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Biomedical subjects

J Toyoda

Publications and source records attributed to J Toyoda.

At least 37 records · Page 2Linked to original sources
PubMed1986

Nitro compounds (isosorbide dinitrate, 5-isosorbide mononitrate and glyceryl trinitrate) on the femoral vein and femoral artery.

In organ bath studies, the selectivity of isolated femoral vein and artery of rabbit to isosorbide dinitrate (ISDN), 5-isosorbide mononitrate (ISMN), major metabolite of ISDN, and glyceryl trinitrate (GTN) was compared. The femoral vein and artery contracted by norepinephrine were relaxed by all the nitro compounds dose-dependently. Potency order was GTN greater than ISDN greater than ISMN. The maximum inhibitory responses to the nitrocompounds and their pIC50 values (negative logarithms of doses to induce the 50% response) were greater in the femoral vein than in the femoral artery. For ISMN a 3 times greater sensitivity of femoral vein than of femoral artery was found.

Animals↗
PubMed1986

Actions of 4-(2-hydroxy-3-[(1-methyl-3-phenylpropyl)amino]propoxy) benzeneacetamide (KF4317) and labetalol on alpha- and beta-adrenoceptors.

Blocking activities of alpha- and beta-adrenoceptors by 4-(2-hydroxy-3-[(1-methyl-3-phenylpropyl)amino]propoxy)benzeneacetamide (KF4317) were tested on the isolated muscles, compared with the action of labetalol. In blocking the beta 1-adrenoceptor, KF4317 was almost as active as labetalol. KF4317 was about 1/10th as potent as labetalol in blocking the beta 2-receptor. KF4317 was beta 1-adrenoceptor selective. KF4317 was about 1/50th as potent as labetalol in blocking the alpha 1-receptor. KF4317 did not interact with the alpha 2-adrenoceptor in concentrations up to 10(-5) M. The present results indicate that KF4317 is a selective beta 1- and alpha 1-adrenoceptor blocker, though the alpha 1-adrenoceptor blocking action is weak.

Animals↗
PubMed1984

Electrical and morphological properties of off-center bipolar cells in the carp retina.

Electrical membrane properties of carp off-center bipolar cells were studied by injecting a ramp of current (changing at a rate of about 0.3 nA/s) through one barrel of a double-barreled electrode and recording the voltage drop through the other barrel. The light-elicited response reversed the polarity at a positive membrane potential. The current-voltage curve showed inward and outward rectifications which modified the amplitude of the light-elicited response. The degree of membrane rectifications varied considerably among the cells sampled. Off-center bipolar cells were stained by iontophoretic injections of Lucifer-yellow dye after studying their electrical properties. There was a significant correlation between the difference in cell morphology and the degree of membrane rectification. The cells, which were characterized by small cell bodies lying close to the proximal part of the inner nuclear layer and by thin primary dendrites, tended to show rectifying membrane properties, compared to those characterized by large cell bodies lying close to the distal part of the inner nuclear layer and by thick primary dendrites. A site showing rectifying membrane properties and the origins of a large variability in membrane rectifications are discussed in detail.

Animals↗
PubMed1984

Application of transretinal current stimulation for the study of bipolar-amacrine transmission.

Transretinal current flowing from the receptor side to the vitreous side depolarizes the axon terminals of retinal cells and facilitates the release of transmitter. Such current elicited a depolarizing response in off-center bipolar cells and a hyperpolarizing response in on-center bipolar cells. It also elicited a response of relatively complex waveform in amacrine cells. The responses elicited in bipolar cells were suppressed in the presence of 5-10 mM glutamate in the perfusing Ringer solution, while the responses of amacrine cells persisted, although their waveform changed to a simple one that showed monotonic depolarization irrespective of the type of amacrine cell and were accompanied by a decrease in the membrane resistance. The results indicate excitatory synaptic transmission from bipolar cells to amacrine cells. Since the response elicited by current in ON-OFF cells was almost identical to those elicited in ON or OFF amacrine cells, the transient nature of their light response cannot be due to their membrane properties. ON-OFF cells responded to transretinal current flowing in the opposite direction with a small hyperpolarization accompanied by a resistance increase. The hyperpolarizing response was suppressed by the addition of GABA in glutamate Ringer solution. The results suggest an activation by the current of GABA-ergic feedback pathways from amacrine cells to bipolar cells.

Animals↗
PubMed1983

Analyses of neural mechanisms mediating the effect of horizontal cell polarization.

Polarization of horizontal cells by current through an intracellular electrode elicited a response in certain other horizontal cells and in bipolar cells. Results were consistent with the hypothesis that the feedback from horizontal cells to photoreceptors play an important role in the center-surround antagonism of bipolar cells and also in the opponent color responses of horizontal cells. The feedback from L-type horizontal cells must be mediated by GABA. The red component of RG-type and RGB-type horizontal cells was suppressed by application of GABA antagonists. GABA receptors was not found in these cells, suggesting that the effect was mediated through photoreceptors.

Animals↗
PubMed1983

GABA and glycine effects on the bipolar cells of the carp retina.

Effects of GABA and glycine applied electrophoretically were examined on bipolar cells in the carp retina. When applied at the outer plexiform layer, GABA produced a small depolarization in on-center cells, but a small hyperpolarization in off-center cells. These effects were concluded to be mediated by photoreceptor cells. When applied at the inner plexiform layer, GABA produced a hyperpolarization in on-center cells but no response in off-center cells. This response was resistant to Co2+ ions. Thus GABA is very like the inhibitory neurotransmitter from amacrine to on-center bipolar cells. Glycine, when applied in either layer, did not have a noticeable effect on either type of bipolar cells.

Animals↗
PubMed1982

Analyses of bipolar cell responses elicited by polarization of horizontal cells.

Simultaneous intracellular recordings were made from a bipolar cell and a horizontal cell in the carp retina. The properties of the bipolar cell were studied while injecting current into the horizontal cell. Hyperpolarization of horizontal cells, irrespective of their type, elicited a hyperpolarizing response in on-center bipolar cells and a depolarizing response in off-center bipolar cells. Analyses of the ionic mechanisms of bipolar cell responses revealed that depolarization of horizontal cells simulated and hyperpolarization opposed the effect of central illumination. The effect of polarization was exerted in such a manner that each type of horizontal cells modified the transmission from those photoreceptors from which they receive main inputs. In on-center bipolar cells, for example, the L-type horizontal cells receiving inputs mainly from red cones modified the cone-bipolar transmission accompanied by a conductance change of K+ and/or Cl- channels, and the intermediate horizontal cells receiving inputs from rods modified the rod-bipolar transmission accompanied by a conductance change of Na+ channels. In off-center bipolar cells, the effect of polarization of any type of horizontal cells was mediated mainly by conductance changes of Na+ channels. Feedback mechanisms from horizontal cells to photoreceptors could explain these results reasonably well.

Action Potentials↗
PubMed1981

Linear information processing in the retina: a study of horizontal cell responses.

A basic question about visual perception is whether the retina produces a faithful or a distorted neural representation of the visual image. It is now well known that in some retinal pathways there are significant nonlinear transductions which distort the neural image. The next natural question is, What are the locations of the nonlinear stages within the retinal network? We report here on an investigation of linearity and nonlinearity of responses of horizontal cells in the turtle retina as an assay of the degree of nonlinearity in the outer plexiform layer of the retina. The visual stimuli were sinusoidal gratings; these patterns were modulated by contrast reversal with a sinusoidal time course. The conclusion from our experiments is that the turtle's horizontal cell responses show evidence only of linear spatial summation even at moderately high contrasts on moderately high background levels. Our work thus indicates that there is no significant distortion of the visual image by the photoreceptors or by the neural summation of photoreceptor signals by horizontal cells under normal physiological conditions. These results are consistent with the view that the major nonlinearities of the retina are proximal to the outer plexiform layer.

Animals↗
PubMed1981

Ionic mechanisms of two types of on-center bipolar cells in the carp retina. II. The responses to annular illumination.

On-center bipolar cells in the dark-adapted carp retina were divided into four types (A, B, C, and D) on the basis of response wave forms, spectral response properties, and electrical membrane properties. Type A and B cells responded to a spot of light with a transient depolarization followed by a plateau, whereas the response of type C and D cells were approximately rectangular in shape. The center and surround responses of type A cells had maximum spectral response of approximately 525 nm in the lower mesopic range; the polarity of both responses was reversed at positive membrane potentials as the membrane was depolarized by extrinsic current. The center and surround responses of type D cells had a maximum spectral response of approximately 625 nm in the mesopic or photopic range; the polarity of both responses was reversed at membrane potentials that were more negative than those at the dark level. The results suggest that the center and surround responses mediated by rods are generated by changes in sodium conductance, but in opposite ways; whereas those mediated by red cones are generated by changes in potassium and/or chloride conductances. In type B and C cells, which probably receive inputs from both rods and/or green cones as well as red cones, the center responses were composed of the two ionic mechanisms described above. The surround responses of many type B and C cells were dominated by only one ionic mechanism with a negative reversal potential, but in some type B cells the surround responses were resulted from two ionic mechanisms similar to those of the center responses.

Animals↗
PubMed1981

[Clinical trials of cefroxadine on skin and soft tissue infections in the field of pediatrics (author's transl)].

CXD was administered orally at an average dose of 28.6 mg/kg (18.3 approximately 42.3 mg/kg) for an average 6 days (3 approximately 12 days) to a total of 99 pediatric cases with skin and soft tissue infections (impetigo 89, abscess 7 and furuncle 3) ranging from 3 months to 9 years old. The drug was given twice to 4 times per day after meals. The clinical and bacteriological effects and adverse reactions of CXD as well as the susceptibility of the causative organisms against CXD and CEX were studied, and the results obtained are as described below: 1. According to judgement of the attending doctors, CXD had a high global efficacy rate of 90.9%. 2. Analysis of the attending physicians' evaluations of the clinical effects on impetigo revealed that a dose of CXD 20.5 approximately 30.4 mg/kg t.i.d. can produce satisfactory responses. 3. According to the assessments by Evaluation Committee, the global clinical effects after 3, 5 and 7 days were 81.4, 91.2 and 94.6%, respectively. This indicates that clinical responses increased with prolongation of the treatment period, viz. better responses obtained after 5 and 7 days. This suggests that a minimum of 5 days administration is required for treating these infections. 4. As for impetigo having the largest number of patients in this study, a dose of CXD 20.5 approximately 30.4 mg/kg per day seemed to produce satisfactory clinical effects. 5. As for dose per day, the t.i.d. regimen of CXD 20.5 approximately 30.4 mg/kg seemed to exhibit satisfactory clinical responses, as already mentioned. Because of quite a small number of patients on the q.i.d. regimen of higher doses, however, the question of whether the t.i.d. treatment with 20.5 approximately 30.4 mg is adequate or not should be determined by a comparative study between the q.i.d. and t.i.d. treatments. 6. As for bacteriological responses, a high global effect of 87.1% was obtained with CXD against S. aureus and S. pyogenes isolated from 74 and 1 cases, respectively. 7. As for impetigo with predominant number of cases, CXD was highly effective bacteriologically at a daily dose of 20.5 approximately 30.4 mg/kg t.i.d. As an appropriate comparative evidence with the q.i.d. treatment was lacking, however, therapeutic validity of the t.i.d. treatment could not be determined definitely. 8. Utility was evaluated by the attending physicians on the total 99 cases, and CXD showed as high as 88.9%. 9. There were neither non-compliances nor adverse reactions to this treatment. 10. CXD showed a distribution of antimicrobial activity similar to that of CEX, against 74 isolates of S. aureus with the MICs of CXD ranging from 1.56 to 25 mcg/ml and those of CEX ranging from 0.78 to 25 mcg/ml, with peak MIC being 3.13 mcg/ml for both drugs. As for S. pyogenes, only one isolate from the same species, CXD was antimicrobial activity at 0.2 mcg/ml and CEX was antimicrobial at 0.39 mcg/ml. The above findings suggest that CXD is highly effective against acute skin and soft tissue infections in pediatrics.

Abscess↗
PubMed1978

Studies on the mechanisms underlying horizontal-bipolar interaction in the carp retina.

Responses of on-center bipolar cells and horizontal cells were recorded simultaneously in the carp retina, and the effect of polarization of horizontal cells on the bipolar cells was studied. Hyperpolarization by extrinsic current of horizontal cells elicited in the bipolar cells a hyperpolarizing response which, unlike the electrical coupling betweeen adjacent horizontal cells, was accompanied by a change in membrane conductance. The bipolar cell responses elicited by polarization of external horizontal cells showed a negative reversal potential, while those elicited by polarization of intermediate horizontal cells showed a positive reversal potential. It was suggested that the external horizontal cells modify the cone-bipolar transmission which involves the conductance change of subsynaptic potassium and/or chloride channels, while the intermediate horizontal cells modify the rod-bipolar transmission which involves the conductance change of sodium channels.

Animals↗
PubMed1976

Comparison of frequency characteristics of photopic and scotopic S-potentials in the carp.

Frequency characteristics of photopic and scotopic L-type S-potentials were studied in the carp retina, using either an impulse or a sinusoidal light input superimposed on a steady background light of various intensities. The photopic type responses were faster than the scotopic responses if their frequency characteristics were compared without background illumination. However, the difference was not absolute. Both types of responses became faster in the presence of background illumination. The stronger the background, the faster was the response. At relatively high background intensities, the response to a flash became diphasic due to the rebound effect which corresponds to a low frequency attenuation in the gain characteristics. The main difference between the two types of responses was found in the phase relation; the scotopic units showed more phase lag indicating an extra delay even under a condition in which the time course of their response was faster than that of the photopic units.

Action Potentials↗
PubMed1974

Frequency characteristics of retinal neurons in the carp.

Frequency characteristics of various retinal neurons in the carp were studied using sinusoidally modulated light as an input. They were affected by both intensity and pattern of illumination. In the horizontal cells, in which the effect of light intensity was studied most extensively, an increase in the light intensity brought about a decrease of the gain, which was more marked at lower frequencies, resulting in a shift of cutoff frequency towards higher frequencies and in a slight low frequency attenuation. A decrease in the area illuminated had an effect similar to a decrease in the light intensity. In the receptor, the low frequency attenuation was not apparent even at high light intensities. The adaptation process in receptors was not sufficient to explain the low frequency attenuation in the horizontal cells, and a possible contribution of negative feedback from horizontal cells to receptors was suggested. In the bipolar cell, the lateral interaction played an important role. An increase in an area resulted in the suppression of the response at low frequencies where the phases of the center and the surround responses were opposed, but in the augmentation near 5 Hz where the two responses were in phase. In amacrine cells, a low frequency attenuation and a phase advance at low frequencies were very prominent, and were considered to be due mainly to a process designated here as the neural adaptation.

Adaptation, Ocular↗