- Email: [email protected]
Occurrence of the parathyroid cyst in golden hamsters
ANNALS OF ANATOMY
Occurrence of the parathyroid cyst in golden hamsters Huayue Chen, Daisuke Hayakawa, Shoichi Emma*, Yuki Ozawa, Hirotaka Taguchi, Ryuichiro Yano and Shizuko Shoumura Department of Anatomy, Gifu University School of Medicine, 40 Tsukasa-machi, Gifu 500-8705, Japan, and *College of Medical Sciences, Gifu University, 1-1 Yanagido, Gifu 501-1193, Japan
Summary. Parathyroid cyst is a rare lesion, but has clinical significance because of it's ability to mimic a thyroid mass and it's association with hyperparathyroidism. The occurrence and morphology of parathyroid cysts in golden hamsters from neonatal to senile periods were investigated using light and electron microscopy. The results demonstrate the presence of chief cell cysts in the parathyroid glands of 5-day-old hamsters. Some chief cells lining the cyst wall showed mitosis and apoptosis. The existence of chief cell cysts may represent the rapid proliferation of the parathyroid chief cells in 5-day-old hamsters. Ciliated cysts were observed in the parathyroid glands of 5-day-, 1- and 3-month-old hamsters. Three cell types were distinguished in the wall of the ciliated cyst: Ciliated, mucous and basal cells. Ciliated cysts possessed the features of the pharyngeal epithelia without endocrine cells and may arise from embryological remnants of pharyngeal pouches in the neck undergoing cystic degeneration and entrapping portions of parathyroid tissue. The frequency of parathyroid cysts decreased with age. Key words: Parathyroid gland - Chief cell cyst - Ciliated cyst - Mucous cell - Golden hamster - Ultrastructure
clinical significance because parathyroid cysts can mimic a thyroid mass and can be associated with hyperparathyroidism (Alvi et al. 1996). The ultrastructure of the mammalian parathyroid glands has been studied extensively (Isono et al. 1990; Shoumura et al. 1988, 1989, 1990; Emura et al. 1995). Most of these studies have been mainly concerned with the parathyroid hormone producing cell, the chief cell; however, only limited information is available on the ultrastructure of parathyroid cysts (Nakagami 1965; Setoguti 1977; Miyauchi et al. 1981; Pemsingh and Atwal 1983; Pemsingh et al. 1985; Kameda 1987). According to the literature, two main kinds of parathyroid cysts can be distinguished: those lined by parathyroid chief cells and those surrounded mainly by ciliated cells. The chief cell cysts were described in humans and rats (Hatakeyama et al. 1970; Miyauchi et al. 1981). Ciliated cysts were described in dog parathyroid glands under normal and experimental conditions (Nakagami 1965; Setoguti 1977; Pemsingh and Atwal 1983; Pemsingh et al. 1985). However, the existence of apoptosis and mucous cells in the wall of the parathyroid cyst has not yet been reported. In this study, we observed parathyroid cysts in golden hamsters from newborn to senile periods to obtain information on the morphology and possible functional significance of the parathyroid cysts.
Introduction A parathyroid cyst is a rare lesion with only about 200 cases having been reported up to 1996 (Alvi et al. 1996). The diagnosis of a parathyroid cyst is difficult, particularly in its differentiation from thyroid cyst, but has Correspondence to: H. Chert E-mail: [email protected]
!1
Ann Anat (2000) 182:493-498 © Urban & Fischer Verlag
http:llwww'urbanfischer'delj°urnalslannanat
Materials and methods We used 1-, and 5-day-, 1-, 3-, and 18-month-old golden hamsters in numbers of 22, 29, 30, 84, and 20 respectively totaling 185 animals. All parathyroid glands were investigated by light and electron microscopy. The parathyroid glands of all animals examined were removed under sodium pentobarbital anesthesia, immersed in a mixture of 2.5% glutaraldehyde and 2% OsO4 in Millonig's 0940-9602/00/182/6-493 $15.00/0
Table 1. Occurrence of parathyroid cysts in 185 hamsters
Results
We found 2 ciliated cysts and 1 chief cell cyst in 60 parathyroid glands of 1-month-old hamsters. The incidence of parathyroid cysts was 5.0%, the cysts being about 80-155 ~tm in diameter. The lumen contained amorphous materials and cell debris (Fig. 4A, B). The cyst walls consisted of single or pseudostratified epithelium containing ciliated cells and mucous cells (Fig. 4A, B). Ciliated cells were generally columnar in shape with the luminal surface of the cell being crowded with numerous cilia and some microvilli (Fig. 4 A, B). Tight junctions and desmosomes were found luminally (Fig. 4A). The cytoplasm contained moderate numbers of rod-shaped mitochondria and a few lysosomes. No secretory granules were seen in the cells (Fig. 4A, B). Mucous cells contained numerous spherical membrane-limited secretory granules (Fig. 4 B) which were 0.7-1.4 gm in diameter and
All hamsters examined had a single pair of parathyroid glands located on the posterolateral surface of the thyroid lobes. We found no cysts in 44 parathyroid glands of the 1-day-old hamsters. We found 7 cysts in 58 parathyroid glands of the 5-day-old hamsters. The incidence of parathyroid cysts was 12.1% with cysts being about 95-170 gm in diameter. They were generally spherical or ellipsoidal in shape (Fig. 1). Two kinds of parathyroid cysts, 2 ciliated cysts and 5 chief cell cysts, were found in 5-day-old hamsters. The cyst walls of the ciliated cysts were lined with single or pseudostratified epithelium composed of ciliated cells and mucous cells (Fig. 2). Ciliated cells predominated in the majority of the cysts. The cytoplasm contained free ribosomes and a variable number of rodshaped mitochondria. Lysosomes were sometimes obServed (Fig. 2). Tight junctions and desmomoses were present between adjacent plasma membranes near the luminal surface. Many cilia and some microvilli were present at the luminal surface of the ciliated cell. Mucous cells were markedly different in appearance from ciliated cells (Fig. 2). The cytoplasm of the mucous cell contained numerous spherical secretory granules. The secretory materials were finely reticulate and of low or moderate density (Fig. 2). Tight junctions were found between mucous and ciliated cells. The cyst wall of the chief cell cysts consisted of columnar cells. The luminal surface of the cells was covered with microvilli (Fig. 3 A, B). The plasma membranes of these cells pursued a tortuous course with complex interdigitations. The cytoplasm contained large lakes of glycogen particles, abundant free ribosomes and relatively well-developed Golgi complexes, which were very similar to those in chief cells (Fig. 3 A, B). Desmosomes were found between the cyst wall cells and parenchyma chief cells (Fig. 3 A). Among the cyst wall cells of chief cell cysts were some cells with nuclear chromatin condensation and rather well-preserved cytoplasmic organelles and plasma membranes. Apoptotic bodies made up of fragmented nuclei with condensed chromatin were also observed in some of the cyst wall cells (Fig. 3 B). Mitoses were also observed in the cyst wall cells.
Fig. 1. Light micrograph of the parathyroid gland in 5-day-old hamster. A ciliated cyst (arrow) is seen in the parathyroid gland (P). T: thyroid. Bar = 50 gm. Fig. 2. An electron micrograph of ciliated cyst in 5-day-old hamster parathyroid gland. A mucous cell (M) and ciliated cells (C) with many cilia at the luminal surface of the cyst are seen. L: cyst lumen. Bar = 2 ~tm.
Age of animals
1-day 5-day I-month 3-month 18-month
Number of animals 22 Number of cysts
0
29
30
84
20
7
3
1
0
~,
buffer at pH 7.4 for 1 hour, dehydrated through ascending concentrations of acetone and embedded in Epon 812. Semi-thin sections were stained with Azur II and examined with a light microscope. Thin sections were cut on a Porter-Blum MT-1 ultramicrotome, stained with nranyl acetate and lead salts, and examined with a Hitachi H-800 electron microscope.
494
Fig. 3. Chief cell cysts in 5-day-old hamster parathyroid gland. A: Epithelial cells contain relatively well-developed Golgi complexes (G) and large lakes of glycogen particles (arrows). Desmosomes (arrowheads) between the cyst wall cell and the parenchyma chief cell (CC) are observed. L: cyst lumen. B: Apoptotic bodies, (arrows) with condensed chromatin are observed in the epithelial cells of the cyst. The cytoplasmic organelles are well preserved. Microvilli (arrowheads) are seen at the apex of the cell. L: cyst lumen. Bar = 2 pm. of low or moderate density. Tight junctions were found to connect the mucous cell and ciliated cells (Fig. 4 B). We found only 1 ciliated cyst in 168 parathyroid glands of 3-month-old hamsters resulting in an incidence of 0.6%. The cyst was oval in shape with a diameter of 86 p m x i 3 2 gm. The lumen was filled, for the most part, with cilia and cellular debris. The cyst wall consisted of pseudostratified columnar cells. Three cell types were distinguished: ciliated, mucous and basal cells (Fig. 5 A). The plasma membrane of the ciliated cells pursued a tortuous course with occasional interdigitations. The adjacent ciliated cells shared tight junctions and desmosomes near the luminal surface (Fig. 5B). The cytoplasm contained microfilaments, occurring singly or in small bundles. Moderate numbers of rod-shaped mitochondria with numerous dense granules about 30-55 nm in diameter were present (Fig. 5 B). There were no secretory granules in the cytoplasm. Mucous cells were cylindrical in shape and arranged separately in the cyst wall. Golgi complexes were well developed. The cytoplasm of the supranuclear part was filled with secretory granules (Fig. 5 A, B) which
sometimes seemed to be expelled into the lumen. The luminal surface was often crowded with microvilli. Basal cells were ovoid or slightly flattened and located close to the basal lamina. The nucleus was round or irregular in shape. Golgi complexes were generally small and the granular endoplasmic reticulum consisted of isolated randomly distributed cisternae. Numerous free ribosomes and some mitochondria were also present (Fig. 5 A). The basal cell and ciliated cell were attached by desmosomes to the chief cells, Serial sections indicated the absence of other kinds of cells such as endocrine cells in the ciliated cyst walls. We found no parathyroid cysts in 18-month-old hamsters.
Discussion According to the immunohistochemical observation, the parathyroid glands of the golden hamsters are considered derivatives of the third pharyngeal pouch, as the para-
495
Fig. 4. Ciliated cysts in 1-month-old hamster parathyroid gland. A: Ciliated cells (C) with numerous cilia and microvilli are seen. The adjacent ciliated cells share tight junctions (arrowheads) and desmosomes (arrows). L: cyst lumen. B: A mucous cell (M) contains large secretory granules (arrows). Tight junctions (arrowheads) are found between the mucous cell and ciliated cells (C). Bar = 2 gin. Fig. 5. Ciliated cysts in 3-month-old hamster parathyroid gland. A: Ciliated cells (C), mucous cell (M) and basal cell (B) are seen in the cyst wall. CC: chief cells. B: Numerous dense granules (arrowheads) are found in the mitochondria of the ciliated cells (C). The adjacent ciliated cells share tight junctions (arrows) near the luminal surface. M: mucous cells; L: cyst lumen. Bar = 2 gm.
496
thyroid III in dogs and humans (Taniguchi et al. 1990). It was reported that human parathyroid chief cells could be grouped into acinar units (Munger and Roth 1963) with such units being characterized by microvilli projecting from the apical surface of the cell into the lumen and by a zonula occludens between adjacent plasma membranes at the luminal surface. Parathyroid chief cells maintain very low levels of proliferative activity throughout their entire lifespan (Parfitt 1994), which may be expected to be matched by similarly low rates of cell death, although apoptosis has not yet been demonstrated in normal parathyroid tissue. The present study showed that chief cell cysts were only observed in 5-day-old hamsters. The same chief cell cysts were reported in human and rat parathyroid glands (Hatakeyama et al. 1970; Miyauchi et al. 1981). The present study also demonstrated that there were some mitoses and apoptoses in the walls of chief cell cysts indicating the rapid proliferation of the chief cells at this age. The presence of ciliated cysts in the parathyroid glands of the dog at the ultrastructural level was previously described (Nakagami 1965; Setoguti 1977; Pemsingh and Atwal 1983: Pemsingh et al. 1985). In the present study, the ciliated cysts were found in the parathyroid glands of 5day-, 1- and 3-month-old hamsters. We found no parathyroid cysts in 18-month-old hamsters. It is generally accepted that the parathyroid cyst wall consists of 2 cell types, ciliated and endocrine cells. Endocrine cells usually are A P U D cells, such as parathyroid chief cells (Hatakeyama et al. 1970; Miyauchi et al. 1981) and thyroid parafollicular cells (Kameda 1971; Pemsingh and Atwal 1983; Pemsingh et al. 1985). As far as we know, there were no reports on the existence of apoptosis and mucous cells in parathyroid cysts; however, the presence of some mucous cells in the ultimobranchial bodies (Zelander and Kirkeby 1977; Chan 1978; Yoshida-Terasawa et al. 1998) has been reported. The present study confirmed the existence of the mucous cell in the ciliated cyst. The content of the secretory granules in the mucous cell needs to be clarified and the function of the mucous cell is not yet clearly established. The presence of cellular debris in the lumen has been interpreted as evidence of holocrine secretion, presumably by the mucous cells. The ultrastructure of the citiated cells studied here is essentially similar to that of dogs as reported earlier (Nakagami 1965; Setoguti 1977; Pemsingh and Atwal 1983; Pemsingh et al. 1985). The ciliated cells are known to contain numerous cilia and some microvilli. In this study, we found that there were many dense granules in the mitochondria of the ciliated cells. It was reported that increased numbers of dense granules in the mitochondria were frequently encountered in tissues that transport large quantities of water and ions (Barnard and Afzelius 1972). The possibility that the ciliated cells are involved in some transport function can not be excluded. Basal cells have been reported in the chicken ultimobranchial follicles (Chan 1978). These cells perhaps represent undifferentiated stem cells for the replacement of desqua-
mated cells. However, it is not known whether the basal cells are capable of differentiating into ciliated or mucous cells as in the respiratory tract. Miyauchi et al. (1981) suggested 4 explanations for the origin of the parathyroid cyst: 1. embryological remnants of the third or fourth pharyngeal pouch; 2. coalescence of microcysts; 3. simple retention of parathyroid secretion; and 4. cystic degeneration in pre-existing adenomas. Serial sections of the ciliated cyst in the present study demonstrated that simple or pseudostratified columnar cells lined the cyst wall, and that there were no tumorous loci. The cysts were surrounded by parathyroid chief cells and the cyst epithelia were attached by desmosomes to the parathyroid chief cells. However, the cysts did not appear to be derived from the parathyroid chief cells as there were no chief cells in the cyst wall. For this reason we conclude that the origin of the ciliated cyst was probably embryological remnants.
References Alvi A, Myssiorek D, Wasserman P (1996) Parathyroid cyst: current diagnostic and management principles. Head Neck 18: 370-373 Barnard T, Afzelius BA (1972) The matrix granules of mitochondria. A review. SubCell Biochem 1:375-393 Chan AS (1978) Ultrastructure of the ultimobranchial follicles of the laying chicken. Cell Tissue Res 195:309-316 Emura S, Hayakawa D, Yamahira T, Terasawa K, Tamada A, Arakawa M, Isono H, Shoumura S (1995) Effects of progesterone on the ultrastructure of the golden hamster parathyroid gland. Histol Histopath 10:907-911 Hatakeyama S, Tuchweber B, Blascheck JA, Garg BD, Kovacs K (1970) Parathyroid cyst formation induced by dihydrotachysterol and calcium acetate. An electron microscopic study. Endocrinol Jpn 17:355-363 Isono H, Shoumura S, Emura S (1990) Ultrastructure of the parathyroid gland. Histol Histopath 5:95-112 Kameda Y (1971) The occurrence of a special parafollicular cell complex in and beside the dog thyroid gland. Arch Histol Jap 33:115-132 Kameda Y (1987) Immunohistochemical demonstration of keratins in the cysts of thyroid glands, parathyroid glands, and Ccell complexes of the dog. Am J Anat 180:87-99 Miyauchi A, Kakudo K, Fujimoto T, Onishi T, Takai S (1981) Parathyroid cyst: analysis of the cyst fluid and ultrastructural observations. Arch Path Lab Med 105:497-499 Munger BL, Roth SI (1963) The cytology of the normal parathyroid glands of man and virginia deer. J Cell Biol 16:379400 Nakagami K (1965) Comparative electron microscopic studies of the parathyroid glands. I. Fine structure of monkey and dog parathyroid glands. Arch Histol Jpn 25:435466 Parfitt AM (1994) Parathyroid growth: normal and abnormal. In: Bilezikian JP (Ed) The parathyroids: basic and clinical concepts. Raven Press, New York, pp 373-405 Pemsingh RS, Atwal OS (1983) Occurrence of APUD-type cells in the ciliated cyst of the parathyroid gland of ozone-exposed dogs. Acta Anat 116:97-105 Pemsingh RS, Atwal OS, MacPherson RB (1985) Atypical cilia in
497
ciliated cysts of the parathyroid glands of dogs exposed to ozone. Exp Path 28:105-110 SetogutiT (1977) Electron microscopic studies of the parathyroid glands of senile dogs. Am J Anat 148:65-84 Shoumura S, Emura S, Ishizaki N, Iwasaki Y, Yamahira T, Ito M, Isono H (1988) Effects of hypergravity environment on the ultrastructure of the golden hamster parathyroid gland. Acta Anat 133:79-85 Shoumura S, Emura S, Ishizaki N, Yamahira T, Chen H, Ito M, Isono H (1989) Effects of hypergravity environment on the parathyroid gland of the propranolol-treated golden hamster. Acta Anat 135:347-353 Shoumura S, Emura S, Ishizaki N, Yamahira T, Chen H, KambaraK, ArakawaM, IsonoH (1990) Electron microscopic study of the parathyroid gland of the calcium-treated hamster
subjected to hypergravity environment. Histol Histopath 5: 17-24 Taniguchi K, Shutoh Y, Mikami S (1990) Immunohistochemical studies on the development of endocrine cells in the thyroid and parathyroid glands in the golden hamster. Jpn J Vet Sci 52:19-27 Yoshida-Terasawa K, Hayakawa D, Chen H, Emura S, Tamada A, Okumura T, Shoumm'a S (1998) Fine structure of the parathyroid and ultimobranchial glands of the snake, Elaphe quadrivirgata. Okajimas Folia Anat Jpn 75:141-154 Zelander T, Kirkeby S (1977) Fine structure of the ultimobranchial cysts in the thyroid of the adult guinea pig. Cell Tissue Res 183:343-351 Accepted May 2, 2000
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Occurrence of the parathyroid cyst in golden hamsters Huayue Chen, Daisuke Hayakawa, Shoichi Emma*, Yuki Ozawa, Hirotaka Taguchi, Ryuichiro Yano and Shizuko Shoumura Department of Anatomy, Gifu University School of Medicine, 40 Tsukasa-machi, Gifu 500-8705, Japan, and *College of Medical Sciences, Gifu University, 1-1 Yanagido, Gifu 501-1193, Japan
Summary. Parathyroid cyst is a rare lesion, but has clinical significance because of it's ability to mimic a thyroid mass and it's association with hyperparathyroidism. The occurrence and morphology of parathyroid cysts in golden hamsters from neonatal to senile periods were investigated using light and electron microscopy. The results demonstrate the presence of chief cell cysts in the parathyroid glands of 5-day-old hamsters. Some chief cells lining the cyst wall showed mitosis and apoptosis. The existence of chief cell cysts may represent the rapid proliferation of the parathyroid chief cells in 5-day-old hamsters. Ciliated cysts were observed in the parathyroid glands of 5-day-, 1- and 3-month-old hamsters. Three cell types were distinguished in the wall of the ciliated cyst: Ciliated, mucous and basal cells. Ciliated cysts possessed the features of the pharyngeal epithelia without endocrine cells and may arise from embryological remnants of pharyngeal pouches in the neck undergoing cystic degeneration and entrapping portions of parathyroid tissue. The frequency of parathyroid cysts decreased with age. Key words: Parathyroid gland - Chief cell cyst - Ciliated cyst - Mucous cell - Golden hamster - Ultrastructure
clinical significance because parathyroid cysts can mimic a thyroid mass and can be associated with hyperparathyroidism (Alvi et al. 1996). The ultrastructure of the mammalian parathyroid glands has been studied extensively (Isono et al. 1990; Shoumura et al. 1988, 1989, 1990; Emura et al. 1995). Most of these studies have been mainly concerned with the parathyroid hormone producing cell, the chief cell; however, only limited information is available on the ultrastructure of parathyroid cysts (Nakagami 1965; Setoguti 1977; Miyauchi et al. 1981; Pemsingh and Atwal 1983; Pemsingh et al. 1985; Kameda 1987). According to the literature, two main kinds of parathyroid cysts can be distinguished: those lined by parathyroid chief cells and those surrounded mainly by ciliated cells. The chief cell cysts were described in humans and rats (Hatakeyama et al. 1970; Miyauchi et al. 1981). Ciliated cysts were described in dog parathyroid glands under normal and experimental conditions (Nakagami 1965; Setoguti 1977; Pemsingh and Atwal 1983; Pemsingh et al. 1985). However, the existence of apoptosis and mucous cells in the wall of the parathyroid cyst has not yet been reported. In this study, we observed parathyroid cysts in golden hamsters from newborn to senile periods to obtain information on the morphology and possible functional significance of the parathyroid cysts.
Introduction A parathyroid cyst is a rare lesion with only about 200 cases having been reported up to 1996 (Alvi et al. 1996). The diagnosis of a parathyroid cyst is difficult, particularly in its differentiation from thyroid cyst, but has Correspondence to: H. Chert E-mail: [email protected]
!1
Ann Anat (2000) 182:493-498 © Urban & Fischer Verlag
http:llwww'urbanfischer'delj°urnalslannanat
Materials and methods We used 1-, and 5-day-, 1-, 3-, and 18-month-old golden hamsters in numbers of 22, 29, 30, 84, and 20 respectively totaling 185 animals. All parathyroid glands were investigated by light and electron microscopy. The parathyroid glands of all animals examined were removed under sodium pentobarbital anesthesia, immersed in a mixture of 2.5% glutaraldehyde and 2% OsO4 in Millonig's 0940-9602/00/182/6-493 $15.00/0
Table 1. Occurrence of parathyroid cysts in 185 hamsters
Results
We found 2 ciliated cysts and 1 chief cell cyst in 60 parathyroid glands of 1-month-old hamsters. The incidence of parathyroid cysts was 5.0%, the cysts being about 80-155 ~tm in diameter. The lumen contained amorphous materials and cell debris (Fig. 4A, B). The cyst walls consisted of single or pseudostratified epithelium containing ciliated cells and mucous cells (Fig. 4A, B). Ciliated cells were generally columnar in shape with the luminal surface of the cell being crowded with numerous cilia and some microvilli (Fig. 4 A, B). Tight junctions and desmosomes were found luminally (Fig. 4A). The cytoplasm contained moderate numbers of rod-shaped mitochondria and a few lysosomes. No secretory granules were seen in the cells (Fig. 4A, B). Mucous cells contained numerous spherical membrane-limited secretory granules (Fig. 4 B) which were 0.7-1.4 gm in diameter and
All hamsters examined had a single pair of parathyroid glands located on the posterolateral surface of the thyroid lobes. We found no cysts in 44 parathyroid glands of the 1-day-old hamsters. We found 7 cysts in 58 parathyroid glands of the 5-day-old hamsters. The incidence of parathyroid cysts was 12.1% with cysts being about 95-170 gm in diameter. They were generally spherical or ellipsoidal in shape (Fig. 1). Two kinds of parathyroid cysts, 2 ciliated cysts and 5 chief cell cysts, were found in 5-day-old hamsters. The cyst walls of the ciliated cysts were lined with single or pseudostratified epithelium composed of ciliated cells and mucous cells (Fig. 2). Ciliated cells predominated in the majority of the cysts. The cytoplasm contained free ribosomes and a variable number of rodshaped mitochondria. Lysosomes were sometimes obServed (Fig. 2). Tight junctions and desmomoses were present between adjacent plasma membranes near the luminal surface. Many cilia and some microvilli were present at the luminal surface of the ciliated cell. Mucous cells were markedly different in appearance from ciliated cells (Fig. 2). The cytoplasm of the mucous cell contained numerous spherical secretory granules. The secretory materials were finely reticulate and of low or moderate density (Fig. 2). Tight junctions were found between mucous and ciliated cells. The cyst wall of the chief cell cysts consisted of columnar cells. The luminal surface of the cells was covered with microvilli (Fig. 3 A, B). The plasma membranes of these cells pursued a tortuous course with complex interdigitations. The cytoplasm contained large lakes of glycogen particles, abundant free ribosomes and relatively well-developed Golgi complexes, which were very similar to those in chief cells (Fig. 3 A, B). Desmosomes were found between the cyst wall cells and parenchyma chief cells (Fig. 3 A). Among the cyst wall cells of chief cell cysts were some cells with nuclear chromatin condensation and rather well-preserved cytoplasmic organelles and plasma membranes. Apoptotic bodies made up of fragmented nuclei with condensed chromatin were also observed in some of the cyst wall cells (Fig. 3 B). Mitoses were also observed in the cyst wall cells.
Fig. 1. Light micrograph of the parathyroid gland in 5-day-old hamster. A ciliated cyst (arrow) is seen in the parathyroid gland (P). T: thyroid. Bar = 50 gm. Fig. 2. An electron micrograph of ciliated cyst in 5-day-old hamster parathyroid gland. A mucous cell (M) and ciliated cells (C) with many cilia at the luminal surface of the cyst are seen. L: cyst lumen. Bar = 2 ~tm.
Age of animals
1-day 5-day I-month 3-month 18-month
Number of animals 22 Number of cysts
0
29
30
84
20
7
3
1
0
~,
buffer at pH 7.4 for 1 hour, dehydrated through ascending concentrations of acetone and embedded in Epon 812. Semi-thin sections were stained with Azur II and examined with a light microscope. Thin sections were cut on a Porter-Blum MT-1 ultramicrotome, stained with nranyl acetate and lead salts, and examined with a Hitachi H-800 electron microscope.
494
Fig. 3. Chief cell cysts in 5-day-old hamster parathyroid gland. A: Epithelial cells contain relatively well-developed Golgi complexes (G) and large lakes of glycogen particles (arrows). Desmosomes (arrowheads) between the cyst wall cell and the parenchyma chief cell (CC) are observed. L: cyst lumen. B: Apoptotic bodies, (arrows) with condensed chromatin are observed in the epithelial cells of the cyst. The cytoplasmic organelles are well preserved. Microvilli (arrowheads) are seen at the apex of the cell. L: cyst lumen. Bar = 2 pm. of low or moderate density. Tight junctions were found to connect the mucous cell and ciliated cells (Fig. 4 B). We found only 1 ciliated cyst in 168 parathyroid glands of 3-month-old hamsters resulting in an incidence of 0.6%. The cyst was oval in shape with a diameter of 86 p m x i 3 2 gm. The lumen was filled, for the most part, with cilia and cellular debris. The cyst wall consisted of pseudostratified columnar cells. Three cell types were distinguished: ciliated, mucous and basal cells (Fig. 5 A). The plasma membrane of the ciliated cells pursued a tortuous course with occasional interdigitations. The adjacent ciliated cells shared tight junctions and desmosomes near the luminal surface (Fig. 5B). The cytoplasm contained microfilaments, occurring singly or in small bundles. Moderate numbers of rod-shaped mitochondria with numerous dense granules about 30-55 nm in diameter were present (Fig. 5 B). There were no secretory granules in the cytoplasm. Mucous cells were cylindrical in shape and arranged separately in the cyst wall. Golgi complexes were well developed. The cytoplasm of the supranuclear part was filled with secretory granules (Fig. 5 A, B) which
sometimes seemed to be expelled into the lumen. The luminal surface was often crowded with microvilli. Basal cells were ovoid or slightly flattened and located close to the basal lamina. The nucleus was round or irregular in shape. Golgi complexes were generally small and the granular endoplasmic reticulum consisted of isolated randomly distributed cisternae. Numerous free ribosomes and some mitochondria were also present (Fig. 5 A). The basal cell and ciliated cell were attached by desmosomes to the chief cells, Serial sections indicated the absence of other kinds of cells such as endocrine cells in the ciliated cyst walls. We found no parathyroid cysts in 18-month-old hamsters.
Discussion According to the immunohistochemical observation, the parathyroid glands of the golden hamsters are considered derivatives of the third pharyngeal pouch, as the para-
495
Fig. 4. Ciliated cysts in 1-month-old hamster parathyroid gland. A: Ciliated cells (C) with numerous cilia and microvilli are seen. The adjacent ciliated cells share tight junctions (arrowheads) and desmosomes (arrows). L: cyst lumen. B: A mucous cell (M) contains large secretory granules (arrows). Tight junctions (arrowheads) are found between the mucous cell and ciliated cells (C). Bar = 2 gin. Fig. 5. Ciliated cysts in 3-month-old hamster parathyroid gland. A: Ciliated cells (C), mucous cell (M) and basal cell (B) are seen in the cyst wall. CC: chief cells. B: Numerous dense granules (arrowheads) are found in the mitochondria of the ciliated cells (C). The adjacent ciliated cells share tight junctions (arrows) near the luminal surface. M: mucous cells; L: cyst lumen. Bar = 2 gm.
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thyroid III in dogs and humans (Taniguchi et al. 1990). It was reported that human parathyroid chief cells could be grouped into acinar units (Munger and Roth 1963) with such units being characterized by microvilli projecting from the apical surface of the cell into the lumen and by a zonula occludens between adjacent plasma membranes at the luminal surface. Parathyroid chief cells maintain very low levels of proliferative activity throughout their entire lifespan (Parfitt 1994), which may be expected to be matched by similarly low rates of cell death, although apoptosis has not yet been demonstrated in normal parathyroid tissue. The present study showed that chief cell cysts were only observed in 5-day-old hamsters. The same chief cell cysts were reported in human and rat parathyroid glands (Hatakeyama et al. 1970; Miyauchi et al. 1981). The present study also demonstrated that there were some mitoses and apoptoses in the walls of chief cell cysts indicating the rapid proliferation of the chief cells at this age. The presence of ciliated cysts in the parathyroid glands of the dog at the ultrastructural level was previously described (Nakagami 1965; Setoguti 1977; Pemsingh and Atwal 1983: Pemsingh et al. 1985). In the present study, the ciliated cysts were found in the parathyroid glands of 5day-, 1- and 3-month-old hamsters. We found no parathyroid cysts in 18-month-old hamsters. It is generally accepted that the parathyroid cyst wall consists of 2 cell types, ciliated and endocrine cells. Endocrine cells usually are A P U D cells, such as parathyroid chief cells (Hatakeyama et al. 1970; Miyauchi et al. 1981) and thyroid parafollicular cells (Kameda 1971; Pemsingh and Atwal 1983; Pemsingh et al. 1985). As far as we know, there were no reports on the existence of apoptosis and mucous cells in parathyroid cysts; however, the presence of some mucous cells in the ultimobranchial bodies (Zelander and Kirkeby 1977; Chan 1978; Yoshida-Terasawa et al. 1998) has been reported. The present study confirmed the existence of the mucous cell in the ciliated cyst. The content of the secretory granules in the mucous cell needs to be clarified and the function of the mucous cell is not yet clearly established. The presence of cellular debris in the lumen has been interpreted as evidence of holocrine secretion, presumably by the mucous cells. The ultrastructure of the citiated cells studied here is essentially similar to that of dogs as reported earlier (Nakagami 1965; Setoguti 1977; Pemsingh and Atwal 1983; Pemsingh et al. 1985). The ciliated cells are known to contain numerous cilia and some microvilli. In this study, we found that there were many dense granules in the mitochondria of the ciliated cells. It was reported that increased numbers of dense granules in the mitochondria were frequently encountered in tissues that transport large quantities of water and ions (Barnard and Afzelius 1972). The possibility that the ciliated cells are involved in some transport function can not be excluded. Basal cells have been reported in the chicken ultimobranchial follicles (Chan 1978). These cells perhaps represent undifferentiated stem cells for the replacement of desqua-
mated cells. However, it is not known whether the basal cells are capable of differentiating into ciliated or mucous cells as in the respiratory tract. Miyauchi et al. (1981) suggested 4 explanations for the origin of the parathyroid cyst: 1. embryological remnants of the third or fourth pharyngeal pouch; 2. coalescence of microcysts; 3. simple retention of parathyroid secretion; and 4. cystic degeneration in pre-existing adenomas. Serial sections of the ciliated cyst in the present study demonstrated that simple or pseudostratified columnar cells lined the cyst wall, and that there were no tumorous loci. The cysts were surrounded by parathyroid chief cells and the cyst epithelia were attached by desmosomes to the parathyroid chief cells. However, the cysts did not appear to be derived from the parathyroid chief cells as there were no chief cells in the cyst wall. For this reason we conclude that the origin of the ciliated cyst was probably embryological remnants.
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