Diabetes can alter the signal transduction pathways in the lens of rats

Diabetes is known to affect cataract formation by means of osmotic stress induced by activated aldose reductase in the sorbitol pathway. In addition, alterations in the bioavailability of numerous extralenticular growth factors has been reported and shown to result in various consequences. We have found that the basic fibroblast growth factor (bFGF) accumulates in the vitreous humor of 3- and 8-week diabetic rats. Consequently, the associating signal transduction cascades were severely disrupted, including upregulated phosphorylation of extracellular signal-regulated kinase (ERK) and the common stress-associated mitogen-activated protein kinases p38 and SAPK/JNK. Conversely, under diabetic condition, we observed a dramatic inhibition of phosphatidylinositol-3 kinase activity in lenses obtained from the same animal. Rats treated with the aldose reductase inhibitor AL01576 for the duration of the diabetic condition showed that the diabetes-induced lenticular signaling alterations were normalized, comparable to controls. However, treatment of AL01576 in vitro was ineffective at normalizing the altered constituents in extracted diabetic vitreous after the onset of diabetes. The effect of AL01576 in the high galactose-induced cataract model in vitro was also examined. Administration of AL01576 to lens organ culture normalized the aberrant signaling effects and morphological characteristics associated with in vitro sugar cataract formation. In conclusion, our findings demonstrate diabetes-associated alterations in the lens signal transduction parameters and the effectiveness of AL01576 at normalizing such alterations. The causes for these alterations can be attributed to elevated vitreal bFGF in conjunction with osmotic stress and associated attenuation in redox status of the lens.

The association of cardiovascular disease with the long-term incidence of age-related maculopathy: the Beaver Dam eye study

PURPOSE

To examine the association between cardiovascular disease and its risk factors and the 10-year incidence of age-related maculopathy.

DESIGN

Population-based cohort study.

PARTICIPANTS

Persons 43 to 86 years of age at baseline examination from 1988 to 1990, living in Beaver Dam, Wisconsin, of whom 3684 persons participated in a 5-year follow-up examination and 2764 participated in a 10-year follow-up examination.

METHODS

Standardized protocols for physical examination, blood collection, administration of a questionnaire, and stereoscopic color fundus photography to determine age-related maculopathy. The Kaplan-Meier (product-limit) survival approach and discrete linear logistic regression were used in the data analysis.

MAIN OUTCOME MEASURES

Incidence and progression of age-related maculopathy.

RESULTS

When age, gender, and history of heavy drinking, smoking, and vitamin use were controlled for, higher systolic blood pressure at baseline was associated with the 10-year incidence of retinal pigment epithelial depigmentation (risk ratio [RR] per 10 mmHg systolic blood pressure, 1.10; 95% confidence interval [CI], 1.01-1.18; P = 0.02) and exudative macular degeneration (RR, 1.22; 95% CI, 1.06-1.41; P = 0.006). Higher pulse pressure at baseline was associated with the incidence of retinal pigment epithelial depigmentation (RR per 10 mmHg, 1.17; 95% CI, 1.07-1.28; P < 0.001), increased retinal pigment (RR, 1.10; 95% CI, 1.01-1.19; P = 0.03), exudative macular degeneration (RR, 1.34; 95% CI, 1.14-1.60; P < 0.001), and progression of age-related maculopathy (RR, 1.08; 95% CI, 1.01-1.17; P = 0.03). Higher serum high-density lipoprotein cholesterol at baseline was associated with pure geographic atrophy (RR per 10 mg/dl high-density lipoprotein cholesterol, 1.29; 95% CI, 1.05-1.58; P = 0.01). Physical activity at baseline was associated with the incidence of geographic atrophy (RR in those who worked up a sweat 5 times a week compared with those who did not, 0.12; 95% CI, 0.02-0.91; P = 0.04) exudative macular degeneration (RR, 0.27; 95% CI, 0.08-0.87; P = 0.05), and progression of age-related maculopathy (RR, 0.69; 95% CI, 0.47-1.00; P = 0.05). Neither a history of stroke nor heart attack was associated with the incidence or progression of age-related maculopathy.

CONCLUSIONS

These findings indicate relationships between higher pulse pressure (a presumed indicator of age-related elastin and collagen changes in Bruch's membrane) and systolic blood pressure with an increased 10-year incidence of some lesions defining early age-related maculopathy and exudative macular degeneration.

Objective measurement of visual function in glaucoma

Of the objective (electrophysiological), functional tests of glaucomatous damage, three hold the most promise. Some evidence suggests that the pattern electroretinogram, the photopic negative response of the electroretinogram, and the multifocal visual-evoked potential can detect early glaucomatous damage, damage that may be missed on static automated achromatic perimetry. However, in their current forms, these tests can supplement, but cannot replace, static automated achromatic perimetry. Further, the multifocal visual-evoked potential is the only one of these tests that supplies topographic information about local damage. In addition, we still lack a complete understanding of the relation between these tests and the underlying damage to ganglion cells. In this context, it has recently been suggested that the signal in the multifocal visual-evoked potential response may be linearly related to the loss of ganglion cells. Finally, more information is needed about these tests from longitudinal or prospective studies.

Peripheral vasospasm and nocturnal blood pressure dipping--two distinct risk factors for glaucomatous damage?

PURPOSE

To evaluate the relationship between peripheral vasospasm and circadian blood pressure rhythm in patients with primary open angle glaucoma (POAG).

METHODS

Nail-fold capillaroscopy, combined with a cold provocation test, and 24-hour blood pressure monitoring was carried out in 130 patients with POAG (M:F 58:72; mean age 60 +/- 14 years), 99 with high-tension glaucoma (HTG) and 31 with normal-tension glaucoma (NTG). Peripheral blood flow parameters were compared for patients with a nocturnal fall in mean systemic blood pressure (MBP) of less than 10% (non-dippers), patients with a nighttime MBP fall of 10-20% (dippers), and patients with a nighttime MBP fall of more than 20% (over-dippers).

RESULTS

Patients with POAG showed a significantly lower blood flow velocity both at baseline (p < 0.01) and after cold provocation (p < 0.02) and a significantly higher percentage of cold-induced blood-flow standstill (p < 0.0001) in the nail-fold capillaroscopy than normal controls. The numbers of non-dippers (50), dippers (66) and over-dippers (14) did not differ between the HTG and NTG group. There were no significant differences between non-dippers, dippers, and over-dippers in peripheral blood flow parameters.

CONCLUSIONS

Our findings indicate that vasospasm and low blood pressure may be distinct risk factors for glaucomatous damage. It also appears that screening for vascular dysregulation and systemic hypotension should not be restricted to NTG patients alone.

Growth Factor, Cytokine and Protease Interactions During Corneal Wound Healing

Healing of corneal injuries is an exceptionally complex process involving the integrated actions of multiple growth factors, cytokines, and proteases produced by epithelial cells, stromal keratocytes, inflammatory cells, and lacrimal gland cells. Following corneal injury, basal epithelial cells migrate and proliferate in response to chemotactic cytokines and mitogenic growth factors, including epidermal growth factor and keratinocyte growth factor. Simultaneously, keratocytes adjacent to the injured area undergo apoptosis under the Fas/Fas ligand system, while more distant keratocytes transform into activated fibroblasts and migrate into the wound, where they begin synthesizing new extracellular matrix components that form the scar tissue under the dominant influence of the TGFb/ CTGF system. Epithelial cells and activated stromal fibroblasts also secrete growth factors and cytokines that have paracrine and autocrine functions. Corneal repair proceeds for the next several weeks to months, during which time the gene expression profile slowly returns to the pre-injury pattern and the provisional scar matrix slowly remodels by actions of matrix metalloproteinases. While minor epithelial injuries heal by regeneration of normal architecture, large stromal injuries heal by repair with irregular scar tissue that impairs the optical properties of the cornea.Also, if the integrated regulation of the wound healing process is interrupted at any point, the wound fails to heal properly and a corneal ulcer develops. Better understanding of the cellular and molecular changes that occur during repair of corneal wounds will provide the opportunity to design agents that selectively modulate key phases of corneal wound healing, resulting in scars that more closely resemble normal corneal architecture.

Oxidative stress-induced mitochondrial DNA damage in human retinal pigment epithelial cells: a possible mechanism for RPE aging and age-related macular degeneration

Oxidative stress is believed to contribute to the pathogenesis of many diseases, including age-related macular degeneration (AMD). Although the vision loss of AMD results from photoreceptor damage in the central retina, the initial pathogenesis involves degeneration of RPE cells. Evidence from a variety of studies suggests that RPE cells are susceptible to oxidative damage. Mitochondrial DNA (mtDNA) is particularly prone to oxidative damage compared to nuclear DNA (nDNA). Using the quantitative PCR assay, a powerful tool to measure oxidative DNA damage and repair, we have shown that human RPE cells treated with H(2)O(2) or rod outer segments resulted in preferential damage to mtDNA, but not nDNA; and damaged mtDNA is not efficiently repaired, leading to compromised mitochondrial redox function as indicated by the MTT assay. Thus, the susceptibility of mtDNA to oxidative damage in human RPE cells, together with the age-related decrease of cellular anti-oxidant system, provides the rationale for a mitochondria-based model of AMD.

Analysis of proteins with caseinolytic activity in a human stratum corneum extract revealed a yet unidentified cysteine protease and identified the so-called "stratum corneum thiol protease" as cathepsin l2

Desquamation is described as a protease-dependent phenomenon where serine proteases with a basic pH optimum play a key role. Recently proteases with an acidic pH optimum were identified in the stratumcorneum and associated with desquamation, e.g., cathepsin D and the stratum corneum thiol protease. The purpose of this study was to investigate if human stratum corneum contains proteases different from the above, exhibiting similar properties. After gel filtration, we identified four distinct proteolytic activities in a human stratum corneum extract, a cathepsin-E-like activity (80 kDa), a cathepsin-D activity (40 kDa), a yet unknown cathepsin-L-like form (28 kDa) exhibiting the highest caseinolytic activity, and a chymotrypsin-like protein (24 kDa) containing the acidic activity of the well described stratum corneum chymotryptic enzyme. We named the new 28 kDa protease stratum corneum cathepsin-L-like enzyme. Characterization of stratum corneum cathepsin-L-like enzyme provided clear evidence that this new protease, despite its membership to the cathepsin-L-like family, is distinct from cathepsin L and from the recently described stratum corneum thiol protease. Its ability to hydrolyze corneodesmosin, a marker of corneocyte cohesion, was in favor of a role of stratum corneum cathepsin-L-like enzyme in the desquamation process. A more detailed analysis did not allow us to identify stratum corneum cathepsin-L-like enzyme at the molecular level but revealed that stratum corneum thiol protease is identical with the recently described cathepsin L2 protease. Reverse transcription polymerase chain reaction studies and the use of a specific antibody revealed that, in contrast to earlier reports, expression of stratum corneum thiol protease in human epidermis is not related to keratinocyte differentiation. Our results indicate that the stratum corneum thiol protease is probably expressed as a pro-enzyme in the lower layers of the epidermis and in part activated by a yet unidentified mechanism in the upper layers during keratinocyte differentiation.

Temporal modulation of scotopic visual signals by A17 amacrine cells in mammalian retina in vivo

We examined function of the feedback pathway from A17 GABAergic amacrine cells to rod bipolar cells (A17 feedback), a critically located inhibitory circuit in the classic rod pathway of the mammalian retina whose role in processing of scotopic visual information is still poorly understood. We show evidence that this A17 feedback has a profound influence on the temporal properties of rod-driven postphotoreceptoral responses (assessed with the scotopic electroretinogram b-wave). Application of a GABA(c) antagonist prolonged preferentially the decay of the scotopic b-wave. The degree of prolongation increased as the light intensity decreased. Application of selective GABA(a) antagonists accelerated the kinetics of the scotopic b-wave. This effect was abolished when the GABA(c) antagonist was coapplied. Selective ablation of A17 cells mimicked the action of the GABA(c) antagonist. In A17 cell-ablated retinas, the GABA(c) antagonist was no longer very effective to slow the decay of the scotopic b-wave. Thus the A17 feedback, activated by light stimulation and mediated mainly by the GABA(c) receptors, makes the scotopic b-wave more transient by accelerating preferentially its decay. The strength of the feedback can be modulated by GABA(a) receptor-mediated inhibition and by light intensity. Our results also suggest that in the mammalian retina the feedback may be a novel mechanism that contributes postphotoreceptorally to the termination of rod signals, especially those elicited by very dim light stimuli.

Clinicopathologic correlation and genetic analysis in a case of posterior polymorphous corneal dystrophy

PURPOSE

To evaluate the clinical history, histopathology, and genetics of posterior polymorphous corneal dystrophy (PPMD) in a woman with a prominent retrocorneal membrane.

DESIGN

Observational case report and genetic analysis of her family, UM:139.

METHODS

Records were reviewed from a case and associated family members. The diagnosis of PPMD was based on clinical examination, immunohistochemical staining, electron microscopy, and screening of genetic markers from regions previously reported to be associated with PPMD.

RESULTS

Over 17 years, the proband with PPMD had 25 ocular procedures performed for glaucoma, cataract, cornea, retina, and postoperative problems. A prominent retrocorneal membrane grew onto the crystalline lens and intraocular lens (IOL). Histopathology revealed stratified epithelial-like cells on iris from an iridectomy and stratified corneal endothelium on a corneal button. Electron microscopy on the cornea revealed microvilli, tonofilaments, and desmosomes consistent with endothelial transformation, which was confirmed by positive anticytokeratin (CK) AE1/AE3 and CAM 5.2 immunoreactivity. Negative immunoreactivity in epithelium and positive in endothelium with anti-CK 7 supported the diagnosis of PPMD rather than epithelial downgrowth. Multiple relatives were affected with PPMD with apparent autosomal dominant inheritance, but surprisingly, the PPMD, congenital hereditary endothelial dystrophy 1 (CHED1) and CHED2 loci on chromosome 20 and the collagen, type VIII, alpha-2 (COL8A2) gene were excluded by linkage and haplotype analyses.

CONCLUSIONS

We are unaware of previous PPMD reports describing the unusual feature of a retrocorneal membrane extending onto the crystalline lens and IOL. In addition, this family suggests another PPMD locus.

Molecular control of Xenopus retinal circadian rhythms

Vertebrate retinas contain endogenous circadian clocks that control many aspects of retinal physiology. Our work has focused on studying the molecular mechanism of this clock and the way in which it controls the many cellular rhythms within the retina. These studies focus on the retina of Xenopus laevis, a well-established model system extensively used for the study of both retinal physiology and circadian function. We have cloned Xenopus homologues of the genes thought to be critical for vertebrate clock function, including Clock, Bmal1, cryptochromes and period, as well as other rhythmic genes such as nocturnin. We have used these genes to manipulate the clock within different subsets of retinal photoreceptors via cell-specific promoters, in order to study the location of the clock within the retina. These in vivo experiments have shown that photoreceptor cells contain clocks that are necessary for the rhythmic production of melatonin. We have also used biochemical approaches to further investigate the molecular events that drive specific rhythmic outputs, such as circadian regulation of nocturnin gene transcription and control of post-transcriptional events within these clock-containing cells.

Genetic, temporal and developmental differences between melatonin rhythm generating systems in the teleost fish pineal organ and retina

Complete melatonin rhythm generating systems, including photodetector, circadian clock and melatonin synthesis machinery, are located within individual photoreceptor cells in two sites in Teleost fish: the pineal organ and retina. In both, light regulates daily variations in melatonin secretion by controlling the activity of arylalkylamine N-acetyltransferase (AANAT). However, in each species examined to date, marked differences exist between the two organs which may involve the genes encoding the photopigments, genes encoding AANAT, the times of day at which AANAT activity and melatonin production peak and the developmental schedule. We review the fish pineal and retinal melatonin rhythm generating systems and consider the evolutional pressures and other factors which led to these differences.

Developmental maturation of passive electrical properties in retinal ganglion cells of rainbow trout

We investigated the electrotonic and anatomical features of the dendritic arbor in developing retinal ganglion cells (RGCs). Cell anatomy was studied by filling individual cells with fluorescent, membrane-bound dyes and using computer-assisted image reconstruction. Electrotonic properties were characterized through an analysis of charging membrane currents measured with tight-seal electrodes in the whole-cell mode. We studied developing RGCs in the peripheral growth zone (PGZ) of a fish retina. The PGZ presents a developmental time-line ranging from pluripotent, proliferating cells at the extreme edge, to mature, fully developed retina more centrally. In the PGZ, RGCs mature through three histologically distinct zones (in developmental sequence): bulge, transition and mature zones. In the most peripheral three-quarters of the bulge zone, cells have rounded somas, lack dendritic extensions and some are coupled so that membrane-bound dyes traverse from one cell to its immediate neighbours. In the more central quarter of the bulge, cells' dendrites are few, short and of limited branching. In the transition zone dendritic arbors becomes progressively more expansive and branched and we present a morphometric analysis of these changes. Regardless of the size and branching pattern of the developing RGC dendritic arbor, the ratio of the diameters of parent and progeny dendrites at any branching nodes is well described by Rall's 3/2 power law. Given this anatomical feature, the RGC passive electrical properties are well described by an equivalent electrical circuit consisting of an isopotential cell body in parallel with a single equivalent cylinder of finite length. We measured the values of the electrical parameters that define this equivalent circuit in bulge, transition and mature RGCs. As RGCs develop the electrical properties of their dendritic arbor change in an orderly and tightly regulated manner, not randomly. Electrically, dendritic arbors develop along either of two distinct modes, but only these modes: isoelectrotonic and isometric. In isoelectrotonic growth, electrotonic properties are constant regardless of the absolute dimensions of the dendritic arbor or its branching geometry. These cells maintain unvarying relative synaptic efficacy independently of the size or pattern of their dendritic arbor. In isometric growth, in contrast, electronic properties change, but the ratio of the changing electrotonic length to electrotonic diameter is constant. In these cells relative synaptic efficacy decreases linearly as dendrites extend.

Delivery of antisense oligonucleotide to the cornea by iontophoresis

We wished to evaluate the potential of iontophoresis to promote the delivery of antisense oligonucleotides (ODN) directed at the vascular endothelial growth factor (VEGF)-R2 receptor (KDR/Flk) to the cornea of the rat eye. Fluorescence (CY5)-labeled ODNs in phosphate-buffered saline (PBS) (20 microM) were locally administered to rat eyes, and their fate within the anterior segment was studied. Thirty-four male, 5-week-old Wistar rats were used for all experiments. The rats were divided in four groups. In group I (12 rats, 12 eyes), the ODNs (20 microM) were delivered by iontophoresis (300 microA for 5 minutes) using a specially designed corneal applicator. In group II (12 rats, 12 eyes), the ODNs (20 microM) were delivered using the same applicator, but no electrical current was applied. In group III (6 rats, 6 eyes), a corneal neovascular reaction was induced prior to the application of ODNs (20 microM), and iontophoresis electrical current was delivered as for group I rats. Group IV (4 rats, 4 eyes) received ODN (60 microM) iontophoresis application (300 microA for 5 minutes) and were used for ODN integrity studies. The animals were killed 5 minutes, 90 minutes, and 24 hours after a single ODN application and studied. Topically applied ODNs using the same iontophoresis applicator but without current do not penetrate the cornea and remain confined to the superficial epithelial layer. ODNs delivered with transcorneoscleral iontophoresis penetrate into all corneal layers and are also detected in the iris. In corneas with neovascularization, ODNs were particularly localized within the vascular endothelial cells of the stroma. ODNs extracted from eye tissues 24 hours after iontophoresis remained unaltered. The iontophoresis current did not cause any detectable ocular damage under these conditions. Iontophoresis promotes the delivery of ODNs to the anterior segment of the eye, including all corneal layers. Iontophoresis of ODNs directed at VEGF-R2 may be used for the design of specific antiangiogenic strategy in diseases of the cornea.

The roles of Hedgehogs and Fibroblast Growth Factors in eye development and retinal cell rescue

Knowledge of normal eye development is crucial for the development of retinal rescue strategies. I shall focus on two signalling pathways that affect retinal development. Fibroblast growth factors function in retinal cell proliferation, retinal ganglion cell axon guidance and target recognition, craniofacial patterning and lens induction. Hedgehog proteins are required for progression of the neurogenic wave, cell proliferation, photoreceptor differentiation, retinal ganglion cell axon growth and craniofacial patterning. These signalling pathways have pleiotropic effects, can interact and have the potential to be used therapeutically. The zebrafish model organism may be well suited to studying how signalling pathways interact.

Pathogenesis and potential antiviral therapy of complications of smallpox vaccination

Vaccination against smallpox may result in a variety of complications, ranging in severity from benign to lethal. Universal vaccination was halted in the US in 1972, so almost half the present population has never been vaccinated. Because side effects occur most often in first-time vaccinees, current plans for rapid large-scale vaccination in the event of bioterrorist attack raise concerns about the occurrence of a large number of adverse events. Most complications result from the excessive replication of vaccinia virus, making them potential targets for antiviral therapy. Effective treatment is especially needed for persons with atopic dermatitis or eczema, who are unusually susceptible to the initiation and spread of vaccinia infection because of defects of innate immunity in the skin, and for individuals with defective cell-mediated immunity, who are unable to eliminate vaccinia infection once it has begun. In the past, many complications were treated with vaccinia immune globulin (VIG) and/or the antiviral drug methisazone, but neither was tested in placebo-controlled trials. New antiviral drugs are now available, but have not yet been evaluated for treating vaccinia infections in humans. Both laboratory research and clinical studies are needed to help prevent serious complications in any major vaccination campaign.

L-NAME protects against acute light damage in albino rats, but not against retinal degeneration in P23H and S334ter transgenic rats

Two previous studies have shown that N(G)-nitro-L-arginine methyl ester (L-NAME), an inhibitor of neuronal nitric oxide synthase, protects retinas of albino rats and mice from damaging levels of light. The aims of the present study were two-fold: (1) to confirm the protective effect of L-NAME on wild type albino rats and (2) to determine if L-NAME protects the retinas of transgenic rats with P23H and S334ter rhodopsin mutations. In the first study, albino rats born and raised in 5-10 lux cyclic light were injected intraperitoneally with either L-NAME or its inactive isomer D-NAME 30 min before being placed in bright light (2700 lux) for 24hr. Electroretinograms (ERGs) were recorded before light treatment and 2 days after cessation of exposure, and eyes were enucleated for morphologic evaluation. L-NAME, but not D-NAME provided structural protection of photoreceptor cells from light damage. The functional rescue was not statistically significant between the drug treated groups. In the second study, albino WT, P23H transgenic, and S334ter transgenic rats were born and raised in 400 lux cyclic light. Three week old animals received daily intraperitoneal injections of L-NAME or D-NAME for 4 weeks, and the same drugs were added to their drinking water. At 7 weeks of age, the ERG sensitivity curves and the outer nuclear layer thickness of both transgenic groups were significantly reduced compared to WT controls. However, administration of L-NAME did not protect against retinal degeneration caused by the rhodopsin mutation in either strain of transgenic (P23H and S334ter) rats. Thus, although photoreceptor cell death in light damage and inherited retinal degenerations share a common apoptotic mechanism, there must be significant 'up-stream' differences that allow selective neuroprotection by L-NAME.

Activated microglia in human retinitis pigmentosa, late-onset retinal degeneration, and age-related macular degeneration

Many gaps exist in our knowledge of human retinal microglia in health and disease. We address the hypothesis that primary death of rod photoreceptors leads to activation of resident microglia in human retinas with retinitis pigmentosa (RP), late-onset retinal degeneration (L-ORD), or age-related macular degeneration (AMD). Regions of ongoing photoreceptor cell death were studied by immunocytochemistry with microglia- and other retinal cell-specific markers. In normal human retinas, quiescent microglia were small, stellate cells associated with inner retinal blood vessels. In retinas with RP, L-ORD, or AMD, numerous activated microglia were present in the outer nuclear layer in regions of ongoing rod cell death. These microglia were enlarged, amoeboid cells that contained rhodopsin-positive cytoplasmic inclusions. We conclude that activated microglia migrate to the outer nuclear layer and remove rod cell debris. In other central nervous system diseases such as stroke, activated microglia phagocytose debris from the primary injury and also secrete molecules that kill nearby normal neurons. By analogy with these diseases, we suggest that microglia activated by primary rod cell death may kill adjacent photoreceptors. Activated microglia may be a missing link in understanding why initial rod cell death in the human diseases RP, L-ORD, and AMD leads to death of the cones that are critical for high acuity daytime vision.

Histological and immunohistochemical findings after laser in situ keratomileusis in human corneas

PURPOSE

To describe histopathological and immunohistochemical findings in human corneas after myopic laser in situ keratomileusis (LASIK) followed by iatrogenic keratectasia and after hyperopic LASIK.

SETTING

Department of Ophthalmology, University of Innsbruck, Innsbruck, Austria.

METHODS

Clinical, histological, and immunohistochemical investigations were performed of 1 human cornea with iatrogenic keratectasia following myopic LASIK and 1 human cornea with irregular astigmatism and central scar formation after hyperopic LASIK. Corneal buttons were obtained during penetrating keratoplasty in both patients.

RESULTS

Histopathological examination showed thinning of the central stroma with a posterior residual thickness of 190 microm in the patient with iatrogenic keratectasia after myopic LASIK and significant midperipheral thinning in the patient who had hyperopic LASIK. However, this characteristic ablation profile of the stroma after hyperopic LASIK was partially mitigated and compensated by the epithelium, which was significantly thinned in the center and markedly thickened in the midperiphery. Traces of wound healing with minimal scar tissue were present at the flap margin after myopic and hyperopic LASIK. In a few sections of the cornea with keratectasia after myopia LASIK, only a few collagen lamellae were visible crossing between the posterior residual stroma and the superficial flap. Immunohistochemical examination revealed minimally increased staining of dermatan sulfate proteoglycan within the stroma adjacent to the interface of the microkeratome incision. Increased staining of hepatocyte growth factor was found on keratocytes/fibroblasts at the flap margin in both corneas.

CONCLUSIONS

The wound-healing response is generally poor after LASIK, which may result in significant weakening of the tensile strength of the cornea after myopic LASIK, probably due to biomechanically ineffective superficial lamella. After LASIK in patients with high hyperopia, compensatory epithelial thickening in the annular midperipheral ablation zone might be partly responsible for regression.

Functional alterations of cat abducens neurons after peripheral tetanus neurotoxin injection

Tetanus neurotoxin (TeNT) cleaves synaptobrevin, a protein involved in synaptic vesicle docking and fusion, thereby preventing neurotransmitter release and causing a functional deafferentation. We injected TeNT into the lateral rectus muscle of adult cats at 0.5 or 5 ng/kg (low and high dose, respectively). In the periphery, TeNT slightly slowed motor axon conduction velocity, and at high doses, partially blocked neuromuscular transmission. TeNT peripheral actions displayed time courses different to the more profound and longer-lasting central actions. Central effects were first observed 2 days postinjection and reversed after 1 mo. The low dose induce depression of inhibitory inputs, whereas the high dose produce depression of both inhibitory and excitatory inputs. Simultaneous recordings of eye movement and neuronal firing revealed that low-dose injections specifically reduced inhibition of firing during off-directed saccadic movements, while high-dose injections of TeNT affected both inhibitory and excitatory driven firing patterns. Motoneurons and abducens interneurons were both affected in a similar way. These alterations resulted in modifications in all discharge characteristic analyzed such as background firing, threshold for recruitment, and firing sensitivities to both eye position and velocity during spontaneous movements or vestibulo-ocular reflexes. Removal of inhibition after low-dose injections also altered firing patterns, and although firing activity increased, it did not result in muscle tetanic contractions. Removal of inhibition and excitation by high-dose injections resulted in a decrease in firing modulation with eye movements. Our findings suggest that the distinct behavior of oculomotor and spinal motor output following TeNT intoxication could be explained by their different interneuronal and proprioceptive control.

The beta-adrenoceptor antagonists metipranolol and timolol are retinal neuroprotectants: comparison with betaxolol

beta-adrenoceptor antagonists are used clinically to reduce elevated intraocular pressure in glaucoma which is characterised by a loss of retinal ganglion cells. Previous studies have shown that the beta(1)-selective adrenoceptor antagonist, betaxolol, is additionally able to protect retinal neurones in vitro and ganglion cells in vivo from the detrimental effects of either ischemia-reperfusion or from excitotoxicity, after topical application. The neuroprotective effect of betaxolol is thought not to be elicited through an interaction with beta-adrenoceptors, but by its ability to reduce influx of sodium and calcium through voltage-sensitive calcium and sodium channels. In the present study it is shown that the non-selective beta-adrenoceptor antagonists, metipranolol and timolol behave like betaxolol. When topically applied they all attenuate the detrimental effect of ischemia-reperfusion. Protection of the retina was determined by evaluating changes in the electroretinogram and by assessing the loss of mRNA for Thy-1, which is expressed in retinal ganglion cells. In addition, studies conducted on neurones in mixed retinal cultures demonstrated that metipranolol, betaxolol and timolol were all able to partially counteract anoxia-induced cell loss and viability reduction. The influence of timolol was, however, not significant. Within the confines of these investigations, an order of neuroprotective efficacy was delineated for the three beta-adrenoceptor antagonists: betaxolol>metipranolol>timolol. The ability of the beta-adrenoceptor antagonists to attenuate ligand-induced stimulation of calcium and sodium entry into neuronal preparations showed a similar order of effectiveness. In conclusion, the ability to confer neuroprotection to retinal neurones is a common feature of three ophthalmic beta-adrenoceptor antagonists (betaxolol, metipranolol and timolol). A comparison of the effectiveness of the individual compounds in protecting retinal cells in vivo was not possible in these studies. However, in vitro studies show that the capacity of the individual beta-adrenoceptor antagonists to act as neuroprotectants appears to relate to their capacity to attenuate neuronal calcium and sodium influx.

Gamma-D crystallin gene (CRYGD) mutation causes autosomal dominant congenital cerulean cataracts

Congenital cataracts are a major cause of bilateral visual impairment in childhood. We mapped the gene responsible for autosomal congenital cerulean cataracts to chromosome 2q33-35 in a four generation family of Moroccan descent. The maximum lod score (7.19 at recombination fraction theta=0) was obtained for marker D2S2208 near the gamma-crystallin gene (CRYG) cluster. Sequencing of the coding regions of the CRYGA, B, C, and D genes showed the presence of a heterozygous C>A transversion in exon 2 of CRYGD that is associated with cataracts in this family. This mutation resulted in a proline to threonine substitution at amino acid 23 of the protein in the first of the four Greek key motifs that characterise this protein. We show that although the x ray crystallography modelling does not indicate any change of the backbone conformation, the mutation affects a region of the Greek key motif that is important for determining the topology of this protein fold. Our data suggest strongly that the proline to threonine substitution may alter the protein folding or decrease the thermodynamic stability or solubility of the protein. Furthermore, this is the first report of a mutation in this gene resulting in autosomal dominant congenital cerulean cataracts.

Effects of benzodiazepines on frog ERG

Effect of flurazepam (water-soluble benzodiazepine) on the amplitude and time course of ERG waves was investigated in superfused frog eyecups (Rana ridibunda). Flurazepam (50 and 100 microM) had inhibitory effect on the b- and d-wave amplitude, which was not accompanied with significant changes in their implicit time. Flurazepam potentiated the depressant effect of GABA (2.5 and 5 mM) on the b- and d-wave amplitude. The inhibitory effect of flurazepam was not blocked by 50 microM bicuculline (BCC), (GABA(A) antagonist), although the blocker markedly potentiated the b- and d-wave amplitude. The suppressive effect of flurazepam on the b- but not d-wave amplitude was blocked by 100 microM BCC. Our results indicate existence of functional benzodiazepine regulatory sites on GABA(A) receptors in distal frog retina.

Pharmacological strategies to block rod photoreceptor apoptosis caused by calcium overload: a mechanistic target-site approach to neuroprotection

PURPOSE

Photoreceptor apoptosis and resultant visual deficits occur in humans and animals with inherited, and disease-, injury- and chemical-induced retinal degeneration. Our aims were three-fold: 1) to determine the kinetics of rod apoptosis and Ca2+ overload in Pde6b9rd1) mice and developmentally lead-exposed rats, 2) to establish a pathophysiologically-relevant model of Ca2+ overload/rod-selective apoptosis in isolated rat retina and 3) to examine different mechanistic based neuroprotective strategies that would abrogate or mollify rod Ca2+ overload/apoptosis.

METHODS

Retinal morphometry and elemental calcium content ([Ca]) determined the kinetics of rod apoptosis and Ca2+ overload. A multiparametric analysis of apoptosis including rod [Ca], a live/dead assay, rod oxygen consumption, cytochrome c immunoblots and caspase assays was combined with pharmacological studies of an isolated rat retinal model of rod-selective Ca2+ overload/apoptosis.

RESULTS

Ca2+ overload preceded rod apoptosis in mice and rats, although the extent and kinetics in each differed significantly. The isolated rat model of rod Ca2+ overload/apoptosis showed that blockade of Ca2+ entry through rod cGMP-activated channels with L-cis diltiazem was partially neuroprotective, whereas blockade of Ca2+ entry into rods through L-type Ca2+ channels with D-cis diltiazem or verapamil provided no protection. Inhibition of the mitochondrial Na+/Ca2+ exchanger with D-cis diltiazem provided no protection. CsA and NIM811, mitochondrial permeability transition pore (mPTP) inhibitors, blocked all Ca(2+)-induced apoptosis, whereas the caspase-3 inhibitor DEVD-fmk only blocked the downstream cytochrome c-induced apoptosis.

CONCLUSIONS

The successful pharmacological neuroprotective strategies for rod Ca2+ overload/apoptosis targeted the rod cGMP-activated channels or mPTP, but not the rod L-type Ca2+ channels.

Stem cells in the teleost retina: persistent neurogenesis and injury-induced regeneration

The retina of the adult teleost fish is an important model for studying persistent and injury-induced neurogenesis in the vertebrate central nervous system. All neurons, with the exception of rod photoreceptors, are continually appended to the extant retina from an annulus of progenitors at the margin. Rod photoreceptors, in contrast, are added to differentiated retina only from a lineage of progenitors dedicated to making rods. Further, when the retina is lesioned, the lineage that produces only rods ceases this activity and regenerates retinal neurons of all types. The progenitors that supply neurons at the retinal margin and rod photoreceptors and regenerated neurons in the mature tissue originate from multipotent stem cells. Recent data suggest that the growth-associated neurogenic activity in the retina is regulated as part of the growth hormone/insulin-like growth factor-I axis. This paper reviews recent evidence for the presence of stem cells in the teleost retina and the molecular regulation of neurogenesis and presents a consensus cellular model that describes persistent and injury-induced neurogenesis in the retinas of teleost fish.

A comparative bioavailability study of three conventional eye drops versus a single lyophilisate

AIM

To study the ocular bioavailability of a triple dose, single application of sodium fluorescein to the human anterior segment from a novel drug delivery device.

METHODS

In a randomised, open label study 22 healthy volunteers applied a single lyophilisate to one eye (+1 minute) and three conventional eye drops (+1, 16, 31 minutes) of fluorescein ophthalmic solution to the fellow eye. The fluorescein dose of the lyophilisate was 204 mg corresponding to three conventional, preservative-free eye drops of 40 ml fluorescein SE Thilo 0.17% (68 micro g each) (Alcon). Fluorophotometry was performed (Fluorotron Master II Ocumetrics, USA) before and +15, 30, 45, 60, 120, 180, 240, 300, 360, 420 minutes after application. The fluorescein concentrations of the corneal stroma and mid-anterior chamber were analysed by paired t test.

RESULTS

Cornea and anterior chamber mean values (ng/ml) were significantly higher (p<0.018, paired t test) in the lyophilisate group up to 7 hours after application with the exception of +45 minutes. The mean fluorescein bioavailability from the lyophilisate was up to 11 times higher in the cornea and up to 8.7 times higher in the anterior chamber compared with the three preservative-free eye drops.

CONCLUSION

A triple dose was delivered to the human eye with a single lyophilisate application for the first time. A significantly better bioavailability was achieved in the cornea and anterior chamber for up to 7 hours by means of drug application with lyophilisates. The application of medications by means of the lyophilisate will improve the treatment of, for example, glaucoma, bacterial, viral and fungal infections, as well as dry eye syndrome.

Remodeling of second-order neurons in the retina of rd/rd mutant mice

This is a brief review of data obtained by analyzing the morphology and the physiology of the retinas in rd/rd and normal, wt mice, aged 10-90 days. Second-order neurons of the rd/rd show abnormalities that start with the anomalous development of rod bipolar cells around P10 and culminate with the atrophy of dendrites in cone bipolar cells, mostly evident at P90. Horizontal cells remodel considerably. Cone-mediated ERGs, (recorded between 13 and 16 days of age) have reduced a-wave and b-wave amplitudes and longer b-wave latency and duration. B-wave abnormalities indicate specific postreceptoral dysfunction. Morphological and ERG changes in rd/rd retinas are consistent with substantial inner retinal remodeling associated to photoreceptor degeneration.

Some current ideas on the pathogenesis and the role of neuroprotection in glaucomatous optic neuropathy

The primary features of glaucomatous optic neuropathy are characteristic changes in the optic nerve head, a decrease in number of surviving ganglion cells and a reduction in vision. It is now generally accepted that a number of factors, including elevated intraocular pressure, could lead to the changes seen in the optic nerve head and to obtain a pharmacological means to treat the causes will vary from patient to patient. In contrast, a cascade of events have been proposed to explain how the changes in the optic nerve head may lead to the slow and differential death of ganglion cells in the disease. It is also proposed that drugs (neuroprotectants) influencing this cascade of events can attenuate ganglion cell death and lead to the treatment of all glaucoma patients.

Neuroprotection as a treatment for glaucoma: pharmacological and immunological approaches

Primary open-angle glaucoma is a chronic, progressive optic neuropathy associated with a gradual decline in visual function, which may lead to blindness. In most cases, the optic neuropathy is associated with increased intraocular pressure. It is now generally accepted, however, that normalization of pressure, although necessary, is often not-sufficient as a remedial measure. This is because of the existence of additional factors, some of which emerge as a consequence of the initial damage. This situation is reminiscent of the response to a traumatic axonal insult, in which some of the damage is immediate and is caused by the insult itself, and some is secondary and is caused by a deficiency of growth-supportive factors as well as by toxic factors derived from the damaged tissue. Accordingly, the author has suggested that glaucoma may be viewed as a neurodegenerative disease and consequently amenable to any therapeutic intervention applicable to neurodegenerative diseases. There is evidence that neuroprotection can be achieved both pharmacologically and immunologically. Pharmacologic intervention neutralizes some of the effects of the nerve-derived toxic factors and possibly increases the ability of the remaining healthy neurons, at any given time, to cope with the stressful conditions. Immunologic intervention boosts the body's repair mechanisms for counteracting the toxicity of physiologic compounds acting as stress signals.

Differential expression of matrix metalloproteinases in monkey eyes with experimental glaucoma or optic nerve transection

Extracellular matrix (ECM) remodeling after neuronal injury and reactive gliosis is carried out by activation of matrix metalloproteinases (MMPs) regulated by their tissue inhibitors (TIMPs). In glaucoma, there is a loss of retinal ganglion cells and extensive ECM remodeling (cupping) at the level of the optic nerve head, frequently associated with elevated intraocular pressure. To determine whether ECM remodeling in the glaucomatous optic nerve head occurs in response to loss of axons or to elevated intraocular pressure we compared the patterns of MMP and TIMP expression in the eyes of monkeys with laser-induced glaucoma or with optic nerve transection. MT1-MMP and MMP1 expression was markedly increased in reactive astrocytes in optic nerve heads with experimental glaucoma but not in the optic nerve head of transected eyes. In normal control eyes retinal ganglion cells expressed MMP2, TIMP1 and TIMP2 constitutively, and the proteins were detected in their axons. At the site of transection, MT1-MMP, MMP1, MMP2, TIMP1 and TIMP2 were expressed by reactive astrocytes. Inflammatory cells, fibroblasts and reactive astrocytes at the transected site expressed MMP3 and MMP9, which were undetectable in the retina and optic nerve head in any condition. Constitutive expression of MMP2, TIMP1 and TIMP2 in retinal ganglion cells suggests a role in maintenance of synaptic integrity and plasticity and maintenance of the periaxonal space. Increased MMP1 and MT1-MMP1 expression in the glaucomatous optic nerve head is specific to tissue remodeling due to elevated intraocular pressure and not secondary to loss of axons.

Differential modulation of light-evoked on- and off-EPSCs by paired-pulse stimulation in salamander retinal ganglion cells

Short-term plasticity of On- and Off-EPSPs, and its potential role in regulation of signal processing was studied in salamander retinal On-Off ganglion cells by whole-cell recording. Paired-pulse light stimulation resulted in a depression of On-, and an enhancement of Off-EPSCs. Recovery from depression and enhancement was exponential and complete by 20 s. Paired-pulse enhancement, but not depression, was abolished with increasing stimulus duration. Blockade of On-EPSC by L-2-amino-4-phosphonobutyrate (AP-4), an agonist at group III mGluRs, significantly increased Off-EPSCs evoked by short (<2 s) duration conditioning light stimuli, resulting in a reversal of the paired-pulse enhancement to depression. The acetylcholinesterase inhibitor eserine reduced Off-EPSC1 and increased the ratio of enhancement. An opposite effect was observed in the presence of the nACh receptor antagonist d-tubocurarine. AP-7, an antagonist of NMDA receptors attenuated the enhancement of Off-EPSCs. In current clamp mode paired-pulse stimulation resulted in a modulation of light evoked, as well as the depolarization-induced spike firing pattern of ganglion cells. The present study suggests that paired light stimulation differently modulates On and Off EPSPs, and the light-evoked spike firing pattern of On-Off ganglion cells.

Altered functionality in rhodopsin point mutants associated with retinitis pigmentosa

Point mutations found in rhodopsin associated with the retinal degenerative disease retinitis pigmentosa have been expressed in mammalian COS-1 cells, purified, and characterised. The mutations characterised-most of them for the first time-have been Met44Thr, Gly114Asp, Arg135Leu, Val137Met, and Pro171Leu in the transmembrane domain; Leu328Pro and Ala346Pro in the C-terminal tail of the cytoplasmic domain; and Gly106Trp in the intradiscal domain. Several of these mutations cause misfolding which results in impaired 11-cis-retinal binding. Two of them, Met44Thr and Val137Met, show spectral and structural features similar to those of wild type rhodopsin (Type I mutants) but significantly increased transducin initial activation rates. We propose that, in the case of these mutants, abnormal functioning resulting in faster activation kinetics could also play a role in retinitis pigmentosa by altering the stoichiometric balance of the different proteins involved in the phototransduction biochemical reactions.

Postoperative blindness

This chapter discusses the cases of postoperative blindness reported in the literature and the theories that attempt to explain the mechanisms involved. Although uncommon, alterations in vision and blindness after anesthesia for major surgical procedures, particularly cardiopulmonary bypass or spine surgery, are well documented, with an incidence varying between 0.05% and 1%. Accurate incidence data are unavailable because it is not known what percentages are reported. However, the large number of case reports over many years has provided some significant information. Although sustained compression of the eye is an important cause, postoperative visual loss may also occur, in an unrelated manner, because of ischemic optic neuropathy, central retinal artery or vein occlusion, or cortical blindness.

Oxidative stress causes ERK phosphorylation and cell death in cultured retinal pigment epithelium: prevention of cell death by AG126 and 15-deoxy-delta 12, 14-PGJ2

BACKGROUND

The retina, which is exposed to both sunlight and very high levels of oxygen, is exceptionally rich in polyunsaturated fatty acids, which makes it a favorable environment for the generation of reactive oxygen species. The cytotoxic effects of hydrogen peroxide (H2O2) induced oxidative stress on retinal pigment epithelium were characterized in this study.

METHODS

The MTT cell viability assay, Texas-Red phalloidin staining, immunohistochemistry and Western blot analysis were used to assess the effects of oxidative stress on primary human retinal pigment epithelial cell cultures and the ARPE-19 cell line.

RESULTS

The treatment of retinal pigment epithelial cells with H2O2 caused a dose-dependent decrease of cellular viability, which was preceded by a significant cytoskeletal rearrangement, activation of the Extracellular signal-Regulated Kinase, lipid peroxidation and nuclear condensation. This cell death was prevented partially by the prostaglandin derivative, 15d-PGJ2 and by the protein kinase inhibitor, AG126.

CONCLUSION

15d-PGJ2 and AG126 may be useful pharmacological tools in the future capable of preventing oxidative stress induced RPE cell death in human ocular diseases.

Gelsolin is a dorsalizing factor in zebrafish

The gene for gelsolin (an actin-binding, cytoskeletal regulatory protein) was shown earlier to be specialized for high corneal expression in adult zebrafish. We show here that zebrafish gelsolin is required for proper dorsalization during embryogenesis. Inhibition of gelsolin expression by injecting fertilized eggs with a specific morpholino oligonucleotide resulted in a range of concentration-dependent ventralized phenotypes, including those lacking a brain and eyes. These were rescued by coinjection of zebrafish gelsolin or chordin (a known dorsalizing agent) mRNAs, or human gelsolin protein. Moreover, injection of gelsolin mRNA or human gelsolin protein by itself dorsalized the developing embryos, often resulting in axis duplication. Injection of the gelsolin-specific morpholino oligonucleotide enhanced the expression of Vent mRNA, a ventral marker downstream of bone morphogenetic proteins, whereas injection of gelsolin mRNA enhanced the expression of chordin and goosecoid mRNAs, both dorsal markers. Our results indicate that gelsolin also modulates embryonic dorsalventral pattern formation in zebrafish.

Glutamate stimulates neurotrophin expression in cultured Müller cells

The uptake of excess extracellular glutamate and the secretion of neurotrophins by glial cells have been suggested to protect CNS neurons from glutamate-induced toxicity. In the retina, perturbation of glutamate transport and decreased retrograde transport of neurotrophic factors such as brain-derived neurotrophic factor (BDNF) may contribute to ganglion cell death in experimental glaucoma. Although many studies show a clear relationship between glutamate and neurotrophic factors, such relationship has not been thoroughly investigated in the retinal environment. In the following study, we determined the effects of glutamate on early passaged rat Müller cells, specifically their expression of neurotrophic factors including BDNF, nerve growth factor (NGF), neurotrophin-3 (NT-3), neurotrophin-4 (NT-4), and glial-cell line derived neurotrophic factor (GDNF); and of glutamate receptors and transporters using immunoblots or enzyme-linked immunosorbent assays. Binding of BDNF to its cognate receptor TrkB was also determined using co-immunoprecipitation studies. Cultured Müller cells grown in the presence of glutamate were also assayed for survival using 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium (MTS). Our study showed that while glutamate treatment did not promote cell death, it upregulated secretion of BDNF, NGF, NT-3, NT-4, and GDNF by Müller cells. While solitary bands at approximately 13-14 kDa were observed for NGF, NT-3, and NT-4; two BDNF-reactive bands were observed in immunoblots: a faster migrating band at the reported size of the BDNF monomer (approximately 13 kDa); and a more intense band at approximately 36 kDa. GDNF-reactive bands were observed at approximately 22, approximately 28, and approximately 55 kDa. Glutamate also induced significant changes in glutamate receptor and transporter proteins, as well maintained the association of BDNF to TrkB in Müller cells. The decreased N-methyl-D-aspartate receptor (NMDAR) levels and sustained activation of TrkB by BDNF could serve as protective mechanisms for Müller cell survival. Moreover, the increased secretion of neurotrophic factors and upregulation of L-glutamate/L-aspartate transporter (GLAST) expression in Müller cells may protect retinal neurons from glutamate toxicity.

Reduced survival of lens epithelial cells in the alphaA-crystallin-knockout mouse

alphaA-Crystallin (alphaA) is a molecular chaperone expressed preferentially in the lens. alphaA transcripts are first detected during the early stages of lens development and its synthesis continues as the lens grows throughout life. alphaA(-/-) mouse lenses are smaller than controls, and lens epithelial cells derived from these mice have diminished growth in culture. In the current work, we tested the hypothesis thatalphaA prevents cell death at a specific stage of the cell cycle in vivo. Seven-day-old 129Sv (wild-type) and alphaA(-/-) mice were injected with 5-bromo-2'-deoxyuridine (BrdU) to label newly synthesized DNA in proliferating cells. To follow the fate of the labeled cells, wholemounts of the capsule epithelial explants were made at successive times after the BrdU pulse, and the labeling index was determined. Immunofluorescence and confocal microscopy showed that both wild-type and alphaA(-/-) cells had a 3-hour labeling index of 4.5% in the central region of the wholemount, indicating that the number of cells in S phase was the same. Twenty-four hours after the pulse, individual cells labeled with BrdU had divided and BrdU-labeled cells were detected in pairs. The 24-hour labeling index in the wild-type lens was 8.6%, but in the alphaA(-/-) lens it was significantly lower, suggesting that some of the cells failed to divide and/or that the daughter cells died during mitosis. TUNEL labeling was rarely detected in the wild-type lens, but was significant and always detected in pairs in the alphaA(-/-) wholemounts. Dual labeling with TUNEL and BrdU also suggested that the labeled cells were dying in pairs in the alphaA(-/-) lens epithelium. Immunolabeling of wholemounts with beta-tubulin antibodies indicated that the anaphase spindle in a significant proportion of alphaA(-/-) cells was not well organized. Examination of the cellular distribution of alphaA in cultured lens epithelial cells showed that it was concentrated in the intercellular microtubules of cells undergoing cytokinesis. These data suggest that alphaA expression in vivo protects against cell death during mitosis in the lens epithelium, and the smaller size of the alphaA(-/-) lens may be due to a decrease in the net production of epithelial cells.

Ryanodine stores and calcium regulation in the inner segments of salamander rods and cones

Despite the prominent role played by intracellular Ca2+ stores in the regulation of neuronal Ca2+ homeostasis and in invertebrate photoreception, little is known about their contribution to the control of free Ca2+ concentration ([Ca2+]i) in the inner segments of vertebrate photoreceptors. Previously, caffeine-sensitive intracellular Ca2+ stores were shown to play a role in regulating glutamate release from photoreceptors. To understand the properties of these intracellular stores better we used pharmacological approaches that alter the dynamics of storage and release of Ca2+ from intracellular compartments. Caffeine evoked readily discernible changes in [Ca2+]i in the inner segments of rods, but not cones. Caffeine-evoked Ca2+ responses in cone inner segments were unmasked in the presence of inhibitors of the plasma membrane Ca2+ ATPases (PMCAs) and mitochondrial Ca2+ sequestration. Caffeine-evoked responses were blocked by ryanodine, a selective blocker of Ca2+ release and by cyclopiazonic acid, a blocker of Ca2+ sequestration into the endoplasmic reticulum. These two inhibitors also substantially reduced the amplitude of depolarization-evoked [Ca2+]i increases, providing evidence for Ca2+-induced Ca2+ release (CICR) in rods and cones. The magnitude and kinetics of caffeine-evoked Ca2+ elevation depended on the basal [Ca2+]i, PMCA activity and on mitochondrial function. These results reveal an intimate interaction between the endoplasmic reticulum, voltage-gated Ca2+ channels, PMCAs and mitochondrial Ca2+ stores in photoreceptor inner segments, and suggest a role for CICR in the regulation of synaptic transmission.

Expression and characterization of the olfactomedin domain of human myocilin

The olfactomedin-domain has been first identified in olfactomedin, an extracellular matrix protein of the olfactory neuroepithelium. Members of this extracellular domain-family have since been shown to be present in several metazoan proteins, such as latrophilins, myocilins, and noelins, but their biological function is unknown. The olfactomedin-domain of myocilin is of considerable interest, since mutations affecting this domain are associated with primary open angle glaucoma. In order to define structural features of this domain-type we have expressed the olfactomedin-domain of human myocilin in Pichia pastoris. The olfactomedin-domain contains a single disulphide-bond connecting Cys-245 and Cys-433 residues; secondary structure predictions and circular dichroism studies indicate that it consists primarily of beta-strands. It is noteworthy that the majority of mutations associated with severe forms of glaucoma affect residues that reside in conserved secondary structural elements of the olfactomedin-domain or are otherwise critical for the integrity of this protein-fold.

The roles of types XII and XIV collagen in fibrillogenesis and matrix assembly in the developing cornea

Corneal transparency depends on the architecture of the stromal extracellular matrix, including fibril diameter, packing, and lamellar organization. The roles of collagen types XII and XIV in regulation of corneal fibrillogenesis and development were examined. The temporal and spatial expression patterns were analyzed using semi-quantitative RT-PCR, in situ hybridization, Western analysis, and immunohistochemistry. Expression of types XII and XIV collagens in cornea development demonstrated that type XII collagen mRNA levels are constant throughout development (10D-adult) while type XIV mRNA is highest in early embryonic stages (10D-14D), decreasing significantly by hatching. The spatial expression patterns of types XII and XIV collagens demonstrated a homogeneous signal in the stroma for type XIV collagen, while type XII collagen shows segregation to the sub-epithelial and sub-endothelial stroma during embryonic stages. The type XII collagen in the anterior stroma was an epithelial product during development while fibroblasts contributed in the adult. Type XIV collagen expression was highest early in development and was absent by hatching. Both types XII and type XIV collagen have different isoforms generated by alternative splicing that may alter specific interactions important in fibrillogenesis, fibril-fibril interactions, and higher order matrix assembly. Analysis of these splice variants demonstrated that the long XII mRNA levels were constant throughout development, while the short XII NC3 mRNA levels peaked early (12D) followed by a decrease. Both type XIV collagen NC1 splice variants are highest during early stages (12D-14D) decreasing by 17D of development. These data suggest type XII collagen may have a role in development of stromal architecture and maintenance of fibril organization, while type XIV collagen may have a role in regulation of fibrillogenesis.

The spectral tuning in the short wavelength-sensitive type 2 pigments

Using site-directed mutagenesis and multiple regression analysis, we have studied the molecular genetics and evolution of short wavelength-sensitive (SWS2) pigments in vertebrates. These analyses suggest that the SWS2 pigment in the vertebrate ancestor had the wavelength of maximum absorption (lambda(max)) of approximately 440 nm and that various lambda(max)'s of the contemporary SWS2 pigments in vertebrates are caused mainly by additive effects of amino acid replacements at ten sites.

Electrophysiology of corneal cold receptor nerve terminals

The mechanisms of sensory transduction in the fine nerve terminals of free nerve endings supplied by Adelta and C sensory axons are largely a matter of speculation. This is because the nerve terminals are small and inaccessible, particularly in intact tissues like skin. However, some of the difficulties associated with investigating the physiology of fine nerve terminals have recently been overcome using an in vitro preparation of the guinea-pig cornea that allows nerve terminal impulses (NTIs) to be recorded extracellularly from single polymodal and cold receptor nerve terminals. For cold receptors, the rate of spontaneously occurring NTIs is increased during cooling and decreased during heating. In addition, heating and cooling differentially modulate the shape of the recorded NTI. At the same temperature, NTIs are larger in amplitude and faster in time course during heating than those during cooling. The differential effect of heating and cooling on NTI shape is not considered to result simply from the temperature dependence of voltage-activated conductance kinetics or activity dependent changes in membrane excitability. Instead, changes in NTI shape may reflect changes in nerve terminal membrane potential that underlie the process of thermal transduction.

Expression of the neurokinin 1 receptor in the rabbit retina

Substance P is the preferred ligand for the neurokinin 1 (NK1) receptor. In vertebrate retinas, substance P is expressed by amacrine, interplexiform and ganglion cells. Substance P influences the activity of amacrine and ganglion cells and it is reported to evoke dopamine release. We investigated NK1 receptor expression in the rabbit retina using affinity-purified NK1 receptor antibodies. NK1 receptors were expressed by two distinct populations of retinal neurons. One is a population of ON-type bipolar cells characterized by axonal arborizations that ramified in the inner plexiform layer near the ganglion cell layer. Double-label studies showed that NK1 receptor-expressing bipolar cells were distinct from rod bipolar cells and from other immunocytochemically identified types of cone bipolar cells. Their density was about 2250 cells/mm2 in the visual streak and 1115 cells/mm2 in ventral mid-periphery. They were distributed in a non-random pattern. In the outer plexiform layer, the dendrites of these bipolar cells converged into heavily immunostained clusters having a punctate appearance. The density of these clusters in mid-peripheral ventral regions (about 13000 clusters/mm2) was similar to the reported cone density [Famiglietti and Sharpe (1995) Vis. Neurosci. 12, 1151-1175], suggesting these dendrites contact all cone photoreceptors. The second NK1 receptor expressing cell population corresponds to the tyrosine hydroxylase-containing amacrine cell population. NK1 receptor immunostaining was localized to the cell body and processes, but not to the processes that form the 'rings' that are known to encircle somata of AII amacrine cells. These findings show that NK1 receptor immunoreactivity is localized to a population of ON-type cone bipolar cells and to dopaminergic amacrine cells, suggesting that substance P acting on NK1 receptors influences multiple retinal circuits in the rabbit retina.