Three-dimensional morphological analysis of ghrelin-producing cells in the rat fundic gland by combining serial section scanning electron microscopy and immunogold technique.

Ghrelin-producing cells (ghrelin cells) in rat fundic glands were analyzed three-dimensionally by combining serial section scanning electron microscopy with immunogold labeling to elucidate their ultrastructural characteristics. This approach enabled unambiguous identification of ghrelin cells and the three-dimensional (3D) reconstruction of their organelles with special reference to primary cilium. Rat ghrelin cells were morphologically classified into two types: ciliated ghrelin cells possessing primary cilia and non-ciliated ghrelin cells. In ciliated cells, primary cilia protruded from basal bodies located near the Golgi apparatus and were largely or entirely enclosed within ciliary pockets. Ghrelin-positive secretory granules were electron-dense and spherical. Ciliated and non-ciliated cells contained both large (250-350 nm) and small (100-200 nm) ghrelin-positive granules. In ciliated cells, the granules were densely accumulated in a localized region of the cytoplasm, being opposite the Golgi apparatus across the nucleus; in non-ciliated cells they were densely distributed throughout the cytoplasm. The ultrastructure of the basement membrane and overall 3D configuration of the Golgi apparatus also differed between the two cell types. Our results provide novel insights into the morphological organization of ghrelin cells, whose 3D ultrastructural features have been unclear in conventional two-dimensional transmission electron microscopy using single ultrathin sections.