[Localization of NADPH-d positive structures in the thymus of rabbits and rats].

In order to provide a morphological basis for understanding the role of nitric oxide (NO) in the thymus, present study was designed to clarify the localization and distribution of nicotinamide adenine dinucleotide phosphate-diaphorase (NADP-d) activity, a marker of NO synthase in rabbit and rat thymuses. The NADPH-d histochemistry revealed a different distribution of diaphorase positive reactivity in both animal species, visible as dark blue structures. The rabbit thymus displayed lightly stained cortex, whereas medulla was seen as a rounded complex of intensively stained cells, without sharp demarcation between them. However, unlike the rat thymus, the NADPH-d positive cells appeared to be arranged in an irregular line of dense staining at the corticomedullary junction. In the rat thymus, the NADPH-d positive nerve fibres were not evident, whereas neuronal-like plexuses were seen in the perivascular topography of the rabbit thymus. These results suggest that NO may participate in the regulation of thymic function. (Fig. 6, Ref. 30.)