Fig. 3: Transient mechanical stimulation evokes action potentials.
a, Fluorescence intensity (green line) of a spontaneously firing neuron expressing the fluorescent calcium reporter GCaMP6s. Blue lines show spike times of the same neuron recorded by the HD-MEA. Red triangles highlight the GCaMP6 fluorescence peaks. The black dotted box shows the alignment of calcium responses and HD-MEA signals. b, Fluorescence intensity (green line) of a neuron expressing GCaMP6s after adding the synaptic-activity blockers DNQX and D-AP5. c, Cartoon showing the mechanical stimulation of a neuron (top panel). Fluorescence images of the rat cortical neuron on the HD-MEA chip expressing GCaMP6s before (left) and compression (right) mechanical stimulation (bottom panel). Red lines outline the free end of the AFM cantilever with the 5 µm bead. Scale bars, 105 µm. d, Normalized fluorescence intensity of mechanically stimulated neurons expressing GCaMP6s. The grey window shows the stimulation period. e, A force–time curve recorded during mechanical stimulation of the neuron. Approach (blue) and retraction (red) of the bead are shown in c. f, Left, fluorescence image of a stimulated neuron with HD-MEA electrodes indicated with different numbers. Right, extracellular potentials detected on the corresponding electrodes (numbers) during mechanical stimulation. Scale bar, 105 µm. g,h, Superimposed waveforms of mechanically evoked (g) and spontaneously occurring (h) action potentials (nspikes = 50 obtained from 16 independent neurons). Comparing the amplitudes and halfwidth of the mechanically evoked (g) and spontaneously occurring action potentials (h) with a Mann–Whitney U-test resulted in P values of 0.098 and 0.11, respectively.
