Accumulation of synaptic vesicle proteins is decreased by blockade of non-NMDA glutamate receptors but not action potential activity in the entire network. (A) Treatment of neurons with the AMPA/kainate receptor inhibitor CNQX resulted in decreased synapsin immunofluorescence intensity, similar to that observed with APV. (B) The apparent size of synapsin puncta was also decreased by CNQX exposure. (C) The effects of APV and CNQX on synapsin accumulation were not additive. Although APV application resulted in a significant decrease in synapsin intensity (P << 0.0001), addition of APV plus CNQX yielded a decrease that is not quantitatively different from the decrease induced by APV application alone (P = 0.15). Similarly, the effect of APV plus CNQX application on the apparent size of synapsin puncta was also not different from that observed with treatment with APV alone (data not shown, P = 0.27). (D) Treatment of neurons with NMDA reversed the effects of CNQX on the intensity of synapsin puncta. (E) Treatment of neurons with TTX did not significantly decrease the intensity of synapsin puncta (P = 0.079). Data are presented as the mean ± standard error of the mean and are normalized to control values. The numbers of puncta measured for each condition are indicated on the plots. N.s., not significant. *, highly significant difference and **, significant difference (P-values are indicated in the figure).