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 specific 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 resembling nerve fibers also showed a low positive reactivity. Our findings indicate that AChE activity in the thymus is specifically located in the thymus cells followed by blood vessels. Biochemical results gave the following decreasing order of the amount of AChE activity: arteries, veins, whole thymus and parenchyma. Histoenzymatic staining and related values of quantitative analysis of images, confirmed biochemical results; moreover, we demonstrated that the intensity of histoenzymatic staining for AChE in thymus of rats strongly 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.