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Estudio histologico de las glandulas salivales de Zaedyus pichiy (Mammalia, Xenarthra, Dasypodidae).

Histological Study of the Salivary Glands in Zaedyus pichiy (Mammalia, Xenarthra, Dasypodidae)

RESUMEN: Se estudio la histologia de las glandulas salivales del armadillo Zaedyus pichiy (Desmarest, 1804). Se identificaron tres pares de glandulas salivales mayores, tubuloacinares compuestas, parotida, submandibular y sublingual. La parotida es histologicamente una glandula serosa. La glandula submandibular posee dos lobulos. El lobulo anterior esta formado por acinos mixtos y serosos. El lobulo posterior es principalmente mucoso. Un reservorio o vesicula salival se relaciona con la glandula submandibular anterior. La glandula sublingual es mixta y esta compuesta por acinos mucosos con escasas semilunas serosas.

PALABRAS CLAVE. Mamiferos; Xenarthra; Armadillos; Dasypodidae; Zaedyuspichiy; Histologia; Glandulas salivales.

SUMMARY: The histology of the salivary glands of the armadillo Zaedyus pichiy (Desmarest, 1804) was studied. Three pairs of major compound tubuloacinar salivary glands, parotid, submandibular and sublingual, were distinguished. The parotid gland is histologically a serous gland. The submandibular gland consists of two lobes. The anterior lobe is composed of mixed and serous acini. The posterior lobe is predominantly mucous. There is a reservoir or salivary bladder, related with the anterior lobe. The sublingual gland is mixed, composed of mucous acini with scattered serous demilunes.

KEY WORDS: Mammals; Xenarthra; Armadillos; Dasypodidae; Zaedyus pichiy; Histology; Salivary glands.

INTRODUCTION

Regarding their morphology, histochemistry and ultrastructure, the salivary glands of mammals have been the subject of numerous studies (Gargiulo et al., 1991; Stolte & Ito, 1996; Watanabe et al., 1996; Tandler et al., 1997, 1998; Junior & Masuko, 1998; Cangussu et al., 2002; Lentle et al., 2002). However, information about the salivary glands of Xenarthra, a group in which they are of big dimensions (Grasse, 1955), is scarce and fragmentary (Pouchet, 1868; Burne, 1901; Ruby, 1978; Cuba Caparo, 1979; Fava de Moraes, 1965; Meyer et al., 1993; Codon et al., 2003); particularly, nothing is known about Zaedyus pichiy (pichi).

This armadillo is a native, typically solitary mammal, that inhabits in grasslands, open pampas and arid regions of southern South America, in central and southern Argentina and Chile, to the Strait of Magellan; it lives in burrows digged in open areas, on the base of small bushes; the diet consists of insects, worms, small vertebrates, some vegetable materials and carrion; local people use it as per and food source (Parera, 2002). The pichi is still abundant and widely distributed in its natural environment, having no special conservation status yet (Diaz & Ojeda, 2000).

In this paper, the histological structure of the salivary glands of Zaedyus pichiy was studied and compared with that of other species of armadillos and of other mammals.

MATERIAL AND METHOD

Salivary glands of eight mature female and male Zaedyus pichiy captured in Bahia Blanca (Province of Buenos Aires, Argentina) region were used. They were fixed in Bouin's fluid, dehydrated in graded ethanol and embedded in paraffin. Sections 5-7 um thick were stained with haematoxylin and eosin, Masson's trichrome, periodic acid Schiff reaction (PAS) and Alcian Blue pH 2.5 (AB). They were examined and photographed with a Nikon AFM microscope.

RESULTS

Three pairs of major salivary glands, parotid, submandibular and sublingual, were distinguished. They are tubuloacinar, exocrine glands. All of them are compartmentalized into several lobules by connective tissue, containing blood vessels, nerves and large excretory ducts.

The parotid gland (Fig. 1) consists of serous acini and intercalated and striated ducts. The serous acini lay close of each other, separated only by thin capillaries and very scarce connective tissue. They are composed of pyramidal cells, having basal basophilic and apical eosinophilic cytoplasm, with rounded and basal nuclei. The heterochromatin is principally confined to the area of the nuclear envelope. Cells showing a strong positive stain to PAS and negative stain to AB were observed. Myoepithelial cells surrounds the acinar cells. The acini drain into the intercalated ducts, composed of a single layer of cuboid epithelium. The intercalated ducts empty into the striated ducts, which have a single layer of cylindrical epithelium, the cells with eosinophilic cytoplasm, having a large nucleus located in the central-basal part. The typical striation was clearly seen. These ducts are surrounded by connective tissue in which blood vessels were observed. The striated ducts end in the interlobular ducts. These ducts are mainly located in the extralobular connective tissue, composed of pseudostratified columnar epithelium.

[FIGURE 1 OMITTED]

The sublingual glands are mixed (Fig.2), composed of mucous acini with scattered serous demilunes. The mucous cells possess spongy cytoplasm and flattened and basal nuclei. They occupy a larger volume of the organ than do the serous ones. The voluminous acini have big and irregular acinar lumen. Histochemically the cells were positive for PAS and AB. The ducts are very scarce.

[FIGURE 2 OMITTED]

The submandibular glands are of greater size and have two lobes, which differs in their histology and histochemistry (Fig. 3). The anterior lobe is composed of mixed and serous acini (Fig. 4). The mucous acini have clear cellular limits; the nuclei are confined to the basal cytoplasm and are capped by large serous demilunes. The acinar lumen is small and irregular. Mucous acinar cells showing a strong positive stain to AB and weakly stain to PAS were observed. The serous acini possess triangular shape cells with central nuclei. The serous cells of demilunes and acini were positive for PAS.

[FIGURES 3-4 OMITTED]

The posterior lobe is bigger than the anterior one. It is predominantly mucous (Fig. 5), been almost exclusively formed by mucous acini with scarce and small serous demilunes. The mucous cells were only slightly stained whit AB and reacted strongly to PAS. The serous cells of demilunes stain to PAS. Intercalated ducts, striated ducts and interlobular ducts were observed in this gland.

[FIGURE 5 OMITTED]

There are a reservoir or salivary bladder (Fig. 6) related with the anterior submaxillary gland. The bladder has pseudostratified columnar epithelium. The major component of the wall is striated skeletal muscle with circular and longitudinal fibbers. The connective tissue is located between the epithelium and the muscular tissue and at the periphery.

[FIGURE 6 OMITTED]

In the three major salivary glands myoepithelial cells were observed in contact with the secretory cells and ducts.

DISCUSSION

The parotid gland of Zaeclyus is a typical serous gland, similar to those of Chaetophractus villosus and vellerosus (Estecondo et al., 1995), Dasypus hybridus (Codon et al., 2003), Cabassous loricatus (Fava de Moraes) and Dasypus novemcinctus (Fava de Moraes & Shackleford, 1963).

The salivary bladder observed in Zaeclyus is histologically similar to that of the species of Xenarthra previously studied (Pouchet; Burne; Fahrenholz, 1973; Meyer et al. and Estecondo et al.). In other mammalian species as rat (Butcher, 1972 and Kim, 1976) and mouse (Matsuoka et al., 1994), a salivary reservoir is found near the oral end of the main excretory duct (MED) of the submandibular gland; a similar structure exist in the MED of the mouse sublingual gland (Matsuoka et al., 1993). These expanded structures can store preformed saliva, that is ejected as needed by contraction of surrounding skeletal muscle. In the bat Tadarida thersites (Tandler et al., 1998) the parotid gland possesses giant ducts which have a huge storage capacity for saliva. An analogous function may be served by the end pieces of the submandibular glands of species of frog-eating bats (Tandler et al., 1996 and 1997). According to Tandler et al. (1998), it seems that any part of the salivary parenchymal tree, from the secretory end piece to the ostium of the MED, can be modified in different mammals to serve as a reservoir for formed saliva.

The presence of two lobes in the submandibular gland of Zaedyus which display significant histological and histochemical differences, being the posterior lobe predominantly mucous and greater in size than the anterior lobe, was also described for Chaetophractus villosus and vellerosus (Estecondo et al.), Dasypus novemcinctus (Shackleford, 1963), Dasypus hybridus (Codon et al.), Chlamydophorus truncatus, Euphractus sexcinctus and Bradypus tridactylus (Burne).

In his review of chiropteran salivary glands, Robin (1881) noted the presence in some species of two sets of submandibular salivary glands, which he labeled principal and accessory (for us anterior and posterior lobe). Binary submandibular glands are not uncommon either in bats or in other kinds of mammals (Nagato et al., 1998). The significance of such glands is debatable. According to Ball (1993), they might partially serve as a form of built-in the excess of saliva. Other hypothesis is that they provide evolutionary opportunities for specialized adaptation (Phillips et al., 1993 and Tandler et al., 1998).

Regarding the sublingual gland of Zaedyus, similar glands were described in Chaetophractus (Estecondo et al.), Chlamydophorus truncatus and Euphractus sexcinctus (Burne). Nevertheless these glands have not been observed in Dasypus hybridus (Codon et al.) and Dasypus novemcinctus (Shackleford).

Finally, the comparative study reveals some similarities as well as some differences between the histology of the salivary glands of diverse species of Xenarthra. Additional studies are needed to clarify if they are related to feeding habits.

Received : 12-10-2004

Accepted: 20-12-2004

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Correspondence to:

Prof. Dra. Silvia Estecondo

Laboratorio de Histologia Animal

Depto. de Biologia, Bioquimica y Farmacia

Universidad Nacional del Sur (UNS)

San Juan 670, 8000 Bahia Blanca

ARGENTINA

E-mail: silviest@criba.edu.ar

* Silvia Estecondo; * Stella Maris Codon & ** Emma Beatriz Casanave

* Laboratorio de Histologia Animal, Depto. de Biologia, Bioquimica y Farmacia, Universidad Nacional del Sur (UNS), Bahia Blanca, Argentina.

** Laboratorio de Fisiologia Animal, Depto. de Biologia, Bioquimica y Farmacia, UNS, Argentina; Member of the Researcher Career of the Consejo Nacional de Investigaciones Cientificas y Tecnicas (CONICET), Argentina.

The paper was supported by Secretaria General de Ciencia y Tecnologia, UNS, Projects 24/B060 and 24/B086 and by ANPCYT, PICTR-BID 00074/02.
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Author:Estecondo, Silvia; Maris Codon, Stella; Casanave, Emma Beatriz
Publication:International Journal of Morphology
Date:Mar 1, 2005
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