Focused ultrasound (US) can modulate neuronal activity noninvasively with high spatial specificity. In intact nervous systems, however, efforts to determine its enigmatic mode of efficacy have been confounded by the indirect effects of US on mechanosensitive sensory cells and the inability to target equivalent populations of cells with pre-cision across preparations. Single-cell approaches, either via cultured mammalian neurons or tractable invertebrate neural systems, hold great promise for elucidating the cellular mechanisms underlying the actions of US. Here, we present evidence from the medicinal leech, Hirudo verbana, that researchers should apply caution when using US in conjunction with single-cell electrophysiological recording techniques, including sharp-electrode intracellular re-cording. Although we found that US could elicit depolarization of the resting membrane potential of single neurons, a finding with precedent, we determined that this effect and others could be reliably mimicked via subtle manual displacement of the recording electrode. Because focused US is known to induce resonance of recording electro-des, we aimed to determine how similarly US-induced depolarizations matched those produced by micro movements of a sharp glass electrode, a phenomenon we believe can account for purported depolarizations measured in this manner. Furthermore, we show that when clonally related homologous neurons, which are essentially isopo-tential, are impaled before the application of focused US, they show a statistically significant change in their membrane potential as compared with the homologous cells that received US with no initial impalement. Future investigations into US’s cellular effects should attempt to control for potential electrode resonance or use alterna-tive recording strategies.
Bibliographical noteFunding Information:
This work was supported by a University of Minnesota MnDRIVE Neuromodulation Fellowship (M.N.C.) and a Grant-in-Aid of Research (K.A.M.). This work was also partially supported by the National Science Foundation Grant #1451007 (to K.A.M.).
- Electrode resonance
- Hirudo verbana
- Intracellular recording
- Leak currents
- Ultrasound neuromodulation