Figure 5.

Changes in firing rate with addition of 20 mM KCl. (A) Spikes were recorded via substrate electrodes from a perfused 3-D cell culture for a baseline period (“Pre”), with 20 mM KCl medium applied to the surface of the culture, and after a 5X washout of the KCl (“Post”). Each black dot represents the mean spike detection rate on a single electrode. The gray bars are the spike rates averaged over all channels ± SEM. The firing rate of the culture increased upon introduction of KCl solution (^*P < 0.05, paired t-test, N = 47 electrodes). (B) Spike rates from an unperfused 3-D cell culture recorded under identical conditions as in (A). There were more channels with lower spiking rates in the unperfused culture, and in particular many more channels without active neurons (dots below 0.1 Hz), but the culture also increased its firing compared to baseline (“Pre”) and after washout (“Post”) conditions (^*P < 0.05, paired t-test, N = 33 electrodes). There was no significant difference in firing rates between the Pre and Post periods in either case. Fluid was added in the same manner for the KCl and “Post” periods in both perfused and unperfused cultures.