Observations about the tongue mucosa of White-Eared-Opossum (Didelphis albiventris), employing scanning and transmission electron microscopy

The White-Eared-Opossum (Didelphis albiventris) is a marsupial that occupies a large variety of habitats, spreading through several Brazilian biomes and some urban areas [1], with an important role in seed dissemination. As a mammalian, its tongue evolved to specialized functions and, in the neonate, in addition to milk suckling, it also serves to keep them attached to the female nipple, as a support for protection within the marsupium, reflecting the success of organogenesis. Furthermore, the lingual papillae provides an indicative of the animal habits, mechanical uses, diet and taxonomic relationships [2]. The organs were collected from individuals found dead by the roads in the state of Rio Grande do Sul, southern of Brazil. This material was previously fixed in modified Karnovsky aqueous solution and, once identified the tissue quality, it was submitted to processing for scanning (SEM) and transmission (TEM) electron microscopy. Through TEM the epithelial layers that forms the lingual mucosa were easily distinguished and identified, both in adults and fetuses. The stratum corneum at both stages demonstrate the epithelial renewal process through the release of the most superficial cells; the granular layer is more tenuous in fetuses than in adults, where many tonofilaments and several keratohyaline granules were observed; the spinous layer was similar in both ages and marked by the large number of desmossomes between the cells. Two adult tongues were used in the SEM study. One was used for the mucosa analysis, and revealed filiform papillae with different morphologies according to the region. The apex is filled with “major” papillae, like acute columns. The space among them is filled with tuft of “minor” thin and flat filiform papillae. This “minor” filiform papillae covers the entire top of the body surface but is much denser than in the apex, giving a velvet appearance to the organ. The fungiform papillae are scattered in the apex and body, and partially covered by an elevation of mucosa, looking like circumvallate papillae, since it present a moat-like trough. Circumvallate papillae are 3 in number and form a triangle on the lingual root, with the apex oriented caudally. Foliate papillae are small and thin elevations in the caudolateral border of the tongue, ranging from 12 to 16. The other SEM study used corrosion with Sodium Hydroxide to remove the epithelial layer, reaching the connective tissue that supports the lingual mucosa. It was observed that the filiform papillae subepithelial tissue is similar to what is seen with the conventional technique. The other types of papillae present an irregular surface with some dorsal depressions. The subepithelial tissue of the two circumvallate papillae, located more rostrally, are oval like the epithelium, while the third is rounded. The characteristics observed in the tongue of D. albiventris are similar to those observed in other marsupial species. Keywords: anatomy; ultrastructure; lingual papillae; didelphidae