Autonomic modulation by low-intensity focused ultrasound stimulation of the vagus nerve

Low-intensity pulsed ultrasound elevates blood pressure for shock

Fluid replacement is the primary treatment for life-threatening shock but is challenging in harsh environments. This study explores low-intensity pulsed ultrasound (LIPUS) as a resuscitation strategy. Cervical LIPUS stimulation effectively elevated blood pressure in shocked rats. It also improved cerebral and multiorgan perfusion. Mechanistically, LIPUS activated pathways related to sympathetic nerve excitation and vascular smooth muscle contraction, increasing plasma catecholamines and stimulating blood pressure-regulating neural nuclei. Partial sympathetic nerve transection reduced LIPUS efficacy, while complete inhibition of these nuclei abolished the response. Preliminary clinical trials demonstrated LIPUS's ability to raise blood pressure in shock patients. The findings suggest that LIPUS enhances sympathetic nerve activity and activates blood pressure-regulating nuclei, offering a noninvasive, neuromodulation-based approach to shock treatment. This method holds potential for improving blood pressure and organ perfusion in shock patients, especially in resource-limited environments.

Advancements and prospects of transcranial focused ultrasound in pain neuromodulation

ABSTRACT

Transcranial focused ultrasound (tFUS) is an emerging noninvasive neuromodulation technology that has shown great potential in pain modulation. This review systematically elucidates the multilevel biological mechanisms of tFUS neuromodulation, from network-wide effects to cellular and molecular processes, as well as broader systemic influences. Preliminary animal pain model studies have revealed tFUS's ability to improve pain behavioral indicators and modulate neural circuit activity under pathological conditions. A small number of clinical studies also suggest that tFUS may have certain benefits in improving symptom experience and emotional state in chronic pain patients. However, current research generally has limitations such as small sample sizes and short follow-up periods. More high-quality studies are needed to verify the long-term effects and safety of tFUS pain treatment. Overcoming these limitations and advancing large-scale clinical translational research will help fully exploit the application potential of tFUS in precision pain medicine and provide new treatment options for pain relief.

Low-Intensity Ultrasound Tibial Nerve Stimulation Suppresses Bladder Activity in Rats

BACKGROUND AND OBJECTIVE

Noninvasive neuromodulation, particularly through low-intensity ultrasound, holds promise in the fields of neuroscience and neuro-engineering. Ultrasound can stimulate the central nervous system to treat neurologic disorders of the brain and activate peripheral nerve activity. The aim of this study is to investigate the inhibitory effect of low-intensity ultrasonic tibial nerve stimulation on both the physiological state and the overactive bladder (OAB) model in rats.

MATERIALS AND METHODS

A total of 28 female Sprague-Dawley rats were used in this study. Continuous transurethral instillation of 0.9% normal saline into the bladder was initially performed to stimulate physiological bladder activity. Subsequently, a solution containing 0.3% acetic acid dissolved in saline was instilled to induce rat models of OAB. The study comprised two phases: initial observation of bladder response to low-intensity ultrasound (1 MHz, 1 W/cm2, 50% duty cycle) in seven rats; subsequent exploration of ultrasound frequency (3 MHz) and intensity (2 W/cm2 and 3 W/cm2) effects in 21 rats. The intercontraction intervals (ICIs) were the primary outcome measure. Histologic analysis of tibial nerves and surrounding muscle tissues determined safe ultrasound parameters.

RESULTS

Low-intensity ultrasound tibial nerve stimulation significantly inhibited normal and OAB activity. Ultrasound stimulation at 1 MHz, 1 W/cm2, with a 50% duty cycle significantly prolonged the ICI in both normal (p < 0.0001) and OAB rats (p < 0.01), as did transitioning to a 3 MHz frequency (p = 0.001 for normal rats; p < 0.01 for OAB rats). Similarly, at an intensity of 2 W/cm2 and 1 MHz frequency with a 50% duty cycle, ultrasound stimulation significantly prolonged the ICI in both normal (p < 0.01) and OAB rats (p < 0.005). Furthermore, switching to a 3 W/cm2 ultrasound intensity also significantly extended the ICI in both normal (p < 0.05) and OAB rats (p = 0.01). However, after different ultrasound intensities and frequencies, there was no statistical difference in ICI ratios (preultrasound stimulation vs postultrasound stimulation/preultrasound stimulation ∗ 100%) in all rats (p > 0.05). Low-intensity ultrasound tibial nerve stimulation did not influence baseline pressure, threshold pressure, or maximum pressure. In addition, a latency period in bladder reflex inhibition was induced by low-intensity ultrasound tibial nerve stimulation in some rats. Histologic analysis indicated no evident nerve or muscle tissue damage or abnormalities.

CONCLUSIONS

This study confirmed the potential of transcutaneous ultrasound tibial nerve stimulation to improve bladder function. According to the findings, the ultrasonic intensities ranging from 1 to 3 W/cm2 and frequencies of 1 MHz and 3 MHz are both feasible and safe treatment parameters. This study portended the promise of low-intensity ultrasound tibial nerve stimulation as a treatment for OAB and provides a basis and reference for future clinical applications.

Using Electrical Muscle Stimulation to Enhance Electrophysiological Performance of Agonist-Antagonist Myoneural Interface

The agonist-antagonist myoneural interface (AMI), a surgical method to reinnervate physiologically-relevant proprioceptive feedback for control of limb prostheses, has demonstrated the ability to provide natural afferent sensations for limb amputees when actuating their prostheses. Following AMI surgery, one potential challenge is atrophy of the disused muscles, which would weaken the reinnervation efficacy of AMI. It is well known that electrical muscle stimulus (EMS) can reduce muscle atrophy. In this study, we conducted an animal investigation to explore whether the EMS can significantly improve the electrophysiological performance of AMI. AMI surgery was performed in 14 rats, in which the distal tendons of bilateral solei donors were connected and positioned on the surface of the left biceps femoris. Subsequently, the left tibial nerve and the common peroneus nerve were sutured onto the ends of the connected donor solei. Two stimulation electrodes were affixed onto the ends of the donor solei for EMS delivery. The AMI rats were randomly divided into two groups. One group received the EMS treatment (designated as EMS_on) regularly for eight weeks and another received no EMS (designated as EMS_off). Two physiological parameters, nerve conduction velocity (NCV) and motor unit number, were derived from the electrically evoked compound action potential (CAP) signals to assess the electrophysiological performance of AMI. Our experimental results demonstrated that the reinnervated muscles of the EMS_on group generated higher CAP signals in comparison to the EMS_off group. Both NCV and motor unit number were significantly elevated in the EMS_on group. Moreover, the EMS_on group displayed statistically higher CAP signals on the indirectly activated proprioceptive afferents than the EMS_off group. These findings suggested that EMS treatment would be promising in enhancing the electrophysiological performance and facilitating the reinnervation process of AMI.

Comparison of Blood Pressure Modulation by Low-Intensity Focused Ultrasound Stimulation of Carotid Sinus, Nodose Ganglion, and Vagus Nerve

Low-intensity focused ultrasound stimulation (FUS) of the vagus nerve has proven effective in lowering blood pressure (BP) in our pilot animal study, opening new possibilities for noninvasive physiotherapy for hypertension. To further explore the impact of BP regulation by FUS on other targets, we compared the BP modulation pattern when applying FUS to the left carotid sinus, nodose ganglion, and vagus nerve trunk, respectively. FUS with different acoustic intensities was applied to each target, while continuous BP waveforms were synchronously recorded in the right common carotid artery. Subsequently, systolic blood pressure (SBP), diastolic blood pressure (DBP), and heart rate (HR) were extracted and analyzed before, during, and after FUS. The results revealed that FUS targeting the carotid sinus and nodose ganglion could also induce reductions in BP. However, both the degree of BP reduction and the sustained duration were less than those achieved with vagus nerve stimulation. Moreover, the ultrasound stimulation intensity threshold for inducing a hypotensive effect is lower when stimulating the vagus nerve compared to stimulating the carotid sinus and nodose ganglion. This study provides compelling evidence supporting the selection of the vagus nerve as the appropriate target for FUS in regulating BP.

The Changes of Cardiovascular Neurotransmitter Levels under Low-Intensity Focused Ultrasound Stimulation of the Vagus Nerve

BACKGROUND

Our previous study has shown that stimulation of the vagus nerve with low-intensity focused ultrasound could modulate blood pressure (BP), but the underlying mechanisms remain unclear. This study investigated the changes of cardiovascular neurotransmitter levels to indirectly evaluate the responses of the autonomic nervous system and renin-angiotensin system under low-intensity focused ultrasound stimulation (FUS) of the vagus nerve.

METHODS

Cardiovascular neurotransmitter levels of epinephrine (EPI), norepinephrine (NE), and angiotensin II (ANGII) were measured and compared before and after the FUS in seven spontaneously hypertensive rats; and were also measured and compared between a target stimulation group (FUS, n = 6) and non-target stimulation group (Control, n = 5) after stimulation to exclude the influence of potential confounding factors.

RESULTS

The t-test results showed that the levels of EPI, NE, and ANGII were significantly decreased (P < 0.05) after stimulation compared to before stimulation. Additionally, the levels of NE and EPI were significantly lower (P < 0.05) in the FUS group than in the Control group after stimulation, indicating that the activities of the sympathetic nervous system and renin-angiotensin system of the vagus nerve might be inhibited by FUS of the vagus nerve.

CONCLUSION

These findings reveal the mechanism of BP lowing in response to FUS of the vagus nerve.Clinical Relevance-This study revealed the mechanism of BP lowering in response to focused ultrasound stimulation of the vagus nerve through analyzing the changes of cardiovascular neurotransmitter levels.