THE PARACORONAL (MARGINAL) CELLS OF FUNGIFORM PAPILLA OF RANA-ESCULENTA

Paracoronal secretory cells can be observed outside the sensorial area of the fungiform papilla of Rana esculenta. The morphology of these c ells, the type of secretion and their function have, to date, only bee n incidentally described. By scanning electron microscopy (SEM), the p aracoronal cells appear as swallow's-nest-shaped formations with openi ngs 10-15 pm in diameter. The walls of paracoronal cells are character ized by laminar processes subdividing the interior hollow, The cavity of these formations is occupied by amorphous material as demonstrated by light microscopy (LM) pictures. The secretory material fills 7/8 of the upper part of the cytoplasm and appears rather transparent. The s ecretory material is PAS-negative, unlike the secretory granules conta ined in laminar processes. By transmission electron microscopy (TEM), they appear as clear ovoid structures, the nucleus of which is situate d in the deeper part of the cell, enveloped by a thin cytoplasmic laye r and characterized by secretory apparatus and the presence of secreto ry granules of middle electron-opacity. The apical part of these cells presents large mucous droplets. These cells adhere both to ciliated a nd parietal cells. Following cytochalasin-B treatment, cells do not sh ow any considerable ultrastructural modification, while after terbutal ine treatment the profiles of secreted paracoronal cells increase grea tly. Histochemical properties of their secretory products are similar to those of parietal cells and their particular anatomical localizatio n may exclude the direct implication of these cells in taste transduct ion.