Embryonic Ganglion Cells Research Articles

Conformal geometry of the retinal nerve fiber layer

The nerve fiber layer of the human retina is made up of the retinal segments of ganglion cell axons. Its geometry can be described mathematically as a fibration of a 2D domain: a partition of a certain region into smooth curves. Here, we present a simple family of curves that closely models the observed geometry of the nerve fiber layer. For each retina, the pattern depends on 2 parameters, A and B: A computer program determines A and B for a given retina and the theory matches the retina with a standard deviation of approximately 6-8 degrees . These particular curves turn out to be the curves that would be generated if the growing ganglion cell axon tip moved down a gradient toward a source of diffusible neuroattractant at the disk and away from a weaker macular diffusible repellant. Thus, this model provides morphological evidence that diffusible substances provide positional information to the embryonic ganglion cell axons in finding their way to the optic nerve head.

Ganglion cell regeneration following whole‐retina destruction in zebrafish

The retinas of adult teleost fish can regenerate neurons following injury. The current study provides the first documentation of functional whole retina regeneration in the zebrafish, Danio rerio, following intraocular injection of the cytotoxin, ouabain. Loss and replacement of laminated retinal tissue was monitored by analysis of cell death and cell proliferation, and by analysis of retina-specific gene expression patterns. The spatiotemporal process of retinal ganglion cell (RGC) regeneration was followed through the use of selective markers, and was found to largely recapitulate the spatiotemporal process of embryonic ganglion cell neurogenesis, over a more protracted time frame. However, the re-expression of some ganglion cell markers was not observed. The growth and pathfinding of ganglion cell axons was evaluated by measurement of the optic nerve head (ONH), and the restoration of normal ONH size was found to correspond to the time of recovery of two visually-mediated behaviors. However, some abnormalities were noted, including overproduction of RGCs, and progressive and excessive growth of the ONH at longer recovery times. This model system for whole-retina regeneration has provided an informative view of the regenerative process.

Association of Optic Nerve Hypoplasia With Mitochondrial Cytopathies

Ocular complications are common in the mitochondrial cytopathies and include optic atrophy and retinal degeneration. We retrospectively reviewed 80 patients with nonsyndromic mitochondrial cytopathies (ie, not Kearns-Sayre syndrome, myoclonus epilepsy associated with ragged red fibers [MERRF], mitochondrial encephalomyopathy, lactic acidosis, and strokelike episodes [MELAS], neuropathy ataxia and retinitis pigmentosa, Leigh disease, maternally inherited diabetes and deafness, and myoneurogastrointestinal disorder and encephalopathy) and found 10 cases of optic nerve hypoplasia. Optic nerve hypoplasia occurs in at least 12% of patients with nonsyndromic mitochondrial cytopathies. Although the exact pathogenesis of optic nerve hypoplasia in the context of mitochondrial cytopathy is unknown, we postulate that it is the result of excessive apoptosis during embryonic ganglion cell and/or axonal development from abnormal mitochondrial function and cellular energy metabolism.

Nerve fibre regeneration across the peripheral-central transitional zone.

Neurons cannot negotiate an elongation across the peripheral (PNS)-central nervous system (CNS) transitional zone and grow into or out of the spinal cord in the mature mammal. The astrocytic rich CNS part of the spinal nerve root is most effective in preventing regeneration even of nerve fibres from transplanted embryonic ganglion cells. Regeneration of severed nerve fibres into the spinal cord occurs when the transition zone is absent as in the immature animal. Before the establishment of a transition zone there is also new growth of neuronal processes from dorsal horn neurons distally to the injured dorsal root. Thus the experimental strategy to reestablish spinal cord to peripheral nerve connectivity has been to delete the transitional region and implant severed ventral or dorsal roots into the spinal cord. Dorsal root implantation resulted in reestablished afferent connectivity by new neuronal processes from secondary sensory neurons in the dorsal horn of the spinal cord extending into the PNS. The ability for plasticity in these cells allowed for a concurrent retention of their original rostral projection. Ventral root implantation into the spinal cord corrected deficit motor function. In a long series of experiments performed in different species, the functional restitution was demonstrated to depend on an initial regrowth of motor neuron axons through spinal cord tissue (CNS). These findings have led to the design of a new surgical strategy in cases of traumatic spinal nerve root injuries.

Ligand- and voltage-gated ion channels are expressed by embryonic mouse retinal neurones.

The present study was intended to investigate whether voltage- and ligand-activated ion channels are expressed during prenatal development by neurones located in the ganglion cell layer of the mammalian retina. Whole cell patch clamp recordings from presumed mouse retinal ganglion cells revealed the expression of Na+, K+ and Ca2+ channels, predominantly of the low-voltage-activated type. Using local application of transmitter substances we further demonstrated that these cells are endowed with glutamate receptors of the N-methyl-D-aspartate (NMDA) and non-NMDA type as well as nicotinic acetylcholine, gamma-amino-butyric acid (GABA)A and glycine receptors. Voltage-gated conductances probably underlie spontaneous action potential generation by embryonic ganglion cells. The early expression of transmitter-gated ion channels indicates important functions of these channels in cell differentiation processes.

Phosphorylated Tau Epitope of Alzheimer's Disease Is Coupled to Axon Development in the Avian Central Nervous System

The monoclonal antibody PHF-1 recognizes phosphorylated tau isoforms present in paired helical filaments of Alzheimer's disease. We have found that PHF-1 immunoreactivity is present in chick brain, which expresses three major PHF-1-reactive proteins at the same molecular weights seen in humans. The developmental pattern of expression suggests a functional role in differentiation, rather than in programmed nerve cell death. Expression of PHF-1 immunoreactivity in developing retina was highly cell selective, showing robust staining of ganglion cells, the only long-axon neuron of the seven major retina cell types. The majority of ganglion cells were PHF-1 positive. The developmental window of expression extended at least from E6 through P0, well outside the period of embryonic ganglion cell death. Mature cells did not show PHF-1 immunoreactivity. In the embryo, staining was particularly robust in ganglion cell axons (optic fiber layer), and association of PHF-1 reactivity with axonal tracts also was seen in developing forebrain. PHF-1 polarization occurred at ages when staining with polyclonal anti-tau did not show axonal selectivity. Similarly, in cell cultures, PHF-1 immunoreactivity became localized to single neurites, but polyclonal anti-tau did not. These results indicate that, rather than being associated with cell degeneration, PHF-1 immunoreactivity in the developing nervous system is associated with early stages of axon information, both in vivo and in vitro. Therefore, expression of PHF-1 immunoreactive proteins in Alzheimer's disease suggests that paired helical filament formation might be triggered by mechanisms related to axon regeneration.

Transient expression of somatostatin peptide is a widespread feature of developing sensory and sympathetic neurons in the embryonic rat.

Previous studies from this and other laboratories demonstrated that many embryonic sensory ganglion cells in the rat transiently express the catecholamine synthesizing enzyme tyrosine hydroxylase (TH), a trait not expressed by most mature sensory neurons. We, therefore, sought to determine whether transient expression was uniquely associated with catecholaminergic traits, or, alternatively, whether embryonic ganglion cells transiently expressed peptidergic properties as well. Of the four peptides examined (somatostatin [somatotropin release inhibiting factor] (SRIF), galanin (Gal), calcitonin gene-related peptide (CGRP), and substance P (SP)), only SRIF was found to be transiently expressed during early stages of sensory gangliogenesis. Surprisingly, SRIF immunoreactivity was observed in virtually all cranial and spinal sensory ganglion cells on embryonic day (E) 12.5. In addition to perikaryal labeling, intense SRIF immunoreactivity was also observed in the central and peripheral processes of E12.5 sensory neurons, suggesting the peptide may be released from nerve endings. The time course of SRIF appearance in cranial ganglion cells paralleled that previously described for TH, and double-labeling studies revealed extensive co-localization of these two phenotypes. By E16.5, however, the number of neurons expressing SRIF had diminished markedly, indicating that SRIF is only transiently expressed by most sensory neurons during early stages of ganglion development. An unexpected finding was that transient expression of SRIF is also a prominent feature of sympathetic ganglion cells; however, the temporal pattern of staining in the sympathetic and sensory ganglia differed substantially. Whereas virtually no SRIF staining was observed in E12.5 sympathetics, the vast majority of cells in the E16.5 superior cervical ganglion (SCG) were labeled. This contrasted sharply with the adult SCG, in which only low levels of SRIF expression were found. These findings demonstrate that SRIF peptide is transiently expressed at high levels in peripheral sensory and sympathetic neurons during embryogenesis. The time course and widespread distribution of SRIF expression indicates that the peptide may play a role in early stages of ganglion cell growth and development. Moreover, these data, in conjunction with previous studies demonstrating SRIF immunoreactivity in developing central neurons, suggest that transient expression of this peptide is a common property of diverse neuronal cell types.

Sodium- and Calcium-Dependent Excitability of Embryonic Leech Ganglion Cells in Culture

ABSTRACT Voltage-dependent Na+ and Ca2+ inward currents underlying the action potential in cultured embryonic ganglion cells of the leech Hirudo medicinalis have been investigated using the gigaseal whole-cell current or voltage-clamp technique. Dissociated ganglion cells were isolated from 7-to 14-day-old embryos, and maintained in primary culture for up to 5 days. More than 95 % of the cultured cells had voltage-dependent K+ currents and about 75 % of the cells had voltagedependent inward currents. Action potentials of 60mV amplitude and 4 ms duration, similar to those in embryonic nerve cells in vivo, could be recorded. Three types of inward currents occurred in these cells: (1) an initial Na+ current, which activated and inactivated rapidly; (2) a second Na+ current, which activated slowly and persisted during membrane depolarization, showing very little inactivation, and (3) a Ca2+-dependent inward current. Both types of Na+ currents were resistant to tetrodotoxin (TTX, 0.2–5 μmoll-1). The Ca2+ current was also carried by Ba2+, and was blocked by cobalt and cadmium. The fast Na+ current was first expressed in cells from 8-day-old embryos, 1 day earlier than the Ca2+ current. Between days 8 and 14 the density of the fast Na+ current increased from 22±3 to 51±6μAcm-2 (±S.D., N= 11), while the Ca2+ current grew from 10μAcm-2 (N=2) to 15±4μAcm-2 (N =10) during this time.

Glycoconjugates of the Avian Eye: The Development and Maturation of the Neural Retina as Visualized by Lectin Binding

The distribution of binding sites for four rhodamine-conjugated lectins has been examined in paraffin-embedded tissue sections of the developing and mature avian neural retina. The method of fixation employed here (95% ethanol:glacial acetic acid) is shown to conserve substantially more in vivo labeled 3H-glycoprotein or 3H-ganglioside than fixation with either 3.7% formaldehyde or 2% glutaraldehyde. Each lectin was shown to be optimally active by direct hemagglutination and inhibitable by the appropriate hapten in the cytochemical assay. Staining with wheat germ agglutinin (→N-acetylglucosamine) occurs predominantly to each of the anuclear retinal layers and progressively disappears from each of the nuclear layers. By adulthood, the inner nuclear layer is stained in a gradient which is highest adjacent to the inner nuclear layer while the nuclear layers are virtually unstained. Although similar to wheat germ agglutinin, staining with concanavalin A (→mannose) is less intense and persists in the adult nuclear layers. Dolichos biflorus agglutinin (→N-acetylgalactosamine) predominantly stains the embryonic ganglion cell layer. With development, this lectin demonstrates profound differences between the major cell types of the inner nuclear layer and the inner (negative) and outer (positive) plexiform layers. Differences between the principal synaptic layers are further accentuated by Ulex europaeus agglutinin I (→fucose): Binding sites are virtually absent from the 12th day embryonic retina, but are abundant throughout the retina by the 18 th day and persist after hatching. However, in the adult retina staining persists in the outer plexiform layer but is lost from the inner plexiform and nerve fiber layers. In contrast to Dolichos biflorus agglutinin, Ulex europaeus agglutinin I stains the inner nuclear layer uniformly. Temporal differences in the characteristic lectin binding patterns exhibited by each of the major nuclear and anuclear layers of the developing avian neural retina are thus documented.

Tumor promoter modulation of epidermal growth factor- and nerve growth factor-induced adhesion and growth factor binding of PC-12 pheochromocytoma cells.

Nerve growth factor (NGF) has previously been shown to increase the rate of adhesion of PC-12 pheochromocytoma cells to cell culture dishes. This increase in the rate of adhesion was postulated to be important in NGF-mediated neurite outgrowth. We now report that epidermal growth factor (EGF) is also able to increase the rate of adhesion of PC-12 cells to cell culture dishes, but does not elicit neurite outgrowth. The dose-response curve for EGF is bell-shaped, in contrast to the more classically shaped dose-response curve obtained with NGF. Tetradecanoyl-phorbol-acetate (TPA), a potent tumor promoter, blocks the EGF-induced increase in adhesion rate of PC-12 cells, but does not alter the NGF-induced increase in adhesion rate. TPA shifts the EGF bindings curve to the right for PC-12 cells, but does not alter maximal EGF binding at saturating concentrations of EGF. The binding of NGF to PC-12 cells is not affected by TPA. NGF-induced neurite formation by PC-12 cells is unaffected by TPA, in contrast to the previously reported delay of neurite outgrowth of serum-deprived neuroblastoma cells and NGF-exposed chick embryonic ganglia cells. NGF and EGF both cause a decrease in the number of short microvilli and an increase in the number of long microvilli on PC-12 cells. TPA blocks the decrease in the number of short microvilli in EGF-treated cells, but not in NGF-treated cells. Long microvilli formation is blocked by TPA in both conditions, suggesting the latter are not involved in the increased adhesion rates.