Optic Nerve Fibre Counts and Retinal Ganglion Cell Counts During Development of Xenopus Laevis (Daudin)

Wilson, Margaret

doi:10.1113/expphysiol.1971.sp002110

Cited by 74 publications

(26 citation statements)

References 7 publications

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“…S2A) confirmed that ON shortening did not interfere with the normal addition of new myelinated axons, known to occur throughout the lifespan of X. laevis (17), or with the continued addition of myelinating oligodendrocytes in the ON during this time (Fig. S2B).…”

Section: Significancesupporting

confidence: 53%

Astrocytes phagocytose focal dystrophies from shortening myelin segments in the optic nerve of Xenopus laevis at metamorphosis

Mills

Davis

Bushong

et al. 2015

Proc. Natl. Acad. Sci. U.S.A.

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Oligodendrocytes can adapt to increases in axon diameter through the addition of membrane wraps to myelin segments. Here, we report that myelin segments can also decrease their length in response to optic nerve (ON) shortening during Xenopus laevis metamorphic remodeling. EM-based analyses revealed that myelin segment shortening is accomplished by focal myelin-axon detachments and protrusions from otherwise intact myelin segments. Astrocyte processes remove these focal myelin dystrophies using known phagocytic machinery, including the opsonin milk fat globule-EGF factor 8 (Mfge8) and the downstream effector ras-related C3 botulinum toxin substrate 1 (Rac1). By the end of metamorphic nerve shortening, one-quarter of all myelin in the ON is enwrapped or internalized by astrocytes. As opposed to the removal of degenerating myelin by macrophages, which is usually associated with axonal pathologies, astrocytes selectively remove large amounts of myelin without damaging axons during this developmental remodeling event.thyroid hormone | glia | lipid droplet | Mfge8 M yelin exists as regularly spaced segments that enable fast and efficient transfer of information across long distances through saltatory propagation of action potentials between nodes of Ranvier (1). The number, length, and thickness of individual segments vary with species and nervous system region (2). The proper thickness and length of myelin segments are likely established, at least in part, during the myelination process itself, which involves the dynamic elongation, shortening, and removal of individual segments (3, 4). However, once established, some myelin segments must be modified further to accommodate axonal growth. Developmental increases in axon diameter are coupled to the addition of membrane wraps to myelin segments, thereby maintaining a near-linear relationship between axon caliber and myelin thickness (5, 6). In the peripheral nervous system, Schwann cell myelin segments can also elongate in proportion to nerve length, increasing internodal distances by as much as a factor of four (3, 7). The regulation of myelin on axons is essential for the proper function of the vertebrate nervous system, because both hypomyelination and hypermyelination lead to neuropathy (8). However, the mechanisms involved in myelin segment plasticity have remained poorly understood, in part, because of the difficulty in studying a process that occurs in mammals during a protracted period as the animals mature (2).During metamorphic remodeling of the head in Xenopus laevis, the optic nerve (ON) and its associated axons rapidly shorten in length (9). A description of this process (10) noted abnormally folded myelin on axons and membranous material inside glial cells, suggesting that myelin might be remodeling, thereby providing a model system in which to study myelin plasticity. The current study set out to determine how myelin segments remodel during ON shortening. Results The ON and Its Myelinated Axons Widen and Shorten During X. laevisMetamorphosis. The head of ...

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Section: Significancesupporting

confidence: 53%

Astrocytes phagocytose focal dystrophies from shortening myelin segments in the optic nerve of Xenopus laevis at metamorphosis

Mills

Davis

Bushong

et al. 2015

Proc. Natl. Acad. Sci. U.S.A.

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“…However, whether this weak retinal specialisation is also functionally comparable, re mains unknown. Xenopus relies minimally on vision for survival and possesses only 52-59 x 104 fibres within its optic nerve [Wilson, 1971], Halophryne pos sesses 45 x 104 cells in the ganglion cell layer which is low in comparison to other teleosts, especially consid- Fig. 4.…”

Section: Australian Frogfishmentioning

confidence: 99%

Retinal Topography in Reef Teleosts

1988

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The retinal ganglion cell layer of five species of teleosts has been studied from Nissl-stained whole-mounts and the distribution of neuronal elements determined quantitatively. Isodensity contour maps of neurons in the ganglion cell layer revealed areas of high density (areae centrales) predominantly in the temporal retina, but other areae were also found in the nasal and dorso-nasal retina. Neuronal densities within the ganglion cell layer at the areae centrales ranged from 0.4 x 10⁴ to 4.7 x 10⁴ cells/mm². Species that were found to lack a horizontal streak of high ganglion cell density appear to be those whose behaviour suggests they possess an interrupted view of the sand-water horizon and are ''enclosed'' species. Concentric density contours around an area centralis seem to be associated with enclosed environments. The relationship between retinal topography and niche is also discussed.

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“…It has been observed that the total number of fibres does not always correspond to the number of cells in the retina ganglion layer. In fact, the retinal ganglion cells are 27% more than the total number of fibres in the optic nerve in Xenopus laevis (Wilson, 1971), 22% more than in Bolitoglossa subpalmata, a plethodontid salamander (Linke et al, 1986), and over 39% more than in Notophtalmus viridescens (Ball & Dickson, 1983). The 'excess cells' are amacrine cells.…”

Section: Introductionmentioning

confidence: 99%

“…In X. laevis, it has been observed that the total number of fibres, at six months, is clearly greater than in the adult (58993 versus 51987), while the 3 396 myelinated fibres in the young animal increase to 7 235 in the adult, as a result of progressive myelinization (Wilson, 1971;Dunlop & Beazley, 1984). The diameter of the myelinated fibres is between 0.3 um and 3.0 um, while that of unmyelinated fibres is in the 0.1-2.0 pm range, with a prevalence of 0.2 um and 0.4 pm fibres.…”

Section: Introductionmentioning

confidence: 99%

A structural study of the optic nerve of Hydromantes genei

Spiga

Sabatini

Siddi

et al. 2000

Italian Journal of Zoology

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The structure of the optic nerve of Hydromantes genei, was investigated by confocal laser scanning microscopy and by the CajalDe Castro method. This nerve appears to be composed of unmyelinated fibres, which is a rare case in amphibians. In view of this and the fact that it contains a relatively small number of nervous fibres, the optic nerve of H. genei, in comparison with other species of Plethodontidae, can be considered a structure with a low level of complication.

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Optic Nerve Fibre Counts and Retinal Ganglion Cell Counts During Development of Xenopus Laevis (Daudin)

Cited by 74 publications

References 7 publications

Astrocytes phagocytose focal dystrophies from shortening myelin segments in the optic nerve of Xenopus laevis at metamorphosis

Astrocytes phagocytose focal dystrophies from shortening myelin segments in the optic nerve of Xenopus laevis at metamorphosis

Retinal Topography in Reef Teleosts

A structural study of the optic nerve of Hydromantes genei

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