Repetitive pulsed-wave ultrasound stimulation suppresses neural activity by modulating ambient GABA levels via effects on astrocytes
Tatsuya Mishima, Kenta Komano, Marie Tabaru, Takefumi Kofuji, Ayako Saito, Yoshikazu Ugawa, Yasuo Terao
Frontiers in Cellular Neuroscience 2024 · 10.3389/fncel.2024.1361242
Abstract
Ultrasound is highly biopermeable and can non-invasively penetrate deep into the brain. Stimulation with patterned low-intensity ultrasound can induce sustained inhibition of neural activity in humans and animals, with potential implications for research and therapeutics. Although mechanosensitive channels are involved, the cellular and molecular mechanisms underlying neuromodulation by ultrasound remain unknown. To investigate the mechanism of action of ultrasound stimulation, we studied the effects of two types of patterned ultrasound on synaptic transmission and neural network activity using whole-cell recordings in primary cultured hippocampal cells. Single-shot pulsed-wave (PW) or continuous-wave (CW) ultrasound had no effect on neural activity. By contrast, although repetitive CW stimulation also had no effect, repetitive PW stimulation persistently reduced spontaneous recurrent burst firing. This inhibitory effect was dependent on extrasynaptic-but not synaptic-GABA A receptors, and the effect was abolished under astrocyte-free conditions. Pharmacological activation of astrocytic TRPA1 channels mimicked the effects of ultrasound by increasing the tonic GABA A current induced by ambient GABA. Pharmacological blockade of TRPA1 channels abolished the inhibitory effect of ultrasound. These findings suggest that the repetitive PW low-intensity ultrasound used in our study does not have a direct effect on neural function but instead exerts its sustained neuromodulatory effect through modulation of ambient GABA levels via channels with characteristics of TRPA1, which is expressed in astrocytes.
Abstract via europepmc.
Exposures
Exposure 1: Cultured hippocampal neurons on astrocytes, 5 MHz PW and CW
Target: cultured neurons, cultured glia — “primary cultured hippocampal cells”
Device: other named manufacturer · KGK · 5C1I ✓
| Waveform | pulsed, continuous | |
|---|---|---|
| Fundamental frequency (kHz) | 5,000 | ✓✓✓ |
| Pulse duration (ms) | 0.5 | ✓✓✓ |
| Pulse repetition frequency (Hz) | 100 | ✓✓✓ |
| Duty cycle (%) | 5, 100sweptpulse duration × PRF gives 5% | ✓✓✓⚑ |
| Sonication duration (s) | 2, 0.1swept | ✓✓✓⚑ |
| Free-field pressure (kPa) | 100 | ✓✓✓ |
|---|---|---|
| Free-field Isppa (W/cm²) | 0.38, 0.7swept | ✓✓✓ |
| Free-field Ispta (W/cm²) | 0.0192 | ✓✓✓ |
| In-situ estimate | not applicable | |
| In-situ pressure (kPa) | not applicable | |
| In-situ Isppa (W/cm²) | not applicable | |
| In-situ Ispta (W/cm²) | not applicable |
Pulsed wave: 0.5-ms tone burst, PRF 100 Hz, DC 5%, 2 s per sonication; continuous wave: 100 ms. Single-shot (2-s PW applied five times at 20-s intervals) versus repetitive (PW repeated 20 times at 10-s intervals, total approx. 192 s; 10 repetitions also tested).
Flags from extraction
exposures[0].unspecified_domain.ispta_w_cm2— Paper gives 19.2 mW/cm2; recorded as 0.0192 W/cm2 (unit conversion only).exposures[0].unspecified_domain.isppa_w_cm2— 0.38 W/cm2 is for the PW pattern and 0.7 W/cm2 for the CW pattern (quoted separately in the text); only the PW sentence is quoted here.exposures[0].unspecified_domain.pressure_kpa— Paper says all stimulation was at 100 kPa (maximum measured 150 kPa); the transducer was calibrated in degassed water but the paper does not label the 100 kPa value as free-field.n_subjects— Group sizes are numbers of independent experiments (PW x10 n=9, PW x20 n=19, control n=25 unstimulated); no total of cultures or animals is stated.exposures[0].timing.sonication_duration_s— List is [PW 2 s, CW 100 ms]; the repetitive protocol totals about 192 s (see protocol_description).exposures[0].timing.duty_cycle_pct— List is [PW 5%, CW 100%].