Indian Journal of Animal Research

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Indian Journal of Animal Research, volume 57 issue 8 (august 2023) : 1007-1010

Ultrastructural Studies on the Thyroid Gland of Dromedary Camel (Camelus dromedarius)

Devendra Singh1,*, Sanjeev Joshi1, Pankaj Kumar Thanvi1, Om Prakash Choudhary2
1Department of Veterinary Anatomy and Histology, College of Veterinary and Animal Sciences, Rajasthan University of Veterinary and Animal Sciences, Bikaner-334 001, Rajasthan, India.
2Department of Veterinary Anatomy and Histology, College of Veterinary Sciences and Animal Husbandry, Central Agricultural University (I), Selesih, Aizawl-796 015, Mizoram, India.
Cite article:- Singh Devendra, Joshi Sanjeev, Thanvi Kumar Pankaj, Choudhary Prakash Om (2023). Ultrastructural Studies on the Thyroid Gland of Dromedary Camel (Camelus dromedarius) . Indian Journal of Animal Research. 57(8): 1007-1010. doi: 10.18805/IJAR.B-4363.
Background: The previously reported information on the ultrastructure of the thyroid gland of the camel is meager as compared to other domestic animals; thus, the present study was designed to provide the ultrastructural features of the thyroid gland in the camel. 

Methods: The thyroid glands were collected from naturally died sixteen camels (n=16) of both sexes from Veterinary Clinical Complex, RAJUVAS, Bikaner, Rajasthan. The transmission electron microscopy (TEM) of the thyroid gland was done at Sophisticated Analytical Instrumental Facility (SAIF), Department of Anatomy, All India Institute of Medical Sciences, New Delhi. The standard protocol of AIIMS, New Delhi, was followed for electron microscopy. 

Result: The thyroid gland of the camel consisted of thyroid follicles comprised of cuboidal thyroid follicular cells. The follicular cells contained a nucleus with heterochromatin concentrated marginally on the nuclear membrane and the euchromatin was well dispersed in the nucleus with well-marked nucleoli. The nucleus of the follicular cell was rounded. The apical regions of the plasma membrane in follicular cells consisted of microvilli, which were numerous, thinner and finger-like in outline. The mitochondria appeared as round, oval, rod-shaped and dumbbell-shaped. The rough endoplasmic reticulum was visible as elongated, irregular, elliptical cisterns. The Golgi complex was well marked and consisted of flattened sacs, vacuoles and small vesicles. The parafollicular cells were found in small numbers and positioned basally between two follicular cells, close to the basement membrane. It can be concluded that the ultrastructure of the thyroid gland of the camel does not differ from that of other mammalian species.
The camel is renowned for its ability to survive the harsh environment of the desert. For survival in the desert environment, camels have physiological, anatomical and behavioral adaptation mechanisms. The endocrine and nervous system play a vital role in maintaining body homeostasis (Jubb et al., 1993). The thyroid gland is one of the largest ductless glands. It is situated on the lateral aspect of the trachea and made up of two lateral lobes and a connecting isthmus as reported earlier in sheep and goat (Jain et al., 1984).

Thyroid hormones have been found to influence the reproduction, growth, milk and fiber properties of domestic animals (Rhind and Kale, 2004; Todini et al., 2005; Todini et al., 2007). However, various factors like breed, age, sex and physiological condition affect blood thyroid hormone concentrations by modulating the hypothalamus-pituitary-thyroid axis in small ruminants (Todini et al., 2007). The ultrastructure of the thyroid gland is still needed to understand its fine structural morphology more precisely; thus, the present study was designed to provide the ultrastructural features of the thyroid gland in the camel.
Collection of the samples

The thyroid glands were collected from naturally died sixteen camels (n=16) of both sexes from Veterinary Clinical Complex, College of Veterinary and Animal Sciences, Bikaner, RAJUVAS, Bikaner, Rajasthan. The dead animals were free from any pathological condition of the thyroid gland. All the procedures involving thyroid gland sample collection from camel were conducted as per the Committee for the Purpose of Control and Supervision of Experiments on Animals (CPCSEA), Ministry of Environment, Forest and Climate Change, Government of India, vide registration number CVAS/IAEC/ CPCSEA/2044/GO/Re/SL/18/2019/07 for the College of Veterinary and Animal Sciences, Rajasthan University of Veterinary and Animal Sciences (RAJUVAS), Bikaner.
 
Processing of the samples for TEM
 
The transmission electron microscopy of the thyroid gland was done at Sophisticated Analytical Instrumental Facility, Department of Anatomy, All India Institute of Medical Sciences, New Delhi. The standard protocol of AIIMS, New Delhi, was used for transmission electron microscopy. For the TEM, 1-2 mm2 size tissues were preserved in Karnovsky’s fixative (a mixture of 4% paraformaldehyde and 1% glutaraldehyde in 0.1 M phosphate buffer). After fixation, tissues were rinsed thoroughly in 0.1 M phosphate buffer to wash off the excess fixative, followed by postfixation in 1% solution of osmium tetraoxide. The tissues were dehydrated by passing through a series of ascending concentrations of ethanol or acetone (Choudhary and Priyanka, 2017). Clearing of tissues was done by xylene or toluene. Then infiltration was carried out with liquid resins followed by embedding using flat molds or plastic capsules and then polymerization. Blocks were prepared and ultrathin sections were cut. Sections were lifted from below on the matted surface of the copper grid. The grids were then stained using uranyl acetate (10-15 min) and alkaline lead citrate (5-10 min). The sections were then viewed under TECNAI 200 Kv (FEI Electron Optics) TEM machine equipped with digital imaging and 35 mm photography system (Priyanka and Choudhary, 2018).
The profiles of small and large follicles at low magnification contained colloids in follicular lumen surrounded by follicular cells that varied in shape and size as mentioned in Bakerwali goat (Dar et al., 2018). The cuboidal follicular cells (Fig 1) contained nucleus with heterochromatin concentrated marginally on the nuclear membrane as an irregular layer and was also present as scattered clumps in the nucleus as reported earlier in West African Dwarf goat (Igbokwe et al., 2015) and Bakerwali goat (Dar et al., 2018).

Fig 1: Transmission electron micrograph of the follicular cell of the thyroid gland of camel showing basement membrane (BM), nucleus (N), nucleolus (n), mitochondria (M), primary lysosome (L), colloidal droplets (Cd), Golgi apparatus (G) and plasma membrane (PM) (X2550).



The euchromatin was well dispersed in the nucleus with well-marked nucleoli (Fig 1). The nuclei were irregular circular or elliptical shape with some indentations as reported in Bakerwali goat (Dar et al., 2018). It has been indicated that the shape of the nucleus in the follicular cell was influenced by the shape of the follicular cell as well as the various cytoplasmic structures in the cell. The thyroid follicular cells were squamous to cuboidal and contained a rounded nucleus as reported in White Fulani cattle (Igbokwe and Ezeasor, 2015); however, the nucleus was round and flattened in the Bakerwali goat (Dar et al., 2018).

The apical regions of the plasma membrane consisted of microvilli (Fig 2). The microvilli on the cuboidal follicular cells were numerous, thinner and finger-like, whereas the microvilli were sparse and short in flat follicular cells in Bakerwali goat (Dar et al., 2018). The microvilli of thyroid follicular cells phagocytose colloid from follicular lumen so that thyroid hormones formed on the scaffold of thyroglobulin could be processed intracellularly and released into circulation (French and Hodges, 1977). The cytoplasm of follicular cells showed mitochondria with varied shapes that were mostly localized on the apical cytoplasm abutting the colloid. The follicular cell mitochondria appeared as round, oval, rod-shaped and dumbbell-shaped (Fig 3) profiles as reported earlier in camel (Mubarak and Sayed, 2005) and Bakerwali goat (Dar et al., 2018).

Fig 2: Transmission electron micrograph of apical cytoplasm of the follicular cell (FC) showing microvilli (Mv), secretory granules (S), phagosome (P) and colloid (Co) (X2550).



Fig 3: Transmission electron micrograph showing follicular cell (FC), parafollicular cell (PFC) and nucleus of parafollicular cell nucleus (N) (X2550).



The rough endoplasmic reticulum (Fig 4) was visible as elongated, irregular, elliptical cisterns in the cytoplasm of thyroid follicular epithelium in camel as earlier reported in White Fulani cattle (Igbokwe and Ezeasor, 2015) and Bakerwali goat (Dar et al., 2018). The cisternae of the rough endoplasmic reticulum were highly dilated in the thyroid glands of camel. These organelles varied in number and size in camel as earlier reported in some mammals (Fujita, 1975) and Bakerwali goat (Dar et al., 2018). These profiles of the rough endoplasmic reticulum were more localized in the basal and lateral aspects of the cytoplasm than in the apical cytoplasm as reported in Bakerwali goat (Dar et al., 2018).

Fig 4: Transmission electron micrograph showing the nucleus of the follicular cell (N), mitochondria (M) and cisternae of the rough endoplasmic reticulum (RER) (X2550).



The Golgi complex (Fig 1) was well marked in thyroid sections of camel and consisted of flattened sacs, vacuoles and small vesicles as mentioned in Bakerwali goat (Dar et al., 2018). The large Golgi complex and colloid droplets were commonly found in thyroid sections of camel that might be an indication of active thyroid. The presence of Golgi complexes, RER and secretory vesicles indicated the activity of follicular cells in the synthesis and secretion of thyroglobulin towards the follicular lumen as mentioned earlier in camel (Abdel-Magied et al., 2000).

The close association of mitochondria to cisternae of RER as mentioned earlier in Bakerwali goat (Dar et al., 2018). The small round and somewhat less dense vesicles were found in the subapical region and large colloid droplets were observed in the thyroid follicle. In the present study, small, highly electron-dense granules were primary lysosome (Fig 1) as reported earlier in West African Dwarf goat (Igbokwe et al., 2015) and Bakerwali goat (Dar et al., 2018).

The secretory granules (Fig 3) containing thyroglobulin were produced in the Golgi complex and moved towards the apical plasma membrane, where they release their contents by exocytosis into the follicular lumen (Kameda et al., 1986). Electron dense granules were seen in the apical cytoplasm of thyroid follicular cells in camel as reported earlier in Bakerwali goat (Dar et al., 2018). The fusion of colloid droplets and lysosomes had indicated the functional role of lysosomes in the release of thyroid hormones from thyroglobulin in the colloid droplets.

Few parafollicular cells or “C” cells (Fig 3) were observed in thyroid sections of camel were positioned basally between two follicular cells, close to the basement membrane but away from the follicular lumen as reported earlier in Bakerwali goat (Dar et al., 2018). These parafollicular cells were mostly oval and round as in the thyroid gland of adult pig, cattle (Igbokwe, 2013), West African Dwarf goats (Igbokwe et al., 2015) and Bakerwali goat (Dar et al., 2018). Mostly one cell was observed per thyroid follicle in camel; however, the parafollicular cells were numerous in mammals such as cat, dog, rabbit, rat (Lupulescu and Petrovici, 1968) and one to two in Bakerwali goat (Dar et al., 2018). The parafollicular cells were scarce in the thyroid gland of humans (Nunez and Gershon, 1978) and deer (Pantic, 1967). The parafollicular cells played a crucial role in calcium metabolism through calcitonin as reported in White Fulani cattle (Igbokwe and Ezeasor, 2015). It may be concluded that the ultrastructure of the thyroid gland of the camel does not differ from that of other mammalian species.
The authors are thankful to the Dean, College of Veterinary and Animal Sciences, Bikaner, RAJUVAS, Bikaner, Rajasthan for providing all the necessary facilities to carry out research work. The authors are also thankful to the technical staff of Sophisticated Analytical Instrumental Facility, Department of Anatomy, All India Institute of Medical Sciences, New Delhi, for their help in the processing of samples for electron microscopy and examination.

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