NADPH-DIAPHORASE POSITIVE CELLS IN THE CHICK AND RAT THYMUS

Nicotinamide-adenine dinucleotide phosphate-diaphorase (NADPH-d) posit ive cells were demonstrated in the medulla of the rat and chick thymus at light microscopic level. The NADPH-d positive cells were present a s clusters and were predominantly localized near the corticomedullary boundary. These clusters were closely associated with the thymic cysts . Some cells were seen in close proximity to blood vessels. The presen ce of nitric oxide (NO) as indicated by the positive NADPH-d reaction in the cells forming the wall of the thymic cyst suggests a modulatory influence of NO over the activities of these cells. Other possible fu nctions of NO are also discussed.