Focused Ultrasound‐Induced Peripheral Nerve Blockade: Duration of Changes to Thermal Withdrawal Latency and Nerve Structure After Focused Ultrasound Application to the Sciatic Nerve in a Rat Model of Acute Pain
Gwen Gao, Zara Thomas, Husniye Kantarci, Cholawat Pacharinsak, J. Bradley Zuchero, Kim Butts Pauly, David C. Yeomans, Thomas A. Anderson
Journal of Neuroscience Research 2025, 103 · 10.1002/jnr.70079
Abstract
Focused ultrasound (FUS) holds potential to inhibit peripheral nerves to manage pain. We previously found FUS parameters resulting in changes to nerve structure and reversible increased mechanical withdrawal threshold as well as reversible inhibition of motor and non-pain sensory fibers. However, as behaviors were only followed for 4 weeks and structure for 2 weeks, the duration of increased thermal withdrawal latency and changes to nerve structure were undetermined. We investigated the duration of increased thermal withdrawal latency and nerve structure alterations after FUS application in an acute pain model. FUS was applied directly to the rat sciatic nerve prior to hindpaw (HP) incision; animal behaviors (thermal and mechanical nociceptive thresholds, HP extension and flexion) were assessed for 12 weeks and nerve structure was assessed for 28 weeks. The primary outcome was the change in HP thermal withdrawal latency. Secondary outcomes were the changes to sciatic nerve structure and HP mechanical withdrawal threshold, extension, and flexion. Compared with controls, after FUS application, animals had increased thermal nociceptive thresholds until week 9, increased mechanical nociceptive thresholds until week 2, decreased HP motor response until week 3.5, and decreased HP plantar sensation until week 4. Nerve ultrastructure changes may have persisted until week 24. In this new longer-term follow-up study, after invasive FUS application to the sciatic nerve in a rodent model of acute incisional pain, we determined the duration of changes to thermal hyperalgesia, mechanical hyperalgesia, motor, and non-pain sensory responses, and changes to nerve structure.
Abstract via europepmc.
Exposures
Exposure 1: Two-pulse-train FUS applied directly to the exposed sciatic nerve
Target: sciatic nerve — “sciatic nerve”
Device: custom-built
| Waveform | pulsed | |
|---|---|---|
| Fundamental frequency (kHz) | 1,470 | ✓✓✓ |
| Pulse duration (ms) | not reportedimplied by duty cycle ÷ PRF: 25 ms (not stated by the paper) | |
| Pulse repetition frequency (Hz) | 20 | ✓✓✓⚑ |
| Duty cycle (%) | 50 | ✓✓✓ |
| Sonication duration (s) | 8 | ✓✓✓ |
| Free-field pressure (kPa) | not reported | |
|---|---|---|
| Free-field Isppa (W/cm²) | not reported | |
| 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 | |
| Pressure, domain unspecified (kPa) | 1,860, 1,970swept | ✓✓✓ |
| Isppa, domain unspecified (W/cm²) | 112, 126swept | ✓✓✓ |
Two pulse trains were applied directly to the exposed sciatic nerve 1 cm proximal to its trifurcation: 1.86 MPa (Isppa 112 W/cm2, MI 1.5) for 8 s, then 2 min later 1.97 MPa (Isppa 126 W/cm2, MI 1.6) for 8 s; each train used a 50 ms burst period and 50% duty cycle. This parameter set was identified through an iterative process to achieve reversible peripheral nerve inhibition.
Flags from extraction
n_subjects— Paper reports only totals across all 4 study arms (INT, C1, C2, C3) combined: 'Animals for behavioral studies: n = 50 ... animals for TEM: n = 49'. It never states the size of the INT (actual FUS) group alone, so the number of animals actually exposed to ultrasound cannot be extracted.n_sessions_per_subject— FUS (two pulse trains, 2 min apart) was applied once per animal before HP incision, but the paper never states a number of stimulation sessions.blinding— Blinding of outcome assessors was only possible 'when possible' (incisions were visible), so blinding was partial/conditional rather than a strict single-blind design.exposures[0].timing.pulse_repetition_frequency_hz— PRF (20 Hz) is derived from the stated 50 ms burst period as a period-to-frequency unit conversion, as permitted by the burst rule; pulse duration itself is not stated directly (would require multiplying duty cycle by period) and is left not_reported.adverse_events— TEM showed nerve ultrastructure alterations (reduced myelinated axon numbers, thin myelination, cytoskeletal density loss, electron-dense abnormalities) persisting up to 24 weeks post-FUS, recorded as an observed structural effect even though behavior returned to baseline and the paper frames it as reversible.