Figure 1

The x-y location of a micropipette can be electrically imaged using an HD-MEA. (a) A micropipette tip, stimulating with a current square wave (50 nA, 1 kHz), was used as a point-current source. The electrical potential landscape of the point source was measured in (b,c) saline and (d,e) in the presence of an acute brain slice of 200 μm thickness by using an HD-MEA. (b) Microscopy images, using infrared differential interference contrast (IR-DIC), show the electrode array (left panel) and the micropipette tip (right panel). One electrode is highlighted; the electrode size is 10.2 μm × 8.6 μm, the electrodes are arranged in a hexagonal pattern, and the center-to-center distance between the electrodes is 17.8 μm. The HD-MEA surface and the micropipette are at z = 0 and 50 μm, respectively. (c) The map illustrates the measured potential spatial distribution of a stimulating micropipette, located at the center of the array at 50 μm z-distance in saline as isotropic conductor medium. The voltage amplitude, detected at each electrode site, is color-coded (blue (0 μV) to red (120 μV)). (d) A 200-μm thick-cerebellar slice atop the HD-MEA is imaged by fluorescence microscopy, using a green-fluorescent-protein (GFP) filter. The acute brain slice was obtained from a GAD67-GFP knock-in mouse, where the majority of the GABAergic neurons were GFP positive³⁶. The cell bodies can be identified as dark spots in the Purkinje cell layer (PCL), and the dendritic arbors, shown in dark gray, indicate the molecular layer (ML). The other layers were determined according to the established cerebellar structure in literature: pia³⁹, granular cell layer (GCL), and white matter (WM). (e) The potential spatial distribution maps similar to those in c were obtained by placing a stimulating micropipette at the ML (left panel) and at the GCL (right panel) of the acute cerebellar slice shown in (d).