Ultrasound modulates neuronal potassium currents via ionotropic glutamate receptors.

BACKGROUND: Focused ultrasound stimulation (FUS) has the potential to provide non-invasive neuromodulation of deep brain regions with unparalleled spatial precision. However, the cellular and molecular consequences of ultrasound stimulation on neurons remains poorly understood. We previously reported that ultrasound stimulation induces increases in neuronal excitability that persist for hours following stimulation in vitro. In the present study we sought to further elucidate the molecular mechanisms by which ultrasound regulates neuronal excitability and synaptic function. OBJECTIVES: To determine the effect of ultrasound stimulation on voltage-gated ion channel function and synaptic plasticity. METHODS: Primary rat cortical neurons were exposed to a 40 s, 200 kHz pulsed ultrasound stimulus or sham-stimulus. Whole-cell patch clamp electrophysiology, quantitative proteomics and high-resolution confocal microscopy were employed to determine the effects of ultrasound stimulation on molecular regulators of neuronal excitability and synaptic function. RESULTS: We find that ultrasound exposure elicits sustained but reversible increases in whole-cell potassium currents. In addition, we find that ultrasound exposure activates synaptic signalling cascades that result in marked increases in excitatory synaptic transmission. Finally, we demonstrate the requirement of ionotropic glutamate receptor (AMPAR/NMDAR) activation for ultrasound-induced modulation of neuronal potassium currents. CONCLUSION: These results suggest specific patterns of pulsed ultrasound can induce contemporaneous enhancement of both neuronal excitability and synaptic function, with implications for the application of FUS in experimental and therapeutic settings. Further study is now required to deduce the precise molecular mechanisms through which these changes occur.

Transient ultrasound stimulation has lasting effects on neuronal excitability.

BACKGROUND: Transcranial ultrasound stimulation can acutely modulate brain activity, but the lasting effects on neurons are unknown. OBJECTIVE: To assess the excitability profile of neurons in the hours following transient ultrasound stimulation. METHODS: Primary rat cortical neurons were stimulated with a 40 s, 200 kHz pulsed ultrasound stimulation or sham-stimulation. Intrinsic firing properties were investigated through whole-cell patch-clamp recording by evoking action potentials in response to somatic current injection. Recordings were taken at set timepoints following ultrasound stimulation: 0-2 h, 6-8 h, 12-14 h and 24-26 h. Transmission electron microscopy was used to assess synaptic ultrastructure at the same timepoints. RESULTS: In the 0-2 h window, neurons stimulated with ultrasound displayed an increase in the mean frequency of evoked action potentials of 32% above control cell levels (p = 0.023). After 4-6 h this increase was measured as 44% (p = 0.0043). By 12-14 h this effect was eliminated and remained absent 24-26 h post-stimulation. These changes to action potential firing occurred in conjunction with statistically significant differences between control and ultrasound-stimulated neurons in action potential half-width, depolarisation rate, and repolarisation rate, that were similarly eliminated by 24 h following stimulation. These effects occurred in the absence of alterations to intrinsic membrane properties or synaptic ultrastructure. CONCLUSION: We report that stimulating neurons with 40 s of ultrasound enhances their excitability for up to 8 h in conjunction with modifications to action potential kinetics. This occurs in the absence of major ultrastructural change or modification of intrinsic membrane properties. These results can inform the application of transcranial ultrasound in experimental and therapeutic settings.