Figure 1.

Distribution and expression of NPY/SOM/NOS⁺ in striatal NPY interneurons in mice. A, Fluorescent photomicrographic montage of a coronal section of a BAC NPY-GFP⁺ mouse brain illustrating the distribution and abundance of NPY interneurons in the neostriatum (Str). Note the sparse distribution of striatal NPY interneurons compared with cortical NPY interneurons. B₁–B₃, Higher-magnification photomicrographs illustrate GFP–NPY fluorescence in B₁, NOS immunofluorescence in B₂, and GFP and NOS merged in B₃. The small arrows indicate dimly fluorescent Type I somata, and the larger arrows indicate brighter Type II somata. Note that only Type I interneurons express NOS. C₁–C₃, GFP–NPY fluorescence in C₁, SOM immunofluorescence in C₂, and GFP and SOM merged in C₃. Note that only Type I interneurons express SOM. D₁–D₃, GFP–NPY fluorescence in D₁, NPY immunofluorescence in D₂, and GFP and SOM merged in D₃. Note that both type I and type II interneurons express NPY. E₁–E₃, NPY and NOS immunofluorescence in striatum from normal C57BL/6J mice shows exactly that same pattern of colocalization as in BAC NPY-GFP⁺ mice. E₁, NPY immunofluorescence reveals two different types of NPY somata, a few very bright ones (presumed Type II NPY interneuron), marked by the white arrows, and more numerous less bright ones (presumed type I NPY interneuron), some marked by white double arrows. E₂, NOS immunofluorescence. Three NOS-immunoreactive neurons are marked by white double arrows. E₃, Overlay of E₁ and E₂ shows that the bright NPY neurons do not colocalize NPY (white arrows), whereas the less bright cells do colocalize NOS (white double arrows). F, Example of an electrophysiologically identified Type I NPY interneuron (arrow) identified by GFP fluorescence (F₁) filled with biocytin (F₂) that also is immunoreactive for NOS (F₃), with the triple overlay shown in F₄. G, Example of an electrophysiologically identified type II NPY interneuron (arrow) identified by GFP fluorescence (G₁) filled with biocytin (G₂) that is not immunoreactive for NOS (G₃), with the triple overlay shown in G₄.