MORPHOLOGY AND DISTRIBUTION OF ECTO-5'-NUCLEOTIDASE-POSITIVE CELLS INTHE RAT CHOROID-PLEXUS

The aim of this report was to find out whether adenosine can be produc ed locally in the choroid plexus of rats. Therefore we investigated th e distribution of the enzyme ecto-5'-nucleotidase which hydrolyzes ext racellular adenosine monophosphate to adenosine and phosphate. Enzyme activity histochemistry and immunohistochemistry demonstrated that ect o-5'-nucleotidase is present in the stroma but not in the epithelium. The positive cells in the stroma were identified as fibroblasts by the ir localization and by their shape. Double-labelling immunohistochemis try actually showed that ecto-5'-nucleotidase was absent from MHC clas s II-positive cells and from vessel walls. These data indicate that ad enosine may be produced in the choroid plexus, and specifically in the interstitium. From there, adenosine would have direct access to nerve s, immune cells, the epithelium and microvessels. Because adenosine ha s been reported to modulate blood supply and the rate of production of cerebrospinal fluid, a local control mechanism involving adenosine mi ght operate in the choroid plexus in a similar way to that described i n other tissues. Effects of adenosine on nerves and immune cells are d iscussed. The exclusive presence of ecto-5'-nucleotidase in the fibrob lasts that are in contact with choroid plexus epithelium suggests that the expression of the enzyme is controlled by factors produced by epi thelial cells, for instance by extracellular nucleotides.