Vascular and leptomeningeal projections of the subcommissural organ in reptiles. Lectin-histochemical, immunocytochemical, and ultrastructural studies

In the snake, Natrix maura, and the turtle, Mauremys caspica, the basal processes of the ependymal cells of the subcommissural organ project toward the local blood vessels and the leptomeninges. These processes and their endings were studied using aldehyde-fuchsin (AF), periodic-acid Schiff (PAS), periodic-acid silver-methenamine (PA-SM), concanavalin A (ConA), wheat germ agglutinin (WGA), immunoperoxidase staining (employing an antiserum against bovine Reissner's fiber; AFRU), and conventional transmission electron microscopy. For the purposes of comparison, the ventricular cell pole was also analyzed. The secretory material located in the ventricular cell pole and that present in ependymal endings had only a few staining properties in common, i.e., affinity for AF, ConA, and AFRU at a dilution of 1:1000. On the other hand, PAS, PA-SM, WGA, and AFRU at a dilution of 1:200,000 stained the apical (ventricular) secretory material but not the secretory material of the ependymal processes. The histochemical features of the secretory material located in the terminals of ependymal processes, as well as the presence at these sites of numerous rough-endoplasmic-reticulum cisternae and secretory granules, suggest that secretory material may be synthesized in these terminals. The probable fate of this material, i.e., release to the perivascular and leptomeningeal spaces or transport to the ventricular cell pole, is discussed.