Biomedical subjects

M Karasek

Publications and source records attributed to M Karasek.

At least 37 records · Page 2Linked to original sources

PubMed1992

Ultrastructure of the mammalian pinealocyte under natural and experimental conditions: quantitative aspects.

This review briefly summarizes data accumulated on the quantitative aspects of the ultrastructure of the mammalian pinealocyte. Quantitative changes have been demonstrated under natural and experimental conditions in pinealocyte cell organelles in various species. Special attention is paid to two cytoplasmic components most frequently studied by means of quantitative electron microscopy, namely, dense-core vesicles and "synaptic" ribbons.

Animals↗

PubMed1992

Morphofunctional aspects of the mammalian pineal gland.

The primary aim of this review is to present the current state of knowledge of the ultrastructure of the mammalian pineal gland, with emphasis on its functional aspects. Basic ultrastructural features of the mammalian pinealocytes are presented with special attention paid to ultrastructural aspects of pineal secretion.

Animals↗

PubMed1992

Influence of melatonin on the proliferation of hepatoma cells in the Syrian hamster: in vivo and in vitro study.

A study was carried out to determine the possible influence of melatonin on the proliferation of Kirkman-Robbins hepatoma cells in Syrian hamsters, both in vivo and in vitro. A highly significant inhibition of the proliferation of transplanted hepatoma cells was observed in vivo following melatonin administration (proliferation index 10.3 +/- 1.5; mean +/- SD) in comparison with controls (proliferation index 23.3 +/- 2.2), whereas in vitro melatonin (at concentrations of 10(-5)-10(-11) M) was ineffective. These results indicate that inhibitory effect of melatonin on transplantable hepatoma cells in vivo may be indirect.

Animals↗

PubMed1990

Circadian variations in plasma melatonin, FSH, LH, and prolactin and testosterone levels in infertile men.

Circadian patterns of plasma melatonin, FSH, LH, prolactin, and testosterone were studied in 10 healthy men, 20 men with oligozoospermia, and 8 men with azoospermia. Circadian rhythms were found in concentrations of melatonin and prolactin, with higher values at night in comparison with daytime levels. In patients with oligozoospermia and azoospermia an elevation in melatonin levels was observed, and an increase in melatonin concentrations occurred before onset of darkness (i.e., at 2000 h). Levels of FSH, LH, and prolactin were elevated in infertile patients. The possibilities that an increase in melatonin concentrations is either the primary feature that leads to the regression of the seminiferous epithelium or is secondary and depends on elevated gonadotropins and/or prolactin levels are discussed.

Adult↗

PubMed1990

"Synaptic" ribbons in the pineal gland of the horse.

Previous studies on the ultrastructure of the horse pineal gland did not report the presence of "synaptic" ribbons, functionally enigmatic pinealocyte organelles regularly occurring in other mammalian species. The aim of the present study was to reinvestigate the horse pinealocyte in this respect. Careful investigations here reported allowed detection of "synaptic" ribbons in the pinealocytes of all the examined animals, although in a relatively low number (5.4 +/- 2.0 per 20,000 microns 2 of pineal tissue; mean +/- SD). The ultrastructure of "synaptic" ribbons in pinealocytes of the horse resembles closely that observed in other mammalian species.

Animals↗

PubMed1990

Comparison of the rat pinealocyte ultrastructure with melatonin concentrations during daytime and at night.

The aim of this study was to investigate the ultrastructure of rat pinealocyte during daytime (1600 h) and at night (0100 h) and to compare these observations with serum melatonin levels in the same animals. In addition, pineal melatonin concentrations were determined in other animals. Both serum and pineal melatonin concentrations were significantly higher at night than during daytime (34 and 21 times, respectively). Sizes of pinealocytes, their nuclei, and nucleoli, as well as cross-sectional areas of mitochondria and granular endoplasmic reticulum were also higher at night than during daytime, whereas areas of lysosomes, Golgi apparatus, and vacuoles containing flocculent material did not differ at the time points studied. In contrast, the number of dense-core vesicles was higher during daytime. The results of the present study show that morphological patterns of higher metabolic activity of the rat pinealocyte at night when compared to those during daytime correlate with melatonin concentrations.

Animals↗

PubMed1990

Ultrastructure of pig pinealocytes in various stages of the sexual cycle: a quantitative study.

Relative volumes of mitochondria (MIT), lysosomes (LYS), Golgi profiles (GP), granular endoplasmic reticulum (GER), membrane bound bodies of type 1 (MBB 1) and type 2 (MBB 2), and the number of dense-core vesicles (DCV), were counted in pinealocytes of female sexually immature pigs, in animals in oestrus and in nursing pigs. Relative volumes of GER, LYS, MBB I and the number of DCV changed in the different stages of the sexual cycle. The highest volumes of GER, LYS and MBB 1 were observed in pigs in oestrus. Pinealocytes of sexually immature pigs were characterized by a considerably higher number of DCV in comparison with mature animals.

Aging↗

PubMed1989

Isolation and growth of adult human epidermal keratinocytes in cell culture. 1978.

Human epidermal keratinocytes may be isolated in high yield from 0.1 mm keratotome sections of adult skin by short-term trypsin release. When plated on a collagen-coated plastic surface or on a collagen gel, keratinocytes attach with high efficiencies (greater than 70%) and form confluent, stratified cultures. Cell populations of predominantly basal cells produce proliferative primary cell cultures while populations of basal cells and malpighian cells result in nonproliferative primary cultures. Both nonproliferative and proliferative primary cultures may be subcultured on collagen gels following dispersion by trypsin and EDTA. Methotrexate strongly inhibits proliferative keratinocytes at low concentrations (0.1 microgram/ml) but has no cytotoxic effect on non-proliferative cells. L-serine and dexamethasone increase the multiplication rate of both primary and subcultured human keratinocytes.

Adult↗

PubMed1988

Influence of a short light pulse at night on the ultrastructure of the rat pinealocyte: a quantitative study.

Although it is generally known that light strongly influences N-acetyltransferase activity and melatonin production in the pineal gland, little information is available concerning morphological changes following light exposure. As exposure of rats to a short light pulse at night rapidly depresses melatonin synthesis, we decided to determine whether this experimental condition produces rapid changes in the pinealocyte organelles. A 30-min light pulse at night (six hours after lights out) provoked rapid changes in the relative volumes of some pinealocyte organelles. The volume fractions of mitochondria, Golgi apparatus and lipid droplets, and the numbers of dense-core vesicles and "synaptic" ribbons decreased, whereas the volume fraction of lysosomes increased. There were no differences in the volumes of granular endoplasmic reticulum and vacuoles containing flocculent material in those animals exposed to light compared with control animals. These results indicate that a short light pulse at night causes ultrastructural changes that can be interpreted as morphological features of diminished activity of pinealocytes.

Animals↗

PubMed1988

Precise annual changes in the numbers of "synaptic" ribbons and spherules in the rat pineal gland.

Although pineal "synaptic" ribbons (SR) are frequently examined by means of quantitative electron microscopy, their functional significance remains unclear. The same is true for related structures--"synaptic" spherules (SPH). In the course of such studies, it has been noted that SR counts may differ from laboratory to laboratory. Because seasonal changes may play a role, a 2-year study was performed on male rats kept under routine laboratory conditions and killed at monthly intervals during daytime or nighttime. Both structures examined showed distinct day-night differences throughout the year, with higher numbers at night than during the day. There were significant annual changes in both SR and SPH during both daytime and nighttime. The comparison of the curves from the 2 years showed that they were virtually identical both during daytime and nighttime. The numbers of SR were the highest in October and the lowest in April; the numbers of SPH had two plateaus, one with lower values from November to April, and the other with higher values from May to October. It appears from the present study that SR and SPH numbers in the rat pineal gland show statistically significant and precisely timed seasonal changes that may well account for the variations of SR numbers in the different publications.

Animals↗

PubMed1987

Adult cutaneous hemangiomas are composed of nonreplicating endothelial cells.

Thirty-four human "cherry" dermal hemangiomas were studied by electron microscopy, immunohistochemistry, and cell culture to assess the neoplastic nature of these lesions. Electron microscopy of nine hemangiomas revealed a pronounced thickening of the basement membrane (0.6 to 14 micron) in 93% of the total 158 vascular structures examined within the lesions. This increase was caused mainly by multiple layers of basal lamina, which were irregular in outline and frequently associated with pericytes. Basement membrane changes were present both in the periphery of the hemangiomas, as well as in the center of the lesions. Immature vessels could not be identified and mitoses were absent in all endothelial cells. Using an immunohistochemical marker (Ki67) specific for proliferating cells in G2 and S phases, positive staining was not found in the endothelial cells lining the hemangiomatous vessels, whereas basal epidermal keratinocytes in the same preparations and cultured microvascular endothelial cells expressed the antigen. Endothelial cells of nine hemangiomas did not stain with an activation-related antibody (E12) specific for endothelial cells. When endothelial cells from 14 hemangiomas were isolated and cultured under conditions that support the growth of normal human skin microvascular endothelial cells, the cells of hemangiomatous origin failed to grow. We conclude that the adult hemangiomas may not be true neoplasms, but a tissue overgrowth composed of mature vessels resembling dermal venules, lined by endothelial cells with virtually no turnover.

Adult↗

PubMed1987

Failure of melatonin to inhibit the mitotic activity of regenerating adrenal cortex in rats.

Although there is little evidence that melatonin may have a direct antimitotic effect on various cells, it has been shown that this pineal compound may influence the cell proliferation of either normal or neoplastic cells. Therefore, the influence of melatonin on the mitotic activity of regenerating adrenal cortex of rats was studied. The mitotic activity was counted in the adrenal cortex or rats on days 2, 7, and 12 following enucleation of the adrenals. Melatonin did not influence the mitotic activity of regenerating adrenal cortex in the rat.

Adrenal Cortex↗

PubMed1986

Effects of long and short photoperiod on the ultrastructure of pinealocytes of the cotton rat (Sigmodon hispidus).

The ultrastructure of the pinealocytes of wild-captured cotton rats (Sigmodon hispidus) housed in either long or short photoperiod was examined. Quantitative comparison of selected pinealocyte organelles revealed larger relative volumes of mitochondria, granular endoplasmic reticulum and ribosomes, Golgi apparatus, and inclusion bodies, as well as a higher number of dense-core vesicles in the animals kept in short photoperiod (LD 8:16) as compared to those in animals kept in long photoperiod (LD 16:8). These observations suggest that restricting the amount of light to which animals are exposed activates pinealocytes of the cotton rat.

Animals↗

PubMed1986

Influence of pinealectomy on the mitotic activity of regenerating adrenal cortex in rats.

There is some evidence that the pineal gland may influence the proliferation of both normal and neoplastic cells. The adrenal cortex has very high capacity for regeneration. Therefore, the effects of pinealectomy on the mitotic activity of regenerating adrenal cortex of rats were studied on the second, seventh and twelfth days following the enucleation of adrenals. Pinealectomy caused a significant decrease in the mitotic index of regenerating adrenal cortex after 2 and 12 days in comparison to sham operated controls.

Adrenal Cortex↗

PubMed1985

Influence of melatonin and serotonin on the number of rat pineal "synaptic" ribbons and spherules in vitro.

Previous studies have shown that the "synaptic" ribbons (SR) and spherules (SS) of the mammalian pineal gland may respond differently under physiological and various experimental conditions. The aim of the present study was to gain insight into the mechanisms that may be responsible for the numerical changes of these organelles during a 24-h cycle. As the possibility exists that the structures are influenced by substances synthesized within the pinealocyte, rat pineal glands were cultured with and without added melatonin or serotonin, using an experimental protocol such that the addition of melatonin and serotonin mimicks the circadian changes of the respective substances within the pineal. The tissue was processed for electron microscopy and the numbers of SR and SS were counted in a unit area of pineal tissue. The results obtained indicate that melatonin added to the incubation medium increases the number of SR in the first half of the night; serotonin decreases SR numbers in the morning. SS numbers, by contrast, decrease following melatonin administration in the afternoon, and increase in the morning following serotonin administration. It thus appears that the numbers of SR and SS are influenced by melatonin and serotonin and that the two structures are regulated by differential, but nevertheless biochemically closely related mechanisms.

Animals↗

PubMed1985

Target specificity and cell surface structures involved in the human cytolytic T lymphocyte response to endothelial cells.

Two long-term cytolytic T lymphocyte (CTL) lines derived from the peripheral blood lymphocytes (PBL) of a single donor were analyzed for target specificity and involvement of cell surface molecules in CTL-target interactions. One line, AH2, was generated after stimulation with B lymphoblastoid cells. Cytolysis by these cells was restricted to targets expressing the appropriate HLA-A2 specificity and was blocked by mAb recognizing CD2, CD3, CD8, LFA-1, and LFA-3. The second line, AE1, was generated after stimulation with cultured endothelial cells derived from human newborn preputial microvessels. These CTL lysed all human target cells tested, except autologous cells and the Class I negative cell line Daudi. In addition, mAb specific for CD2, CD3, and CD8 did not affect cytolysis. Anti-LFA-1 and -LFA-3 mAb blocked cytolysis of B lymphoblastoid targets but not endothelial targets. These results indicate that some CTL utilize as yet uncharacterized cell surface structures for CTL-target interactions.

Antigens, Surface↗

PubMed1984

Effects of experimentally induced chronic hyperprolactinemia on the ultrastructure of pinealocytes in male rats.

The influence on the ultrastructure of pinealocytes of long-term hyperprolactinemia caused by ectopic pituitary transplants and of suppression of prolactin release by bromocriptine was examined morphometrically in male rats. Hyperprolactinemia resulted in an increase in the relative volumes of granular endoplasmic reticulum, vacuoles containing a flocculent material, mitochondria, and lipid droplets. Treatment of grafted rats with bromocriptine reversed the effects of hyperprolactinemia. However, bromocriptine had no apparent influence on the pinealocytes of intact rats. The effects of hyperprolactinemia on the ependymallike secretory process in the pinealocyte were especially pronounced.

Animals↗

PubMed1984

Melatonin inhibits prostaglandin E release from the medial basal hypothalamus of pinealectomized rats.

The effects of pinealectomy and of melatonin administration on prostaglandin E synthesis in the medial basal hypothalamus were studied in male rats. Melatonin treatment significantly decreased prostaglandin E release from the medial basal hypothalamus in pinealectomized rats. The results of the present study suggest that melatonin modulates hypothalamo-hypophyseal function, at least in part, via inhibition of hypothalamic prostaglandin synthesis.

Animals↗