Reduced nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d) histochemistry in the hippocampal formation of the New World monkey (Saimiri sciureus).

Nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d) containing fibers and neurons within the hippocampal formation and entorhinal cortex of the new world monkey were determined using a direct histochemical procedure. Occasional intensely stained bipolar NADPH-d positive neurons were seen in the polymorphic zone within the hilus of the dentate gyrus and molecular layer of the hippocampus. Although virtually no intensely stained cells were seen in the CA subfields, a few small oval lightly stained NADPH-d perikarya were found subjacent to CA2. An occasional intensely stained multipolar NADPH-d containing neuron was observed in the subiculum, presubiculum and parasubiculum. In the entorhinal cortex, NADPH-d cells were scattered in all layers with the greatest preponderance in layers 5-6 and underlying white matter. Dense bands of NADPH-d fibers occurred in the outer layer of the molecular layer of the dentate gyrus and the hippocampo-subicular border. NADPH-d fibers also were seen in pre- and parasubicular regions. NADPH-d fiber staining in entorhinal cortex varied mediolaterally with an increasing laminar distribution more caudally. The heaviest bands of NADPH-d fibers occurred in layers 1 and 4 and the white matter-layer 6 border. The distribution patterns of this select neuronal population may be relevant to the study of hippocampal and entorhinal areas in neurodegenerative diseases.