Expression of NGF receptor and NGF receptor mRNA in the developing and adult rat retina

Ciliary neurotrophic factor is an axogenesis factor for retinal ganglion cells

Although mature mammalian retinal ganglion cells normally fail to regrow injured axons, exposure to the molecular environment of the peripheral nervous system stimulates regenerative growth. The present study used dissociated rat retinal ganglion cells purified by immunopanning to identify peripheral nervous system-derived factors that promote axonal outgrowth. Of the multiple growth factors investigated, only ciliary neurotrophic factor and the related cytokine, leukemia inhibitory factor, had striking neuritogenic activity, with half-maximal effects at 1-2 ng/ml. Brain-derived neurotrophic factor stimulated retinal ganglion cell survival nearly as well as ciliary neurotrophic factor, but had only minor effects on outgrowth. Thus, the neuritogenic effects of ciliary neurotrophic factor are not a simple consequence of increased survival. Ciliary neurotrophic factor-stimulated outgrowth was correlated with increased expression of the growth-associated membrane phosphoprotein, GAP-43, a hallmark of optic nerve regeneration in vivo. A high molecular weight fraction from media conditioned by rat optic or sciatic nerve mimicked the effect of ciliary neurotrophic factor in inducing axonal outgrowth. Ciliary neurotrophic factor was detected in the conditioned media on western blots, and the biological activity of the conditioned media was neutralized with an anti-ciliary neurotrophic factor antibody. These results indicate that ciliary neurotrophic factor has specific effects on axon outgrowth in retinal ganglion cells that are dissociable from its effects on cell survival, and that ciliary neurotrophic factor accounts for most of the axon-promoting activity for retinal ganglion cells present in either the sciatic or optic nerve.

Neurotrophins and their receptors in the tench retina during optic nerve regeneration

To understand the role of neurotrophins in the visual system, we investigated the distribution of both neurotrophins and their receptors within the retina of a fish that has the capacity to spontaneously regenerate its optic nerve axons after lesion. Intact retinas and retinas from tench, whose optic nerve had been crushed, were analyzed by immunohistochemistry and in situ hybridization. Trk receptors were mainly immunolocalized in cells of the inner nuclear and ganglion cell layers, a distribution coincident with that of their mRNAs. Nerve growth factor (NGF) immunoreactivity was detected exclusively in Müller cell processes, and brain-derived neurotrophic factor (BDNF) was found in both neuronal bodies and Müller cell processes. Neurotrophin-3 (NT-3) was detected in most of the cell nuclei, and neurotrophin-4/5 (NT-4/5) was localized in fibers and in a few cells in the inner retina. An increase in both TrkA protein and mRNA was detected during axonal regeneration within the retinal ganglion cell layer, reaching a maximum 30 days postcrush and returning to normal levels by day 90, when optic nerve regeneration is almost completed in this fish. None of the other neurotrophins and receptors showed appreciable changes. The heterogeneous distribution patterns of neurotrophins and their receptors in fish retina, their differences from the distribution observed in other species, and the TrkA changes after optic nerve crush suggest an important role for these molecules in the normal physiology of the fish retina and during the regeneration process.

Experience-dependent changes in the importance of N-methyl-D-aspartate (NMDA) receptors for visual transmission in superior colliculus

The excitatory amino acid transmitter glutamate mediates visual activity in the superficial grey layer (SGS) of superior colliculus. At eye opening N-methyl-d-aspartate receptors (NMDA-rs) convey little of the visual response, but with age their role in visual transmission increases to a peak at P21, then falls to the lower adult level. Visual deprivation which begins before eye opening causes NMDA-rs to assume a greater importance for visual transmission in SGS. Here we explore the possibility that these experience-dependent changes in the role of NMDA-rs in the SGS are limited by age. We find that the effects of visual deprivation on NMDA-r mediated visual activity are recoverable even after extensive dark rearing. Also, a short episode of visual experience is sufficient to allow the normal situation to be established and subsequent dark rearing is ineffective. Four-day periods of visual experience beginning at P14 or P25 have the same effect. Given that NMDA-rs take little part in visual transmission prior to P18, these data prompt a reconsideration of the role of NMDA-r mediated sensory transmission in the mechanisms by which early environmental experience influences the development of the visual system.

The effects of central administration of neurotrophins or transplants of fetal tectal tissue on retinal ganglion cell survival following removal of the superior colliculus in neonatal rats

In neonatal rats, intraocular injections of brain-derived neurotrophic factor (BDNF) or neurotrophin 4/5 (NT-4/5) enhance the survival of retinal ganglion cells (RGCs) following superior colliculus (SC) ablation [Q. Cui, A.R. Harvey, At least two mechanisms are involved in the death of retinal ganglion cells following target ablation in neonatal rats, J. Neurosci., 15, 1995, pp. 8143-8155.]. The aim of the present study was to determine if: (i) fetal tectal tissue grafted into the lesion site, or (ii) neurotrophins applied centrally to the injured SC, also decreased lesion-induced RGC death. Nuclei of tectally projecting RGCs were identified by injecting diamidino yellow (DY) into the left SC of 2-day-old (P2) Wistar rats. Injected SCs were lesioned at P4. In some animals, embryonic (E16) tectal tissue was then implanted into the lesion cavity; host rats were perfused 24 h or 20 days later. In short-term (24-h) studies, the number of DY-labelled pyknotic profiles was compared to the number of normal DY-labelled RGCs in retinal wholemounts (right eyes). The proportion of dying RGCs in animals with grafts (10.7%, n = 17) was not significantly different from lesion-only rats (13.2%, n = 26). Nonetheless, the long-term (20-day) study showed that, in most rats, fetal tectal tissue survived in the lesion cavity and in some cases, the grafts received host retinal input. In another group, different doses of BDNF or NT-4/5 were applied to the SC after P4 tectal lesions. Rats were perfused 24 h later and the number of pyknotic vs. normal DY-labelled RGCs was determined. Initial trials in which SC lesions were filled with gelfoam soaked in BDNF or NT-4/5 were unsuccessful; however, RGC death was reduced (p < 0.05, Dunnett's test) in rats that received gelfoam implants as well as focal neurotrophin injections into SC rostral to the lesion. The lowest pyknotic rate in individual animals from the BDNF and NT-4/5 groups was 2.41% and 2.01%, respectively. Overall, the proportion of dying RGCs was 7.0% (n = 8) for BDNF and 7.4% (n = 17) for NT-4/5 treated rats. Normal RGC densities were also significantly higher in these animals. NT-4/5 topically applied to the posterior surface of the eye did not reduce RGC death. The data show that the viability of injured neonatal RGCs is increased by specific retrograde neurotrophin-mediated survival signals which can be activated from the SC.

Immunohistochemical distribution of neurotrophins and their receptors in the rat retina and the effects of ischemia and reperfusion

1. Neurotrophins are molecules that regulate the survival, development and maintenance of specific functions in different populations of nerve cells. 2. In the present work, we studied the localization, at the cellular level, of the different neurotrophins and their receptors within the rat retina in control and after ischemia-reperfusion of the retina. We found variations in the localization of some of these molecules depending on the reperfusion time of the retina after the ischemic lesion. 3. Thus it is suggested that the changes in the distribution and concentration of neurotrophins and their receptors caused by ischemia are protective reactions related to neuronal damage and synaptic reorganization.

Nerve growth factor (NGF) reduces and NGF antibody exacerbates retinal damage induced in rabbit by experimental ocular hypertension

BACKGROUND

It has been shown that intravitreal injection of NGF inhibits ganglion cell degeneration after optic nerve transection and ischemic injury. The aim of our study was to investigate the presence of NGF in aqueous humor and its involvement in retinal damage during ocular hypertension.

METHODS

We used an experimental model of ocular hypertension in rabbit. Before treatment and 4, 10 and 15 days after induction of hypertension, we evaluated histological retinal damage and NGF levels in aqueous humor using an immunoenzymatic assay. Polyclonal anti-NGF antibodies were injected intravitreally into one eye of each rabbit (n = 6), and the animals were killed after 4 days of hypertension. Another group of rabbits (n = 12) was injected retro-ocularly with NGF and killed after 10 or 15 days of treatment for histologic evaluation of the retina.

RESULTS

Our data show that experimental ocular hypertension in adult rabbits induces retinal damage and enhances local NGF levels. The highest NGF value was found after 4 days of intraocular hypertension: high levels persisted, though to a lesser extent, for up to 15 days. Histological examination revealed that the number of retinal ganglion cells (RGC) remained unchanged during the first 4 days but decreased at 10 days. These studies also showed that retro-ocular administration of NGF reduced RGC loss, whereas intraocular injection of NGF antibodies, which inhibited the endogenous NGF, exacerbated the retinal insult.

CONCLUSION

These findings demonstrate a protective effect of NGF on RGC damaged by ocular hypertension and prompt further investigations to evaluate a possible therapeutic use of NGF to retard RGC death in humans.

Immunohistochemical analysis of the neurotrophins BDNF and NT-3 and their receptors trk B, trk C, and p75 in the developing chick retina

The neurotrophins are trophic and mitogenic factors critical for the development of specific classes of neurons in the central and peripheral nervous systems. In the retina, BDNF and NT-3 have been shown to promote the survival of differentiated ganglion cells (Rodriguez-Tebar et al., 1989; De La Rosa et al., 1994). NT-3 has also been demonstrated to support the survival of amacrine cells and facilitates the differentiation of retinal neurons in culture (De La Rosa et al., 1994). Here, we examine immunohistochemically the expression of BDNF and NT-3 proteins, their cognate receptors, trk B and trk C, respectively, and the p75 neurotrophin receptor in the developing chick retina. At E8, the earliest stage of retinal development examined, all of these proteins exhibit diffuse expression throughout the width of the retina, with the strongest reactivity in the innermost layers. A gradual restriction in expression to ganglion cells and amacrine cells, the staining of which is most prominent at E15, is followed by a downregulation of expression with the strongest immunoreactivity persisting in the ganglion cell layer. Overlapping patterns of expression throughout embryonic development indicate a colocalization of the neurotrophins and their receptors, although NT-3 and p75 alone are present in the inner plexiform layer and only p75 is observed in the outer plexiform layer. Although some of the immunoreactivity for BDNF, NT-3, and their receptors in retina may reflect trophic mechanisms operating in association with the optic tectum and isthmo-optic nucleus, the colocalization of ligands and receptors in retina strengthens the assertion that these neurotrophins function locally during development.

Sources of p75-nerve growth factor receptor-like immunoreactivity in the rat suprachiasmatic nucleus

In mammals, the suprachiasmatic nucleus is critical for the generation of circadian rhythms and their entrainment to environmental cues. In the rat, the ventrolateral aspect of the suprachiasmatic nucleus receives a robust retinal input. This region also exhibits the most intense immunolabeling for the low-affinity nerve growth factor receptor in the forebrain. Our study was aimed at identifying the sources of this low-affinity nerve growth factor receptor immunoreactivity using immunohistochemistry combined with retrograde tract-tracing, and orbital enucleation. To determine the origin of the low-affinity nerve growth factor receptor immunoreactivity from sources extrinsic to the suprachiasmatic nucleus, unilateral injections of the retrograde tracer, Fluorogold, were made into the suprachiasmatic nucleus. Retrogradely labeled neurons that were also immunopositive for the low-affinity nerve growth factor receptor were found in both the basal forebrain and the retina. In the basal forebrain, such cells were found throughout its rostrocaudal extent, with the majority also being immunoreactive for the cholinergic marker, choline acetyltransferase. In the retina, cells retrogradely labeled with Fluorogold that were immunoreactive for low-affinity nerve growth factor receptor were located in the ganglion cell layer. Orbital enucleations were performed to confirm the findings observed following retrograde labeling in the retina. Unilateral orbital enucleations resulted in a significant reduction in low-affinity nerve growth factor receptor immunoreactivity in the contralateral suprachiasmatic nucleus compared to that seen on the ipsilateral side when examined one week post-surgery. Bilateral enucleations resulted in an equal decrease on both sides of the suprachiasmatic nucleus. Similar low-affinity nerve growth factor-like immunoreactivity was seen in the suprachiasmatic nucleus even two to four weeks after bilateral enucleations. Taken together, these findings suggest that low-affinity nerve growth factor receptors in the suprachiasmatic nucleus derive from multiple sources. While some receptors may be intrinsic to suprachiasmatic nucleus neurons, most appear to be of extrinsic origin and are located on axon terminals of basal forebrain cholinergic neurons and retinal ganglion cells.

Suppression of trkB expression by antisense oligonucleotides alters a neuronal phenotype in the rod pathway of the developing rat retina

trkB is the high-affinity receptor for brain-derived neurotrophic factor (BDNF), a trophic molecule with demonstrated effects on the survival and differentiation of a wide variety of neuronal populations. In the mammalian retina, trkB is localized to both ganglion cells and numerous cells in the inner nuclear layer. Much information on the role of BDNF in neuronal development has been derived from the study of trkB- and BDNF-deficient mutant mice. This includes an attenuation of the numbers of cortical neurons immunopositive for the calcium-binding proteins, parvalbumin, and calbindin. Unfortunately, these mutant animals typically fail to survive for > 24-48 hr after birth. Since most retinal neuronal differentiation occurs postnatally, we have devised an alternative scheme to suppress the expression of trkB in the retina to examine the role of BDNF on the postnatal development of neurons of the inner retina. Neonatal rats were treated with intraocular injection of an antisense oligonucleotide (1-2 microliters of 10-100 microM solution) targeted to the trkB mRNA. Immunohistochemistry with a polyclonal antibody to trkB showed that the expression of trkB in retinal neurons was suppressed 48-72 hr following a single injection. Northern blot analysis demonstrated that antisense treatment had no effect on the level of trkB mRNA, even after multiple injections. This suggests an effect of trkB antisense treatment on protein translation, but not on RNA transcription. No alterations were observed in the thickness of retinal cellular or plexiform layers, suggesting that BDNF is not the sole survival factor for these neurons. There were, however, alterations in the patterns of immunostaining for parvalbumin, a marker for the narrow-field, bistratified AII amacrine cell-a central element of the rod (scotopic) pathway. This was evidenced by a decrease in both the number of immunostained somata (> 50%) and in the intensity of immunolabeling. However, the immunostaining pattern of calbindin was not affected. These studies suggest that the ligands for trkB have specific effects on the neurochemical phenotypic expression of inner retinal neurons and in the development of a well-defined retinal circuit.

Signal-regulated proteins and fibroblast growth factor receptors: comparative immunolocalization in rat retina

We compared the immunolocalization of fibroblast growth factor (FGF)-R1 and FGF-R2 with that of several intracellular signalling proteins in rat neural retina. Only the serine/threonine extracellular signal-related kinases (ERK) and lipocortin/annexin 6, a major calcium-binding protein, appeared to be co-localized with FGF-R1 and FGF-R2 in all subfields of the neural retina. In particular, ERK appeared to be present in perikarya of ganglion cells and synaptic layers as did these receptors. Possible implications of these results with regard to neuroprotective role of FGF are discussed.

Nerve growth factor delays retinal degeneration in C3H mice

BACKGROUND

The aim of the present study was to investigate the biological role of nerve growth factor (NGF) on retinal degeneration in the C3H mouse strain. This strain is characterized by a single gene mutation (rd) which leads to photoreceptor degeneration resembling human retinitis pigmentosa.

METHODS

Neural retinas from 1- to 25 day-old C3H mice were dissected from outer ocular tissues, dissociated in cell suspension, stained with a vital dye and counted in a hemocytometer. For in vivo study, NGF was injected into the intraocular or retro-ocular area, and at the end of the treatment the mice were killed. The eyes were enucleated, fixed and cut by cryostat into 14-microns serial sections. The serial sections were stained with hematoxylin-eosin and the outer nuclear layer (ONL) was measured using a computerized image analysis system.

RESULTS

An intraocular injection of NGF, or repeated retro-ocular injections, induced a significant increase in ONL thickness compared to controls.

CONCLUSION

Our data show that NGF inhibits retinal degeneration in C3H mice. The mechanism(s) underlying the protective action of NGF against retinal cell death remains to be established.

Nerve growth factor prevents both neuroretinal programmed cell death and capillary pathology in experimental diabetes

BACKGROUND

Chronic diabetes causes structural changes in the retinal capillaries of nearly all patients with a disease duration of more than 15 years. Acellular occluded vessels cause hypoxia, which stimulates sight-threatening abnormal angiogenesis in 50% of all type I diabetic patients. The mechanism by which diabetes produces acellular retinal capillaries is unknown.

MATERIALS AND METHODS

In this study, evidence of programmed cell death (PCD) was sought in the retinas of early diabetic rats, and the effect of nerve growth factor (NGF) on PCD and capillary morphology was evaluated.

RESULTS

Diabetes induced PCD primarily in retinal ganglion cells (RGC) and Muller cells. This was associated with a transdifferentiation of Muller cells into an injury-associated glial fibrillary acidic protein (GFAP)-expressing phenotype, and an up-regulation of the low-affinity NGF receptor p75NGFR on both RGC and Muller cells. NGF treatment of diabetic rats prevented both early PCD in RGC and Muller cells, and the development of pericyte loss and acellular occluded capillaries.

CONCLUSIONS

These data provide new insight into the mechanism of diabetic retinal vascular damage, and suggest that NGF or other neurotrophic factors may have potential as therapeutic agents for the prevention of human diabetic retinopathy.

Ontogeny of the opioid growth factor, [Met5]-enkephalin, and its binding activity in the rat retina

The endogenous opioid peptide [Met5]-enkephalin is a tonically active opioid growth factor (OGF) with an inhibitory action on DNA synthesis in the developing rat retina. In this study, the ontogeny of the spatial and temporal expression of OGF and its binding activity was examined. OGF-like immunoreactivity was detected in the retina at gestation day (E) 20, but not at E18, and was localized to ganglion cell and neuroblast layers; immunochemical reaction was no longer seen in the retina by postnatal day 6. Native OGF was further identified and characterized by high-performance liquid chromatography (HPLC) studies and immunodot assays, which revealed that [Met5]-enkephalin was present in the neonatal, but not adult, rat retina. OGF binding activity was detected as early as E18 using [125I]-[Met5]-enkephalin and in vitro receptor autoradiography. Little OGF binding activity was noted for prenatal retinas, but appreciable activity was observed from birth to postnatal day 4; no OGF binding could be detected after postnatal day 5 or in the adult. These results reveal the transient appearance of the OGF, [Met5]-enkephalin, and its receptor binding activity in the developing mammalian retina, and show that their ontogeny coincides with the timetable of DNA synthesis of retinal neuroblasts.

Plasticity following neonatal visual cortex damage in cats

We have used the cat visual system as a model system to investigate how remaining areas of the brain are able to take over functions that are lost following brain damage and why neonates show better behavioral recovery than adults. Anatomical studies with both anterograde and retrograde tracing methods reveal an increased projection from retina through thalamus to the posteromedial lateral suprasylvian (PMLS) extrastriate visual area of cortex in the damaged hemisphere of cats with a neonatal visual cortex (areas 17, 18, and 19; VC) lesion. No such enhanced projection is seen after an adult lesion. In addition, single-cell neurophysiological studies indicate that physiological compensation is present in PMLS cortex after a neonatal VC lesion but not after an adult lesion. The physiological compensation replaces (or maintains) properties that are characteristic of PMLS neurons; there is little or no improvement to replace the superior spatial properties of striate cortex (or areas 18 or 19) neurons that were lost. Immunohistochemical studies of the possible roles of neuronal growth factors in the compensation indicate that low- and high-affinity receptors are present that would allow several neurotrophins to influence the normal retina throughout life. Furthermore, these receptors are upregulated transneuronally following neonatal VC damage and thus could play a role in lesion-induced changes in the retina and its central projections. Ongoing studies are continuing to examine the presence of neurotrophins and their receptors in the retina and brain during normal development and after VC damage. In addition, studies of the effects of administering neuronal growth factors are underway to determine whether compensation for VC damage can be improved in neonates or even be produced in adults.

Changes of compound action potentials in retrograde axonal degeneration of rat optic nerve

Electrophysiological recordings of compound action potentials (CAPs) were made from the optic nerve (ON) following unilateral optic tract (OT) transection in adult rats. In response to optic chiasm stimulation CAPs recorded from the ON ipsilateral to the transected OT, i.e., the ON of control side, revealed three positive waves, termed n1, n2, and n3 components, corresponding to fast-, intermediate-, and slow-conducting fibers. Two weeks after OT transection, CAPs recorded from the ON contralateral to the transected OT, i.e., the ON of cut side, were generally smaller in amplitude than those recorded from the ON of control side. The degree of amplitude reduction was different among three components; n3 component was severely reduced and n2 component was moderately reduced, whereas n1 component relatively persisted. These tendencies were more marked in CAPs recorded at 4 weeks after OT transection; n3 component disappeared, whereas n1 and n2 components decreased in amplitude with elongation of latency. Cross sections of the ON after unilateral OT transection were examined electron microscopically, in which significant decrease in fiber density, demyelination, and distorted fibers were verified in the cut side. The present study suggests that slower-conducting ON fibers, that is, smaller-diameter ON fibers are initially and remarkably thrown into retrograde degeneration, while larger-diameter ON fibers are relatively resistant to axotomy.

Expression of the proto-oncogene, trk, receptors in the developing rat retina

The neurotrophins, including nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT-3) and NT-4/5 are important in a variety of developmental processes in the peripheral and central nervous systems. These molecules bind to a low-affinity receptor and to distinct high-affinity receptors. The high-affinity receptor for NGF is the proto-oncogene product, p140trkA(trkA). Isoforms of p140trkA, p145trkB(trkB), and p140trkC(trkC), are the primary high-affinity receptors for BDNF and NT-3, respectively. We evaluated the developmental regulation of the high-affinity neurotrophin receptors in the rat retina using polyclonal antibodies directed to a highly conserved region of the C-terminus of the p140trkA isoforms (pantrk) and antibodies directed to unique amino-acid sequences of p140trkA, p145trkB, and p140trkC. Immunoreactivities for trkA and trkB, as well as pantrk, were detected in the developing retina and showed similar distributions. At similar antibody concentrations, trkC immunoreactivity was not detected. In the embryo, immunoreactivties were present in cells located throughout the neuroblastic retina, especially in the inner retinal layers, and in fibers in the nerve fiber layer and optic nerve. In the newborn retina, immunoreactivities for these two receptor isoforms were localized to numerous somata in the inner nuclear layer (INL), as well as to cells in the ganglion cell layer (GCL) and axons in the nerve fiber layer and optic nerve. A similar pattern of immunostaining persisted throughout the first postnatal week. By postnatal day-10, immunostaining was confined to large-diameter cells in the GCL, both heavily stained and lightly stained cells in the INL and a plexus of processes in the inner plexiform layer (IPL).(ABSTRACT TRUNCATED AT 250 WORDS)

Nerve growth factor reduces apoptosis of axotomized retinal ganglion cells in the neonatal rat

It has recently been reported that the degeneration of retinal ganglion cells induced by transection of the optic nerve in the neonatal rat is due to an active process of apoptosis, as opposed to passive necrosis. Here we tested whether the administration of the trophic factor nerve growth factor could prevent the apoptotic death of the axotomized cells. We administered nerve growth factor by two intraocular injections, one immediately after the lesion and the second 12 h later. The retinas were taken at 24 h post-lesion and stained as whole mounts with Cresyl Violet. Pyknotic as well as surviving cells were counted in the retinal ganglion cell layer. In this layer at least 95% of the total cell population is composed by ganglion cells, as revealed by retrogradely labelling these cells with horseradish peroxidase injected in the superior colliculi. We found that intraocular administration of nerve growth factor diminishes the degeneration induced by optic nerve transection in the neonatal rat. After nerve growth factor injection, in fact, the number of pyknotic cells is reduced by 39% compared with controls (lesioned, injected with saline); in addition, nerve growth factor also increases the survival of retinal ganglion cells by 30% at 24 h post-lesion.

Survival factors in retinal degenerations

Recent experiments on the retina have examined the effectiveness of various factors (e.g. growth factors, neurotrophins and cytokines) for enhancing survival and reducing injury of retinal neurons, such as photoreceptors and ganglion cells, whose death leads to blindness in degenerative retinal diseases. It has also been shown that retinal injury stimulates intrinsic survival mechanisms that promote survival of these neurons.

Characterization and growth-dependent regulation of the nerve growth factor receptor gp140trk in rat C6 glioma cells

The glioma cell line C6 was used to study the expression and growth-dependent regulation of the nerve growth factor (NGF) tyrosine kinase receptor gp140trk, which is the mature protein product of the trk proto-oncogene. Chemical cross-linking of 125I-NGF to C6 cells, followed by immunoprecipitation with polyclonal anti-NGF antibodies and separation by polyacrylamide gel electrophoresis, revealed the presence of 90-95 and 150 kDa species. Immunocytochemical staining of C6 cells with antibodies directed against either the low-affinity NGF receptor gp75NGFR or trk proto-oncogene products demonstrated a heterogeneous cellular distribution of both antigens. Brief treatment of C6 cells with NGF led to the tyrosine phosphorylation of 80, 110 and 140 kDa protein species, as detected on anti-phosphotyrosine Western blots. Similar molecular weight species were found with anti-Trk antibodies in the NGF-treated cells. Intracellular localization of Trk-like immunoreactivity in C6 cells released from a growth-arrested state indicated an initial immunostaining of the nuclear periphery, progressing to cytoplasmic vesicles and finally to the plasma membrane. These observations at the light microscopic level were confirmed using immunoelectron microscopy with the same anti-Trk antibodies, and showed clearly the trafficking of Trk-like immunostained particles from the endoplasmic reticulum to the plasmalemma. The cellular localization of trk gene products also appeared to depend on their glycosylation state. Such growth-dependent expression of NGF receptors on glial cells may be important in controlling autocrine regulatory processes of glia to NGF, which these cells produce.

BDNF in the development of the visual system of Xenopus

To explore the role of BDNF during Xenopus visual system development, the expression of BDNF and TrkB, as well as the effect of BDNF during retinal ganglion cell (RGC) development in culture, was examined. BDNF mRNA was found to be expressed in both the developing eye and tectum, peaking at stage 45/46. The expression of BDNF coincided with RGC expression of full-length trkB transcripts, suggesting a functional role for BDNF. In culture, BDNF significantly increased the number of RGCs. The ability of BDNF to rescue differentiated RGCs that had projected to the tectum, the time course of the effect, and the lack of mitogenic response indicate that this neurotrophin promotes survival. The expression of BDNF and TrkB and the responsiveness of RGCs to BDNF coincide with retinal axon terminal arborization and patterning. Our results indicate that BDNF is a relevant neurotrophin for Xenopus RGC development and suggest that it plays a role during visual system patterning.

The effect of cycloheximide and ganglioside GM1 on the viability of retinotectally projecting ganglion cells following ablation of the superior colliculus in neonatal rats

The time-course and extent of death of retinal ganglion cells (RGCs) following ablation of the superior colliculus (SC) in neonatal Wistar rats has recently been described [Harvey, A. R. and Robertson, D. (1992) J. Comp. Neurol., 325, 83-94]. Normal and pyknotic nuclei of retinotectally projecting ganglion cells were visualized using the fluorescent retrograde tracer diamidino yellow (DY), which had been injected into the SC at P2 (day of birth = P0), 2 days prior to tectal removal. The present report sets out to determine whether cycloheximide, an inhibitor of protein synthesis, or ganglioside GM1 reduced this lesion-induced RGC death. All surgery was carried out under ether anaesthesia; DY was injected into the left SC at P2 and the injected area was removed at P4. Cycloheximide (20-500 ng) was injected into the vitreous chamber of the right eye immediately after the lesion and again 11-12 h later. In some rats, cycloheximide administration was delayed until 12 h after the SC ablation. Control rats received SC lesions alone or lesions plus sham eye injections of saline. Different doses of GM1 were applied i.p. or intraocularly. Rats were perfused 24 h after the SC lesion, at the time of peak RGC death. Retinae of lesion only or sham eye injected rats contained approximately 11% pyknotic RGCs and the density of normal RGCs was approximately 3400/mm2. The rate of pyknosis in cycloheximide treated retinae was reduced to approximately 3%. Normal RGC density in these retinae was approximately 5500/mm2, similar to that found in retinae of unlesioned animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Neuritogenesis of retinal ganglion cells is differentially promoted by target extract

Labeled retinal ganglion cells from neonatal rats extended neurites in dissociated cell culture as a cell type-specific response to the influence of a superior collicular extract. The molecule responsible for this neuritogenic effect is soluble and non-dialysable (> 12 kDa). Nerve growth factor had a neuritogenic effect both on ganglion cells and other types of retinal cells.

Effects of nerve growth factor on neuronal plasticity of the kitten visual cortex

1. The effect of intraventricular administration of nerve growth factor (NGF) by means of a cannula-minipump system was studied in kittens monocularly deprived during the critical period. The ocular dominance of area 17 neurones of NGF-treated and control kittens was determined by conventional extracellular recordings. The soma size of cells in A and A1 laminae of the lateral geniculate nucleus (LGN) was also evaluated in Cresyl Violet preparations. 2. Binocularly responsive neurons were found to be significantly more numerous in NGF-treated than in control kittens. The shrinkage of cells from the deprived LGN laminae normally observed in control kittens was prevented by NGF administration. 3. Following an initial period of monocular deprivation (MD) kittens subsequently treated with NGF showed a substantial recovery of functional binocular connections. 4. These findings indicate that the administration of NGF during the period of deprivation reduces the amblyopic effects of MD, while its administration to kittens with both eyes open following the initial deprivation promotes recovery of the deprived eye. 5. Neurotrophic factors may contribute to the regulation of experience-dependent modifications of synaptic connectivity in the visual cortex.

Flunarizine enhances rat retinal ganglion cell survival after axotomy

After axotomy most central nervous neurons including retinal ganglion cells (RGCs) die in a few weeks, although their somata are not injured. This neuronal death could be due to lack of retrogradely transported target derived neurotrophic factors or due to a calcium overload after excessive release of excitatory amino acids from dying cells. Flunarizine, as a potent blocker of voltage dependent Ca2+ channels and in higher concentration being an inhibitor of the Ca2+/calmodulin-dependent protein kinase II, is able to mimic the neurotrophic effect of NGF on dorsal root ganglion (DRG) neurons. To examine its neuroprotective value in the central nervous system (CNS), flunarizine (5 mg/kg body weight) was given daily to rats after unilateral axotomy of the optic nerve. The density of retrogradely labelled retinal ganglion cells (RGCs) was determined 14 days after axotomy. It could be demonstrated that flunarizine significantly enhanced RGC survival after axotomy in adult rats (P < 0.001; 1065 +/- 142 vs. 922 +/- 237 RGCs/mm2).

Immunocytochemical demonstration of nerve growth factor (NGF) receptor in the pineal gland: effect of NGF on pinealocyte neurite formation

Nerve growth factor receptor immunoreactivity (NGFRI) in the pineal gland was examined both light and electron microscopically using the monoclonal antibody 192IgG. NGFRI was located on sympathetic fibers and on perivascular cells resembling macrophage/microglia. A pineal gland dispersed cell culture model confirmed the presence of NGFRI in cells that exhibited processes of varying lengths and were distributed among pinealocytes and other flat cells. Pinealocytes in dispersed cell culture were identified immunocytochemically by their expression of S-antigen, their round shape and small size and their tendency to extend neurites in the direction of the flat cells in culture. The length of pinealocyte neurites showed a significant increase when cultured in the presence of NGF (25 ng/ml), suggesting that trophic factors, mediated by these macrophage/microglial cells, are important to the morphogenesis of these neuroendocrine cells. Neurotrophic activation of these neuroendocrine macrophage/microglia may have neuro-immunomodulatory implications leading to expression of proteins encoded by the major histocompatibility complex.

Expression of JUN, KROX, and CREB transcription factors in goldfish and rat retinal ganglion cells following optic nerve lesion is related to axonal sprouting

Goldfish and rat optic nerves were cut and crushed, respectively, and the expression of the transcription factor proteins c-JUN, JUN B, JUN D, c-FOS, FOS B, KROX-24, and CREB was investigated in retinal ganglion cells (RGCs) by immunocytochemistry. Immunoreactivities (IRs) were followed up to 350 days in the goldfish and up to 22 days in the rat. In RGCs of untreated goldfish and rats, all JUN, FOS, and KROX proteins were absent whereas CREB was constitutively expressed. After optic nerve cut in goldfish, a JUN-like immunoreactivity (JUN-IR) appeared in a small number of RGCs of central retina after 24 h, reached a maximum within 5 days, declined after 30 days, and was on a half-maximal level after 50 days. Between 100 and 200 days, JUN-IR was only visible in a few RGCs and was completely absent after 350 days. Specific antibodies against c-JUN, JUN B, and JUN D gave no distinct immunoreactive signal. Thus, we could not determine which member of the JUN family contributed to the JUN-IR. The expression of CREB declined after 5 days. The number of CREB-labeled RGCs was reduced (not significant) and the intensity of labeling faded out. After 50 days, CREB-IR had returned to basal level. c-FOS, FOS B, and KROX-24 could not be detected in goldfish RGCs following optic nerve cut. After optic nerve crush in the rat, c-JUN, JUN D, and KROX-24 appeared in a substantial number of RGCs after 24 h, had a maximal expression after 5 days, and strongly declined after 8 days. c-JUN and KROX-24 were completely absent after 22 days whereas JUN D was still present in a few rat RGCs. The number of CREB-labeled RGCs decreased after 5 days and had declined by 50% after 22 days. Expression of JUN B, c-FOS, FOS B could not be detected in rat RGCs after optic nerve crush. Our data demonstrate that the decrease of CREB and the increase of JUN and KROX-24 transcription factors precedes and parallels both the alteration of de novo protein synthesis and the axonal sprouting, which are long lasting in goldfish and transient in rat.

Intravitreal injections of neurotrophic factors support the survival of axotomized retinal ganglion cells in adult rats in vivo

After transection of the optic nerve (ON) in adult rats, retinal ganglion cells (RGC) progressively degenerate until, after two months, a residual population of only about 5% of these cells survives. In this study, we investigated the effect of regeneration-associated factors from sciatic nerve (ScN), BDNF, and CNTF on the survival of adult rat RGC after intraorbital ON transection. Neurotrophic factors were injected into the vitreous body. Rats were allowed to survive 3, 5, or 7 weeks, and the remaining viable RGC were then labelled by retrograde staining with the carbocyanine dye, 4Di-10Asp, which was applied onto the proximal nerve stump in vivo. The animals were sacrificed 3 days later and RGC counted in retinal whole mounts. Due to progressive degeneration following nerve transection the number of surviving RGC decreased to about 10% of the initially labelled population after 3 weeks, to about 8% after 5 weeks, and to about 5% after 7 weeks. Survival of axotomized cells could be prolonged using either of the neurotrophic factors: after 3 weeks a 2-3-fold increase in the number of viable RGC could be obtained compared to uninjected controls and to those which received injection of buffer. The prolonged survival effect vanished after 5 and 7 weeks, and no additive effect could be seen when combining brain-derived neurotrophic factor (BDNF) and ciliary neuronotrophic factor (CNTF) treatment. Morphometric analysis of labelled cells revealed that all neurotrophic factors supported predominantly large RGC with somal areas > 250 micron 2. In retinae from rats that survived the ON transection for several months, a characteristic population of axotomy-resistant RGC remained alive. Their few, very large, and often curled dendrites showed signs of placticity in the depleted inner nuclear layer of the adult rat retina. We conclude that the intraocular injection of CNTF, BDNF, and ScN-derived medium, which retard the process of lesion-induced RGC degeneration, may be successfully used as a subsidiary strategy in transplatation protocols. This would result in larger populations of RGC which can be recruited to regenerate their axons and provide a basis for functional recovery.

Growth factor-induced retinal regeneration in vivo

It is apparent from a number of studies that the RPE has a remarkable ability to regenerate neural retina. While retinal regeneration from the RPE has not been reported in adult vertebrates, with the exception of the newt, there is evidence that many vertebrate species have the ability to regenerate a new neural retina during the early development. Studies of retinal regeneration in the chicken embryo have provided some insight into the requirements for this process. Recent investigations using copolymer implants as an intraocular delivery system for growth factors have demonstrated that the state of differentiation of RPE cells in the stage 22-24 chicken embryo can be altered in vivo by specific growth factors, aFGF and bFGF. These results raise the distinct possibility that variations in the local production of FGFs and their receptors in the eye during development may, in part, regulate the pathway of differentiation of RPE and neural retina precursors. Further research on the role of FGFs and their receptors in retinal development and regeneration will not only contribute to our understanding of how the differentiated state is achieved and maintained but may provide a foundation for future attempts to develop methods of treatment for various degenerative and proliferative diseases of the eye.

Regeneration of adult rat CNS axons into peripheral nerve autografts: ultrastructural studies of the early stages of axonal sprouting and regenerative axonal growth

If one end of a segment of peripheral nerve is inserted into the brain or spinal cord, neuronal perikarya in the vicinity of the graft tip can be labelled with retrogradely transported tracers applied to the distal end of the graft several weeks later, showing that CNS axons can regenerate into and along such grafts. We have used transmission EM to examine some of the cellular responses that underlie this regenerative phenomenon, particularly its early stages. Segments of autologous peroneal or tibial nerve were inserted vertically into the thalamus of anaesthetized adult albino rats. The distal end of the graft was left beneath the scalp. Between five days and two months later the animals were killed and the brains prepared for ultrastructural study. Semi-thin and thin sections through the graft and surrounding brain were examined at two levels 6-7 mm apart in all animals: close to the tip of the graft in the thalamus (proximal graft) and at the top of the cerebral cortex (distal graft). In another series of animals with similar grafts, horseradish peroxidase was applied to the distal end of the graft 24-48 h before death. Examination by LM of appropriately processed serial coronal sections of the brains from these animals confirmed that up to several hundred neurons were retrogradely labelled in the thalamus, particularly in the thalamic reticular nucleus. Between five and 14 days after grafting, large numbers of tiny (0.05-0.20 microns diameter) nonmyelinated axonal profiles, considered to be axonal sprouts, were observed by EM within the narrow zone of abnormal thalamic parenchyma bordering the graft. The sprouts were much more numerous (commonly in large fascicles), smoother surfaced, and more rounded than nonmyelinated axons further from the graft or in corresponding areas on the contralateral side of animals with implants or in normal animals. At longer post-graft survival times, the number of such axons in the parenchyma around the graft declined. At five days, some axonal sprouts had entered the junctional zone between the brain and the graft. By eight days there were many sprouts in the junctional zone and some had penetrated the proximal graft to lie between its basal lamina-enclosed columns of Schwann cells, macrophages and myelin debris. Within the brain, sprouts were in contact predominantly with other sprouts but also with all types of glial cell.(ABSTRACT TRUNCATED AT 400 WORDS)

Nerve growth factor (NGF) receptors in a central nervous system glial cell line: upregulation by NGF and brain-derived neurotrophic factor

The neurotrophic proteins nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF) are related in their primary amino acid structures. In this study we investigated the extent to which the low-affinity NGF receptor (LNGFR) in C6 glioma cells can discriminate between the neurotrophins NGF and BDNF. LNGFR-immunoreactivity (IR) was studied in C6 cells treated for 16 hr with NGF (50 ng/ml) or BDNF (10 ng/ml), using immunogold labelling and electron microscopic morphometric analysis. The cells were exposed to the anti-NGFR antibody 192-IgG, followed by immunoglobulin conjugated with colloidal gold. Untreated C6 cells exhibited some surface gold label (positive LNGFR-IR). Cells treated with NGF or BDNF displayed significantly increased LNGFR-IR on all surfaces in terms of gold labeling, which was more pronounced in NGF-treated cells. LNGFR-IR was also localized in coated endocytotic vesicles, in smooth endoplasmic reticulum, and in secondary multivesicular lysosomes in neurotrophin-treated and untreated cells. The increase in LNGFR protein was further substantiated by a correspondingly higher content of LNGFR mRNA detected after 15 hr of either NGF or BDNF treatment. These results suggest that the LNGFR in glial cells can be upregulated by the structurally related neurotrophins NGF and BDNF.

Expression of nerve growth factor (NGF) receptors in the brain and retina of chick embryos: comparison with cholinergic development

The expression of nerve growth factor receptor (NGFR) transcripts was investigated with in situ hybridization techniques in the CNS of chick embryos from 3 days of incubation (E3) to 14 days posthatch (P14). The time course and distribution of NGFR expression was compared with the development of the cholinergic phenotype. Cholinergic properties were assessed by immunolabeling for choline acetyltransferase (ChAT) and histochemistry for acetylcholinesterase (AchE) activity. NGFR transcripts are expressed transiently in the inner plexiform layer and ganglion cell layer of the retina (E4-P1), neostriatum and hippocampus (E18), infundibular hypothalamus (E7-18), spiriform complex (E9-15), layers 2, 3 (E9-18), and 10 (E11-18) of the optic tectum, nucleus mesencephalicus profundus, pars ventralis (E9-18), parvicellular isthmic nucleus (E7-P1), magnocellular isthmic nucleus (E9-E18), nucleus semilunaris (E7-18), isthmo-optic nucleus (E7-P14), rostral motor nuclei (E5-18), developing cerebellum (E7-15), internal granule cell layer (E11-18) and Purkinje cell layer (E15-P14) of the cerebellar cortex, and the inferior olivary nucleus (E9-15). A small number of neuronal populations with embryonic expression of NGFR remain strongly NGFR-positive in the posthatch animal:habenular nuclei (labeled after E5), nucleus subrotundus (after E9), mesencephalic trigeminal nucleus (after E5), caudal parts of locus ceruleus and nucleus subceruleus (after E7), medullar reticular nuclei (after E11), and motor nuclei IX, X, and XII (after E9). The majority of neuronal populations with NGFR expression show cholinergic properties in development, and NGFR expression always precedes the onset of ChAT immunoreactivity. Postnatal expression of growth factor receptors is largely confined to neurons of the reticular type. NGFR expression in avian CNS nuclei differs from that in mammals. Early loss of NGFR expression in the cholinergic basal forebrain (which remains strongly NGFR positive in mammals) and persistent NGFR expression in parts of the avian locus ceruleus indicate changes of growth factor receptor expression and growth factor requirements in phylogeny. Knowledge of the time and distribution of NGFR expression in the chick embryo will facilitate the assessment of specific functions of NGF and NGF-like molecules in an embryonic model with easy access for experimental manipulations.(ABSTRACT TRUNCATED AT 400 WORDS)