SCANNING ELECTRON MICROSCOPIC STUDY OF THE TONGUE OF
CHINCHILA (Chinchilla laniger)

ESTUDIO AL MICROSCOPIO ELECTRONICO DE BARRIDO DE LA LENGUA DE
CHINCHILLA (Chinchilla laniger)

^* Department of Morphology and Pathology, Federal University of São Carlos (UFSCar), São Carlos/SP, Brazil.
^** Department of Anatomy, Institute of Biosciences, State University of São Paulo (UNESP), Rubião Júnior, Botucatu/SP, Brazil.
^*** Department of Anatomy, Institute of biomedical Sciences, University of São Paulo (USP), São Paulo. SP, Brazil.

SUMMARY: The three-dimensional structure of the lingual papillae and the connective tissues of the tongue of chinchila were observed by scanning electron microscopy. The NaOH cell maceration method were used to remove the epithelial layer to visualize the connective tissue architecture. The dorsum of the tongue is covered by keratinized stratified squamous epithelium and possessed four types of papillae: filiform, fungiform, foliate and vallate. SEM images demonstrated the epithelial cell surfaces with microridges, distinct intercellular borders and taste pores. The connective tissue core of filiform papillae of the anterior and intermediate part of the tongue consisted of two or three rod-like protrusions while on the posterior part demonstrated large base with several apical protrusions. The lamina propria of the fungiform papillae were columnar and vallate papillae presented a central groove surrounded by numerous connective tissue papillae; the foliate papillae demonstrated elliptical holes surrounded by small connective tissue papillae.

Key words: 1. Epithelium; 2. Connective Tissue; 3. Tongue; 4. Chinchila; 5. SEM

INTRODUCTION

Chinchilas are rodents from the Andes mountains. According to MERÇON (1976) the Chinchilidae family present three species: Chinchila real, Chinchila brevicaudata and Chinchila laniger. Chinchila real is extinct and laniger shows high commercial value due their skin that are used to make coats.

The mucous membrane of the dorsum of the tongue is classified like specialized one cause is related to specific functions like gustation and lining. In mammals, it frequently possess filiform, fungiform, foliate and vallate papillae. The morphological aspects of these important structures are variable according to the analyzed species as demonstrated by FERNANDEZ et al. (1978); KRAUSE & CUTTS (1982); STEFLIK et al. (1983); IWASAKI & MIYATA (1989); KOBAYASHI et al. (1987, 1988, 1989, 1998); KOBAYASHI (1990, 1992); AGUNGPRIYONO et al. (1995); WATANABE et al. (1992, 1995, 1997); KUMAR et al. (1998) and MARTINEZ et al. (1998).Taste buds are found in the epithelial layer of the tongue mucosa of foliate, fungiform and vallate papillae (KOBAYASHI et al. 1989; KOBAYASHI & WANICHANON 1992). According to FAHRENHOLZ (1937), Von Ebner`s glands are related to gustation because their secretions wash out the taste buds (BARALDI & BOURN, 1953) removing the alimentary debris.

Several methodologies were developed in the last to remove the epithelial layer for the visualization of the lamina propria (KLEIN-SZANTO & SCHROEDER, 1977; LOW & MCCLUGAGE, 1984; HULL & WARFEL, 1986; KOBAYASHI, 1992). One of the methods is the NaoH maceration introduced by OHTANI (1987; 1992) and OHTANI et al. (1988).

The purpose of the paper is to examine the morphological features of the tongue of chinchila and compare to other species described in the literature.

MATERIAL AND METHOD

Eight adult chinchila, Chinchilla laniger, of both sexes were used in the present paper. The tongues were washed with distilled water and dissected. For observations on the dorsum of the tongue we used the conventional SEM method. For studies of the lamina propria, three tongues were fixed with modified Karnovsky solution, containing 2.5% glutaraldehyde, 2.0% paraformaldehyde in 0.1 M phosphate buffer, pH 7.2. Then, the specimens were rinsed and immersed in a 10% aqueous solution of NaOH, for 4-7 at room temperature according to the method of OHTANI (1987, 1992). The samples were rinsed in distilled water and post-fixed with 1% osmium tetroxide solution for 2 hrs. After immersion in a 1.0% aqueous solution of tannic acid for 1 hr and 30 minutes (MURAKAMI, 1974), they were rinsed again in distilled water for several hours and dehydrated in an increasing series of ethanol. The samples were dried in a critical point using CO2 liquid (Balzers CPD-010), coated with gold ions in a SEM coating (Balzers MED-010) and examined under a Philips FEM-515 scanning electron microscope at 15-20 Kv.

RESULTS

The tongue of chinchila is triangular in shape and presented 3,2 cm of lenght; it is lined by keratinized stratified squamous epithelium. Numerous filiform papillae were distributed on the dorsum of the tongue mucosa. The tip of these structures displayed 1 or 2 pointed projections on the anterior and intermediate part of the tongue (Figs. 1 and 2). On the posterior third of the tongue around the vallate papillae were observed small filiform papillae with large base and the tip without projections (Fig.5). The fungiform papillae were abundant in the tip of the tongue and scattered among the filiform papillae on the dorsal surface. These projections showed round shape and convex and were surrounded by filiform papillae (Figs. 1 and 3). Higher magnification demonstrated desquamating polygonal cells, typical intercellular boundaries and the microridges. The microridges were arranged in a irregular pattern. (Fig. 4). The fungiform papillae possessed numerous openings of the taste buds. The taste pores were circular and crater-like shape (Fig.4). The top of fungiform papillae is lower than the tips of the filiform papillae. Two elongated vallate papillae are situated on the posterior third surrounded by small filiform papillae (Fig. 5). Foliate papillae are situated at the postero-lateral margin of the both sides on the posterior third of the tongue and consisted in small grooves arranges vertical to the long axis of the tongue (Fig.6).

After the epithelial layer removed, the architecture of the connective tissue was observed. The connective tissue core of filiform papillae of the anterior and intermediate part of the tongue consisted of two or three rod-like protrusions (Figs. 7 and 9).The shape of these structures on the posterior part demonstrated large base with several apical protrusions (Fig. 8). The lamina propria of the fungiform papillae were columnar in shape and their tip showed many round depressions (Fig. 7). At higher magnification it was possible to note that the papillae were constituted by collagen fibers predominantly disposed in longitudinal arrangements (Fig. 9). The lamina propria of the vallate papillae presented a central groove surrounded by numerous connective tissue papillae with different heights (Fig. 10). When the grooves of the foliate papillae were removed by NaOH, elliptical holes surrounded by small connective tissue papillae were found (Fig. 11).

DISCUSSION

The mucosa of the oral cavity can be classified into three parts: lining, masticatory and specialized mucosa. The lining mucosa corresponds to lip, cheek and soft palate; the masticatory mucosa includes hard palate and gingiva and the dorsum of the tongue is the specialized mucosa. Many works have been published demonstrating the three-dimensional architecture of these mucosa. KOBAYASHI et al. (1987, 1988, 1989, 1998), WATANABE et al. (1992, 1995, 1997), NAKANO (1991, 1992), HERREL et al. (1998), PARKS & WHITEHEAD (1998), MARTINEZ et al. (1995, 1997, 1998) and ABE & OSAWA (1999).

In the last years several methodologies of epithelial maceration were developed and described in the literature for scanning electron microscopy, HORSTMAMN (1954) used acetic acid, KLEIN-SZANTO & SCHROEDER used EDTA, LOW & MCLUGAGE used ultrasonication and KOBAYASHI et al. (1987) employed HCL to remove the epithelial tissue. The present paper used NaOH maceration method to remove the epithelial layer permitting the visualization of the connective tissue of the lingual papillae. According to OHTANI (1987, 1992), this technique eliminates the cellular elements more effectively than any other method and preserve the integrity of the lamina propria.

The dorsum of the tongue of the chinchila is lined by keratinized stratified squamous epithelium. The superficial cells had polygonal shape with distinct borders and microridges. Similar characteristics were reported in opossum Didelphis virginiana (KRAUSE & CUTTS), horse and cow (CHAMORRO et al., 1986), armadillo (MORAIS et al., 1988), rat snake (IWASAKI & KUMAKURA, 1994), lesser mouse deer (AGUNGPRIYONO et al. and WATANABE et al., 1995) and opossum (MARTINEZ et al., 1998). The microridges must protects the superficial cells keeping more quantity of mucous between adjacent cells (ANDREWS, 1976).

The shape and the size of the filiform papillae presented some regional differences in the tongue of chinchila. According to KOBAYASHI (1990) these morphological differences may be related to the complexity of the masticatory movements. The connective tissue core of the filiform papillae also demonstrated regional differences in accordance with the regional differences of the external shape of the papillae. Similar results were obtained by KOBAYASHI (1992) and WATANABE et al. (1992).

Concerning the fungiform papillae, their connective tissue morphology was similar to those of treeshrew described by KOBAYASHI & WANICHACON (1992).

According to these authors, the architecture of these papillae became more specific from Insectivores to Primates and rodents presented fungiform papillae with columnar shape as observed in chinchila.

The posterior third of the dorsum of the chinchila´s tongue presented a pair of vallate papillae. Similar number of vallate papillae is also observed in insectivores (SONNTAG, 1923), in great anteater (KUBOTA et al., 1962), in armadillo (MORAIS & WATANABE) and in opossum (MARTINEZ et al., 1998). Some rodents like rat, mouse and hamster have one vallate papillae while others species like several primates, including man, (KUBOTA & HAYAMA, 1964) or elephants (KUBOTA, 1967) can have four or more vallate papillae. According to KUBOTA (1988), there is an intimate relationship between the feeding habits and the development of the vallate papillae. Our findings described that the connective tissue of the vallate papillae presented a central groove surrounded by numerous connective tissue papillae with different heights. Different morphologies of the connective tissue of the vallate papillae were described by KOBAYASHI & WANICHANON (1992) in treeshrew and WATANABE et al. (1995) in the Macaca fuscata.

The morphology of the fungiform papillae and the underlying connective tissue core in the chinchila was similar to those described in the rat by (IINO & KOBAYASHI, 1988) and in the guinea pig by (KOBAYASHI 1990).

The literature shows that the number or the morphology of lingual papillae changes according with the zoological stage and other important aspect is that the structure of the papillae is probably related with the feed habits of each species. In conclusion, the morphological characteristics of the tongue of chinchila support the pattern observed in the literature.

RESUMEN: A través de la microscopía electrónica de barrido se observó la estructura tridimensional de las papilas linguales y el tejido conectivo de la lengua de chinchilla. Se utilizó la técnica de maceración celular con NaOH para remover la capa epitelial y visualizar la arquitectura del tejido conectivo. El dorso de la lengua está cubierto por epitelio escamoso estratificado queranitizado y posee cuatro tipos de papilas: filiformes, fungiformes, foliadas y valadas. Las imágenes de microscopía de barrido mostraron superficies de las células epiteliales con micropuentes distintos de los bordes intercelulares y poros linguales. El tejido conectivo central de las papilas filiformes de las partes anterior e intermedia de la lengua, presentaban dos o tres protrusiones semejantes a vástagos, mientras que en la parte posterior se observó una amplia base con varias protrusiones apicales. La lámina propia de las papilas fungiformes era columnar y las papilas valadas presentaron una muesca central rodeada por numeroso tejido conectivo papilar; las papilas foliadas presentaban orificios elípticos rodeados por escaso tejido conectivo papilar

PALABRAS CLAVE: 1. Epitelio; 2. Tejido conectivo; 3. Lengua; 4. Chinchilla laniger; 5. SEM.

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Correspondence to:
Prof. Dr. Marcelo Martinez
Departamento de Morfologia e Patologia
Universidade Federal de São Carlos
Rod. Washington Luís Km 235 s/n°
CEP: 13.565.905
São Carlos / SP,
BRASIL

Tel: 55-016-2608330
Fax: 55-016-2608326
e-mail: martinez@power.ufscar.br

Recibido : 07-03-2000
Aceptado: 02-05-2000