Localization of Inhibition of Platelet Aggregation by Incubation of Platelet Rich EDTA-Plasma at 37°C

By photometric and microscopic technics investigations have been carried out to determine the nature of the inhibition of platelet aggregation caused by incubating platelet rich EDTA-plasma at 37° C. The results clearly indicate that the inhibition must arise from alterations in the platelets themselves. The appearance of an inhibitory substance in plasma and the release of such a substance from the platelets into the plasma have been excluded. Addition of ADP to the inhibited platelets did not influence the inhibition of platelet aggregation.

Force-sensitive detents improve user performance for linear selection tasks

Haptic technology, providing force cues and creating a programmable interface, can assist users in more accurately using an interface. This paper investigates haptic assistance in combination with auditory feedback instead of visual feedback. A user test is carried out in which participants select fundamental frequencies from a continuous range to play brief musical melodies. Two control conditions are compared with two detent-based haptic assistance conditions. The detents gently guide the users toward locations of equal tempered fundamental frequencies. Results from the user test confirm improved accuracy brought about by the detents. It is further helpful to provide regulation of the strength of haptic assistance in real time, allowing the user to remain always in control. This concept motivated the force-sensitive detent condition, which enables the user to adjust the strength of the haptic assistance in real time by changing the downward force applied to the haptic device. The work implies that users of graphical user interfaces could similarly benefit from force-sensitive detents and more generally real-time regulation of the strength of haptic assistance.

Syndromic retinitis pigmentosa: ERG and phenotypic changes

PURPOSE

Our aim was to review the phenotype and extent of ERG changes in syndromic RP (SRP).

PATIENTS AND METHODS

A retrospective review of charts of 82 patients seen over the last 20 years with SRP was carried out. Clinical data were compared with changes in ERG. Full-field ERGs comprised selective rod-driven, maximal dark-adapted mixed responses, and isolated cone-driven signals. Occasionally, ERGs were recorded under brief general anaesthesia. ERG changes were classified as normal, reduced or extinguished.

RESULTS

Syndromic RP was diagnosed for the following entities: Usher (45 patients), Laurence-Moon-Bardet-Biedl (LMBB, 17 patients), Kearns-Sayre (10), Batten (6), Refsum (3), Senior-Loken (1). ERG changes varied in every subgroup and were therefore not specific for the syndromes.

CONCLUSION

There was wide variation of clinical presentation in SRP, much as seen in isolated RP, often without obvious ophthalmoscopic changes. ERG testing is a prerequisite for differential diagnosis as well as for early detection of multiple handicaps.

Retinal research using the perfused mammalian eye

The effort to isolate and maintain alive in vitro an intact mammalian eye is rewarded by the full control provided over the arterial input and exclusion of systemic regulatory or compensatory mechanisms. Electrical recording of typical light-evoked field potentials from retina and optic nerve can be complemented by single-cell recording. Thus, light-induced electrical activity reflects the function of the retinal pigment epithelium, of the layers of the retina and of the ganglion cells or their axons. Retinal function in vitro is documented by electrophysiological and morphological methods revealing subtle features of retinal information processing as well as optic nerve signals that approach-at threshold stimulus intensity-the human psychophysical threshold. Such sensitivity of third-order retinal neurons is described for the first time. This well controlled in vitro preparation has been used successfully for biophysical, metabolic and pharmacological studies. Examples are provided that demonstrate the marked sensibility of the rod system to changes in glucose supply. Moreover, histochemical identification of glycogen stores revealed labeling of the second- and third-order neurons subserving the rod system, in addition to labeling of Müller (glial) cells in the cat retina. The glycogen content of the cat retina is augmented by prolonged anesthesia, largely depleted by ischemia after enucleation and enhanced by insulin. Pharmacological experiments using agonists and antagonists of putative retinal neurotransmitters are summarized and outlined using the muscarinic cholinergic agonist QNB as an example. Actions and uptake of the neuromodulator adenosine are presented in detail, including inhibitory effects on physiologically characterized ganglion cells. Neuronal effects of adenosine are distinguished from those resulting from vasodilatation and from glycogenolysis induced by the neuromodulator. To open the blood-retina barrier, a hyperosmotic challenge can be applied transiently. This process is monitored histochemically using FITC-albumin and with electrophysiological parameters. Changes in vitreo-scleral resistance and in the amplitude of the EOG-light peak appear to reflect the open/closed status of the barrier. This overview of the uses of the isolated perfused mammalian eye in retinal research concludes with a discussion of potential implications for clinically relevant topics.

The mouse ERG before and after light damage is independent of p53

Death of retinal photoreceptors by apoptosis is observed under many physiological and pathological conditions such as histogenesis, retinal dystrophies and light-induced photoreceptor degeneration. To date, little is known about regulatory mechanisms for apoptosis in the retina. The tumor suppressor gene p53 is a regulator of apoptosis in a number of systems, however, p53-independent apoptosis has also been described. We have therefore investigated whether the lack of p53 influences the dark-adapted ERG in C57BL/6 p53-/- mice compared to p53+/+ control littermates under physiological (regular light-dark cycle) conditions. We also recorded ERGs at 12 to 14 h in darkness following diffuse bright light exposure to 8,000 or 15,000 lux for 2 h. ERG analysis over a range of 6 logarithmic units of light intensity revealed normal and virtually identical a-, b-, c-waves and oscillatory potentials in dark-adapted p53+/+ and p53-/- mice. After exposure to diffuse white fluorescent light strong decreases of all ERG components were found to be very similar in both genotypes. These data support the notion that the p53 protein is neither essential for normal retinal function nor for processes involved in light-induced depression of the ERG in mice.

Effect of verapamil enantiomers and metabolites on cardiac K+ channels expressed in Xenopus oocytes

The effect of verapamil and its enantiomers and metabolites on cardiac action potential repolarizing potassium channels was tested. For this purpose, the potassium channels Kv1.1, Kv1.5, Kir2.1, and HERG, and the IsK subunit of the IKs-channel complex were expressed in Xenopus oocytes and two-electrode voltage-clamp experiments were performed. Verapamil induced a concentration-dependent block of Kv1. 1-, Kv1.5-, IKs-, and HERG-induced currents with IC50 values of 14.0 +/- 2.7 microM (n = 4), 5.1 +/- 0.5 microM (n = 6), 161.0 +/- 26.3 microM (n = 4), and 3.8 +/- 0.2 microM (n = 5), respectively. The same potency of HERG channel inhibition was observed for the optical enantiomers (+)-verapamil (IC50 = 3.5 +/- 0.4 microM, n = 5) and (-)-verapamil (IC50 = 4.0 +/- 0.7 microM, n = 4), as well as the derivatives norverapamil (D591; IC50 = 3.8 +/- 0.3 microM, n = 4) and D703 (IC50 = 2.2 +/- 0.4 microM, n = 4). The verapamil metabolites D620 and D617 did not block HERG-induced currents at concentrations of up to 30 microM (n = 3). These results demonstrate that cardiac delayed rectifier potassium currents are sensitive targets to calcium channel blockers.

[Stargardt's disease and its intrafamilial variability]

BACKGROUND

Because of its considerable differential diagnosis and a wide range of phenotypic variation, Stargardt's disease (juvenile macular dystrophy) can cause diagnostic problems. Moreover, ample variability in course and outcome of the disease has been described.

PATIENTS AND METHODS

The diagnosis and variable course of Stargardt's disease of three affected siblings have been documented by clinical manifestation, fluorescein angiography and Ganzfeld-ERG including the ISCEV standard protocol.

RESULTS

All three siblings presented with retinal abnormalities. However, only the youngest brother revealed symptoms for more than 10 y in terms of reduced visual acuity. The two elder ones had preserved central vision. Classical findings of contact lens biomicroscopy, fluorescein angiography and changes in the Ganzfeld-ERG confirmed the diagnosis of Stargardt's disease.

CONCLUSIONS

The diagnosis of Stargardt's disease can be made as late as in the 7th decade of life. Tremendous variability can occur in course and outcome even within the same family. Therefore, visual prognosis is uncertain and has to be made with caution. In most cases the diagnosis can be established with the above mentioned methods.

[Effect of insulin on retinal glycogen content]

BACKGROUND

The effect of insulin on glucose and glycogen metabolism in peripheral organs is well known. However, information about the action of this peptide in the retina is incomplete. We addressed the questions whether insulin influences glycogen content in the cat retina and whether glycogen breakdown is triggered by lack of glucose.

MATERIAL AND METHODS

Eyes from adult cats were enucleated under deep barbiturate and fentanylanesthesia. Retinas were snap frozen either before or following arterial in vitro perfusion. Three conditions were studied: a) Perfusion with a glucose- and insulin-free medium; b) perfusion with the addition of physiologic glucose concentration; and c) in combination with insulin. Glycogen content was determined by in vitro measurement of glucose converted from glycogen.

RESULTS

The reference value for retinal glycogen after enucleation (10 min of ischemia) is 2.4 micrograms glucose/mg protein. Glucose- and insulin-free perfusion for 80 min following "normoglycemia" reduced the amount of retinal glycogen by one third. Perfusion for 3 h with 5.5 mM glucose led to a small increase of the partly depleted glycogen stores. Insulin, in contrast, markedly augmented the glycogen content.

CONCLUSIONS

Insulin led to an increase in retinal glycogen content, indicating an influence of this peptide on retinal glucose and glycogen metabolism. However, it appears that glycogen might play a dynamic role in retinal metabolism as a buffer between abrupt changes in focal metabolic demands that occur during normal glucose supply rather than acting solely as an emergency energy reserve for neural function during hypoglycemia.

The retina of c-fos-/- mice: electrophysiologic, morphologic and biochemical aspects

PURPOSE

Mice without a functional c-Fos protein (c-fos-/- mice) do not exhibit light-induced apoptotic cell death of rods in contrast to their wild-type littermates (c-fos+/+ mice). To analyze the consequences of the absence of c-fos in the retina, we investigated whether the retinas of c-fos-/- mice have a reduced capacity to absorb and transduce light compared with c-fos+/+ mice.

METHODS

Retinal function was evaluated in dark-adapted mice by full-field electroretinograms (ERGs) over more than 6 log units of intensity. Retinal morphology was studied by light- and electron microscopy. Arrestin and the heat shock protein 70 (Hsp70) were detected by Western blot analysis. The rhodopsin content and the kinetics of rhodopsin regeneration were determined in retinal extracts.

RESULTS

Although the configuration of the ERGs was comparable in both groups of mice, c-fos-/- mice showed a marked variability in all quantitative ERG-measures with lower mean amplitudes, longer latencies, and a 0.9-log-unit lower b-wave sensitivity on average. Morphometry showed that c-fos-/- mice have 23% fewer rods on average, whereas the number of cones was comparable among c-fos+/+ and c-fos-/- mice. Arrestin levels appeared slightly reduced in c-fos-/- mice when compared with c-fos+/+ mice, whereas Hsp70 levels were comparable in both genotypes. The kinetics of rhodopsin regeneration were similar, but c-fos-/- mice had a 25% lower rhodopsin content on average.

CONCLUSIONS

Compared with c-fos+/+ mice, retinal function in c-fos-/- mice is attenuated to a variable but marked degree, which may be, at least in part, related to the reduced number of rods and the reduced rhodopsin content. However, c-fos does not appear to be essential for the ability to absorb photons, nor for phototransduction or the function of second-order neurons. The resistance to light-induced apoptosis of photoreceptor cells in c-fos-/- mice may result from the acute deficit of c-fos in the apoptotic cascade rather than from developmental deficits affecting rod photoreceptor function.

c-fos controls the "private pathway" of light-induced apoptosis of retinal photoreceptors

White light (5 klux for 2 hr) induces apoptosis of rod photoreceptors in wild-type mice (c-fos(+/+)) within 24 hr, whereas rods of c-fos knock-out mice (c-fos(-/-)) are protected (). The range of this protection was tested by analyzing retinas of c-fos(+/+) and c-fos(-/-) mice up to 10 d after exposure to threefold increased light intensities (15 klux for 2 hr). In c-fos(-/-) mice, rods were unaffected, whereas they were destroyed in c-fos(+/+) mice. After light exposure, mitochondrial damage in rods was observed exclusively in c-fos(+/+) mice. Electroretinograms recorded 48 hr after exposure revealed a decrease of all components in c-fos(+/+) mice but indicated no light-induced loss of function in c-fos(-/-) mice. Thus, in c-fos(-/-) mice, light-induced apoptosis is blocked or its threshold is elevated more than threefold. Increased activity of the transcription factor activator protein-1 (AP-1) in retinas of light-exposed c-fos(+/+) mice indicated an acute contribution of AP-1 to apoptosis induction. AP-1 activity increased already during exposure and peaked approximately 6 hr thereafter, coinciding with the appearance of major morphological signs of apoptosis. Activated AP-1 mainly consisted of c-Fos/Jun heterodimers. In c-fos(-/-) mice, AP-1 activity remained unchanged, indicating that no other Jun- or Fos-family member could substitute for c-Fos. Like damaging light, N-methyl-N-nitrosourea (MNU) induced AP-1 containing c-Fos in c-fos(+/+) mice and did not induce AP-1 in c-fos(-/-) mice. In contrast to light, however, MNU induced apoptosis in rods of c-fos(-/-) mice. Thus, c-Fos is essential for a specific premitochondrial "private apoptotic pathway" induced by light but not for the execution of apoptosis induced by other stimuli.

[The electroretinogram (ERG) of the mouse: normal values, optimal stimulation and recording]

PURPOSE

The electroretinogram (ERG) is an appropriate method to evaluate the retinal function in a variety of animal models. In this study we present suitable conditions of stimulation and recording in the dark-adapted mouse.

METHODS

Mice (n = 15) were dark-adapted during 14 hours and anesthetized with a single intraperitoneal injection of xylazine/ketamine. Pupils were dilated and a d.c.-silk-silver electrode or a AgCl-contact-lens electrode was placed on the cornea. The electroretinogram (ERG) was obtained by Ganzfeld stimulation over a range of 6 log units of intensity (8 x 10(-2) - 8 x 104 cd/m2). Intensity, duration and the interval of the light stimuli were varied separately.

RESULTS

Reproducible values of the intensity-response functions are obtained for the a-, b- and c-waves of the ERG under well controlled adaptation- and stimulus-conditions. C-wave amplitudes are best evaluated using d.c.-recording and a stimulus duration of 4 seconds. The position of the d.c.-silk-silver electrode on the cornea can affect the ERG-amplitudes. Using a contact-lens electrode, the recorded b-wave amplitudes are on average 20% below those recorded with a centrally positioned d.c.-silk-silver electrode. Stimulus-intervals of at least 60 seconds are recommended at high intensities.

CONCLUSIONS

An unequivocal assessment of retinal function requires reproducible ERG-values over a wide range of intensities. To obtain these, well controlled and standardized experimental conditions are required.

[From the symptom to electroretinography diagnosis]

Retinal function can be documented noninvasively and objectively by electroretinography, complementing clinical examinations. Symptoms of nightblindness and of dayblindness with photoaversion, nystagmus, poor vision in infants or unclear visual field defects are meaningful indications for ERG testing. We use standardized (ISCEV) full-field single flash ERGs to evaluate the function of the rod- and of the cone-system. In infants, general anesthesia is useful to combine an abbreviated ERG protocol with ophthalmoscopy and fundus photography. ERG testing facilitates to distinguish between functional deficits in the rod- and cone-system, between congenital-stationary retinal dysfunction and progressive retinal heredo-degenerations. Frequently a functional deficit of the retina without ophthalmoscopic changes can be assessed. These entities include achromatopsia, congenital stationary night blindness, early stages of retinitis pigmentosa (RP) or progressive cone dystrophy, as well as toxic retinal changes. Congenital amaurosis Leber (LCA), infantile RP, Usher's syndrome and retinal involvement in other neuropediatric or metabolic syndromes can be diagnosed or excluded by ERG recording early-on. Synoptic evaluation of the full-field ERG, pattern-ERG and VEP completes neuro-ophthalmological screening.

A simple and stable d.c.electrode for ocular electrophysiology

We describe the fabrication of a simple silver-silk electrode which permits remarkably stable d.c.recording of the electroretinogram (ERG) and the optic nerve response (ONR). A saline soaked wick of surgical silk, guided into a polyethylene tube connects the tissue to a coil of Ag/AgCl wire placed in a small glass vial, which is filled with 0.9% NaCl. The vial that holds the tube and the wire is closed with a rubber cap allowing easy refilling with NaCl. Examples of the usefulness of the new silver-silk electrode are shown. We applied it in experimental work in the isolated arterially perfused cat eye for d.c.recordings of the ERG and the optic nerve response (ONR), and also in vivo, in anesthetized mice to record c-waves.

Effects of adenosinergic agents on the vascular resistance and on the optic nerve response in the perfused cat eye

The function of A1- and A2a-adenosine receptors in the control of vascular resistance and in the modulation of light-evoked neuronal activity was investigated in the isolated perfused cat eye. The A1 agonist CCPA, the A1 antagonist CPT, the A2a agonist CGS 21680 and the A2 antagonist DMPX were used. The agents were applied intra-arterially at concentrations in the low nanomolar to micromolar range during rod-selective photic stimulation. The flow rate of perfusate, reflecting vascular resistance and the light-evoked optic nerve response (ONR) were recorded. Our results show a vasodilating effect of both A1 and A2 agonists and a vasoconstricting effect of the respective antagonists. The dose-effect relationships are suggestive, however, of an A2a receptor-mediated mechanism. The amplitude of the ONR-ON component was decreased during application of both adenosine-agonists. Analysis of the dose-effect relationships and the blockade of the CCPA-induced decrease by CPT suggests that inhibition is mediated by A1 receptors. However, CGS 21680-mediated inhibition cannot be explained by unspecific binding at A1 receptors alone and suggests the involvement of inhibitory A2a receptors.

[Leber congenital amaurosis: diagnosis, follow-up and differential diagnosis]

AIM OF THE STUDY

Leber's congenital amaurosis (LCA) had been diagnosed on/in 42 children between 1968 and 1996 at the Deptm. of Ophthalmology, University Hospital Zurich. We reexamined critically this rare diagnosis in retrospect and with new examinations where possible.

PATIENTS AND METHODS

Clinical and electroretinographic (ERG) results, often obtained in general anesthesia, were re-evaluated and when possible repeated in new examinations.

RESULTS

Thirty-three of the total 42 patients presented with an extinguished, 35 with markedly reduced, and 6 with minimal ERGs. A profound visual loss (from no light perception to 20/200), nystagmus and strabismus were the principal symptoms. The heterogeneity of retinal findings ranged from normal to salt and pepper or bone spicules pigmentation and pronounced chorioretinal atrophy. Vascular attenuation and rarification were frequent. Patients with nonocular findings such as mental retardation (n = 12), renal (n = 3) and skeletal (n = 4) abnormalities revealed no differing ERG- or retinal findings. The oculodigital sign (eye-poking) was found in 25%, and parental consanguinity was evident in 10% of the cases. In 16 patients that were reexamined, the progression of the disease was characterized by an increase in retinal pigmentary changes, attenuation of retinal vessel, and further diminuation of the visual acuity (n = 6).

CONCLUSION

Upon review, the diagnosis had to be revised in 8 patients as juvenile retinitis pigmentosa and in one as infantile Refsum syndrome. Bilateral visual impairement in infants should be assessed clinically and electroretinographically within the first year. Neuropediatric and metabolic examinations meaningfully complement the diagnostic procedures.

Light-induced cell death of retinal photoreceptors in the absence of p53

PURPOSE

Cell death by apoptosis is essential for normal development and tissue homeostasis, and it is involved also in a variety of pathologic processes. Apoptosis is the final common pathway of photoreceptor cell death in retinal dystrophies and degeneration. So far, little is known about genes regulating apoptosis in the retina. The tumor-suppressor gene product p53 is a potent regulator of apoptosis in numerous systems. However, p53-independent apoptotic pathways also have been described. In this study the authors investigated the role of p53 in the light-induced apoptosis of retinal photoreceptors using mice lacking p53.

METHODS

Free-moving p53-/- and p53+/+ mice were dark adapted and were exposed to 8,500 or 15,000 lux of diffuse, cool, white fluorescent light for 2 hours. Animals were killed before and immediately after light exposure or at 12 hours in darkness after light exposure. Eyes were enucleated and processed for light and electron microscopy and histochemistry (TdT-dUTP terminal nick-end labeling method). Isolated retinas were subjected to the extraction of total retinal DNA. Electroretinogram (ERG) recordings were performed at all time points.

RESULTS

Morphologic, biochemical, histochemical, and ERG analysis showed that the retinas of untreated p53-/- mice and wild-type control mice were structurally and functionally indistinguishable. After exposure to diffuse white fluorescent light, light-induced photoreceptor cell death was analyzed and was found to be the same in both groups of mice.

CONCLUSIONS

These data suggest that light-induced apoptosis of photoreceptors is independent of functional p53.

Glucose concentration and retinal function

The rod and cone systems of the mammalian retina differ in their structure and functional properties as well as in their metabolic characteristics. This article summarizes basic observations on retinal glucose metabolism reflected in retinal electrophysiology. Metabolic factors might be related to the complex pathogenesis of diabetic retinopathy. Effects of changing glucose concentration and, independently, of insulin on retinal responses obtained in an isolated mammalian eye preparation in vitro and also in vivo are presented. Electron microscopy (EM)-histochemical data reveal a distinctive distribution of glycogen in glia and in various subclasses of neurons in the cat retina. Low glucose, corresponding to hypoglycemia in vivo, affected the light-evoked electrical responses from the rod system, but not from the cone system in vitro. This could be confirmed in the anesthetized cat under glucose clamp conditions. Insulin had no influence on physiological retinal function, except under conditions of low glucose, where it enhanced the reduction in b-wave amplitude. This effect is interpreted as a sign of increased glucose utilization by the retinal Müller (glial) cells.

Effects of insulin under normal and low glucose on retinal electrophysiology in the perfused cat eye

PURPOSE

To investigate the short-term effects of fast-acting insulin on the electroretinogram-b-wave, optic nerve response, standing potential, and flow rate in the arterially perfused cat eye under normal conditions and during low glucose levels.

METHODS

Enucleated cat eyes were perfused with a glucose- and insulin-free tissue culture medium, to which glucose was applied at normal (5.5 mM) and reduced (2 and 1 mM) concentrations. Photic stimulation was performed in the rod-matched intensity range before, during, and after insulin application at postprandial (5 ng/ml) and at 10 and 20 x higher concentrations.

RESULTS

Insulin failed to affect retinal signals at normal glucose levels. However, insulin enhanced the low glucose-induced decrease in rod-driven b-wave amplitude (P < 0.05 at 2 mM; P < 0.01 at 1 mM) without affecting the corresponding changes in the optic nerve response. The standing potential increased by as much as 0.75 mV in response to insulin. The perfusate flow rate was not altered by insulin.

CONCLUSIONS

Insulin was not required for normal retinal function as observed during 10 hours of perfusion. The differential responsiveness to insulin under low glucose of the b-wave versus the optic nerve response is thought to reflect suppression of glucose use by Müller (glial) cells rather than neuromodulation, as the neuronal optic nerve response is unaffected. The postulated insulin sensitivity of Müller cells (changes in b-wave amplitude) indicates a possible difference in the mechanism of glucose metabolism of glia versus neurons. The electrophysiological effect of insulin under low glucose suggests its passage across the blood-retina barrier. The increase in the standing potential is likely to be a receptor-mediated retinal pigment epithelium effect. These results provide evidence in the retina for the reported multifunctional nature of the insulin receptor.

Full characterization of the maculopathy associated with an Arg-172-Trp mutation in the RDS/peripherin gene

The objective of this study was to fully characterize the macular dystrophy phenotype and genotype in a large family of the Zermatt area of Switzerland. Clinical and molecular studies of the family included a comprehensive eye examination and a mutational analysis of the RDS, rhodopsin, and TIMP-3 genes. In selected cases, fluorescein angiography, perimetry, and electroretinography were performed. Forty-two family members at risk of expressing the maculopathy were studied. Of these, 24 were found to be clinically affected. The severity of macular disease in these patients was clearly age-related and different stages of progression were identified. Central pigmentary alterations were seen in adolescent patients, while patients in their late teens and twenties exhibited drusen-like deposits. Later, these defects formed focal areas of atrophy which eventually led to central geographic atrophy with severe visual loss by the fifth decade and cone-rod dysfunction. The transmission of this condition is autosomal dominant with complete penetrance. The underlying genetic defect is a mutation in codon 172 of the RDS/peripherin gene, a gene expressed in both rods and cones, which results in the substitution of tryptophan for an arginine residue at that position. 'Zermatt macular dystrophy' is a dominant, age-related, progressive macular dystrophy which in later stages resembles atrophic age-related macular degeneration. The size of the family studied allowed definition of the clinical spectrum of this condition and identification of the related genetic defect which allows more precise diagnosis and counseling.

Histochemical demonstration of glycogen in neurons of the cat retina

PURPOSE

To demonstrate histochemically the cellular distribution of particulate glycogen in the cat retina and to correlate it with glucose sensitivity of neuronal electrical activities.

METHODS

Free-floating, ultrathin sections of cat eyes (without glucose challenges) were stained by the periodic acid-thiocarbohydrazide-silver proteinate procedure and examined by electron microscopy.

RESULTS

Muller cells were filled uniformly with fine-grain glycogen throughout all retinal layers. Particle density was higher in Muller cells of the peripheral retina than in those of central retina. Astrocytes contained little, if any, particulate glycogen. Alpha and beta ganglion cells had a heavy content of clumped glycogen granules. Rod bipolar and A17 amacrine cells of the rod pathway were stained intensely with particulate glycogen. No glycogen was seen in photoreceptor cells, cone bipolar cells, and the majority of amacrine cells, including AII cells of the rod pathway. However, one type of cone bipolar-driven amacrine cell was intensely glycogen positive. Its ultrastructural morphology, stratification pattern, and synaptology suggest that is a wide-field, axon-bearing type called A22.

CONCLUSIONS

Except for the cone bipolar-driven ON-OFF A22 amacrine cell, it appears that glycogen staining preferentially labels neurons of the rod pathway. These observations are compatible with the reported sensitivity of the rod-driven electroretinogram and optic nerve response to glucose in the cat retina.

Cholinergic effects on cat retina In vitro: changes in rod- and cone-driven b-wave and optic nerve response

To identify cholinergically mediated components in the optic nerve response (ONR) we studied effects of cholinergic agonists and antagonists in the arterially perfused cat eye. Acetylcholine, carbachol, scopolamine, quinuclidinylbenzilate and mecamylamine were applied intra-arterially in micromolar concentrations. Recordings of rod- and cone-driven ERG accompanied those of the ONR and revealed: (i) cholinergic agonists enhanced the b-wave, particularly under photopic conditions, whereas scopolamine decreased the b-wave. Mecamylamine induced biphasic effects (decrease followed by increase) in the amplitudes of the rod- and cone-driven b-waves. The effects on the cone-driven ERG were more marked than those on the rod-driven ERG. (ii) The ON-component of the ONR was increased, then decreased by acetylcholine. The cholinergic antagonists exerted complex changes in the ONR-ON component depending on dosage and adaptation. Scopolamine increased, then decreased the rod-driven ON-component, but mainly increased the cone-driven ON-component. Mecamylamine tended to increase the cone-driven, but to decrease the rod-driven ON-component of the ONR. (iii) The configuration of the rod- as well as for the cone-driven ONR, in particular the early plateau and OFF-components, were consistently and reversibly changed by cholinergic agonists, as well as by both muscarinic and nicotinic antagonists. Agonists decreased, and antagonists increased the amplitude of the plateau-component. We conclude that the ERG b-wave was enhanced by acetylcholine, but decreased by cholinergic antagonists. Cholinergic agonists and antagonists affect the same specific components of the ONR in a dose-related and reversible fashion, indicating a major contribution of cholinergic mechanisms to information processing in the cat retina.

Wagner vitreoretinal degeneration. Follow-up of the original pedigree

PURPOSE

Wagner disease belongs to a heterogeneous group of hereditary vitreoretinal degenerations. The authors have observed complications of this disorder that have not been reported before and therefore re-examined Wagner's original pedigree to further delineate the spectrum of the associated findings and its prognosis.

METHODS

Sixty members of the family agreed to be examined. All had complete clinical eye examinations, 40 had dark adaptation studies as well as single-flash and Ganzfeld rod and cone electroretinography. Fluorescein angiograms were performed in selected patients.

RESULTS

Twenty-eight family members were affected. The most consistent finding was an empty vitreous cavity with avascular strands or veils. Chorioretinal atrophy and cataract increased with the patients' age and had occurred in all patients older than 45 years of age. Four patients had a history of a rhegmatogenous retinal detachment in one eye at a median age of 20 years. The authors observed peripheral tractional retinal detachments in 55% of eyes among patients older than 45 years. Glaucoma was present in ten eyes (18%), four of which showed neovascular glaucoma. Of all patients, 63% showed elevated rod and cone thresholds on dark adaptation, and 87% showed subnormal b-wave amplitudes of the rod- and of the cone system on the electroretinography.

CONCLUSIONS

Clinical expressivity of Wagner disease varies from unaffected carriers to bilateral blindness. Rhegmatogenous retinal detachment is observed infrequently, whereas peripheral traction retinal detachment, chorioretinal atrophy, and cataracts are present in most of the elderly affected individuals. Progression of the chorioretinal pathology is paralleled by electrophysiologic abnormalities.

[Binding and electrophysiology of the muscarinic antagonist QNB in the mammalian retina]

PURPOSE

Based upon the extensive information from various laboratories on cholinergic enzymes and receptors in mammalian retina as well as cholinergic effects on retinal neurons we became interested in studying (1) retinal binding of a muscarinic antagonist, Quinuclidinyl benzilate (QNB) and (2), effects of the antagonist on retinal information processing.

METHODS

Eyes from deeply anesthetized cats were used for homogenate of freshly isolated retina in the binding study, or they were arterially perfused for electrophysiology in vitro. The electroretinogram (ERG) and the compound action potential of the optic nerve (optic nerve response, ONR) were recorded under rod- and cone-stimulating conditions. QNB was infused intraarterially for 10-30 min, followed by washout (avoiding recycling or extraocular metabolism).

RESULTS

3H-QNB revealed a high affinity to muscarinic receptors with a dissociation constant KD of 0.27 nM and a relatively high density of muscarinic binding sites of 110 fmol per mg protein. QNB enhanced the amplitude of the ERG b-wave, but decreased dose-dependently and reversibly the components of the ONR. In addition, we observed a moderate vasoconstriction as indicated by a slight, dose-related decrease in flow rate of perfusion.

CONCLUSION

The biochemical data on binding of 3H-QNB in connection with the marked electrophysiological changes induced by QNB suggest a substantial contribution of muscarinic cholinergic transmission in the cat retina.

Genetic linkage of Wagner disease and erosive vitreoretinopathy to chromosome 5q13-14

BACKGROUND

Wagner disease and erosive vitreoretinopathy are potentially blinding autosomal dominant diseases that share some similarities with Stickler syndrome. However, both disorders have associated retinal pigment epithelial changes, poor night vision, visual field defects, and abnormal electroretinographic findings, which are not found in families with COL2A1-associated Stickler syndrome. In addition, rhegmatogenous retinal detachments are uncommon in Wagner disease but occur in approximately 50% of patients with either Stickler syndrome or erosive vitreoretinopathy.

OBJECTIVES

To identify the chromosomal location of the genes involved in Wagner disease and erosive vitreoretinopathy and to distinguish these conditions genetically from Stickler syndrome.

METHODS

Fifteen affected members of a family affected with erosive vitreoretinopathy and 24 affected descendants of the pedigree described by Wagner were genotyped with a set of short tandem repeat polymorphisms distributed across the genome.

RESULTS

Significant linkage was observed in each family between the disease phenotype and markers that map to chromosome 5q13-14. The highest lod score for the family affected with erosive vitreoretinopathy was 4.2 and was obtained with marker GATA3H06 (theta = 0). The highest lod score for the family affected with Wagner disease was 5.8 and was obtained with marker D5S815 (theta = 0). A candidate gene (cartilage link protein) that is known to lie near the linked interval was screened for mutations, but none was found in either family.

CONCLUSIONS

These data suggest that erosive vitreoretinopathy and Wagner disease are allelic disorders and demonstrate that they are genetically distinct from COL2A1-associated Stickler syndrome.

[A PC program for evaluating electrophysiologic signals of mammalian eyes]

BACKGROUND

Electrophysiological measurements in the mammalian eye in vivo or in vitro, i.e. in the arterially perfused cat eye, require storage and analysis of a large amount of data: light-evoked signals, including the electroretinogram (ERG) and the optic nerve response (ONR) are stimulus-related and have to be measured in a triggered mode, whereas the DC-standing potential and flow rate of perfusion medium should be measured continuously.

METHOD AND RESULT

In order to facilitate the analysis of these various signals, we developed a computer program, that allows an on-line data analysis and a trend indication for pharmacologically induced changes in signal size as well as efficient storage. The flexible system is based on a "labview" program, the application and efficiency of which are discussed.

[Increase in the amplitude of the b-wave of the cone electroretinogram during light adaptation]

BACKGROUND

In experimental and in clinical electrophysiology, cone electroretinograms (ERG) undergo typical changes of the b-wave during the course of light adaptation.

METHODS AND RESULTS

B-Waves obtained from twenty healthy subjects, exposed to a rod-desensitizing adapting field for ten minutes show an increase of amplitude. This increase was observed using a short wavelength as well as with a long wavelength stimulus. The cone ERG implicit times decrease slightly during light adaptation.

CONCLUSIONS

To avoid considerable variation in clinical cone-ERG it is necessary to wait a certain period of time before measuring cone b-waves and comparing them with normative values. Possible mechanisms underlying these adaption-induced ERG changes are discussed.

Confocal microscopy and computer-assisted image reconstruction of astrocytes in the mammalian retina

The distribution of astrocytes in the vascularized retina of pigs, rats and cats was investigated by confocal microscopy and computer-assisted image processing. In whole mounts, immunocytochemical identification was done by staining astrocytes for glial fibrillary acidic protein (GFAP), and blood vessels for alpha-smooth muscle actin or collagen IV. Double-staining was followed through consecutive optical sections and made it possible to precisely align the two markers in the inner retina. The resulting computer-assisted image reconstructions revealed asymmetric ensheathment of blood vessels by GFAP-positive fibres. The ultrastructural basis for this asymmetry, as studied by electron microscopy, was found to be different in pigs and cats. In the pig, astrocytes firmly ensheathed the vessel circumference, but glial filaments were much more abundant on the vitreal and lateral than on the scleral side. By contrast, in the cat astrocytes were generally confined to regions occupied by axonal bundles and constituted only part of the vascular glia limitans, else formed by Müller cells. Moreover, our observations unambiguously showed that individual astrocytes maintained simultaneous contact with axons and blood vessels and lined the vitreous body. The physical links provided by astrocytes suggest that they are able to function as central communicating elements between ganglion cells, the vasculature and the vitreous body.

[Diagnostic electroretinography in the young child]

As soon as visual impairment is suspected in a newborn or an infant by an ophthalmologist or pediatrician, it becomes important to document retinal function. Electroretinography (ERG) in general anesthesia as an outpatient procedure allows to assess the functional state of the retina. In addition, we make use of the anesthesia for ophthalmoscopopy, photography, slit lamp examination and occasionally tonometry. Within the first 10 min of dark adaptation we can electroretinographically distinguish between rod- and cone-mediated b-waves. Anesthesia is performed with Ketamine, occasionally supplemented with Halothane and additional oxygen under noninvasive monitoring of the oxygen saturation. The expenditure of a pediatric check-up and general anesthesia is in our view justified in the light of the opportunity to assess or to exclude a degenerative retinal disease early on. In Leber's congenital amaurosis, a disorder accounting for about 3.5% of blindness in infants, the ERG result is essential, particularly when ophthalmoscopic changes are missing. The prevailing diagnoses in our cases include, in decreasing frequency, congenital cataract, ROP, tapetoretinal degenerations, pediatric-neurologic syndromes, and microphthalmus.

Effect of multidrug-resistant P-glycoprotein gene expression on chloroaluminum tetrasulfonate phthalocyanine concentration

The effect of multidrug-resistant P-glycoprotein gene expression (MDR1) in 3T3 cells on cellular concentrations and cytotoxicity induced by the photodynamic agent chloroaluminum tetrasulfonate phthalocyanine (AlSPc) was evaluated. 3T3 cells transfected with a retroviral vector expressing human MDR1 cDNA were resistant to colchicine. Resistant cells incubated with daunomycin accumulated only 40-50% of the quantity of daunomycin accumulated in control cells. Resistant cells incubated with daunomycin in the presence of verapamil had intracellular daunomycin concentrations approximately equal to control cells without verapamil. When these MDR1 3T3 cells were incubated with AlSPc, cellular concentrations of AlSPc did not differ between cells resistant to colchicine and those that were not. Similarly, there was little difference in cytotoxicity demonstrated by 51Cromium release in the two cell lines exposed to AlSPc and light (675 nm; 6 J/cm2). This study suggests photodynamic therapy using AlSPc may be a useful treatment modality for tumors in which the MDR1 P-glycoprotein confers resistance to cancer chemotherapeutics.

Changes in glucose level affect rod function more than cone function in the isolated, perfused cat eye

The glucose concentration (gl) in mammalian serum incorporates a normal range of variation of several millimoles. We studied the effects of such variations on light-evoked electrical signals in the in vitro arterially perfused cat eye, avoiding extraocular regulatory mechanisms that might confound data interpretation. Changes in gl from the nominal control value of 5 mmol/l were maintained for 5-40 min. Stimuli of near rod threshold intensity were presented in full dark adaptation, and stimuli of higher intensity were presented in the presence of a white background for cone responses. We recorded the dc-electroretinogram (ERG), the scotopic threshold response (STR), the optic nerve response (ONR), and the transretinal slow P-III and transepithelial retinal pigment epithelium c-wave from the subretinal space. The ocular standing potential changed by up to +/- 2 mV in parallel with an increase and decrease in gl, independent of the adaptation condition. Our results show that the rod-ERG, STR, and rod-driven optic nerve response (ONR) have a marked sensitivity to small changes in gl (+/- 1 to 3 mmol/l). The field potentials increased and decreased in parallel with changes in gl. The cone ERG and cone ONR, in contrast, failed to respond consistently to increases in gl and revealed decreases in amplitudes only with an extreme decrease in gl. Decrease in gl, down to 2 mmol/l and less, is known to induce drastic behavioral and electrophysiologic phenomena in the central nervous system. Our results imply that the "normal" glucose level, at least in the cat, could be marginal for rod-mediated retinal function. The results also suggest a marked difference in metabolic mechanisms for cone versus rod photoreceptors.

[Changing glucose concentration affects rod-mediated response in the perfused cat eye]

The effects of changing glucose concentration on the ERG b-wave and optic nerve response (ONR) were studied in dark adapted, arterially perfused cat eyes. Changes in glucose concentration in the perfusate induced remarkable effects on both electrical responses. The ERG b-wave and ONR amplitudes were enhanced with increasing the glucose concentration above the standard level (5.5 mM), and were transiently decreased below the control after termination of the increase in glucose. Furthermore, a control perfusate with higher glucose concentrations (8-10 mM) was used, transient addition of glucose failed to elicit consistent increase in amplitudes of the b-wave and ONR. We conclude that the optimal supply of glucose to the mammalian retina is crucial for recording b-wave and ONR in-vitro under dark adaptation. A higher glucose level (8-10 mM) than 5.5 mM in the standard tissue culture medium is suggested for maintaining the retinal function in-vitro.

Clinical and ERG data in a family with autosomal dominant RP and Pro-347-Arg mutation in the rhodopsin gene

In a family with autosomal dominant retinitis pigmentosa, documented over six generations, a previously undescribed point mutation in the rhodopsin gene could be identified. The mutation found in the six affected members examined but in none of the controls, including healthy members of the family, was a point mutation in codon 347 predicting a substitution of the amino acid arginine for proline, designated Pro-347-Arg. Six affected members from two generations were examined clinically and with ganzfeld rod and cone electroretinography. The cone and, more dramatically, the rod electroretinograms were reduced to residual b-wave amplitudes or were non-detectable as early as ages 18 to 22 years. The Pro-347-Arg mutation resulted in a subjectively and clinically homogeneous phenotype: early onset of night blindness before age 11, relatively preserved usable visual fields until about age 30, blindness at ages 40 to 60, and change from an initial apparently sine pigmento to a hyperpigmented and atrophic fundus picture between 30 and 50 years of age.

Pro-347-Arg mutation of the rhodopsin gene in autosomal dominant retinitis pigmentosa

It has been shown recently that autosomal dominant retinitis pigmentosa may be caused by point mutations of the rhodopsin gene in a portion of families. In this communication, a large six-generation family with autosomal dominant RP is described. Molecular analysis by PCR amplification followed by restriction digestion or heteroduplex analysis suggested a point mutation in codon 347, in which two different mutations (Pro-347-Ser and Pro-347-Leu) have already been reported. Direct sequencing of the patients' DNA revealed a previously undescribed CCG----CGG transversion in codon 347 predicting a Pro----Arg substitution. Ophthalmological data of the patients are summarized and compared to those of patients with other mutations in the rhodopsin gene.

[The effect of glucose on rod function in the isolated, perfused cat eye]

Effects of changing glucose concentration on light-evoked, rod-matched electrophysiological responses were studied in isolated, arterially perfused cat eyes. 1. changes in glucose concentration in the perfusate induced remarkable effects in the electrical responses of retinal pigment epithelium neural retina, and optic nerve. 2. The ERG b-wave and the optic nerve response (ONR) were enhanced when glucose concentrations were increased above the standard level (5.5 mM), and were less than normal after termination of the increase in glucose, prior to recovery. 3. Decreasing glucose from the standard led to attenuation of b-wave and ONR. Both responses recovered completely upon returning to 5.5 mM glucose 4. When the control perfusate contained higher glucose concentrations (8-10 mM), additional glucose failed to elicit significant effects on the b-wave and on the ONR. 5. Increasing glucose induced a small transient decrease in standing potential, followed by a marked and maintained increase. Decreasing glucose induced changes of similar magnitude but opposite polarity. 6. Supply of glucose to mammalian retina in vitro is crucial for optimal sensitivity as shown in rod-matched signals from the perfused cat retina.

[Early diagnosis and heterogeneity of retinitis pigmentosa]

Early diagnosis of retinitis pigmentosa and related diseases is based on a specific history, on perimetry of the outer isopters, and on rod/cone electroretinography. The remarkable variability of phenomenology, age of onset and genetic pattern, however, often complicate early diagnosis. Continuous consulting and documentation of the course of the disease are considered a meaningful care by the physician and represent the basis for the tasks of the geneticist.

[Effects of adenosine on the electrophysiology of the retina]

To the authors' knowledge, adenosine has not yet been shown to play any functional role in the mammalian retina, although it has been shown that it induces neuromodulation and an antiepileptogenic action of the purine in the brain. In order to test effects on retinal function, adenosine was administered intraarterially, in micromolar concentrations, to dark-adapted, isolated, perfused cat eyes. Light-evoked (rod-matched) electrical signals were recorded. Adenosine induced a marked increase in the amplitude of the ERG b-wave, a dose-dependent depression of the optic nerve response, and an increase in the flow rate of the perfusate - indicative of vasodilation. These data, together with autoradiographically demonstrated uptake of adenosine (2) are the first evidence that adenosine plays a functional role at several sites in the cat retina.

Adenosine: autoradiographic localization and electrophysiologic effects in the cat retina

Autoradiography with 3H-adenosine was used to localize cells that accumulate adenosine in the cat retina. Electrophysiologic effects elicited by adenosine on DC-electroretinograms (ERG) and optic nerve responses (ONR) were studied in isolated, arterially perfused cat eyes. Subpopulations of cells localized in the ganglion cell layer and inner nuclear layer showed clear labeling for adenosine. This purine nucleoside enhanced the ERG b-wave and the standing potential; depressed the light peak; and markedly depressed the ONR, in which it reduced the amplitudes of the ON-, plateau-, and OFF-components. A vasodilatory action of adenosine was documented by an increase in perfusion flow rate. Our data suggest that adenosine in cat retina has complex modulatory effects, involving the retinal pigment epithelium, neuronal structures, blood vessels, and probably glial cells.

Hyperprolinaemia type I and white matter disease: coincidence or causal relationship?

We describe a 10-year-old boy with hyperprolinaemia type I and severe neurological abnormalities (mental retardation, cerebral palsy, epilepsy, nystagmus). Magnetic resonance imaging showed diffuse white matter involvement and electroretinography confirmed tapetoretinal degeneration. In view of reports in the literature, hyperprolinaemia type I may not be a benign condition, as usually assumed, but may lead to marked neurological abnormalities, particularly in affected males.

Vincristine-induced changes in the retina of the isolated arterially-perfused cat eye

We have attempted to determine in this study whether the arterial administration of vincristine produces in cat the functional defects associated with hereditary and vincristine-induced night blindness in man. Using the isolated perfused cat eye, it has been possible to mimic some of the essential features of human night blindness, namely, retention of normal rhodopsin chemistry and normal photoreceptor activity, with marked suppression of the ERG b-wave. In addition, we find that vincristine produces an early, rapid fall in the c-wave, a potential that arises largely in the pigment epithelium. Ultrastructurally, it appears that many classes of retinal neuron are affected by the drug, but the principal changes in cytoarchitecture are seen in the photoreceptors. Except for the outer segments, paracrystalline deposits were found in all parts of the visual cell. The disruption of the normal microtubular organization of these cells suggests that the drug interferes with the functional integrity of the transport system by which synaptic activity is maintained. By reducing the efficacy of communication between visual cells and their second-order neurons, the electrical responses of post-synaptic elements is degraded. The route by which vinca alkaloids reach the neural retina is still uncertain, but our preliminary studies using HRP indicate that the relatively high concentration of vincristine used in this study may be responsible for compromising the blood-retinal barrier.

[Indications for electrophysiologic studies of the eye]

The phenomena of light-evoked electrical activity of the retinal pigment epithelium, retina, and visual cortex can be used for specific diagnostic testing. The EOG, with standing potential and light peak, reflects the functional state of the pigment epithelium; the ERG reflects the function of the photoreceptors (a-wave) and inner nuclear layer (b-wave), and the visual evoked response (VER) provides information on signal conduction along the entire visual pathway. The indications for electroretinography are discussed in detail, resulting in a broad spectrum including degenerative, metabolic, inflammatory and toxic changes of the retina. In addition, a condensed table of diagnoses that can hardly be established without ERG is proposed. The value of ERG recordings is extended by the possibility to document rate of progression and relative involvement of the rod- and/or the cone system of the retina. VER procedures are mainly directed towards demyelinating diseases of the CNS. We attempt to interpret results of electrophysiologic testing synoptically with subjective complaints and clinical observations.

[Examination strategies in the diagnosis of drug-induced retinal damage]

The large number of potentially retinotoxic drugs and their effects at multiple structural sites, from pigment epithelium to retina and optic nerve, imply complex diagnostic procedures rather than a single test. Early diagnosis of retinotoxicity, however, can be established by through history, ophthalmoscopy and routine (simple) functional tests carried out by the responsible ophthalmologist. In case of suspected damage of the retina or of the optic nerve electrophysiology, angiography, selective perimetry and color vision tests are recommended. In this outline chloroquine retinopathy is discussed in detail.