Targeted gene transfer of different genes to presynaptic and postsynaptic neocortical neurons connected by a glutamatergic synapse.

Genetic approaches to analyzing neuronal circuits and learning would benefit from a technology to first deliver a specific gene into presynaptic neurons, and then deliver a different gene into an identified subset of their postsynaptic neurons, connected by a specific synapse type. Here, we describe targeted gene transfer across a neocortical glutamatergic synapse, using as the model the projection from rat postrhinal to perirhinal cortex. The first gene transfer, into the presynaptic neurons in postrhinal cortex, used a virus vector and standard gene transfer procedures. The vector expresses an artificial peptide neurotransmitter containing a dense core vesicle targeting domain, a NMDA NR1 subunit binding domain (from a monoclonal antibody), and the His tag. Upon release, this peptide neurotransmitter binds to NMDA receptors on the postsynaptic neurons. Antibody-mediated targeted gene transfer to these postsynaptic neurons in perirhinal cortex used a His tag antibody, as the peptide neurotransmitter contains the His tag. Confocal microscopy showed that with untargeted gene transfer, ~3% of the transduced presynaptic axons were proximal to a transduced postsynaptic dendrite. In contrast, with targeted gene transfer, ≥ 20% of the presynaptic axons were proximal to a transduced postsynaptic dendrite. Targeting across other types of synapses might be obtained by modifying the artificial peptide neurotransmitter to contain a binding domain for a different neurotransmitter receptor. This technology may benefit elucidating how specific neurons and subcircuits contribute to circuit physiology, behavior, and learning.