Low-intensity pulsed ultrasound stimulation (LIPUS) modulates microglial activation following intracortical microelectrode implantation

Fan Li, Jazlyn Gallego, Natasha N. Tirko, Jenna Greaser, Derek Bashe, Rudra Patel, Eric Shaker, Grace E. Van Valkenburg, Alanoud S. Alsubhi, Steven Wellman, Vanshika Singh, Camila Garcia Padilla, Kyle W. Gheres, John I. Broussard, Roger Bagwell, Maureen Mulvihill, Takashi D. Y. Kozai

Nature Communications 2024, 15 · 10.1038/s41467-024-49709-9

rodentothercellular imaginginvasive electrophysiologyhistology molecular

Abstract

Microglia are important players in surveillance and repair of the brain. Implanting an electrode into the cortex activates microglia, produces an inflammatory cascade, triggers the foreign body response, and opens the blood-brain barrier. These changes can impede intracortical brain-computer interfaces performance. Using two-photon imaging of implanted microelectrodes, we test the hypothesis that low-intensity pulsed ultrasound stimulation can reduce microglia-mediated neuroinflammation following the implantation of microelectrodes. In the first week of treatment, we found that low-intensity pulsed ultrasound stimulation increased microglia migration speed by 128%, enhanced microglia expansion area by 109%, and a reduction in microglial activation by 17%, indicating improved tissue healing and surveillance. Microglial coverage of the microelectrode was reduced by 50% and astrocytic scarring by 36% resulting in an increase in recording performance at chronic time. The data indicate that low-intensity pulsed ultrasound stimulation helps reduce the foreign body response around chronic intracortical microelectrodes.

Abstract via europepmc.

Speciesmouse (CX3CR1-GFP transgenic); rat (Sprague-Dawley)

Subjects7, 4swept animals

Sessions per subject11, 17swept

Randomisednot reported

Blindingnot reported

Sham / controlno treatment control, undescribed

Auditory controlnot reported

Readout timingoffline

Anaesthesiaanaesthetised

Readoutscellular imaging, invasive electrophysiology, histology molecular — Two-photon imaging of microglia migration/activation/surveillance and vasculature; multi-unit/single-unit electrophysiology recorded from implanted microelectrodes; GFAP and BDNF immunohistochemistry

Direction of effectmixed or unclearLIPUS increased microglial migration velocity, expansion/retraction, and total surveillance at early time points (day 1, 3, 7), and decreased microglial morphological activation, probe coverage, vessel-associated microglia ratio, blood vessel diameter, and astrocyte (GFAP) activation at later time points (day 6-28); LIPUS also increased chronic single-unit recording performance.

Adverse eventsnone observedTemperature change at the stimulation site was kept below 1 degC during LIPUS exposure (verified with an implanted thermocouple), and ISPTA was kept below FDA intensity thresholds for low-power ultrasound.

Exposures

Exposure 1: LIPUS to mouse visual cortex following microelectrode implantation

Target: visual cortex — “visual cortex”
Device: custom-built · American Piezo · #1219, 851 Material, Wrap Electrode

Pulse timing
Waveform	pulsed
Fundamental frequency (kHz)	1,130	✓✓✓
Pulse duration (ms)	22	✓✓✓
Pulse repetition frequency (Hz)	2	✓✓✓
Duty cycle (%)	4.4pulse duration × PRF gives 4.4%	✓✓✓
Sonication duration (s)	300	✓✓✓

Pressure and intensity, by domain
Free-field pressure (kPa)	not reported
Free-field Isppa (W/cm²)	not reported
Free-field Ispta (W/cm²)	0.3	✓✓✓
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

LIPUS delivered on days 0, 1, 2, 3, 4, 5, 6, 7, 14, 21 and 28 post-implantation, above the cranial window over visual cortex. Each session comprised a total of 15 min of LIPUS exposure divided into three 5-min intervals, with 5 min of non-exposure between each sonication.

Exposure 2: LIPUS over implanted microelectrode in rat primary somatosensory (whisker barrel) cortex

Target: primary somatosensory cortex — “right primary whisker barrel cortex”
Device: custom-built · American Piezo · #1219, 851 Material, Wrap Electrode

Pulse timing
Waveform	pulsed
Fundamental frequency (kHz)	1,130	✓✓✓
Pulse duration (ms)	22	✓✓✓
Pulse repetition frequency (Hz)	2	✓✓✓
Duty cycle (%)	4.4pulse duration × PRF gives 4.4%	✓✓✓
Sonication duration (s)	300	✓✓✓

Pressure and intensity, by domain
Free-field pressure (kPa)	not reported
Free-field Isppa (W/cm²)	not reported
Free-field Ispta (W/cm²)	0.3	✓✓✓
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

LIPUS or sham was applied daily for the first week following electrode implantation, then twice weekly for the remaining 5 weeks; each stimulation session consisted of 3 x 5 min stimulation periods interleaved with 5 min quiescence periods.

Flags from extraction

n_subjects — Study combines two species (mice N=7 LIPUS, rats N=4 LIPUS) reported in separate sentences; given as a list rather than summed since they are different cohorts/species.
n_sessions_per_subject — Mouse cohort (11 sessions over days 0-28) and rat cohort (7 daily + 10 twice-weekly = 17 sessions) followed different schedules; both counts derived from the stated day lists/schedule, given as a list.
sham_type — Mouse control group received no procedure at all (no transducer used); rat control/sham mechanism is not described beyond 'sham treatment'; mechanism not specified for either.