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Biomedical subjects

Y Shirao

Publications and source records attributed to Y Shirao.

At least 37 records · Page 2Linked to original sources
PubMed1995

Development of electroretinographic alterations in streptozotocin-induced diabetes in rats.

Development of electroretinographic alterations in 9-week-old experimental diabetic rats was studied for up to 6 weeks after a single intraperitoneal injection of streptozotocin (STZ, 60 mg/kg). The amplitudes and the peak latencies of the a and b waves in the diabetic rats did not differ significantly from those in the control rats. In contrast, the diabetic rats showed a significantly smaller amplitude of the second oscillatory potential (OP) 6 weeks after STZ treatment, and furthermore significantly delayed OP peaks as early as 2-3 weeks after STZ treatment. Vitreous fluorophotometric abnormality developed 6 weeks after STZ treatment. None of the diabetic rats had fundus angiographic changes. These results suggest that hyperglycemia or its related changes rapidly affects the light-induced electrical activities of the retina.

Animals↗
PubMed1995

Non-toxic concentrations of cephem antibiotics for intravitreal application--evaluation by in vitro electroretinogram.

Non-toxic concentrations of ceftazidime (CAZ), cefuzonam sodium (CZON) and cefmetazole sodium (CMZ) for intravitreal use were assessed by the electroretinogram in in vitro perfused eyecups of albino rabbits. None of the a-wave, the b-wave and the oscillatory potentials deteriorated with 300 microM CAZ, 300 microM CZON or 500 microM CMZ. The oscillatory potentials were delayed and/or diminished at the concentration which did not change the a- and b-waves (500 microM and 1.0 mM for CAZ and CZON, 1.0 mM for CMZ). Thus, the oscillatory potentials were more vulnerable to these chemicals than the a- and b-waves. Not only the classical a- and b-waves, but also the oscillatory potentials should be examined in retinal toxicology studies by the electroretinogram.

Animals↗
PubMed1994

[Alteration of frog in vitro electroretinographic c-wave in modified extracellular cation concentration].

Effects of extracellular cation (Ca2+, Mg2+, Na+) concentrations on the electroretinographic c-wave were studied in the isolated neural retina-retinal pigment epithelium-choroid tissue of the bullfrog. Among the conditions studied (Ca2+, 0.5-5.0 mM: Mg2+, 0.5-5.0 mM: Na2+, 89.0-109.0 mM), only Ca2+ concentration significantly affected the c-wave. Between 1.0 mM and 5.0 mM Ca2+, the amplitude and the rise time (interval from the light onset to 90% amplitude) of the c-wave were positively and reversely correlated to Ca2+ concentration, respectively. The present results suggest that Ca2+ is one of the major determinants in the extracellular milieu on the c-wave, which is presumably due to its effects on the photoreceptoral activities.

Animals↗
PubMed1993

Open heart surgery under total extracorporeal circulation in a patient with advanced glaucoma.

A patient with Wolff-Parkinson-White syndrome and severe glaucoma underwent division of the accessory pathway under total extracorporeal circulation (ECC). During ECC, systolic systemic pressure was maintained at 60-80 mmHg. Arterial pressure in the optic nerve terminal is reported to be half to one-third of systemic arterial pressure and approximates 20 mmHg during ECC. In the case presented, intraocular pressure was maintained below 15 mmHg throughout ECC. Postoperative examination of the patient revealed no change in visual acuity. During ECC, intraocular pressure may exceed the ocular bottom pressure, placing the optic nerve at risk of ischaemia. In cases where optic nerve ischaemia from ECC is likely, preoperative examination by an ophthalmologist is needed.

Adult↗
PubMed1992

Evaluation of retinal integrity in eyes with retained intraocular metallic foreign body by ERG and EOG.

In three eyes with a retained intraocular metallic foreign body, the neural retina and retinal pigment epithelial (RPE) integrity were evaluated by means of ERG (a-wave, b-wave, oscillatory potentials) and non-photic EOG responses from the RPE (hyperosmolarity response, Diamox response, bicarbonate response). All three cases were judged in an early stage of retinal impairment on the basis of a well-preserved or supernormal b-wave amplitude and showed good postoperative prognosis. Out of three non-photic responses from the RPE, only the bicarbonate response was preoperatively reduced in two out of the three eyes.

Adult↗
PubMed1991

[Effects of extracellular K+ concentration on the ERG c-wave].

The effects of K+ concentration in the perfusate on ERG were examined in bullfrog neural retina-retinal pigment epithelium-choroid preparations. In the range of K+ concentration between 1.0 and 6.0 mM, an increase in K+ concentration caused a decline in the b-wave amplitude, while leaving the b-wave peak latency almost unchanged. An increase in K+ concentration in the range between 1.0 and 3.0 mM enhanced the c-wave amplitude, while an increase in K+ concentration in the range between 4.0 and 6.0 mM diminished it. An increase in K+ concentration tended to shorten the time course of the c-wave. These results suggest that variations in the K+ concentration in tissue fluid may partially account for the marked inter- and intra-individual variations of the c-wave.

Animals↗
PubMed1990

Electroretinographical changes due to antimicrobials.

We evaluated the retinal toxicity of antimicrobials (sulbenicillin, cefazolin, flomoxef, gentamicin, sisomicin, netilmicin, tobramycin, amikacin, vancomycin, ofloxacin, lomefloxacin, and miconazole) by the electroretinogram, before and after a single-shot intravitreal injection in rabbits. The clinical dosage for single-shot intravitreal injections which we recommend are 2 mg for sulbenicillin, 0.25 mg for cefazolin, 0.2 to 0.4 mg for flomoxef, 0.1 mg for gentamicin, 0.1 to 0.2 mg for netilmicin, 0.2 to 0.4 mg for amikacin, 0.2 mg for tobramycin, 1 mg for vancomycin, 0.2 mg for ofloxacin, 0.2 mg for lomefloxacin, and 0.05 mg for miconazole.

4-Quinolones↗
PubMed1989

[Effects of aminoglycosides on the rabbit in-vivo ERG].

We evaluated the retinal toxicity of aminoglycosides (gentamicin, sisomicin, netilmicin, tobramycin and amikacin) by ERG, before and after a single-shot intravitreal injection in rabbits. Gentamicin 200 micrograms abolished the c-wave one week after injection, only slightly diminishing the b-wave and the oscillatory potentials (OPs). Gentamicin 80 micrograms did not alter the ERG up to at least 8 weeks after injection. All the ERG components examined were abolished by 200 micrograms and were irreversibly suppressed by 80 micrograms of sisomicin for the entire period of follow-up. Netilmicin (200 micrograms) or tobramycin (200 micrograms) transiently suppressed the b-wave, c-wave and the OPs. Amikacin (200 micrograms) caused no ERG changes for at least 8 weeks after injection. The clinical doses for single-shot intravitreal injections that we recommend are 100 micrograms for gentamicin, 200 micrograms for netilmicin, 200 micrograms for tobramycin and 200-400 micrograms for amikacin.

Aminoglycosides↗
PubMed1989

[Effects of vancomycin and ofloxacin on rabbit ERG in vivo].

The retinal toxicity of vancomycin and ofloxacin was studied by electroretinogram (ERG) before and after intravitreal injection in rabbits. Vancomycin is known to be effective on methicillin-resistant Staphylococcus aureus. A dose of 1mg vancomycin caused no ERG change for at least eight weeks after injection. The feature that ERG became non-recordable during one to four weeks after an intravitreal injection of 10mg vancomycin, with recovery of only the c-wave was conspicuous. A dose of 200 micrograms ofloxacin did not cause deterioration of the b-wave, the c-wave or the oscillatory potentials throughout the follow-up period up to eight weeks. Judging from the susceptibility of each ERG component to antimicrobials and taking into account the difference of vitreous volume between rabbits and humans, clinical doses of intravitreal single-shot injection should be less than 1mg for vancomycin and 200 micrograms for ofloxacin.

Animals↗
PubMed1988

Retinal toxicity of antibiotics: evaluation by electroretinogram.

Toxicity of an intravitreal injection of gentamicin sulfate, disodium sulbenicillin and cefazolin sodium on the retina was investigated by electroretinogram in albino and pigmented rabbits. Recordings were made before injection and 2 hours and 3, 7, 14, and 21 days after injection. Significant differences were found in the susceptibility of the electroretinogram components to various antibiotics as follows. Gentamicin 0.24 mg/0.1 ml irreversibly abolished all the components examined. Sulbenicillin 4.0, 8.0, or 12 mg/0.1 ml transiently suppressed the b-wave and the oscillatory potentials incrementally with increasing dose. Cefazolin 0.5, 2.0, or 5.0 mg/0.1 ml selectively reduced the oscillatory potentials, leaving the a- and b-waves almost unattenuated. The cefazolin-suppressed oscillatory potentials recovered within 14 days after injection. Judging from the most susceptible electroretinogram components to each antibiotic, we recommend intravitreal doses of these antibiotics for clinical use as follows: gentamicin 0.1 mg/0.1 ml, sulbenicillin 2 mg/0.1 ml, and cefazolin 0.25 mg/0.1 ml.

Animals↗
PubMed1987

Mechanisms of effects of small hyperosmotic gradients on the chick RPE.

This paper presents electrophysiological findings of the effects of small trans-tissue osmotic gradients on the chick retinal pigment epithelium (RPE). These gradients are similar to those produced in the human "hyperosmolarity response," a clinical test of RPE integrity. Effects of 25 mOsm osmotic gradients (mannitol) were observed on the electrical parameters of the tissue and on light-evoked responses in a preparation of chick neural retina-RPE-choroid. Making the retinal perfusate hyperosmolar to the choroidal side, (retinal hyperosmolarity), depolarized the RPE basal membrane and increased the amplitude of the light-evoked c-wave of the ERG. Retinal hyperosmolarity also decreased RPE basal membrane resistance as estimated from measurements of resistance parameters (trans-tissue resistance and a, the RPE membrane resistance ratio), and of RPE membrane polarizations during the c-wave. Choroidal hyperosmolarity led to a hyperpolarization of the basal membrane and a decrease in the amplitude of the light-evoked c-wave. Measurements of resistance parameters indicated an increase in basal membrane resistance. In addition, hyperosmolar loads of either direction decreased the amplitude of the light peak of the DC-ERG. The effects on the light-evoked c-wave and light-peak responses did not occur with bilateral hyperosmolarity, indicating that a trans-epithelial osmotic gradient is necessary for the effects on the RPE. We conclude that the basal membrane of the RPE is the principal site of the effects of small hyperosmotic loads of either direction, and that the ERG c-wave is a sensitive measure of the effects on RPE basal membrane resistance.

Animals↗
PubMed1985

Ba2+ unmasks K+ modulation of the Na+-K+ pump in the frog retinal pigment epithelium.

This paper presents electrophysiological evidence that small changes in [K+]o modulate the activity of the Na+-K+ pump on the apical membrane of the frog retinal pigment epithelium (RPE). This membrane also has a large relative K+ conductance so that lowering [K+]o hyperpolarizes it and therefore increases the transepithelial potential (TEP). Ba2+, a K+ channel blocker, eliminated these normal K+-evoked responses; in their place, lowering [K+]o evoked an apical depolarization and TEP decrease that were blocked by apical ouabain or strophanthidin. These data indicate that Ba2+ blocked the major K+ conductance(s) of the RPE apical membrane and unmasked a slowing of the normally hyperpolarizing electrogenic Na+-K+ pump caused by lowering [K+]o. Evidence is also presented that [K+]o modulates the pump in the isolated RPE under physiological conditions (i.e., without Ba2+). In the intact retina, light decreases subretinal [K+]o and produces the vitreal-positive c-wave of the electroretinogram (ERG) that originates primarily in the RPE from a hyperpolarization of the apical membrane and TEP increase. When Ba2+ was present in the retinal perfusate, the apical membrane depolarized in response to light and the TEP decreased so that the ERG c-wave inverted. The retinal component of the c-wave, slow PIII, was abolished by Ba2+. The effects of Ba2+ were completely reversible. We conclude that Ba2+ unmasks a slowing of the RPE Na+-K+ pump by the light-evoked decrease in [K+]o. Such a response would reduce the amplitude of the normal ERG c-wave.

Animals↗