Distribution of reduced-nicotinamide-adenine-dinucleotide-phosphate diaphorase-positive cells and fibers in the cat central nervous system.

Previous histochemical studies have suggested that reduced nicotinamide adenine dinucleotide phosphate (NADPH) diaphorase exists in distinct subsets of neurons that neither belong to a single transmitter type nor embrace all the neurons using a single transmitter. As a step toward establishing the role of this enzyme, the distribution of NADPH-diaphorase-positive neurons and fibers in the cat central nervous system was mapped by using a direct histochemical method. Heavily stained NADPH-diaphorase-positive neurons with many prominent cell processes were observed in the cerebral cortex, white matter, caudate nucleus, putamen, nucleus accumbens, septal nucleus, amygdala, anterior, lateral and posterior hypothalamic areas, dorsolateral part of the periaqueductal gray, superior colliculus, central tegmental field (Berman) (pedunculopontine tegmental area), dorsal tegmental nucleus, nucleus coeruleus, mesencephalic and pontine reticular formation, gigantocellular and magnocellular tegmental fields, nucleus facialis, and motor nucleus of the vagus. Moderately stained neurons with two or three prominent cell processes were observed in the nucleus of the diagonal band of Broca, globus pallidus, and substantia innominata. Medium-size, moderately stained neurons that had round large nuclei and no visible cell processes were found in the subthalamic nucleus, pontine gray, trapezoid body, and infratrigeminal, cochlear, and vestibular nuclei. Very dense NADPH-diaphorase-positive nerve terminal fields were seen in the olfactory tubercle, cortex, caudate nucleus, putamen, dentate gyrus, and interpeduncular nucleus. Intensely stained NADPH-diaphorase-positive nerve fibers were found in the stria terminalis, marginal region of the central tegmental field, dorsal tegmental nucleus, and spinal trigeminal tract as well as around the brachium conjunctivum. Although the staining of neurons and tracts was highly selective, they did not correspond to any single known neuronal or neurotransmitter type. Positive staining occurred in discrete subsets of neurons known to be associated with a variety of peptides and classical neurotransmitters. The functional significance of high NADPH diaphorase activity is unknown.