Topography of the NADPH-diaphorase system in the chameleon brain.

The NADPH-diaphorase histochemical technique, which reflects the activity of nitric oxide synthase was used in order to map the corresponding chameleon brain structures. In the forebrain, stained neurons were found particularly in the dorsal ventricular ridge and the ventral telencephalon, but no stained somata were observed in the cortical areas nor in the septum. In the midbrain, few NADPH-stained structures were seen. The stained cells were confined in the nucleus dorsomedialis, the nucleus geniculatus lateralis dorsalis, and the ventromedial hypothalamus. More caudally, some stained neurons were observed in the nucleus opticus mediodorsalis hypothalami posterior. In the brainstem, NADPH-stained cells were located in the optic tectum, the torus semicircularis, the substantia nigra, the ventral tegmental area, and all motor nuclei of the cranial nerves. The present results showed some striking differences and similarities with birds and mammals. Moreover, the presence of NADPH-staining in most of retinofugal, retinopetal and oculomotor nuclei suggests that nitric oxide system plays a prominent role in the visual and oculomotor functions.