Light and electron microscopy of granules in the toad choroid plexus

Summary Two types of granules can be distinguished in the toad choroid plexus under the light microscope: pigment granules, mainly localized in the cells that line the free ends of the choroidal villi, and Gomori-positive granules, present in most epithelial cells.The ultrastructural analysis of the choroid plexus reveals three types of granules: multivesicular bodies (MVB), multigranulous bodies (MGB) and dense bodies (DB), and intermediate stages between the last two bodies. The pigment granules seen under the light microscope probably correspond to the DB of the electron micrographs, and the Gomori-positive granules to the MGB. The probable role of these bodies is discussed and so is the significance of the glycogen present in the choroidal cells, their processes and endothelium.This study was partially supported by the Consejo Nacional de Investigaciones Científicas y Técnicas de la República Argentina and the Rockefeller Foundation (School grant RF — 58028).Fellow of the Consejo Nacional de Investigaciones Científicas y Técnicas de la República Argentina. The author wishes to thank Prof. M. H. Burgos for his constant interest. His thanks are also due to Prof. H. Heller for providing certain facilities in his department and for his criticism.