Direct and safe manipulation of neurons by external means is an increasingly studied therapeutic modality with the potential to treat many neurological diseases. Anticipating such future applications, we investigated reversible bioeffects of very low dose focused ultrasound on neuronal cell morphology and function in vitro. To test morphological changes, undifferentiated PC12 cells were serum-cultured. The culture plates were placed on an inverted optical microscope. An f/1.1 ultrasound transducer with a water-filled coupling cone was focused on the culture and excited with 30-ms 4.67-MHz 100-kPa pulses. To test functional changes, rat hippocampal slices were cultured and individually transferred to the well of a 60-channel multi electrode array. An f/2.1 ultrasound transducer with a water-filled coupling cone was focused on a culture and excited with 100-Ps 4.04-MHz 77-kPa pulses. The culture was stimulated before and after the ultrasonic stimulus with a 100-Ps 100-PA biphasic electrical stimulus. Optical microscopy of PC12 cultures under insonification revealed that cells that were clustered near the ultrasound focal region elongated by approximately 2 Pm during insonification and returned to approximately their original shapes following insonification. We conclude that the acoustic radiation force is capable of reversibly deforming cultured cells. In the rat hippocampal cultures, the ultrasonically and electrically evoked responses exhibited similar biphasic waveforms. In addition, robust electrically evoked responses following insonification indicated that the insonified cultures remained viable. We conclude that low-dose ultrasound can stimulate neurons; the mechanism is currently under investigation.

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.

No abstract