Demonstration of cell specificity for the hybridization of TPH riboprobe in monkey brain. A andC depict sections of substantia nigra. Band D depict sections of raphe. In A andB, TH riboprobe was applied to the substantia nigra (A) and the raphe (B). The TH probe hybridized only to the dopaminergic neurons of the nigra as indicated by the black arrow (A). InC and D, TPH riboprobe was applied to the substantia nigra (C) and the raphe (D). The TPH riboprobe hybridized only to the serotonergic neurons of the raphe as indicated by the black arrow(D). These are computer-generated images (digitized) of scanned autoradiographs, which are not as sharp as photomicrographs obtained directly through a microscope lens.