Morphological and molecular expression patterns of neural precursor cells derived from human fetal spinal cord in two-, three-dimensional, and organoid culture environments.

Recently, interest in three-dimensional (3D) cell or tissue organoids that may, in vitro, overcome not only the practical problems associated with fetal tissue transplantation, but also provide a potential source for the regeneration of injured spinal cords, has been increasing steadily. In this study, we showed that human neural precursor cells (hNPCs) derived from the fetal spinal cord could be incubated in serum free medium at two dimensional (2D), three dimensional (3D) and tissue organoid-systems. Additionally, we investigated morphological changes over time along with the expression of proteoglycans, collagen, or myelin in 2D, 3D and tissue-like organoids. 2D cells exhibited a spindle-shaped morphology with classic hill and valley growth patterns, while 3D cells grew as clusters of undifferentiated cells and cell sheets (tissue organoids) that gradually rolled up like a carpet without forming a circular cell mass. Immunostaining was performed to demonstrate the expression of TUJ-1, MAP-2, GAD 65/67 and ChAT in 2D cells or tissue-like organoids, which stained positively for them. In addition, we observed the immunoreactivity of HNu, NG2, TUJ-1, and GFAP in tissue-like organoids. The organoid culture system studied in our work may be used as therapeutic agents for spinal cord injury (SCI), and as raw materials needed for development of new medicines to improve human responses and cure diseases.

Nonlinear Diffusion for Bacterial Traveling Wave Phenomenon.

The bacterial traveling waves observed in experiments are of pulse type which is different from the monotone traveling waves of the Fisher-KPP equation. For this reason, the Keller-Segel equations are widely used for bacterial waves. Note that the Keller-Segel equations do not contain the population dynamics of bacteria, but the population of bacteria multiplies and plays a crucial role in wave propagation. In this paper, we consider the singular limits of a linear system with active and inactive cells together with bacterial population dynamics. Eventually, we see that if there are no chemotactic dynamics in the system, we only obtain a monotone traveling wave. This is evidence that chemotaxis dynamics are needed even if population growth is included in the system.

On the modelling of spatially heterogeneous nonlocal diffusion: deciding factors and preferential position of individuals.

We develop general heterogeneous nonlocal diffusion models and investigate their connection to local diffusion models by taking a singular limit of focusing kernels. We reveal the link between the two groups of diffusion equations which include both spatial heterogeneity and anisotropy. In particular, we introduce the notion of deciding factors which single out a nonlocal diffusion model and typically consist of the total jump rate and the average jump length. In this framework, we also discuss the dependence of the profile of the steady state solutions on these deciding factors, thus shedding light on the preferential position of individuals.

Evolution of dietary diversity and a starvation driven cross-diffusion system as its singular limit.

We rigorously prove the passage from a Lotka-Volterra reaction-diffusion system towards a cross-diffusion system at the fast reaction limit. The system models a competition of two species, where one species has a more diverse diet than the other. The resulting limit gives a cross-diffusion system of a starvation driven type. We investigate the linear stability of homogeneous equilibria of those systems and rule out the possibility of cross-diffusion induced instability (Turing instability). Numerical simulations are included which are compatible with the theoretical results.

Dose-Dependent Cytotoxicity of Gold Nanoparticles on Human Neural Progenitor Cells and Rat Brain.

Gold nanoparticles (GNPs) are utilized as diagnostic and therapeutic tools to detect and treat human disease. Researchers in the field of nanotoxicity are working to determine the physicochemical properties of nanoparticles that lead to toxicity in an effort to establish safe design rules. In this study, we performed the MTT and terminal transferase dUTP nick end labeling (TUNEL) assays to verify the cytotoxicity of GNPs on rat brain tissue and human neural progenitor cells (NPCs). As results, we observed that GNPs induced apoptosis in NPCs. NPCs were markedly damaged following the administration of 200 µM and 2 mM GNPs, whereas 2 µM GNPs showed slightly increased damage relative to that of the control. In addition, TUNEL-positive cells were densely distributed at regions surrounding the GNP injection site in the brain 7 days after the GNPs injection. During long-term GNPs exposure, TUNEL-positive cells were rarely observed in the cerebral cortex. In this study, we observed that apoptosis increased in proportion to GNP concentrations in the brain and in cultivated NPCs. These result suggest that large GNPs (<100 nm) are toxic and that the cytotoxicity increased as the concentration of GNPs increased in NPCs or in the brain.

Predator-prey equations with constant harvesting and planting.

We propose Lotka-Volterra type predator-prey equations which include small constant terms. Depending on its sign, the constant may model various things. To see the effect of the constants clearly we drop all other functional responses except the ones in the original Lotka-Volterra equations. We add a small negative constant for the harvesting or the Allee effect. A positive constant is added to model the planting or external influx. We find the predator-prey equations with constant terms produce most of dynamic and static patterns observed from other predator-prey models with various functional responses.

Dispersal towards food: the singular limit of an Allen-Cahn equation.

The effect of dispersal under heterogeneous environment is studied in terms of the singular limit of an Allen-Cahn equation. Since biological organisms often slow down their dispersal if food is abundant, a food metric diffusion is taken to include such a phenomenon. The migration effect of the problem is approximated by a mean curvature flow after taking the singular limit which now includes an advection term produced by the spatial heterogeneity of food distribution. It is shown that the interface moves towards a local maximum of the food distribution. In other words, the dispersal taken in the paper is not a trivialization process anymore, but an aggregation one towards food.

A Discrete Velocity Kinetic Model with Food Metric: Chemotaxis Traveling Waves.

We introduce a mesoscopic scale chemotaxis model for traveling wave phenomena which is induced by food metric. The organisms of this simplified kinetic model have two discrete velocity modes, [Formula: see text] and a constant tumbling rate. The main feature of the model is that the speed of organisms is constant [Formula: see text] with respect to the food metric, not the Euclidean metric. The uniqueness and the existence of the traveling wave solution of the model are obtained. Unlike the classical logarithmic model case there exist traveling waves under super-linear consumption rates and infinite population pulse-type traveling waves are obtained. Numerical simulations are also provided.

Decoding intravesical pressure from local field potentials in rat lumbosacral spinal cord.

Chronic monitoring of intravesical pressure is required to detect the onset of intravesical hypertension and the progression of a more severe condition. Recent reports demonstrate the bladder state can be monitored from the spiking activity of the dorsal root ganglia or lumbosacral spinal cord. However, one of the most serious challenges for these methods is the difficulty of sustained spike signal acquisition due to the high-electrode-location-sensitivity of spikes or neuro-degeneration. Alternatively, it has been demonstrated that local field potential recordings are less affected by encapsulation reactions or electrode location changes. Here, we hypothesized that local field potential (LFP) from the lumbosacral dorsal horn may provide information concerning the intravesical pressure. LFP and spike activities were simultaneously recorded from the lumbosacral spinal cord of anesthetized rats during bladder filling. The results show that the LFP activities carry significant information about intravesical pressure along with spiking activities. Importantly, the intravesical pressure is decoded from the power in high-frequency bands (83.9-256 Hz) with a substantial performance similar to that of the spike train decoding. These findings demonstrate that high-frequency LFP activity can be an alternative intravesical pressure monitoring signal, which could lead to a proper closed loop system for urinary control.

Evolution of Dispersal with Starvation Measure and Coexistence.

Many biological species increase their dispersal rate if starvation starts. To model such a behavior, we need to understand how organisms measure starvation and response to it. In this paper, we compare three different ways of measuring starvation by applying them to starvation-driven diffusion. The evolutional selection and coexistence of such starvation measures are studied within the context of Lotka-Volterra-type competition model of two species. We will see that, if species have different starvation measures and different motility functions, both the coexistence and selection are possible.

Cytotoxicity of gold nanoparticles in human neural precursor cells and rat cerebral cortex.

Nanoparticles are promising tools for the advancement of drug delivery, medical imaging, and as diagnostic sensor. Medical nanodevices should develop miniaturization, because it would be injected into a human body. Gold nanoparticles (GNPs) with different sizes and shapes have therapeutic potential as a result of their small size, robust nature, excellent biocompatibility and optical properties. However, the application of GNPs as medical nanodevices it is necessary to know the biodegradation, biocompatibility, and development of surface coating which avoid the accumulation of nanoparticles. In this study, we carry out an in vitro toxicity and in vivo gene expression study using two kinds of GNPs. We found that GNPs toxicity is dependent on the dose or size administrated after the injected GNPs into the brain, and small particle size GNPs appeared more nestin expression compared to large particle size at short term implantation. These findings of toxicity of GNPs may play an important role in development of in vivo tools for the safety of GNPs.

Comparison of collagen characteristics of sea- and freshwater-rainbow trout skin.

Proximate composition, volatile basic nitrogen content, and concentrations of collagen in skin samples from either sea- (S-RT) or freshwater-rainbow trout (F-RT) were characterized and compared, to assess the effect of the sea or freshwater habitat on these parameters. Results of amino acid composition, sodium dodecyl sulfate-polyacrylamide gel electrophoresis, thermal denaturation assay and Fourier transform infrared (FT-IR) spectroscopy of acid-soluble collagens were comparable between the two sample sets. Both acid-soluble collagens from sea- and freshwater-rainbow trout skins contained glycine as the major amino acid and high alanine, proline, and hydroxyproline contents, and was found to be predominantly composed of α1-, α2-, and ß-chains. FT-IR spectra of ASCs from S-RT and F-RT skins were quite similar. These findings suggest that different rainbow trout habitats (seawater and freshwater) do not affect amino acid composition and molecular weight properties of ASCs from S-RT and F-RT skins.

Processing optimization of restructured jerky from sea rainbow trout frame muscle.

This study determined optimal drying temperature and time on the moisture content, hardness, and overall sensory acceptance of restructured jerky from sea rainbow trout frame muscle (RJ-SRTF) using response surface methodology. The optimal drying conditions with respect to the above variables were 67.2°C for drying temperature and 8.6 h for drying time. The predicted values of response optimal conditions were 18.8 g/100 g for moisture content, 495.8 g/cm2 for hardness, and a score of 7.2 for overall sensory acceptance. The actual values obtained in this experiment were 19.1±0.6 g/100 g for moisture content, 453.9±91.0 g/cm2 for hardness, and a score of 7.4±0.5 for overall sensory acceptance. Both actual and predicted values were nearly identical. In conclusion, the models are adequately fitted to experimental data and suitable for optimization.

Cytotoxicity of Gold Nanorods and Nanowires on Cultivated Neural Precursor Cells.

Given the emergence of nanotherapeutics and nanodiagnostics as key tools in today's medicine, it has become of critical importance to define the interactions of nanomaterials with biological systems. The biomedical applications of nanoparticles (NPs) in chemical sensing, biological imaging, drug delivery, photothermal therapy and cancer treatment have been demonstrated. Gold NPs as new biomedical tools are the focus of research due to their ease of synthesis, chemical stability and unique optical properties. Therefore, there is a need to establish the toxicity, side effects and safety of gold NPs for human applications. To study the in vitro cytotoxicity of gold NPs, we performed MTT assay using two types of gold NPs such as gold nanorods (GNRs) and gold nanowires (GNWs). The percentage cytotoxicity of damaged neural precursor cells (NPCs) that were treated with 100 mg GNRs was 97.5±3.9%; and proportion of damaged NPCs following the administration of the same dose of GNWs was 98.8±0.3%. The cytotoxicity of 10 mg GNRs in NPCs was 54.4±8.3%, whereas it was 98.7±0.6% for the same dose of GNWs. Then, to verify that gold NPs induced apoptotic cell death in NPCs, the LIVE/DEAD Viability/Cytotoxicity assay was performed. We observed that cell death of NPCs increased with an increase in quantity of both types of gold NPs. Cell viability assessed the overall dose-dependent toxicity of NPs in cultured cells. As the results suggest, this study demonstrated that treatment with gold NPs resulted in cellular toxicity in a dose-dependent manner in cultured NPCs.

Anomalous cyclic voltammetric response from pores smaller than ion size by voltage-induced force.

Nanoporous carbons, with different micropore size distributions, were prepared based on waste coffee grounds by a chemical activation process in order to elucidate the correlation between desolvated ions and pores smaller than the sizes of ions using an organic electrolyte. The pore structure of the coffee-based nanoporous carbon was strongly dependent on the heat-treatment temperature prior to the activation process. Cyclic voltammograms of the nanoporous carbons mainly dominated by the smaller pore relative to that of the bare ion size clearly showed deviation from an ideal feature of the current response. It was clearly envisaged that even a bare ion of a size larger than the pore size can penetrate into the pore by voltage-induced force.

Bacterial chemotaxis without gradient-sensing.

Chemotaxis models are based on spatial or temporal gradient measurements by individual organisms. The key contribution of Keller and Segel (J Theor Biol 30:225-234, 1971a; J Theor Biol 30:235-248, 1971b) is showing that erratic measurements of individuals may result in an accurate chemotaxis phenomenon as a group. In this paper we provide another option to understand chemotactic behavior when individuals do not sense the gradient of chemical concentration by any means. We show that, if individuals increase their dispersal rate to find food when there is not enough food, an accurate chemotactic behavior may be obtained without sensing the gradient. Such a dispersal has been suggested by Cho and Kim (Bull Math Biol 75:845-870, 2013) and was called starvation driven diffusion. This model is surprisingly similar to the original Keller-Segel model. A comprehensive picture of traveling bands and fronts is provided.

Global asymptotic stability and the ideal free distribution in a starvation driven diffusion.

We study a logistic model with a nonlinear random diffusion in a Fokker-Planck type law, but not in Fick's law. In the model individuals are assumed to increase their motility if they starve. Any directional information to resource is not assumed in this starvation driven diffusion and individuals disperse in a random walk style strategy. However, the non-uniformity in the motility produces an advection toward surplus resource. Several basic properties of the model are obtained including the global asymptotic stability and the acquisition of the ideal free distribution.

Evolution of dispersal toward fitness.

It is widely believed that the slowest dispersal strategy is selected in the evolutional if the environment is temporally invariant but spatially heterogeneous. Authors claim in this paper that this belief is true only if random dispersals with constant motility are considered. However, if a dispersal strategy with fitness property is included, the size of the dispersal is not such a crucial factor anymore. Recently, a starvation driven diffusion has been introduced by Cho and Kim (Bull. Math. Biol., 2013), which is a random dispersal strategy with a motility increase on starvation. The authors show that such a dispersal strategy has fitness property and that the evolutional selection favors fitness but not simply slowness. Such a conclusion is obtained from a stability analysis of a competition system between two phenotypes with different dispersal strategies of linear and starvation driven diffusions.

Starvation driven diffusion as a survival strategy of biological organisms.

The purpose of this article is to introduce a diffusion model for biological organisms that increase their motility when food or other resource is insufficient. It is shown in this paper that Fick's diffusion law does not explain such a starvation driven diffusion correctly. The diffusion model for nonuniform Brownian motion in Kim (Einstein's random walk and thermal diffusion, preprint http://amath.kaist.ac.kr/papers/Kim/31.pdf , 2013) is employed in this paper and a Fokker-Planck type diffusion law is obtained. Lotka-Volterra type competition systems with spatial heterogeneity are tested, where one species follows the starvation driven diffusion and the other follows the linear diffusion. In heterogeneous environments, the starvation driven diffusion turns out to be a better survival strategy than the linear one. Various issues such as the global asymptotic stability, convergence to an ideal free distribution, the extinction and coexistence of competing species are discussed.