Spike frequency–dependent inhibition and excitation of neural activity by high-frequency ultrasound
Martin Loynaz Prieto, Kamyar Firouzi, Butrus T. Khuri-Yakub, Daniel V. Madison, Merritt Maduke
Journal of General Physiology 2020, 152 · 10.1085/jgp.202012672
Abstract
Ultrasound can modulate action potential firing in vivo and in vitro, but the mechanistic basis of this phenomenon is not well understood. To address this problem, we used patch-clamp recording to quantify the effects of focused, high-frequency (43 MHz) ultrasound on evoked action potential firing in CA1 pyramidal neurons in acute rodent hippocampal brain slices. We find that ultrasound can either inhibit or potentiate firing in a spike frequency-dependent manner: at low (near-threshold) input currents and low firing frequencies, ultrasound inhibits firing, while at higher input currents and higher firing frequencies, ultrasound potentiates firing. The net result of these two competing effects is that ultrasound increases the threshold current for action potential firing, the slope of frequency-input curves, and the maximum firing frequency. In addition, ultrasound slightly hyperpolarizes the resting membrane potential, decreases action potential width, and increases the depth of the after-hyperpolarization. All of these results can be explained by the hypothesis that ultrasound activates a sustained potassium conductance. According to this hypothesis, increased outward potassium currents hyperpolarize the resting membrane potential and inhibit firing at near-threshold input currents but potentiate firing in response to higher-input currents by limiting inactivation of voltage-dependent sodium channels during the action potential. This latter effect is a consequence of faster action potential repolarization, which limits inactivation of voltage-dependent sodium channels, and deeper (more negative) after-hyperpolarization, which increases the rate of recovery from inactivation. Based on these results, we propose that ultrasound activates thermosensitive and mechanosensitive two-pore-domain potassium (K2P) channels through heating or mechanical effects of acoustic radiation force. Finite-element modeling of the effects of ultrasound on brain tissue suggests that the effects of ultrasound on firing frequency are caused by a small (<2°C) increase in temperature, with possible additional contributions from mechanical effects.
Abstract via europepmc.
Exposures
Exposure 1: 43 MHz continuous-wave ultrasound applied to CA1 pyramidal neurons in acute hippocampal brain slices
Target: CA1 — “CA1 pyramidal neurons, hippocampus, acute rodent brain slices”
Device: custom-built
| Waveform | continuous | |
|---|---|---|
| Fundamental frequency (kHz) | 43,000 | ✓✓✓ |
| Pulse duration (ms) | not applicable | |
| Pulse repetition frequency (Hz) | not applicable | |
| Duty cycle (%) | 100 | ✓? |
| Sonication duration (s) | 1 | ✓✓✓ |
| Free-field pressure (kPa) | not reported | |
|---|---|---|
| Free-field Isppa (W/cm²) | 50 | ✓✓✓ |
| Free-field Ispta (W/cm²) | not reported | |
| 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 |
A 1-s, continuous-wave ultrasound pulse at 43 MHz and 50 W/cm2 was applied either 500 ms before the start of a 2-s current injection, or 1 s after the start of a 3-s current step, to compare firing in the presence versus absence of ultrasound in the same cell; the interval between ultrasound applications was at least 12 s, and control/ultrasound trials were alternated with the first condition tested varying randomly on a cell-by-cell basis.
Consistency checks: f0 out of range.
Flags from extraction
n_subjects— n=66 refers to individual patch-clamped neurons/cells (from an unspecified number of slices/animals), not distinct tissue preparations or animals; subject_unit 'preparation' is an approximation since the vocabulary has no explicit 'cell' category.exposures[0].in_situ— The ultrasound is applied directly to an ex vivo brain slice via a thin polystyrene film with no intervening skull or other tissue path; treated analogously to a bath/dish preparation with in_situ fields null.auditory_control— Not applicable: acute ex vivo brain slice preparation has no capacity for auditory perception.