Scanning Electron Microscopy of the Rat Tongue Mucosa with Special Attention to the Bacteria on Epithelial Cell Membranes

Aracy Akiko MOTOYAMA1
Ruberval A. LOPES2
Cristina Ioshie MIZUSAKI2

1Departamento de Anatomia, Instituto de Ciências Biomédicas, Universidade de São Paulo, São Paulo, SP, Brasil
2Departamento de Morfologia, Fisiologia e Estomatologia, Faculdade de Odontologia de Ribeirão Preto, Universidade de São Paulo, Ribeirão Preto, SP, Brasil

Braz Dent J (1999) 10(1): 1-60 ISSN 0103-6440

| Introduction | Material and Methods | Results | Discussion | Acknowledgments | References |

The authors examined the filiform and fungiform papillae surfaces of rat tongue by scanning electron microscopy showing the numerous groupings of bacteria on the epithelial cell membranes. The fungiform papillae were round in shape and present few bacteria. The epithelial cell of filiform papillae revealed numerous streptococci. The grouping of the bacteria are attached on the epithelial cell membrane, demonstrating three-dimensional SEM images.

Key Words: epithelial cell, rat, tongue, papilla, SEM, streptococcus, bacteria.


    Several authors have studied the characteristics of the tongue mucosa using scanning electron microscopy, such as the tongue surface of beagle dog (Iwasaki and Sakata, 1985), crab-eating frog Rana cancrivora (Iwasaki and Wanichanon, 1993), rat (Yoshioka and Muto, 1976), and mouse (Watanabe, 1989). There are few studies of the adhesion of bacteria on the cell membranes (Brady et al., 1975; Kimura and Pearsal, 1978; Howelet and Squier, 1980; McCourtie and Douglas, 1981; Tokunaga et al., 1990; Watanabe et al., 1997). This paper reports the presence of bacteria on the surface of filiform and fungiform papillae of rats using scanning electron microscopy.

Material and Methods

    The tongues of 3 Wistar rats were fixed with modified Karnovsky solution containing 2.5% glutaraldehyde, 2% paraformaldehyde in 0.1 M sodium phosphate buffer (pH 7.4) for 12 h at 4ºC. The specimens were postfixed in 2% osmium tetroxide solution, rinsed in distilled water, and immersed in 2% tannic acid solution for 1 h at 21ºC (Murakami, 1974). The samples were dehydrated in a series of ethanol, immersed in isoamyl acetate, critical point dried with Balzers, CPD-030, and mounted on metal stubs, and coated with gold. The samples were examined with a scanning electron microscope (Jeol, JSM-6100F; Tokyo, Japan).


    Numerous filiform and scattered fungiform papillae were observed on the dorsal surface of rat tongue examined by the scanning electron microscope (Figure 1). The fungiform papilla present polygonal epithelial cells of different forms (Figure 1). On the surface of fungiform and filiform papillae there was adherence of several groupings of bacteria (Figures 1 and 2). The filiform papillae were small in size and round in shape at the base (Figure 3). At high magnification, the cell membrane showed numerous microplicae (Figure 3).
    The groupings of the bacteria such as streptococci are noted in numerous filiform papillae, presenting three-dimensional images (Figure 3). The streptococci found in the rat tongue surfaces were round in shape and located at random. The groupings of bacteria were attached on the microplicae of the epithelial cell membranes (Figure 3).


    Our results clearly revealed the presence of filiform and fungiform papillae of lingual mucosa of rats. The epithelial cells showed numerous microplicae which were similar to those reported by Iwasaki and Sakata (1985), Yoshioka and Muto (1976) and Watanabe (1989). The rat tongue surface presented groupings of microorganisms which were attached to the cell membranes. Previously, Brady et al. (1975) reported bacteria in the filiform papillae of rat tongue. Our results demonstrated the adherence of the microorganisms on the outer surface of queratinized epithelial cell membranes. Barnett (1973) reported that the proteins of streptococci may provide the adherence of the microorganisms on the epithelial cell of the filiform and fungiform papillae.
    This investigation revealed microorganisms present on the surface of epithelial cells, with adhesion to host cells through an interaction between fibrillar components and the structure of microplicae (Tokunaga et al., 1986, 1990). Howelett and Squier (1980) also described observations about the adhesion of Candida albicans. However, the adhesion mechanisms involved in the interaction of bacteria with the epithelial cell membrane have not been clarified. Additional research is needed using different methods of electron microscopy to elucidate the aspects of microorganism adhesion.


    This research was supported by CNPq and FAPESP.


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Correspondence: Prof. Dr. Ii-sei Watanabe, Departamento de Anatomia, Instituto de Ciências Biomédicas, Universidade de São Paulo, Cidade Universitária, 05508-900 São Paulo, SP, Brasil. E-mail:

Accepted November 12, 1998
Electronic publication: September, 1999