Prolonged stimulation with low‐intensity ultrasound induces delayed increases in spontaneous hippocampal culture spiking activity

• Published in: Journal of neuroscience research 2017-03, Vol.95 (3), p.885-896
• Main Authors: Kim, Hyun‐Bum, Swanberg, Kelley M., Han, Hee‐Sok, Kim, Jung‐Chae, Kim, Jun‐Woo, Lee, Sungon, Lee, C. Justin, Maeng, Sungho, Kim, Tae‐Seong, Park, Ji‐Ho
• Format: Article
• Language: English
• Subjects: Action Potentials - drug effects; Action Potentials - physiology; Animals; Animals, Newborn; Dose-Response Relationship, Radiation; electrophysiology; Excitatory Amino Acid Agents - pharmacology; hippocampus; Hippocampus - cytology; In Vitro Techniques; Microelectrodes; multielectrode array; Neurons - drug effects; Neurons - physiology; Organ Culture Techniques; Rats; Receptors, Glutamate - metabolism; Sodium Channel Blockers - pharmacology; spike detection; spontaneous activity; Temperature; Tetrodotoxin - pharmacology; Time Factors; Ultrasonics - methods; unfocused pulsed ultrasound
• ISSN: 0360-4012; 1097-4547
• DOI: 10.1002/jnr.23845

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/cm2) 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. Ultrasonic stimulation induced sustained or delayed increases in spontaneous organotypic hippocampal spiking activity at a lower intensity than those previously asserted. Ultrasound‐mediated increases in spiking were blocked by glutamate receptor inhibition and may be region‐ and spike amplitude‐specific.