zapERtrap can be used to locally release cargoes from the ER within defined regions of the dendritic arbor. (A) TfR-GFP-DHFR was released from the dendritic segment under the purple box by local illumination with 405-nm light. The adjacent dendrite (white rectangle) serves as a nonphotoactivated control. Scale bar, 10 µm. (B) Somatic TfR-GFP-DHFR signal showed no detectable difference before and 10 min following local dendritic release. Scale bar, 5 µm. (C) Time-lapse of intracellular TfR signal following local dendritic release in the targeted branch and an adjacent control branch (white box in A). Note the rapid appearance of punctate trafficking organelles (arrowheads) in the released branch but not the control branch. Scale bar, 5 µm. (D) Zoomed-out images of the dendrite shown in C, starting 14 min after local dendritic photorelease (purple box). An example of a mobile intracellular cargo vesicle (blue arrowhead) exiting the photoactivated region is shown. Scale bar, 10 µm.