Immunocytochemical studies on differentiation of the thyroid gland in rabbit fetuses and chick embryos

Summary The morphogenesis of the thyroid gland in rabbit fetuses and chick embryos was investigated using the PAS stain and an immunoperoxidase method with anti-19S-thyroglobulin antiserum. In rabbit fetuses, the reaction for precursor components was firstly detected in the apical portions of follicular cells, arranged in clusters but not yet forming follicles, at 16 days of gestation. Although the first primordial follicles storing colloid droplets were observed on day 18, a drastic increase of follicle formation, the true onset of thyroid function, did not occur until day 22. The colloid in primordial follicles revealed very strong immunoreactivity for 19S-thyroglobulin. The follicles gradually increased in size with age. At 25 days of gestation the cytoplasm of follicular cells was stained densely by slightly diluted 19S-thyroglobulin antiserum, whereas the colloid was stained with highly diluted antiserum; these immunoreactions of follicular cells and colloid were comparable to those of postnatal animals. In chick embryos, significant numbers of primordial follicles were observed throughout the whole thyroid parenchyma at 9 days of incubation. On day 12, the follicles stored more PAS-positive and immunoreactive colloid. At 14 days of incubation follicles with enlarged follicular lumina, having an immunoreactivity similar to mature rollicles, became increasingly common.     

Peculiarities of the ovary structure in the rat offspring developing under conditions of the removed thyroid gland of female rat with the thyroxine replacement therapy and external radiation exposure in utero

The influence of a single external gamma-radiation at a dose of 1.0 Gy (dose rate 9.08 x 10(-4) Gy/sec) on the 15th day of gestation in case of the removed complex of thyroid and parathyroid glands (thyroidparathyroidectomy) on the first day of gestation, as well as introduction of thyroxin and CaC12 on the structure of offspring ovary in postnatal ontogenesis (30-day old animals) was studied. It has been shown that thyroidparathyroidectomy of a female mother rat with thyroxine replacement therapy and irradiation, as well as the combination of these factors disturb the structure of ovarian tissues of the offspring. A single external irradiation on the 15th day of embryogenesis causes death of a considerable part of primordial follicles in the offspring ovary and growth of follicular layers in the secondary follicles. Thyroidparathyroidectomy of female rat on the first day of gestation with thyroxine replacement therapy causes delay in the development of follicles in the ovary at the early stages of maturation of 30-day old animals. The radiosensitivity of the ovarian tissues of the offspring that has been developed under the combined effect of the factors studied increases and results in an almost full loss of pool cells in the ovary of infant rats.     

Immunohistochemical study of the C-cell complex of dog thyroid glands with reference to the reactions of calcitonin,C-thyroglobulin and 19S thyroglobulin

Summary Continued from the previous study in fetal animals (Kameda et al. 1980), the development and maturation of C-cell complexes in postnatal dogs from newborn to adult were investigated by use of an immunoperoxidase method using antisera to calcitonin, C-thyroglobulin (C-Tg) and 19S thyroglobulin, respectively. The younger the animals were, the more numerous were undifferentiated cells and high columnar epithelial cells in the complexes. With increasing age, the constituent elements of the complexes progressively differentiated. In one type of complex there are a large number of C-cells in various developmental stages, as well as undifferentiated cells and cysts. C-cell complexes composed mostly of mature C-cells were regarded as the more highly differentiated structures of this type. A second type contains follicular cells in various stages of differentiation in addition to undifferentiated cells and C-cells, i.e., 19S-positive cell masses not yet organized into follicles, primordial follicles with small lacunae and comparatively larger follicles. The follicular cells in the complexes were similar with respect to immunoreaction and folliculogenesis to the cells of fetal thyroids, but they developed very slowly. In conclusion, the present study indicates that follicular thyroid cells can differentiate within C-cell complexes, i.e., they develop from cells of ultimobranchial body origin.     

Structural–functional condition of the thyroid gland of red deer at different stages of postnatal ontogenesis

The histological structure and morphometric and some histochemical indices of thyroid gland of maral as a subspecies of red deer at the postnatal stage of ontogenesis were studied. It was established that the gland was structurally formed by the time of the birth. C-cells are detected at 6 months of age. With age, the ratio of follicles of different sizes changed: smaller forms predominate in newborns and those 6 months old, medium and large predominate in adults and in old deer. Histological, morphometric, and histochemical data indicate to activation of the thyroid gland in the period of intensive growth for up to 6 months and a gradual decrease in activity over the next years of life. During aging, along with an increase in stromal elements, large follicles with colloid are stretched and resorption processes in the follicles are reduced.     

Features of the development of the pituitary-thyroid system of the Wrangel Island hoofed lemming Dicrostonyx torquatus at stages of growth and peak population

By means of morphometric techniques, peculiarities in formation of the hypophyseal-thyroid system during prenatal and early postnatal periods have been studied in lemmings (Dicrostonyx torquatus) from the Wrangel island at growth stages and at the peak of the population quantity. Folliculoformation rate, time when the organ reaches the definitive structure, periods for establishing connection with the regulating center--the anterior hypophyseal lobe, correlation of differentiation rates of histo- and ultrastructures of the organ distinctly react to changes in the density population of the animals. Periods of initiation of folliculoformation are early and comparable at both stages of the population cycles. However, further at the peak of the population quantity, an essential retardation in the development of both histo- and ultrastructures of the thyroid cells is observed; formation of the histostructure significantly overtakes differentiation of the ultrastructures composing its cellular elements. The follicular structure begins to form only in newborn animals, the folliculogenesis completes on the 1st-6th days of the postnatal period. At the stage of growth of the population quantity, the folliculogenesis lasts 2 days (the 15th-17th days of the prenatal development), the organ's structure becomes definitive on the 17th day, at the same period connections are established with the anterior hypophyseal lobe. The role of the thyroid hormones in formation of reprodactive and adaptive potencies of the organism at various stages of the population cycle is discussed.     

Difference between the thyroid gland of normal and hypomyelinated jimpy mice--a light microscopic study

A light microscopic quantitative analysis was performed on normal and jimpy male mice for studying the difference between the structures of the thyroid glands of the two animals. The results of this analysis showed that the thyroid gland of the normal mice consisted of numerous homogenous round follicles with cuboidal follicular cells, separated by thin interlobular and interfollicular connective tissue and a few adipose tissue. The thyroid gland of jimpy mice consisted of a few, small follicles surrounded by columnar follicular cells and intraepithelial capillaries, separated by thick connective tissue and abundant adipose tissue. The number of thyroid follicles are significantly less in the jimpy mice than in the normal mice. Another striking difference is that almost every follicular cell surrounding the follicular lumen of jimpy mice is accompanied by an intraepithelial capillary. In addition, the ratio of the number of intraepithelial capillaries to the number of the thyroid follicular cells are significantly higher in the jimpy mice than in the normal mice. The S-follicles or ultimobranchial cysts of the thyroid gland are well developed in the jimpy mice. The parafollicular cells are normal in appearance. Morphological evidence suggested that the thyroid follicular cells of the jimpy mice are very active in the transport, synthesis and release of thyroglobulin, and secretion of thyroid hormones. But owing to the significantly decreased number of thyroid follicles, the inadequate secretion of the thyroid hormones result in the hypothyroidism and the hypomyelination of the jimpy mice.     

Morphological changes in the human thyroid gland cultivated in continual flow system

In the present pilot study, the human thyroid gland tissue was cultivated under continuous culture conditions in the culture chambers of the ACUSYST-S system to determine morphological changes as well as the secretion of thyreoglobulin (Tgl) and thyroid hormones. After 24 hours of cultivation the follicular structure of the tissue was preserved in peripheral parts only, and there were regressive changes in the epithelium center. After 72 hours the regressive changes appeared in isolated follicles only; the size of the follicles increased, the height of the follicular epithelium decreased and there were macrophages present with phagocytized cell debris. After 144 hours disintegration of epithelia took place in the centre, while at the periphery the original follicles survived and very tiny new follicles formed, consisting of only 6 to 8 cells each and surrounding in section the homogeneous colloid. The parenchyma picture suggests a possibility of functional regeneration as an expression of adaptation to the conditions newly arisen during cultivation in a culture chamber. There was no significant influencing of the thyroid hormone secretion during cultivation. On the other hand, the Tgl secretion decreased throughout cultivation.     

APPEARANCE AND FUNCTION OF ENDOGENOUS PEROXIDASE IN FETAL RAT THYROID

Iodination within the thyroid follicle is intimately associated with a thyroid peroxidase. In order to locate the in vivo site of iodination, the initial cytochemical appearance of this enzyme has been determined in fetal rat thyroid and its presence correlated with the onset of iodinated thyroglobulin synthesis. Peroxidase first appears in follicular cells during the 18th day of gestation. It is seen first in the perinuclear cisternae, the cisternae of the endoplasmic reticulum, and within the inner few Golgi lamellae. These organelles presumably represent sites of peroxidase synthesis. During the 19th and 20th days of gestation, there is a tremendous increase in peroxidase activity. In addition to the stained sites described, there are now many peroxidase-positive apical vesicles in the follicular cells. Newly forming follicles stain most conspicuously for peroxidase, the reaction product being heavily concentrated at the external surfaces of apical microvilli and in the adjacent colloid. Iodinated thyroglobulin becomes biochemically detectable in thyroids during the 19th day of gestation and increases greatly during the 20th day. The parallel rise in peroxidase staining that just precedes, and overlaps, the rise in iodinated thyroglobulin, suggests that apical vesicles and the apical cell membrane are the major sites of iodination within the thyroid follicle.     

Histometry of normal thyroid glands in neonatal and adult rats

The present histometric study is on thyroid glands of Wistar rats ranging in age from 0 to 120 days. The mean volume of one lobe of the thyroid in 4-month-old animals was some 22-, 10-, 5-, and 3-fold greater, respectively, than the volumes in the newborn, 5-, 10-, and 30-day-old rats. At 4 months of age the mean length of the lobe was 3 times greater than at birth. The volumetric fractions (Vv) of the different histological components (follicular cells, C-cells, colloid, and interstitial tissue) changed considerably in the course of development. The Vv of follicular cells diminished from 61.4% at birth to 37.2% at 4 months. C-cells increased from 2.9% in the newborn to 4% at 15 days, with no further significant change at 4 months. Colloid and stroma together represented 35.7% at birth, increasing to 58.5% at 120 days. In the course of the first 4 months of life, the absolute volumes occupied by follicular cells, C-cells, colloid, and stroma increased 13.25, 30.75, 38.6, and 33.7 times, respectively; these changes reflect the variations that occur in the volume of the gland and the Vv throughout postnatal development.     

Origin of cholinesterase-containing follicle cells and parafollicular cells of the developing thyroid gland in the rat

Summary The location of cholinesterase-containing cells in the thyroid gland and its precursors (median thyroid primordium and ultimobranchial bodies) has been investigated light-microscopically in rat embryos from the 13 to the 20th day of gestation.From the 13th to the 16th day of gestation the median thyroid primordium and the ultimobranchial bodies are distinct from each other. Cholinesterase-containing cells are found in both. On the 17th–18th day of gestation the reacting ultimobranchial cells spread into the median thyroid primordium where they take up a parafollicular position. At the 19th–20th day of gestation the distribution of cholinesterase-containing cells is as in the adult rat. The results seem to show that cholinesterase-containing follicular cells derive from the median thyroid primordium and cholinesterase-containing parafollicular cells from the ultimobranchial body.     

Structural and ultrastructural differentiation of the thyroid gland during embryogenesis in the grass snake Natrix natrix L. (Lepidosauria, Serpentes)

The differentiation of the thyroid primordium of reptilian species is poorly understood. The present study reports on structural and ultrastructural studies of the developing thyroid gland in embryos of the grass snake Natrix natrix L. At the time of oviposition, the thyroid primordium occupied its final position in the embryos. Throughout developmental stages I-IV, the undifferentiated thyroid primordium contained cellular cords, and the plasma membranes of adjacent cells formed junctional complexes. Subsequently, the first follicular lumens started to form. The follicular lumens were of intracellular origin, as in other vertebrate species, but the mechanism of their formation is as yet unclear. At developmental stages V-VI, the thyroid anlage was composed of small follicles with lumens and cellular cords. Cells of the thyroid primordium divided, and follicles were filled with a granular substance. At developmental stage VI, the cells surrounding the follicular lumen were polarized, the apical cytoplasm contained dark granules and the Golgi complex and the rough endoplasmic reticulum (RER) developed gradually. Resorption of the colloid began at developmental stage VIII. At the end of this stage, the embryonic thyroid gland was surrounded by a definitive capsule. During developmental stages IX-X, the follicular cells contained granules and vesicles of different sizes and electron densities and a well-developed Golgi apparatus and RER. At developmental stage XI, most follicles were outlined by squamous epithelial cells and presented wide lumens filled with a light colloid. The Golgi complex and RER showed changes in their morphology indicating a decrease in the activity of the thyroid gland. At developmental stage XII, the activity of the embryonic thyroid gradually increased, and at the time of hatching, it exhibited the features of a fully active gland.     

Alterations within the rat thyroid gland during vitamin A deficiency

Thyroid glands from female rats kept vitamin A deficient for one, two, and three months were examined by electron microscopy. After one month on the diet, no consistent alterations were noted. After two months, the colloid in some follicles displayed a peripheral zone of decreased density. In addition, ultimobranchial follicles within the gland had become keratinized. After two to three months on the diet, cells were seen entering the colloid. Many of these cells were identified as follicular cells since they often occurred in groups and occasionally exhibited remnants of desmosomes. Often the cells within the colloid appeared vacuolated, and by light microscopy were thought to contain lipid. However, electron microscopy revealed that these cells contained many digestive vacuoles rather than lipid droplets. Quantitative and autoradiographic studies indicated that thyroids of vitamin A deficient rats took up less radioiodide than thyroids of control rats. The keratinization of ultimorbranchial follicles in vitamin-A deficiency has been suggested as preliminary in the histogenesis of squamous cell carcinoma. However, an effect of vitamin A deficiency on thyroid follicular cells has not heretofore been reported. It's possible that the presence of follicular cells in the colloid reflects an accelerated turnover of these cells and could indicate an early pathological sign.     

Immunohistochemical localization of NPY, VIP and 5-HT in the thyroid gland of the lizard, Podarcis sicula

The thyroid gland of the lizard Podarcis sicula was immunohistochemically studied in adult male specimens using specific antibodies against NPY, VIP and 5-HT and the avidin-biotin peroxidase complex (ABC) procedure to localize the three peptides. Fine beaded VIP-immunoreactive nerve fibers ran between the follicles, and VIP-immunoreactivity was evenly distributed in the apical cytoplasm of follicular cells. NPY-immunoreactive fibers were found around the follicles, and, in the cells, immunoreactivity was localizated only in the cellular apices. Immunoreactivity to 5-HT was observed in the colloid, with a concentration in the follicular lumen exceeding that in the follicular cells. In fact, most follicles showed immunoreactivity in the cytoplasmic bridges formed between the apical portion of the follicular cells and the colloid.     

Proliferating cell nuclear antigen of the rat thyroid gland before and after birth]

We were studied the proliferative activity of the thyroid gland's cells of embryo and adult Wistar rats due to using the antiserum against the cell nuclear antigen (PCNA). The 100% of cells in thyroid's embryo was a positive on the 16th, 17th, 18th stages of the embryonic development (stages by Kornegy). The percent of PCNA-positive cells considerably increased to 67% on the 19th stage. This fact the 20th and 21th stages of prenatal development relatively the previous stage coordinate with starting of the thyroid hormones in fetal thyroid gland and the first follicles formation. The small increasing of number of PCNA-positive cells detected on the 20th and 21th stages of prenatal development relatively the previous stage. Considerable elevation of the proliferating cells to 75% immediately before the birth (22th stage). An infant rats had have the 39% of proliferating cells. The 51% cells divided on the 5th day of postnatal development. Considerable decreased of the cell's division was occurred until the postnatal day 60. Using of the PCNA antiserum allowed to study cell proliferation in thyroid gland during pre- and postnatal rat development.     

Influence of passive immunization against GnRH on pregnancy and parturition in the tammar wallaby, Macropus eugenii

Pouch young were removed from 10 wallabies in lactational diapause, and half the animals were injected intravenously with 8 ml normal wallaby serum or 8 ml GnRH antiserum every 3rd day from the day of removal of pouch young until Day 30. Laparotomies were performed on Day 24 to monitor luteal size, follicular development and uterine enlargement. The pouches were examined daily for the presence of newborn young from Days 26 to 30, and all the animals were killed on Day 30. The corpora lutea had hypertrophied in all the animals of both groups by Day 24, but none of the antiserum-treated animals showed any signs of follicular development (follicles less than 1 mm diam.), whereas all the control animals had large follicles (mean 3.5 mm diam.). In each group 4/5 animals were visibly pregnant at laparotomy, and parturition occurred normally in 3 of the experimental animals and 1 of the controls. At autopsy, none of the antiserum-treated animals showed any evidence of follicular development or post-partum ovulation, whereas 3 of the controls had new corpora lutea and the other 2 had large preovulatory follicles. These differences were reflected in the weights of the lateral vaginae; the treated animals showed no evidence of oestrogenic stimulation (4.9 +/- 0.2 g), whereas the controls showed the hypertrophy characteristic of oestrus (9.5 +/- 1.2 g). Lactogenesis, as measured by an increase in mammary gland lactose concentrations, was established in all animals, regardless of treatment.(ABSTRACT TRUNCATED AT 250 WORDS)     

The postnatal development of the pelage and ventral gland of the male gerbil

The postnatal development of the pelage and ventral gland of male Mongolian gerbils ranging from newborn to 86 days of age was studied. The development of the gerbil pelage follows a pattern similar to that observed for other rodents. The length of the dorsal and ventral skin juvenile hair cycle was found to be 26 to 28 days with a 15 to 18 day anagen and a ten to 11 day catagen and telogen. Hair follicles in the ventral gland began growth ten days later than those of the general pelage and secondary follicles budded from the sides of primary follicles. The ventral gland area differed from the general pelage in that it lacked a panniculus carnosus. The ventral gland is a complex of pilosebaceous glands which, in the adult, fill the entire hypodermis. The length and width of the pilosebaceous canals of the gland units are greater than those of the dorsum. The period of telogen of the hair follicles in the ventral gland is very short. The mid-ventral gland of the male gerbil appears to be a secondary sexual characteristic.     

The effects of synthetic salmon calcitonin on thyroid C and follicular cells in adult female rats

Structural and morphometric features of thyroid C and follicular cells were studied in adult rat females after treatment with synthetic salmon calcitonin (CT). The animals were chronically treated with either a low (10 IU/kg b.w) or a high (100 IU/kg b.w) dose of CT. A stereological method was applied to determine the volume density and the number of immunoreactive C cells. The height and volume density of follicular epithelium, colloid, interstitium and the follicles (epithelium plus colloid), as well as the index of activation rate were calculated. A significant decrease in body weight, as well as the volume density of immunoreactive C cells and the number of C cells per mm2, was observed in rats treated with both doses of CT. The height and volume density of follicular epithelium and follicles, as well as the index of activation rate were significantly increased in the animals given the high CT dose, while the volume densities of colloid and interstitium were reduced. No significant changes in the examined morphometric parameters were detected after treatment with the low CT dose. According to these results it can be concluded that the structural features of thyroid C and follicular cells were affected by the high dose CT treatment in the opposite manner, while the low dose CT treatment influenced only C cells.     

Postnatal regulation of germ cells by activin: the establishment of the initial follicle pool

Mammalian females enter puberty with follicular reserves that exceed the number needed for ovulation during a single lifetime. Follicular depletion occurs throughout reproductive life and ends in menopause, or reproductive senescence, when the follicle pool is exhausted. The mechanisms regulating the production of a species-specific initial follicle pool are not well understood. However, the establishment of a follicular reserve is critical to defining the length of reproductive cyclicity. Here we show that activin A (rh-ActA), a known regulator of follicle formation and growth in vitro, increased the number of postnatal mouse primordial follicles by 30% when administered to neonatal animals during the time of germline cyst breakdown and follicle assembly. This expansion in the initial follicle pool was characterized by a significant increase in both germ cell and granulosa cell proliferation. However, the excess follicles formed shortly after birth did not persist into puberty and both adult rh-ActA- and vehicle-treated animals demonstrated normal fertility. A follicle atresia kinetic constant (k(A)) was modeled for the two groups of animals, and consistent with the empirical data, the k(A) for rh-ActA-treated was twice that of vehicle-treated animals. Kinetic constants for follicle formation, follicle loss and follicle expansion from birth to postnatal day 19 were also derived for vehicle and rh-ActA treatment conditions. Importantly, introduction of exogenous rh-ActA revealed an intrinsic ovarian quorum sensing mechanism that controls the number of follicles available at puberty. We propose that there is an optimal number of oocytes present at puberty, and when the follicle number is exceeded, it occurs at the expense of oocyte quality. The proposed mechanism provides a means by which the ovary eliminates excess follicles containing oocytes of poor quality prior to puberty, thus maintaining fertility in the face of abnormal hormonal stimuli in the prepubertal period.     

Studies on the development of endocrine glands in fishes. V. Development of the thyroid gland in two species of teleosts.

In Channa punctatus the thyroid anlage is seen 40 h after hatching and is recognized as cells aggregating in the form of follicles with no colloid. During subsequent stages of development the thyroid follicles increase in number and in 5 days old larva an active division of cells and many follicles in the form of epithelial cords are seen. In 2 months old juvenile fish several thyroid follicles and lymphatic vessels are seen enclosed by connective tissue capsule. In Clarias batrachus the thyroid anlage is seen as a group of cells around tiny colloid droplets and is situated just below the bifuration of the 1st branchial artery. This stage is seen in 60 h old larva and is developed into thyroid follicles which is a long chain along the jugular vein and ventral aorta during latter stages of development. It is concluded that during early larval period of these fishes, the thyroid cells begin to trap iodine from the blood and synthesize it in the form of thyroid hormone which is stored as colloid and is also liberated in blood stream simultaneously. The compact nature of the thyroid gland in C. punctatus is because of development of connective sheath around follicles during early stages.     

State of the rat thyroid gland in coarctation of the abdominal aorta]

In order to study connections between blood vessels and follicular thyrocytes, the method of modulation (a purposeful change of state in one element with registration of states in other elements of the system) was used. In rats chronic increase of blood stream was produced in the thyroid gland; in 15 days it was 54% as high as in the control. The volume of the vascular bed increased by 28% and that of follicles by 26%. Volumetric ratio between the thyroid epithelium and colloid did not changed. Follicular thyrocytes grew high and the nuclear volumes of these cells increased. Thyrocytes greately varied in their height. The number of mast cells in the thyroid gland remained the same. Iodine absorption by the thyroid gland increased as it is dependent on the volume of the vascular bed of the organism (+0.82). The data obtained demonstrate a significant connection existing between the follicular thyrocytes and blood vessels.