Distribution of NADPH-diaphorase and nitric oxide synthase in relation to catecholaminergic neuronal structures in the brain of the lizard Gekko gecko.

A recent study of the distribution of NADPH-diaphorase (NADPHd) and nitric oxide synthase (NOS) in a turtle brain (Brüning et at. [1994]: J. Comp. Neurol. 348:183-206) has revealed that these enzymes are not only widely distributed throughout the brain, but also seem to be colocalized with other classical neurotransmitters, such as catecholamines and acetylcholine. The main goals of the present study were 1) to determine sites of colocalization of NADPHd/NOS with tyrosine hydroxylase (TH, as marker for catecholamines), and 2) by studying a representative of another reptilian radiation, to assess primitive and derived traits of the distribution of NADPHd and NOS in the brains of reptiles. For that purpose, single (NADPHd or NOS) and double staining (NADPHd with TH, or NOS with TH) techniques were applied to the brains of adult gekkonid lizards (Gekko gecko). The distribution of NADPHd and NOS in Gekko was largely comparable to that in turtles, which implies involvement in certain functions of these enzymes. Notable differences, however, were observed in the thalamus and pretectum. Colocalization was observed in numerous cells of the ventral tegmental area, the substantia nigra, and the retrorubral dopaminergic cell group. In other catecholaminergic cell groups, e.g., the locus coeruleus and the solitary tract nucleus, TH-immunoreactive cells and NADPHd/NOS-positive cells were closely intermingled, but not double-stained. From the present evidence, it is concluded that extensive colocalization of NADPHd/NOS with catecholamines occurs in the midbrain dopaminergic cell groups of reptiles and birds, but not (or only sparsely) in the corresponding cell groups of amphibians and mammals.