Effect of beta-adrenoreceptor blockade on cell division processes in the corneal and tongue epithelium of white rats with chronic oxygen starvation

A study was made of the changes in the mitotic activity, DNA synthesis, and the number of pathological mitoses after administration of the beta-adrenoblocker propranolol in the corneal and tongue epithelium of white rats kept in pressure chamber for 7 days (4 h daily) at a "height" of 9000 meters. The mitotic and the label indices (inclusion of 3H-thymidine by the epithelium nuclei) were analysed for mitotic activity and DNA synthesis, respectively. The experiments showed that the mitotic activity, DNA synthesis, the number of pathological mitoses were stabilized due to the propranolol administration.     

Ultrastructural changes and proliferation of pituicytes in mouse posterior lobe during water deprivation and rehydration

Ultrastructural changes and proliferation of pituicytes during water deprivation and rehydration were studied in the posterior lobe of C57BL/Tw mice. Deprivation for 3 days brought about a significant increase in the number of electron-dense bodies (lysosomes) in pituicyte perikarya and their processes. The frequency of pituicytes enclosing neurosecretory axons in their cytoplasm significantly decreased as compared with that of the controls. 12-hour rehydration following deprivation for 3 days induced extensive development of rough endoplasmic reticulum and Golgi apparatus and an increase in frequency of neurosecretory axons enwrapped by pituicyte cytoplasm. However, at 2 days of rehydration the morphology of pituicytes was no more different from that of the controls. Mitotic figures of pituicytes were not encountered throughout the deprivation period of 6 days, but rehydration for 12 h and 1, 2, or 3 days following deprivation for 3 or 6 days was effective in eliciting an increase in mitotic activity. The present results indicate that pituicytes in the mouse posterior lobe are intimately related with the secretory mechanism of neurosecretory material from the neurosecretory axons and that the proliferation of pituicytes is stimulated in conditions of reaccumulation of neurosecretory material.     

Changes in the proliferative activity of the corneal epithelium and the regenerating liver in partial splenectomy in mice

The mitotic activity in epithelial cells of the mouse cornea was studied 4 h, 1, 2, 5, 8 and 14 days after a sham operation or partial (2/3) splenectomy. The decrease in the number of dividing cells in the corneal epithelium was observed within two days after a sham operation and within five days after partial splenectomy. On the contrary, partial hepatectomy increased the number of mitoses in the corneal epithelium. Liver regeneration against the background of a sham operation or partial splenectomy was accompanied by a lesser number of mitoses (by a factor of 2.5-4) in hepatocytes than in the animals subjected to partial hepatectomy only.     

Temporal pattern of changes in mitotic frequency in the epidermis and other larval tissues of Bombyx mori

Temporal changes in mitotic frequency were examined in various tissues through late larval life of Bombyx mori. From the second larval ecdysis to the third and from the third larval ecdysis to the fourth, there was a definite temporal change of mitotic pattern in each tissue. In the epidermis as well as in the tracheal epithelium, mitoses began to appear about 1 day after an ecdysis, and showed a maximum 1 to 2 days after an ecdysis. In the fat body, mitoses were observed continuously through the instars, and the mitotic frequency showed a maximum state just before an ecdysis. In the abdominal muscle the frequency was highest at about the middle of the period between two successive ecdyses. Furthermore, epidermal mitoses coincided with the time when the density of epidermal nuclei per unit area decreased to a half. This suggests that epidermal mitoses may be initiated by some process related to the increase in cell size.     

Evaluating Mitotic Activity in Canine and Feline Solid Tumors: Standardizing the Parameter

Three different methods for evaluating mitotic activity (mitotic count, mitoses/area, mitotic index) were applied to different types of canine and feline solid tumors to determine the method that is most objective and correlates best with other parameters of cell proliferation. Mitotic activity was evaluated on toluidine blue stained his-tological sections. Slides stained with histochemical (AgNOR proteins) and im-munohistochemical (MEB1, PCNA) markers of cell proliferation were available for each case. Quantitation of mitotic activity and cell proliferation parameters was performed with an image analyzer. Mitotic activity assessment was compared with cell proliferation indices and its ability to discriminate tumors grouped on histologically based criteria including the histological type, malignant or benign characteristics, and grade. A significant correlation by linear regression analysis with other parameters assessing cell proliferation revealed that mitotic index correlated 100% and mitoses/area and mitotic count correlated 40% of the time. In discriminating the proliferative activity of tumors grouped by histological criteria, mitotic index and mitotic count revealed 100% concordance with the other parameters of cell proliferation, while mitoses/areas showed 80% concordance.     

The distribution of mitoses in the imaginal disks of third-instar Drosophila melanogaster larvae

Development of Drosophila imaginal discs is accompanied by a high-ordered cell proliferation. However, the distinctions in the topographic distribution of mitoses at different developmental stages are insufficiently studied. In this work, we have analyzed the distribution of mitoses in the wing disc of third-instar larvae and determined the regions where mitotic clustering. The results obtained demonstrate that the proliferation rate is region-specific, which is determined by the location of cell cycle regulators and/or the location of growth factors. A comparison of the topography of mitoses with the activity patterns of the regulatory regions of gene string (stg), a known regulator of the mitotic M phase, has demonstrated a similarity between the topography and the activity pattern of one of these regions. The similarity between mitotic distributions in the left and right discs of the same larva (compared with the similarity of gene neuralized expression patterns is considered, and the degree of histone H3 phosphorylation at various mitotic stages is analyzed.     

Nycthemeral variations of mitotic activity in the adrenal cortex of the rat]

Working on histologic sections 7 microns thick in the equatorial part of male rat adrenal cortex, we found two high mitotic activity periods. The first one stays at midnight and shows an average number of 42 mitoses per section; the second one occurs at 5 a.m. with an average number of mitoses of 70,1 per section. If we except these particular points, the mitotic activity is low, the average number of mitoses being 13,2 per section.     

MITOTIC ACTIVITY IN THE CAMBIAL ZONE OF PINUS STROBUS

Mitotic activity in the cambial zone of 20-year-old Pinus strobus L. trees was determined quantitatively, using mitotic counts from serial tangential sections of sample pieces. Counts from nine cores 1.6 mm in diameter from each sample piece were averaged and expressed as the number of mitoses per core with the sampling error. Estimation of the number of cambial zone cells per core permitted calculation of mitotic indices. In the fourth internode from the ground the first mitoses were observed on April 15 and the last on September 15. The number of mitoses per sample piece was comparable throughout each internode at any one sampling, but the number was higher in internodes within the crown than in those below it. Mitotic index was not appreciably higher within the crown, but it decreased from 3.7 in spring to 2.0 in fall. An internode in the crown sampled May 11–13 showed afternoon peaks in mitotic activity, but an internode below the crown showed no peaks, nor did other internodes sampled later in the season.     

Proliferative activity of the epithelium of the rat large intestine during carcinogenesis]

Labelling index and mitotic regimen in the epithelium of the rat descending colon and the ileum was studied during the tumour induction with 1,2-dimethylhydrazine. One month after the beginning of the experiments there was a marked increase of abnormal mitoses (up to 51%) and a change in the proportion of the mitotic phases with the metaphase prevalence (up to 73%). Later, these parameters were unchanged. Beginning from the 3rd month of the experiment there was found an increase in the labelling index (especially, in the carcinoma in situ) and of the mitotic index. In the mucosa of the ileum (where the tumours never developed) no changes of the proliferative activity and of mitotic regimen were found.     

Cytochalasin induces spindle fusion in the syncytial blastoderm of the early Drosophila embryo.

Microfilament integrity is needed to maintain the regular arrangement of the spindle microtubules and to guarantee the normal progression of the last syncytial mitoses in Drosophila embryo. To investigate when and how microfilaments participate in this process, we incubated permeabilized embryos with the inhibitor of actin polymerization, cytochalasin B, at different times during the nuclear cycle. Our results suggest that the correct microfilament distribution is only required for the appropriate segregation of nuclei during the 11th, 12th and 13th syncytial mitoses rather than during the 10th mitosis when the spindles are too far apart to interact. When cytochalasin B treatment was performed during the last syncytial mitoses many spindles fuse among them and the regular mitotic progression is perturbed.     

The distribution of mitoses in the imaginal disks of third-instar <Emphasis Type="Italic">Drosophila melanogaster</Emphasis> larvae

Development of Drosophila imaginal discs is accompanied by a high-ordered cell proliferation. However, the distinctions in the topographic distribution of mitoses at different developmental stages are insufficiently studied. In this work, we have analyzed the distribution of mitoses in the wing disc of third-instar larvae and determined the regions where mitotic clustering. The results obtained demonstrate that the proliferation rate is region-specific, which is determined by the location of cell cycle regulators and/or the location of growth factors. A comparison of the topography of mitoses with the activity patterns of the regulatory regions of gene string (stg), a known regulator of the mitotic M phase, has demonstrated a similarity between the topography and the activity pattern of one of these regions. The similarity between mitotic distributions in the left and right discs of the same larva (compared with the similarity of gene neuralized expression patterns is considered, and the degree of histone H3 phosphorylation at various mitotic stages is analyzed.     

Mitotic Figures in the Median Eminence of the Hypothalamus

The median eminence of the hypothalamus is part of the avenue by which neurosecreted hormones from the hypothalamic nuclei reach the pars nervosa (neural lobe) of the pituitary and eventually the bloodstream. Lithium treatment and osmotic stress increases the transport of neurosecretory hormones to the pituitary in the adult rat. Specialized astrocytes termed pituicytes in the pars nervosa of the pituitary participate in the secretory process and also develop considerable mitotic activity. The present work reveals similar mitotic figures in cells within the median eminence following 3 days of lithium treatment. The location and appearance of these mitoses add to the evidence that pituicytes are present in the median eminence. Moreover, mitoses occur within the ependymal (tanycyte) layer of the median eminence. Thus, the present results suggest that the tanycyte layer may contain pituicytes, indicating that the hypothalamus possesses specialized cells for modulating neurosecretion in response to osmotic challenges.     

Cell cycles in the male accessory glands of mealworm pupae

During the pupal stage of Tenebrio molitor, the accessory reproductive glands of males grow by cell division. Within the secretory epithelium of the bean-shaped accessory glands (BAGs), cell numbers triple. In the tubular accessory glands (TAGs), the increase is 14-fold. There are two mitotic maxima in each gland. The first maximum occurs at 1-2 days while the second is at 4-5 days. The second maximum coincides with the major ecdysteroid peak described by Delbecque et al. [Dev. Biol. 64, 11-30 (1978)]. Nuclei were isolated from TAGs during the pupal mitotic bouts and during mitotic inactivity in the adult. After Feulgen or propidium iodide staining, the DNA content of these nuclear populations was measured by absorption cytophotometry or by fluorescence flow cytometry, respectively. The proportion of cells in each phase of the cycle was calculated using an iterative model. After mitoses have ended in the late pupa, the cells were arrested in G2. [3H]Thymidine was injected into 1- and 4-day pupae to pulse-label cells of the TAGs. After allowing various periods from 4 to 60 hr for cells to progress through G2 to reach mitosis, fractions of labelled mitoses were determined by autoradiography. From the combined cytometric and autoradiographic data, the duration of each phase of the cell cycle was calculated assuming the population was in exponential growth. Cell cycles in 4-day pupal TAGs take 48 hr. G1, S, G2, and, M lasted 13, 14, 17, and 4 hr, respectively.     

Differentiation of the epithelium of the pronephros and the primary kidney in frogs]

The kidneys of tadpoles of different developmental stages were examined in preparations processed histologically and histochemically. It was found that differentiation of the provisory excretory organ tubules in frogs was "shortened" or "accelerated" after P. P. Ivanov's terminology, and developed differently as compared with differentiation of tubules of the definitive organ of excretion -- the primary kidney. When differentiating the epithelium of the proximal portion of the primary kidney nephron passes the stage of the high prismatic false-stratified epithelium. The pronephros tubules do not pass this stage and the epithelium becomes a strict monolayer from the very beginning. No mitoses are observed in the pronephros tubule epithelium even at the earliest differentiation stages. Later on, the beginning of tubule functioning, and with the reduction, and later disappearance of yolk granules in the epithelium solitary mitoses make their appearance. The mitotic activity of the primary kidney tubule epithelium is very high (70%) at the early stage of differentiation. Then its mitotic activity decreases (30%), and after the beginning of the tubule functioning mitoses in its epithelium become solitary.     

Hunting the mechanisms of self-renewal of immortal cell populations by means of real-time imaging of living cells

The causes of the indefinite propagation of immortalized cell populations remain insufficiently understood, that hinders the research of such fundamental processes as ageing and cancer. In this study the interrelations between clonal proliferation and abnormalities of mitotic divisions in the immortalized cell line established from the mouse embryo were investigated with the aid of computerized microscopy of living cells. 3 mitoses with three daughter cells and 7 asymmetric mitoses which generated two daughter cells of conspicuously different sizes were registered among 71 mitotic divisions in the individual cell genealogy. Abnormal mitotic divisions either did not slow the proliferation in cell clones compared with progenies of cells that divided by means of normal mitoses or were followed by the acceleration of divisions in consecutive cell generations. These data suggest that abnormal mitotic divisions may contribute to the maintenance of the immortalized state of cell populations by means of generating chromosomal instability.     

Prostaglandin E2-induced hyperplasia of the rat antral epithelium is followed by a secondary inhibition of the mitotic activity

The aim of the study was to examine the mitotic activity in the antral and duodenal epithelium of Sprague-Dawley rats given trophic doses of E2 prostaglandins during a prolonged period of time. Natural prostaglandin E2 (dose range: 0.2-5.0 mg.k-1) and 15 (R) 15 methyl prostaglandin E2 (dose range: 0.03-2.0 mg.kg-1) were administered for 11 days, and mitoses were arrested with vincristine for 4 h before estimation of the cumulative mitotic index. A dose-related hyperplasia of the antral glands was observed after treatment with prostaglandin E2 and the synthetic analogue (p less than 0.05). The proliferative zone was enlarged in rats treated with high doses of the analogue but natural prostaglandin E2 did not affect the limits of the proliferative zone. A dose-related reduction of the mitotic index was observed in animals treated with prostaglandin E2 despite the presence of hyperplastic changes. All doses of the analogue induced antral hyperplasia without affecting the mitotic index except in rats given the highest dose who had a significantly lower mitotic index than controls (p less than 0.05). Hyperplasia of both crypts and villi was observed in the duodenum of rats given high doses of E2 prostaglandins (p less than 0.05) whereas the mitotic index and the growth fraction were not affected by treatments. It is concluded that hyperplasia by prostaglandins is developed in absence of changes of the mitotic activity. The observed reduction of the mitotic index is interpreted as a secondary phenomenon, possibly mediated by a regulatory mechanism of cell proliferation which is triggered to reduce further epithelial growth. It is suggested that prostaglandin E2 might influence such regulatory mechanisms.     

Circadian rhythm of the mitotic activity and of the number of nuclei synthesizing DNA in sarcoma 37 in white mice]

Circadian variations in the frequency of mitoses and the number of nuclei labed with thymidine-H3 in sarcoma-37 of mice were investigated. It was shown that the circadian rhythm of mitotic activity was composed of diurnal variations in the frequency of labeled and unlabeled mitoses. The G2-phase of mitotic cycle of the cells with labeled mitosis was approximately one hour. The G2-phase of the cells with unlabed mitosis lasted four hours and more. It is suggested that there are two cell populations in sarcoma-37.