Modulating Peripheral Neural Activity: Prolonged Low-Intensity Ultrasound for Controlled Excitation and Suppression in Rat Sciatic Nerve
Heba M. Badawe, Pierre D. Mourad, Massoud L. Khraiche
2024 · 10.1101/2024.12.26.630403
Abstract
Objective Low-intensity, low-frequency ultrasound has shown promise for neuromodulation, particularly for influencing peripheral neural activity. However, the precise parameters required to modulate neuronal activity consistently remain poorly understood, limiting its broader application. Here, we investigate the effects of varying sonication duration (SD) and duty cycle (DC) on motor neuronal responses in the rat sciatic nerve, focusing on understanding how cumulative energy exposure influences the activation, enhancement, or suppression of peripheral neural activity during ultrasound neuromodulation. Approach We apply low-intensity, low-frequency ultrasound to the rat sciatic nerve in vivo at different sonication durations (30s, 60s, 90s, and 120s) and duty cycles (30%, 50%, and 80%). The cumulative energy exposure is calculated as the product of spatial-peak pulse-average intensity, SD, and DC. Electromyographic (EMG) activity in the gastrocnemius muscle is measured, and the thermal effects are monitored to ensure a non-cavitational, non-thermal application. Main Results Our findings demonstrate that higher cumulative energy exposures suppress EMG activity in the gastrocnemius muscle (enervated by the sciatic nerve). However, lower cumulative energy exposures enhance EMG activity and motor stimulation. Notably, the ultrasound-induced EMG changes persisted for 5 minutes post-sonication – three to five times longer than the application duration -- underscoring the therapeutic potential of ultrasound for precise neural control. In vivo evaluations suggest the mechanical nature of the observed effects without any significant temperature increase or induction of cavitation. In vivo evaluations suggest the mechanical nature of the observed effects without any significant temperature increase or induction of cavitation. Significance Interestingly, our results show a switch from excitation to suppression of electrically evoked EMG activity following ultrasound sonication depending on the acquired cumulative energy. This study establishes a safe parameter space for prolonged neuromodulation, demonstrating its potential for therapeutic applications that can precisely modulate peripheral nervous system activity. These findings contribute to the development of ultrasound-based treatments for neurological conditions, offering a novel and controllable method for peripheral nerve stimulation.
Abstract via europepmc.
Exposures
Exposure 1: Sciatic nerve, varying sonication duration and duty cycle (electrically-evoked EMG)
Target: sciatic nerve — “left sciatic nerve”
Device: other named manufacturer · Mana Instruments · E0525-SU ✓
| Waveform | pulsed | |
|---|---|---|
| Fundamental frequency (kHz) | 500 | ✓✓✓ |
| Pulse duration (ms) | 0.25 | ✓✓✓ |
| Pulse repetition frequency (Hz) | not reported | ⚑ |
| Duty cycle (%) | 30, 50, 80swept | ✓✓✓ |
| Sonication duration (s) | 30, 60, 90, 120swept | ✓✓✓ |
| Free-field pressure (kPa) | not reported | |
|---|---|---|
| Free-field Isppa (W/cm²) | 1.4, 3.39swept | ✓✓✓⚑ |
| Free-field Ispta (W/cm²) | not reported | |
| In-situ estimate | not reported | |
| In-situ pressure (kPa) | not reported | |
| In-situ Isppa (W/cm²) | not reported | |
| In-situ Ispta (W/cm²) | not reported |
In each of three trials per rat, a single sonication duration (30, 60, 90 or 120 s) was held constant while duty cycle (30%, 50% or 80%) was varied; ultrasound was applied concurrently with ongoing electrical nerve stimulation (2 Hz, 2 ms pulses) after a 30-s electrical-only baseline (Region A), followed by a 5-min electrical-only recovery period whose final 30 s (Region B) was used to quantify sustained effects; a 15-min rest separated trials.
Flags from extraction
n_sessions_per_subject— Appears to be a single acute terminal surgical session per animal (exposed sciatic nerve, three trials, then euthanised for histology), but the paper does not state a session count explicitly.exposures[0].timing.pulse_repetition_frequency_hz— Duty cycle was varied 'by altering the burst period', but the paper never states the resulting period/PRF values numerically, so PRF cannot be computed without assuming unstated burst-period values.exposures[0].free_field.isppa_w_cm2— Intensity was measured with a calibrated hydrophone in a degassed-water tank at the tip of the coupling cone (free field), separate from the in vivo sciatic-nerve exposures.