Figure 7.

Early postnatal NP1/2 KO mouse retinas maintain activity characteristics important for eye-specific segregation. A, Correlation indices for electrically isolated RGC spikes in a single P4 WT retina versus distance between electrodes. The correlation index represents the likelihood that a cell recorded at one electrode fired a spike within a 100 ms time window of any spike from an RGC at another electrode. Each point represents the index for one such RGC pair plotted against the inter-electrode distance; the solid line is the best-fit single exponential for the population of distances. As expected, correlations are higher for cells that are nearer one another. B, Correlation indices calculated from the spikes of all RGC pairs recorded from a single P4 NP1/2 (neuronal pentraxin double knock-out) retina are shown. As in the WT retina, correlations are high for near-neighbor cells and decrease with increasing distance between them. C, Example spike rasters from a 9 s period of recording show the responses of individual RGCs as a wave travels across a P4 NP1/2 retina (the same one quantified in B). Inset illustrates the relative position of the electrodes (1–4) on the array. Electrodes 2, 3, and 4 were 200, 500, and 700 μm from electrode 1, respectively. This wave traveled at a speed of ∼130 μm/s across the recorded retinal area. D–G, Dark gray bars show WT values, and light gray bars show NP1/2 values. D, The interwave interval (and thus wave frequency) was not significantly different in NP1/2 retinas compared with WT retinas. E, The overall spike rate of cells recorded from NP1/2 retinas was significantly higher than in WT mice. F, When the amount of firing at ≥10 Hz for each recorded cell was normalized to the spike rate of that cell, NP1/2 RGCs had slightly more of this high-frequency firing compared with WT retinas. G, As waves of activity pass across the retina, individual ganglion cells fire bursts of spikes after periods of relative silence. The mean burst duration calculated from all recorded NP1/2 RGCs was significantly longer than the mean WT burst duration. H, Information on the near-neighbor relationships of RGCs can be carried by the level of correlated activity, with the spikes of near neighbors having high correlations and those of RGCs distant from one another having lower correlations. The overall spike rate and number of synchronous spikes for RGC pairs within a given time window (100 ms here) were higher for the NP1/2 retinas compared with the WT retinas. To determine for each RGC whether a near-neighbor RGC could still be distinguished from a spatially distant RGC based on the amount of correlated activity, we calculated the difference in the amount of correlated spiking between near-neighbor pairs and distant pairs. Pairs recorded on electrodes <150 μm apart were considered near neighbors, whereas those ≥600 μm apart were considered distant from one another. The difference in the median values for each retina was plotted against the overall median spike rate. Black circles represent WT retinas, and gray triangles represent NP1/2 retinas. The solid line is a linear fit to the WT data. The proximity of the NP1/2 data points to this line indicate that the difference in correlated activity in the NP1/2 retinas is very similar to that of the WT retinas. This suggests that the correlated activity in the NP1/2 retinas still contains retinotopic information. I, Histograms of median burst durations for RGCs of WT (thick line) and NP1/2 (thin line) are shown. The distributions show that the significant difference between burst durations shown in F result from (1) slightly longer bursts in many RGCs, (2) a few RGCs with much longer bursts in the NP1/2 retinas, and (3) a large group of RGCs with shorter burst durations in the WT retinas. Analyses of retinal wave parameters were based on 5 min periods of spike activity from P4 and P5 WT retinas (n = 10) and P4 NP1/2 retinas (n = 7) recorded on a multi-electrode array. D, F, G, Bars indicate SEM; in G they represent medians and quartiles, respectively. ∗p < 0.001. n.s., Not significant.