Histochemistry for NADPH-d in sections of hippocampus from the brains of handled (A, C, E, G) and nonhandled (B, D, F, H) rats. A, B, Low-power photomicrographs of similar levels in the hippocampus where it can clearly be seen that the principal cells are generally NADPH-d-negative, except for neurons in the subiculum (s). The number of NADPH-d-reactive neurons is not related to the apparent darkness of staining (compare Aand B, C and D), which reflects only the longer incubation time for B. The exact shape of the structures is dependent on the precise plane of section. The upper boxed areas (CA1) appear inC and D, the boxed areasto the right in E and F(CA2/3), and the boxed areas to the left(dentate gyrus) in G and H, respectively. In C–F, the layers st. oriens (so), st. pyramidale (sp), and st. radiatum (sr) are indicated, as is the st. lacunosum-moleculare (slm) in C and D. In G andH, the layers of the dentate gyrus, the st. moleculare (sm), st. granulosum (sg), and st. polymorphe (sp) are indicated. In the CA1 region (C, D) it is possible to identify two types of NADPH-d-reactive neurons: a large, densely stained type (asterisks) often associated with the alvear fibers, and a less densely stained type (arrows) found in all layers. Scale bars: A, B, 500 μm; C–H, 200 μm.