Fibroblast growth factor induces proliferating cell nuclear antigen-immunoreactive cells in goldfish retina

Comparative analysis of the immune responses of CcIgZ3 in mucosal tissues and the co-expression of CcIgZ3 and PCNA in the gills of common carp (Cyprinus carpio L.) in response to TNP-LPS

Fish live in an aquatic environment rich in various microorganisms and pathogens. Fish mucosal-associated lymphoid tissue (MALT) plays a very important role in immune defence. This study was conducted to characterize the immune response mediated by CcIgZ3 in common carp (Cyprinus carpio.) and investigate the proliferating CcIgZ3+ B lymphocytes in gill. We determined the expression of CcIgZ3 in many different tissues of common carp following stimulation by intraperitoneal injection of TNP-LPS (2,4,6-Trinitrophenyl hapten conjugated to lipopolysaccharide) or TNP-KLH (2,4,6-Trinitrophenyl hapten conjugated to Keyhole Limpet Hemocyanin). Compared with TNP-KLH, TNP-LPS can induce greater CcIgZ3 expression in the head kidney, gill and hindgut, especially in the gill. The results indicate that the gill is one of the main sites involved in the immune response mediated by CcIgZ3. To examine the distribution of CcIgZ3+ B lymphocytes, immunohistochemistry (IHC) experiments were performed using a polyclonal antibody against CcIgZ3. The results indicated that CcIgZ3 was detected in the head kidney, hindgut and gill. To further examine whether CcIgZ3+ B lymphocytes proliferate in the gills, proliferating CcIgZ3+ B cells were analysed by immunofluorescence staining using an anti-CcIgZ3 polyclonal antibody and an anti-PCNA monoclonal antibody. CcIgZ3 and PCNA (Proliferating Cell Nuclear Antigen) double-labelled cells in the gills were located within the epithelial cells of the gill filaments of common carp stimulated with TNP-LPS at 3 dps and 7 dps, and relatively more proliferating CcIgZ3+ B cells appeared in the gills of common carp at 7 dps. These data imply that CcIgZ3+ B cells in the gills might be produced by local proliferation following TNP-LPS stimulation. In summary, compared with those in TNP-KLH, CcIgZ3 preferentially affects the gills of common carp following challenge with TNP-LPS. CcIgZ3+ B cells proliferate in the gills to quickly produce the CcIgZ3 antibody. In addition, CcIgZ3+ B cells can be activated to induce a strong immune response very early locally in the gill and produce the antibody CcIgZ3, which helps exert an immune-protective effect. These results suggest that an effective vaccine can be designed to promote production of the mucosal antibody CcIgZ3.

Mechanisms of RhoA inactivation and CDC42 and Rac1 activation during zebrafish optic nerve regeneration

When axons of the mammalian central nervous system (CNS) are injured, they fail to regenerate, while those of lower vertebrates undergo regeneration after injury. Wingless-type MMTV integration site family (Wnt) proteins play important roles in the CNS, and are reported to be activated after mammalian spinal cord or brain injury. Moreover, for axon growth to proceed, it is thought that small G-proteins, such as CDC42 and Rac1, need to be activated, whereas RhoA must be inactivated. However, the cell and molecular mechanisms involved in optic nerve regeneration remain unclear. In this study, we investigated axonal regeneration after injury using the zebrafish optic nerve as a model system. We sought to clarify the role of Wnt proteins and the mechanisms involved in the activation and inactivation of small G-proteins in nerve regeneration. After optic nerve injury, mRNA levels of Wnt5b, TAX1BP3 and ICAT increased in the retina, while those of Wnt10a decreased. These changes were associated with a reduction in β-catenin in nuclei. We found that Wnt5b activated CDC42 and Rac1, leading to the inactivation of RhoA, which appeared to be dependent on increased TAX1BP3 mRNA levels. Furthermore, we found that mRNA levels of Daam1a and ARHGEF16 decreased. We speculate that the decrease in β-catenin levels, which also further reduces levels of active RhoA, might contribute to regeneration in the zebrafish. Collectively, our novel results suggest that Wnt5b, Wnt10a, ICAT and TAX1BP3 participate in the activation and inactivation of small G-proteins, such as CDC42, Rac1 and RhoA, during the early stage of optic nerve regeneration in the zebrafish.

Prospective purification and characterization of Müller glia in the mouse retina regeneration assay

Reactive gliosis is an umbrella term for various glia functions in neurodegenerative diseases and upon injury. Specifically, Müller glia (MG) in some species readily regenerate retinal neurons to restore vision loss after insult, whereas mammalian MG respond by reactive gliosis-a heterogeneous response which frequently includes cell hypertrophy and proliferation. Limited regeneration has been stimulated in mammals, with a higher propensity in young MG, and in vitro compared to in vivo, but the underlying processes are unknown. To facilitate studies on the mechanisms regulating and limiting glia functions, we developed a strategy to purify glia and their progeny by fluorescence-activated cell sorting. Dual-transgenic nuclear reporter mice, which label neurons and glia with red and green fluorescent proteins, respectively, have enabled MG enrichment up to 93% purity. We applied this approach to MG in a mouse retina regeneration ex vivo assay. Combined cell size and cell cycle analysis indicates that most MG hypertrophy and a subpopulation proliferates which, over time, become even larger in cell size than the ones that do not proliferate. MG undergo timed differential genomic changes in genes controlling stemness and neurogenic competence; and glial markers are downregulated. Genes that are potentially required for, or associated with, regeneration and reactive gliosis are differentially regulated by retina explant culture time, epidermal growth factor stimulation, and animal age. Thus, MG enrichment facilitates cellular and molecular studies which, in combination with the mouse retina regeneration assay, provide an experimental approach for deciphering mechanisms that possibly regulate reactive gliosis and limit regeneration in mammals.

Stem Cells and Regeneration in the Retina: What Fish Have Taught Us about Neurogenesis

Many species of fish grow for much of their lifetimes and add neurons to the CNS continuously. The retina has proved to be a convenient model in which to study neurogenesis, both the normal variety associated with growth and regeneration in response to a lesion. Initial neurogenesis in the embryonic eye cup begins in a tiny cluster of neuroepithelial cells that steadily enlarges to produce a central disk of neurons. Subsequent growth occurs mainly at the edge of this disk, in the circumferential germinal zone, where the retina adds annuli of new neurons of all varieties except the rod photoreceptors. A few proliferative cells persist to adulthood in central retina and normally produce only rods, but when the retina is damaged, these cells contribute to the production of new neurons of diverse classes. Recent work has revealed two additional populations of dividing cells in central retina; they normally proliferate so slowly that special methods are required to reveal them. We suggest that the three proliferative cell types are related through lineage in a model similar to those described for hematopoiesis. The persistent neurogenesis of fish retina seems to resemble qualitatively the neurogenesis of the mammalian brain, but quantitatively the neurogenesis is much more vigorous in the fish.

Reactive microglia and macrophage facilitate the formation of Müller glia-derived retinal progenitors

In retinas where Müller glia have been stimulated to become progenitor cells, reactive microglia are always present. Thus, we investigated how the activation or ablation of microglia/macrophage influences the formation of Müller glia-derived progenitor cells (MGPCs) in the retina in vivo. Intraocular injections of the Interleukin-6 (IL6) stimulated the reactivity of microglia/macrophage, whereas other types of retinal glia appear largely unaffected. In acutely damaged retinas where all of the retinal microglia/macrophage were ablated, the formation of proliferating MGPCs was greatly diminished. With the microglia ablated in damaged retinas, levels of Notch and related genes were unchanged or increased, whereas levels of ascl1a, TNFα, IL1β, complement component 3 (C3) and C3a receptor were significantly reduced. In the absence of retinal damage, the combination of insulin and Fibroblast growth factor 2 (FGF2) failed to stimulate the formation of MGPCs when the microglia/macrophage were ablated. In addition, intraocular injections of IL6 and FGF2 stimulated the formation of MGPCs in the absence of retinal damage, and this generation of MGPCs was blocked when the microglia/macrophage were absent. We conclude that the activation of microglia and/or infiltrating macrophage contributes to the formation of proliferating MGPCs, and these effects may be mediated by components of the complement system and inflammatory cytokines.

Müller glia: Stem cells for generation and regeneration of retinal neurons in teleost fish

Adult zebrafish generate new neurons in the brain and retina throughout life. Growth-related neurogenesis allows a vigorous regenerative response to damage, and fish can regenerate retinal neurons, including photoreceptors, and restore functional vision following photic, chemical, or mechanical destruction of the retina. Müller glial cells in fish function as radial-glial-like neural stem cells. During adult growth, Müller glial nuclei undergo sporadic, asymmetric, self-renewing mitotic divisions in the inner nuclear layer to generate a rod progenitor that migrates along the radial fiber of the Müller glia into the outer nuclear layer, proliferates, and differentiates exclusively into rod photoreceptors. When retinal neurons are destroyed, Müller glia in the immediate vicinity of the damage partially and transiently dedifferentiate, re-express retinal progenitor and stem cell markers, re-enter the cell cycle, undergo interkinetic nuclear migration (characteristic of neuroepithelial cells), and divide once in an asymmetric, self-renewing division to generate a retinal progenitor. This daughter cell proliferates rapidly to form a compact neurogenic cluster surrounding the Müller glia; these multipotent retinal progenitors then migrate along the radial fiber to the appropriate lamina to replace missing retinal neurons. Some aspects of the injury-response in fish Müller glia resemble gliosis as observed in mammals, and mammalian Müller glia exhibit some neurogenic properties, indicative of a latent ability to regenerate retinal neurons. Understanding the specific properties of fish Müller glia that facilitate their robust capacity to generate retinal neurons will inform and inspire new clinical approaches for treating blindness and visual loss with regenerative medicine.

Turning Müller glia into neural progenitors in the retina

Stimulating neuronal regeneration is a potential strategy to treat sight-threatening diseases of the retina. In some classes of vertebrates, retinal regeneration occurs spontaneously to effectively replace neurons lost to acute damage in order to restore visual function. There are different mechanisms and cellular sources of retinal regeneration in different species, include the retinal pigmented epithelium, progenitors seeded across the retina, and the Müller glia. This review briefly summarizes the different mechanisms of retinal regeneration in frogs, fish, chicks, and rodents. The bulk of this review summarizes and discusses recent findings regarding regeneration from Müller glia-derived progenitors, with emphasis on findings in the chick retina. The Müller glia are a promising source of regeneration-supporting cells that are intrinsic to the retina and significant evidence indicated these glias can be stimulated to produce neurons in different classes of vertebrates. The key to harnessing the neurogenic potential of Müller glia is to identify the secreted factors, signaling pathways, and transcription factors that enable de-differentiation, proliferation, and neurogenesis. We review findings regarding the roles of mitogen-activated protein kinase and notch signaling in the proliferation and generation of Müller glia-derived retinal progenitors.

The teleost retina as a model for developmental and regeneration biology

Retinal development in teleosts can broadly be divided into three epochs. The first is the specification of cellular domains in the larval forebrain that give rise to the retinal primordia and undergo early morphogenetic movements. The second is the neurogenic events within the retina proper-proliferation, cell fate determination, and pattern formation-that establish neuronal identities and form retinal laminae and cellular mosaics. The third, which is unique to teleosts and occurs in the functioning eye, is stretching of the retina and persistent neurogenesis that allows the growth of the retina to keep pace with the growth of the eye and other tissues. The first two events are rapid, complete by about 3 days postfertilization in the zebrafish embryo. The third is life-long and accounts for the bulk of retinal growth and the vast majority of adult retinal neurons. In addition, but clearly related to the retina's developmental history, lesions that kill retinal neurons elicit robust neuronal regeneration that originates from cells intrinsic to the retina. This paper reviews recent studies of retinal development in teleosts, focusing on those that shed light on the genetic and molecular regulation of retinal specification and morphogenesis in the embryo, retinal neurogenesis in larvae and adults, and injury-induced neuronal regeneration.

Regeneration of inner retinal neurons after intravitreal injection of ouabain in zebrafish

We examined the regenerative capacity of the adult zebrafish retina by intravitreal injection of a low ouabain concentration to rapidly damage the ganglion cell layer (GCL) and inner nuclear layer (INL) with minimal photoreceptor cell damage. By 24 h after ouabain injection, maximal numbers of terminal deoxynucleotidyl transferase-mediated biotinylated UTP nick end labeling (TUNEL)-positive cells were detected in the INL and GCL, with low numbers of TUNEL-positive cells in the outer nuclear layer. Immunolabeling revealed that approximately 85% of the HuC/D-positive amacrine and ganglion cells were lost by 7 d post-ouabain injection (dpi). This ganglion cell loss was consistent with the small, but statistically significant, decrease in the optic nerve diameter. The regeneration response began within 1 dpi with increased proliferating cell nuclear antigen (PCNA) expression in both the INL and GCL. By 3 dpi, PCNA expression is primarily restricted to the Müller glia. By 5 dpi, most of the PCNA expression was localized to neuronal progenitors expressing the olig2:egfp transgene rather than the Müller glia. By 7 dpi, the neuronal progenitors began committing to the ganglion cell fate based on the coexpression of the atoh7:EGFP transgene and the zn5 antigen. The regeneration of ganglion and amacrine cells continued until 60 dpi, when they reached 75% of their uninjected control number. This demonstrates that inner retinal damage, without extensive photoreceptor damage, is sufficient to induce a regeneration response that is marked by the Müller glial cells reentering the cell cycle to produce neuronal progenitor cells that regenerate INL and ganglion cells in the zebrafish retina.

A role for alpha1 tubulin-expressing Müller glia in regeneration of the injured zebrafish retina

Alpha1 tubulin (alpha1T) is a neuron-specific microtubule protein whose expression is induced in the developing and regenerating CNS. In the adult CNS, alpha1T expression remains high in neural progenitors. Transgenic zebrafish harboring a 1.7 kb alpha1T promoter fragment along with the first exon and intron express the transgene in a manner that recapitulates expression of the endogenous gene. We recently showed that this promoter mediates gene induction in retinal ganglion cells during optic nerve regeneration and in a subset of Müller glia that proliferate after retinal injury (Senut et al., 2004). To further characterize these Müller glia, we generated transgenic fish harboring an alpha1T promoter fragment that is specifically induced in these cells after retinal damage. Transgene expression, bromodeoxyuridine (BrdU) labeling, and stem cell marker expression suggested that alpha1T-expressing Müller glia dedifferentiate and become multipotent in response to injury. In addition, green fluorescent protein and BrdU-mediated lineage tracing combined with retinal gene expression analysis indicated that alpha1T-expressing Müller glia were capable of generating retinal neurons and glia. These data strongly suggest alpha1T-expressing Müller glia dedifferentiate and mediate regeneration of the injured zebrafish retina.

Persistent and injury-induced neurogenesis in the vertebrate retina

The brains of all vertebrates are persistently neurogenic. However, this is not true for the neural retinas. Only three extant classes of vertebrates show significant posthatch/postnatal retinal neurogenesis: amphibians, birds and fish. The retinas of these animals contain an annulus of progenitors at the margin, from which differentiated neurons emerge. In posthatch amphibians and fish the vast majority of the adult retina is added from the margin and neurogenesis is lifelong, whereas in posthatch birds neurogenesis is limited. Unique to fish, rod photoreceptors are added in situ from stem cells within the mature retina. Strikingly, for each class of animal retinal lesions stimulate neuronal regeneration, however the cellular source differs for each: the retinal pigmented epithelium in amphibians and embryonic birds, Müller glia in posthatch birds and intrinsic stem cells in fish. The molecular events surrounding injury-induced neuronal regeneration are beginning to be identified.

Mitotic activation of proliferative cells in the inner nuclear layer of the mature fish retina: regulatory signals and molecular markers

New neurons continuously differentiate within the otherwise mature retina of teleost fish, both under normal conditions and in response to injury. We investigated the effects of surgical injury and intraocular injection of neurotrophic factors on the mitotic rate of proliferative inner nuclear layer cells (PINC). PINC are continually born in the inner nuclear layer and then migrate to the outer nuclear layer (ONL). Surgical excision of a part of a retina activates PINC mitotic activity near and far from the lesion. In the injured eye, up-regulation of PINC cells is largest in the dorsonasal sector of the retina, regardless of the site of lesion. Up-regulation extends even to the unlesioned contralateral eye, where it occurs in the same dorsonasal sector. Intraocular injection of ciliary neurotrophic factor mimics the effect of injury on PINC in the treated eye but not on the untreated contralateral retina. We searched for the expression in PINC of Pax6, a transcription factor linked to retinal progenitor cells and found that less than 0.5% of all PINC cells express it. Importantly, the number of Pax6-expressing PINC does not change significantly in the retinas subjected to any of the experimental manipulations tested. Under normal conditions, the default fate of PINC cells is to migrate to the ONL and, likely, replenish the rod progenitor pool. PINC respond to injury (both surgical and light-dependent) by increasing their mitotic rate; this increase is long lived, but there are no changes in the expression level of Pax6. PINC probably are a heterogenous cell population that can be specified for ultimate, different purposes: creating rod precursors, creating founder cells, creating cone precursors. Several fates are recognized now, but others may also be possible.

Characterization of primary culture of rainbow trout (Oncorhynchus mykiss) skin explants: growth, cell composition, proliferation, and apoptosis

A trout (Oncorhynchus mykiss) epidermal skin primary explant system was evaluated over 8 d by light and electron microscopy. Three distinct regions of the explant outgrowth were identified on the basis of cell composition. The area immediately adjacent to the founder tissue contained mainly small migrating cells and mucous cells. Of the former. about 20% were mitotic and 6% apoptotic. The middle area was characterized by differentiated pavement cells and mucous cells, with fewer small migrating cells. Proliferation was approximately 30% and apoptosis 5%. Over time, total cell numbers halved as more pavement cells differentiated. The growing front contained many mucous and small migrating cells initially, with few pavement cells. About 50% of the cells were in the proliferative phase, and 5% were apoptotic. Later, there were fewer migrating and mucous cells, with a higher number of pavement cells. About 9% of the cells were apoptotic, and 70% of the cells were proliferating. As in vivo, pavement cells had apical microridges, although they were vacuolated and contained phagocytosed apoptotic bodies. The data and observations are based on the numbers of cell cultures prepared from separate trout giving the sample size n = 7. As this culture system is reproducible and closely approximates the epidermis of trout, it is a powerful tool to study the effects of pollutants, parasites, and endocrine factors on fish skin, eliminating whole-animal factors and reducing the number of experimental animals required.

Putative stem cells and the lineage of rod photoreceptors in the mature retina of the goldfish

The retinas of teleost fish grow continuously, in part, by neuronal hyperplasia and when lesioned will regenerate. Within the differentiated retina, the growth-associated hyperplasia results in the generation of new rod photoreceptors only, whereas injury-induced neurogenesis results in the regeneration of all retinal cell types. It is believed, however, that both new rod photoreceptors and regenerated neurons originate from the same populations of intrinsic progenitors. Experiments are described here that attempt to identify in the normal retina of goldfish neuronal progenitors intrinsic to the retina, particularly those which have remained cryptic because they divide infrequently. Long-term, systemic exposure to bromodeoxyuridine (BrdU) was used to label these cells. Five populations of proliferative cells were labeled: microglia, which are briefly described but not studied further; retinal progenitors in the circumferential germinal zone (CGZ); and rod precursors in the outer nuclear layer (ONL), both of which have been well characterized previously; and two populations of slowly-dividing cells in the inner nuclear layer (INL). The majority of these cells have a fusiform morphology, whereas the remaining ones are spherical. Longitudinal BrdU labeling suggests that the fusiform cells migrate to the ONL to replenish the pool of rod precursors. A subset of the spherical cells express pax6, although none are stained with markers of differentiated amacrine or bipolar cells. It is hypothesized that these rare, pax6-expressing cells are retinal stem cells, which give rise to the pax6-negative fusiform cells. Based on these data, two models are proposed: the first describes the lineage of rod photoreceptors in goldfish; the second is a consensus model of neurogenesis in the retinas of all teleosts.

Light-induced rod and cone cell death and regeneration in the adult albino zebrafish (Danio rerio) retina

Light-induced photoreceptor cell degeneration has been studied in several species, but not extensively in the teleost fish. Furthermore, the continual production of rods and cones throughout the teleost's life may result in regeneration of lost rods and cones. We exposed adult albino zebrafish to 7 days of constant darkness, followed by 7 days of constant 8000 lux light, followed by 28 days of recovery in a 14-h light:10-h dark cycle. We characterized the resulting photoreceptor layer cell death and subsequent regeneration using immunohistochemistry and light microscopy. Within the first 24 h of constant light, the zebrafish retina exhibited widespread rod and cone cell apoptosis. High levels of cell proliferation within the inner nuclear layer (INL) were observed within the first 3 days of constant light, as assessed by immunodetection of proliferating cell nuclear antigen and BrdU labeling. The proliferating cells within the INL were closely associated with the radial processes of Müller glia, similar to the pluripotent retinal stem cells observed during embryonic development. Using antibodies generated against the individual zebrafish opsins, we determined that rods and the green, blue, and ultraviolet cone cells were replaced within the 28 day recovery period. While both rods and cones were replaced, the well-ordered cone cell mosaic was not reestablished.

Antibodies against Pax6 immunostain amacrine and ganglion cells and neuronal progenitors, but not rod precursors, in the normal and regenerating retina of the goldfish

Pax6 is a developmental regulatory gene that plays a key role in the development of the embryonic brain, eye, and retina. This gene is also expressed in discrete groups of neurons within the adult brain. In this study, antibodies raised against a fusion protein from a zebra fish pax6 cDNA were used to investigate the expression of the pax6 gene in the mature, growing, and regenerating retina of the goldfish. On western blots of retinal proteins, the pax6 antibodies recognize a single band at the approximate size of the zebra fish pax6 protein. In retinal sections, the antibodies label the nuclei of mature amacrine and some ganglion cells. At the retinal margin, where neurogenesis and cellular differentiation continually occur in goldfish, the antibodies label neuronal progenitors and the newly postmitotic neurons. Following injury and during neuronal regeneration, the antibodies label mitotically active progenitors of regenerating neurons. Rod precursors, proliferating cells that normally give rise solely to rod photoreceptors and are the presumed antecedents of the injury-stimulated neuronal progenitors, are not immunostained by antibodies to the pax6 protein. The results of this study document the identity of pax6-expressing cells in the mature retina and demonstrate that in the goldfish pax6 is expressed in neuronal progenitors during both retinal growth and regeneration.

Selective regeneration of photoreceptors in goldfish retina

Previous work has shown that the neural retina in adult goldfish can regenerate. Following retinal damage elicited by surgical or cytotoxic lesions, missing neurons are replaced by foci of proliferating neuroepithelial cells, which previous studies have suggested are derived from rod precursors. In the intact retina, rod precursors proliferate but produce only new rods. The regenerative responses observed previously have involved replacement of neurons in all retinal layers; selective regeneration of specific neuronal types (except for rod photoreceptors) has not been reported. In the experiments described here, we specifically destroyed either cones alone or cones and rods with an argon laser, and we found that both types of photoreceptors regenerated within a few weeks. The amount of cone regeneration varied in proportion to the degree of rod loss. This is the first demonstration of selective regeneration of a specific class of neuron (i.e., cones) in a region of central nervous tissue where developmental production of that class of neuron has ceased. Selective regeneration may be limited to photoreceptors, however, because when dopaminergic neurons in the inner retina were ablated with intraocular injections of 6-hydroxydopamine, in combination with laser lesions that destroyed photoreceptors, the dopaminergic neurons did not regenerate, but the photoreceptors did. These data support previous studies which showed that substantial cell loss is required to trigger regeneration of inner retinal neurons, including dopaminergic neurons. New observations here bring into question the presumption that rod precursors are the only source of neuronal progenitors during the regenerative response. Finally, a model is presented which suggests a possible mechanism for regulating the phenotypic fate of retinal progenitor cells during retinal regeneration.

5-Fluorouracil reduces proliferating cell nuclear antigen immunoreactive cells in goldfish retina

A pyrimidine analogue, 5-fluorouracil (5-FU), was injected intravitreally into one eye of the goldfish, either alone, or before or after injection of the same eye with the dopaminergic neurotoxin, 6-hydroxydopamine (6-OHDA). Effects of these agents were explored by measuring their actions on numbers of proliferating cell nuclear antigen-immunoreactive (PCNA-ir) cells, representing mitotically active rod precursor cells (RPCs) in normal conditions, in both treated and untreated retinas. At various intervals (5-45 days after the first injection of drug), the retinas (n = 6 for each treatment group) were isolated and processed as wholemounts by an indirect immunohistochemical method for PCNA. Some retinas were cryosectioned and processed for certain immunoreactive cells other than PCNA. Changes in the mean density of PCNA-ir cells, following intravitreal 5-FU (10 micrograms/2 microliter saline on 3 consecutive days) alone or in combination with intravitreal 6-OHDA (2.5 micrograms/2 microliter), were statistically compared for interval vs. day 0 (control from intact retinas) and for treated vs. contralateral (untreated or treated) retinas, in both outer and inner nuclear layers (ONL and INL, respectively). 5-FU at this dose drastically reduced the densities of endogenous and 6-OHDA-induced PCNA-ir cells in the ONL of treated retinas, but transiently increased them in the contralateral untreated retinas, probably reflecting an injury influence from the treated retina. The density of PCNA-ir cells at the retinal margin was also greatly reduced in treated retinas. Such changes peaked on days 10-15, and gradually disappeared over days 30-45.(ABSTRACT TRUNCATED AT 250 WORDS)