Next, we examined the number of Arc mRNA puncta within the perfused dendrites to determine if the newly transcribed Arc mRNAs are delivered to the region of synaptic stimulation. We quantified the number of puncta within a 100 μm section of the perfused dendrite (includes the perfusion channel and 50 μm proximal to the channel). We chose this region to quantify because we wanted to include Arc mRNA targeted to the perfusion region, including transcripts which may still be in transit due to the 20 min incubation [Arc mRNA are reported to be transported at a rate of 300 μm/h;(Wallace et al., 1998)]. The results show a significantly higher number of Arc mRNA puncta in the DHPG perfused dendrites over control perfusion, suggesting that following Arc transcription there is a redistribution of Arc mRNA into synaptic regions. Together, these results demonstrate that local group I mGluR activation at synapses triggers a signaling cascade to the nucleus to increase Arc transcription followed by Arc mRNA targeting into the perfused dendritic region.
