Study by scanning electron microscopy of the morphogenesis of three types of lingual papilla in the rat

Abstract

Background: Many mammals have four different types of lingual papilla, namely filiform, fungiform, circumvallate, and foliate papillae, on the dorsal or lateral surface of the tongue. However, details of the morphogenesis of these lingual papillae have not been reported. We have investigated the changes in the three-dimensional ultrastructure that occur during the morphogenesis of filiform, fungiform, and circumvallate papillae in rats during fetal and postnatal development.

Methods: Tongues were removed from rat fetuses on days 12 (E12) and 16 (E16) of gestation from newborns (P0) and from juveniles on days 7 (P7) and 14 (P14), and 21 (P21) after birth. Scanning electron microscopy was used for all observations.

Results: In fetuses at E12, the rudiments of fungiform papillae could be observed as two rows of bulges that extended bilaterally and parallel to the median sulcus on the anterior half of the dorsal surface of the tongue. In fetuses at E16, the arrangement of the rudiments of fungiform papillae was relatively regular, with a latticelike pattern. At this stage, the outline of the rudiment of the circumvallate papilla could be recognized on the median line between the lingual body and the lingual radix. No rudiments of filiform papillae were visible. At P0, rudiments of filiform papillae were compactly distributed over the dorsal surface in the same way as in the adult. The width of these rudiments was about one-fourth that of fungiform papillae, and their tips were round as compared with those of filiform papillae in the adult. The fungiform and circumvallate papillae were large, and their outlines were somewhat irregular, as in the adult. In juveniles at P7, filiform papillae were long and slender. On the intermolar eminence, filiform papillar structures were quite large. A taste pore was clearly visible at the center of each fungiform papilla at this stage. The shape of the circumvallate papilla was similar to that in the adult. In juveniles at P14 and P21, the shapes of all three types of papilla were almost same as those in the adult.

Conclusions: The rudiments of each of the three different kinds of lingual papilla appeared at a different respective stage of development in rats. The rudiments of the fungiform and circumvallate papillae, which are related to the sense of taste, were visible earlier than those of the filiform papillae, which are not involved in this sense.