Axonal regeneration in the organotypically cultured monkey retina: biological aspects, dependence on substrates and age-related proteomic profiling

Injury to the mature primate and subprimate optic nerve results in irreversible impairment and loss of vision, because the retinal ganglion cells (RGCs) fail to regenerate their cut axons within the optic nerve interior. This study was performed to examine whether aging monkey RGCs retain the ability to regenerate their axons in organ culture and whether axonal regeneration is associated with specific proteomic profile. Retinal stripes obtained from marmoset eyes (C. jacchus) were cultured between the day of birth and adult stages on different substrates like laminin-1, laminin-2, collagen, matrigel and poly-D-lysine. No neurotrophic factors were added to the medium. Axonal growth was monitored with microscopy and immunohistochemistry. Onset and rate of growth was examined with time-lapse videography. Vigorous regeneration of axons occurred from identifiable morphological types of RGCs throughout all stages of life, although the numbers of axons decreased with age. Axonal growth occurred virtually only on laminin-1. Growth correlated with re-expression of the laminin-1 receptor alpha6-integrin and sustained staining for GAP-43 as shown by immunohistochemistry and immunoblotting. At proteomic level, there is a maturation-dependent change in the protein immunostaining within the retina. When retinal slices of the same age were compared, regeneration-specific protein staining included calmodulin, fatty acid binding protein, alpha-crystallin, IFN-gamma, cyclin-dependent kinase inhibitor (p21), beta-hemoglobin, 60s-ribosomal protein, GAP-DH and ADP-ribosylation factor (ARF). To our knowledge these data are the first from subhuman animals to suggest that axonal regeneration of injured RGCs is correlated to expression of identifiable proteins within the retina.

Emerging syphilitic optic neuropathy: critical review and recommendations

BACKGROUND

Infection with Treponema pallidum causes multiorgan manifestations including isolated optic nerve involvement at any stage of the disease. This is of particular interest for resulting in severe visual impairment, which is reversible if treated adequately.

PURPOSE

To review clinical and diagnostic findings in patients with optic nerve affection in neurosyphilis and to focus on the visual outcome after administering adjunctive cortisone to the standard therapy regimes with penicillin G.

METHODS/PATIENTS

The review is based on a retrospective case serial of 4 patients (three males: mean age 40 years, range 37-42 years; one female: mean age 62 years) with optic nerve involvement in neurosyphilis treated in our hospital, and on a literature review of recent publications. Patients were treated with systemic penicillin either with or without adjunctive cortisone. The major outcome measure of therapy was improvement of visual acuity.

RESULTS

Visual outcome in our case serial showed total restoration if cortisone was also administered. The bibliographic survey, which was based on 60 patients, also revealed a better improvement of vision when antibiotic medication was combined with cortisone.

CONCLUSIONS

The data show that the causal therapy of choice is undoubtedly penicillin G, with adjunctive steroids playing a crucial role in improvement of optic nerve functional outcome. Physicians should consider the use of cortisone in SON whenever clinically harmless, although prospective randomized multicenter studies are required to support this recommendation.

Crystallins of the beta/gamma-superfamily mimic the effects of lens injury and promote axon regeneration

Adult retinal ganglion cells (RGCs) can survive axotomy and regrow lengthy axons when exposed to lens injury (LI). The neuroprotective and axon-growth-promoting effects of LI have been attributed to an infiltration of activated macrophages into the inner eye and recently also to astrocyte-derived CNTF. The present work reveals that certain purified lens proteins (crystallins) cause the effects of LI. Intravitreal injections of beta- or gamma-crystallins, but not of alpha-crystallin, strongly enhanced axon regeneration from retinal explants in culture, within peripheral nerve grafts or the crushed optic nerve. Deposition of the effective crystallins within the vitreous body was also associated with an influx of circulating macrophages and an activation of retinal astrocytes, Müller cells, and resident microglia. Furthermore beta-crystallin induced CNTF expression in retinal astrocytes and activation of CNTF's major downstream signaling pathway (JAK/STAT3) when intravitreally injected or added to the culture medium ex vivo. Consistently, in culture the addition of beta- and gamma-crystallins to the medium also increased axon regeneration from retinal explants. These results demonstrate that crystallins of the beta/gamma-superfamily are the lens-derived activators of cascades, which lead to axonal regeneration and suggest that their effects might be mediated by astrocyte-derived CNTF.

Reduced expression of the gap junction protein Connexin 43 in keratoconus

PURPOSE

The purpose of the present study was to examine whether keratoconus, which is a bilateral noninflammatory corneal ectasia with multifactorial aetiology, shows altered expression of Connexin (Cx43). Cx43 is an important gap junction protein that contributes crucially to epithelial and stromal integrity of cornea.

METHODS

Eight keratoconic human corneal buttons were examined with immunohistochemistry and Western blotting and compared with eight normal human corneal buttons, to unravel changes in Cx43 expression.

RESULTS

All normal corneas exhibited similar epithelial Cx43 expression patterns, with the protein located in the basal epithelial layer. In contrast, some keratoconic corneas showed an altered pattern of immunostaining and Western blotting confirmed a decreased expression of Cx43 in keratoconic corneas.

CONCLUSIONS

Our results indicate that a decrease in Cx43 amount together with functional alteration of the protein is associated with keratoconus pathophysiology However, these changes apply only to some of the corneas examined and may not generally account for the development of keratoconus.

Systemic Adverse Events: A Comparison between Topical and Peribulbar Anaesthesia in Cataract Surgery

AIMS

To evaluate the safety of topical anaesthesia (TA) versus peribulbar anaesthesia (PBA) in patients undergoing routine cataract surgery on the basis of systemic adverse events.

METHODS

In this retrospective study, a total of 2,020 consecutive cases of cataract surgery performed by one surgeon on 1,621 patients with PBA (n = 1,010; between 1998-1999) or TA (n = 1,010; between 1999-2001) were evaluated on the basis of intra-operative and early postoperative adverse events requiring medical intervention.

RESULTS

The rate of pre-existing risk factors in patients undergoing cataract surgery is high (97%). Complications are significantly less frequent in TA than in PBA in the intra-operative (p < 0.001) and postoperative (p = 0.022) courses. The incidence of intra-operative complications is higher in elderly patients (>or=65 years of age) than in younger patients (p < 0.001).

CONCLUSION

The results from the present study indicate that intra-operative complications are less likely in patients that receive TA, suggesting the use of TA for routine cataract surgery both in young patients and particularly in elderly patients when there are no contraindications in the individual case.

Regeneration of retinal ganglion cell axons in organ culture is increased in rats with hereditary buphthalmos

This study used organ cultures to examine whether retinal ganglion cells (RGCs) retain their ability to regenerate axons in buphthalmos. A rat mutant with hereditary buphthalmos was used to (1) determine whether the extent of RGC loss corresponds to the severity and duration of elevated intraocular pressure (IOP), (2) examine whether RGCs exposed to an elevated IOP are able to regenerate their axons in a retina culture model, and (3) analyze the proteome of the regenerating retina in order to identify putative regeneration-associated proteins. Retrograde labeling of RGCs revealed a decrease in their numbers in the retinas of buphthalmic eyes that increased with age. Quantification of axons growing out of retinal explants taken at different stages of the disease demonstrated that buphthalmic RGCs possess a remarkable potential to regrow axons. As expected, immunohistochemistry and immunoblotting revealed that elevated IOP was associated with upregulation of certain known proteins, such as growth-associated protein 43, glial fibrillary acidic protein, and endothelin-1. In addition, two-dimensional polyacrylamide gel electrophoresis and mass spectrometry revealed several spots corresponding to proteins that were specifically regulated when buphthalmic RGCs were permitted to regrow their axons. Out of the proteins identified, heat-shock protein (HSP)-60 was constantly expressed during axonal growth at all stages of the disease. Antibodies against HSP-60 reduced axonal growth, indicating the involvement of this protein in regenerative axonal growth. These data are the first to show that diseased retinal neurons can grow their axons, and that HSP-60 supports neuritogenesis. This model may help to elucidate the fundamental mechanisms of optic neuropathy at stages preceding death caused by chronic injury, and aid in the development of neuroprotective strategies.

Elongation of axons during regeneration involves retinal crystallin beta b2 (crybb2)

Adult retinal ganglion cells (RGCs) can regenerate their axons in vitro. Using proteomics, we discovered that the supernatants of cultured retinas contain isoforms of crystallins with crystallin beta b2 (crybb2) being clearly up-regulated in the regenerating retina. Immunohistochemistry revealed the expression of crybb within the retina, including in filopodial protrusions and axons of RGCs. Cloning and overexpression of crybb2 in RGCs and hippocampal neurons increased axonogenesis, which in turn could be blocked with antibodies against beta-crystallin. Conditioned medium from crybb2-transfected cell cultures also supported the growth of axons. Finally real time imaging of the uptake of green fluorescent protein-tagged crybb2 fusion protein showed that this protein becomes internalized. These data are the first to show that axonal regeneration is related to crybb2 movement. The results suggest that neuronal crystallins constitute a novel class of neurite-promoting factors that likely operate through an autocrine mechanism and that they could be used in neurodegenerative diseases.

Growth-associated protein-43 expression in the lens of rats and primates

Growth-associated protein-43 is a specific neuronal protein that regulates differentiation, growth and plasticity. In the present study, growth-associated protein-43 expression was studied in the lens of rats and primates (including man) at different postnatal ages by immunoblotting, immunohistochemistry and quantitative real-time polymerase chain reaction. Growth-associated protein-43 was expressed at all ages in primates and in developing, but not in adult rats. We demonstrate that the lens - a tissue that is devoid of nerves - expresses growth-associated protein-43 throughout life in primates, and in rats during development but not in adulthood. These results suggest that growth-associated protein-43 is involved in differentiation processes also outside the nervous system.

Implantable visual prostheses

Visual impairment and blindness is primarily caused by optic neuropathies like injuries and glaucomas, as well as retinopathies like agerelated macular degeneration (MD), systemic diseases like diabetes, hypertonia and hereditary retinitis pigmentosa (RP). These pathological conditions may affect retinal photoreceptors, or retinal pigment epithelium, or particular subsets of retinal neurons, and in particular retinal ganglion cells (RGCs). The RGCs which connect the retina with the brain are unique cells with extremely long axons bridging the distance from the retina to visual relays within the thalamus and midbrain, being therefore vulnerable to heterogeneous pathological conditions along this pathway. When becoming mature, RGCs loose the ability to divide and to regenerate their accidentally or experimentally injured axons. Consequently, any loss of RGCs is irreversible and results to loss of visual function. The advent of micro- and nanotechnology, and the construction of artificial implants prompted to create visual prostheses which aimed at compensating for the loss of visual function in particular cases. The purpose of the present contribution is to review the considerable engineering expertise that is essential to fabricate current visual prostheses in connection with their functional features and applicability to the animal and human eye. In this chapter, 1) Retinal and cortical implants are introduced, with particular emphasis given to the requirements they have to fulfil in order to replace very complex functions like vision. 2) Advanced work on material research is presented both from the technological and from the biocompatibility aspect as prerequisites of any perspectives for implantation. 3) Ultimately, experimental studies are presented showing the shaping of implants, the procedures of testing their biocompatibility and essential modifications to improve the interfaces between technical devices and the biological environment. The review ends by pointing to future perspectives in the rapidly accelerating process of visual prosthetics and in the increasing hope that restoration of the visual system becomes reality.

Pathological changes in human retinal ganglion cells associated with diabetic and hypertensive retinopathy

BACKGROUND

To examine whether systemic diseases like diabetes and arterial hypertension, which frequently cause retinopathies leading to blindness effect the morphology of retinal ganglion cells (RGC).

METHODS

Histological retina material with a history of being untreated, or laser-coagulated (LC) diabetic retinopathy (DR), or arterial hypertensive retinopathy (AHR) was used. The RGC were labeled by introducing crystals of the fluorescent carbocyanine dye DiI into the nerve fiber layer, which contains ganglion cell axons.

RESULTS

The typical silhouettes of both major types of RGC, parasol and midget cells, were identified. The axons in DR and AHR retinas showed morphology changes such as irregular swelling and beading. Dendritic field sizes were significantly reduced in RGC of both the hypertonic and diabetic retinas. A significant reduction in branching frequency was evident in both the diabetic and hypertonic retinas, in both the midget and the parasol cells. In LC retinas, both parasol and midget RGC were observed within the LC spots, although their numbers were dramatically decreased compared with normal retinas.

CONCLUSIONS

The data suggest that diabetes and arterial hypertonia have similar effects on the morphology of RGC, in addition to causing microvascular alterations and bleeding. Therefore, therapeutic measures and prognostic outcomes in diabetic and hypertensive retinopathy should also consider regressive changes in retinal neurons.

Retinal gene profiling in a hereditary rodent model of elevated intraocular pressure

PURPOSE

To characterize the changes in retinal gene expression induced by elevated intraocular pressure (IOP) in a hereditary rodent model.

METHODS

A rat model derived from the RCS-rdy- strain develops IOP elevation spontaneously without experimental manipulation. Retinal gene expression after IOP elevation was compared with age-matched RCS-rdy- retinas having normal IOP levels The MWG Rat 10k array, which comprises 9715 rat genes spotted onto one array was used. Quantitative real-time PCR (qRT-PCR) was used to verify the expression of heat shock protein-27 (Hsp-27), SA hypertension-associated gene, c-myc, tissue inhibitor of matrix metalloproteinase-1 (TIMP-1), vascular endothelial growth factor (VEGF), myocilin, interleukin-7 (IL-7), mitogen activated protein kinase 13 (MAPK-13) and crystallin beta-A1 (Cryba1). The cellular distribution of c-myc, glial fibrillary acidic protein (GFAP), VEGF, and SA was assessed using immunohistochemistry.

RESULTS

Elevated IOP of 37.7+/-5.0 mmHg shifted the retina's program of gene expression, with 75 genes being upregulated (equal to or higher than 3.0 fold) and 45 genes being downregulated (equal to or lower than 0.3 fold). These genes mediate various cellular processes such as cell adhesion, cell structure, hypertension, immunity, protein sythesis, proteolysis, transcription, and signaling. The regulation pattern of SA, VEGF, c-myc, IL-7, and MAPK-13, which are uniquely regulated in our model were confirmed by qRT-PCR experiments. The regulation of Hsp-27, TIMP-1, myocilin, and Cryba1, which have previously been associated with elevated IOP were also confirmed with qRT-PCR. The protein products of c-myc, SA, and GFAP were localized to astrocytes and Müller cells. Neurons in the ganglion cell layer and inner nuclear layer were VEGF-immunopositive.

CONCLUSIONS

This study identified some of the genes that are differentially regulated, probably in response to long-term IOP exposure, in this animal model. The expression pattern of many genes is common to experimental models of elevated IOP and other retinal disorders such as diabetic retinopathy. However many genes are uniquely expressed in the retina of our model. This suggests that the mode of IOP elevation be it experimental or spontaneous could be relevant in determining which genes are regulated. Müller glia acquire a reactive phenotype as indicated by the upregulation of GFAP, c-myc, SA, and other Müller cell markers, emphasizing their relevance in pressure related- and other types of retinal injury. These data provide further evidence that IOP-mediated retinal injury is multifactorial and depends upon the interaction of different neuronal, glial, extracellular matrix, and vasogenic components.

Morphometric examination of human and monkey retinal ganglion cells within the papillomacular area

PURPOSE

To examine the morphology of the retinal ganglion cells (RGCs) in the lesser characterized area lying between the optic disk and the macula that consists of the central papillomacular area (PMA) and the arcuate papillomacular bundle (PMB).

METHODS

Nineteen human and 10 monkey (Macaca fascicularis) retinas obtained after death were used in the study. Perikaryal, axonal, and dendritic silhouettes were examined by postvital application of the fluorescent dye DiI, which specifically labeled RGCs when placed onto the optic fiber layer. The retinas were freed from surrounding tissue, prepared as flat mounts on a nitrocellulose filter, and fixed overnight in 4% paraformaldehyde. DiI diffuses along the membranes of ganglion cell axons, thereby completely labeling them, their cell bodies, and dendrites, which enables the RGCs to be examined with fluorescence microscopy.

RESULTS

In both species, midget cells represented most of the RGCs within the PMA (96.15%) and possessed small, umbrella-like dendrites oriented toward the deeper retinal layers. Parasol cells were less abundant in both species and had small, typical symmetric dendrites. Also along the PMB, midget cells represented most cells (91.52%), whereas only 8.47% could be categorized as parasol cells. In both species, parasol cells of the PMB extended dendrites, which were oriented perpendicular to the axons.

CONCLUSIONS

The data show that the PMA and PMB mainly contain small midget cells of typical morphology and size but with atypically oriented dendrites, which are only characteristic for this retinal area.

Bounds on the overlap of the Hartree-Fock, optimized effective potential, and density functional approximations with the exact energy eigenstates

In this paper, we examine the limits of accuracy of the single determinant approximations (Hartree-Fock, optimized effective potential, and density functional theory) to the exact energy eigenstates of many electron systems. We show that an approximate Slater determinant of S(z)=M gives maximum accuracy for states with S=M, provided that perturbation theory for the spin up minus spin down potential is applicable. The overlap with the exact energy eigenstates with S not equal M is much smaller. Therefore, for the case that the emphasis is on wave functions, one must use symmetry preserving theories, although this is at the expense of accuracy in energy.

Cortisol promotes survival and regeneration of axotomised retinal ganglion cells and enhances effects of aurintricarboxylic acid

BACKGROUND

Neuroprotection is essential for repair processes after a traumatic insult in the central nervous system. We have demonstrated previously significant neuroprotective properties of the anti-apoptotic drug aurintricarboxylic acid in the model of axotomised retinal ganglion cells. Glucocorticoids are widely used to treat injuries of the nervous system. Due to the anti-inflammatory and microglia-inhibiting properties of glucocorticoids, we studied the neuroprotective effects of intravitreally administered cortisol after an optic nerve cut.

METHODS

Ninety-eight adult Sprague-Dawley rats were used in this study. The optic nerve was cut intra-orbitally. Either vehicle or compound solution was injected intravitreally. Fluorescent dye was put onto the optic nerve stump to label retinal ganglion cells retrogradely. Retinal whole mounts were prepared 2 weeks after axotomy, and surviving retinal ganglion cells were counted.

RESULTS

Two weeks after axotomy, up to 50+/-7% of all retinal ganglion cells survived if cortisol was injected into the eye compared with 17+/-5% survival if only vehicle solution was injected. The neuroprotective effects of aurintricarboxylic acid (43+/-5% survival) could be further enhanced if combined with cortisol (up to 61+/-5% survival). Regeneration of cut retinal ganglion cell axons into a peripheral nerve graft could also be enhanced by an intravitreal injection of cortisol (169+/-42 regenerating retinal ganglion cells per mm2 vs. 73+/-12 cells per mm2 after vehicle injection). The increase was not as high as with aurintricarboxylic acid (192+/-40 cells per mm2), although more retinal ganglion cells survived with cortisol. This indicates that neuronal survival alone is not sufficient for subsequent axonal regeneration. Nevertheless, regeneration could be markedly increased if aurintricarboxylic acid and cortisol were combined (308+/-72 cells per mm2).

CONCLUSIONS

Whereas aurintricarboxylic acid seems to act directly on lesioned retinal ganglion cells, cortisol seems to act on the glial environment, as indicated by microglial cell morphology and enhanced glial fibrillary acidic protein expression. The results show that both neuroprotection and regeneration can be enhanced by the combination of two simple compounds acting on different sites.

Transformation of adult retina from the regenerative to the axonogenesis state activates specific genes in various subsets of neurons and glial cells

The purpose of this study was to identify the gene expression profile of the regenerating retina in vitro. To achieve this goal, three experimental groups were studied: (1) an injury control group (OC-LI group) that underwent open crush (OC) of the optic nerve and lens injury (LI) in vivo; (2) an experimental group (OC-LI-R group) that comprised animals treated like those in the OC-LI group except that retinal axons were allowed to regenerate (R) in vitro; and (3) an experimental group (OC-LI-NR group) that comprised animals treated as those in the OC-LI group, except that the retinas were cultured in vitro with the retinal ganglion cell (RGC) layer facing upwards to prevent axonal regeneration (NR). Gene expression in each treatment group was compared to that of untreated controls. Immunohistochemistry was used to examine whether expression of differentially regulated genes also occurred at the protein level and to localize these proteins to the respective retinal cells. Genes that were regulated belonged to different functional categories such as antioxidants, antiapoptotic molecules, transcription factors, secreted signaling molecules, inflammation-related genes, and others. Comparison of changes in gene expression among the various treatment groups revealed a relatively small cohort of genes that was expressed in different subsets of cells only in the OC-LI-R group; these genes can be considered to be regeneration-specific. Our findings demonstrate that axonal regeneration of RGC involves an orchestrated response of all retinal neurons and glia, and could provide a platform for the development of therapeutic strategies for the regeneration of injured ganglion cells.

Multifocal Electroretinography Changes in the Macula at High Altitude: A Report of Three Cases

BACKGROUND

To evaluate the short- and long-term effects of high-altitude hypobaric hypoxia on macula morphology and function during ascents, acclimatizations, and descents between 500 m and 5,650 m, macula function was evaluated in three healthy climbers of a trekking expedition.

METHODS

Macula physiology was tested with multifocal electroretinography (MF ERG), near and farvisual acuity, and Amsler grid tests. Macula morphology was tested with optical coherence tomography (OCT) and with stereoscopic fundoscopy obtained 1 week before ascent, as well as 1 week and 2 weeks after high-altitude exposure. The following physiological parameters indicative of acclimatization were compared daily during the expedition at altitudes between 500 m and 5,050 m: hemoglobin, oxygen saturation, resting heart rate, retinal findings, and the Lake Louise score of acclimatization.

RESULTS

The central macula MF ERG responses were significantly reduced 1 week after high-altitude exposure, and had recovered by the follow-up examination performed during the following week. Near visual acuity and Amsler grid tests remained unaffected at both follow-up examinations. No significant changes were found in the follow-up OCT and daily fundoscopy examinations in all three well-acclimatized climbers.

CONCLUSIONS

High-altitude hypobaric hypoxia affects the function of the highly sensitive macula region. This suggests that the exposure of persons with macula diseases such as age-related macula degeneration, tapetoretinal degeneration, or diabetic retinopathy to high altitudes may influence the disease progression. For this reason, this population should avoid prolonged and unnecessary high-altitude exposure without proper acclimatization.

Intraocular pressure changes during high-altitude acclimatization

BACKGROUND

To evaluate the relationship between hypobaric hypoxia acclimatization and intraocular pressure (IOP) during ascent, acclimatization, and descent between 2286 m and 5050 m.

METHODS

The following acclimatization-indicative physiological parameters were compared daily with IOP changes in eight healthy climbers of the 2003 Greek Karakorum expedition in altitude stages between 500 m and 5050 m: hemoglobin oxygen saturation (PO2), resting heart rate, blood pressure, retinal findings, and the Lake Louise score for acclimatization grading.

RESULTS

IOP decreased significantly in the ascent phase (0.58 mmHg/100 m) and recovered (0.71 mmHg/100 m) during acclimatization and descent. A direct proportional correlation between decreases in PO2 and IOP was evaluated. Arterial blood pulse and pressure increased during acclimatization, while IOP decreased. No retinal hemorrhages were observed in well-acclimatized and incompletely acclimatized climbers.

CONCLUSIONS

Every new active exposure to hypobaric hypoxia in the ascent phase induced a decrease in the IOP parallel to the PO2 decrease and to the level of acclimatization. The results from our study suggest that IOP changes are related to hypoxia-induced respiratory alkalosis and acclimatization stage, which could be used as a simple mobile screening test for acclimatization level to reveal acute mountain sickness and its severe consequences.

Lens epithelium supports axonal regeneration of retinal ganglion cells in a coculture model in vitro

The purpose of this study was to determine whether the lens epithelium influences the survival or axonal growth of regenerating retinal ganglion cells. The optic nerves of adult albino rats were injured in order to induce axonal regeneration, and axon growth was then studied in retinal explants in the presence of cocultivated lens capsules carrying living epithelial cells. In the first series of experiments, cocultivation of retinal explants with lens epithelium in immediate proximity resulted in penetration of fibers into the lens epithelium, indicating that it supported axonal growth. In the second series of experiments, co-explants were placed 0.5-1.0mm from each other. The numbers of outgrowing retinal axons were determined both with respect to the retinal eccentricity and the topological relationship with the lenticular co-explant. The Wilcoxon matched-pairs signed-rank test was used to determine if the numbers of axons differed significantly between four regions of the explants. Significantly more axons grew out from the retinal edge facing the lenticular explant than from its opposite side, indicating that the lens epithelium supports axon growth. The numbers of surviving retinal ganglion cells in culture were determined after retrograde prelabelling with a neuroanatomical tracer. The number of fluorescent ganglion cells within the retinal explants did not significantly differ between the groups (Mann-Whitney test). These findings indicate that the lens epithelium influences both the amount of axonal regeneration and the direction of growth without affecting the survival rate of retinal ganglion cells in vitro.

Unilateral optic nerve crush induces bilateral retinal glial cell proliferation

The post-injury responses of retinal ganglion cells elicit a number of glial reactions which have not been completely understood. The bilateral pattern of non-neuronal retinal cell proliferation was examined in association with the differential fates of unilaterally injured adult retinal ganglion cells by means of bromodeoxyuridine (BrdU) immunocytochemistry. Lateralization of the glioproliferative events was studied by analysing both the experimental and the uninjured contralateral as well as matched retinas of sham-operated animals. Control adult rat retina included very few BrdU-positive cells within the nerve fibre and ganglion cell layers; however, experimental retinas of degenerating groups exhibited statistically significantly higher densities of newborn cells in most layers. Clusters of labelled cells were found in the inner plexiform layer related to OX-42 staining, indicating their microglial nature. Indeed, double-labelling experiments, after short-term unilateral optic nerve crushing, identified proliferating retinal glial cells in vivo. Both types of glia, astroglial and microglial cells, exhibited BrdU-positive labelling in injured as well as uninjured experimental rat retinas. Moreover, microglial proliferating cells were also identified in explanted retinal pieces after 2 days in culture. Affected and contralateral retinas responded similarly to the unilateral experimental manipulations applied with respect to BrdU labelling. The acute glial responses observed suggest that bilateral glial proliferation might represent a common response related to degeneration events in both retinas, i.e. ipsi- and contralateral to the experimental injury.

Switching mature retinal ganglion cells to a robust growth state in vivo: gene expression and synergy with RhoA inactivation

The inability of mature CNS neurons to regenerate injured axons has been attributed to a loss of inherent growth potential of cells and to inhibitory signals associated with myelin and the glial scar. The present study investigated two complementary issues: (1) whether mature CNS neurons can be stimulated to alter their gene expression profile and switch into a strong growth state; and (2) whether inactivating RhoA, a convergence point for multiple inhibitory signals, is sufficient to produce strong regeneration even without activating the growth state of neurons. In the mature rat, retinal ganglion cells (RGCs) normally fail to regenerate axons through the injured optic nerve but can be stimulated to do so by activating macrophages in the eye (e.g., by lens injury). To investigate underlying changes in gene expression, we retrogradely labeled RGCs with a fluorescent dye, performed optic nerve surgery with or without lens injury, and 4 d later, dissociated retinas, isolated RGCs by fluorescence-activated cell sorting, and examined their profiles of gene expression using microarrays. To investigate the effects of inactivating RhoA, we transfected RGCs with adeno-associated viruses carrying a gene for C3 ribosyltransferase. Our results show that, with appropriate stimulation, mature CNS neurons can undergo dramatic changes in gene expression comparable with those seen in regenerating neurons of the PNS, and that RhoA inactivation by itself results in moderate regeneration, and strongly potentiates axon regeneration through the mature optic nerve when the growth state of neurons is activated.

Ultrasonic visualization of the effect of blinking on the lacrimal pump mechanism

BACKGROUND

The role of the lacrimal sac (LS) and the medial canthal tendon in the lacrimal pump mechanism is controversial. This study used ultrasonic visualization to analyze this phenomenon.

METHODS

Movements of the LS and the medial canthal tendon during blinking were visualized with sonography. In addition, the maximal profile area of the LS was measured before and after blinking using 15-MHz sonography in 14 individuals with a normal lacrimal drainage system and in six patients with lacrimal duct obstruction.

RESULTS

The upper part of the LS could be located as an echolucent structure between the lacrimal bone and the medial canthal tendon. The medial canthal tendon appeared to compress the LS during lid closure and release the LS during lid opening. The measured profile area of the visible normal LS at the compression time decreased by 50%. The dilated LS of patients with obstruction could also be compressed by the orbital muscle on blinking, but the maximum area decrease was only 15.5%.

CONCLUSION

The findings imply that the lacrimal part of the orbicularis muscle contracts during blinking, with the medial canthal tendon compressing the LS in a cranial direction. Completion of lid closure then compresses both canaliculi and LS, forcing the intrasacral fluid through the drainage system. The expansion of the LS during the opening phase of the blink causes suction, and after opening of the punctal areas the canaliculi and LS vacuum breaks to reload with tear fluid. These findings demonstrate the importance of the orbicularis muscle and the medial canthal tendon for the lacrimal pump mechanism during blinking.

Recovery of visual evoked potentials after regeneration of cut retinal ganglion cell axons within the ascending visual pathway in adult rats

PURPOSE

Following optic nerve damage, retinal ganglion cells (RGCs) fail to regenerate their axons and soon undergo apoptosis. However, many RGCs survive axotomy and regenerate lengthy axons after a lens injury (LI). If the cut optic nerve is re-sutured, RGC axons grow into the distal part of the optic nerve and reach their natural targets within the thalamus and midbrain. In this study, we check time-dependence and extent of restoration of flash visual evoked potentials (FVEPs) to examine the functional relevance of the regenerated retinogeniculate pathway.

METHODS

The optic nerve in adult rats was cut and re-sutured. The lens was injured transsclerally using a pointed glass capillary. FVEPs were measured starting at the time point of surgery, and then repeatedly up to an age of several months.

RESULTS

Detectable FVEPs appeared approximately ten weeks after the surgery, and their amplitudes increased during the next months to reach eventually 15-40% of their values before surgery.

CONCLUSIONS

Partial restoration of FVEPs indicates that some regenerating RGC axons have "bridged" the distance between the eye and the central targets forming a functional re-connection of the corresponding RGC with thalamic target neurones to elicit recordable activation of the visual cortex.

Can lenticular factors improve the posttrauma fate of neurons?

The intraocular lens has recently been recognized as a potential source for neuroprotective and neurite-promoting activities. The lens is ontogenetically and functionally a peculiar intraocular tissue with the unique feature of performing incomplete cellular apoptosis throughout the lifetime. The ectodermally derived epithelial cells permanently divide to produce the nuclei- and organelle-free lens fibre cells that allow for the optical transparency. The underlying extremely specific physical, biochemical, metabolic and structural mechanism lead to efficient protection from photo-oxidative stress caused by exposure to short-wavelength light. The fact that fibre cells undergo incomplete apoptosis is also of crucial importance to other cellular systems. In particular, injured nerve cells such as axotomized retinal ganglion cells may profit from the apoptosis-blocking mechanisms operating within the lens fibres. In this review we first discuss some factors involved in the lens differentiation and partial apoptosis as a basic principle of long-term survival. We then present recent experimental evidence that lenticular factors also operate outside the lens, and in particular within the retina to contribute to axonal regeneration, e.g. after a trauma. In turn, factors such as GAP-43 that were thought to be exclusively expressed within nervous tissue have now also been discovered within the lenticular tissue. Experiments of the direct confrontation of lenticular epithelial and fibre cells with regenerating ganglion cell axons in vitro are presented. It is concluded that survival factors supplied by the lens might be used to facilitate survival within neuronal tissue.