Hippocampal culture stimulus with 4-megahertz ultrasound

Abstract

Among current modalities, ultrasound uniquely offers both millisecond and millimeter accuracy in noninvasively stimulating brain tissue. In addition, by sweeping the ultrasound beam within the refractory period of the neuronal tissue, ultrasonic neuromodulation can be adapted to target extended or multiply connected regions with quasi-simultaneity. Towards the development of this safe brain stimulus technique, the response of rat hippocampal cultures to ultrasound was investigated. Hippocampal slices, 0.4-mm thick, were obtained from 8-day old Sprague Dawley rats and cultured for 6 days. The in vitro cultures were exposed to multiple 100-ms 4.04-MHz ultrasound pulses from a 42-mm diameter, 90-mm spherical cap transducer. Peak pressure ranged from 0 through about 77 kPa. Responses in the form of electrical potentials from a sixty channel electrode array were digitized and recorded. The DG and CA1 regions of the hippocampus exhibited similar ultrasonically-evoked field potentials.

Ultrasound Stimulations Induce Prolonged Depolarization and Fast Action Potentials in Leech Neurons

“…The fact that more than 50% of the recorded cells responded with spikes to US suggests a threshold mechanism associated to US stimulus intensity. These results are in accordance with in vitro studies [31] , [32] , which observed in different regions of rat hippocampal slice cultures that US induced intensity dependent responses, and hypothesized a threshold mechanism and a fatigue effect associated to US stimulus intensity. Moreover, the high variability of responses and success rates observed across recorded cells, similarly as in previous studies [8] , [11] , [31] , [32] , could be explained by different densities of mechanosensitive ion channels expressed in the same cell type.…”

“…Several works suggest that US acts on voltage gated ion channels [4] , [13] , [31] , [32] , [35] . However, the exact dynamics of this interaction is still unclear.…”

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

“…In 1942, 835‐kHz “supersound” focused into the cortex was shown to disrupt neural function in the living mammal (Lynn et al, ); by 1958, it had been demonstrated that these effects could be both focused subcortically and reversed (Fry, ). Further investigations of frequencies as low as 250 kHz (Tufail et al, ) have impelled recognition that ultrasound, with its millimeter‐level spatial resolution, millisecond‐level temporal resolution (Muratore, ), and deep but noninvasive penetration of brain tissues (Tyler, ; Yoo et al, ), may be an attractive neurostimulatory device. Consequently, in addition to its use in thrombolysis (Hitchcock and Holland, ) and ablative neurosurgery (Martin et al, ; Lipsman et al, ), ultrasound has been proposed as a means to modulate neural activity therapeutically in epilepsy (Yang et al, ), traumatic brain injury (Demirtas‐Tatlidede et al, ; Villamar et al, ), and Parkinson's disease (Strauss et al, ).…”

“…Although the mechanisms behind ultrasound‐mediated neural stimulation are still unclear, a few mutually compatible factors have been suggested, including tissue hyperthermia (Bachtold et al, ), membrane potential alteration by pericellular fluid mechanics (Tyler, ), mechanosensitive ion channel stimulation (Tyler, ), neurotransmitter release (Tyler et al, ), and tissue cavitation (Muratore, ). In contrast to the variety of hypotheses about the possible mechanisms of neural stimulation by ultrasound, the body of existing research in this field has examined the phenomenon within only a narrow range of possible parameters.…”

“…In contrast to the variety of hypotheses about the possible mechanisms of neural stimulation by ultrasound, the body of existing research in this field has examined the phenomenon within only a narrow range of possible parameters. For example, although ultrasound's effects on evoked potentials have been previously examined on time scales on the order of several minutes (Bachtold et al, ), investigations of spontaneous activity have been confined to postexposure times on the order of milliseconds (Tyler et al, ; Tufail et al, ; Muratore, ) or a maximum of 1 min (Khraiche et al, ). Furthermore, the lowest‐intensity reported systematic investigation of ultrasonic stimulation of neural activity reported a minimum I SPPA of 75 mW/cm 2 (Tyler et al, ; Tufail et al, ), despite previous preliminary evidence showing neurophysiological effects at intensities less than 0.3% of this value (Han, ).…”