Fig. 1

Neuronal voltage changes and IOS changes near the site of CSD induction elicited by CSD subthreshold and threshold KCl stimuli. A High KCl puffs of increasing duration were applied onto the slice surface (L2/3) up to the threshold duration eliciting a CSD and, simultaneously, the IOS at the site of KCl application and at different distances from it (indicated by the colored dots in the inset) and the membrane potential of a L2/3 pyramidal neuron located at 100 µm from the KCl puffer were recorded (inset). Upper panels: representative membrane potential changes recorded in a L2/3 pyramidal cell located at 100 µm from the site of application of KCl puffs of increasing duration (as indicated below the black traces) up to the threshold duration eliciting a CSD (red trace). The voltage values of the first two peaks of the depolarization produced by the just subthreshold stimulus (-25 and -16 mV, respectively) are similar to those of the first two peaks of the depolarization produced by the CSD threshold stimulus (indicated with 1p and 2p in the threshold trace: -25 and -12 mV, respectively). The CSD threshold stimulus produces a third depolarization peak to -5 mV. Lower panels: normalized IOS changes recorded simultaneously at the same site in response to the same KCl puffs; the traces were normalized relative to the amplitude of the IOS change induced by the CSD threshold stimulus. The beginning of the steep IOS rise produced by the threshold KCl stimulus (red trace) occurs with a delay of 6.6 s from the KCl application and temporally coincides with the development of the third peak of the voltage change produced by the same stimulus. B Left: entire membrane potential change comprising the repolarization phase following the peak of the depolarization elicited by the CSD threshold KCl stimulus (same CSD trace as in panel A; duration at half amplitude, HW = 123 s). Right: IOS changes recorded at different distances from the KCl puffer (as indicated above the traces and cf inset in panel A for color code) in response to the CSD threshold (upper panel) and just subthreshold (lower panel) KCl stimulus in the same representative experiment. The steep IOS rise elicited by the CSD threshold stimulus propagates at a rate of 2.9 mm/min. C Left: average rate of propagation of CSD: 2.49 ± 0.09 mm/min; average CSD threshold: 251 ± 9 ms; average delay of CSD relative to the KCl puff: 7.4 ± 0.5 s (n = 16, N = 15)