Biomedical subjects

S Usui

Publications and source records attributed to S Usui.

At least 73 records · Page 4Linked to original sources

PubMed1997

Desensitization of the GABAA receptor shifts the dynamic range of retinal horizontal cells due to light and dark adaptation.

The effects of the GABAergic pathway on the dynamic range of the light response of cone-driven horizontal cells (HCs) in the carp retina were investigated using conventional intracellular recordings and computer simulations. The amplitude of the HC responses to repetitive test flashes was altered by background illumination in control Ringer's solution, but was not changed following the application of picrotoxin or bicuculline, which suggests that GABAA receptors mediate the subsequent change in light response. This phenomenon was simulated by introducing the desensitization mechanism of the GABAA receptor into a cone-HC network model. These results suggest that desensitization of the GABAA receptor shifts the dynamic range of the HCs due to light and dark adaptation.

Adaptation, Ocular↗

PubMed1997

[Difference of blood cell counts with reference blood cell counters in different makers: Part II].

This is the second report of evaluation on the difference of blood cell counting among different automated blood cell counters in Japan. We tested reference blood cell counters of 6 different companies: Coulter, Sysmex, Bayer-Sankyo, Nihon Kohden, Horiba and Dainabot. Forty ml of whole blood were taken from 3 healthy persons and EDTA-2K anticoagulated blood samples (Sample 1, 2 and 3) were sent to each company to determine blood cell counts with a reference automated counter. As a result, the following items showed more than 10% difference among makers: RBC between Dainabot and Horiba in Sample 3, hematocrit values between Coulter and Dainabot in Sample 2, WBC between Nihon Kohden and each of three makers (Sysmex, Horiba and Dainabot) in all 3 samples and that between Bayer-Sankyo and each of two makers (Sysmex and Horiba) in Sample 3 and platelet count between Dainabot and each of 3 makers (Bayer-Sankyo, Nihon Kohden and Horiba) in all 3 samples. The following items showed difference between 5 and 10%: MCV between Coulter and each of two makers (Bayer-Sankyo and Horiba), WBC between each of two makers (Coulter and Nihon Kohden) and each of other 4 makers, and platelet count between each of two makers (Nihon Kohden and Horiba) and each of 3 makers (Coulter, Sysmex and Bayer-Sankyo). Recently Japanese Committee for Clinical Laboratory Standards proposed minimum clinical allowance of blood cell count as follows: hemoglobin 3%, RBC 4%, MCV 4%, WBC 7% and platelet count 10%. It is suggested that all of the items showing the difference more than above allowance among makers should be improved for clinical use to have good external quality control in blood cell counting by automated instruments.

Blood Cell Count↗

PubMed1996

Phloroglucinols from Baeckea frutescens.

Two new phloroglucinols, named BF-1 and BF-2, were isolated from the dried leaves of Baeckea frutescens. Their structures were determined by their 1H and 13C NMR and mass spectral data. BF-2 exhibited strong cytotoxic activity (IC50 = 5.0 micrograms ml-1) against leukaemia cells (L 1210) in tissue culture.

Antineoplastic Agents, Phytogenic↗

PubMed1996

Reconstruction of retinal horizontal cell responses by the ionic current model.

An ionic current model of the retinal horizontal cell is constructed. The horizontal cell models are interconnected by gap junctions to form a horizontal cell layer. The light response properties of the L-type horizontal cell are analyzed using this model. We demonstrate the functional role of each ionic current and the role of the feedback loop between cones and horizontal cells. The present study provides insight into the dynamic relationships between characteristics on the cellular level and on the multi-cellular level for producing the light response in horizontal cells.

Action Potentials↗

PubMed1996

Ionic current model of the vertebrate rod photoreceptor.

We describe voltage- and calcium-dependent ionic currents in the photoreceptor inner segments similar to the Hodgkin and Huxley (Journal of Physiology, 117, 500-544, 1952) equations. The model is used to describe both rods and cones by adjusting parameters. To simulate the light response, the inner segment model was connected with the phototransduction model proposed by Torre et al. (Cold Spring Harbor Symposia on Quantitative Biology, 55, 563-573, 1990). The role of individual ionic currents in the inner segment in shaping the light response was analyzed through computer simulations. The results suggest that: (1) the transient hyperpolarization to a bright flash is generated by Ih; (2) the oscillation after prolonged hyperpolarization in rods results from the interaction among Ica, IK(Ca), and ICI(Ca). Since the present model describes the biophysical processes from phototransduction to voltage response, the model can be used for analyzing the light response properties of the photoreceptors quantitatively.

Animals↗

PubMed1996

Ionic current model of bipolar cells in the lower vertebrate retina.

We propose an ionic current model of bipolar cells based on the published experimental data. Five types of ionic currents identified in bipolar cell bodies, Ih, IKv, IA, ICa and IK(Ca) were described by a mathematical formulation similar to the Hodgkin and Huxley (Journal of Physiology, 117, 500-544, 1952) equations. The model parameters were estimated from the voltage clamp data. In simulation, we demonstrate that the present model reproduces not only the voltage clamp responses but also the current clamp responses of the bipolar cells. As a result, the model provides a better understanding of the functional role of the ionic currents in bipolar cells in generating the electrical responses.

Animals↗

PubMed1996

Effect of 3-deoxyglucosone on the activities of enzymes responsible for glucose metabolism in mouse liver.

Crude extracts containing the enzymes obtained from mouse liver were incubated with 3-deoxyglucosone (3-DG), and then subjected to assay of the activities of enzymes responsible for glucose metabolism. Hexokinase and glucose-6-phosphate dehydrogenase activities were decreased by 3-DG and hexokinase activity was strongly inhibited time and concentration dependently, while glucokinase, glucose-6-phosphatase, and phosphofructokinase activities were scarcely affected. These results suggest that 3-DG inhibits the intake of glucose in the liver and a connection with development of diabetes.

Animals↗

PubMed1996

Polysaccharides in fungi. XXXVII. Immunomodulating activities of carboxymethylated derivatives of linear (1-->3)-alpha-D-glucans extracted from the fruiting bodies of Agrocybe cylindracea and Amanita muscaria.

Immunomodulating activities of three carboxymethylated derivatives (AG-AL-CMS, AG-AL-CMI, and AM-APP-CM) of linear (1-->3)-alpha-D-glucans from Agrocybe cylindracea and Amanita muscaria were evaluated with murine peritoneal macrophages playing an important role in tumor immunity. The ratio of macrophages in peritoneal exudate cells increased more than 50% after the administration of three carboxymethylated (1-->3)-alpha-D-glucans. These carboxymethylated (1-->3)-alpha-D-glucans exhibited higher potentiating activities for macrophages than carboxymethylated linear (1-->3)-beta-D-glucan (CMPS) in the potency of reduction of nitro blue tetrazolium, products of nitric oxide and the soluble cytotoxic factor, the amount of glucose consumption, and the activation of acid phosphatase. AG-AL-CMS, AG-AL-CMI, and AM-APP-CM were found to induce the tumor regressing factor in mouse serum, although the ability of the induction of this factor was weaker than that of CMPS. The reticuloendothelial system-potentiating activation of three carboxymethylated alpha-D-glucans was similar to that of the carboxymethylated beta-D-glucan. AG-AL-CMS and AG-AL-CMI, but not AM-APP-CM, were suggested to possess a higher-order structure, resulting from the formation of a fluorescent complex with aniline blue.

Acid Phosphatase↗

PubMed1996

Polysaccharides in fungi. XXXVI. Hypoglycemic activity of a polysaccharide (CS-F30) from the cultural mycelium of Cordyceps sinensis and its effect on glucose metabolism in mouse liver.

A polysaccharide (CS-F30) obtained from the cultural mycelium of Cordyceps sinensis showed potent hypoglycemic activity in genetic diabetic mice after intraperitoneal administration, and the plasma glucose level was quickly reduced in normal and streptozotocin-induced diabetic mice after intravenous administration. Administration of CS-F-30 to normal mice significantly increased the activities of hepatic glucokinase, hexokinase and glucose-6-phosphate dehydrogenase, although the glycogen content in the liver was reduced. Furthermore, CS-F30 lowered the plasma triglyceride level and cholesterol level in mice.

Animals↗

PubMed1996

Evidence of sensory conflict and recovery in carp exposed to prolonged weightlessness.

BACKGROUND: Evidence in support of the sensory conflict hypothesis for space motion sickness (SMS) is still needed. HYPOTHESIS: We hypothesized that sensory conflict and recovery processes should be demonstrated in intact fish during initial days of microgravity exposure, as a disturbance and restoration of the dorsal light response (DLR; a functional model of visual-graviceptor interaction), respectively. We also expected that this would be true in an otolith-removed fish if it had been fully compensated for dysfunction before the exposure. METHODS: The DLR of carp (Cyprinus carpio) was examined intermittently during the 8-d mission of Spacelab-J. Two carp, normal and labyrinthectomized (LB), made the flight. RESULTS: In the normal carp, the DLR was unstable for the first 3 d inflight but gradually recovered thereafter. The recovery was characterized by gradual restoration of the DLR tilt speed. The LB fish whose otoliths had been removed 2 mo before the flight maintained DLR at the first inflight test session (22 h after launch), but DLR was disrupted at 2 d as in normal fish. The recovery process could not be evaluated in this fish, because the EEG cable which was attached to the fish for supplementary study became tightly twisted and thus immobilized the fish for the remainder of the experiment. CONCLUSION: These findings provided additional evidence in fish for sensory-motor disorder and readjustment during the early phase of microgravity, thus supporting the sensory conflict hypothesis for SMS.

Animals↗

PubMed1995

Polysaccharides in fungi. XXXV. Anti diabetic activity of an acidic polysaccharide from the fruiting bodies of Tremella aurantia.

An acidic polysaccharide (TAP) was isolated from a hot-water extract of the fruiting bodies of Tremella aurantia. It showed remarkable hypoglycemic activity in normal mice and two diabetic mouse models, streptozotocin-induced diabetes and genetic diabetes, following intraperitoneal administration. Continuous oral administration of TAP solution (0.5g/l) for a long period was found to be also effective in hyperglycemia in glucose-loaded mice and no harmful physical effects were found. TAP had an [alpha]D -7 degrees in water, and its molecular weight was estimated to be about 1500000. TAP is composed of mannose, xylose, glucuronic acid and glucose (molar ratio, 4:2:1:0.3), and it contains 2.2% of O-acetyl groups.

Animals↗

PubMed1995

Preparation and antitumor activities of beta-(1-->6) branched (1-->3)-beta-D-glucan derivatives.

The formylmethylated and aminoethylated derivatives of schizophyllan (SPG), a beta-(1-->6)-branched (1-->3)-beta-D-glucan from Schizophyllum commune Fries, were prepared through dimethoxyethylated SPG which was synthesized by the reaction of SPG with dimethylchloracetal under an alkaline condition. The degree of the substitution of formylmethyl groups in the formylmethylated derivative of SPG was estimated as approximately 0.19, and the locations of formylmethyl groups in the derivative were predominantly located at O-6 and/or O-4 positions in glucose residues. The molecular weights of these derivatives were similar to that of SPG, and the helical structure of the derivatives did not seem to be different. The antitumor activities of the formylmethylated and aminoethylated derivatives of SPG against subcutaneously implanted sarcoma 180 solid tumor in mice by intraperitoneal (i.p.) administration were increased more effectively than that of SPG at a dose of 10 mg/kg/d for 7 d starting from 7 d after transplantation of sarcoma 180. The activities inducing tumor regressing factor of the formylmethylated and aminoethylated derivatives were 1.5 to 2 times stronger than that of SPG at a dose of 100 mg/kg. Formylmethylated and aminoethylated derivatives of SPG as well as SPG itself retained the potentiating activity for the reticuloendothelial system. The productions of soluble cytotoxic factors secreted from murine macrophages by the administration of the formylmethylated and aminoethylated derivatives of SPG, which were probably superoxide anion and tumor necrosis factor as measured by the potency of the nitro blue tetrazolium reduction and the cytotoxic activity against L929 cells, respectively, appeared to be more efficient than that of SPG.

Animals↗

PubMed1995

Eye movements in monkeys with local dopamine depletion in the caudate nucleus. I. Deficits in spontaneous saccades.

The basal ganglia contribute to the suppression and initiation of saccadic eye movements through the inhibitory connection from the substantia nigra pars reticulata (SNr) to the superior colliculus. This mechanism consists of serial and parallel connections, which are mostly inhibitory and GABAergic. Dopamine is known to exert powerful modulatory effects on the basal ganglia function, but its nature and mechanism are still unclear, especially in relation to voluntary behavior. The purpose of this series of investigation was to study the role of dopamine in the control of saccadic eye movements. We examined, in the monkey, whether and how the deficiency of the nigrostriatal dopaminergic innervation affects saccadic eye movements. The present article is focused on spontaneous saccades that the monkey made with no incentive to obtain reward; the next paper will describe task-specific saccades. Using an osmotic minipump we infused 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) unilaterally into the head-body junction of the caudate nucleus of monkeys where presaccadic neurons were clustered. Tyrosine hydroxylase activity, visualized using an immunohistochemical method, decreased locally around the injection site with some effects extending into the ipsilateral putamen and locally in the ipsilateral substantia nigra. Changes of eye movements started to appear 3-5 d after starting the infusion. Spontaneous saccades became less frequent. The area scanned by the saccades became narrower and shifted to the hemifield ipsilateral to the infusion site. The saccade amplitudes and peak velocities decreased; durations were prolonged. These effects were more prominent for saccades directed toward the side contralateral to the infusion site. These monkeys showed no obvious skeletomotor symptoms. These results suggest that the local deprivation of the dopaminergic innervation in the caudate nucleus facilitates neuronal activity of the SNr leading to suppression of saccadic eye movements.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine↗

PubMed1995

Eye movements in monkeys with local dopamine depletion in the caudate nucleus. II. Deficits in voluntary saccades.

Unilateral infusion of MPTP into the monkey caudate nucleus produced deficits in task-specific saccades, in addition to the deficits in spontaneous eye movements (preceding article). We trained three monkeys to perform two kinds of saccade tasks: (1) saccade task for eliciting visually guided saccades and (2) delayed saccade task for eliciting memory-guided saccades. After the MPTP infusion, dopaminergic function, estimated by tyrosine hydroxylase (TH) immunoreactivity, was shown to be decreased locally around the infusion site at the head-body junction of the caudate. We found that the deficits were prominent in the saccades directed to the side contralateral to the infusion (contralateral saccades). Memory-guided saccades were sometimes misdirected to the ipsilateral side even when the cue stimulus was presented on the contralateral side. Among the parameters of saccades, a selective change was found in the saccade latency: the latency was prolonged consistently in contralateral memory-guided saccades. The amplitude and velocity of saccades decreased in contralateral saccades, either memory guided or visually guided. The duration of saccades tended to increase in visually-guided saccades and memory-guided saccades, in both directions. Only one monkey, in which the decrease in TH activity included a large part of the putamen and the head of the caudate, showed prolongation of manual reaction time for lever release.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine↗

PubMed1994

Role of subunit IV in the cytochrome b-c1 complex from Rhodobacter sphaeroides.

Rhodobacter sphaeroides mutants lacking subunit IV (M(r) = 14,384) of the cytochrome b-c1 complex (representative mutant strain, RS delta IV-2) have been constructed by site-specific recombination between the wild-type genomic subunit IV structural gene (fbcQ) and a suicide plasmid containing a defective fbcQ sequence. RS delta IV-2 gives rise to a photosynthetically competent phenotype after a period of adaptation. The chemical compositions, spectral properties, and cytochrome b-c1 complex activities in subunit IV-deficient chromatophores from adapted RS delta IV-2 are similar to those in wild-type chromatophores. However, the apparent Km for Q2H2 for the b-c1 complex in subunit IV-deficient chromatophores from adapted RS delta IV-2 cells is about four times higher than that in chromatophores from wild-type cells. The cytochrome b-c1 complex activity in subunit IV-deficient chromatophores of adapted RS delta IV-2 cells is more labile to detergent treatment than that from wild-type cells. The specific activities of dodecylmaltoside-solubilized fractions of RS delta IV-2, based on cytochrome b, are only one-fourth that of the untreated chromatophores. Introducing a wild-type fbcQ operon on a stable low copy number plasmid, pRK415, into RS delta IV-2 restores photosynthetic growth behavior, the apparent Km value for Q2H2, and tolerance to detergent treatment to that of wild-type cells. Cytochrome b-c1 complex purified from adapted RS delta IV-2 contains only three subunits. It has only 25% of the activity of the four-subunit enzyme. This low activity is accompanied by an increase of the apparent Km for Q2H2 from 3 to 13 microM, suggesting that subunit IV may be involved in quinone binding in addition to its structural role.

Base Sequence↗

PubMed1994

Acquisition of color opponent representation by a three-layered neural network model.

This paper discusses color representation in the visual system by analysis of a three-layered neural network model. The model incorporates physiological knowledge of color representation at the sensor level (broad-band trichromatic representation by cones) and the higher level (narrow-band color representation by color-coded cells in V4). We trained the model to perform a mapping between these color representations by the back propagation algorithm and analyzed the acquired characteristics of the hidden units. It turned out that the hidden units learned characteristics similar to those of the color opponent cells found in the visual system. It was concluded that the R-G and Y-B color opponent representations reflect the efficiency of the color representation in the visual system from investigations on the efficiency of color representation in the hidden layer and on the capability of the color recognition task of the model.

Color Perception↗

PubMed1994

Spatial distribution of local flash electroretinogram by multi-input stimulation.

A method was developed for recording the distribution of the local flash electroretinogram with multi-input stimulation. With the use of a long flash interval, such as 100 ms, the principle and the method are useful for clinicians who know the method for recording the conventional local flash electroretinogram with single-input stimulation. This method results in a long recording time, yet it presents real local flash electroretinogram waveforms at the output.

Electroretinography↗

PubMed1994

Space experiment using large-sized fish: in case of carp in Spacelab-J mission.

Two carp of 26 cm in size, intact and otolith-removed (LB), were flown on the Spacelab-J for 8 days in September 12-20, 1992. Light-dependent reaction to alternating direction of illumination was recorded for 10 min twice a day together with the cerebellar EEG activity, on 2 days before the launch, during the flight and for 4 days after the landing, in same fish chamber. Reproducing the video image, it was revealed that both carp were healthy during the mission, but the LB fish was almost immobilized from the 3rd test session (48 hours in flight) by tight twisting of the EEG cable. Both fish after landing tended to stay still on the bottom of the fish chamber. Findings that the body weight reduced remarkably in both fish and that nitrite and nitrate levels of the fish water were usually high, suggested that the fish metabolism might have been enhanced during the flight.

Animals↗