Immobilization of cesium with alkali-activated blast furnace slag.

Alkali-activated binders (AABs), as a promising alternative to Portland cement, are now being used on a commercial scale in various applications around the world, including hazardous and radioactive waste immobilization. In this paper, the leaching resistance, strength, and nanostructural alteration of alkali-activated blast furnace slag (AABFS) doped with 2 % and 5 % cesium were investigated. The addition of cesium caused a significant increase in the compressive strength of AABFS, followed by mild strength reduction after leaching. AABFS can be considered a potentially efficient matrix for cesium immobilization, since the mean leachability index in both cases (2 % and 5 % of Cs added) was above the threshold value of 6. Both doping with Cs and leaching caused the transformation of the AABFS nanostructure. The majority of the aluminum that was released from the C-A-S-H gel due to leaching remained within the AABFS matrix, initiating gel reconstruction: the C-A-S-H gel was converted to C-S-H gel, and an additional N-(C)-A-S-H gel was also formed. Cesium was preferentially associated with the N-(C)-A-S-H gel rather than with the C-A-S-H gel. The results of this research seem to be in good agreement with the Cross-linked Substituted Tobermorite Model (CSTM).

A safety and feasibility study of the use of 670 nm red light in premature neonates.

OBJECTIVE: Retinopathy of prematurity (ROP) is a vasoproliferative disorder of the retina affecting extremely preterm or low birth weight infants The aim of this study was to assess the feasibility and safety of 670 nm red light use in a neonatal intensive care unit. STUDY DESIGN: Neonates <30 weeks gestation and <1150 g were enrolled within 48 h of birth. Data collected included cause of preterm delivery, Apgar scores and birthweight. 670 nm red light was administered for 15 min per day from a distance of 25 cm, delivering 9 J cm(-)(2), from the time of inclusion in the study until 34 weeks postmenstrual age. Infants were assessed daily for the presence of any skin burns or other adverse signs. RESULT: Twenty-eight neonates were enrolled, seven 24 to 26 weeks and twenty-one 27 to 29 weeks gestation. The most common cause for preterm delivery was preterm labor (14/28) with five of these having evidence of chorioamnionitis. There were no skin burns or other documented adverse events. Entry into the study was readily achieved and treatment was well accepted by parents and nursing staff. CONCLUSION: 670 nm red light appears to be a safe and feasible treatment for further research in respect to ROP.

Real-time high-resolution X-ray imaging and nuclear magnetic resonance study of the hydration of pure and Na-doped C3A in the presence of sulfates.

This study details the differences in real-time hydration between pure tricalcium aluminate (cubic C(3)A or 3CaO·Al(2)O(3)) and Na-doped tricalcium aluminate (orthorhombic C(3)A or Na(2)Ca(8)Al(6)O(18)), in aqueous solutions containing sulfate ions. Pure phases were synthesized in the laboratory to develop an independent benchmark for the reactions, meaning that their reactions during hydration in a simulated early age cement pore solution (saturated with respect to gypsum and lime) were able to be isolated. Because the rate of this reaction is extremely rapid, most microscopy methods are not adequate to study the early phases of the reactions in the early stages. Here, a high-resolution full-field soft X-ray imaging technique operating in the X-ray water window, combined with solution analysis by (27)Al nuclear magnetic resonance (NMR) spectroscopy, was used to capture information regarding the mechanism of C(3)A hydration during the early stages. There are differences in the hydration mechanism between the two types of C(3)A, which are also dependent on the concentration of sulfate ions in the solution. The reactions with cubic C(3)A (pure) seem to be more influenced by higher concentrations of sulfate ions, forming smaller ettringite needles at a slower pace than the orthorhombic C(3)A (Na-doped) sample. The rate of release of aluminate species into the solution phase is also accelerated by Na doping.

The foveal avascular region of developing human retina.

OBJECTIVE: To study the development of the perifoveal retinal vasculature. METHODS: We studied 7 retinas aged between 26 weeks' gestation and 1 week postnatal (41 weeks' gestation). Sections were imaged using high-resolution digital photography and blood vessel profiles identified at 200% to 300% magnification. Flat mounts were immunolabeled using antibodies to CD31 and factor VIII to identify blood vessels and antibodies to rhodopsin to identify the rod-free zone. RESULTS: The foveal region was identified by the absence of rod photoreceptors in the outer retina and/or presence of a shallow depression in the inner retina. The whole mount at 26 weeks' gestation showed a blood vessel-free region centered on the rod-free zone that was open along the horizontal meridian on the temporal side. At 37 weeks' gestation, the foveal avascular zone formed a complete circle. In sections, the foveal avascular zone was approximately 500 microm in diameter at 35 weeks' gestation and 300 to 350 microm at 40 weeks' gestation; in whole mounts, it was 150 to 170 microm in diameter at 37 and 41 weeks' gestation. CONCLUSIONS: The foveal region is normally avascular during development, as in adult life. We found no evidence of foveal vascularization during development of the human retina. Clinical Relevance Instances of vascularization of the foveal region are not due to failed regression of a transient vasculature.

Reaction mechanisms in the geopolymeric conversion of inorganic waste to useful products.

High-performance materials for construction, waste immobilisation and an ever-growing range of niche applications are produced by the reaction sequence known as 'geopolymerisation'. In this process, an alkaline activating solution reacts with a solid aluminosilicate source, with solidification possible within minutes and very rapid early strength development. Geopolymers have been observed to display remarkable chemical and thermal stability, but due to their largely X-ray amorphous nature have only recently been accurately characterised. It has previously been shown that both fly ash and ground granulated blast furnace slag are highly effective as solid constituents of geopolymer reaction slurries, providing readily soluble alumina and silica that undergo a dissolution-reorientation-solidification process to form a geopolymeric material. Here a conceptual model for geopolymerisation is presented, allowing elucidation of the individual mechanistic steps involved in this complex and rapid process. The model is based on the reactions known to occur in the weathering of aluminosilicate minerals under alkaline conditions, which occur in a highly accelerated manner under the conditions required for geopolymerisation. Transformation of the waste materials to the mixture of gel and nanocrystalline/semicrystalline phases comprising the geopolymeric product is described. Presence of calcium in the solid waste materials affects the process of geopolymerisation by providing extra nucleation sites for precipitation of dissolved species, which may be used to tailor setting times and material properties if desired. Application of geopolymer technology in remediation of toxic or radioactive contaminants will depend on the ability to analyse and predict long-term durability and stability based on initial mix formulation. The model presented here provides a framework by which this will be made possible.

Endothelial cell proliferation in the choriocapillaris during human retinal differentiation.

BACKGROUND: Differentiation patterns of the neural retina and its retinal vasculature are not well matched. The foveal region differentiates first, however the central retina is not vascularised until late in gestation. The authors explored the hypothesis that higher rates of endothelial cell proliferation in the choriocapillaris of the central retina might compensate for the slow growth of central retinal vessels, providing supplementary nutrients to the region during the early stages of neuronal maturation. METHODS: Frozen sections of five human fetal eyes (14-18.5 weeks' gestation), were examined for Ki-67 and CD34 immunoreactivity using confocal microscopy. Measurements of choriocapillaris area and the number of proliferating choroidal endothelial cells were used to calculate the rate of choroidal endothelial proliferation at five different chorioretinal locations. RESULTS: The choriocapillaris area is consistently greater in the foveal region than at other locations and increases progressively with age. A higher rate of endothelial cell proliferation was found in parts of the choriocapillaris associated with the undifferentiated (proliferating) neural retina, compared with the differentiated, central region. CONCLUSION: The findings suggest that mechanisms regulating proliferation and growth of the choroidal vasculature are independent of differentiation in the neural retina, and are thus profoundly different from mechanisms that regulate formation of the retinal vasculature.

Muller cell expression of glutamate cycle related proteins and anti-apoptotic proteins in early human retinal development.

AIMS: The distribution of glutamate cycle related proteins (glutamine synthetase (GS) and GLAST) and anti-apoptotic proteins (Bcl-2 and Bcl-X) was investigated in Müller cells during early human retinal development, relative to the onset of expression of synaptophysin, a presynaptic vesicle protein. METHODS: Using frozen sections of human fetal eyes (13-22 weeks gestation) (n = 10), Bcl-2, Bcl-X, GS, GLAST, and synaptophysin immunoreactivities (IR) were imaged using fluorescence microscopy and plotted as a function of eccentricity from the incipient fovea. Frozen sections of adult human retina (n = 4) were immunolabelled with antibodies to Bcl-2 and Bcl-X. RESULTS: Müller cell immunoreactivity for GS, GLAST, and Bcl-2 was initially detected in the incipient fovea, and then at more peripheral locations with increasing age. Synaptophysin-IR appeared earlier than all other target proteins. Within the synaptophysin-IR region, mature (differentiated) Müller cells expressed both Bcl-2 and Bcl-X-IR from 13 weeks gestation, ahead of GS-IR and GLAST-IR that were first seen at 14 weeks gestation. Additionally, from as early as 13 weeks gestation, ganglion cells and immature neuronal progenitor cells across the entire retina expressed Bcl-2-IR and Bcl-X-IR, respectively. In adult retina, ganglion cells and some bipolar cells expressed Bcl-X but not Bcl-2. CONCLUSION: Müller cells express Bcl-2 and Bcl-X after synaptogenesis has commenced, but before the onset of GS and GLAST expression, suggesting a protective role for these proteins in Müller cells during the onset of glutamatergic transmission in early human retinal development.

Development of the primate retinal vasculature.

Human and macaque retinae have similar retinal vascular anatomy. The general features of the retinal vascular anatomy of these two primates have much in common with more widely studied animal models such as rat and cat. However, primates are unique amongst mammals in having a region in temporal retina specialized for high visual acuity, which includes the fovea centralis (or 'fovea'). Several features distinguish the fovea from other parts of the retina, including a very high local density of cone photoreceptors, a high density of inner retinal cells during development, and an absence of retinal blood vessels. The retinal vascular complex comprises a number of cell types, in addition to vascular endothelial cells, including pericytes, microglia, astrocytes-none of which is intrinsic to the retina. In addition, amacrine-like cells make bouton-like associations with retinal vessels and may be involved in the autoregulation of blood flow. During development endothelial cells 'invade' the retina, accompanied by a population of microglial cells; glial fibrillary acidic protein (GFAP)-immunoreactive astrocytes are also seen associated with the developing vasculature, and are in advance of the vascular front by a few hundred microns. Recent findings indicate that astrocytes at the vascular front proliferate in response to factors released by endothelial cells, including leukemia inhibitory factor. Better understood is the role of GFAP-immunoreactive astrocytes just in advance of the developing vessels. These astrocytes are sensitive to hypoxia and in response release vascular endothelial growth factor (VEGF) which in turn promotes the migration, differentiation and proliferation of vascular endothelial cells. This hypoxia/VEGF-mediated process of migration, proliferation and differentiation appears common to the retinae of a variety of species, including human. However, in human and macaque retina, different mechanisms appear to govern the development of the retinal vessels growing along the horizontal meridian of the retina towards the central area, which contains the fovea. Despite the relatively advanced state of differentiation and maturation of cells in the central area compared with the periphery, the growth of retinal vessels into the central area has been described as 'retarded', and the incidence of cell proliferation associated with these vessels is lower than in peripheral vessels. Furthermore, neither retinal vessels nor their accompanying astrocytes grow into a circumscribed region which, at a later stage, develops into the foveal depression. These observations suggest that molecular markers define the foveal region and inhibit cell proliferation and vascular growth at the fovea and, perhaps, along the horizontal meridian. The findings also suggest that at the fovea, the retina is adapted morphologically to its blood supply, since in the vicinity of the fovea, the development of retinal vessels is retarded or inhibited. The limitations on vascularization of central retina has implications for its vulnerability to degenerative changes, as seen in age-related macular degeneration.

Immunological and aetiological aspects of macular degeneration.

Aetiological and immunological aspects of AMD, a leading cause of blindness in Western countries, have been reviewed. Developmental studies suggest that anatomical features unique to the fovea result in a critical relationship between metabolic demand and blood supply at the macula, which is maintained throughout life. Recent studies show a sufficient degree of consistency in the link between smoking and both dry and wet AMD to regard it as causative. Dry AMD is considered to be the natural endstage of the disease; epidemiological and morphological studies point to choroidal vascular atrophy as the causative event and it is suggested that signals associated with acute vascular compromise lead to the development of subretinal neovascularisation. The relationship between sub-pigment epithelial deposits, including basal laminar deposit, and the pathogenesis of AMD is examined. Much of the literature is consistent with a choroidal origin for the constituents of drusen. The blood-retinal barrier preserves the physiological environment of the neural retina and limits inflammatory responses. The factors, including cytokines, adhesion molecules and the presence of resident immunocompetent cells (microglia), which determine the immune status of the retina are considered. Historical descriptions of the involvement of inflammatory cells are provided, evidence implicating inflammation in the pathogenesis of AMD involving macrophages, giant cells and microglia has been derived from observations of human and animal subretinal neovascular lesions. The role of humoral factors such as anti-retinal autoantibodies and acute phase proteins together with clinical observations has been surveyed. Taken together these data demonstrate the involvement of both cellular and humoral immunity in the pathogenesis of AMD. It remains to be determined to what degree the influence of immunity is causative or contributory in both wet and dry AMD, however, the use of anti-inflammatory agents to ameliorate the condition further indicates the existence of an inflammatory component.

Triamcinolone acetonide modulates permeability and intercellular adhesion molecule-1 (ICAM-1) expression of the ECV304 cell line: implications for macular degeneration.

Whilst animal studies and a pilot clinical trial suggest that intravitreal triamcinolone acetonide (TA) may be useful in the treatment of age-related macular degeneration (AMD), its mode of action remains to be fully elucidated. The present study has investigated the capacity of TA to modulate the expression of adhesion molecules and permeability using a human epithelial cell line (ECV304) as a model of the outer blood-retinal barrier (BRB). The influence of TA on the expression of ICAM-1 and MHC-I was studied on resting and phorbol myristate acetate (PMA)- or interferon-gamma (IFN-gamma)- and/or tumour necrosis factor-alpha (TNF-alpha)-activated cells using flow cytometry and immunocytochemistry. Additionally, ECV304 cells were grown to confluence in uncoated Transwell chambers; transepithelial resistance (TER) across resting and PMA-activated cells was monitored. TA significantly decreased the paracellular permeability of ECV304 cells and down-regulated ICAM-1 expression, consistent with immunocytochemical observations. PMA-induced permeability changes were dose-dependent and TA decreased permeability of both resting and PMA-activated monolayers. MHC-I expression by ECV304 cells however, was not significantly affected by TA treatment. The modulation of TER and ICAM-1 expression in vitro correlate with clinical observations, suggesting re-establishment of the BRB and down-regulation of inflammatory markers are the principal effects of intravitreal TA in vivo. The results further indicate that TA has the potential to influence cellular permeability, including the barrier function of the retinal pigment epithelium (RPE) in AMD-affected retinae.

Astrocytes and blood vessels define the foveal rim during primate retinal development.

PURPOSE: To investigate the relationship between development of the perifoveal blood vessels and formation of the foveal depression. METHODS: Retinal sections and flatmounts from monkeys aged between fetal day (Fd)80 and 2 years of age were double labeled using antisera to CD31 or von Willebrand factor to detect vascular endothelial cells and antiserum to glial fibrillary acidic protein to detect astrocytes. Sections were studied by fluorescence or confocal microscopy. RESULTS: From Fd88 to 115, vessels on the horizontal meridian were found only at the level of the ganglion cell layer (GCL)-inner plexiform layer (IPL) border where they form the ganglion cell layer plexus (GCP). Stellate astrocytes accompany GCP vessels and extend closer to the fovea than vessels. The foveal avascular zone was present within the GCP at Fd101, and at Fd105 a shallow foveal depression encircled by the GCP was present. The GCP foveal margin had the same dimensions as the adult foveal pit. Both blood vessels and astrocytes were excluded from the emerging fovea throughout development. After Fd140, capillary plexuses in the outer retina anastomosed with the GCP on the foveal slope to form a perifoveal plexus, but this plexus did not mature until a month or more after birth. After Fd142, astrocytes rapidly disappeared from the GCP and most of central retina. CONCLUSIONS: An avascular area is outlined by the GCP before the foveal pit begins to form, suggesting that molecular factors in this region exclude both vessels and astrocytes. These factors may also guide neuronal migration to form the pit. Because the perifoveal plexus is formed during late gestation, both capillary growth and foveal development may be affected adversely by prematurity.

The human hyaloid system: cell death and vascular regression.

The present study had investigated the roles of apoptosis and necrosis in the regression of the human fetal hyaloid vasculature. Normal human fetal hyaloid specimens (n = 67) ranging from 10 to 20 weeks' gestation were studied. Specimens were either immunolabeled with anti-von Willebrand factor and major histocompatibility complex class I antibodies or investigated using the terminal-deoxyribonucleotidyl transferase-mediated dUTP-biotin DNA nick-end labeling technique. A fluorescent DNA-binding dye acridine orange/ethidium bromide mixture was also applied to unfixed flat mounts of hyaloid vasculature and some specimens were processed for transmission electron microscopy. Vascular regression including cell loss in the connecting vessels, stretching and thinning of the vasa hyaloidea propria, tunica vasculosa lentis and the pupillary membrane was clearly evident after 13 weeks' gestation. Cresyl violet staining revealed condensed cells and pyknotic bodies throughout the hyaloid system; cell death occurred either in single cells or along small capillary segments associated with vascular regression. Acridine orange/ethidium bromide staining showed DNA condensation at early and late stages of cell death. Similarly, DNA nick-end labeling was positive in endothelial cells, pericytes and vessel and non-vessel associated hyalocytes. The observation of hyalocytes juxtaposed to cytolysed endothelial cells may indicate a role for these cells in vascular regression. Features of apoptosis were more evident during early vascular regression whilst necrosis was increasingly evident at later stages.

Astrocyte proliferation during development of the human retinal vasculature.

Wholemounts of human fetal retinas were labeled with antibodies to Ki67 or proliferating cell nuclear antigen, to map the distribution of proliferating cells in the developing primary vasculature and neural retina. Double labeling was used to determine the relative proportions of endothelial cells (CD34), astrocytes (glial fibrillary acidic protein - GFAP) and microglia (major histocompatability complex class II) associated with the developing vessels. The differentiated region of neural retina (cold spot) was 3.5 mm(2)at 15 weeks gestation (WG), centred on the incipient fovea, and increased in size with age to 80.5 mm(2)by 23-24 WG. Ki67 immunoreactive cells were distributed throughout the developing vasculature at all ages. The mean density of dividing cells in the neural retina increased with gestational age from 146 mm(-2)at 15 WG, to 624 mm(-2)at 23-24 WG. By 20 WG proliferation in the vasculature overlapped the margins of the cold spot, which was almost completely vascularized by 23-24 WG, except for a narrow strip on the horizontal meridian, which included the incipient fovea. Counts of CD34/Ki67 immunoreactive cells indicated that 15-52% of proliferations in the developing vasculature at 18 WG are endothelial cells. In contrast, in the fellow retina 65-85% cells were Ki67/GFAP immunoreactive, indicating proliferation of astrocytes in situ. No dividing microglia were observed. The findings suggest that large numbers of proliferating astrocytes accompany the developing vessels as they migrate across the primate retina.

Apoptosis during development of the human retina: relationship to foveal development and retinal synaptogenesis.

Apoptosis in the ganglion cell (GCL) and inner nuclear (INL) layers of human fetal retinae aged 14-35 weeks of gestation (WG) was investigated in relation to synaptogenesis and foveal depression formation. Terminal transferase dUTP-biotin nick end labeling (TUNEL) was used to identify apoptosis, and synapse development was demonstrated by synaptophysin immunoreactivity (-IR). The distribution of apoptotic cells and synaptophysin-IR was studied as a function of eccentricity. Between 14 and 23-24 WG in the GCL, rates of apoptosis were relatively low in central retina. A shallow fovea was detected at 23-24 WG. In the central GCL, the rate of apoptosis was 0.21% of viable cells compared with a higher incidence of 0.79-1.64% peripherally. Apoptosis in the INL was 2-8 times greater than that in the GCL. At 14-15 WG, peak death occurred at the incipient fovea; however, by 20 WG the distribution was bimodal, with peaks at more eccentric locations on either side of the incipient fovea with increasing age. Approximately 90% of INL apoptotic cells were in the middle and outer regions, suggesting that bipolar cells formed the majority of dying neurons. Synaptophysin-IR was present in cones, bipolar cells, and processes in the inner and outer plexiform layers at the incipient fovea at 14 WG and spread peripherally with increasing age. The peripheral margin of synaptophysin-IR coincided with areas of peak INL apoptosis. This pattern suggests that bipolar cell elimination is associated with the onset of synaptogenesis. Apoptosis in the GCL and INL is not a significant factor in foveal depression morphogenesis.

Mechanisms of photoreceptor death and survival in mammalian retina.

The mammalian retina, like the rest of the central nervous system, is highly stable and can maintain its structure and function for the full life of the individual, in humans for many decades. Photoreceptor dystrophies are instances of retinal instability. Many are precipitated by genetic mutations and scores of photoreceptor-lethal mutations have now been identified at the codon level. This review explores the factors which make the photoreceptor more vulnerable to small mutations of its proteins than any other cell of the body, and more vulnerable to environmental factors than any other retinal neurone. These factors include the highly specialised structure and function of the photoreceptors, their high appetite for energy, their self-protective mechanisms and the architecture of their energy supply from the choroidal circulation. Particularly important are the properties of the choroidal circulation, especially its fast flow of near-arterial blood and its inability to autoregulate. Mechanisms which make the retina stable and unstable are then reviewed in three different models of retinal degeneration, retinal detachment, photoreceptor dystrophy and light damage. A two stage model of the genesis of photoreceptor dystrophies is proposed, comprising an initial "depletion" stage caused by genetic or environmental insult and a second "late" stage during which oxygen toxicity damages and eventually destroys any photoreceptors which survive the initial depletion. It is a feature of the model that the second "late" stage of retinal dystrophies is driven by oxygen toxicity. The implications of these ideas for therapy of retinal dystrophies are discussed.

The human hyaloid system: cellular phenotypes and inter-relationships.

We have investigated the expression of leucocyte markers, phenotypic characteristics and cellular relationships of the normal human fetal hyaloid vasculature using immunohistochemistry, light and electron microscopy. Antibodies against von Willebrand Factor, alpha-smooth muscle actin, glial fibrillary acidic protein, vimentin, major histocompatibility complex classes-I and -II, CD45 (leucocyte-common antigen) and calcitonin gene-related peptide were used to identify the cellular constituents of the hyaloid vasculature in whole mounts. Additional morphological features were described at the ultrastructural level. Endothelial cells throughout the hyaloid system were immunoreactive to von Willebrand Factor and major histocompatibility complex class-I antibodies. Pericytes were immunoreactive to alpha-smooth muscle actin antibody; labeled cells were distributed along large branches of the hyaloid artery, vasa hyaloidea propria, tunica vasculosa lentis and pupillary membrane but no immunoreactivity was detected on small connecting capillaries. Vessel and non-vessel-associated hyalocytes on the hyaloid artery, vasa hyaloidea propria, tunica vasculosa lentis, pupillary membrane and vitreous were immunoreactive to major histocompatibility complex classes-I and -II, CD45 and calcitonin gene-related peptide antibodies. Anti-glial fibrillary acidic protein reactivity was detected on Bergmeister's papilla but not on the hyaloid artery. Cells immunoreactive for vimentin were present throughout the hyaloid vasculature including small connecting capillaries. Ultrastructural observations of the hyaloid vasculature revealed junctional complexes, including zonulae adherens, macula adherens and possible zonulae occludens, between adjacent endothelial cells. Fenestrae were not observed in the gestational ages included in the present study. The use of whole mounts in conjunction with specific antisera has provided novel immunohistochemical definitions of the structure and cellular constituents of the human hyaloid. The results indicate that hyalocytes are a heterogeneous population of leucocyte-lineage cells.

Isolation, culture and characteristics of human foetal and adult retinal pigment epithelium.

BACKGROUND: Current methods for the isolation and culture of adult retinal pigment epithelium (RPE) provide successful primary culture. However, most methods result in contamination with other cell types and low cell yields. The isolation and culture of human foetal RPE presents further problems associated with the limited size of the eye cup and adherence among cells. Reliable methods are necessary for the culture of human RPE and subsequent functional studies. METHODS: The present procedure is based on mechanical peeling of the whole RPE layer under the dissecting microscope. Dissected pieces are subsequently explanted to a 35 mm culture dish and are cultured with Dulbecco's modified Eagle's medium containing 10% foetal bovine serum. Peroxidase immunohistochemical methods were used to investigate cell phenotypes. RESULTS: Primary cultures were obtained within 10-14 days with high yields, good viability and purity in subsequent culture. Cultured cells were vimentin and cytokeratin positive and CD31 negative. CONCLUSIONS: This mechanical dissection technique is recommended for the isolation of foetal and young adult RPE cells, while the enzyme digestion method is preferred for aged adult tissue.

Modulation of the resistance of a human endothelial cell line by human retinal glia.

BACKGROUND: Human umbilical endothelial cells were used to model the vascular component of the blood-retinal barriers and to examine the capacity of glial cultures to modulate endothelial cell resistivity in vitro. METHODS: Endothelial cell resistivity was monitored with and without cocultured human retinal glia. Immunohistochemistry indicated that both macroglia and microglia were present in one culture, while only macroglia were detectable in the second culture. RESULTS: Both cocultures produced increased resistivity in the target endothelial cells; however, a further significant increase in resistivity was noted with the glial coculture containing microglia. The results suggest that the presence of microglia significantly increases the capacity of astrocytes and Müller cells to modulate endothelial cell resistivity.

Ontogeny of the primate fovea: a central issue in retinal development.

The formation of the primate fovea has fascinated a substantial number of histologists, pathologists, ophthalmologists and physiologists for more than a century. In this article, using data from the literature as well as our own observations, we identify events which we believe are crucial in this process and present a developmental neurobiologist's view of the formation of the primate fovea. The fovea is a region of the retina specialized for diurnal, high acuity functions which require a high spatial density of cone photoreceptors as well as a large number of inner retinal cells in order to establish the distinct retinofugal pathways (ganglion cell axons) receiving from individual cones in the foveal cone mosaic. A unique feature of the fovea is the displacement of cells connected to the foveal cones onto the rim of the fovea. It is generally believed that this displacement counteracts the problems caused by the scattering of the incoming light by cells and blood vessels of the inner retina. We believe that one of the crucial events in the formation of the primate fovea is the early centripetal migration of photoreceptors towards the central area (centripetal displacement). This process, initiated early in development, continues throughout intrauterine life until some months or years postnatal. We propose that the displacement of cells from the inner layers is related to the earlier developmental accumulation of photoreceptors and inner retinal cells centrally. This, we propose, leads to metabolic "starvation" of the inner retina, resulting from the complete absence of retinal vessels from the vicinity of the incipient fovea. It is suggested that these factors in turn trigger centrifugal displacement of inner retinal cells towards the encroaching perifoveal capillary network and lead to the formation of the foveal depression.