Comparative histological and histochemical study of thyroid cartilage in Deccani sheep and Bidri goat

Introduction

Socioeconomic growth and national economy of the country has been significantly backed by small ruminants sector. Small ruminants contribute about 10% GDP in the total value of livestock sector. Sheep and goat are the important source of food (milk & meat) and main source of income for small and marginal farmers. The heavy mortality in the small ruminants especially in goats has been reported due to respiratory tract disease. The larynx is a conducting part of respiratory system which protects the lower respiratory passage against inundation. Thyroid cartilage being one of the important cartilage and unpaired one. The predominant breeds of sheep and goat in Bidar district are Deccani sheep and Bidri goat respectively and limited scientific work has been carried out, hence the present study was undertaken to study and to correlate any histological and histochemical variations in the thyroid cartilage of Deccani sheep and Bidri goat.

Materials and methods

The materials for the study were collected from Six Deccani sheep and Six Bidri goat immediately after slaughter from local slaughter house. The collected thyroid cartilage samples were washed in normal saline and fixed in different fixatives like 10% Neutral buffered formalin, Zenker's fluid and Bouin's fluid. The samples were processed in isopropyl alcohol-xylene sequence and embedded in paraffin by routine method (Luna, 1968) [9] . Sections were cut at 5-6μm thickness and were utilized for histomorphological and histochemical studies. The thyroid cartilage tissue fixed in Neutral buffered formalin were pre-frozen for 1-2 hrs and embedded in freezing media; using cryostat 6-7 μm thickness sections were cut and utilised for lipid studies. The histomorphological study of thyroid cartilage was carried out by Ehrlich's Haematoxylin and Eosin stain (Luna, 1968) [9] , Van Geison's stain for collagen fibers (Bancroft et al., 2008) [3] , Gomori's method for reticular fibers (Luna, 1968) [9] , Verhoeff's method for elastic fibers (Bancroft et al., 2008) [3] and Toludine blue method for mast cells (Singh and Sulochana, 1996) [10] whereas histochemical study was carried out using PAS technique for mucopolysaccharides (Bancroft, et al., 2008) [3] , Alcian blue pH 2.5 for sulphated sulfomucins and sialomucins (Bancroft et al., 2008) [3] and Oil red O for lipids (Luna, 1968) [9] .

Results & discussion

Histomorphology The thyroid cartilage in Deccani sheep and Bidri goat showed lamina epithelia, lamina propriasubmucosa, muscular layer, cartilaginous layer and tunica adventitia (Eurell and Frappier, 2006 and Alsadi 2006) [1,6] (Fig. 1, Fig 2 and Fig. 8). The thyroid cartilage of Deccani sheep and Bidri goat was lined by pseudostratified columnar epithelium (Eurell and Frappier, 2006 Alsadi, 2006 and Arup, 2014) [1,2,6] (Fig. 1, Fig 8). However, it differ with earlier report in goat (Kahwa and Purton, 1996) [7] , in buffaloes, camels and donkeys (Eshra et al., 2016) [5] where it is lined by pseudostratified ciliated columnar epithelium and in Bactrian Camel pseudostratified ciliated columnar epithelium with numerous goblets and basal cells (Chunhui et al., 2009) [4] . This may be due to change in climatic condition or variation in breed and species. The lamina propria-submucosa were continues and composed of loose connective tissue containing elastic fibers, collagen fibers, reticular fibers. Fibroblast, fibrocyte, mast cells, macrophages and more number of plasma cells were also observed (Fig. 3 [4,5,6,12] (Fig. 1, Fig 7).

The presence of large number of plasma cells and diffuse lymphatic aggregation below the epithelium indicates the role in immune response against the infection and also play role in defense mechanism (Fig. 1, Fig 6 and Fig 8). The glands were sero-mucous in nature. The lobules were separated from each other by loose connective tissue fibers consisted of more collagen fibers, few elastic and reticular fibers (Fig. 3,Fig 4). Serous secretory cells were more compared to mucous secretory cells. The sero-mucous glands help in secretion of the watery and mucous fluids that moistens the surface epithelium and the air (Alsadi, 2006 and Sinha et al., 2012) [1,11] (Fig. 1). However, it differed with the earlier report in camels where serous glands were observed (Eshra et al., 2016) may be due to species variation. In Deccani sheep and Bidri goat the acini and tubules of serous secreting units were lined by pyramidal to columnar shaped cells containing oval to spherical shaped basal nuclei with indistinct cell boundaries. The mucous acini and tubules were lined by pyramidal shaped cells with basally placed flattened nuclei with indistinct cell boundaries. The acini consisted of small round lumen whereas, the tubular portion contained long narrow lumen. The myoepithelial cell at the base of secretory unit was noticed which indicates its role in contraction and release of secretory product in the duct system. (Eurell and Frappier, 2006) [6] (Fig. 1, Fig 6 and Fig. 8). The muscular layer was observed below the submucosa which consisted of skeletal muscle in thyroid cartilage of Deccani sheep and Bidri goat (Trautmann and Fiebiger, 2002 and Alsadi, 2006) [1,12] (Fig 2). The thyroid cartilage in Deccani sheep and Bidri goat was hyaline in nature surrounded by perichondrium (Fig. 1, Fig 2). The chondrocytes were present in the lacunae, these lacunae were elliptical towards the perichondrium and pyramidal shaped in the deeper part of the cartilage. The chondrocytes were separated by interterritorial matrix; some lacunae were present as groups (cell nests). The perichondrium consisted of two layers chondrogenic layer made up of elliptical lacunae and the other consisting of collagen and elastic fibers. Tunica adventitia consisted of loose connective tissue with the presence of blood vessels were also observed ( [1,2,4,5,6,11,12] (Fig. 2, Fig 5 and Fig. 10).

Histochemistry. The glands of thyroid cartilage in Deccani sheep showed moderate PAS positive reaction whereas in Bidri goat all cells of the glands showed weak PAS positive reaction indicating presence of mucopolysaccharides and variation in the secretory nature of the glands (Fig. 9). Few cells of the gland and the cartilage showed strong reaction for Alcian Blue at pH 2.5 in the present study indicating presence of sulfated sialomucins and sulfomucins in the gland and the ground substance of cartilage (Kahwa and Purton, 1996 and Sinha et al., 2012) [7,11] (Fig. 7).

References

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