Collection, fixation, processing and staining of tissues The lacrimal glands were collected from five apparently healthy young pigs of local mixed breed of either sex. The pig eyes were collected from local slaughter house immediately after decapitation and the tissues were fixed in a 10% neutral buffered formalin solution for 48-72 hrs. The tissues were processed for light microscopic examination and embedded in paraffin blocks. The paraffin sections (5-6 ^) were made through the entire gland and stained with routine Harris' hematoxylin and eosin stain for general histomorphological examination, Gomori's stain for reticular fibres, Weigert's method for elastic fibres (Luna, 1968) and Crossman's trichrome stain for collagen fibres (Crossman, 1937). In addition, selected sections were processed for histochemical demonstration of mucopolysaccharides using PAS-Alcian blue, Alcian blue, PAS (|McManus') method, colloidal iron method and Mayer's mucicarmine method (Luna, 1968).

How to cite this article: Gahlot, P.K., Singh, A. and Parkash, T. (2020). Histoarchitecture and histochemical studies on the lacrimal gland of pig (Sus scrofa). J. Anim. Res., 10 (1): 117-121.

The gland was located on dorso-lateral aspect of the eye in the orbital cavity as reported in pigs (Kleckowska- Nawrot and Dziegiel, 2008; Henker et al., 2013). Similar observations were reported in other animals like sheep (Singh et al., 2018), Iranian river buffalo (Abbasi et al.,2014) and dogs (Shaker et al., 2016). The gland was a multilobar tubuloacinar gland with predominance of acini over tubules (Fig. 1a).

It was covered by a thick connective tissue capsule, consisting of collagen and elastic fibers. The capsular connective tissue penetrated into the glandular parenchyma forming the septa, which divided the gland into lobes and lobules. These lobules were represented by the secretory end pieces and duct system. The glandular tissue was consisted of serous acini and mucous acini and sero-mucous (mixed) secretory units (Fig. 1a and 1b) which were in agreement with the findings in pigs (Kuhnel and Scheele, 1979; Gargiulo, et al., 1999), sheep (Singh et al., 2018) and buffaloes (Girgiri and Kumar, 2018). In contrast, canine lacrimal glands were reported as being purely mucus-secreting glands (Martin et al., 1988) and goat as serous (Alsafy, 2010). The lacrimal gland in camel was consisted of serous and mucous acini (Ibrahim and Abdalla, 2015). The acini of irregular lumen were composed of conical to pyramidal cells surrounded by basal myoepithelial cells. The big and round secretory cell nuclei were located in their basal part. These cells showed weakly eosinophilic and granular cytoplasm.

The plasma cells with a characteristic basophilic nucleus and eosinophilic cytoplasm and sparse amount of lymphocytes were observed in the glandular interstitial tissue (Fig. 1b). The secretory units were followed by a duct system. The excretory duct system was made up of intercalated, intralobular, interlobular and large excretory ducts (Fig 1a, 1b. ) as revealed in pigs (Kuhnel and Scheele, 1979) and other species like sheep (Singh et al., 2018) and buffaloes (Girgiri and Kumar, 2018). In contrast, the duct system of lacrimal gland of dog was started with intralobular (Shaker and AL-Obeady, 2016). The intercalated tubules with large lumen were composed of single layer of cuboidal cells with round nuclei, located in the basal area of the cells which were in agreement with the findings in pig (Kuhnel and Scheele, 1979). The intralobar ducts were varied from bistratified cuboidal to simple columnar type. The interlobar ducts showed irregular lumen and lined with stratified columnar epithelium with large goblet cells. The blood vessels and nerve bundles were observed in between inter lobular spaces.

Histochemical studies indicated the strong presence of neutral mucopolysaccharides in the acini, which was demonstrated with the help of PAS method (Fig. 2a). These observations were in agreement with the earlier findings in sheep (Singh, et al., 2018), camel (Mohammadpour, 2011), however a strong PAS positive reaction was observed in mucous cells and a weak PAS positive reaction in seromucous cells of small ruminants Gargiulo et al. (1999). The acini showed strong presence of acidic and neutral mucopolysaccharides with PAS-AB stain (Fig. 2b) as reported in buffalo (Girgiri and Kumar, 2018), whereas in sheep (Singh et al., 2018) showed presence of both acidic and neutral mucopolysaccharides with predominanace of neutral one. The strong alcianophilic activity was observed towards the Alcian blue (pH 2.5) showing presence of weakly acidic sulfated mucosubstances, sialomucins and hyaluronic acids in glandular parenchyma of the gland (Fig. 2c) as reported in buffalo (Girgiri and Kumar, 2018), whereas sheep (Singh et al., 2018) and small ruminants (Triveni et al., 2017) alcianophilic activity was moderately positive. The reaction towards Colloidal iron (Fig. 2d) and Meyer's mucicarmine was observed positive in acini as reported in sheep (Singh et al., 2018). The goblet cells in the stratified ducts also showed strong positive activity towards the same. The epithelium of all ducts showed negative reaction for PAS, PAS-AB and AB methods. However, the goblet cells in the interlobular ducts of small ruminants showed strong positive activity towards PAS, PAS- AB, Alcian blue and colloidal iron (Figs. 2c and 2d) as reported in sheep (Singh et al., 2018) and small ruminants (Triveni et al., 2017).

It may be concluded that the lacrimal gland was a capsulated multilobular tubulo-acinar in nature. The lobes consisted of acini, which were of mixed in nature but predominantly sero-mucous in nature. The excretory duct system was made up of intercalated, intralobular, interlobular and large excretory ducts. The acini showed strong presence of glycogen, mixed mucosubstances, sialomucins and hyaluronic acids in the acini. The ducts showed very weak reaction for presence of glycogen and mucosubstances.