• BMB Reports
• /
• 제48권1호
• /
• pp.13-18
• /
• 2015

Alzheimer's disease severely compromises cognitive function. One of the mechanisms to explain the pathology of Alzheimer's disease has been the hypotheses of amyloid-pore/channel formation by complex $A{\beta}$-aggregates. Clinical studies suggested the moderate alcohol consumption can reduces probability developing neurodegenerative pathologies. A recent report explored the ability of ethanol to disrupt the generation of complex $A{\beta}$ in vitro and reduce the toxicity in two cell lines. Molecular dynamics simulations were applied to understand how ethanol blocks the aggregation of amyloid. On the other hand, the in silico modeling showed ethanol effect over the dynamics assembling for complex $A{\beta}$-aggregates mediated by break the hydrosaline bridges between Asp 23 and Lys 28, was are key element for amyloid dimerization. The amyloid pore/ channel hypothesis has been explored only in neuronal models, however recently experiments suggested the frog oocytes such an excellent model to explore the mechanism of the amyloid pore/channel hypothesis. So, the used of frog oocytes to explored the mechanism of amyloid aggregates is new, mainly for amyloid/pore hypothesis. Therefore, this experimental model is a powerful tool to explore the mechanism implicates in the Alzheimer's disease pathology and also suggests a model to prevent the Alzheimer's disease pathology.

• Journal of Environmental Science International
• /
• 제20권10호
• /
• pp.1221-1232
• /
• 2011

We investigated the toxic effects of difenoconazole on the development in the African clawed frog, Xenopus laevis. To test the toxic effects, frog embryo teratogenesis assays using Xenopus were performed. Embryos were exposed to various concentrations of difenoconazole (0-30 ${\mu}M$). $LC_{100}$ for difenoconazole was 30 ${\mu}M$, and the $LC_{50}$ determined by probit analysis was 27.19 ${\mu}M$. Exposure to difenoconazole concentrations ${\geq}$5 ${\mu}M$ resulted in 10 different types of severe external malformation. Histological examinations revealed dysplasia of the eye, heart, liver, somatic muscle, and swelling of the pronephric ducts. The tissue-specific toxic effects were investigated with an animal cap assay. Blood cells were normally induced at a high frequency by mSCF and activin A. However, the induction of blood cells was strongly inhibited by the addition of difenoconazole. Electron micrographs of tested embryos showed the degeneration of somatic muscle and the shrinkage of microvilli on pronephric duct. The gene expression of cultivated animal cap explants was investigated by reverse transcriptase-polymerase chain reaction (RT-PCR). It revealed that the expression of the blood-specific marker(${\beta}$-globin II) and muscle-specific marker (XMA) were more strongly inhibited than the neural-specific marker(XEn2) by the addition of difenoconazole.

• Journal of Environmental Science International
• /
• 제19권8호
• /
• pp.1001-1012
• /
• 2010

We investigated the toxic effects of tebuconazole on development in the African clawed frog, Xenopus laevis. To test the toxic effects, frog embryo teratogenesis assays using Xenopus were performed. Embryos were exposed to various concentrations of tebuconazole($0-100\;{\mu}M$). $LC_{100}$ for tebuconazole was $100\;{\mu}M$, and the $LC_{50}$ determined by probit analysis was $82.35\;{\mu}M$. The exposure to tebuconazole concentrations ${\geq}40\;{\mu}M$ resulted in 11 different types of severe external malformations including gut dysplasia. Histological examinations revealed various dysplasia in the eye, heart, liver, intestine, somatic muscle, and in the pronephric ducts. The tissue-specific toxic effects were investigated with an animal cap assay. Blood cells are generally induced at a high frequency by the combination of mSCF and activin A, however, the induction of blood cells was strongly inhibited by the addition of tebuconazole. Electron micrographs of tested embryos showed many of multivesicular bodies and dysplasia of photo-receptive cell, however, the somatic muscle degeneration was not severe. The gene expression of cultivated animal cap explants was investigated by reverse transcriptase-polymerase chain reaction and revealed that expression of the blood-specific marker, $\beta$ globin II and muscle-specific marker, muscle actin were more strongly inhibited than the neural-specific marker, XEn2.

• The Korean Journal of Pharmacology
• /
• 제27권2호
• /
• pp.99-108
• /
• 1991

The effect of racemic Ketamine HCl was observed on excitable membranes of sciatic nerve fibres and toe muscles from frog. Ketamine significantly depressed the amplitude of the action potential, maximum rate of rise and that of fall of action potentials of sciatic nerve by dose-dependent and time-course manner, and also it produced the inhibition of $K^+-contracture$ in toe muscle. We used two different ways of sucrose gap method to to obtain the better results from sciatic nerve. We observed and compared the effect of ketamine on sciatic nerve with naloxone, 4-AP (4-aminopyridine) and TEA (Tetraethylammonium). Naloxone significantly but not totally blocked the effect of ketamine both on nerve and on skeletal muscle. 4-AP or TEA by itself had a significant depressant effect on the action potentials on nerve by central perfusion (extracellular perfusion), but both of these drugs did not much affect the action of Ketamine on nerve. The reversibility of effect of Ketamine (10 mM) was observed both on nerve and on skeletal muscles when exposed to drug for short duration. The effects of racemic ketamine described may provide to support that one of the mechanisms of the action of Ketamine on nerve and on muscles of frog might be related to non-specifically effect on receptors within the ion channels $(K^+-channel,\;Na^+-channel\;or\;slow\;Ca^{++}\;channel)$ at higher dose which produces anesthetic effect and also it interacts specifically with one of the opioid receptors or subtype of these receptors which is sensitive to Naloxone at lower dose which produces analgesia.

• Korean Journal of Environment and Ecology
• /
• 제18권3호
• /
• pp.340-345
• /
• 2004

The embryotoxic effects of PCB (Aroclor 1248) on a Korean frog, Rana dybowskii was deter-mined by using the FETAX (Frog Embryo Teratogenesis Assay-Xenopus) protocol. The rates of mortality and malformed larvae were investigated by probit analysis. The results showed that PCB is highly embryolethal. From LC$_{50}$ of 1.48ppb and from EC$_{50}$ of 0.25ppb and TI of 5.7 were derived, which indicates PCB is to be considered a teratogenic compound. Specific malformations occurred in 62.0% as edema at the 0.1ppb, in 32.0% as tail deformations at the 1ppb, and in 68.0% as profound deformations at the 5ppb of PCB concentration which living embryos were exposed to. PCB suppressed the growth of head-tail length at a relatively low concentration (1.0ppb), and therefore growth inhibition as assessed by embryo length can be used as a sensitive indicator to evaluate the toxicity of pollutants in the environment. In conclusion, PCB must be considered highly embryotoxic to Rana dybowskii.

• Journal of Ecology and Environment
• /
• 제30권1호
• /
• pp.57-62
• /
• 2007

To obtain demographic information on threatened gold-spotted pond frog (Rana chosenica Okada, 1931) populations, we determined the ages of 45 male and 13 female frogs (20 males and 9 females from Cheongwon and 25 males and 4 females from Tae-an) and compared the age structures and growth patterns of the two populations in 2006. The snout-vent length (SVL) and body weight of female frogs were greater than those of male frogs in both populations. Male frogs' ages ranged 2 to 7 years old and females' ages ranged 3 to 6 years old. In both populations, 4 years old male frogs were the most abundant age-sex class. The age structures of the two populations were significantly different and the growth coefficients of male frogs from the Cheongwon population were greater than those from the Tae-an population. The mean age of males from the Tae-an population was higher than that from the Cheongwon population. However, the SVL and body weights of male frogs were not different between two populations and there was no difference between the two populations in the mean male SVL at any age. The results could increase our understanding of the life-history of this threatened frog and may be useful in conservation planning.

• Ecology and Resilient Infrastructure
• /
• 제4권4호
• /
• pp.200-206
• /
• 2017

The damage and fragmentation of habitat due to urbanization pose a great threat to amphibians worldwide. To understand the effect of urbanization on the distribution and abundance of Hyla japonica, we measured their population sizes by listening frog calling and investigated the habitat their population sizes and land use in the 18 rice paddy fields located in Incheon and its surroundings. Abundance of H. japonica was 0 - 17 male adults / habitat or 0 - 41 male adults / ha in Incheon. The number of the frog was increased as the distance between the habitat and the road became longer or the ratio of circumstance / area of the habitat increased. Unlike the general prediction, the density of H. japonica showed a negative correlation with the size of the habitat and a positive correlation with the surrounding land use intensity. Our results suggested that H. japonica could be concentrated in a narrow habitat due to the habitat size decrease and the periphery development according to the urbanizaion.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• 제19권8호
• /
• pp.1595-1611
• /
• 1994

In this paper, the numerical wave propagation properties of the finite difference-time domain(FD-TD) method is investigated as a discrete model describing electromagnetic(EM) wave propagation phenomena. The leap-frog approximation of Maxwell's curl equations in time-space simulates EM wave propagation in terms of the numerical characteristic and the domain of dependence. A geometrical interpretation of the FD-TD numerical procedure is presented. The numerical dispersion error due to the leap-frog approximation and its dependence on the stability factor are illustrated. The FD-TD method using the leap-frog approximation is inherently a descriptive model. Thus, not only any physical picture about EM wave propagation phenomena can be drawn through this model, but also physical or engineering parameters in the frequency domain can be extracted from descriptive results. E-plane filter characteristics in the WR-28 rectangular waveguide and reflection property of an inductive iris in the WR-90 rectangluar waveguide extracted from simulation of the FD-TD model is included.

• The Korean Journal of Physiology
• /
• 제16권2호
• /
• pp.119-128
• /
• 1982

The frog truncus arterious were studied with conventional glass microelectrode technique in order to elucidate the underlying mechanism of spontaneous pacemaker activity. The analyses were focussed on the ionic nature of pacemaker current by changing the concentrations of extracellular $K^+$ and, $Na^+$, or by using blockers of K- and Ca-current and chronotropic transmitters. 1) The action potential of the spontaneously active truncus arteriosus has some characteristic feature of maximal distolic potential ranged from -65 to -75 mV, resting potential from -45 to -50 mV and overshoot voltage about +30 mV, respectively. Duration of the action potential taken from rapid upstroke to maximal diastolic potential was about 600 msec. Usual discharge rate was $25{\sim}30/min$ at room temperature $(18{\sim}20^{\circ}C)$. 2) The sensitivity of the resting membrane potential to change extracellular potassium concentrations $(0{\sim}12\;mM)$ was relatively low. Transient hyperpolarization was appeared in the 12 mM K Ringer after 10 min exposure to 0 mM K and it could be related to Na-pump reactivation by high potassium. 3) Reduction of extracellular sodium concetrations diminished the amplitude and frequency of the action potential. In Ringer solution containing 30% Na (substituted by equimolar Tris), spontaneous activity stopped but reappeared as very slow and small action potential. There was no spotaneous activity in zero Na Ringer solution. 4) Caesium(10 mM), K-current blocker decreased the frequency of the action potential and also pacemaker depolarization. Manganese (2 mM) known to be Ca-current antagonist, blocked spontaneous activity completely. 5) Adrenaline and acetylcholine had no chronotropic effect. But adrenaline increased the duration of plateau phase and the magnitude of the action potential in the follower cell. It is concluded that K-, Na-and Ca-current components are involved in the genesis of spontaneous activity of the frog truncus arteriosus like cardiac pacemaker tissues. But the insensitivity of truncus arteriosus to adrenaline and acetylcholine indicates that there are some different control mechanisms of spontaneous rhythm in two tissues.

• The Korean Journal of Physiology
• /
• 제13권1_2호
• /
• pp.13-22
• /
• 1979

Studies have been conducted using isolated surviving skin of Rana temporalia in an attempt to evaluate the effect of N-ethylmaleimide (NEM) on the epithelial $Na^+$ transport. Active transport of $Na^+$ across the skin was estimated by measuring short circuit current (SCC). NEM administered to the outside surface of the skin in concentration of $0.5{\times}10^{-4}-2.5{\times}10^{-4}M$ induced $20{\sim}40%$ increase during the first 30 mintues, followed by a gradual reduction in SCC. With NEM above $4{\times}10^{-4}M$, SCC was inhibited from the beginning. Qualitatively similar results were obtained when NEM was added to the inside bathing medium. However, the concentration of NEM for a similar effect was much higher with the drug in the inside bathing medium than in the outside bathing medium. The oxygen consumption of the skin was inhibited by NEM of above $10^{-4}M$, the effect being of approximately the same magnitude as that on SCC. The activity of $Na^+-K^+$ ATPase of the skin was not inhibited by NEM below $10^{-3}M$, but it was dramatically reduced with $1.2{\times}M$ NEM. The effects of NEM $(10^{-4}M)$ on the SCC and oxygen consumption could be eliminated by adding cysteine $(10^{-4}-10^{-3}M)$ in the medium, indicating that the SH group is involved in the action of NEM in the frog skin. On the basis of these results, the mode of action of NEM on the $Na^+$ transport across the frog skin was discussed.