When we analyzed our data after including as few as 6 randomly selected cluster size measurements per cell, a Kruskal–Wallis test gave highly significant p-values for three cultures (p = 0.001, n = 174 sites (6 *29 cells)) and five cultures (p = 0.005, n = 294 sites (6 *49 cells)).
We note here that while the two wild-type strains respond very similarly to activity blockade, the mean mEPSC amplitude in untreated cultures was different between the two strains, 13.9 ± 0.7 pA, wild type from Rab3a +/− colony; 11.0 ± 0.6 pA, wild type from Rab3a +/ Ebd colony, but this difference did not reach statistical significance in a Tukey means comparison after a two-way ANOVA (p = 0.27).
Because there was a clear trend toward increased GluA2 receptor cluster size, but the receptor response appears more variable, we performed immunofluorescence measurements on two additional cortical cultures, both of which showed modest increases after TTX treatment ( Figure 5C ).
Further, the amplitude data show a strong trend towards smaller amplitude following NASPM treatment (Fig 3B).
The mean for size of GluA2-immunofluorescent receptor clusters showed a trend toward higher values after activity blockade (18.1%) that was of similar magnitude to the mEPSC amplitude increase (19.7%), but did not reach statistical significance for three cultures ( Figure 5E ) or five cultures ( Figure 5F ; Table 1 ).