Nitric oxide synthase in rat brain: age comparisons quantitated with NADPH-diaphorase histochemistry.

We examined age-related differences in nicotinamide adenine dinucleotide phosphate diaphorase (NADPH-d) containing neurons and neuropil in the striatum and hippocampus of male Fischer 344 rats at 6, 12, and 26 mo of age. NADPH-d staining is considered to be a marker for neurons and neuronal processes containing nitric oxide synthase. Rat brains were processed for NADPH-d histochemistry and analyzed morphometrically using computerized image analysis. The following NADPH-d histochemical parameters were examined: neuronal density, neuronal size, and neuropil staining optical density of selected regions. In the striatum, significant age-related declines were observed in NADPH-d-positive neuronal density and in neuropil staining, while neuronal size increased between 6 and 12 mo and then declined between 12 and 26 mo. In the hippocampus no significant age-related changes were noted in NADPH-d-positive neuronal density or size, or in the optical density of the molecular layer of the hippocampal dentate gyrus. Thus, age differences in NADPH-d histochemistry appear to be regionally specific in the Fischer 344 rat.