Here we asked if DHPG applied at discrete synaptic regions was sufficient to signal back to the nucleus and increase Arc transcription. We next asked if the recently transcribed mRNA were targeted to the perfused synaptic regions. In μLP chambers housing mature (15-20 DIC) cultured neurons, we perfused DHPG (500 μM) over dendritic segments in the local perfusion channel for 10 min. Twenty minutes following the end of perfusion, we used fluorescence in situ hybridization (FISH) to visualize the location of the Arc mRNA puncta (Figure 8). We saw a significant increase in the number Arc mRNA puncta in the somata of dendrites perfused with DHPG compared to vehicle control. This increase in Arc transcript number was blocked when the group I mGluR antagonist, (RS)-1-Aminoindan-1,5-dicarboxylic acid (AIDA) (1 mM) was co-perfused with DHPG, suggesting that DHPG applied to synaptic regions <50 μm in length is sufficient to signal to the nucleus and increase Arc transcription. To determine if the increase in Arc mRNA was due to new transcription, and not an increase in stability of existing Arc mRNA, we performed
