Figure 4.

Blockade of endogenous GABA_A receptor activity alters the structure of spontaneous firing patterns. Ai, Multielectrode array recordings from a P5 mouse retina in the absence (left) and presence (right) of gabazine. The firing rate of all electrodes was binned into 1 s intervals. Aii, The number of active electrodes (out of 61) for the recordings shown in Ai. An electrode was considered active if its firing rate in a given bin exceeded the average firing rate recorded on the electrode over the course of 30 min by more than two SDs. Bi, Correlation index computed for pairs of spike trains and plotted as a function of the distance between electrodes on which the spikes were recorded. Data are from one P5 mouse retina in the absence and presence of gabazine (5 μm). Error bars are omitted for better readability; the values of SD are summarized in Table 3. Bii, Summary plots combine whole-electrode data from five P5–P6 mice and indicate a significant increase in correlation index at all distances. Error bars represent SD. The statistics summary for these data is included in Table 4. C, Summary of the changes in the interburst interval and burst duration measured on 139 individual electrodes (five mouse retinas) under control conditions and in gabazine. Each data point corresponds to a single electrode, with the ratio of burst duration in gabazine to burst duration in control plotted along the x-axis, and the ratio of interburst intervals plotted along the y-axis. The ratios were computed for the values of interburst interval and burst duration averaged over the course of a 30 min recording. GBZ, Gabazine.