Werner Sickel

Antibiotics and Light Responses in Superfused Bovine Retina

Abstract1. Our objective was to study effects of clindamycin and ciprofloxacin on the electroretinogram (ERG) of isolated bovine retinas.2. Electroretinograms of isolated superfused bovine retinas were recorded under normal conditions and during application of clindamycin and ciprofloxacin. The b-wave reduction was plotted against the drug concentration. In several cases retinal oxygen uptake was also measured. Clindamycin was available only in a preparation containing benzyl alcohol. To differentiate between effects caused by the antibiotic and the alcohol, ERGs were also recorded under superfusion with benzyl alcohol. To record drug effects on photoreceptors synaptic transmission was blocked using 1 mM aspartate.3. At concentrations between 0.3 and 10 mM clindamycin significantly reduced the amplitude of the b-wave of the ERG. A comparable reduction of retinal oxygen uptake was found at concentrations 10-fold higher. Clindamycin, 3 mM, did not affect the a-wave after preincubation with aspartate. Benzyl alcohol at concentrations of 0.3 and 1 mM did not affect the b-wave, whereas at higher concentrations the b-wave was found to be reduced. Considerable b-wave reductions were found with ciprofloxacin at concentrations of between 0.03 and 0.6 mM. All effects proved to be fully reversible and dose-dependent.4. Ciprofloxacin and clindamycin did both alter neural function in the isolated superfused bovine retina. The nontoxic dosages found here differ considerably from results in rabbits after intravitreal injections. This is probably due to species differences.

Delayed electrical responses from the isolated frog retina

ZusammenfassungVon der umströmten Netzhaut wurden Lichtantworten registriert, die mit zunehmender Reizstärke eine Zunahme der Latenz und eine zeitliche Dehnung zeigten. Sie sind über einen Bereich von Lichtintensitäten graduiert, der den für abgestufte on-Antworten übersteigt. Von den off-Antworten kurzer Latenz lassen sie sich durch unterschiedliches spektrales Verhalten abgrenzen. Die verzögerten Antworten erscheinen in gleicher Weise als intra- oder transretinale Gleichspannungsänderungen wie auch als Impulsaktivität einzelner Einheiten. Der Registrierort der Impulsaktivität lag extern zu den retinalen Ganglienzellen, die Einheiten umfassen mehrere Gruppen unterschiedlichen Aktivitätsmusters.SummaryResponses to homogeneous light stimulation were recorded from the isolated perfused retina which at increased light intensity showed increased latency and prolonged duration of activity. They were found graded over a range of intensities which exceeded that for the on-effects. From the early off-effects they could be distinguished by a different spectral behavior. The delayed responses were equally seen in intra- or trans-retinal slow waves and unit activity. The unit activity was recorded from a site external to the ganglion cell layer and may comprise several types of outlasting activity.

Effects of Protein Tyrosine Kinase Inhibitor Genistein on Retinal Function in Superfused Vertebrate Retina

The aim of this study was to evaluate safe concentrations of genistein for a potential intraocular application using the isolated retina technique on bovine retina preparations. Bovine retinas were isolated and perfused with an oxygen pre-equilibrated standard solution. The electroretinogram (ERG) was recorded as a transretinal potential using silver/silver-chloride electrodes. After recording of stable ERG amplitudes, genistein was added to the solution in different concentrations. The percentage of b-wave reduction under the drug was calculated. We also studied the influence of genistein on the a-wave amplitude. After the addition of aspartate, the b-wave amplitude was reduced continuously until unmasked a-wave amplitudes were reached. Genistein was then added to the aspartate containing perfusate. The percentage of a-wave amplitude reduction under the drug was calculated. Concentrations of 3.3 microMol/l and higher were found to reduce the b-wave amplitude. The a-wave amplitude was not changed by the applied concentrations. The ERG only showed toxic effects from genistein beyond concentrations that were found to inhibit endothelial cell growth in vitro. In previous studies, beneficial effects on trabecular meshwork cells were present for genistein concentrations which are distinctly higher than the maximum nontoxic concentration reported here. It was shown that the photoreceptor layer is not affected at the examined concentration range. Therefore, we attribute the toxic effects to postsynaptic interaction of genistein. Intraocular application of genistein in a sufficient concentration seems possible.

Identification of fast spurts of pyridine nucleotide oxidation evoked by light stimulation in the isolated perfused vertebrate retina

Transitory increases of ultraviolet transmission on stimulation with light were recorded simultaneously with electroretinogram on and off effects from isolated vertebrate retina. The spectral distribution of the optical light responses coincided with that of NADH reduction. The correlation of the optical, or respiratory, responses and the electrical responses were very close within a wide range of stimulus parameters, suggesting an interpretation in terms of supply and demand of energy with a tight coupling between the two kinds of evoked activity. Prerequisite to the response behaviour was the preservation of synaptic signal transmission from first- to higher-order retinal neurons.

The triple flash electroretinogram and its significance in macular diseases

Abstract• Purpose: The purpose of this study was to evaluate recovery data for the b-wave of the electroretinogram (ERG) elicited using multiple flash stimulation with increasing stimulus intervals in normal controls and in patients with macular diseases. The results will describe effects of age and macular disease and define indexes characterizing the recovery process. • Methods: Scotopic Ganzfeld flash ERGS were elicited using interstimulus intervals of 140, 280, and 560 ms. Relative b-waves were calculated as the ratio b140 ms/ b560 ms and b280 ms/b560 ms, respectively. Responses obtained in 134 eyes of 134 normal controls served as reference data. Fifty-four patients with different macular diseases were also examined and their data compared to the reference data. • Results: Relative b-wave amplitudes correlated with interstimulus interval and with flash luminance, but not with age. All patients had a normal ERG when recorded following the standard of clinical electroretinography. A sigmoidal model was suggested, providing three indexes characterizing the b-wave recovery process. Relative b-waves and recovery indexes varied in age-related macular degeneration, central serous retinopathy, vitelliform macular degeneration, Stargardts disease, and pattern dystrophy. • Conclusion: The triple flash ERG reflects energy-yielding and -utilizing mechanisms. It proved to be more sensitive in detecting functional lesions in macular diseases than the standardized explorating procedure. The b-wave recovery model allows differentiation between two independent mechanisms contributing to the b-wave recovery process. One or more of the three characterizing indexes are affected in different macular diseases.

Effects of etoposide (VP16) on vertebrate retinal function

AbstractEtoposide (VP16), a clinically available anticancer compound known as a potent inhibitor of topoisomerase II, was demonstrated to inhibit irreversibly cytomegalovirus (CMV) replication. This study was performed to evaluate nontoxic concentrations of etoposide for intravitreal injection and vitrectomy infusion in patients with CMV retinitis. We used the isolated perfused vertebrate retina technique, an electrophysiological in vitro technique, for examination of retinal toxicity in higher vertebrates. Bovine and human retina preparations were perfused with an oxygen-preequilibrated standard solution. The electroretinogram (ERG) was recorded as transretinal potential using AgAgCl electrodes. The ERG serves as an indicator of the integrity of the photoreceptors, the first retinal synapse, and higher retinal neurons. After recording of stable ERG amplitudes, the drug was added to the solution for 45 min in the following concentrations: 0.0063, 0.021,0.063,0.21, mMol/L. The preparation was then reperfus...

Effects of Clindamycin on Neural Function in the Isolated Perfused Vertebrate Retina

The application of antibiotics during vitrectomy has become an established technique in treatment of bacterial endophthalmitis. During surgery antibiotics are used in the vitreous replacement fluid and as an intraocular injection at the end of the surgical procedure. A number of morphological and electrophysiological studies have been performed to evaluate non-toxic dosages of the antibiotics. Testing retinal toxkaty of a substance being directly injected into the vitreous poses a main problem: the distribution of the drug on the retinal surface may be not homogenous due to inhomgenities of the vitreal structure. As a consequence different retinal areas may be exposed to different concentrations of the drug. Thus may lead to confusing results in retinal toxicity testing. It has been suggested to perform these tests in the vitrectomized eye in order to better model the situation during vitrectomy.