( inarily coats rabies virus particles wa...)Deconstructing brain wiring, one neuron at a time

inarily coats rabies virus particles was replaced with its equivalent from a bird virus. This prevented the modified rabies virus from infecting mammalian neurons at all ?unless they had been engineered to express the bird virus's receptor, a bird cell surface protein known as TVA. Such neurons will then be "disguised" as bird cells and the rabies virus ?now acting like a bird virus ?will infect them.

"The bottom line is that you need two genes expressed in the cell or cell type of interest: TVA, to get the rabies virus in, and the missing viral gene so the virus can spread to connected cells," says Wickersham.

Experimenting on slices of neonatal rat brain, the Salk researchers inserted these two genes into selected neurons ?as well as a gene that fluoresces red when expressed. Then they applied the modified rabies virus, which had furthermore been given the ability to make infected cells fluoresce green. The result was spectacular: as expected, these red cells were selectively infected by the virus, which spread to hundreds of surrounding cells, turning them brilliantly fluorescent green.

While these experiments were conducted using slices of brain, it is possible to produce transgenic mice that will express specific genes in a targeted class of neurons, Callaway says. "All neurons of the type we select will then express the avian viral receptor and the rabies virus protein, allowing the modified rabies virus to infect targeted cells and spread only once to connecting cells," he adds. The wiring map can be constructed step by step as subsequent populations of cells are imaged.

The recombinant rabies virus could contain genes for any proteins of interest, Callaway says, and he adds that once scientists can identify a neural circuit, they can then deactivate it, and test for changes in brain function.

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Source:Salk Institute


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