Confocal images show targeted gene transfer across synapses is supported by the artificial peptide neurotransmitter containing the Secretogranin DCV domain. The presynaptic vector containing the Secretogranin DCV domain was injected into POR cortex; 8 days later, a 1:1 mixture of the targeting and control postsynaptic vectors was injected into PER cortex; and 8 days later, the rats were sacrificed. PER cortex was costained for transduced presynaptic axons and transduced postsynaptic dendrites. (A-C) The targeting postsynaptic vector: (A) axons, His-tag-IR; (B) dendrites, GFP-IR; and (C) merge. Arrows, costaining. (D-F) The control, untargeted postsynaptic vector: (D) axons, His-tag-IR; (E) dendrites, flag-IR; and (F) merge. Arrowheads, His-tag-IR only. Scale bar: 20 μm.