Transcranial Ultrasound Stimulation of the Anterior Cingulate Cortex Reduces Neuropathic Pain in Mice

Xiangjun Feng, Lili Niu, Meng Long, Kaixuan Luo, Xiaowei Huang, Moxian Chen, Zhengrong Lin, Wei Zhou, Shasha Yi, Lijuan Ao

Evidence-Based Complementary and Alternative Medicine 2021, 2021, 1-14 · 10.1155/2021/6510383

rodentchronic painbehaviourinvasive electrophysiologyhistology molecular

Abstract

Focused ultrasound (FUS) is a potential tool for treating chronic pain by modulating the central nervous system. Herein, we aimed to determine whether transcranial FUS stimulation of the anterior cingulate cortex (ACC) effectively improved chronic pain in the chronic compress injury mice model at different stages of neuropathic pain. The mechanical threshold of pain was recorded in the nociceptive tests. We found FUS stimulation elevated the mechanical threshold of pain in both short-term ( p p < 0.05) experiments. Furthermore, we determined protein expression differences in ACC between the control group, the intervention group, and the Sham group to analyze the underlying mechanism of FUS stimulation in improving neuropathic pain. Additionally, the results showed FUS stimulation led to alterations in differential proteins in long-term experiments, including cellular processes, cellular signaling, and information storage and processing. Our findings indicate FUS may effectively alleviate mechanical neuropathic pain via the ACC's stimulation, especially in the chronic state.

Abstract via europepmc.

Speciesmouse (C57BL/6J)

Subjects6, 6, 12swept animals

Sessions per subject21

Randomisedyes

Blindingnot reported

Sham / controlinactive transducer

Auditory controlnot reported

Readout timingboth

Anaesthesiaanaesthetised

Readoutsbehaviour, invasive electrophysiology, histology molecular — Von Frey mechanical allodynia test; thermal (laser) allodynia test; sciatic functional index; multielectrode array (MEA) recording of ACC brain slices; iTRAQ quantitative proteomics; Western blotting (Hnrnph1, Hnrnpd, Snrpb, Dhx16); HE staining

Direction of effectinhibitoryFUS stimulation of the ACC increased the mechanical withdrawal threshold (reduced allodynia) in both short- and long-term neuropathic pain experiments, and FUS2 stimulation of ACC brain slices significantly decreased the spike frequency of neuronal discharges.

Adverse eventsnone observedHE staining of ACC brain tissue and the CCI surgical site showed no neurofibrillation, axon irregularities, myelin damage, inflammatory infiltration, or cell degeneration; local temperature increase was less than 0.1 degC and peak negative pressure was much lower than the inertial cavitation threshold (40 MPa).

Exposures

Exposure 1: FUS1 and FUS2 stimulation of ACC (Cg)

Target: anterior cingulate cortex — “anterior cingulate cortex (ACC, Cg region)”
Device: custom-built

Pulse timing
Waveform	pulsed
Fundamental frequency (kHz)	3,700	✓✓✓
Pulse duration (ms)	not reportedimplied by duty cycle ÷ PRF: 0.0667 ms (not stated by the paper)	⚑
Pulse repetition frequency (Hz)	1,500	✓✓✓
Duty cycle (%)	10	✓✓✓
Sonication duration (s)	900	✓✓✓

Pressure and intensity, by domain
Free-field pressure (kPa)	not reported
Free-field Isppa (W/cm²)	15.98, 34.98swept	✓✓✓
Free-field Ispta (W/cm²)	1.6, 3.5swept	✓✓✓
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

Protocol, in the paper’s words

Ultrasound stimulation was performed through a collimator just touching the scalp, 15 min/day for 21 days, under isoflurane anesthesia (2% induction, 0.6% maintenance). Short-term experiment started FUS on day 7 after CCI surgery (FUS1, FUS2 and sham groups, 6 mice/group); long-term experiment started FUS2 stimulation on day 91 after CCI surgery (FUS, Control-sham-operation, and Sham groups, 12 mice/group). Nociceptive tests were repeated every 6-7 days following stimulation onset.

Flags from extraction

exposures[0].timing.pulse_duration_ms — Paper states PRF (1.5 kHz) and duty cycle (10%) but never states a separate pulse duration in ms; left not_reported rather than computed.
n_subjects — Ultrasound was applied only to FUS1/FUS2 (short-term, 6/group) and FUS (long-term, 12/group) groups; other groups received no real ultrasound and no single total is stated, so group sizes are listed.
exposures[0].in_situ — Paper states acoustic intensity attenuation through the skull was up to 80% but gives no explicit derated in-situ pressure or intensity value.