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.

Renal allograft tolerance in DLA-identical and haploidentical dogs after nonmyeloablative conditioning and transient immunosuppression with cyclosporine and mycophenolate mofetil.

BACKGROUND: Canine models of bone marrow and renal transplantation have provided important preclinical data relevant to developing novel therapeutic protocols for hematopoietic and solid organ transplantation in human beings. Nonmyeloablative transplantation has been shown to induce stable mixed hematopoietic chimerism in normal dogs and correct the phenotype of canine pyruvate kinase deficiency and Glanzman's thrombasthenia. In this study, we investigated the potential for inducing renal allograft tolerance using a nonmyeloablative bone marrow transplantation strategy that induces mixed chimerism in DLA-identical dogs. METHODS: Reciprocal renal allografts were performed in 4 DLA-identical and 4 DLA-haploidentical dogs with nonmyeloablative conditioning (200 cGy total body irradiation [TBI]) and transient immunosuppression with cyclosporine (CSP) and mycophenolate mofetil (MMF) with and without simultaneous bone marrow transplantation. Two DLA-identical control dogs received reciprocal renal allografts without TBI or immunosuppression with CSP and MMF. Serum creatinine (Cr) concentration was monitored to assess renal allograft function. RESULTS: The renal allografts were acutely rejected in the 2 DLA-identical dogs without TBI or immunosuppression. There was long-term (>1 year) renal allograft survival as evidenced by a normal (<2.0 mg/dL) serum Cr concentration in both the DLA-identical and DLA-haploidentical dogs that underwent 200 cGy TBI and transient immunosuppression with CSP and MMF either with or without simultaneous bone marrow transplantation. CONCLUSIONS: Nonmyeloablative conditioning (200 cGy TBI) and transient immunosuppression with CSP and MMF induce renal allograft tolerance in DLA-identical and DLA-haploidentical dogs without donor/host mixed hematopoietic chimerism. These findings suggest it may be possible to induce tolerance to solid organ transplants without the need for chronic immunosuppressive therapy or stable hematopoietic chimerism in the setting of both DLA-matched and haploidentical transplants.

Isolation and characterization of canine hematopoietic progenitor cells.

The purpose of this study was to purify and characterize canine hematopoietic progenitor cells for surface antigen phenotype and reconstitution ability. Canine hematopoietic progenitor cells were isolated by density gradient sedimentation, lineage depletion with monoclonal antibodies, and fluorescence-activated cell sorting (FACS) for selection of cells with low-forward and right-angle scatter that were rhodamine 123 (Rh-123)(dull). Isolated cells were characterized for expression of CD34, c-kit, and Flt-3. A canine/murine xenograft model and a mixed-chimerism assay were used to examine the in vivo proliferative potential of isolated cells. The lineage-positive (Lin(+)) cells represented 80 +/- 11% (n = 22) of the input mononuclear cells. Lineage depletion resulted in a fourfold increase in colony-forming unit granulocyte/monocyte (CFU-GM), a 2.5-fold increase in burst-forming unit-erythroid (BFU-E), and a twofold increase in the number of Rh-123(dull) cells over nonlineage-depleted bone marrow mononuclear cells (BMMCs). Lineage depletion led to a 2.7-fold enrichment of CD34 cells, a 10.4-fold enrichment of c-kit cells, and a 10.8-fold enrichment of CD34/c-kit(+1) cells over total BMMCs. Nineteen percent of lineage-negative (Lin(-)) cells were positive for Flt-3. Injection of canine cells into irradiated (400 rads) NOD/SCID mice resulted in the detection of canine CD45(+) cells with BMMCs, Lin(-) cells, or Rh-123(dull) cells. Transplantation of purified Lin(-) cells in dog leukocyte antigen-matched littermates resulted in low-level engraftment for at least 10 weeks. The development of methods for purification and characterization of canine hematopoietic progenitor cells should enhance the utilization of the canine model for a variety of experimental and therapeutic purposes.

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.

Severe canine hereditary hemolytic anemia treated by nonmyeloablative marrow transplantation.

Severe hemolytic anemia in Basenji dogs secondary to pyruvate kinase (PK) deficiency can be corrected by marrow allografts from healthy littermates after a conventional high-dose myeloablative conditioning regimen. The nonmyeloablative conditioning regimen used here, which consisted of a sublethal dose of 200 cGy total body irradiation before and immunosuppression with mycophenolate mofetil and cyclosporine after a dog leukocyte antigen (DLA)-identical littermate allograft, has been found to be effective in establishing stable mixed donor/host hematopoietic chimerism in normal dogs. We explored the feasibility of nonmyeloablative marrow allografts for the treatment of canine PK deficiency and studied the effect of stable allogeneic mixed hematopoietic chimerism on the natural course of the disease. Five affected dogs received transplants, of which 3 dogs had advanced liver cirrhosis and myelofibrosis. Both complications were presumed to be due to iron overload. All 5 dogs showed initial engraftment. Two rejected their grafts after 6 weeks but survived with completeautologous marrow recovery and return of the disease. One died from liver failure on day 27 with 60% donor engraftment. Two dogs have shown sustained mixed donor/host chimerism for more than a year with 85% and 12% donor hematopoietic cells, respectively. Overall clinical response correlated with the degree of donor chimerism. The dog with the low degree of chimerism achieved partial resolution of hemolysis, but the disease symptoms persisted as manifested by increasing iron overload resulting in progression of marrow and liver fibrosis. The dog with the high degree of donor chimerism achieved almost complete resolution of hemolysis with a decrease of marrow iron content and resolution of marrow fibrosis. These observations suggest that mixed hematopoietic chimerism can be relatively safely established in dogs with PK deficiency even in the presence of advanced liver cirrhosis. However, although effective in correcting or delaying the development of myelofibrosis, a low degree of mixed chimerism was not sufficient to prevent continued hemolysis of red blood cells of host origin. Complete donor chimerism appears necessary to achieve a long-term cure.

[Effect of insulin on retinal glycogen content]. / Die Wirkung des Insulins auf den Glykogengehalt der Netzhaut.

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.

[Stargardt's disease and its intrafamilial variability]. / Morbus Stargardt mit intrafamiliärer Variabilität.

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.

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]. / Das Elektroretinogramm (ERG) der Maus: normative Werte, optimierte Stimulation und Ableitung.

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]. / Vom Symptom zur Elektroretinographie-Diagnose.

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.

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.

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]. / Kongenitale Amaurose Leber: Diagnose, Verlauf und Differentialdiagnose.

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.

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.

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.