Histochemical study of Magellanic penguin (Spheniscus magellanicus) minor salivary glands during postnatal growth

Abstract

The histological and histochemical features of the minor salivary glands during postnatal development have been generally associated with the type of food ingested. However, recent studies support the fact that these salivary glands develop independently of the diet; in fact, minor salivary glands have similar morphological and histochemical characteristics in adult individuals of species with different diet regimens. Thus, the aim of this study was to characterize the developmental morphology of the penguin minor salivary glands and to contrast them with minor salivary glands of other species. The tongue, palatine, and mouth cavity (bottom) minor salivary glands of newborn, 1- to 20-day-old, and adult magellanic penguins were studied with hematoxylin-eosin, periodic acid-Schiff, alcian blue, toluidine blue, and lectin histochemistry. Minor salivary glands were present at all ages, although they were only moderately developed in animals less than 15 days old. After this age, glands were abundant in all age groups; in addition, cells from the glandular epithelium were functionally mature and secreted mucins. Nevertheless, in newborn to 15-day-old penguins, mucins were located only at the apical cytoplasm of mucous cells. In all ages, mucous cells displayed periodic acid-Schiff-positive, alcianophilic, and metachromatic reactions; among mucous cells, other orthochromatic cells appeared interspersed. From 15 days on, histochemical reactions became more intense until adulthood, and the cytoplasm of secretory cells was filled with glycoproteins and sulfomucins. Moreover, lectins bound to different oligosaccharides in mucous cells, depending on the stage of maturation of the glands. In conclusion, penguin minor salivary glands are already present at birth, and show progressive and quantitative increases in mucous secretion during postnatal development. These changes are necessary not only for nutrient ingestion, but also for nonimmune protection of the buccal cavity.

Histomorphological structure of the palate and histochemical profiles of the salivary palatine glands in the Chukar partridge (Alectoris chukar, Gray 1830)

“…Although the most common type of gland found in all domestic and wild bird species is the tubular type, researchers have also identified simple branched tubulo‐alveolar, alveolar and complex alveolar glandular structures in birds (Samar et al . ; Crole and Soley ). It has been reported that, in the emu and ostrich, the palate has two regions, one glandular and the other aglandular, which are located rostrally and caudally to the choanal cleft.…”

“…Only a limited number of studies are available on the anatomical and histological structure of the avian palate (Samar et al . , , ; Tivane ; Igwebuike and Eze ; Crole and Soley ; Erdogan and Alan ). It has been reported that in the ostrich, the anterior two‐thirds of the hard palate is divided by a median longitudinal mucosal fold into two regions, which lack papillae, whilst the caudal portion and the periphery of the choanal cleft contain small and fine papillae (Tadjalli et al .…”

“…Salivary mucins establish a barrier between the oral mucosa and bacterial flora, and thereby, form a protective layer on the oral mucosa against desiccation, mechanical damage, external toxic substances and microbial toxins (Samar et al . , ; Crole and Soley ).…”

“…Furthermore, a limited number of studies are also available on the histological structure of the palate and the histochemical features of the palatine glands in domestic fowl and wild birds (Samar et al . , , ; Tivane ; Crole and Soley ).…”

“…The presence of glandular structures is a characteristic feature of the upper digestive tract (including the tongue, palate and pharynx) of avian, and glandular tissue has been demonstrated in many avian species (Samar et al . , , ; Kobayashi et al . ; Arthitvong et al .…”