Immunocytochemical localization of nitric oxide synthase in the brain of the chicken.

The distribution of neuronal nitric oxide synthase (NOS) in the chicken brain was investigated by immunocytochemistry. Strongly stained neurones were concentrated in the paleostriatum augmentatum, lobus parolfactorius, ventral pallidum, olfactory tubercle, parts of the neostriatum, mesencephalic reticular formation and locus coeruleus. Cells in these areas have previously been shown to stain for NADPH-diaphorase, a histochemical activity associated with NOS. However, various structures which NADPH-diaphorase staining has suggested to contain NOS were not immunoreactive: these included the glomeruli of the olfactory bulb, magnocellular preoptic neurones, the median eminence, subcommissural organ and mesencephalic trigeminal neurones. NOS was sparsely present in the hyperstriatum ventrale, providing evidence against the involvement of nitric oxide in certain forms of learning and memory processes known to occur in this region.