Biological aspect of the surface structure of the tongue in the adult red kangaroo (Macropus rufus) - light and scanning electron microscopy

The aim of this study was to identify the lingual surface and posterior lingual glands in the red kangaroo (Macropus rufus) using light and scanning electron microscopy (SEM). Haematoxylin and eosin (H&E), Masson-Goldner trichrome and Azan trichrome stainings were used for the histological examinations of both the papillae and concomitant glands, located beneath the body of the papillae. The samples were stained also with Alcian blue pH 2.5 and periodic acid-Schiff for histochemical observations. A scanning electron microscope (Tesla BS - 300) was used to examine the lingual surface. Small, giant and elongated filiform mechanical papillae and fungiform, vallate and foliate gustatory papillae were recognized. No typical conical or lenticular papillae were found on the lingual surface. The distribution of each group of papillae varied on the whole surface of the tongue. The majority of the fungiform papillae resembled "bud-like" shapes, and rotund taste buds were present within the fungiform papillae epithelium. The SEM study showed that the apical part of the vallate papilla was oval with an irregular surface. Additionally, the internal wall of this papilla had many intraepithelial cylindrical or rod-shaped taste buds. The papillary leaves did not have any typical appearance, however, the histological study showed the presence of intra-epithelial taste buds in the wall of the foliate papillae area. Furthermore, two types of posterior mixed mucoserous and serous lingual glands were observed. In conclusion, the morphology of the lingual surface as well as the structure of the lingual glands facilitates the consumption of particular foods in the red kangaroo. Additionally, there are typical microstructural features of the red kangaroo tongue, which are different than in other marsupials.