Biomedical subjects

A Kress

Publications and source records attributed to A Kress.

At least 19 recordsLinked to original sources

PubMed2005

Control of vertically coupled InGaAs/GaAs quantum dots with electric fields.

Controllable interactions that couple quantum dots are a key requirement in the search for scalable solid state implementations for quantum information technology. From optical studies of excitons and corresponding calculations, we demonstrate that an electric field on vertically coupled pairs of In(0.6)Ga(0.4)As/GaAs quantum dots controls the mixing of the exciton states on the two dots and also provides controllable coupling between carriers in the dots.

Journal Article↗

PubMed2005

Direct observation of controlled coupling in an individual quantum dot molecule.

We report the direct observation of quantum coupling in individual quantum dot molecules and its manipulation using static electric fields. A pronounced anticrossing of different excitonic transitions is observed as the electric field is tuned. A comparison of our experimental results with theory shows that the observed anticrossing occurs between excitons with predominant spatially direct and indirect character and reveals a field driven transition of the nature of the molecular ground state exciton wave function. Finally, the interdot quantum coupling strength is deduced optically and its dependence on the interdot separation is calculated.

Journal Article↗

PubMed2004

Modeling the spread of annual influenza epidemics in the U.S.: the potential role of air travel.

The role of air travel in the global spread of influenza has been the subject of a significant body of research, but this question has yet to be explored within the U.S. The goal of this research is to explore whether knowledge of U.S. air travel patterns and volumes leads to better forecasting of epidemics. We report the results of a series of simulations for the 1998-1999 through 2000-2001 influenza seasons using a standard compartmental model coupled with air transportation data. These preliminary results suggest that air travel may play an important role in the spread of annual influenza within the U.S., particularly in cities with large air travel volumes.

Aircraft↗

PubMed2002

A computed tomography assessment of femoral and acetabular bone changes after total hip arthroplasty.

Using computed tomography-assisted (CT) osteodensitometry, we studied the bone changes that occurred in 12 patients at 2 weeks and again at 1 year after total hip arthroplasty with insertion of a press-fit acetabular cup and an uncemented femoral tapered stem. There was a greater decrease in full bone density (BD) lateral to the femoral stem when compared to the medial side, at the proximal end of the femur this difference was significant (-22.1% versus -16.2%) ( P<0.001). At the tip of the stem cortical BD had decreased between 2.3% and 1.9% only. Proximal to the cup, the cortical BD increased by about 3.4% ( P< or =0.05), while the full BD decreased markedly by 8% ( P< or =0.001). These changes represent a response to a decrease in regional bone stress induced by the presence of the press-fit implant, and this might be considered as retro-acetabular stress shielding. No focal bone resorption was found.

Acetabulum↗

PubMed2001

Evaluation of a rapid optical immunoassay for influenza viruses (FLU OIA test) in comparison with cell culture and reverse transcription-PCR.

The FLU OIA test was evaluated with 146 throat swab specimens from subjects with a flu-like illness in six Canadian clinics during the 1999-2000 flu season. The rate of positivity of the FLU OIA test (41.5%) was significantly lower than that of cell culture (55.2%) or reverse transcription-PCR (55.9%) during a season in which only influenza A virus was detected.

Adolescent↗

PubMed2001

Oogenesis in the marsupial stripe-faced dunnart, Sminthopsis macroura.

The timetable of oogenesis in Sminthopsis macroura is accelerated like in other marsupials showing relatively early maturation of the female. On the day of parturition (day 0) migration of primordial germ cells to the indifferent gonads has been completed. Follicular growth seems not to correspond to the biphasic pattern, in which oocyte and follicle grow synchronously until antral stages when only the follicle increases in size, but shows a continuous growth of the oocyte and the follicle up to the time of ovulation. During primordial and early primary follicle stage a paranuclear complex is present in the oocyte, consisting mainly of smooth tubules of endoplasmic reticulum. Cortical granules appear early in oocytes in secondary follicles. The conspicuous inclusions in the antral follicle are the clusters of electron-lucent vesicles in the oocyte. These inclusions grow from multivesicular bodies (MVB), which are formed from Golgi and endoplasmic reticulum vesicles. Further increase in the size of MVB involves the incorporation of endocytic vesicles and the coalescence of larger vesicles. The polarized nature of the oocyte at ovulation is due in part to the to accumulation of these vesicles in the cytoplasm opposite the eccentrically placed nuclear material.

Animals↗

PubMed1999

Modulation of C5a-mediated effector functions of human polymorphonuclear leukocytes by tumor necrosis factor alpha and granulocyte macrophage colony-stimulating factor.

At the site of acute inflammation, leukocytes are confronted with multiple mediators which are expected to modulate each other with respect to cell responses to the individual ligand. In the present study, we compared the effects of the classical chemoattractants FMLP, PAF and LTB4, of the chemokine IL-8 and of TNFalpha, GM-CSF, IFN-gamma and IL-1beta on C5a-induced chemotaxis, degranulation, oxidative burst and expression of adhesion molecules of human neutrophils in vitro. Upon preincubation, TNFalpha as well as GM-CSF dose-dependently inhibited C5a-mediated chemotaxis, but augmented the release of elastase as well as respiratory burst activity. The effects of the two cytokines were accompanied by a downregulation of C5a receptors as determined by Scatchard analysis using (125)I-labeled C5a. Compared on a molar basis, TNFalpha was more effective than GM-CSF. C5a-induced expression of beta(2)-integrins was only moderately influenced by TNFalpha and GM-CSF. C5a itself diminished chemotaxis as well as degranulation and oxidative burst in response to a second dose of the same ligand (homologous desensitization), whereas heterologous desensitization by FMLP and IL-8 was restricted to C5a-induced degranulation or not observed (PAF, LTB4]. The cytokine effects are likely to be a consequence of altered C5a receptor expression as well as of postreceptor events. In concert with C5a, certain cytokines may shift neutrophil effector functions from migration to exocytosis, an essential step within the sequence of events in a coordinated inflammatory response.

CD18 Antigens↗

PubMed1996

A comparison of oocyte organelles in Monodelphis domestica with those of other marsupials and eutherians.

This paper reviews the current knowledge of oocyte cytology in marsupials, particularly Monodelphis domestica, and eutherian mammals. Some of the conspicuous features will be described and their function discussed. Despite many fundamental similarities between the oocytes of eutherian mammals and marsupials, some aspects are different (e.g. growth pattern, final size, timetable of cytoplasmic maturation and utilization of storage material during early cleavage stages), when most of the vesicles are extruded into the perivitelline space in marsupials.

Animals↗

PubMed1995

Cytokeratin expression in the developing vagina of the postnatal gerbil (Meriones unguiculatus).

During postnatal development the vaginal epithelium of the Mongolian gerbil is transformed from two to three layers into a stratified, first mucified subsequently keratinized squamous epithelium. Changes in the expression of cytokeratins were studied and the immunohistochemical results compared with the ultrastructural findings at the corresponding stage. The first 10 postnatal days (days pn) were characterized by a moderate, positive immunoreaction for pancytokeratin in all vaginal cell layers. A faint reaction was caused by mAB CK 18.01 against CK 1, 5, 6 and 8. The appearance of mucous granules in the luminal cells after 15 pn seemed to coincide with an increase in cytokeratins. The immunoresponse for pancytokeratin in these cells was very intense compared with the reaction in the basal cell layers. Mucocytes during development and at proestrus were the only cells which reacted faintly positive with mAB against CK 18 alone. The keratinizing epithelium, which differentiates after day 40 pn, reacted strongly positive for pancytokeratin in the keratinizing layers, desquamating, fully keratinized cells, however, showed a negative reaction. The data indicate that mucocytes are not transformed squamous keratinized cells, but represent a cell category with its individual differentiation potential. Vimentin was not expressed. Neither the epithelium of the sinus vagina nor of the Müllerian vagina displayed any response.

Aging↗

PubMed1994

Isolation of granulosa-like cells from the bovine secretory corpus luteum and their characterization in long-term culture.

BACKGROUND: The isolation of cells termed type 5 from the bovine corpus luteum was recently reported. Since these cells were reminiscent of immature granulosa cells, their morphological and functional relationship requires further investigation in view of the novel concept of corpus luteum growth. It suggests that putative stem cells of unknown origin supply the pool of small luteal cells. METHODS: Bovine corpora lutea were mechanically dispersed, cell suspensions separated over a Percoll density gradient, and type 5 cells purified by colony transfer. Granulosa cells were harvested from small-sized antral follicles. Observations were carried out at the light and electron microscopical level. 3 beta-Hydroxy-steroid-dehydrogenase was localized histochemically in addition to intracellular lipid droplets stained with nile red. Immunolocalization was used to study Factor VIII antigen presence, the architecture of the cytoskeleton, as well as the occurrence of neuronal cell adhesion molecules, and of neuronal cadherin-like molecules. The uptake of acetylated low density lipoprotein was examined. As for progesterone concentration, cells were seeded at low density on day zero. Cell numbers and progesterone levels of supernatants were determined on day 10 in culture. RESULTS AND CONCLUSIONS: Type 5 cells behaved morphologically like immature granulosa cells, yet the total cell number and the progesterone concentration differed for type 5 cells compared to granulosa cells. The addition of LH had no influence on the progesterone concentration as seen for either type 5 cells or for granulosa cells. It is concluded that type 5 cells, which were originally mistaken for microvascular endothelial cells, display similarities with immature granulosa cells. Type 5 cells may play a role in renewal of luteal cells.

Animals↗

PubMed1994

Postnatal development of the vaginal epithelium in the Mongolian gerbil (Meriones unguiculatus).

This study examines the normal postnatal (p.n.) development of the Mongolian gerbil's vagina from birth to the age when consistent cyclic changes of the estrus occur. At birth, the Müllerian vagina has a lumen and is lined by a pseudostratified or 2- to 3-layered epithelium. The cells contain large amounts of glycogen. The sinus vagina forms a solid plate and contains hardly any glycogen. During the first few p.n. days the cell layers separate, and the newly formed lumen becomes continuous with the Müllerian vagina. Only a vaginal closure membrane persists. Between p.n. days 10 and 15 the epithelium increases in height reaching 2-5 cell layers. The amount of glycogen diminishes, but in the luminal cells the first mucous granules develop. Leukocyte diapedesis starts, and immature Langerhans cells become discernible. Between p.n. days 18 and 30 the apical cells become mucified, and some shedding of these cells begins. Between p.n. days 36 and 45 bundles of keratin filaments appear in many of the luminal mucous cells intermingled with the mucous granules. In the middle layers keratin filaments, keratohyalin granules and membrane-coating granules indicate the beginning of the keratinization process. Diapedesis of leukocytes may lead to cell aggregations below top layers. By day 50 the shedding of the mucous cell layers reveals the underlying keratinized cell layers which then become exfoliated. The first steps of the estrous cycle show a heterogeneous pattern. At about p.n. day 60 the cycle becomes established.

Animals↗

PubMed1992

Postnatal development of the cervical epithelium in the Mongolian gerbil.

This study analyzes the postnatal development of the Mongolian gerbil's cervical epithelium, in relation to its future functions. In the newborn gerbil the outline of the cervical canal is smooth, showing hardly any signs of folding. The epithelium consists of 1 to 3 layers. The cervical cells have rounded apices of regular outline and contain a large amount of glycogen. The first secretory products of specific mucus type appear about day 23 postnatally (p.n.). Initially two types of vesicles can be identified, as compared with only one type in sexually mature animals. The process of mucification begins in the vagina and the external os of the cervix and spreads towards the cervical horns. The cervical canal, besides growing longer, becomes increasingly folded during development. At about day 50 p.n., with the onset of sexual maturity, an upper endocervix and a lower ectocervix can be distinguished within the cervical canal. In the fully mature animal, the endocervix consists of 4 to 5 layers, in which apical cells mucify and exfoliate. In the ectocervix, the epithelium can be divided into 4 to 5 basal layers and 5 to 7 upper layers which mucify, keratinize, and exfoliate, according to the cyclic phases of the vagina. Diapedesis of leucocytes through the epithelium starts around day 45 p.n.

Age Factors↗

PubMed1992

Ultrastructural aspects of oocyte growth in the marsupial Monodelphis domestica (grey short-tailed opossum).

The growth of the opossum Monodelphis oocyte does not correspond to the strict biphasic pattern so far described in eutherians and marsupials. The oocyte increases appreciably in size during the last stage of antral follicle development. During the primordial and primary follicle stage Balbiani bodies or paranuclear complexes are not detectable in Monodelphis oocytes. Organelles are randomly distributed. In addition to the nucleolus, perichromatin and ribonucleoprotein particles are other intranuclear structures which occur as regular components in the early Monodelphis oocyte. Clusters of particles are mostly seen in close association with the nuclear envelope. Similar material has been encountered in the cytoplasm as a type of freely-existing 'nuage' material but never as mitochondria-associated 'nuage' or 'cement'. Both types of particles, intranuclear and cytoplasmic, disappear by the time antral follicle formation begins. Mitochondria are at first of the typical transformed shape seen in most mammalian oocytes. They are large, round or oval in outline with a few, often arched, cristae and a light matrix. During the primary follicle stage, mitochondrial size and complexity decrease and the matrix becomes electron dense. A close relationship between mitochondria and endoplasmic reticulum appears early in the primordial and later in the primary follicle oocyte. Regularly detected structures in the ooplasm of preantrum oocytes are paired or 'confronting' cisternae of endoplasmic reticulum, which are lamellar complexes comprised of 2 or more parallel cisternae with intervening electron-dense material. The most conspicuous inclusions in the Monodelphis oocytes of the tertiary and graafian follicles are vesicles. All other organelles are confined to the peripheral zone of the oocyte. Golgi and endoplasmic vesicles both take part in the formation of multivesicular bodies which seems to be the starting point for the vesicle accumulation. Further increase in size involves the incorporation of endocytotic vesicles and the coalescence of larger vesicles. Ordinary fixation procedure leave the vesicles empty. Cortical granules are found only in small numbers.

Animals↗

PubMed1991

Healing of the transected anterior cruciate ligament in the rabbit.

Healing of the anterior cruciate ligament was studied in 170 male rabbits. One group included immature animals that had open epiphyses, and a second group consisted of only mature animals. In one knee of each animal, the anterior cruciate ligament was transected either completely or partially, and in the contralateral knee a sham operation was carried out. Mechanical testing and histological studies of the ligaments were done immediately postoperatively and at two weeks, six weeks, three months, and one year. As we expected, there was no regeneration after complete transection of the anterior cruciate ligament, and all of the animals in which this procedure was done had severe osteoarthrosis of the joint at three months. Postoperatively, the partially sectioned ligaments exhibited one-third of the strength of the ligaments on the side on which the sham operation had been done in the immature animals and one-fourth of the strength of the ligaments on the side on which the sham operation had been done in the mature animals. Subsequently, there was secondary complete rupture of 20 per cent of the partially sectioned ligaments. The remaining 80 per cent of the partially sectioned ligaments were clearly weaker two weeks after the operation than immediately postoperatively, but this was also true on the side on which the sham operation had been done. At six weeks, the initial postoperative strength of the partially sectioned ligaments had been regained. At one year, the ligaments of the immature animals were two-thirds as strong as those on the contralateral side, and those of the mature animals were three-fourths as strong as those on the contralateral side. The ligaments were markedly elongated, especially in the mature animals. At three months, stiffness of the ligaments returned to normal. Histologically, the defect was filled with tissue that was still somewhat different from normal ligamentous tissue.

Aging↗

PubMed1990

Postnatal development of the Mongolian gerbil uterus.

The postnatal development of the gerbil uterus has been investigated. Special attention has been paid to the luminal surface epithelium. In the newborn gerbil, the uterus contains already some fluid and the uterine luminal epithelium seems to possess mechanisms for the regulation of the fluid contents. Among them are apical protrusions and microvilli, endo- and exocytotic vesicles of different nature, highly active Golgi complexes and dilated rER vesicles and also very distinct junctional complexes between the cells in the apical areas.

Animals↗

PubMed1990

Postnatal development of the Mongolian gerbil uterine glands.

The development of gerbil uterine glands has been described. Gland formation starts about day 6 postnatally (p.n.). At day 10 p.n. the glandular lumen contains already some fluid, and the glandular cells are in an activated state. The apical shape of the glandular cells depends mainly on the width of the lumen. Secretory vesicles in early developmental stages are electron-lucent. As sexual maturity is reached, secretory granules become electron-dense. This change in secretory granular structure indicates a change in the quality of uterine gland fluid.

Animals↗

PubMed1989

A purification method for apolipoprotein A-I and A-II.

Apolipoproteins A-I and A-II were isolated from precipitates obtained by cold ethanol fractionation of human plasma. The starting material used in this report was precipitate B of the Kistler and Nitschmann method which corresponds approximately to fraction III of the Cohn and Oncley procedure. Through the use of urea, chloroform, and ethanol in appropriate concentrations, apolipoproteins A-I and A-II were isolated by a simple extraction technique avoiding time-consuming ultracentrifugation. Starting from 10 g of centrifuged precipitate B, approximately 100 mg of apolipoprotein A-I and 10 mg of apolipoprotein A-II were obtained. When incubated with normal human or rabbit plasma, both apolipoproteins were readily incorporated into high-density lipoproteins. Apolipoprotein A-I obtained by the cold ethanol method activated lecithin-cholesterol acyltransferase to the same extent as apolipoprotein A-I prepared by the classical flotation method. Apolipoprotein A-II had no such properties by itself, but was capable of potentiating lecithin-cholesterol acyltransferase activity of apolipoprotein A-I.

Apolipoprotein A-I↗

PubMed1989

Scanning microscopy of the developing vagina in postnatal gerbils.

Scanning electron microscopy of postnatally developing gerbil vagina (birth to maturity) shows that longitudinal folds form prior to transverse folds; the process of fold formation is initiated on the dorsal wall and proceeds ventrally. From days 1 to 7 postnatally, the vaginal epithelium is composed of either flat or bulging cells, depending on the vaginal region. The luminal cell surface is covered with uniform stubby microvilli and solitary cilia. Between days 9 and 20, the flat cells with distinct cell boundaries spread toward more proximal areas, leading to the formation of mixed patches of cells with flat or rounded apices. Individual elongated microvilli or tufts of forked microvilli may sprout from their surfaces. Solitary cilia gradually disappear. The transition from immature to mature vaginal epithelium starts around day 20, when individual cells recess below the level of neighboring cells. This process spreads throughout the vagina during the following days, reflecting local changes in the subsurface layers of the epithelium preparatory to exfoliation. Around day 40 the actual exfoliation of the luminal cell layer starts. By this time the surface characteristics of many of the desquamating cells have changed. In addition to microvilli, microridges are being formed. The process of exfoliation is finished by about day 60. The newly appearing cell layers now transform into typical cornified cells of the cycling vaginal epithelium.

Animals↗