Recombinant Fluorescent Rabies Virus Vectors for Tracing Neurons and Synaptic Connections

Recombinant rabies virus (RV) vectors expressing fluorescent proteins allow staining of neurons from many mammalian species and enable the study of neuron morphology. Because viral spread occurs only between neurons that have synaptic connections, these vectors also permit transsynaptic tracing. A recently established system for restriction of transsynaptic tracing to a single transsynaptic jump, dubbed monosynaptic tracing, uses glycoprotein gene-defective, pseudotyped RV. This allows infection of defined cells and transient complementation with the glycoprotein in situ to support a single step of transsynaptic crossing to presynaptic cells. Here, we introduce protocols describing the production of RV vectors, including the recovery of recombinant RV from complementary DNA (cDNA) and virus pseudotyping in vitro. This allows retrograde staining of neurons projecting to the inoculation site.