Protection From Ischemic Cell Death by the Induction of Cytoglobin

Methods to reduce beta-cell loss after islet isolation and transplantation must be developed if islet transplantation is to become a preferred treatment for diabetes. Most recent research has focused on the reduction of toxicity from immunosuppressants and the enhancement of revascularization by growth factors such as vascular endothelial growth factor. Cytoglobin is an intracellular oxygen-binding protein found in islet beta-cells, inducible by hypoxia. It is our hypothesis that cytoglobin induction and overexpression may improve survival and function of transplanted islets by preventing ischemic cell death. Lewis rat islets and MIN6 cells were transfected with the cytoglobin gene. Control and transfected cells and islets were held for 4 hours at 20% oxygen before glucose challenge. Another group of islets and cells was held for 4 hours at 20% and then 1% oxygen prior to glucose challenge. Untreated or transfected Lewis rat islets (n = 800) were transplanted beneath the renal capsule of streptozotocin diabetic Lewis rats. In another study, Sprague-Dawley islets were transfected and transplanted into streptozotocin diabetic Lewis rats. Fasting blood glucose was used as an indicator of islet function and survival. Cytoglobin transfected islets and cells retained the ability to secrete insulin at low oxygen concentrations in contrast to controls. Cytoglobin over expression reduced the development of central islet necrosis after 5 days in tissue culture. Cytoglobin inhibited the onset of immunorejection (14 +/- 2 days) as compared with controls islets (5 +/- 2 days). Cytoglobin induction may be a useful adjunct to islet transplantation.

Beta-Cell sparing in transplanted islets by vascular endothelial growth factor

We have reported that vascular endothelial growth factor (VEGF) promotes the revascularization of transplanted islets, thereby reducing the initial number required to prevent diabetes. The present study was undertaken to assess other mechanisms of beta-cell sparing by VEGF. For in vitro studies, islets were cultured for 14 days with versus without 20 ng/mL VEGF. Viability, necrosis, and apoptosis were examined by specific staining (Alcein AM, propidium iodide, and annexin/phosphatidylserine). The effects of VEGF on islets were also examined in a proteomic study. In vivo streptozotocin-treated diabetic Lewis rats received 1000 Lewis or Sprague-Dawley islets beneath the renal capsule. Oxygen levels at the transplant site were monitored by a Clark-type oxygen electrode. Fasting blood glucose served as an indicator of islet survival and function. VEGF enhanced oxygen levels at the transplant site. Syngeneic recipients were euglycemic for over 6 months, whereas control islets failed within 30 to 60 days. VEGF prevented allograft rejection for over 14 days, whereas controls were rejected within 6 to 7 days. Immunostaining suggested that VEGF inhibited the presentation of MHC II antigen and promoted islet survival by the inhibition of necrosis and apoptosis. Our proteomic study suggested VEGF preserved systems required for cellular preservation (heat shock proteins) and insulin secretion. VEGF promotes the preservation of isolated and transplanted islets by a variety of mechanisms, including enhanced oxygenation and inhibition of immune rejection, necrosis, and apoptosis. The provision of exogenous VEGF may be a useful adjunct to islet transplantation.

Pattern generation by two coupled time-discrete neural networks with synaptic depression

Numerous animal behaviors, such as locomotion in vertebrates, are produced by rhythmic contractions that alternate between two muscle groups. The neuronal networks generating such alternate rhythmic activity are generally thought to rely on pacemaker cells or well-designed circuits consisting of inhibitory and excitatory neurons. However, experiments in organotypic cultures of embryonic rat spinal cord have shown that neuronal networks with purely excitatory and random connections may oscillate due to their synaptic depression, even without pacemaker cells. In this theoretical study, we investigate what happens if two such networks are symmetrically coupled by a small number of excitatory connections. We discuss a time-discrete mean-field model describing the average activity and the average synaptic depression of the two networks. Depending on the parameter values of the depression, the oscillations will be in phase, antiphase, quasiperiodic, or phase trapped. We put forward the hypothesis that pattern generators may rely on activity-dependent tuning of synaptic depression.

[Cervix cytology: Cervex Brush versus conventional cotton swab]

Cervical smears should contain endocervical cells to be accepted as representative for a cytologic diagnosis. In this prospective study with 200 women we compared cytologic specimens obtained by Cervex-Brush (100 women) or by conventional cotton-swab (100 women) technique. The incidence of smears containing cylindrical and metaplastic cells was 85% in the Cervex-Brush group and only 58% in the cotton-swab group. We believe that the application of the Cervex-Brush or a similar instrument should result in fewer repeat smears and fewer false-negative smears and thus in an improvement of the cervical cytology.

Size principle and information theory

The motor units of a skeletal muscle may be recruited according to different strategies. From all possible recruitment strategies nature selected the simplest one: in most actions of vertebrate skeletal muscles the recruitment of its motor units is by increasing size. This so-called size principle permits a high precision in muscle force generation since small muscle forces are produced exclusively by small motor units. Larger motor units are activated only if the total muscle force has already reached certain critical levels. We show that this recruitment by size is not only optimal in precision but also optimal in an information theoretical sense. We consider the motoneuron pool as an encoder generating a parallel binary code from a common input to that pool. The generated motoneuron code is sent down through the motoneuron axons to the muscle. We establish that an optimization of this motoneuron code with respect to its information content is equivalent to the recruitment of motor units by size. Moreover, maximal information content of the motoneuron code is equivalent to a minimal expected error in muscle force generation.

Transmitter concentration profiles in the synaptic cleft: an analytical model of release and diffusion

A three-dimensional model for release and diffusion of glutamate in the synaptic cleft was developed and solved analytically. The model consists of a source function describing transmitter release from the vesicle and a diffusion function describing the spread of transmitter in the cleft. Concentration profiles of transmitter at the postsynaptic side were calculated for different transmitter concentrations in a vesicle, release scenarios, and diffusion coefficients. From the concentration profiles the receptor occupancy could be determined using alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor kinetics. It turned out that saturation of receptors and sufficiently fast currents could only be obtained if the diffusion coefficient was one order of magnitude lower than generally assumed, and if the postsynaptic receptors formed clusters with a diameter of roughly 100 nm directly opposite the release sites. Under these circumstances the gradient of the transmitter concentration at the postsynaptic membrane outside the receptor clusters was steep, with minimal cross-talk among neighboring receptor clusters. These findings suggest that for each release site a corresponding receptor aggregate exists, subdividing an individual synapse into independent functional subunits without the need for specific lateral diffusion barriers.