescent materials, ultrasound-tissue interaction, to the unique neuroscience opportunities of "scanning optogenetics".

On minimal focal distance of a focused ultrasound probe for neuromodulation

Focal distance is a key parameter for a focused ultrasound probe, especially in mouse brain stimulation where targets are right below the skull. A closed-form solution for the minimal focal distance with a given transducer size was derived in this study to facilitate precise focal spot alignment with targets in the mouse brain. The spherical profile corresponding to the minimal focal distance does not produce accurate focusing. An iterative algorithm based on Snell's law was introduced for lens profile calculation. With a suitable step size, an accurate lens profile can be obtained for the minimal focal distance.

Ultrasound modulates neuronal potassium currents via ionotropic glutamate receptors

BACKGROUND

Focused ultrasound stimulation (FUS) has the potential to provide non-invasive neuromodulation of deep brain regions with unparalleled spatial precision. However, the cellular and molecular consequences of ultrasound stimulation on neurons remains poorly understood. We previously reported that ultrasound stimulation induces increases in neuronal excitability that persist for hours following stimulation in vitro. In the present study we sought to further elucidate the molecular mechanisms by which ultrasound regulates neuronal excitability and synaptic function.

OBJECTIVES

To determine the effect of ultrasound stimulation on voltage-gated ion channel function and synaptic plasticity.

METHODS

Primary rat cortical neurons were exposed to a 40 s, 200 kHz pulsed ultrasound stimulus or sham-stimulus. Whole-cell patch clamp electrophysiology, quantitative proteomics and high-resolution confocal microscopy were employed to determine the effects of ultrasound stimulation on molecular regulators of neuronal excitability and synaptic function.

RESULTS

We find that ultrasound exposure elicits sustained but reversible increases in whole-cell potassium currents. In addition, we find that ultrasound exposure activates synaptic signalling cascades that result in marked increases in excitatory synaptic transmission. Finally, we demonstrate the requirement of ionotropic glutamate receptor (AMPAR/NMDAR) activation for ultrasound-induced modulation of neuronal potassium currents.

CONCLUSION

These results suggest specific patterns of pulsed ultrasound can induce contemporaneous enhancement of both neuronal excitability and synaptic function, with implications for the application of FUS in experimental and therapeutic settings. Further study is now required to deduce the precise molecular mechanisms through which these changes occur.

Weak Ultrasound Contributes to Neuromodulatory Effects in the Rat Motor Cortex

Transcranial focused ultrasound (tFUS) is a novel neuromodulating technique. It has been demonstrated that the neuromodulatory effects can be induced by weak ultrasound exposure levels (spatial-peak temporal average intensity, I_SPTA < 10 mW/cm²) in vitro. However, fewer studies have examined the use of weak tFUS to potentially induce long-lasting neuromodulatory responses in vivo. The purpose of this study was to determine the lower-bound threshold of tFUS stimulation for inducing neuromodulation in the motor cortex of rats. A total of 94 Sprague-Dawley rats were used. The sonication region aimed at the motor cortex under weak tFUS exposure (I_SPTA of 0.338-12.15 mW/cm²). The neuromodulatory effects of tFUS on the motor cortex were evaluated by the changes in motor-evoked potentials (MEPs) elicited by transcranial magnetic stimulation (TMS). In addition to histology analysis, the in vitro cell culture was used to confirm the neuromodulatory mechanisms following tFUS stimulation. In the results, the dose-dependent inhibitory effects of tFUS were found, showing increased intensities of tFUS suppressed MEPs and lasted for 30 min. Weak tFUS significantly decreased the expression of excitatory neurons and increased the expression of inhibitory GABAergic neurons. The PIEZO-1 proteins of GABAergic neurons were found to involve in the inhibitory neuromodulation. In conclusion, we show the use of weak ultrasound to induce long-lasting neuromodulatory effects and explore the potential use of weak ultrasound for future clinical neuromodulatory applications.

Pressure and ultrasound activate mechanosensitive TRAAK K + channels through increased membrane tension

TRAAK is a mechanosensitive two-pore domain K ⁺ (K2P) channel found in nodes of Ranvier within myelinated axons. It displays low leak activity at rest and is activated up to one hundred-fold by increased membrane tension. Structural and functional studies have led to physical models for channel gating and mechanosensitivity, but no quantitative analysis of channel activation by tension has been reported. Here, we use simultaneous patch-clamp recording and fluorescent imaging to determine the tension response characteristics of TRAAK. TRAAK shows high sensitivity and a broad response to tension spanning nearly the entire physiologically relevant tension range. This graded response profile distinguishes TRAAK from similarly low-threshold mechanosensitive channels Piezo1 and MscS, which activate in a step-like fashion over a narrow tension range. We further use patch imaging to show that ultrasonic activation of TRAAK and MscS is due to increased membrane tension. Together, these results provide mechanistic insight into TRAAK tension gating, a framework for exploring the role of mechanosensitive K ⁺ channels at nodes of Ranvier, and biophysical context for developing ultrasound as a mechanical stimulation technique for neuromodulation.

Superiorly Stable Three-Layer Air Microbubbles Generated by Versatile Ethanol-Water Exchange for Contrast-Enhanced Ultrasound Theranostics

Microbubbles have been widely used as ultrasound contrast agents in clinical diagnosis. Moreover, most current preparation methods for microbubbles are uncontrollable, and the as-obtained microbubbles are unstable in aqueous solution or under ultrasound. Here, we report a strategy to prepare superiorly stable microbubbles with three-layer structures by the ethanol-water exchange. This versatile method can also be applied to prepare different kinds of protein microbubbles with various sizes for advanced biomedical applications. To demonstrate this, the protein air microbubbles are created, which is stable in water for several days with intact structures and exhibits excellent contrast-enhanced ultrasound imaging. Moreover, the protein air microbubbles can also deliver a mass of drugs while maintaining their stable structures, making them a platform for ultrasound imaging-guided drug delivery. The versatile protein air microbubbles have great potential for the design and application of theranostic platforms.