Fig. 11.

Components in the connectivity template of Fig. 1 that can be expected to become labeled when various neurotropic virus tracers and viral vectors are applied. a Classical neurotropic viruses: HSV-1, rabies virus, and swine rabies virus (PRV), retrogradely infect first-order neurons and proceed transsynaptically to second-order neurons, and so on. After several transfers, all neurons are infected and will stain. b Glycoprotein deficient virus lacks the gene that is responsible for transsynaptic transfer and, therefore, retrogradely labels only first-order neurons. c A focally injected, genetically engineered, non-replicating AAV virus infects a small population of neurons in ACh-Cre-dependent mice and inserts a reversed eYFP-coding gene in the genome of these neurons. Only neurons expressing a specific gene [in this case, the gene that codes for the choline acetyltransferase enzyme (ChAT) that synthesizes acetylcholine (ACh)] also express DNA recombinase that subsequently is responsible for ‘restoring’ eYFP expression. eYFP accumulates in all neuronal processes of these cells and acts as ‘anterogradely transported’ tracer. Cells that do not express the ChAT gene do not express DNA recombinase and, therefore, cannot express eYFP