Renate Hanitzsch

On-bipolar cells and depolarising third-order neurons as the origin of the ERG-b-wave in the RCS rat

In the retinas of Royal College of Surgeons (RCS) rats light induces an increase in distal extracellular potassium irrespective of the age, between days 19-24 and days 29-35 postpartum, but by days 29-35 the ERG b-wave has become reduced. The synaptic blocker 2-amino-4-phosphonobutyric acid (APB) causes the abolition of both the b-wave and the potassium increase at any age. MgCl2 greatly reduces the b-wave at all ages and abolishes the potassium increase in older rats, but in younger rats the potassium increase is enlarged. Since this increase occurs in the absence of the b-wave it is unlikely that the on-bipolar cells are the only sources of the b-wave. Because the NMDA receptor blocker ketamine reduces the b-wave, third order neurons, which possess NMDA receptors, could contribute to the b-wave.

Spezielle Überlebensbedingungen für isolierte Netzhäute verschiedener Warmblüter

The isolated perfused retina of the rabbit produces a normal electroretinogram only if the perfusion fluid contains blood plasma and is kept at 30°C. At a temperature of 20°C, the electroretinogram consists mainly of a negative component (P III) which is greatly diminished in absence of plasma in the perfusion fluid.

Intraretinal isolation of PIII subcomponents in the isolated rabbit retina after treatment with sodium aspartate

Abstract By treating the isolated rabbit retina with a plasma-Tyrode mixture containing sodium aspartate the cornea-negative component PIII was intraretinally subdivided into three subcomponents. These subcomponents have been named; (1) an aspartate-insensitive distal PIII, (2) an aspartate-sensitive PIII and (3) an aspartate-insensitive slow PIII. The aspartate-insensitive distal PIII was recorded in the receptor layer after application of aspartate; it is assumed to be the receptor potential. The aspartate-sensitive PIII is eliminated by aspartate, it probably corresponds to the proximal PIII of the frog. The aspartate-insensitive slow PIII can be found during the influence of aspartate proximal to the receptor potential and extends to a depth where the cornea-positive component PII is present if the isolated rabbit retina is perfused with a control solution.

Methodische voraussetzungen zur ableitung mit mikroelektroden an der isolierten menschlichen netzhaut

Abstract An der isolierten menschlichen Netzhaut gelang es, insbesondere durch sehr schnelle Umstro¨mung (20–40 ml/min) des Pra¨parates mit der verwendeten Lo¨sung, einu¨ber viele Stunden stabiles ERG von 300–400 μV abzuleiten. Das durch eine b-Welle, ein sich anschliessendes langsames Potential und einen positiven off-Effekt ausgezeichnete ERG bildete die Grundlage fu¨r extrazellula¨re Ableitungen mit Mikroelektroden in verschiedenen Netzhauttiefen; aus der Potentialdifferenz zwischen zwei verschiedenen Tiefen ergibt sich die in diesem Gebiet hinzugekommene Spannung.

Der nachweis langsamer potentiale im menschlichen ERG

Resume Bei drei Patienten wurde in Narkose (Lachgas-Fluothane) das ERG mit Gleichspannungsverstarkung registriert. Augen- und Lidbewegungen sowie Reaktionen von Iris und Ciliarmuskel waren mit Sicherheit ausgeschaltet. Wie im Gleichspannungs-ERG der isolierten umstromten Netzhaut des Menschen konnte auch in situ ein positives Plateaupotential nachgewiesen werden. Dieses positive Dauerpotential schliesst sich unmittelbar an die b-Welle an und fallt erst nach Belichtungsende allmahlich zum Basiswert ab. Es ist im ERG des dunkeladaptierten Auges bei Reizlichtern von niedriger Intensitat und l sec Dauer deutlich ausgepragt. NachUberschreiten eines Sattigungswertes wird das Plateaupotential mit steigender Reizintensitat kleiner und an seine Stelle tritt schliesslich bei hohen Intensitaten ebenso wie bei Helladaptation ein langsames negatives Potential ( b − -bzw . b′-Welle ). Damit sind im ERG Komponenten nachgewiesen, die nicht wie on- und off-Reaktion die Lichtanderung widerspiegeln, sondern dem Zustand der Belichtung entsprechen. Ausser diesen langsamen Potentialen konnte mit Reizen von hoher Intensitat und mehreren Sekunden Dauer auch im menschlichen ERG eine ausgepragte c-Welle nachgewiesen werden.

Intraretinal abgeleitete erg-komponenten der isolierten kaninchennetzhaut

Abstract Using micropipettes the components PII and PIII of the ERG were separated in the ERG of the isolated rabbit retina, the component PI was missed. The best differentiation of PII and PIII was possible in a depth corresponding to 57 per cent of the whole thickness of the retina measured from the receptor-side and 43 per cent from the ganglion-cell-side respectively. This depth corresponds histologically to the distal parts of the inner nuclear layer. Here the influence of increasing light intensity was studied on the isolated PII and PIII. There are some reasons to suspect that PIII consists of two subcomponents like the PIII of cold blooded vertebrates.

The effect of GABA and the GABA-uptake-blocker NO-711 on the b-wave of the ERG and the responses of horizontal cells to light

BackgroundThe effects of GABA in the retina have now become of special interest because the anti-epileptic drug vigabatrin, a GABA analogue, can cause visual field loss in humans. Vigabatrin inhibits the GABA-aminotransferase, which finally results in GABA accumulation in the extracellular space. The b-wave of the electroretinogram (ERG), which originates partly in on-bipolar cells, is influenced by both GABAergic horizontal cells (HCs) and GABAergic amacrine cells (ACs). Their influences, however, are difficult to separate. In an attempt to isolate the effect of GABAergic ACs, use has been made of the specific effect of the GABA-uptake-blocker NO-711, which blocks only the GABA transporter GAT1 of GABAergic ACs.MethodsThe ERG and the intracellular responses of HCs to light were recorded in the isolated rabbit retina, and the effects of GABA and NO-711, when added separately to the superfusate, were determined. ResultsGABA reduced significantly both the light responses of HCs and the b-wave. NO-711 enlarged the b-wave drastically, but did not affect the responses of HCs to light.ConclusionsAn increase in the extracellular GABA concentration decreases the b-wave; an impairment of the function of ACs increases the b-wave. These conditions are discussed in the context of the lack of consistent changes to the b-wave during therapy with vigabatrin.

The influence of HEPES on light responses of rabbit horizontal cells

HEPES-buffered solutions, mostly used in studies of isolated cells, and bicarbonate-buffered solutions, mostly used in studies of isolated retinal tissues, have both been used to superfuse an isolated rabbit retina preparation. The responses of horizontal cells (HCs) to light, detected by intracellular microelectrodes filled with Lucifer Yellow, were recorded. Buffering of the superfusate with 100% HEPES completely, but reversibly, abolished the responses of A-type HCs, and is not, therefore, suitable for studies on isolated rabbit retinas. The responses remained when buffering was partially with HEPES and partially with bicarbonate, but were changed: in A-type HCs the overshoot was reduced and the afterpotential was increased. The overshoot may be caused by feedback of HCs on the cones and might be dependent on pHi at the synaptic structure between HCs and photoreceptors.

Do horizontal cells contribute to the rabbit ERG

An increase in the amplitude of horizontal cell (HC) potentials, a decrease in the extracellular potassium around the photoreceptors and an increase in the PIII component of the ERG that occur with increasing light stimulus intensity are shown to be concomitant occurrences, which could, therefore, be causally related. With high intensity light stimuli the PIII component is prominent and the HC potentials exhibit an afterpotential. Within the range of intensities tested the peak times of the HC afterpotentials coincide with the peak times of PIII. This indicates the likelihood that the HC potential contributes to the PIII, although these results do not allow a quantitative assessment of the contribution of HC potentials to the PIII-component.

Two neuronal retinal components of the electroretinogram c-wave

Although the rising phase of the b-wave seems to be generated mainly in the rod bipolar cells and the cone on-bipolar cells, the slow component of the electroretinogram, the c-wave, evidently originates in the Müller cells and the pigment epithelium. The c-wave has three components. One cornea-positive component derives from the pigment epithelium, while a distal cornea-negative component (slow PIII) and a proximal slow component originate in the Müller cells. This third proximal component of the c-wave differs between mammalian species: it is negative in the rat retina, positive in the rabbit and human retina and may be lacking in the cat retina.