Abnormal UP/DOWN Membrane Potential Dynamics Coupled with the Neocortical Slow Oscillation in Dentate Granule Cells during the Latent Phase of Temporal Lobe Epilepsy

Method to compare the incidence and power of slow oscillations in the membrane potential of dentate granule cells from control and post-SE rats. A, Top, V_m of a DGC from a control rat. The recording was bandpass filtered (0.1-40 Hz). Bottom, Time-varying power in the slow-frequency range (0.1-2 Hz) extracted from the time–frequency spectrogram of the V_m trace computed over a 5 s sliding window in 0.2 s steps. B, Same as in A except that the cell from a post-SE rat was spontaneously firing (unlike the cell in A), and spikes were digitally removed from the recording. Scale bar, as in A. C1, For each recording in controls, the 90th percentile highest value of the SWO band (0.1-2 Hz) power (Xi) was determined. The mean of all these values for control cells gives a unique threshold (SWOThr), which is then used to determine the SWO epochs in all DGCs from both control and post-SE rats. C2, Example of the time-varying SWO power for the two recordings shown in A (top, blue) and B (bottom, red). Dashed lines correspond to the threshold for significant SWO epochs detection (green arrow). The epochs of high SWO power (green horizontal bars) are defined as epochs when the SWO power is above the threshold for >4 s. C3, Illustration of detected SWO epochs corresponding to the light blue- and orange-shaded areas in C2, Top, V_m traces. Bottom, Time–frequency spectrogram. Superimposed white lines represent the time-varying power values in the SWO band (0.1-2 Hz). Dashed white lines (green arrows) indicate the threshold used for SWO epochs detection (horizontal green bars above the traces).

Increased slow-oscillatory UP/DOWN state dynamics of the membrane potential of dentate granule cells in post-SE rats. A1, Neurolucida reconstruction of the morphology of a recorded dentate granule cell from a control rat (top) and voltage responses to intracellularly injected depolarizing and hyperpolarizing current pulses (500 ms duration, bottom). A2, Top, V_m of the cell illustrated in A1 during a 60 s recording. Bottom, Time–frequency power spectrogram (5 s sliding window, 0.2 s steps) corresponding to the top trace. Superimposed white line represents the time-varying power values in the SWO frequency range (0.1-2 Hz). Dashed white line (green arrow) indicates the SWO detection threshold used to detect SWO epochs (horizontal green bars). A3, Top, Distribution of V_m values for the trace shown in A2, Bottom, Relative proportion of DGCs according to the distribution of their V_m (Ske., skewed; Sym., symmetric; n = 10). B, Same as in A for the post-SE condition. Note the presence of a continuous band in the slow-frequency range (∼0.8 Hz), and bimodal distribution of the V_m in the DGC from post-SE, but not control, rat (Bim., bimodal). C, Power spectrum of the traces shown in A (blue) and B (red). D, Average power spectrum for all recorded DGCs in control (blue line; n = 10) and post-SE (red line; n = 8). E, Autocorrelogram of the traces shown in A (blue) and B (red). F, Mean autocorrelogram for all recorded DGCs in control (blue line; n = 10) and post-SE (red line; n = 8). Light blue- and pink-shaded areas correspond to ±SEM.

Increased slow-oscillatory epochs in the membrane potential of dentate granule cells in post-SE rats. A, B, Examples of detected SWO epochs in the membrane potential of dentate granule cells from a control rat (A) and a post-SE rat (B; spikes digitally removed). In each panel, the V_m (top), time–frequency power spectrogram (bottom) and time-varying power in the SWO band (0.1-2 Hz; superimposed white line) are represented at low (1) intermediate (2), and high (3) temporal resolution. In all cases, green horizontal bars below the trace highlight detected SWO epochs (Scale bars in B, same as in A). C, Box plots of the duration of single SWO epochs detected in the V_m of DGCs in control (n = 6) and post-SE (n = 8) conditions. D, Box plots of the percentage of recording time with significant oscillations in the SWO frequency range in the V_m of DGCs in control (n = 10) and post-SE (n = 8) rats. E, Box plots of the power in the SWO frequency range averaged over all recorded cells and recording times in the V_m of DGCs in control (n = 10) and post-SE (n = 8) rats. For these and subsequent box plots, the box extends from the 25th to 75th percentile. The line in the middle of the box is the median. The whiskers go down to the smallest value and up to the largest. *p < 0.05; **p < 0.01; ***p < 0.001.

Comparing neocortical local field potential slow oscillations between control and post-SE rats. A, Example LFP recorded in the parietal cortex in a control rat, with the threshold levels used to detect UP or DOWN states indicated by horizontal bars (green, DOWN state; purple, UP state). B, Histogram of the distribution of LFP values for the trace shown in A. The level for DOWN state detection (green vertical line) was set at the lower two-thirds of the distance between the peaks of the bimodal distribution of LFP values. The level for UP state detection (purple vertical line) was set at the higher two-thirds of the distance between the peaks of the bimodal distribution of LFP values. C, Example LFP recorded in the parietal cortex from a post-SE rat. D, Mean power spectrum of the LFPs recorded in the parietal cortex. Control (n = 10) and post-SE (n = 10) in D–H. E, Average autocorrelogram of LFPs in control (blue line) and post-SE (red line) conditions with a nonsignificant difference at the negative peaks. F, Box plots of the frequency of the neocortical SWO in control and post-SE rats. G, Box plots of neocortical UP state duration in control and post-SE rats. H, Box plots of neocortical DOWN state duration in control and post-SE rats. Light blue- and pink-shaded areas in D and thinner lines in E indicate SEM. ns, p > 0.05; *p < 0.05. For description of box plots, see the legend of Figure 3.

Strong temporal correlation between the membrane potential of dentate granule cells and the parietal cortex local field potential in post-SE rats, but not in control rats. A, V_m of a DGC from a control rat (top) and simultaneously recorded LFP in the parietal cortex (bottom). B, Same as in A for a DGC from a post-SE rat. Scale bars are as in A. C, V_m vs LFP cross-correlograms for all individual DCGs from control rats (n = 10). D, Same as in C for DGCs from post-SE rats (n = 8). E, Average V_m vs LFP cross-correlogram of all DGCs recorded in control rats (blue line, n = 10) and post-SE rats (red line, n = 8). F, DOWN–UP transition-triggered V_m for all individual DGCs from control rats (n = 10). G, Same as in F for DGCs from post-SE rats (n = 8). H, Average DOWN–UP transition-triggered V_m for DGCs recorded in control rats (blue line, n = 10) and post-SE rats (red line, n = 8). Thinner lines in E and H represent ±SEM.

Modulation of the action potentials of dentate granule cells by the neocortical slow oscillation in post-SE and control rats. A, E, Membrane potential of a DGC (top) recorded in a post-SE rat (A) or a control rat after depolarization to induce spontaneous firing (E) and simultaneously recorded local field potentials in the parietal cortex (bottom). B, Box plots of the firing frequency of intracellularly recorded DGCs from control rats (with no added depolarization; n = 10) and post-SE rats (n = 8). C, Box plots of the percentage of neocortical UP phases associated with at least one AP in the control condition (with no added depolarization; n = 10) and post-SE condition (n = 8). D, Phase distribution histogram of APs recorded in the DGC shown in A in reference to SWO phase in the parietal cortex. The orange-shaded area depicts the UP phase of SWO simultaneously recorded in the parietal cortex. F, Same as in B for DGCs from control rats before and after depolarization to induce spontaneous firing (n = 8). G, Same as in C for DGCs from control rats before and after depolarization to induce spontaneous firing (n = 8). H, Same as in D for the cell illustrated in E. *p < 0.05; **p < 0.01. For a description of box plots, see the legend of Figure 3.

Lack of a significant increase in slow oscillations in the membrane potential of dentate granule cells by depolarization in control rats. A1, A2, Top, Membrane potential of a dentate granule cell from a control rat before (A1) and after (A2) artificial depolarization through direct current injection to ∼-55 mV (spikes digitally removed). Scale bar in A1 is the same as in A2. Bottom, Corresponding time–frequency power spectrograms (5 s sliding window, in 0.2 s steps). Superimposed white lines represent the time-varying power in the SWO band (0.1–2 Hz). Dashed white line (green arrow) indicates the SWO detection threshold used to detect SWO epochs highlighted by green horizontal bars below the traces. B, Box plots of the mean power in the SWO band over all recorded cells (n = 8) and recording times before (Cont) and after (Depol) depolarization. p = 0.43^jj; Paired Student’s t test. C, Box plots of the mean duration of single intracellular SWO epochs before (Cont) and after (Depol) depolarization. p = 0.44^kk; n = 6; Wilcoxon signed rank test. D, Box plots of the percentage of intracellular SWO before (Cont) and after (Depol) depolarization. p = 0.24^ll; n = 8; Paired Student’s t test. ns, p > 0.05. For a description of box plots, see the legend of Figure 3.

Increased rate and slow temporal modulation of multiunit activity in the dentate granule cell layer in post-SE vs control rats. A, B, High-pass-filtered (1000 Hz) local field potential recording in the dentate granule cell layer (DGCL; top) showing MUA (vertical bars) and simultaneously recorded local field potential in the parietal cortex (PC; bottom) in a control rat (A) and a post-SE rat (B). The scale bar values in B are the same as in A. C, D, Phase histogram of MUA from the recording shown in A (C) and simultaneously recorded in the parietal cortex (D). The blue-shaded area depicts the UP phase of SWO in the parietal cortex. E, F, Same layout as C and D for the recordings illustrated in B. The orange-shaded area depicts the UP phase of the SWO in the parietal cortex. G, Box plots of the frequency of MUA recorded in the DGCL. n = 7 control and n = 17 post-SE rats in this and all subsequent panels. H, Box plots of the length of Rayleigh vector of MUA recorded in the DGCL in control and post-SE rats. I, Box plots of the preferred phase of MUA recorded in the DGCL for all recordings in control and post-SE rats in reference to SWO recorded in the PC. J, Box plots of the dispersion of DGCL MUA around the mean phase of SWO recorded in the PC in control and post-SE rats. Ns, p > 0.05; *p < 0.05. For a description of box plots, see the legend of Figure 3.