Figure 4.

Synaptic size dynamics in chronically silenced networks. A, Magnitude of synaptic size fluctuations in silenced and control networks. The SD of normalized fluorescence was calculated for each synapse over 24 h periods. Each data point is the average of these values for one field-of-view (∼100 synapses, typically belonging to 1 neuron). Twenty-three and 20 fields-of-view for each condition from 5 and 6 separate experiments, respectively. Indicated p values are for t tests assuming unequal variances. B, Same as A but for coefficients of variation calculated for each synapse. C, Same as A but for range/mean values [= (max − min)/mean] calculated for each synapse. D–F, Normalized PSD-95:EGFP fluorescence values of individual synapses in control networks plotted at three time points (2, 12, and 24 h) against their fluorescence at t = 1. Dashed lines are linear regression fits, whose parameters and coefficients of determination (R²) are indicated. Synapses (1922) from six separate experiments. G–I, Same as D–F for chronically silenced networks. Synapses (2032) from five experiments. J, Slopes of linear regression fits in plots such as those of D–I at increasing time points. Filled circles, Synapses tracked for 24 h (same data as in D–I); open circles, a smaller dataset in which synapses were tracked for 48 h (959 and 957 synapses, Control and Silenced networks, respectively). Lines are fits based on <ϵ> values derived from multilinear regression analysis of synapses tracked for 48 h. For further details on this analytical approach, see Statman et al., 2014. K, Coefficients of determination (R²) in plots such as those of D–I at increasing time points. Filled and open circles as in J. L, Changes in normalized PSD-95:EGFP fluorescence after 24 h (fluorescence _{t = 24} − fluorescence _{t = 1}) plotted as a function of fluorescence at t = 1. Lines are linear regression fits to the data. Same data as in F and I. Note the significantly shallower slope of the linear regression fit in silenced networks. Also note that as all data are provided in normalized fluorescence (that is, normalized to mean fluorescence levels of each neuron) the greater absolute PSD-95:EGFP fluorescence in silenced networks is not apparent in these plots.