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E Guenther

Publications and source records attributed to E Guenther.

At least 37 records · Page 2Linked to original sources
PubMed1999

Developmental changes in voltage-activated potassium currents of rat retinal ganglion cells.

Ca2(+)-independent voltage-activated potassium currents were investigated during the differentiation of rat retinal ganglion cells. Whole-cell patch-clamp recordings of Ca2(+)-independent voltage-activated potassium currents and their individual current components, i.e. a sustained, tetraethylammonium-sensitive current, a transient, 4-aminopyridine-sensitive current, and a slowly decaying current that was blocked by Ba2+, revealed distinct ontogenetic modifications in current densities and in activation and inactivation parameters. All three current types were expressed simultaneously at embryonic day 17/18 and were present in all retinal ganglion cells thereafter without showing any significant changes until the end of the first postnatal week. Ca2(+)-independent voltage-activated potassium current densities then increased strongly from postnatal day 8 onwards. Tetraethylammonium-sensitive current density increased about eightfold from 74 pA/pF in embryonic stages to 586 pA/pF in adult cells, whereas the transient potassium currents blocked by 4-aminopyridine increased only about 2.5-fold from 174 pA/pF to 442 pA/pF. The Ba2(+)-sensitive current increased simultaneously from 35 pA/pF to 332 pA/pF. The much higher increase in the sustained current components during retinal ganglion cell differentiation accounted for the changes in decay kinetics of Ca2(+)-independent voltage-activated potassium current observed in later postnatal stages. Alterations in current densities were paralleled by pronounced changes in current kinetics. From postnatal day 8 onwards, activation of Ca2(+)-independent voltage-activated potassium current was right-shifted for about 10 mV owing to a shift in tetraethylammonium-sensitive current-activation, whereas activation of other K+ components remained unaltered. Tetraethylammonium-sensitive current steady-state inactivation was incomplete at all developmental stages. About 50% of the tetraethylammonium-sensitive current elicited by a depolarization to +36 mV did not inactivate after prepulse potentials positive to -10 mV. In contrast, transient potassium current blocked by 4-aminopyridine almost fully inactivated during embryonic stages, whereas in adult retinal ganglion cells about 40% of this current component did not inactivate after prepulse potentials positive to -20 mV. Parallel investigation of the resting membrane potential during retinal ganglion cells differentiation showed an exponential increase from -3 mV at embryonic day 15/16 when no voltage-activated ion currents were expressed to a final value of -58 mV at postnatal day 8. These results show that fundamental potassium current modifications occur relatively late in retinal ganglion cell development and only after the resting potential is at its final value.

4-Aminopyridine↗
PubMed1999

Angiotensin II receptor subtype gene expression and cellular localization in the retina and non-neuronal ocular tissues of the rat.

In addition to its function as a peripheral hormone, angiotensin II (AngII) has been shown to act as a neuromodulator in various brain regions. AngII effects are mediated by two major AngII receptor subtypes, AT1 and AT2, and different AT1 receptor isoforms AT1A and AT1B are described in rat brains. The purpose of the present study was to analyse the expression pattern of AT receptors in different parts of the rat eye with special emphasis on the retina. Specific primers were constructed and the gene expression of AngII receptor subtypes was investigated by means of reverse transcription-polymerase chain reaction (RT-PCR). An antibody was used for cellular localization of AT1 receptor in the retina. AT2 receptor mRNA was localized by in situ hybridization (ISH). We examined the retinas of different developmental stages as well as non-neuronal ocular tissues, e.g. choroid and anterior uveal tract of rats (Brown Norway and Wistar strain), for the gene expression of AT receptors. Our results show that AT1A and AT2 mRNAs are expressed in rat choroid, iris/ciliary body and retinas, whereas AT1B mRNA is not expressed in the retina but in all other ocular tissues under investigation. AT1 receptor immunohistochemistry of the retina showed strong labelling in the ganglion cell layer (GCL), and some cells in the inner nuclear layer (INL), suggesting putative ganglion cell but also amacrine cell labelling. In the retina, ISH for AT2 mRNA revealed labelling in the GCL and a faint labelling in the inner nuclear layer. No AT2 ISH-signal was found in the other ocular tissues. These data suggest that there is a specific distribution pattern of AT receptors in rat ocular tissues, especially in the retina. The expression of AT receptors on retinal ganglion cells confirms the AngII action on these cell types and supports the role of AngII as a retinal neurotransmitter or neuromodulator.

Animals↗
PubMed1998

Gene expression of the P2X receptors in the rat retina.

Molecular-biological methods were used to demonstrate the expression of six P2X receptor subunits (P2X1-P2X6) in retina and choroid. Despite the considerable evidence for signalling by extracellular nucleotides in other sensory systems, few studies have been undertaken in the eye. RT-PCR for the detection of P2X subunit mRNA in the rat of different postnatal developmental stages (P23-P210) revealed the presence of P2X2 and P2X4 mRNA in the retina and choroid; P2X3, and P2X5 were detected only in the retina. There was no evidence for P2X1 and P2X6 mRNA in the ocular tissue under investigation. Our data suggest that extracellular ATP may have influences on visual processing.

Animals↗
PubMed1998

Alterations in channel density and kinetic properties of the sodium current in retinal ganglion cells of the rat during in vivo differentiation.

Changes in the kinetic properties of voltage-activated sodium currents (I(Na)) were studied in rat retinal ganglion cells during in vivo differentiation. Whole-cell recordings from cells maintained as retinal slices or whole-mounts were examined using the patch-clamp technique in the perforated patch mode. Voltage-clamp recordings revealed significant ontogenetic modifications in key properties of I(Na) and the present study described for the first time the detailed time course of such alterations. I(Na) was first expressed on embryonic day 17/18 (E17/18). Current density increased during development from an average of -81 pA/pF on E17/18 to a maximum of -747pA/pF on postnatal day 10/12 (P10/12). Simultaneously, the activation of I(Na) shifted towards more negative potentials, reflected by a shift in the potential of half-activation from -14.1 mV on E17/18 to - 37.5 mV on P10/12. No significant changes in these parameters were observed after P10/12. Steady-state inactivation shifted first towards more positive potentials, reflected by a shift in the potential of half-inactivation from -51 mV on E17/18 to -38 mV on P3/5, but shifted back towards more negative values thereafter (-44 mV in the adult). The most striking feature of I(Na) in rat RGCs was a transient slowing of I(Na) kinetics that was never described before. Time to peak and decay time constants increased between E20 and P5, resulting in slow and broad sodium currents within a developmental period that is characterized by intensive synaptogenesis in the target structures of retinal ganglion cells and maximum retinal ganglion cell death. Thereafter, time to peak and decay time constants decreased again to values found before E20, resulting in rapid sodium spikes. In conclusion, sodium currents in rat retinal ganglion cells displayed substantial electrophysiological changes during pre- and postnatal development. These changes in the sodium system had different temporal time patterns, indicating that they may play specific roles during the development of the visual system.

Aging↗
PubMed1997

Angiotensin II-induced inhibition and facilitation of calcium current subtypes in rat retinal ganglion cells.

Whole cell patch-clamp recordings were performed on freshly dissociated rat retinal ganglion cells to determine the action of Angiotensin II (AngII) on voltage-activated calcium current subtypes in this cell type. AngII had no effect on a toxin-resistant calcium current component; N-type currents were reduced by 27 +/- 5% in all retinal ganglion cells (RGCs) tested; L-type currents were reduced by 33 +/- 7% in 59% of the RGCs but increased by 31 +/- 6% in 41% of the cells. AngII effects were reversible within a few seconds through reperfusion with bath solution and calcium current kinetics and current-voltage relations remained unaffected. The net effect of AngII in a single RGC is either a reduction or an enhancement of the total calcium current, dependent on (1) the number of L-type channels compared to N-type channels and (2) on the kind of action AngII exerts on L-type channels.

Angiotensin II↗
PubMed1997

[Animal models for retinitis pigmentosa research].

Retinitis pigmentosa (RP) is the general term given to a group of genetically determined, degenerative retinal diseases which afflict some 1.5 million humans worldwide. Molecular genetic studies in recent years have shown that RP cannot be explained by a single genetic defect but rather that the hereditary aberration responsible for triggering the onset of the disease is localized in different genes and at different sites within these genes. A fuller understanding of these processes is possible only if the pathogenesis of the diseases can be followed as they develop. Animal models are an indispensable requirement for this. Only in the animal model is it possible to observe progressive degenerations in "time-lapse photography" as it were and to examine the biochemical, functional and morphological changes which appear at specific times in the retina. This article gives an overview of the animal models presently used in RP research, with a short description of genetic backgrounds and the progression of the disease in individual animals. In addition, a look at the future is provided of new molecular techniques which make it possible to create specific animal models with gene mutations identical to those appearing in human RP. Since hereditary human retinal degenerations can be brought about by numerous different genetic defects, comparative studies using animals with clearly defined genetic defects are essential. Only in this way is it possible to arrive at conclusions concerning this specialized syndrome and to clarify the mechanisms which are common to all retinal degenerations.

Animals↗
PubMed1997

The development of subretinal microphotodiodes for replacement of degenerated photoreceptors.

There are presently several concepts to restore vision in blind or highly visually handicapped persons by implanting electronic devices into the eye in order to partially restore vision. Here, the approach to replace retinal photoreceptors by a subretinally implanted microphotodiode array (MPDA) is summarized. A survey is given on the present state of the development of MPDAs, the possibility of in vitro and in vivo tests as well as first results on biocompatibility and histology. Additionally, electrophysiological recordings in rabbits and rats are presented which have received such subretinal implants.

Animals↗
PubMed1997

Persistent decrease of the dopamine-synthesizing enzyme tyrosine hydroxylase in the rhesus monkey retina after chronic lead exposure.

One of the toxic effects of lead in the CNS is an altered functional state of the catecholamine system, especially a reduction in the activity of tyrosine hydroxylase (TH), the rate-limiting enzyme of catecholamine synthesis. Here we report on a lead-induced decrease in TH-content in neurones of the rhesus monkey retina. Rhesus monkeys were pre- and postnatally exposed to 0, 350, or 600 ppm of lead acetate (Pb) in the diet over 9 years. Lead exposure was followed by a 35-month period of lead-free diet. During this period, blood lead levels of the treated animals declined to nearly those of the untreated controls. Subsequently the animals were sacrificed and the retinas processed for TH immunocytochemistry. The fluorescent dye FITC was used to visualise the antibody reaction. Photometric measurements of the fluorescence intensity of stained neurones were made with a laser scanning microscope. In the rhesus monkey retina two types of TH-immunoreactive neurones are present. In the bright fluorescent type, lead exposure resulted in decreased fluorescence intensity and altered the intensity profile of the TH-immunoreactive cells in a dose-dependent manner. In these cells, fluorescence intensity was 0.53 and 0.22 for 350 ppm Pb and 600 ppm Pb respectively when the fluorescence intensity of the untreated controls (0 ppm Pb) is taken as 1. Both lead doses also reduced the number of ascending fibres in the inner nuclear layer and the dense staining of fibres in sublayer 1 of the inner plexiform layer. The weakly fluorescent cell type disappeared to a large extent under 350 ppm Pb treatment and was not detectable in the 600 ppm Pb group. The results demonstrate that lead exposure affects the dopaminergic retinal amacrine cells by reducing the TH-content in these neurones and that this neurotoxic effect persists beyond the end of exposure.

Animals↗
PubMed1996

Two-fold effect of Angiotensin II on voltage-dependent calcium currents in rat retinal ganglion cells.

Angiotensin II (AngII) is one of the most important vasoconstrictive hormones but is also known to act as a neuromodulator in the central nervous system (CNS). Recently, AngII-containing neurons have been identified in the inner nuclear layer and the ganglion cell layer of the retina of various vertebrate species. The present study was undertaken to investigate the physiological effect of AngII on voltage-activated ion channels in retinal ganglion cells of the rat, Ion currents were recorded in freshly dissociated cells in the whole-cell configuration of the patch-clamp technique. AngII concentrations of 1 to 100 microM had no effect on sodium currents but modulated the influx through high voltage-activated (HVA) calcium channels in a 2-fold manner. AngII (100 microM) increased the HVA-calcium current by 15 to 65% in 41% of the cells, whereas a current reduction of 18 to 69% was observed in 59% of the cells. AngII effects were reversible within a few seconds of reperfusion with bath solution. Calcium-current kinetics and current-voltage relations remained unaffected.

Angiotensin II↗
PubMed1996

Developmental regulation of voltage-activated Na+ and Ca2+ currents in rat retinal ganglion cells.

The developmental regulation of voltage-gated Na+ and Ca2+ current expression was investigated in rat retinal ganglion cells (RGCs) using whole cell patch clamp recordings. Experiments were performed on retinal whole mounts and slices from embryonic day 14 (E14), the developmental stage where RGCs start to differentiate from their precursor cells, to postnatal day 25 (P25) where the retina is fully differentiated and the animals have opened their eyes. No voltage-activated ion currents could be detected earlier than E17. From E17/18 on, small voltage-gated Na+ and Ca2+ currents could be measured which increased remarkably in amplitude until P16. Analysis of current kinetics and application of specific calcium channel antagonists revealed an alteration in the contribution of different Ca2+ current components to the voltage-activated whole cell Ca2+ current in RGCs during development.

Action Potentials↗
PubMed1995

Changes in Thy-1 antigen immunoreactivity in the rat retina during pre- and postnatal development.

Although Thy-1 is one of the most abundant surface glycoproteins in mammalian central neurons, its functional role is still not clarified. In this study we demonstrate that Thy-1 expression in the rat retina starts only at embryonic day 19 on both the cell somas and processes of retinal ganglion cells. Thy-1 immunoreactivity in the ganglion cell layer increases until postnatal day 14 and is paralleled by an increase in the thickness of the inner plexiform layer. Thus, the beginning of Thy-1 expression is correlated with a developmental stage when axonal elongation and neurite sprouting of ganglion cells has finished and refinement of synaptic structures in the colliculus superior begins. From postnatal day 9 on, Thy-1 immunoreactivity can also be observed on cell somas at the border of the inner plexiform/inner nuclear layer.

Animals↗
PubMed1994

Inhibitory action of haloperidol, spiperone and SCH23390 on calcium currents in rat retinal ganglion cells.

Patch-Clamp measurements in the whole-cell configuration were performed on isolated rat retinal ganglion cells to record voltage-activated calcium currents in the presence of dopamine antagonists. We report here that, in the absence of dopamine, application of the receptor antagonists haloperidol, spiperone and SCH23390 reduced calcium influx between 8% and 77%. The effect was fully reversible. After application of haloperidol and SCH23390, Ca2+ currents (ICa) recovered rapidly and completely within 30 s of washing. Current recovery after application of spiperone was completed only after 2 min of washing. I-V plots showed no change in the voltage-dependence of ICa during drug application. Also current kinetics remained unaffected by the dopamine antagonists.

Action Potentials↗
PubMed1994

Separation of calcium currents in retinal ganglion cells from postnatal rat.

A culture system of the postnatal rat retina was established to investigate Ca2+ currents and synaptic transmission in identified neurons. Methods are described that allowed us to select retinal ganglion neurons (RGNs) in short term cultures (up to 48 h in vitro) and in long-term cultures (3 to 21 days in vitro). The specific aim of the present study was to identify channel specific components in whole-cell Ca2+ currents of RGNs and to clarify the potential use of the lanthanide Gd3+ as a selective Ca2+ channel blocker. About one third of freshly dissociated RGNs generated both low voltage activated Ca2+ currents (ICa(LVA)) and high voltage activated Ca2+ currents (ICa(HVA)). The remaining 2/3 or RGNs in short term culture and most RGNs in long-term culture displayed only ICa(HVA). The latter comprised at least three different components that were functionally rather similar, but could be separated pharmacologically. A significant portion (about 40%) of ICa(HVA) was irreversibly blocked by the N channel antagonist omega-CgTx (5 microM). The L channel antagonist nifedipine (10 microM) eliminated about 25% of ICa(HVA). Thus, about 1/3 of the HVA Ca2+ or Ba2+ current remained unaffected by either omega-CgTx or nifedipine. omega-AgaTx (200 nM) completely failed to block HVA Ca2+ or Ba2+ currents in RGNs. Gd3+ exerted contrasting actions on LVA and HVA Ca2+ currents. While ICa(LVA) consistently increased in the presence of Gd3+ (0.32-3.2 microM), ICa(HVA) always decreased, especially when using higher concentrations of Gd3+ (10-32 microM). The blocking action of Gd3+ was not restricted to the omega-CgTx-sensitive HVA current component, but also concerned omega-CgTx- and nifedipine-resistant components. The decay of Ca2+ currents was accelerated in the presence of Gd3+. Even in RGNs lacking ICa(LVA), application of 3.2 microM Gd3+ significantly reduced the time constant of decay from an average of 64 ms to 36 ms (voltage steps from -90 to 0 mV; 10 mM [Ca2+]o; 26 degrees C). This is in contrast to what had to be expected if an N-type HVA current component was selectively suppressed by Gd3+.Gd3+ diminished glutamatergic spontaneous synaptic activity in retinal cultures tested during the 3rd week in vitro. Both frequency and amplitude were reduced. Occasionally, the application was followed by a rebound increase of EPSC frequency. A stimulatory effect during application of Gd3+ has never been observed. These experiments indicate that RGNs express at least 4 different types of Ca2+ currents, that resemble in some aspects T, N and L channel currents.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1994

In vitro identification of retinal ganglion cells in culture without the need of dye labeling.

We here describe a method for the identification of a distinct neuronal phenotype at all stages of development in culture without the need of any staining procedure. Based purely on a size criterion we can rapidly select vital retinal ganglion cells (RGCs) for further studies out of a mixed culture of rat retinal cells. In order to establish a size criterion for retinal cells of various age, RGCs were first labeled immunocytochemically with antibody against the ganglion cell-specific surface glycoprotein Thy-1. Soma diameters were then determined for labeled and unlabeled cells between embryonic day 16 (E16) and postnatal day 90 (P90). Unlabeled neurons of all ages had soma diameters between 3.6 microns and 12 microns (mean diameter: 6.3 microns). In contrast, soma diameters of RGCs ranged from 8.4 microns to 28 microns and the number of RGCs with large soma diameters increased with age. Thus, in a mixed retinal cell culture only RGCs are larger than 12 microns and can be selected solely based on their size. The validity of the size criterion during the whole period of retinal cell differentiation offers the possibility to study the development of cellular functions and ion channel properties in a distinct type of cell without the risk of artifacts introduced by staining.

Animals↗
PubMed1993

Differences in adaptation between on- and off-centre ganglion cells and rod-mediated cone sensitization in cat retina.

1. Response properties of on- and off-centre retinal ganglion cells were investigated in cats. The stimulus parameters were selected so as to demonstrate interactions between the rod and the cone systems. 2. Response versus log stimulus intensity (R-log I) functions were determined for the receptive field centres while both test stimulus irradiance and the background illumination were varied over a range up to 7 log units. In order to determine the course of adaptation to chromatic stimuli, threshold versus intensity (t.v.i.) functions were measured over a wide range of adaptation levels. 3. An increase in background illuminance produced a shift of the R-log I functions to higher irradiances of test stimuli in most ganglion cells, indicating a desensitization of the centre response in the presence of background lights. Using test stimuli which most efficiently stimulate the rods (501 nm), clear differences could be seen in the adaptation behaviour of on- and off-centre ganglion cells. Chromatic backgrounds (blue-green and orange) reduced the responses of off-centre cells more than those of on-centre cells (the difference between them amounting to as much as 2 log units). Simultaneously, equivalent t.v.i. functions had significantly steeper slopes (0.94 and 1.1) in the linear proportions of off-centre cells compared to on-centre cells (0.76 and 0.75) under light levels mediated by rods. Such differences were not observed when a test stimulus of 575 nm was used which resulted primarily in stimulating the long-wavelength cone (L-cone) system. 4. In a subpopulation of off-centre cells (20% of the total number of off-centre cells recorded), a strikingly different adaptation behaviour was observed. Here, the presentation of a dim short-wavelength background produced a shift of R-log I functions to lower test stimulus irradiances. The receptive field centre became even more sensitive, by up to 1.5 log units, in the presence of dim adapting backgrounds rather than in the dark-adapted state. Accordingly, the t.v.i. function did not increase monotonically but showed a 'dip' in the presence of dim backgrounds. Only at photoic levels, the t.v.i. functions revealed a response behaviour similar to the other ganglion cells. The sensitization with dim backgrounds was only observed in the case of test stimuli designed to stimulate the cone system (575 nm) and in the presence of a rod-adapting blue-green background.(ABSTRACT TRUNCATED AT 400 WORDS)

Adaptation, Physiological↗
PubMed1993

The spectral sensitivity of dark- and light-adapted cat retinal ganglion cells.

The spectral sensitivity of cat retinal ganglion neurons (RGNs) was determined by means of extracellular recordings under scotopic and photopic conditions, in both receptive field center and surround. Test stimuli were presented either as square-wave single flashes or as flicker stimuli. Chromatic adaptation was achieved by a large steady monochromatic background field. In the dark-adapted state the spectral sensitivity of the majority of ganglion cells (92%) was rod mediated (peak sensitivity at 501 nm). Under photopic conditions all neurons received input from a long-wavelength-sensitive (L-cone) system with a peak sensitivity of 550 nm. Input from a short-wavelength-sensitive (S-cone) system (peak sensitivity at 450 nm), however, was found only in 15% of the ganglion cells. A small cell population (8%) located within the area centralis revealed a different receptive field organization. In these cells, spectral sensitivity in the field center peaked at 520 nm in the dark-adapted state and response threshold was about 1 log unit higher than in cells with a peak sensitivity of 501 nm. Critical flicker fusion was reached at 60-70 Hz, a frequency that usually is mediated by cones. We therefore postulate an additional input of a midspectral receptor system (M-system) other than rods in cat retinal ganglion cells. This input was found only in the receptive field center of some ganglion cells in the dark-adapted state, whereas the surround sensitivity was mediated in all cells by rod signals under scotopic and predominantly by L-cone signals under photopic conditions.

Adaptation, Physiological↗
PubMed1990

New congenic rat strains for the separate study of MHC and non-MHC genetic effects in the development of diabetes in BB rats.

Diabetes in BB rats is genetically determined by at least two genes, the one gene mapping to the MHC, the other residing in the genetic background. In order to be able to study the role of MHC and non-MHC genes in diabetogenesis we have established rat strains which combine the diabetes-resistant LEW genetic background with the RT1u haplotype of diabetic BB rats (LEW.1BB) or carry the diabetes-resistant RT1 haplotype of LEW.1A rats on the diabetic BB genetic background (BB.1A). BB rats of two different sublines (BB/OK and BB/PhiK) were used for this purpose. In these rat strains diabetes relevant traits were studied longitudinally, the RT1 haplotypes were analyzed at DNA level and 18 non-MHC linked immunogenetic and enzyme loci were monitored. The results demonstrate the successful transfer of genes with potential relevance for diabetes development in BB rats.

Animals↗