FLOOR PLATE AND THE SUBCOMMISSURAL ORGAN ARE THE SOURCE OF SECRETORY COMPOUNDS OF RELATED NATURE - COMPARATIVE IMMUNOCYTOCHEMICAL STUDY

The subcommissural organ of vertebrates secretes glycoproteins into th e third ventricle that condense to form Reissner's fiber (RF). Antibod ies raised against the bovine RF-glycoproteins reacted with the floor plate (FP) cells of two teleost (Oncorhynchus kisutch, Sparus aurata) and two amphibian (Xenopus laevis, Batrachyla taeniata) species. At th e ultrastructural level, the immunoreactivity was confined to secretor y granules, mainly concentrated at the apical cell pole. In the rostro -caudal axis, a clear zonation of the FP was distinguished, with the h indbrain FP being the most, or the only (Batrachyla taeniata), immunor eactive region of the FP. In all the species studied, the caudal FP la cked immunoreactivity. Both the chemical nature of the immunoreactive material and the rostro-caudal zonation of the FP appear to be conserv ative features. Evidence was obtained that the FP secretes into the ce rebrospinal fluid a material chemically related to the RF-glycoprotein s secreted by the subcommissural organ. Thus, in addition to being the source of contact-mediated and diffusible signals, the FP might also secrete compounds into the cerebrospinal fluid that may act on distant targets. (C) 1998 Wiley-Liss, Inc.