Prolonged stimulation with low‐intensity ultrasound induces delayed increases in spontaneous hippocampal culture spiking activity
Hyun‐Bum Kim, Kelley M. Swanberg, Hee‐Sok Han, Jung‐Chae Kim, Jun‐Woo Kim, Sungon Lee, C. Justin Lee, Sungho Maeng, Tae‐Seong Kim, Ji‐Ho Park
Journal of Neuroscience Research 2017 · 10.1002/jnr.23845
Abstract
Ultrasound is a promising neural stimulation modality, but an incomplete understanding of its range and mechanism of effect limits its therapeutic application. We investigated the modulation of spontaneous hippocampal spike activity by ultrasound at a lower acoustic intensity and longer time scale than has been previously attempted, hypothesizing that spiking would change conditionally upon the availability of glutamate receptors. Using a 60-channel multielectrode array (MEA), we measured spontaneous spiking across organotypic rat hippocampal slice cultures (N = 28) for 3 min each before, during, and after stimulation with low-intensity unfocused pulsed or sham ultrasound (spatial-peak pulse average intensity 780 μW/cm 2 ) preperfused with artificial cerebrospinal fluid, 300 μM kynurenic acid (KA), or 0.5 μM tetrodotoxin (TTX) at 3 ml/min. Spike rates were normalized and compared across stimulation type and period, subregion, threshold level, and/or perfusion condition using repeated-measures ANOVA and generalized linear mixed models. Normalized 3-min spike counts for large but not midsized, small, or total spikes increased after but not during ultrasound relative to sham stimulation. This result was recapitulated in subregions CA1 and dentate gyrus and replicated in a separate experiment for all spike size groups in slices pretreated with aCSF but not KA or TTX. Increases in normalized 18-sec total, midsized, and large spike counts peaked predominantly 1.5 min following ultrasound stimulation. Our low-intensity ultrasound setup exerted delayed glutamate receptor-dependent, amplitude- and possibly region-specific influences on spontaneous spike rates across the hippocampus, expanding the range of known parameters at which ultrasound may be used for neural activity modulation. © 2016 Wiley Periodicals, Inc.
Abstract via europepmc.
Exposures
Exposure 1: Unfocused pulsed ultrasound over organotypic hippocampal slice, 0.5 MHz, 3 min
Target: brain slice, hippocampus — “organotypic hippocampal slice cultures”
Device: other named manufacturer · TKS Co. · water-immersion transducer (10 x 10 mm square crystal element) ✓
| Waveform | pulsed | |
|---|---|---|
| Fundamental frequency (kHz) | 500 | ✓✓✓ |
| Pulse duration (ms) | 0.0021 | ✓✓✓⚑ |
| Pulse repetition frequency (Hz) | 1,160 | ✓✓✓ |
| Duty cycle (%) | not reportedpulse duration × PRF gives 0.243% | |
| Sonication duration (s) | 180 | ✓✓✓ |
| Free-field pressure (kPa) | 11.52 | ✓✓✓⚑ |
|---|---|---|
| Free-field Isppa (W/cm²) | 0.00078 | ✓✓✓⚑ |
| 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 |
3 min of baseline recording, 3 min of unfocused pulsed ultrasound (or sham, pulser off), then 3 min of recording; pulse duration 2.097 microseconds at 1.16 kHz PRF.
Consistency checks: intensity pressure inconsistent free field.
Flags from extraction
exposures[0].free_field.isppa_w_cm2— Text reads '780 lW/cm2' (OCR of microW/cm2); converted to 0.00078 W/cm2.exposures[0].timing.pulse_duration_ms— Text reads '2.097 lsec' (OCR of microseconds); converted to 0.002097 ms.n_subjects— N=28 rats stated, but experiment 1 (8 slices) plus experiment 2 (6 groups of 6) implies more; recorded as stated.exposures[0].device.family— Transducer maker named as TKS Co. though a figure legend calls the transducer custom-made; pulser MKPR-1025 (MKC Korea).exposures[0].free_field.pressure_kpa— Hydrophone scan in degassed water; slice exposed through aCSF.