Figure 1
Potentiation of the evoked response induced by GabT. A, Examples of the evoked activity's time course for a single trial for three representative electrodes located at 0.5, 1 and 2 mm distance (see inset) from the stimulating electrode respectively (black bar in inset). The number of evoked spikes increases following the GabT. Hippocampal cultures were stimulated with the lowest intensity (200–450 mV) evoking a response. 40 pulses (trials) with an inter-pulse interval 4s were used. Inset, graphical representation of the MEA grid. Each square represents an electrode. Distance between electrodes is 500 μm. Black bar corresponds to the stimulated electrodes and grey numbered squares to the electrodes whose activity is shown in (A). B, Raster plots of the spikes evoked in one electrode analyzed at each time point. Each horizontal line represents the response to one trial recorded up to 250 ms after the stimulus onset. C, Time course of the NFR. The total number of evoked spikes was counted in 10 ms bins, following electrical stimulation. The increase of evoked spikes is especially pronounced in the first 100 ms following stimulation. Data from a single experiment shown in (A-C). D, Average time course of the NFR (n = 5 cultures). The NFR was normalized relative to control values. Bin size was 250 ms. E, Ten overlapping spike traces in control conditions (black traces) and 3 h after gabazine washout (red traces) of an individual electrode showing the decrease of the latency of the first evoked spike. Artifacts have been truncated for clarity. F, Time course of the latency (blue traces) and jitter (red traces) of the first spike for three neurons showing that latency and jitter decrease after GabT. Each symbol corresponds to a different neuron. G, Time course of propagation constant (λ see Methods) showing the increase of the activity spread following GabT. Inset, the number of spikes in a 100 ms time window was counted and averaged, for electrodes located at 0.5, 1 and 2 mm from the stimulated bar of electrodes, and fitted with an exponential function Ae-d/λ(grey line). Colours as in (E).