Development of the optic nerve in Xenopus laevis

Development ◽  
1982 ◽  
Vol 72 (1) ◽  
pp. 251-267
Author(s):  
Charles Cima ◽  
Philip Grant
Keyword(s):  
Electron Microscopy ◽  
Optic Nerve ◽  
Xenopus Laevis ◽  
Light And Electron Microscopy ◽  
Ependymal Cells ◽  
Glia Limitans ◽  
Nerve Development ◽  
Myelinated Fibres ◽  
Cytoplasmic Processes ◽  
Time Of Origin

We studied the time of origin, development and location of glial elements in the developing optic nerve of Xenopus with light and electron microscopy. The first cells acting as a primitive glia are ependymal cells lying dorsal to the chiasmatic optic nerve (CON) at Nieuwkoop & Faber (1956) NF stage 39. Later (stage 47/48), immature astrocyte cell bodies migrate from the periphery of the middle optic nerve (MON) into the central fibre mass along cytoplasmic processes extending from the outer glia limitans. Shortly thereafter, oligodendrocyte cell bodies appear in the centre of the fibre mass and myelination begins, first in the middle of the MON, spreading from the centre distally towards the chiasm and proximally to the retina. In late tadpoles myelinated fibres appear first in the CON then in the retinal optic nerve (RON) increasing markedly in juveniles and adults. Segment-specific patterns of glia and myelination appear during optic nerve development. During metamorphic climax, the ptic nerve shortens (Cullen & Webster, 1979), a process involving myelin and axon remodelling primarily in the MON. Neither the profound changes during metamorphosis, nor the processes of gliogenesis and myelination significantly alter the underlying chronotopic ordering in the tadpole nerve. In juvenile and adult optic nerves, however, as myelination and gliogenesis increase, and as more axons mature and grow in diameter, the dorsoventral chronotopic arrangement of axons becomes less apparent.

Development of the optic nerve in Xenopus laevis

Development ◽  
1982 ◽  
Vol 72 (1) ◽  
pp. 225-249
Author(s):  
Charles Cima ◽  
Philip Grant
Keyword(s):  
Electron Microscopy ◽  
Optic Nerve ◽  
Xenopus Laevis ◽  
Ganglion Cell ◽  
Light And Electron Microscopy ◽  
Near Neighbour ◽  
Dorsoventral Axis ◽  
Fibre Size ◽  
Autoradiographic Analysis ◽  
Young Old

Development of the Xenopus laevis optic nerve was studied by light and electron microscopy from embryonic stage 26, before the retina has formed, to juveniles, 8 months post-metamorphic. Low-power EM photographs of sections through the retinal optic nerve (RON), middle optic nerve (MON) and chiasmatic optic nerve (CON) were prepared at different stages and the areas containing large axons (0·5 μm) were traced in optic nerve reconstructions. Ordering of fibre size along a dorsoventral axis was noted in the embryonic nerve, and this pattern persisted throughout development. Most large fibres, myelinated and unmyelinated, occupy an eccentric dorsocentral position in the MON while small axons are seen in a ventral peripheral crescent. In the CON, the dorsal one third to one half is occupied by large fibres while the ventral CON contains small fibres exclusively. If, as assumed, large axons are older than small axons (0·1–0·3 μm), then patterns of large and small axons along the nerve might reveal a chronotopic fibre ordering. Chronotopic ordering was confirmed by autoradiographic analysis of the distribution of old, labelled fibres and young, unlabelled newly arriving fibres in optic nerves between stage 51 and 57. The young—old labelling pattern corresponds to the small and large axon patterns respectively, in all sections of the optic nerve. Chronotopic ordering of fibres in the developing optic nerve can be explained, in part, by the dorsoventral asymmetric marginal growth of the developing retina and the phenomenon of fibre following as ganglion cell axons join near neighbour fascicles in the retina, converge at the optic disc and grow through the optic nerve.

Fine Structure of the Eye of a Nudibranch Mollusc, Hermissenda Crassicornis

1967 ◽  
Vol 2 (3) ◽  
pp. 349-358
Author(s):  
R. M. EAKIN ◽  
JANE A. WESTFALL ◽  
M. J. DENNIS
Keyword(s):  
Electron Microscopy ◽  
Fine Structure ◽  
Optic Nerve ◽  
Light And Electron Microscopy ◽  
The Other ◽  
Sensory Cells ◽  
Nerve Fibres ◽  
Supporting Cells ◽  
Small Bodies ◽  
Receptor Cells

The eye of a nudibranch, Hermissenda crassicornis, was studied by light and electron microscopy. Three kinds of cells were observed: large sensory cells, each bearing at one end an array of microvilli (rhabdomere) and at the other end an axon which leaves the eye by the optic nerve; large pigmented supporting cells; and small epithelial cells, mostly corneal. There are five sensory cells, and the same number of nerve fibres in the optic nerve. The receptor cells contain an abundance of small vesicles, 600-800 Å in diameter. The lens is a spheroidal mass of osmiophilic, finely granular material. A basal lamina and a capsule of connective tissue enclose the eye. In some animals the eye is ‘infected’ with very small bodies, 4-5 µ in diameter, thought to be symbionts.

The effects of high hydrostatic pressure on microfilaments and microtubules in Xenopus laevis

Development ◽  
1978 ◽  
Vol 44 (1) ◽  
pp. 281-295
Author(s):  
Paul-Emil Messier ◽  
C. Seguin
Keyword(s):  
Electron Microscopy ◽  
Hydrostatic Pressure ◽  
Xenopus Laevis ◽  
Cell Elongation ◽  
High Hydrostatic Pressure ◽  
Light And Electron Microscopy ◽  
Duration Of Treatment ◽  
Neuroepithelial Cells ◽  
Exerted Pressure ◽  
Xenopus Laevis Embryos

Xenopus laevis embryos of stages 14–20 were subjected, for periods of 5–330 min, to hydrostatic pressures ranging from 500 to 10000 psi. The specimens were fixed under corresponding pressures and their neuroepithelium was studied under light and electron microscopy. A pressure of 3000 psi, maintained for as long as 180 min, did not inhibit neurulation though it induced slight deformities of the neuroepithelium. A pressure of 4000 psi, applied for 180 min, disrupted the apical ring of microfilaments and blocked neurulation. The cells lost their dissymmetry. The effect was reversible. Lengthening the duration of treatment to 330 min caused the neuroepithelial cells to loose their microtubules and to become round. This situation was not reversible. Our results indicated that microfilaments are more sensitive than microtubules, that both organelles became increasingly sensitive as the exerted pressure was increased and that microtubules of older embryos exhibited a better resistance. Finally, we showed a correlation between the presence of microfilaments and the constricted state of the cellular apices and a relationship between the presence of microtubules and cell elongation.

Ultrastructure of region of a low safety factor in inhomogeneous giant axon of the cockroach

1976 ◽  
Vol 39 (4) ◽  
pp. 900-908 ◽  
Author(s):  
M. Castel ◽  
M. E. Spira ◽  
I. Parnas ◽  
Y. Yarom
Keyword(s):  
Electron Microscopy ◽  
Glial Cells ◽  
Extracellular Space ◽  
Light And Electron Microscopy ◽  
Giant Axon ◽  
Serial Sections ◽  
Giant Axons ◽  
Chemical Synapses ◽  
Cytoplasmic Processes ◽  
Periaxonal Space

1. The structure of the ventral giant axons of the cockroach at the level of ganglion T3 was studied by means of light and electron microscopy. 2. From serial sections and cobalt injections, the axons diameter was found to range between 40 and 60 mum at the caudal end of ganglion T3; toward the center of T3 they narrow to 20-40 mum, and again expand to 30-45 mum anteriorly in ganglion T3. 3. Each giant axon sends off several branches, 1-15 mum in diameter, into the neuropil. The giant axons and the bases of their branches are enveloped by cytoplasmic processes of glial cells. The periaxonal space is about 100-200 A. 4. Distally the branches are devoid of glial envelopes and the extracellular space between the branches and other axonal profiles is about 200 A. Terminals with presumptive chemical synapses on the giant axon branches were found. Clear vesicles, 300-400 A in diameter, are seen clustered together. The width of the supposedly synaptic gap is about 100 A. 5. In some areas the branches and other axonal profiles form close appositions.

The migration of presumptive primordial germ cells through the endodermal cell mass in Xenopus laevis: A light and electron microscopic study

Development ◽  
1980 ◽  
Vol 59 (1) ◽  
pp. 1-17
Author(s):  
Michiko Kamimura ◽  
Minoru Kotani ◽  
Kenzo Yamagata
Keyword(s):  
Xenopus Laevis ◽  
Germ Cells ◽  
Intercellular Space ◽  
Primordial Germ Cells ◽  
Cell Mass ◽  
Light And Electron Microscopy ◽  
Morphological Characteristics ◽  
Light Microscope Level ◽  
Cytoplasmic Processes ◽  
Germinal Plasm

Presumptive primordial germ cells (pPGCs) were examined during migration from their deep endodermal position to the endodermal crest in Xenopus laevis, using light and electron microscopy with Epon sections, and several morphological characteristics of pPGCs, associated with their migration, were revealed. pPGCs displayed polymorphism, with smooth contours. The intercellular space around the pPGCs was large and variable in width and cytoplasmic processes from pPGCs were occasionally observed in it. It was shown quantitatively that pPGCs at the migratory stage had a tendency to move with the leading end, towards which the nucleus was localized, dragging the germinal plasm behind. These polarized pPGCs were frequently associated with large intercellular spaces, both at their leading and trailing ends. Cytoplasmic processes of polarizing pPGCs found in the large intercellular space at the leading end were conspicuous. Ultrastructurally, the nuclei of pPGCs were euchromatic, and the nucleolus was prominent. The germinal plasm at the light microscope level corresponded to the cytoplasmic area near the nucleus where a large number of mitochondria with well-developed cristae and most of the other organelles were aggregated. Centrioles and centriole-associated microtubules observed in the aggregate were thought to be important structures responsible for the cell polarization mentioned above. It was demonstrated quantitatively that the size of mitochondria in pPGCs was larger on average than that of mitochondria in neighbouring somatic endodermal cells. Numerous irregularly shaped small yolk platelets characterized pPGCs. These ultrastructural features suggested that pPGCs were in an activated metabolic state. It was concluded that the migration of pPGCs was attributable to active movement with high cell metabolism, causing the formation of cell processes and intracellular polarization.

scholarly journals Comparative morphology of the rat optic nerve using light and electron microscopy

2010 ◽  
Vol 24 (S1) ◽  
Author(s):  
Joshua Kyle Duncan ◽  
Bryan Anderson ◽  
Jason A. Kaufman ◽  
Andrew Iwaniuk ◽  
T. Bucky Jones ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Optic Nerve ◽  
Light And Electron Microscopy ◽  
Comparative Morphology

Haemangioblastoma of the optic nerve. Case report with study by light and electron microscopy

Pathology ◽  
1981 ◽  
Vol 13 (2) ◽  
pp. 357-364 ◽  
Author(s):  
Robert P. Eckstein ◽  
E.J. Wills ◽  
J.N. Segelov
Keyword(s):  
Electron Microscopy ◽  
Case Report ◽  
Optic Nerve ◽  
Light And Electron Microscopy

Fine structure of the pecten oculi of the mallard (Anas platyrhynchos)

1990 ◽  
Vol 68 (3) ◽  
pp. 427-432 ◽  
Author(s):  
Charlie R. Braekevelt
Keyword(s):  
Electron Microscopy ◽  
Fine Structure ◽  
Endothelial Cell ◽  
Optic Nerve ◽  
Blood Vessels ◽  
Anas Platyrhynchos ◽  
Light And Electron Microscopy ◽  
Mallard Duck ◽  
Pecten Oculi ◽  
Region Form

The pecten oculi of the mallard duck (Anas platyrhynchos) has been examined by light and electron microscopy. In this species, the pecten is of the pleated type and 12–14 accordion folds are joined apically by a heavily pigmented bridge of tissue which holds the pecten in a fanlike shape, widest at the base. It is situated over the optic nerve head and extends out into the vitreous. The entire pecten is enclosed by a fine basal lamina and hyalocytes are often present on its outer surface. Within each fold are numerous capillaries, larger blood vessels, and melanocytes. The capillaries are surrounded by thick fibrillar basal laminae which often contain pericytes. These capillaries display extensive microfolds on both the luminal and abluminal borders. The endothelial cell bodies are extremely thin, with most organelles present in a paranuclear location. The melanocytes, which are most plentiful in the bridge region, form an incomplete sheath around the capillaries and other blood vessels. The morphology of the pecten in the mallard is indicative of a heavy involvement in the transport of materials.

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