THE DEVELOPMENT OF FILIFORM AND FUNGIFORM PAPILLAE ON THE BODY OF THE TONGUE IN THE PRE- AND POSTNATAL LIFE OF 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 77 tongues of the domestic rabbit (Oryctolagus cuniculus f. domestica), which were collected at day 15, 18, 20, 22 and 26 of prenatal life (p.c.) and at day 1, 15 and 30, and in the 6^th month of postnatal life (p.p.). Material for examinations came from an abattoir.

Tissues were collected from the dorsal part of the body of the tongue and were prepared for examination under a light microscope. On the basis of microscopic observations heights of filiform and fungiform papillae and their primordia were measured, along with the thickness of the epithelium covering them.

In view of the conducted examinations an increase was shown in the values of analyzed features of the lingual mucosa in successive stages of pre- and postnatal life in the rabbit. It was also found that between day 22 p.c. and day 1 p.p., the developing fungiform papillae are higher than filiform paillae surrounding them. Between day 15 p.p. and the 6th month p.p. the growth rate in the height of fungiform papillae is lower than that for filiform papillae, as a result of which they are lower. The thickness of the epithelium covering fungiform papillae is bigger in the period from day 22 and day 26 p.c., while the trend was opposite between day 1 and the 6^th month p.p.

Key words: rabbit, lingual papillae, development, morphometry.

INTRODUCTION

Numerous research studies investigate morphogenesis of lingual papillae in various animal species [4, 5] and in the human [13]. To illustrate changes occurring during the development of papillae on the tongue studies were conducted based on observations under both a light and electron microscope [3, 12]. It is known from available literature that generally studies focus on the analysis of the mucous membrane, taking into consideration quantitative changes in lingual papillae and taste buds [1, 8, 9, 10]. In this whole set of publications there are no sources describing the rate of changes in the height of papillae on the tongue and the thickness of the epithelium covering them during their pre- and postnatal development.

The aim of the study was morphometric analysis of selected features of the mucous membrane on the body of the tongue in the rabbit and on their basis the determination of the dynamics of changes occurring during the development of filiform and fungiform papillae in the period from day 15 p.c. to the 6th month p.p. This study also broadens the scope of investigations concerning the development of lingual papillae in the rabbit, conducted using a light microscop [6, 7].

MATERIAL AND METHODS

Material for investigations consisted of tongues of 77 domestic rabbits (Oryctolagus cuniculus f. domestica). Tongues were collected from animals of both sexes 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.). Experimental material came from an abattoir.

The age of embryos was determined on the basis of the CRL (Crown-Rump-Length) value, describing the development of the rabbit [2].

Tissues for observations were fixed in 10% neutralized formalin or Bouin solution, next dehydrated in a series of alcohols (from 50% to 96%), embedded in paraffin and sliced with a microtome into sections with a thickness from 3 to 5 µm. In the experiments the following staining methods were applied: HE and Masson-Goldner. Microscopic images were documented using a Jenaval light microscope (Carl Zeiss Jena), coupled with a camera equipped with a computer image analysis software MultiScan V.6.08.

For the purpose of morphometric analysis measurements were taken after previous calibration of the system using a micrometric scale. In the analyzed periods of pre- and postnatal life in the rabbit the height of filiform and fungiform papillae was measured, along with the height of their primordia, found on the dorsum of the body of the tongue. Moreover, the thickness of the epithelium covering the developing papillae was also measured.

On the basis of the measurements the primary statistical parameters were calculated, i.e. mean value (X), minimum value (Min), maximum value (Max) and standard deviation (SD). Using the F test or Student’s t-test statistical differences were shown between mean values of measured features in successive periods of pre- and postnatal life in the rabbit.

RESULTS

At day 15 p.c. on the dorsum of the body of the tongue in the rabbit no primordia of lingual papillae were found, while at day 18 and 20 p.c. primordia of fungiform papillae were observed in the form of epithelial thickenings. The thickness of the epithelium covering the area devoid of papillae on the dorsum of the body of the tongue increases from day 15 to day 20 p.c. Statistical analysis of this feature at day 15, 18 and 20 p.c. showed statistically highly significant differences (P≤0.01). Moreover, an increase was observed in values describing epithelial thickenings in the period from day 18 to day 20 p.c., for which no significant differences (P>0.05) were shown between mean values (Table 1).

As a result of developmental changes occurring in the mucous membrane, during which at day 22 p.c. primordia of filiform and fungiform papillae appear, having a connective tissue core, the height of these primordia was measured along with the thickness of the epithelium covering them. Primordia of fungiform papillae form distinct projections on the surface of the dorsum of the lingual body and are higher than primordia of filiform papillae (Tables 2 and 4). The mean thickness of the epithelium covering primordia of filiform papillae is at that time lower than the mean thickness of the epithelium covering the primordia of fungiform papillae (Tables 3 and 5).

At day 26 p.c. the mean thickness of the epithelium covering the primordia of filiform papillae increased in relation to the mean value of this feature from the previous analyzed period by 10.56 µm, while the thickness of the epithelium on primordia of fungiform papillae increased by 10.77 µm (Tables 3 and 5).

Measurements of the height of primordia of filiform and fungiform papillae at day 26 p.c. indicate increasing values of this trait in comparison to the previous analyzed period of life in the rabbit. Values describing these changes are given in Tables 2 and 4. Developing fungiform papillae are higher than neighboring primordia of filiform papillae.

At day 1 p.p. a further increase was reported in the values describing the height of analyzed papillae on the body of the tongue. Fungiform papillae are still higher than filiform papillae (Tables 2 and 4). In the analyzed period the thickness of the epithelium covering fungiform and filiform papillae was also found to increase. However, the rate of increase for this trait in case of filiform papillae is faster than for fungiform papillae. As a result the mean thickness of the epithelium of filiform papillae is larger than the mean thickness of the epithelium of fungiform papillae (Tables 3 and 5).

At day 15 of postnatal life in the rabbit the height of filiform papillae increased on average by 69.22 µm, while the thickness of the epithelium covering them by 21.79 µm in comparison to data obtained at day 1 p.p. At the same time the mean value describing the height of fungiform papillae increased on average by 47.31 µm, while the thickness of the epithelium of these papillae by 12.10 µm, respectively. Measurement results indicate that at day 15 p.p. fungiform papillae on the body of the tongue are lower than filiform papillae. Basic statistical characteristics of analyzed traits are given in Tables 2 to 5.

In the next analyzed period in the life of rabbits, i.e. at day 30 p.p., a further increase is observed in the height of analyzed lingual papillae on the dorsum of the body of the tongue and in the thickness of the epithelium covering them. The difference between the mean height of filiform and fungiform papillae increased (Tables 2-5).

In rabbits in the 6th month p.p. on the dorsum of the body of the tongue fungiform papillae are found among filiform papillae exceeding them in height. The mean thickness of the epithelium covering fungiform papillae is smaller than the mean thickness of the epithelium of filiform papillae. Basic statistical characteristics for both types of papillae are presented in Tables 2 to 5.

On the basis of the conducted analysis statistically highly significant differences were shown (P≤0.01) in the height of filiform and fungiform papillae and their primordia found on the body of the tongue in the rabbit and in the thickness of the epithelium covering these papillae between successive analyzed periods from day 22 p.c. to the 6^th month p.p. (Tables 2 and 3).

Statistical analysis showed also statistically highly significant differences (P≤0.01) in the height of fungiform papillae and their primordia and in the thickness of the epithelium covering them in the analyzed periods of pre- and postnatal life in the rabbit (Tables 4 and 5).

DISCUSSION

After junction of lingual primordia in prenatal life the formed organ is composed of the apex, body and root. In successive stages of prenatal development this organ grows and adapts in its shape and size to the oral cavity in which it is located [11]. This process takes place also in the postnatal life, thus undoubtedly affecting the increase in the analyzed traits of developing filiform and fungiform papillae.

On the basis of taken measurements of heights of filiform and fungiform papillae and their primordia, studied between day 22 p.c. and the 6^th month p.p., mean values describing this trait were found to increase. In these periods the epithelium covering filiform papillae changed as well. On the basis of measurements the thickness of epithelium in successive analyzed periods of pre- and postnatal life was shown to increase in the rabbit. Observed changes are reflected in the results of microscopic observations, connected with a change in the morphological structure of lingual papillae [Kulawik, unpublished data].

Thanks to morphometric analyses it was also possible to follow the rate of morphogenesis of fungiform papillae. Epithelial thickenings, the presence of which was shown on the dorsum of the body of the tongue in the rabbit at day 18 and 20 p.c., are the earliest forms of primordia of fungiform papillae. In this study their thickness was measured, as a result of which it was found that epithelial thickenings showed an increase in the numerical values describing them, which is connected with an increasing number of layers of cells forming these thickenings in the analyzed periods [6].

Measured heights of developing fungiform papillae and their primordia on the dorsum of the body of the tongue, in the period from day 22 p.c. to the 6^th month p.p., showed their successive growth. Developing fungiform papillae are higher than filiform papillae up to day 1 p.p., while starting from the analyzed day 15 p.p. an opposite situation was reported. The thickness of the epithelium covering fungiform papillae and their primordia between day 22 p.c. and the 6^th month p.p. increased as well, which is connected with a change in its structure in the successive analyzed periods.

A lack of available literature describing morphogenesis of lingual papillae in view of morphometric studies in the rabbit and other animal species, as well as the human makes it impossible to compare the results found in this study.

CONCLUSIONS

1. The thickness of the epithelium covering the area devoid of papillae on the dorsum of the body of the tongue in the period from day 15 to day 20 p.c., as well as the thickness of the first forms of primordia of fungiform papillae, the so-called epithelial thickenings, increase from day 18 to day p.c.

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

3. Fungiform papillae, developing on the dorsum of the body of the tongue, in the period from day 22 p.c. to day 1 p.p. are higher than developing filiform papillae.

4. From day 15 p.p. to the 6th month p.p. the growth rate of the height of fungiform papillae is slower than that of filiform papillae. As a result, filiform papillae are higher than fungiform papillae.

REFERENCES

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The study was carried out within the framework of a grant for a Ph.D. thesis supervision no. 5P06D01719 financed by the Committee for Scientific Research

Accepted for print: 21.01.2007

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