Localization of NADPH-diaphorase in the brain of the chicken.

NADPH-diaphorase, an enzyme catalyzed reaction thought to reflect the activity of nitric oxide synthase in the mammalian nervous system, was mapped in the brain of the chicken. Intensely stained neurons and fibers were found in most parts of the telencephalon, in particular in the neostriatum, paleostriatum augmentatum, olfactory tubercle, lobus parolfactorius, hyperstriatum accessorium, and hyperstriatum ventrale. Medial to the nucleus taeniae, an accumulation of stained cells was observed that appeared to merge with a band of stained neurons located dorsal to the occipitomesencephalic tract. These are considered to belong to the nucleus interstitialis of the dorsal olfactory projection. Further caudally, neurons with different staining intensities were found in the lateral hypothalamic area, lateral mammillary nucleus, periventricular organ, ventral tegmental area, medial spiriform nucleus, optic tectum, isthmooptic nucleus, mesencephalic trigeminal nucleus, interpeduncular nucleus, and central gray of the mesencephalon. A particularly dense cluster of NADPH-diaphorase positive neurons was located in the locus coeruleus. It is proposed that these might represent cholinergic cells intermingled with catecholaminergic neurons, thus forming the avian counterpart of the tegmental cholinergic nuclei of mammals. Several NADPH-diaphorase reactive neurons were seen in the parabrachial nucleus and medial and dorsal vestibular nucleus, as well as scattered in the reticular formation. In the caudal medulla, intensely stained cells were grouped around the central canal. Therefore the pattern of expression of NADPH-diaphorase, and thus possibly of nitric oxide synthase, within the avian and mammalian brain might be largely conserved.