Elevated PGC-1α activity sustains mitochondrial biogenesis and muscle function without extending survival in a mouse model of inherited ALS

The transcriptional coactivator PGC-1α induces multiple effects on muscle, including increased mitochondrial mass and activity. Amyotrophic lateral sclerosis (ALS) is a progressive, fatal, adult-onset neurodegenerative disorder characterized by selective loss of motor neurons and skeletal muscle degeneration. An early event is thought to be denervation-induced muscle atrophy accompanied by alterations in mitochondrial activity and morphology within muscle. We now report that elevation of PGC-1α levels in muscles of mice that develop fatal paralysis from an ALS-causing SOD1 mutant elevates PGC-1α-dependent pathways throughout disease course. Mitochondrial biogenesis and activity are maintained through end-stage disease, accompanied by retention of muscle function, delayed muscle atrophy, and significantly improved muscle endurance even at late disease stages. However, survival was not extended. Therefore, muscle is not a primary target of mutant SOD1-mediated toxicity, but drugs increasing PGC-1α activity in muscle represent an attractive therapy for maintaining muscle function during progression of ALS.

Characterization of Pax2 expression in the goldfish optic nerve head during retina regeneration

The Pax2 transcription factor plays a crucial role in axon-guidance and astrocyte differentiation in the optic nerve head (ONH) during vertebrate visual system development. However, little is known about its function during regeneration. The fish visual system is in continuous growth and can regenerate. Müller cells and astrocytes of the retina and ONH play an important role in these processes. We demonstrate that pax2a in goldfish is highly conserved and at least two pax2a transcripts are expressed in the optic nerve. Moreover, we show two different astrocyte populations in goldfish: Pax2⁺ astrocytes located in the ONH and S100⁺ astrocytes distributed throughout the retina and the ONH. After peripheral growth zone (PGZ) cryolesion, both Pax2⁺ and S100⁺ astrocytes have different responses. At 7 days after injury the number of Pax2⁺ cells is reduced and coincides with the absence of young axons. In contrast, there is an increase of S100⁺ astrocytes in the retina surrounding the ONH and S100⁺ processes in the ONH. At 15 days post injury, the PGZ starts to regenerate and the number of S100⁺ astrocytes increases in this region. Moreover, the regenerating axons reach the ONH and the pax2a gene expression levels and the number of Pax2⁺ cells increase. At the same time, S100⁺/GFAP⁺/GS⁺ astrocytes located in the posterior ONH react strongly. In the course of the regeneration, Müller cell vitreal processes surrounding the ONH are primarily disorganized and later increase in number. During the whole regenerative process we detect a source of Pax2⁺/PCNA⁺ astrocytes surrounding the posterior ONH. We demonstrate that pax2a expression and the Pax2⁺ astrocyte population in the ONH are modified during the PGZ regeneration, suggesting that they could play an important role in this process.

The Usher 1B protein, MYO7A, is required for normal localization and function of the visual retinoid cycle enzyme, RPE65

Mutations in the MYO7A gene cause a deaf-blindness disorder, known as Usher syndrome 1B.  In the retina, the majority of MYO7A is in the retinal pigmented epithelium (RPE), where many of the reactions of the visual retinoid cycle take place.  We have observed that the retinas of Myo7a-mutant mice are resistant to acute light damage. In exploring the basis of this resistance, we found that Myo7a-mutant mice have lower levels of RPE65, the RPE isomerase that has a key role in the retinoid cycle.  We show for the first time that RPE65 normally undergoes a light-dependent translocation to become more concentrated in the central region of the RPE cells.  This translocation requires MYO7A, so that, in Myo7a-mutant mice, RPE65 is partly mislocalized in the light.  RPE65 is degraded more quickly in Myo7a-mutant mice, perhaps due to its mislocalization, providing a plausible explanation for its lower levels.  Following a 50–60% photobleach, Myo7a-mutant retinas exhibited increased all-trans-retinyl ester levels during the initial stages of dark recovery, consistent with a deficiency in RPE65 activity.  Lastly, MYO7A and RPE65 were co-immunoprecipitated from RPE cell lysate by antibodies against either of the proteins, and the two proteins were partly colocalized, suggesting a direct or indirect interaction.  Together, the results support a role for MYO7A in the translocation of RPE65, illustrating the involvement of a molecular motor in the spatiotemporal organization of the retinoid cycle in vision.

Harmonin in the murine retina and the retinal phenotypes of Ush1c-mutant mice and human USH1C

PURPOSE

To investigate the expression of harmonin in the mouse retina, test for ultrastructural and physiological mutant phenotypes in the retina of an Ush1c mutant mouse, and define in detail the retinal phenotype in human USH1C.

METHODS

Antibodies were generated against harmonin. Harmonin isoform distribution was examined by Western blot analysis and immunocytochemistry. Retinas of deaf circler (dfcr) mice, which possess mutant Ush1c, were analyzed by microscopy and electroretinography (ERG). Two siblings with homozygous 238_239insC (R80fs) USH1C mutations were studied with ERG, perimetry, and optical coherence tomography (OCT).

RESULTS

Harmonin isoforms a and c, but not b are expressed in the retina. Harmonin is concentrated in the photoreceptor synapse where the majority is postsynaptic. Dfcr mice do not undergo retinal degeneration and have normal synaptic ultrastructure and ERGs. USH1C patients had abnormal rod and cone ERGs. Rod- and cone-mediated sensitivities and retinal laminar architecture were normal across 50 degrees -60 degrees of visual field. A transition zone to severely abnormal function and structure was present at greater eccentricities.

CONCLUSIONS

The largest harmonin isoforms are not expressed in the retina. A major retinal concentration of harmonin is in the photoreceptor synapses, both pre- and post-synaptically. The dfcr mouse retina is unaffected by its mutant Ush1c. Patients with USH1C retained regions of normal central retina surrounded by degeneration. Perhaps the human disease is simply more aggressive than that in the mouse. Alternatively, the dfcr mouse may be a model for nonsyndromic deafness, due to the nonpathologic effect of its mutation on the retinal isoforms.

Melanoregulin (MREG) modulates lysosome function in pigment epithelial cells

Melanoregulin (MREG), the product of the Mreg(dsu) gene, is a small highly charged protein, hypothesized to play a role in organelle biogenesis due to its effect on pigmentation in dilute, ashen, and leaden mutant mice. Here we provide evidence that MREG is required in lysosome-dependent phagosome degradation. In the Mreg(-/-) mouse, we show that loss of MREG function results in phagosome accumulation due to delayed degradation of engulfed material. Over time, the Mreg(-/-) mouse retinal pigment epithelial cells accumulate the lipofuscin component, A2E. MREG-deficient human and mouse retinal pigment epithelial cells exhibit diminished activity of the lysosomal hydrolase, cathepsin D, due to defective processing. Moreover, MREG localizes to small intracellular vesicles and associates with the endosomal phosphoinositide, phosphatidylinositol 3,5-biphosphate. Collectively, these studies suggest that MREG is required for lysosome maturation and support a role for MREG in intracellular trafficking.

Amyloid precursor protein-induced axonopathies are independent of amyloid-beta peptides

Overexpression of amyloid precursor protein (APP), as well as mutations in the APP and presenilin genes, causes rare forms of Alzheimer's disease (AD). These genetic changes have been proposed to cause AD by elevating levels of amyloid-beta peptides (Abeta), which are thought to be neurotoxic. Since overexpression of APP also causes defects in axonal transport, we tested whether defects in axonal transport were the result of Abeta poisoning of the axonal transport machinery. Because directly varying APP levels also alters APP domains in addition to Abeta, we perturbed Abeta generation selectively by combining APP transgenes in Drosophila and mice with presenilin-1 (PS1) transgenes harboring mutations that cause familial AD (FAD). We found that combining FAD mutant PS1 with FAD mutant APP increased Abeta42/Abeta40 ratios and enhanced amyloid deposition as previously reported. Surprisingly, however, this combination suppressed rather than increased APP-induced axonal transport defects in both Drosophila and mice. In addition, neuronal apoptosis induced by expression of FAD mutant human APP in Drosophila was suppressed by co-expressing FAD mutant PS1. We also observed that directly elevating Abeta with fusions to the Familial British and Danish Dementia-related BRI protein did not enhance axonal transport phenotypes in APP transgenic mice. Finally, we observed that perturbing Abeta ratios in the mouse by combining FAD mutant PS1 with FAD mutant APP did not enhance APP-induced behavioral defects. A potential mechanism to explain these findings was suggested by direct analysis of axonal transport in the mouse, which revealed that axonal transport or entry of APP into axons is reduced by FAD mutant PS1. Thus, we suggest that APP-induced axonal defects are not caused by Abeta.

Evidence for increased proton dissociation in low-activity forms of dephosphorylated squash-leaf nitrate reductase

The pH dependence of squash-leaf nitrate reductase has been studied. It has been found that high- and low-activity forms of purified nitrate reductase (both forms dephosphorylated) have different optimum pH values. A high-activity form has always a higher pH optimum compared with a low-activity form. Model computations show that the decrease in activity and the corresponding change of the pH optimum is apparently due to a conformation-dependent increase of proton dissociation of the enzyme. As previously shown, this behavior is also observed in leaf extracts during the conversion (and probably phosphorylation of nitrate reductase) from a high-active form to a low-active form when plants are transferred from light to darkness.

Roles and interactions of usher 1 proteins in the outer retina

Our studies demonstrate that harmonin and myosin VIIa are not localized in the same compartments in the mouse and human retinas, indicating that they do not interact in this organ, contrary to what has been shown in the inner ear. The enrichment of harmonin in the photoreceptor synapses indicates that this protein may form multiple complexes with others to maintain the synaptic structure or to mediate in the release of synaptic vesicles.

Lentiviral gene replacement therapy of retinas in a mouse model for Usher syndrome type 1B

One of the most disabling forms of retinal degeneration occurs in Usher syndrome, since it affects patients who already suffer from deafness. Mutations in the myosin VIIa gene (MYO7A) cause a major subtype of Usher syndrome, type 1B. Owing to the loss of function nature of Usher 1B and the relatively large size of MYO7A, we investigated a lentiviral-based gene replacement therapy in the retinas of MYO7A-null mice. Among the different promoters tested, a CMV-MYO7A chimeric promoter produced wild-type levels of MYO7A in cultured RPE cells and retinas in vivo. Efficacy of the lentiviral therapy was tested by using cell-based assays to analyze the correction of previously defined, MYO7A-null phenotypes in the mouse retina. In vitro, defects in phagosome digestion and melanosome motility were rescued in primary cultures of RPE cells. In vivo, the normal apical location of melanosomes in RPE cells was restored, and the abnormal accumulation of opsin in the photoreceptor connecting cilium was corrected. These results demonstrate that a lentiviral vector can accommodate a large cDNA, such as MYO7A, and mediate correction of important cellular functions in the retina, a major site affected in the Usher syndrome. Therefore, a lentiviral-mediated gene replacement strategy for Usher 1B therapy in the retina appears feasible.

Lipofuscin accumulation, abnormal electrophysiology, and photoreceptor degeneration in mutant ELOVL4 transgenic mice: a model for macular degeneration

Macular degeneration is a heterogeneous group of disorders characterized by photoreceptor degeneration and atrophy of the retinal pigment epithelium (RPE) in the central retina. An autosomal dominant form of Stargardt macular degeneration (STGD) is caused by mutations in ELOVL4, which is predicted to encode an enzyme involved in the elongation of long-chain fatty acids. We generated transgenic mice expressing a mutant form of human ELOVL4 that causes STGD. In these mice, we show that accumulation by the RPE of undigested phagosomes and lipofuscin, including the fluorophore, 2-[2,6-dimethyl-8-(2,6,6-trimethyl-1-cyclohexen-1-yl)-1E,3E,5E,7E-octatetraenyl]-1-(2-hyydroxyethyl)-4-[4-methyl-6-(2,6,6,-trimethyl-1-cyclohexen-1-yl)-1E,3E,5E-hexatrienyl]-pyridinium (A2E) is followed by RPE atrophy. Subsequently, photoreceptor degeneration occurs in the central retina in a pattern closely resembling that of human STGD and age-related macular degeneration. The ELOVL4 transgenic mice thus provide a good model for both STGD and dry age-related macular degeneration, and represent a valuable tool for studies on therapeutic intervention in these forms of blindness.

Axonopathy and transport deficits early in the pathogenesis of Alzheimer's disease

We identified axonal defects in mouse models of Alzheimer's disease that preceded known disease-related pathology by more than a year; we observed similar axonal defects in the early stages of Alzheimer's disease in humans. Axonal defects consisted of swellings that accumulated abnormal amounts of microtubule-associated and molecular motor proteins, organelles, and vesicles. Impairing axonal transport by reducing the dosage of a kinesin molecular motor protein enhanced the frequency of axonal defects and increased amyloid-beta peptide levels and amyloid deposition. Reductions in microtubule-dependent transport may stimulate proteolytic processing of beta-amyloid precursor protein, resulting in the development of senile plaques and Alzheimer's disease.

Toxicity of Familial ALS-Linked SOD1 Mutants from Selective Recruitment to Spinal Mitochondria

One cause of amyotrophic lateral sclerosis (ALS) is mutation in ubiquitously expressed copper/zinc superoxide dismutase (SOD1), but the mechanism of toxicity to motor neurons is unknown. Multiple disease-causing mutants, but not wild-type SOD1, are now demonstrated to be recruited to mitochondria, but only in affected tissues. This is independent of the copper chaperone for SOD1 and dismutase activity. Highly preferential association with spinal cord mitochondria is seen in human ALS for a mutant SOD1 that accumulates only to trace cytoplasmic levels. Despite variable proportions that are successfully imported, nearly constant amounts of SOD1 mutants and covalently damaged adducts of them accumulate as apparent import intermediates and/or are tightly aggregated or crosslinked onto integral membrane components on the cytoplasmic face of those mitochondria. These findings implicate damage from action of spinal cord-specific factors that recruit mutant SOD1 to spinal mitochondria as the basis for their selective toxicity in ALS.

Investigation of the migration path for new rod photoreceptors in the adult cichlid fish retina

In the retina of adult teleost, precursor cells divide in the outer nuclear layer and give rise to new rod photoreceptors. These new rods migrate from the outer limiting membrane to the inner edge of the outer nuclear layer (ONL) before differentiating. In order to understand which cues these cells use during migration and insertion at the appropriate location we combined cell-specific stains in the retina of the cichlid fish Haplochromis burtoni, viewed with confocal laserscan microscopy: Dividing cells were labeled with bromodeoxyuridine (BrdU), Müller glial cells, cone photoreceptors, and horizontal cells were detected by specific antibodies. During the migration phase (24 to 48 h after BrdU uptake) up to 46% of BrdU-labeled cells were spindle shaped and radially oriented. Most of them were in direct proximity to Müller cell processes. Four days after BrdU-uptake, most labeled cells (91%) were found in the inner portion of the ONL and displayed a spherical shape. This marks the end of the movement of the new rods. At this stage, the labeled cells showed no preference to lie near glial fibers but were often found close to the pedicles of double cones. The leading edge of migrating cells reached into the outer plexiform layer (OPL) but not further than processes of horizontal cells. This is beyond the location of mature rods. We hypothesize that the cells are repelled in the OPL and insert back in the ONL to differentiate as rods.

The degenerative and regenerative processes after the elimination of the proliferative peripheral retina of fish

We have analyzed the modifications in the tench (Tinca tinca) retina after the complete cryo-elimination of the proliferative growing zone (PGZ), which participates in the continuous growth of the retina throughout the life of the fish. By using immunohistochemistry and electron microscopy we demonstrated that, after the lesion, degenerative and regenerative processes take place in the PGZ, in the ciliary zone, and in the transition zone located between the PGZ and the central retina. After 120 days postlesion, the PGZ was completely regenerated and its composition was similar to that of the control animals. Numerous proliferative PCNA-positive cells reappeared and new ganglion cells were formed. In the transition zone and the central retina numerous proliferative PCNA-positive cells also appeared. These are arranged, on occasion, as columnar units from the inner to the outer nuclear layer where the rod precursors and the progenitor cells, respectively, were located. The Müller cells, closely associated with these columnar units, appeared to use them as guides to migration during the regenerative process. Notably, modifications occurred in the ciliary zone, whose cells acquired similar characteristics to the PGZ cells. The ciliary zone cells, the Müller cells, the rod precursors, and the proliferative cells located in the inner nuclear layer appear to participate actively in the regeneration of the PGZ.

The glial design of a teleost optic nerve head supporting continuous growth

This study demonstrates the peculiarities of the glial organization of the optic nerve head (ONH) of a fish, the tench (Tinca tinca), by using immunohistochemistry and electron microscopy. We employed antibodies specific for the macroglial cells: glutamine synthetase (GS), glial fibrillary acidic protein (GFAP), and S100. We also used the N518 antibody to label the new ganglion cells' axons, which are continuously added to the fish retina, and the anti-proliferating cell nuclear antigen (PCNA) antibody to specifically locate dividing cells. We demonstrate a specific regional adaptation of the GS-S100-positive Müller cells' vitreal processes around the optic disc, strongly labeled with the anti-GFAP antibody. In direct contact with these Müller cells' vitreal processes, there are S100-positive astrocytes and S100-negative cells ultrastructurally identified as microglial cells. Moreover, a population of PCNA-positive cells, characterized as glioblasts, forms the limit between the retina and the optic nerve in a region homologous to the Kuhnt intermediary tissue of mammals. Finally, in the intraocular portion of the optic nerve there are differentiating oligodendrocytes arranged in rows. Both the glioblasts and the rows of developing cells could serve as a pool of glial elements for the continuous growth of the visual system.

Non-neuronal cells involved in the degeneration and regeneration of the fish retina

In the present work we show that during the degenerative process occurring after the cryo-elimination of the tench peripheral growing zone many non-neuronal cell types in addition to the resident microglial cells, appear within the affected areas. Some of them are normally found in the retina, such as the retinal pigmented epithelium cells and others originate from extra-retinal tissues. We identified these as granular leukocytes and macrophages. The microglial cells and macrophages, those resident in the sub-retinal space, and the invasive ones, act as phagocytes. The analysis of the injured retina following lesion shows that the invasive macrophages, arising from the scleral extra-retinal tissues, penetrate the neural retina, and migrate from the scleral to the vitreal portion. In contrast those coming from the vitreal extra-retinal tissues migrate in the opposite direction. Moreover, the retinal pigmented epithelium cells present remarkable modifications in their morphology and distribution and enter the neural retina, where they disrupt the surrounding tissue. We have also observed that this cryo-lesion causes an inflammation mediated by a type of granular leukocyte, denominated heterophils which penetrate the neural retina and probably come from the blood supply. Our results suggest that, during the first days after the lesion, the participation of diverse non-neuronal cells removing cell debris from the damaged zone should create a favourable environment allowing the regeneration of the neural retina.

A comparative study of protein kinase C-like immunoreactive cells in the retina

The present study is a morphological and quantitative analysis of protein kinase C-like immunoreactive (PKC-L ir) bipolar cells in the retinas of five different vertebrate species (chicken, tench, zebrafish, goldfish and rat). The morphology of PKC-L-ir bipolar cell axon terminals in fish differs significantly from those of chicken and rat retinas. Fish have bulky terminals whereas chicken and rat have their terminals in the form of small knob-shaped branches. In tench and goldfish, PKC-L-ir bipolar cells gradually decrease in size from the medial (i.e., in tench: mean +/- SD soma area of 30.09 +/- 5.98 microm2) to the peripheral (i.e., in tench: 19.93 +/- 1.73 microm2) retinal regions. This is not observed in chicken, rat or zebrafish where there is more homogeneity in s oma and axon terminal sizes between different retinal regions. Except in chicken, cell density increases from the central (i.e., in tench: mean +/- SD 1795.88 +/- 242.35 cells/mm2) to the peripheral (i.e., in tench: 4295.41 +/- 279.23 cells/mm2) retina. This study provides data that show relevant differences in the PKC-L-ir bipolar morphology and density among birds, fish and mammals. Moreover, these structural variations could mean not only differences in the cellular physiology, but also in the patterns of development and maintenance of the retina in each species.

Growing and regenerating axons in the visual system of teleosts are recognized with the antibody RT97

We have analyzed the immunolabeling with the antibody RT97, a good marker for ganglion cell axons in several species, in the normal and regenerating visual pathways of teleosts. We have demonstrated that RT97 antibody recognizes several proteins in the tench visual system tissues (105, 115, 160, 200, 325 and 335 kDa approximately). By using immunoprecipitation and Western blot we have found that after crushing the optic nerve the immunoreactivity to anti RT97 increased markedly in the optic nerve. In immunohistochemical analysis we also found a different pattern of labeling in normal and regenerating visual pathways. In normal tench RT97 is a good marker for the horizontal cells in the retina, for growing ganglion cell axons which run along the optic nerve from the retina to the optic tectum and of the axon terminals in the stratum opticum and stratum fibrosum and griseum superficiale in the optic tectum. After optic nerve crush, no immunohistochemistry modifications were observed in the retina. However, in accordance with Western blot experiments, in the optic nerve intensely stained groups of regenerating axons appeared progressively throughout the optic nerve as far as the optic tectum. We conclude that the antibody RT97 is an excellent marker of growing and regenerating axons of the optic nerve of fish.

Phytochrome and post-translational regulation of nitrate reductase in higher plants

The possible influence of phytochrome on the activity state of nitrate reductase (NR) was investigated in etiolated plants where the expression of the NR gene is known to be under the control of phytochrome. Activity state is defined as NR activity assayed in the presence of Mg(2+) as percentage of NR activity measured in the absence of Mg(2+). This measurement is assumed to reflect non-phosphorylated NR as percentage of total NR. Beside etiolated barley and maize leaves, a photosynthetic mutant of Lemna aequinoctialis was investigated and compared with the wild type. The increase of NR activity following a red light pulse, mediated via phytochrome, was confirmed in all etiolated plant species investigated as well as in both strains of L. aequinoctialis cultivated in glucose-containing medium. The effect of continuous red light surpassed the effect of a single red light pulse in each case. However, the results did not show any stimulating effect of phytochrome on the activity state caused by post-translational modulation. The activity state was strongly increased by continuous red light in the wild type of L. aequinoctialis but not in the photosynthetic mutant. These results show that the phytochrome system is not important for the post-translational regulation of NR.

Deletion of the nitrate reductase N-terminal domain still allows binding of 14-3-3 proteins but affects their inhibitory properties

Nitrate reductase (NR) is post-translationally regulated by phosphorylation and binding of 14-3-3 proteins. Deletion of 56 amino acids in the amino-terminal domain of NR was previously shown to impair this type of regulation in tobacco (Nicotiana plumbaginifolia) (L. Nussaume, M. Vincentez, C. Meyer, J.-P. Boutin, M. Caboche [1995] Plant Cell 7: 611-621), although both full-length NR and deleted NR (DeltaNR) appeared to be phosphorylated in darkness (C. Lillo, S. Kazazaic, P. Ruoff, C. Meyer [1997] Plant Physiol 114: 1377-1383). We show here that in the presence of Mg(2+) and phosphatase inhibitors, NR and endogenous 14-3-3 proteins copurify through affinity chromatography. Assay of NR activity and western blots showed that endogenous 14-3-3 proteins copurified with both NR and DeltaNR. Electron transport in the heme-binding domain of DeltaNR was inhibited by Mg(2+)/14-3-3, whereas this was not the case for NR. This may indicate a different way of binding for 14-3-3 in the DeltaNR compared with NR. The DeltaNR was more labile than NR, in vitro. Lability was ascribed to the molybdopterin binding domain, and apparently an important function of the 56 amino acids is stabilization of this domain.

Enzyme histochemical identification of microglial cells in the retina of a fish (Tinca tinca)

Histochemistry for nucleoside diphosphatase was used to study the microglial cells in the adult tench retina. An abundant population of microglial cells was located in the vascular membrane, nerve fibre layer, inner and outer plexiform layers and scattered cells were observed in the inner nuclear layer. Rounded and amoeboid cells could be seen close to the vessel in the vascular membrane, bipolar cells in the nerve fibre layer and ramified cells in the rest of the layers. Several microglial forms could correspond to developing cells. The pattern of distribution was similar to that described in other vertebrates, but with several differences, such as the presence of microglial cells in the vascular membrane and inner nuclear layer and the overlap of processes in the plexiform layers.

Response of microglial cells after a cryolesion in the peripheral proliferative retina of tench

We studied the glial response after inducing a lesion in the zone of the peripheral retina of tench, where there is proliferative neuroepithelium. In the retina and optic nerve, the microglial response was analysed with tomato lectin and the macroglial response with antibodies against GFAP and S-100. In lesioned retinas, there was a temporal-spatial distribution pattern of microglia. One day after lesion, primitive ramified cells appeared in the nerve fibre layer. These cells appeared progressively from the vitreal to the scleral layers until day 7 when cells appeared in all layers, with the exception of the outer plexiform layer. From this point, labelling decreased. In the optic nerve, 3 days after lesion, an increase in the number of microglial cells was observed, first in the nerve folds and from day 15 in specific areas of the optic nerve. In the central retina, in the optic nerve head and within the optic nerve itself, the appearance of microglial cells, after the lesion, near the blood vessels, could indicate a vascular origin of microglia, as has been proposed by many authors. However, we cannot discount the idea that some of the reactive microglial cells arise by proliferation of the microglia existing in the normal state. Using GFAP and S-100 antibodies, no important changes in the retina were observed, however in the optic nerve there was response to the lesion. Thus, the macroglial cells appeared to be involved in reorganisation of the optic nerve axons after lesion.