THE DEVELOPMENT OF FOLIATE PAPILLAE ON THE TONGUE IN THE RABBIT IN VIEW OF MORPHOMETRIC STUDIES

Mirosława Kulawik¹, Szymon Godynicki^2
1 Institute of Zoology, Department of Animal Anatomy, Poznań University of Life Sciences
² Department of Histology and Embryology, Institute of Zoology, Poznań University of Life Sciences

ABSTRACT

Studies were conducted on 59 tongues of the domestic rabbits (Oryctolagus cuniculus f. domestica), of both sexes, being at day 15, 18, 20, 22 and 26 of prenatal life (p.c.) and at day 1, 15 and 30 and in the 6th month of postnatal life (p.p.).
Primordia of foliate papillae were observed starting from day 22 of fetal development in the rabbit in the posterior part of the tongue, on its dorso-lateral side. The height of developing foliate papillae and the thickness of the epithelium covering them were measured in the study. Selected traits were analyzed statistically using the F test.
Morphometric analyses showed that both the height of foliate papillae and their primordia, as well as the thickness of the epithelium covering developing foliate papillae increased in the successive investigated periods of pre- and postnatal life in the rabbit. The highest growth rate of foliate papillae was recorded between day 30 and the 6th month p.p., while the lowest – between day 26 p.c. and day 1 p.p. The highest dynamics of changes in the thickness of the epithelium were recorded between day 15 and 30 p.p., while the lowest – between day 26 p.c. and day 1 p.p.

Key words: rabbit, tongue, foliate papillae, morphometry.

INTRODUCTION

In rabbit, being popular laboratory animal [1,14], the foliate papillae are one of the three types of gustatory papillae, next to fungiform and vallate papillae [7]. Foliate papillae have also been identified on the tongues of other laboratory animal species, e.g. in the albino rat [11], hamster [9,10] and mouse [12,13].

Literature sources contain descriptions of the development of foliate papillae in different animal species, e.g. the albino rat [11], the guinea pig [4] and the rabbit [3]. Investigations were based on observations conducted using a light microscope, scanning electron microscope and transmission electron microscope. However, no description of the development of foliate papillae in view of morphometric analyses was found in available literature.

The aim of this study was to describe the dynamics of the development of foliate papillae on the tongue in the rabbit, based on the statistical analysis of the height of foliate papillae and their primordia and the thickness of the epithelium, which covers them in individual periods of pre- and postnatal life.

MATERIAL AND METHODS

Studies were conducted on 59 tongues, collected from rabbits (Oryctolagus cuniculus f. domestica), of both sexes, being at day 15, 18, 20, 22 and 26 of prenatal life (p.c.) and from rabbits at day 1, 15 and 30 and in the 6th month of postnatal life (p.p.). The age of fetuses was determined on the basis of the CRL value (Crown-Rump-Length), [2]. Material for the examinations came from a slaughterhouse.

Specimens for observations under a light microscope (LM) were fixed in 10% neutralized formalin or Bouin’s solution, dehydrated in a series of alcohols with increasing concentrations (50%-96%), embedded in paraplast and sliced into sections with thickness ranging from 3 to 5 µm in the median and transverse planes. The Masson-Goldner staining or HE were applied in this study.

Morphometric studies were conducted on the basis of images of histological specimens, observed under a light microscope, mounted with a camera with a computer image analysis program MultiScan V. 6.08. The height of the foliate papillae, their primordia and thickness of the epithelium covering them in individual periods of the pre- and postnatal life of rabbits were analyzed morphometrically. On the basis of the obtained results the primary statistical characteristics were determined: mean (x), minimum value (Min), maximum value (Max) and standard deviation (SD). Using the F test statistical differences were determined for mean values of the measured trait in successive periods of pre- and postnatal life of rabbits.

RESULTS

In the period between day 15 and 20 of prenatal development no symptoms of the formation of foliate papillae were observed on the tongue in the rabbit. The dorsum of the body of the tongue in that period was covered by a one- or two-layer epithelium. The first primordia of foliate papillae were found at day 22 of intrauterine life, in the dorsal part of the body of the tongue, on its dorso-lateral side. Morphometric analyses showed that the mean height of primordia of foliate papillae at that time was 93.08 µm, while the mean thickness of the epithelium covering them was 14.18 µm. In the next analyzed period, i.e. at day 26 p.c. the mean height of primordia of foliate papillae increased by 41.45 µm, while the mean thickness of their epithelium increased by 28.64 µm.

At day 1 p.p. in rabbits a further increase was observed in the values of analyzed characteristics. The mean height of papillae increased by 30.17 µm, while the thickness of the epithelium on their surface increased on average by 8.69 µm. In the successive periods in the life of rabbits, i.e. at day 15 and 30, and in the 6th month p.p. the height of developing foliate papillae increased by 49.02, 65.81 and 111.75 µm, respectively. In the above mentioned periods of life the mean thickness of the epithelium increased as well. Values describing this trait increased in the successive periods on average by 17.16 µm, 64.12 and 26.73 µm, respectively.

As a result of progressing developmental changes in foliate papillae in individual periods of pre- and postnatal life in rabbit the height of these papillae and the thickness of the epithelium covering them increased, as it is documented in Tables 1 and 2.

An increase in the height of foliate papillae and their primordia was more uniform than the increase in the thickness of their epithelium (Fig. 1).

Differences between mean values of the height of foliate papillae and their primordia in the period from day 22 p.c. to the 6th month p.p. were statistically highly significant (P ≤ 0.01), (Table 3).

The analysis of the thickness of the epithelium covering foliate papillae and their primordia did not show statistically significant differences between mean values of the measured trait (P > 0.05) in the period between day 26 p.c. and day 1 p.p., and between day 1 and 15 p.p. Statistically significant differences (P ≤ 0.05) were shown between mean values of this trait in the period between day 22 and 26 p.c., as well as day 26 p.c. and day 15 p.p. In the other compared periods of life in rabbits mean values differed statistically highly significantly (P ≤ 0.01), (Table 4).

DISCUSSION

On the basis of measurements of the height of foliate papillae and their primordia it was shown that the dynamics of changes in this trait increased in successive analyzed periods of pre- and postnatal life in the rabbit. Only between day 22 p.c. and day 1 p.p. a slight lowering of the growth rate was recorded for the height of developing foliate papillae. The highest growth in the height of foliate papillae was recorded between day 30 and the 6th month p.p. The rate of changes in the height of foliate papillae in the postnatal life corresponds to the fast increase in the size of the tongue, which adapts its dimensions and shape to the oral cavity, in which it is found [Kulawik, unpublished data].

Morphometric analyses showed that the epithelium covering the developing foliate papillae increased in thickness in individual periods of life in the rabbit. The biggest increase in the values of the analyzed trait was recorded between day 15 and 30 p.p., while the lowest – between day 26 p.c. and day 1 p.p. Bigger fluctuations in successive periods in the life of rabbits were found for the increase in the thickness of the epithelium, than for the increase in the height of papillae. The changing thickness of the epithelium is accompanied by changes in its structure [Kulawik, unpublished data], during which the two-layer epithelium was transformed into the nonkeratinized stratified squamous epithelium. Similar observations were reported during morphogenesis of fungiform papillae in the rabbit [5,6,8].

A lack of available literature describing the development of measurable traits of foliate papillae on the tongue in the rabbit or other animal species makes it impossible to confront the above results with similar studies.

CONCLUSIONS

1. The height of developing foliate papillae and the thickness of the epithelium covering them increase in the period from day 22 p.c. to the 6th month p.p.

2. The biggest growth rate in the height of foliate papillae was observed between day 30 p.p. and the 6th month p.p., whereas the highest growth rate for the thickness of the epithelium was recorded between day 15 and 30 p.p.

REFERENCES

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Accepted for print: 6.08.2007

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