Localisation of NADPH-diaphorase-positive structures in the thymus of the rat, mouse and rabbit

Localisation of the diaphorase activity of nicotinamide adenine dinucleotide phosphate (NADPH-d), acting as a marker of nitric oxide synthesis (NOS), was studied in the thymus of the rat, mouse and rabbit. The NADPH-d-active cells observed in the rat thymus were irregular in shape with numerous projections and were located on the boundary between the cortex and the medulla. The NADPH-d-active cells in the thymus of the mouse were located predominantly in the medulla. They varied in coloration and their shape was oval, round, or irregular. NADPH-d-positive nerve fibres were located perivascularly. The rabbit thymus displayed a lightly stained cortex, whereas the medulla was seen as a rounded complex of intensively stained cells, without sharp demarcation between them. In the rat thymus, the NADPH-d-positive nerve fibres were not evident, whereas NADPH-d-positive nerve fibres were seen in the perivascular topography of the mouse and the rabbit thymus. These results suggest that NO may participate in the regulation of the thymic function in the species. In summary, the present results reveal the distribution of NADPH-diaphorase-d-positive structures in the rat, mouse and rabbit thymus.