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Revista chilena de anatomía

Print version ISSN 0716-9868

Rev. chil. anat. vol.19 n.3 Temuco Dec. 2001

http://dx.doi.org/10.4067/S0716-98682001000300003 

SCANNING ELECTRON MICROSCOPY STUDY OF THE DORSAL SURFACE
OF THE TONGUE IN Chaetophractus vellerosus (MAMMALIA, DASYPODIDAE)

ESTUDIO AL MICROSCOPIO ELECTRÓNICO DE BARRIDO DE LA SUPERFICIE DORSAL
DE LA LENGUA DE Chaetophractus vellerosus (MAMMALIA, DASYPODIDAE)
*Silvia Estecondo; *Stella Maris Codón & **Emma Beatriz Casanave

*Lab. de Histología Animal, Depto. de Biología, Bioquímica y Farmacia (DBByF), Universidad Nacional del Sur (UNS),
Bahía Blanca, Argentina.
**Lab. de Fisiología Animal, DBByF, UNS, Bahía Blanca, Argentina, Research Carrier Member, Consejo Nacional de Investigaciones Científicas y Técnicas, CONICET.
This study was supported by grants from SGCyT-UNS, Project 24/BO60.

SUMMARY: The characteristics of the dorsal surface of Chaetophractus vellerosus tongue were studied by scanning electron microscopy. Simple or branched filiform, fungiform and vallate papillae are described. Simple conical filiform papillae appear in the apex, lateral edges and posterior third, caudally to the circumvallated ones. The branched papillae are densely distributed all over the dorsal surface of the lingual body. Fungiform ones are scattered among the branched filiform papillae. In the posterior third there are two vallate papillae. Filiform papillae have mechanical role, meanwhile fungiform and vallate ones are gustatory papillae showing taste buds and taste pores. Microplicae are visible at high magnification in all type of papillae as well as in the interpapillari zone.

KEY WORDS. 1. Mammals; 2. Armadillo; 3. Dasypodidae; 4. Tongue; 5. Lingual Papillae.

INTRODUCTION

The little hairy armadillo Chaetophractus vellerosus (Gray, 1865), is an omnivorous terrestrial mammal, belonging to the family Dasypodidae, in the South-American order Xenarthra (Edentata). It inhabits in Bolivia, Paraguay and Argentina, has fossorial habits, and is well adapted to the life in arid regions (Redford & Eisenberg, 1992 and Greegor, 1975, 1980; 1985). In Argentina, it is commonly hunted for food and the shells are used for making musical instruments and handicrafts. Nevertheless, it seems not to have special problems of conservation and it was categorized as a low care species (Díaz & Ojeda, 2000). Little is known about its morphology (Estecondo et al., 1995, 1997) and nothing about the structure of the dorsal surface of the tongue.

The lingual mucosa of mammals has a highly differentiated papillary system. The papillae are disseminated on the lingual surface and have two specific functions: gustatory and mechanical (Chamorro et al., 1994). Their form differs slightly from one species to another and their development reflects the food intake habits of the animals (Kobayashi et al., 1994, 1997).

There are SEM studies of the tongue papillae in many mammals as horse and cow (Steflik et al., 1983; Chamorro et al., 1986; Paz Cabello et al., 1988); wild boar and pig (Chamorro et al., 1994; Kobayashi et al., 1997; Amreek Singh et al., 1997); chinchilla (Martínez et al., 2000); dog (Singh et al., 1980; Iwasaki & Sakata, 1985a; Kobayashi et al., 1987; Holland et al., 1989); cat (Boshell et al., 1982; Chamorro et al., 1987; Kobayashi et al., 1988); rabbit (Toyoshima & Shimamura, 1981; Liu & Lee, 1982; Chamorro et al., 1987; Kobayashi, 1992); rat (Liu & Lee, 1982; Iida et al., 1985; Iwasaki & Kumakura, 1994); mouse (Cameron, 1966; Hume, 1976); bat (Kobayashi & Shimamura, 1982; Pastor et al., 1993); monkey (Arvidson, 1975; Kobayashi et al., 1989; Iwasaki et al., 1992; Watanabe et al., 1995); and opossum (Krause & Cutts, 1982; Martínez et al., 1998).

In armadillos, histological observations of the dorsal tongue epithelium by light and scanning electron microscopy were performed in Dasypus novemcinctus (Morais et al., 1991, 1994; Watanabe et al., 1992), D. hybridus (Cuba Caparo, 1979) and Euphractus sexcinctus (MORAIS & Watanabe, 1988).

In this paper we analyze the morphology of the dorsal surface of the tongue in the armadillo Chaetophractus vellerosus by scanning electron microscopy (SEM), with special consideration of the lingual papillae and their morphological characteristics, pointing out the possible morphofunctional correlations.

MATERIAL AND METHOD

Tongues from eight mature female and male armadillos captured in Bahía Blanca region were used. They were fixed in modified Karnovsky solution, containing 2.5% glutaraldehyde and 2% paraformaldehyde in 0.1 M, sodium cacodylate buffer (pH 7.4), for three days, at 4 ºC. Small pieces of tissue were dissected from some areas of the dorsal tongues. They were washed in 0.1 M sodium cacodylate, buffer (pH 7.4) and treated with 8 N hydrochloric acid at 60 ºC for 1 hr, to remove any extracellular mucous substance from the lingual surface. Then, dehydration, critical-point drying and gold-ion sputtering were done. Observations were made with a Jeol JSM-35 CF scanning electron microscope at 15 kV.

RESULTS

Macroscopically, the tongue of Chaetophractus vellerosus is triangular, elongated in the anteroposterior direction, with a sharp apex. Filiform, fungiform and vallate papillae can be observed.

Scanning electron microscopy revealed that filiform papillae lie in rows and are compactly distributed over the entire dorsal surface of the tongue. They are simple (conical) or branched in the extremity. The conical ones have a wide base and narrowed to a thin apex (Fig. 1). The branched ones are crown-shaped, with a basally concave central area, surrounded by several pointed filamentous processes bent backwards (Fig. 2). In the base, these papillae are encircled by a groove.


Fig. 1. Apex of the tongue of Chaetophractus vellerosus with simple conical (big arrow) and branched (small arrow) filiform papillae and fungiform papillae (*). 54X.
Fig. 2. The anterior third of the tongue showing filiform papillae with three branches, surrounded by a groove (small arrow) and fungiform papillae (*). 200X.

In the anterior third of the tongue, there are prominent and conical filiform papillae located in the apex (Fig. 1). Filiform branched papillae generally have three branches, being the middle one the largest and the widest (Fig. 3). In the middle third of the tongue, they have three to five branches (Fig. 4). In the posterior third, they decrease in height (Fig. 5). In this region conical filiform papillae, oriented posteriorly, are also observed. They decrease in height, caudally to the vallate papillae. At both lateral edges there are conical and three branches filiform papillae (Fig. 6). At higher magnification microridges are distinguished in the branches, but there are no taste pores.


Fig. 3. Shows three branched filiform papillae. 260X.
Fig. 4. The middle third of the tongue showing filiform papillae with five branches. 200X.


Fig. 5. The posterior third of the tongue showing filiform papillae. 200X.
Fig. 6. Lateral edge of the tongue with conical (*) and three branched (small arrow) filiform papillae. 200X.
Dome-shaped fungiform papillae, 150-250 µm in diameter, surrounded by a groove, are scattered among the filiform papillae (Fig. 7). They are shorter in height and larger in diameter when compared with filliform papillae (Fig. 2). On their surface deciduous epithelium is clearly observed (Fig. 2). Taste pores (Fig. 8) open on the papillary surface, as well as in the papillary groove. At higher magnification the surface appears to be covered by microridges (Fig. 8).

There are only two circumvallated papillae in the posterior third of the tongue, one on each side of the midline, keeping an oblique position. They are large-sized (400-600 µm in diameter), elliptical, with a convex surface. A papillary groove, wide and deep, encircles them (Fig. 9). They are surrounded by numerous filiform papillae. The taste pores open on the papillary surface as well as in the papillary groove. At higher magnification, a network of clear microridges was observed. In the interpapillar area, epithelial cell surfaces with microridges were also observed.


Fig. 7. Fungiform papillae showing deciduous epithelium and taste pores (small arrow). 320X.
Fig. 8. Higher magnification of the surface of a fungiform papillae with microridges and a taste pore (small arrow). 5400X.
Fig. 9. Shows a vallate papillae (*) and several filiform papillae (small arrow). 110X.

DISCUSSION

In this study, the acid hydrolysis method (Iwasaki et al., 1984, Iwasaki & Sakata, 1985b) was applied to the armadillo tongue, and the results clearly showed that fixed mucus was almost completely removed from the lingual surface, while there was no evidence of damage to the cell surface itself.

The presence of filiform papillae in the surface of the tongue mucosa of C. vellerosus coincides with the observed in other armadillos as E. sexcinctus (Morais & Watanabe, 1988) and D. novemcinctus (Morais et al., 1991; 1994; Watanabe et al., 1992). Nevertheless, in other Xenarthra as Tamandua (Kubota et al., 1962; Brazao et al., 1983) and Myrmecophaga as well as in the Pholidota Manis (Sontag, 1923) filiform papillae were not observed.

The increase of the number of branches in the filiform branched papillae of C. vellerosus described by us in the middle third of the tongue, was also reported in E. sexcinctus (Morais & Watanabe) and D. novemcinctus (Morais et al., 1994). The absence of taste pores allows to establish that filiform papillae have only mechanical function. As in other species (Paz Cabello et al., 1988), the wide distribution and high number of branched filiform papillae highly suggest a protective role of the lingual surface. Also, the caudal inclination of branched and conical papillae suggests a possible role in the prehension of food fragments (Paz Cabello et al.; Chunhabundit, 1992). According to Iwasaki et al. (1987a), the reason for the distribution of different types of filiform papillae in different areas of the tongue is thought to be based on their functional differences. Thus, the anterior part of the tongue of C. vellerosus may possibly contribute to the touch and prehension of the food, while the posterior part may facilitate the swallowing of the masticated food.

The morphology of fungiform papillae observed in this species is comparable to the one reported for E. sexcinctus (Morais & Watanabe), D. novemcinctus (Morais et al., 1994; Watanabe et al., 92) and other mammals (Iwasaki et al., 1987b; 1988; 1992). Also, the disposition of filiform papillae surrounding the fungiform ones suggests a protective role, as in other mammals (Chamorro et al., 1987). Furthermore, the presence of taste buds in the fungiform papillae observed in C. vellerosus, is common in other species (Arvidson, 1975; Arvidson & Friberg, 1980; Arvidson et al., 1981; Mistretta & Baum, 1984; Chamorro et al., 1986).

Concerning the vallate papillae, their number varies considerably in mammals (Kubota & Hayama, 1964; Kubota, 1967). The presence of only two vallate papillae as in C. vellerosus, was also reported in the armadillos E. sexcinctus (Morais & Watanabe), D. novemcinctus (Morais et al., 1991; 1994; Watanabe et al., 1992) and D. hybridus (Cuba Caparo) as well as in some other mammals as tamandua (Kubota et al., 1962), porcupine (Kubota et al., 1966), insectivores (Sontag; Kobayashi et al., 1983), bat (Pastor et al.; Kobayashi & Shimamura, 1982), wild boar and pig (Chamorro et al., 1994; Amreek Singh et al.; Kobayashi et al., 1997), opossum (Martinez et al., 1998), chinchilla (Martinez et al., 2000) and rabbit (Chamorro et al., 1987).

Microridges observed in the filiform, fungiform, vallate and interpapillar surface are similar to those reported in E. sexcinctus (Morais & Watanabe), and in other mammals as the wild boar and pig (Chamorro et al., 1994), mouse (Utiyama et al., 1995), monkey (Iwasaky et al., 1992), opossum (Martínez et al., 1998; Krause & Cutts, chinchilla (Martinez et al., 2000) and horse and cow (Chamorro et al., 1986). They provide a structure that probably enhances the spreading and adhesion of the mucous coat (Sperry & Wassersug, 1976), which protect the superficial cells (Andrews, 1976; Nair & Schroeder, 1981). As was suggested by Iwasaki et al. (1987a) for other mammals, filiform papillae and microridges may also function in armadillos as a supporting structure for food-uptake, mastication and swallowing.

RESUMEN: A través de la microscopía electrónica de barrido, fueron analizadas las características de la superficie dorsal de la lengua de Chaetophractus vellerosus. Fueron observadas papilas filiformes simples y ramificadas, fungiformes y caliciformes. Papilas filiformes simples cónicas, se observaron en el ápice, bordes laterales y tercio posterior, caudalmente a las papilas caliciformes. Las ramificadas estaban densamente distribuidas en toda la superficie dorsal de la lengua. Las papilas fungiformes se observaron entre las papilas filiformes ramificadas. En el tercio posterior fueron visualizadas dos papilas caliciformes. Las papilas filiformes tienen función mecánica, en tanto que las fungiformes y caliciformes son gustativas, y en ellas se ubicaban corpúsculos y poros gustativos. Con mayor aumento fueron observados micropliegues en todos los tipos de papilas y entre éstas.

PALABRAS CLAVE. 1. Mamíferos; 2. Armadillo; 3. Dasypodidae; 4. Lengua; 5. Papilas linguales.

Dirección para correspondencia:
Prof. Dra. Silvia Estecondo
Laboratorio de Histología Animal
Departamento de Biología, Bioquímica y Farmacia (DBByF)
Universidad Nacional del Sur (UNS)
San Juan 670, 8000
Bahía Blanca
ARGENTINA

Email:silviest@criba.edu.ar

Recibido : 12-06-2001
Aceptado: 13-08-2001

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