Suppression of crosstalk in multielectrode arrays with local shielding.

Electrical crosstalk can constrain the performance of multielectrode arrays in electro- and neurophysiology, in terms of both stimulation and recording. This is especially so at high electrode density, desirable for spatiotemporal mapping of bioelectrical signals from multiple cells. Channel interference due to crosstalk is currently only partially addressed, via continuous interleaved sampling or post-data acquisition spike sorting. Here, we show that a locally-shielded electrode architecture significantly suppresses crosstalk, and enables multi-site recording at high electrode density without the need for spike sorting. Arrays of shielded electrodes, prepared by micro- and nanofabrication techniques in a vertically-oriented coaxial geometry, demonstrate at least a 400 times improvement in spatial density over the unshielded case.

An extended core nanocoax pillar architecture for enhanced molecular detection.

Biosensors that incorporate nanomaterials and nanofabrication techniques enable molecular detection of chemical and biological macromolecules with a high degree of specificity and ultrasensitivity. Here, we present a novel fabrication process that yields a nanostructure capable of detecting biological macromolecules. The extended core nanocoax (ECC) structure builds on a previously reported nanocoaxial-based sensor. The fabrication of the device incorporates an extended inner pillar, with controllable extension above the annulus and into the surrounding solution. This new design eliminates structural constraints inherent in the original nanocoax architecture. We also provide results demonstrating improvement in biosensing capability. Specifically, we show the capability of the new architecture to detect the B subunit of the Vibrio cholerae toxin at improved sensitivity (100 pg/ml) in comparison to optical enzyme-linked immunosorbant assay (1 ng/ml) and previously reported coaxial nanostructures (2 ng/ml).

Modelling a tethered mammalian sperm cell undergoing hyperactivation.

The beat patterns of mammalian sperm flagella can be categorised into two different types. The first involves symmetric waves propagating down the flagellum with a net linear propulsion of the sperm cell. The second, hyperactive, waveform is classified by vigorous asymmetric waves of higher amplitude, lower wavenumber and frequency propagating down the flagellum resulting in highly curved trajectories. The latter beat pattern is part of the capacitation process whereby sperm prepare for the prospective penetration of the zona pellucida and fusion with the egg. Hyperactivation is often observed to initiate as sperm escape from epithelial and ciliary bindings formed within the isthmic regions of the female oviducts, leading to a conjecture in the literature that this waveform is mechanically important for sperm escape. Hence, we explore the mechanical effects of hyperactivation on a tethered sperm, focussing on a Newtonian fluid. Using a resistive force theory model we demonstrate that hyperactivation can indeed generate forces that pull the sperm away from a tethering point and consequently a hyperactivated sperm cell bound to an epithelial surface need not always be pushed by its flagellum. More generally, directions of the forces generated by tethered flagella are insensitive to reductions in beat frequency and the detailed flagellar responses depend on the nature of the binding at the tethering point. Furthermore, waveform asymmetry and amplitude increases enhance the tendency for a tethered flagellum to start tugging on its binding. The same is generally predicted to be true for reductions in the wavenumber of the flagellum beat, but not universally so, emphasising the dynamical complexity of flagellar force generation. Finally, qualitative observations drawn from experimental data of human sperm bound to excised female reproductive tract are also presented and are found to be consistent with the theoretical predictions.

Recovery of limited-extent images aliased because of spectral undersampling.

In imaging situations where observations are made in spatial-frequency space, it is often desirable to lower the number of observations to fewer than that imposed by the Nyquist criterion. It is shown that patterns of regular spectral undersampling lead to aliasing that can be partially eliminated from some regions of a limited-extent image. An algorithm is presented for determining which regions are recoverable and which are not for a given pattern. Noniterative recovery, analogous to that proposed by Walsh and Nielsen-Delaney [J. Opt. Soc. Am. A 11, 572 (1994)], is shown to be feasible in cases of regular undersampling. The work has particular relevance to magnetic resonance imaging and aperture synthesis telescopy.

Contraception in the patient with liver disease.

Selection of a method of contraception in patients with liver disease can be complicated. Tubal ligation should be considered in the setting of chronic liver disease for those patients who have completed families. Multiple reversible methods of contraception are currently available but may affect hepatic disease. Estrogen-containing contraceptive methods are contraindicated in patients with acute liver disease. Progestin contraceptives appear to be safe and multiple delivery systems are available. With rare exception, barrier methods and the intrauterine device may be offered as alternative methods.

PIP: Women with liver disease require careful contraceptive management. Of particular salience is the impact of sex steroids on liver function. If patients with chronic liver disease have completed their families, tubal ligation should be considered. Estrogen-containing oral contraceptives have been associated with cholestasis and development of hepatic adenoma and are contraindicated in women with acute liver disease. Progestin-containing hormonal methods appear to be safe, however. IUDs or barrier methods such as condoms and diaphragms can be selected, but they have lower efficacy rates.

Mesenchymal stem cell surface antigen SB-10 corresponds to activated leukocyte cell adhesion molecule and is involved in osteogenic differentiation.

Bone marrow contains a rare population of mesenchymal stem cells (MSCs) capable of giving rise to multiple mesodermal tissues including bone, cartilage, tendon, muscle, and fat. The cell surface antigen recognized by monoclonal antibody SB-10 is expressed on human MSCs but is lost during their developmental progression into differentiated phenotypes. Here we report on the immunopurification of the SB-10 antigen and its identification as activated leukocyte-cell adhesion molecule (ALCAM). Mass spectrometry establishes that the molecular mass of ALCAM is 80,303 +/- 193 Da and that it possesses 17,763 +/- 237 Da of N-linked oligosaccharide substituents. Molecular cloning of a full-length cDNA from a MSC expression library demonstrates nucleotide sequence identity with ALCAM. We also identified ALCAM homologs in rat, rabbit, and canine MSCs, each of which is over 90% identical to human ALCAM in their peptide sequence. The addition of antibody SB-10 Fab fragments to human MSCs undergoing osteogenic differentiation in vitro accelerated the process, thereby implicating a role for ALCAM during bone morphogenesis and adding ALCAM to the group of cell adhesion molecules involved in osteogenesis. Together, these results provide evidence that ALCAM plays a critical role in the differentiation of mesenchymal tissues in multiple species across the phylogenetic tree.

Assessment of argyrophilic nucleolar organizer region quantification in benign and malignant bone tumors.

Quantification of argyrophilic nucleolar organizer regions has been proposed as a technique that may aid in diagnosing and predicting the biologic behavior of a variety of neoplasms. A 1-step silver staining technique was used to identify and quantify argyrophilic nuclear organizer regions in a series of 96 bone tumor specimens. Malignant bone tumors had a higher mean argyrophilic nuclear organizer region count (3.05 +/- 0.82) than giant cell tumors (1.39 +/- 0.14, p < 0.001) and benign bone tumors (1.51 +/- 0.42, p < 0.001). Despite these differences in mean counts, an overlap of argyrophilic nuclear organizer region scores was observed in some benign and malignant cases. The argyrophilic nuclear organizer region counts of the osteosarcomas were analyzed to determine whether they correlated with tumor behavior. The mean argyrophilic nuclear organizer region count of specimens from patients in whom metastatic disease developed was not significantly different than that of patients who remained disease free.

Retinoic acid stimulates interstitial collagenase messenger ribonucleic acid in osteosarcoma cells.

The rat osteoblastic osteosarcoma cell line UMR 106-01 secretes interstitial collagenase in response to retinoic acid (RA). The present study demonstrates by Northern blot analysis that RA causes an increase in collagenase messenger RNA (mRNA) at 6 h, which is maximal at 24 h (20.5 times basal) and declines toward basal level by 72 h. This stimulation is dose dependent, with a maximal response at 5 x 10(-7) M RA. Nuclear run-on assays show a greater than 20-fold increase in the rate of collagenase mRNA transcription between 12-24 h after RA treatment. Cycloheximide blocks RA stimulation of collagenase mRNA, demonstrating the need for de novo protein synthesis. RA not only causes an increase in collagenase secretion, but is known to decrease collagen synthesis in UMR 106-01 cells. In this study, the increase in collagenase mRNA is accompanied by a concomitant decrease in the level of alpha 1(I) procollagen mRNA, which is maximal at 24 h (70% decrease), with a return to near-control levels by 72 h. Nuclear run-on assays demonstrated that the decrease in alpha 1 (I) procollagen expression does not have a statistically significant transcriptional component. RA did not statistically decrease the stability of alpha 1 (I) procollagen mRNA (calculated t1/2 = 8.06 +/- 0.30 and 9.01 +/- 0.62 h in the presence and absence of RA, respectively). However, transcription and stability together probably contribute to the major decrease in stable alpha 1 (I) procollagen mRNA observed. Cycloheximide treatment inhibits basal level alpha 1 (I) procollagen mRNA accumulation, demonstrating the need for on-going protein synthesis to maintain basal expression of this gene.

Prostanoid-induced expression of matrix metalloproteinase-1 messenger ribonucleic acid in rat osteosarcoma cells.

Individual prostanoids have distinct potencies in activating intracellular signaling pathways and regulating gene expression in osteoblastic cells. The E-series prostaglandins (PGs) are known to stimulate matrix metalloproteinase-1 (MMP-1) synthesis and secretion in certain rodent and human osteoblastic cells, yet the intracellular events involved remain unclear. To further characterize this response and its signal transduction pathway(s), we examined prostanoid-induced expression of the MMP-1 gene in the rat osteoblastic osteosarcoma cell line UMR 106-01. Northern blot analysis demonstrated that prostaglandin E2 (PGE2) and PGE1 were very potent stimulators (40-fold) of MMP-1 transcript abundance, PGF2 alpha and prostacyclin were weak stimulators (4-fold), and thromboxane-B2 had no effect. The marked increase in MMP-1 transcript abundance after PGE2 treatment was first detected at 2 h, became maximal at 4 h, and persisted beyond 24 h. This response was dose dependent and elicited maximal and half-maximal effects with concentrations of 10(-6) and 0.6 x 10(-7) M, respectively. Cycloheximide, a protein synthesis inhibitor, completely blocked this effect of PGE2, suggesting that the expression of other genes is required. Nuclear run-on experiments demonstrated that PGE2 rapidly activates MMP-1 gene transcription, with a maximal increase at 2-4 h. The second messenger analog, 8-bromo-cAMP, mimicked the effects of PGE2 by stimulating a dose-dependent increase in MMP-1 messenger RNA (mRNA) levels, with a maximal effect quantitatively similar to that observed with PGE2. Thus, in UMR 106-01 cells, different prostanoids have distinct potencies in stimulating MMP-1 mRNA abundance. Our data suggest that PGE2 stimulation of MMP-1 synthesis is due to activation of MMP-1 gene transcription and a subsequent marked increase in MMP-1 mRNA abundance. This effect is dependent on de novo protein synthesis and is mimicked by protein kinase-A activation.

Confocal imaging of a stratified medium.

The confocal imaging of stratified media (for example, thin-film structures) is investigated. A simple model is introduced for the imaging of a single layer in order to explore the axial resolution attainable. A rigorous model is also described and compared with experimental results from thin surface films. A theoretical treatment of imaging of stratified media with a continuously varying refractive index is presented, and the inverse problem of reconstructing the refractive-index profile from a confocal image is discussed.

Is "wheelchair wrist drop" a new syndrome to watch for?

All in all, the present-day wheelchair is a poor place for nursing home patients to spend any length of time. Unfortunately, though, if you walk through a nursing home, you will find that a large number of patients spend many hours sitting in wheelchairs. We feel that the increased use of a wheelchair for daytime and evening sitting was a prominent causative factor of the radial nerve paralysis in the cases reported here, and we suspect that this syndrome is being overlooked. Since early diagnosis and prompt therapy may favorably improve the outcome, and awareness of the problem may prevent it altogether, we urge physicians to be wary of this apparently new syndrome and take precautionary measures where applicable.

Toxic shock-like syndrome associated with necrotizing Streptococcus pyogenes infection.

Two patients with toxic shock-like syndrome are presented. Both patients had necrotizing cellulitis due to Streptococcus pyogenes, and both patients required extensive surgical debridement. The association of Streptococcus pyogenes infection and toxic shock-like syndrome is discussed.

A simulator-based approach to training in aeronautical decision making.

The effectiveness of a simulator-based approach to training pilot skills in risk assessment and decision making was evaluated in a sample of pilots enrolled in a university aviation science program. The 16 experimental group subjects received 4 hours (h) of classroom instruction designed to enhance pilot judgment skills, followed by 4 simulated cross-country flights during which several critical inflight events occurred. Subjects in the control group received classroom instruction in basic instrument flying, followed by simulator sessions emphasizing instrument flight. Measures of pilot judgment were obtained on all subjects before and after the training, and subjects in the experimental judgment-trained group performed significantly better on the posttraining simulation than did control group subjects. The findings suggest that significant gains in pilot decision-making skill can be obtained through the use of the judgment training materials along with simulator practice.

The nuclear power industry in the United States: status and projections.

One sixth of the electricity in the United States is now being generated in nuclear power plants, a remarkable achievement for a technology whose basic nuclear reaction was not even known 50 years ago. On the other hand, many of the nation's electric utilities are experiencing great difficulties completing the construction of their nuclear plants; 41 partially constructed plants have been abandoned. Those abandoned plants plus about 110 in operation and 15 still to be completed comprise the first generation of nuclear power plants in the United States. When, and even if, there will be a second generation is much in doubt. Data are presented to show that the absence of a second generation of nuclear plants will place large demands on the fossil fuels, with attendant high energy prices and high environmental costs the expected outcome. It appears that the future will bring large economic forces to start new orders for nuclear plants. On the other hand, the opposing institutional forces appear equally strong. Among the problems creating these institutional forces are the difficulty the United States is having in finding a politically acceptable approach to nuclear waste disposal and the vulnerability of power plant builders and operators to litigation and high financial risk. At present, the issue of a second generation of nuclear plants is stalemated.

Effects of bilayer cholesterol on human erythrocyte hexose transport protein activity in synthetic lecithin bilayers.

In this study, we describe the effects of altered bilayer cholesterol content on reconstituted, protein-mediated sugar transport. The system used was the human erythrocyte sugar transporter (band 4.5) reconstituted into the bilayers of large unilamellar vesicles. Vesicle preparations were formed from synthetic lecithins whose bilayer cholesterol content ranged from 0 to 50 mol %. Transport was measured by microturbidimetric analysis over the temperature range of 0-65 degrees C while bilayer physical state was characterized by differential scanning calorimetry. Reconstituted transport activity was irreversibly lost between 62 and 65 degrees C. The Km for reconstituted transport was found to increase only slightly with increasing temperature and was not systematically affected by bilayer cholesterol content. The most striking observation of this study is that over certain critical cholesterol concentrations, as little as a 2.5% change in bilayer cholesterol can result in as much as a 100-fold change in Vmax per reconstituted protein. Our findings run counter to the view that increasing bilayer cholesterol content monotonically transforms a membrane into a state of "intermediate fluidity". Abrupt, cholesterol-induced bilayer reorganizations occurring at 15-20 and 30 mol % bilayer cholesterol are markedly reflected in altered sugar transport rates. Increasing the cholesterol content of crystalline distearoyllecithin bilayers inhibits the activity of the reconstituted transporter. It is apparent from these studies that bilayer "fluidity" is neither the sole nor a major determinant of the Indeed, we find the effect of cholesterol on transport activity is independent of its ability to fluidize membranes.

Effect of bilayer cholesterol content on reconstituted human erythrocyte sugar transporter activity.

The influence of altered bilayer cholesterol content on the catalytic activity of the human red cell hexose transporter was examined by reconstitution of the transport protein (band 4.5) into bilayers of large unilamellar vesicles formed from dipalmitoyl lecithin and varying amounts of cholesterol. The physical state of the bilayers was characterized by differential scanning calorimetry. The major findings are as follows: changes in bilayer phase behavior occur at membrane cholesterol levels of 15 to 20 mol % and 30 to 40 mol %; and the catalytic activity of the reconstituted transporter (Vmax/transporter) correlates with bilayer phase behavior. In crystalline bilayers, this is seen as an abrupt, stimulation of activity at 15 mol % cholesterol (which is reversed at 17.5 mol %) and a gradual acceleration of activity between 30 to 40 mol % cholesterol. In fluid bilayers (where activity is high), activity is unaffected by 10, 20, and 30 mol % cholesterol. However, 12.5 and 17.5 mol % cholesterol reduce activity by 100-fold. These studies demonstrate that small changes in bilayer cholesterol content result in drastic alterations in transporter activity. Transporter sensitivity to cholesterol is a complex rather than monotonic function of bilayer cholesterol content and appears to be primarily determined by bilayer composition rather than by bilayer "fluidity."