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.     

Morphofunctional features of lymph nodes, thyroid gland and testis of rats during adaptation reactions to stress and activation

The morphofunctional state of lymphatic nodes, thyroid gland and testis have been studied with morphometric, cell photometric and biochemical methods in experiments on adult white rats under the influence of nonspecific adaptation stress and activation reactions caused by small doses of adrenaline (125 mg/kg and 5 mg/kg). The research showed that the changes in the structure and function of the lymphatic organs under stress and activation were markedly different. If stress results in depression of functional state of these organs, the activation reaction, on the contrary, stimulates it.     

Morphofunctional changes in the pineal gland during adaptation to hypothermia

The influence of hypothermal stress (+4 degrees during 3 h) on the ways of serotonin metabolism in pineal gland and its structure has been studied in dynamics on adult male Wistar rats. It has been revealed that melatonin-producing epiphyseal function suffers from phase changes in dynamics of adaptation--significant rising during 15 min. after beginning of the experiment, rehabilitation up to normal--in 30 min, and fast suppressing--in 3 hrs. Suppressing of the functional pineal activity is not due to switched serotonin metabolism with melatonin and new indoles release, but to a partial pinealocytes breaking from their active function.     

Morphofunctional characteristics of the thyroid gland in intact and partially sympathectomized rats of different age groups

The morphological and functional age-dependent changes have been studied in the thyroid gland of infantile (1-month-old), immature (2- and 3-month-old) and sexually mature (6-month-old) male rats. The decrease in thyroid functional activity with ageing was proved. Chemical sympathectomy (guanethidine at a dose of 15 mg/kg intramuscularly for 14 days after birth) was accompanied not only by morphological reconstruction of the thyroid tissue, but also (especially in 1-month-old rats) by a delay in transport-organic phase of iodine metabolism and a decline in thyroid hormone serum level. Later on, the compensatory hormonogenesis reinforcement occurs as a result of partial adrenergic innervation recovery.     

The B chromosome system in the varying lemming Dicrostonyx torquatus Pall., 1779 from natural and laboratory populations

In varying lemmings from seven natural populations (from Bolzhezemel'skaya tundra to Chukotka Peninsula), the number of B chromosomes ranged from 0 to 15. In populations surveyed for several years, B chromosome frequencies were stable. Two laboratory colonies (founded by Dicrostonyx torquatus from the Polar Urals and D. t. chionopaes from Yakutia) produced more than 3000 animals, of which 1699 were karyotyped. A small excess of B chromosomes in the progeny over that in their parents was observed in each generation. Coefficients of transmission k1 of additional chromosomes were on average 0.519 in D. t. torquatus and 0.511 in D. t. chionopaes. In oocytes I and II, an accumulation of B chromosomes was observed as compared to somatic cells (k2 = 0.66). The reproductive output of animals from both laboratory colonies did not depend on size of the B genome. The reduction of body and scull sizes observed in animals carrying numerous B chromosomes may confer negative selective value in the conditions of the Extreme North. In general, the system of B chromosomes in D. torquatus is well balanced and very stable, being apparently under strong genetic control.     

Morphofunctional transformations of the yolk syncytial layer during zebrafish development

The yolk syncytial layer (YSL) is a provisory extraembryonic structure of teleost fishes and representatives of some other taxa with meroblastic cleavage. The YSL of teleosts is a symplast with polymorphous polyploid nuclei. It is known to perform nutritional, morphogenetic, immune, and, probably, other functions. Data about the YSL organization, functioning and regulation is fragmentary. Although gene expression patterns and other aspects of YSL functioning have been studied in Danio rerio, the morphology of its YSL has not been described in detail. The study of zebrafish YSL structure on sequential developmental stages is necessary to recognize specific features of this important polyfunctional system in this model organism and to extend our knowledge about provisory systems. The thickness of the YSL and the distribution of its nuclei are not uniform on each stage and change during development. During oblong and sphere stages the internal YSL (I‐YSL) is filled with yolk inclusions; interphase yolk syncytial nuclei (YSN) and mitotic asters can be seen. During doming and epiboly the external YSL (E‐YSL) is thicker than I‐YSL. On the subsequent stages the YSL is thickened caudally. The dorsal YSL part is thickened during early segmentation stages and becomes the thinnest YSL region later. The anterior part of the YSL is thin, but enlarges during larval period. The YSN of different size and diverse forms, from regular to lobed, are present and form clusters. The number of irregular‐shaped nuclei increases during development. The YSL thickens in the end of endotrophic and in the course of endo‐exotrophic period, and its cytoplasm contains numerous yolk inclusions. After yolk exhaustion the YSL is flat. As the YSL degrades , the YSN become pycnotic, and the YSL remnant probably is cleared by phagocytes. J. Morphol. 275:206–216, 2014. © 2013 Wiley Periodicals, Inc.     

Ultrastructural changes in thyroid epithelium during involution of the hyperplastic thyroid gland

The ultrastructure of the thyroid epithelial cell was examined at various time intervals after induction of involution of the hyperplastic thyroid gland. Thyroids were made hyperplastic by the feeding of thiouracil in a Remington low-iodine diet to male Fischer rats for 3 weeks. Involution was induced by replacing the thiouracil-containing diet with Purina Laboratory Chow, a high-iodine diet. During involution, organelles that play a role in the synthesis and secretion of thyroglobulin, such as the rough endoplasmic reticulum, Golgi apparatus, and apical vesicles, were well preserved and prominent features of the epithelial cell. The apical plasma membrane of many cells was highly irregular for approximately 2 weeks with signs suggesting rapid discharge of apical-vesical contents into the lumen of the follicle. Pseudopods and colloid droplets were present but were not very prominent features of the cell. No signs of extensive autophagy or obvious increased incidence of lysosomes were present, although there was an elevation in the incidence of small dense bodies starting about day 8, and prominent by 15 days. Some of these may be phagosomes formed from luminal debris. The observations indicate that involution of the hyperplastic thyroid in which there is maintenance of the protein synthetic apparatus and little sign of autophagy or death of the epithelial cells is remarkably different from phenomena occurring during involution of prostate or mammary glands.     

The hypothalamo-hypophysial system of the lemming, Dicrostonyx torquatus Pallas. III. Population aspects of neuroendocrine regulation

The structure and ultrastructure of the following regions of the hypothalamo-hypophysial neurosecretory system (HHNS) in the population cycle of lemming were studied: supraoptic (SON), paraventricular (PVN) and arcuate nuclei (AN), the median eminence (ME) and posterior pituitary (PP). Being compared to the state of endocrine glands and gonads, and the level of reproduction stress in the population cycle of the lemming described earlier, the obtained data revealed a certain regularity. First, at the stages of decrease, increase and in the first period of the stage of population peak the activity of the SON-PP complex and AN is gradually increased. This coincides with intensified reproduction, intensified functioning of the thyroid gland and adrenal cortex. Second, while the population is decreasing, all the above functions become depressed, except that of the thyroid gland which, on the contrary, becomes active. In the second period of the stage of population peak, when reproduction stops abruptly, this regularity, however, does not hold, the activity of SON-PP complex and AN is sharply lowered, whereas that of PVN becomes very high. The structure of the thyroid damaged as a result of previous hyperfunction, is restored, and the adrenal cortex shows signs of hypercorticism. The present work is devoted to specificity of the HHNS functioning at the stage of population peak, referred to as crucial, and the pathways and mechanisms by which neurohormones produced by this system can affect the endocrine glands. In addition, the causes likely to lead to the mass death of animals at this stage, and biological significance of this fact are also given attention to.     

The topography of Gomori positive neurosecretory elements of the hypothalamus of the lemmings Dicrostonyx torquatus and Lemmus sibiricus]

Under study was the structure of the hypothalamo-hypophyseal neurosecretory system in two species of lemmings of the Wrangel island: the collared lemming, (Dicrostonyx torquatus) and the Ob lemming (Lemmus sibiricus). Inspite of the similarity in the general organization of this system in all rodents, certain species features were found in the topography of neurosecretory elements in the animals studied. In the Ob lemming there is a great similarity in the structures of the neurosecretory system with the albino rat than in the collared lemming. In both species of lemmings, and in the collared lemming in particular, the supraoptic nucleus is located more dorso-caudally and the paraventricular one-more dorsally. A greater amount of neurosecretory cells is found which from additional groups. The hypothalamo-hypophyseal and extrahypothalamic pathways are well pronounced. The postoptical nucleus is considerably developed. In the collared lemming it is almost equal to the supraoptic one in the amount of cells composing it. The ratio of the cells in the supraoptic and postoptic nuclei is suggested to be related to the level of the water-salt metabolism and the specific ecology of lemmings.     

Calcitonin cell population and distribution in the thyroid gland of the rat

Calcitonin-containing cells (C cells) were identified in male Wistar white rats using an immunoperoxidase technique. They occupied a central position within the thyroid; very few were found peripherally, inferiorly, and superiorly; and none were present in the isthmus. The number of calcitonin-containing cells present per gram of body weight increased with age up to 70 days and had declined by 100 days. Determining the true total C-cell count through the entire thyroid is a very laborious procedure. However, a simple estimate of this total count can be made; the total number of C cells in every tenth section (6 microns) of thyroid was found to be highly correlated with the weight of the animal expressed as an allometric function. A better estimate can be derived from counts of just three sections: the tenth, twentieth, and thirtieth after the section of greatest cross sectional area.     

Estrous cycle of the Arctic lemming (Dicrostonyx torquatus Pall.) maintained and breeding under laboratory conditions]

Reproductive functions and life at laboratory conditions were studied in the lemming. Standard cage-terrariums with a wheel for motion and a plate for drinking are quite convenient. The main ration includes: hay, oats with some carrot added, some apples two--three times a week, sunflower seeds. The animals feel well and reproduce at +8 degrees and +20 degrees in well ventilated rooms. The estrous cycle in lemming females studied by microscopy of vaginal smears is not regular. Only two stages are definitely seen: diestrus and estrus. Intermediate stages--proestrus and metaestrus--can be identified by a successive studies of vaginal smears of the same animal.     

Follicular epithelium of the ovary in the prenatal and early postnatal periods of ontogenesis of the Wrangell Island lemming Dicrostonyx torquatus Pall

In 69 representatives of the Arctic lemming the ovaries have been studied. Morphologucal peculiarities of prefollicular and follicular cells have been revealed during various periods of folliculogenesis, as well as changes in the volumetric density arrangement of cellular organells in the process of their differentiation. It is supposed that during the period preceding formation of the follicles (15.5-20 days of embryonal development and the first three days after birth) the prefollicular cells possess several functions (participation in regulating spatial organization of ovogonia, fagocytosis), the secretory one including. During formation of primordial follicles (1-3 days after birth) the follicular epithelium cells become flatten and their structures orient towards supporting-mechanical function. The following morphological changes of folliculocytes are connected with further growth of follicles, granulosa formation, secretion of follicular fluid in cavitary follicles that form at the beginning of the third week. A coinside in time is noted in formation of primordial follicles and in beginning of their growth in laboratory rodents and in the lemmings, nevertheless, transformation of the growing follicles into the cavitary ones occurs more quickly in the lemming.