Mast cells in the amphibian brain during development.

This is the first descriptive study of ontogenesis and anatomical distribution of mast cells in the developing brain of three different amphibian species. In the toad and the green frog, mast cells are preferentially located in: (i) the meningeal lining (pia mater), (ii) the choroid plexuses, both anterior and posterior, and (iii) the neuropil, in close association with the epithelial cell lining of blood vessels. It is only in the perennially aquatic African clawed frog that mast cells never appear inside brain ventricles and within the neuropil. Mast cells first become identifiable in brain of different species in different stages of development. While there are differences in the number of mast cells in different species at different stages of development, the number nearly doubles in all three species during the transition from pro-metamorphic stage of larval development to the peak of metamorphic climax. Furthermore, the number of mast cells is comparatively higher in the toad and remarkably lower in the fully aquatic Xenopus laevis, in which species the first appearance of identifiable mast cells during larval development occurs much later than in equivalent stages of development of the toad and the green frog. The secretory nature of mast cells can be assumed by the presence of cytoplasmic granules, which may show species-specific texture. Further experimental analyses are required to unveil the usefulness of mast cells in the amphibian brain.