Patch Clamp Technology for Focused Ultrasonic (FUS) Neuromodulation

Electrical stimulation of neural tissue, such as deep brain stimulation (DBS) and cortical stimulation, is widely applied therapeutic neuromodulation techniques for neurologic disorders. Penetrating electrodes (e.g., microwires and silicon probes) for DBS provide high spatial resolution, but are invasive, displacing neural tissue, producing acute insertion trauma, and potentially eliciting a foreign-body response. Surface electrodes, while less invasive, cannot generate a highly localized electrical field. Motivated by these limitations, the goal of this chapter is to provide a protocol to run patch clamp experiments on rat brain slices with a focused ultrasonic transducer that offers minimally invasive and highly localized neuronal stimulation (and that is thin enough to let light to pass through for optical observation of neuron cells for patching). Though focused acoustic beams with high energy are traditionally used for cellular ablation, the goal here is to use low acoustic energy to avoid any ablation or lesion, exploiting the unprecedented features of self-focusing acoustic transducers (SFATs) that can focus 2–20 MHz sound waves at a submillimeter-sized area. The experimental procedures described here will allow intracellular and extracellular experiments to determine the value and underlying mechanisms of neuromodulation effects induced by SFAT-based ultrasonic stimulation. The aims of this protocol are (1) to fabricate SFATs for the proposed intracellular and extracellular experiments and (2) to characterize the neuromodulatory function evoked by SFAT-based ultrasound stimulation in normal brain slices. Using patch clamp methods, one can monitor ionic flux and local field potentials, while varying the acoustic stimulation frequency, intensity, pulse width, pulse shape and pulse repetition frequency as well as the focal spot(s), focal size and force direction. The patch clamp experiments will provide insights into biologic mechanisms of ultrasonic neural stimulation, and could be a critical step toward the development of a minimally invasive alternative to neuromodulation by electrical stimulation in the treatment of neurologic disorders such as epilepsy. If the underlying mechanisms of ultrasonic neural stimulation are well understood, a transcranial focused ultrasound beam can possibly modulate pathological neural activities, without surgery, running wire, or any damaging effects from penetrating probe.