TSPO in situ hybridization in adult song system and along P1 lateral ventricles. In situ hybridization with antisense-configured riboprobes showed that TSPO is expressed within all four major song nuclei - LMAN, Area X, HVC, and RA - in adult male brain. Antisense-configured riboprobes do not label the cells surrounding the lateral ventricle in P1 brains. Song nuclei and region of the lateral ventricle are identified with arrows. Hybridization of adjacent brain sections with negative control sense-configured riboprobes shows very low levels of label, suggesting specific labeling with antisense probes. High magnification images of each region of interest show cellular labeling. Scale bars for whole brain images = 1 mm; scale bar for high magnification images = 500 μm.