Distribution of acetylcholinesterase activity in thymus of juvenile and aged rats

The occurence and distribution of acetylcholinesterase (AChE) activity were examined in the thymus of juvenile, adult and old rats, using biochemical and histoenzymatical methods. Quantitative image analysis showed that speci fic AChE reactivity was primarily confined to the thymic microenvironment, followed by the arteries and, to a lesser extent, to the veins. Only a low level of activity could be observed in association with the subcapsular and medullary parts of the parenchyma of the thymus. Many structures resemblin g nerve fibers also showed a low positive reactivity. Our findings indicate that AChE activity in the thymus is specifically located in the thymus cel ls followed by blood vessels. Biochemical results gave the following decrea sing order of the amount of AChE activity: arteries, veins, whole thymus an d parenchyma. Histoenzymatic staining and related values of quantitative an alysis of images, confirmed biochemical results; moreover, we demonstrated that the intensity of histoenzymatic staining for AChE in thymus of rats st rongly decreases with age. On the basis of our results we hypothesize that AChE activity may play a role in the specific functions of the thymus.