Figure 4.

ID responses as the optical signal of cell death. A, Averaged trace of ID response (n = 6) triggered by a short application of glutamate (30 μm, 30 s) and recorded over almost 4 h. Note that, after a rapid decrease in the phase signal during the first 20 min, the signal continues to decrease with a slower slope until it reaches a plateau. Calibration: 20 min and 10°. B, With a glycine (10 μm) and Mg²⁺-free extracellular solution, application of glutamate (30 μm, 30 s, arrowhead) triggers an ID response, in the presence of DNQX (n = 3; full line) or TTX (n = 1; dotted line). Calibration: 2 min and 10°. C, Coupled recording of phase (full line) and current (dotted) obtained after application of glutamate (30 μm, 30 s, arrowhead) shows that the ID response is associated with a strong inward current with an initial peak (amplitude, −7 nA). This inward current, after the peak, stabilized to reach a plateau. Calibration: 2 min, 5°, and 1 nA. D1, Example of an optical trace corresponding to an ID response triggered by application of glutamate (30 μm, 30 s, arrowhead). Calibration: 10 min and 15°. D2, Phase images of a neuron before (a) and 30 min after application of glutamate (b). The square in the middle of the cell corresponds to the region of interest where the phase signal is recorded in C1. In b′, the image shows the same neuron as in b after propidium iodide staining. Note that the strong labeling essentially localized to the nucleus of the cell. Scale bars, 10 μm.