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. 2009 Jul 7;4(7):e6099. doi: 10.1371/journal.pone.0006099

Figure 2. Viral-mediated expression of ChR2-YFP into a class of inhibitory interneurons in the mouse auditory cortex.

Figure 2

(A) Neurons within the rodent auditory cortex can be excitatory or inhibitory. To express ChR2 in inhibitory parvalbumin expressing neurons of the mouse auditory cortex, we injected AAV carrying floxed ChR2-YFP in the left auditory cortex of PV-Cre mice, which express Cre recombinase only in fast-spiking interneurons. Although the virus can infect any cell, ChR2 is expressed only in PV-positive neurons. (B) Confocal micrograph of a section including the mouse primary auditory cortex shows fluorescence in cells expressing ChR2-YFP. (C) To test for PV specificity, the section was treated with an antibody against PV and counterstained with a red fluorescent dye. (D) Merging of the two channels shows that cells expressing YFP also counterstain for PV (merged cells show as yellow). Note that all ChR2+ (green) cells are also PV-positive (red) (i.e. there are only a few false positives), but that not all red PV-positive cells express ChR2.