Comparative histological and histochemical study of cricoid 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. Cricoid 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 Cricoid 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 Cricoid 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) [10] . Sections were cut at 5-6 μm thickness and were utilized for histomorphological and histochemical studies. The Cricoid 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 Cricoid cartilage was carried out by Ehrlich's Haematoxylin and Eosin stain (Luna, 1968) [10] , Van Geison's stain for collagen fibers (Bancroft et al., 2008) [3] , Gomori's method for reticular fibers (Luna, 1968) [10] , Verhoeff's method for elastic fibers (Bancroft et al., 2008) [3] and Toludine blue method for mast cells (Singh and Sulochana, 1996) [12] 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) [10] .

Results and Discussion

The cricoid cartilage in Deccani sheep and Bidri goat consisted of lamina epithelia, lamina propria-submucosa, muscular layer, a cartilaginous layer and tunica adventitia (Sinha et al., 2012) [13] (Fig. 1 and Fig. 4). The Cricoid cartilage in Deccani sheep and Bidri goat was lined by pseudostratified columnar epithelium containing goblets cells within them (Fig. 2). There were more number of goblet cells in the epithelium of Deccani sheep than the epithelium of Bidri goat (Chunhui et al. 2009 and Sinha et al. 2012) [4,3] . However, it differs with the earlier reports in ruminants (Eurell and Frappier, 2006) [7] in sheep and goat (Alsadi, 2006) [1] in Camel Dromadarius (Ebrahimi et al., 2010) [5] . The lamina propria and submucosa were continuous with no distinct boundary. lamina propriasubmucosa was composed of loose connective tissue fibers collagen, elastic and reticular fibers, and consisted of fibroblast, fibrocytes, mast cells, macrophages, blood vessels and nerve fibers were also noticed (Fig. 1, Fig. 3, Fig. 5, Fig. 6, Fig. 7 and Fig. 8). More number of plasma cells were noticed in this region. Large amount of fat cells were observed in the lamina propria-submucosa (Fig. 1) [14,7,4,13,2,6] . The presence of large number of plasma cells and diffuse lymphatic aggregation below the epithelium indicates role in immune response against the infection and also play role in defense mechanism.

The glands were sero-mucous in nature (Fig. 9) ( [14,1,7,4,2,6] . The sero-mucous glands help in secretion of the watery and mucous fluids that moistens the surface epithelium and the air. The glandular lobules were separated from each other by connective tissue fibers consisted of collagen, reticular and elastic fibers (Fig. 3, Fig. 5 and Fig. 7). However, it differs in camels where serous glands were observed (Eshra et al., 2016) [6] . The glands were tubuloacinar type of glands (Fig. 9). However, in Bactrian camel glands were branched coiled tubulo-alveolar types of glands (Chunhui et al., 2009) [4] . This may be due to species variation.

The acini and tubules of serous secreting units were lined by pyramidal to columnar shaped cells with basally placed nuclei. The mucous acini and tubules were lined by pyramidal shaped cells with basally placed flattened nuclei. The acini consisted of small round lumen whereas, the tubular portion contained long narrow lumen (Eurell and Frappier, 2006) [7] . The skeletal muscle was observed between submucosa and cartilage. The cartilage was of hyaline type and continuous plate like surrounded by perichondrium, which had two distinct layer Viz., chondrogenic layer consisting of elliptical lacunae and fibrous layer consisting of collagen and elastic fibers (Fig. 1 and Fig. 4). The lacunae were polyhedral in shape contained chondrocytes. The chondrocytes were separated from each other by interterritorial matrix. The perichondrium consisted of two layers chondrogenic layer made up of elliptical lacunae, and the other consisting of collagen and elastic fibers (Fig. 4) ( [14,1,7,4,9,5,13,2,6] . The histochemical study of Cricoid cartilage in Deccani sheep and Bidri goat showed moderate PAS positive reaction in the gland and epithelium indicating the presence of mucoplolysaccharides (Fig. 10 and Fig. 12). The epithelium and some glandular cells showed strong positive reaction for Alcian Blue reaction at pH 2.5 (Fig. 11) indicating the occurrence of sulfated sialomucins and sulfomucins (Majid, 1986 and Kahwa and Purton, 1996) [11,8] whereas acidic and neutral reaction for Alcian blue-PAS stains was noted in Bactrian camel (Chunhui et al., 2009) [4] .

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