Changes in fiber organization within the chiasmatic region of mammals

1992 ◽  
Vol 9 (6) ◽  
pp. 527-533 ◽  
Author(s):  
Benjamin E. Reese ◽  
Gary E. Baker
Keyword(s):  
Optic Nerve ◽  
Optic Tract ◽  
Visual Pathway ◽  
Optic Chiasm ◽  
Retinal Surface ◽  
Classical View ◽  
The Difference ◽  
Fiber Organization ◽  
Sensory Surface ◽  
Retinotopic Map

AbstractIntroductionClassical views of the optic chiasm maintain four propositions about the retinofugal pathways: (1) each optic nerve contains a retinotopic representation of its respective retinal surface; (2) this retinotopic map in the nerve is the basis for the subsequent segregation of the decussating from the non-decussating fibers; (3) this retinotopy in the nerve is also the basis for the presence of retinotopy found within the half-retinal maps in the optic tracts; and (4) the half-retinal maps from each optic nerve are brought together within the chiasm to yield a unified, binocularly congruent, map in the optic tract (Brodal, 1969; DukeElder, 1961; Polyak, 1957; Wolff, 1940). The appeal of this classical view is in its simplicity, based on the assumption that the retinofugal pathway should replicate the sensory surface along its course. We now know that each of these four propositions is incorrect, and that the error is not one simply of degree or extent (Guillery, 1982, 1991). Rather, the above description of the visual pathway is fundamentally flawed because it has failed to take into account the constraints under which the pathway develops. We shall first consider the evidence for rejecting the classical view, from recent studies on the organization of the retinofugal pathway in adult animals and on the development of that organization. We shall then describe three transformations in the fiber order which all occur in the chiasmatic region, two of which were only recently recognized, and for which we must account.Observations from adult organizationThe difference in the fiber order in the optic nerve and tract

The Optic Chiasm of Australian Marsupials

1995 ◽  
Vol 43 (5) ◽  
pp. 467
Author(s):  
AM Harman
Keyword(s):  
Nervous System ◽  
Optic Nerve ◽  
Central Region ◽  
Optic Tract ◽  
Optic Chiasm ◽  
Lateral Part ◽  
Guidance Cues ◽  
Optic Axons ◽  
The Brain

The optic chiasm of mammals is the region of the nervous system in which optic axons have a choice of route, either they enter the optic tract on the same side of the brain or they cross the chiasm and enter the opposite optic tract. in eutherian (placental) mammals, axons approach the midline of the chiasm and then either continue across the chiasm or turn back to enter the tract on the same side of the brain. The midline of the chiasm provides guidance cues that repel uncrossed but not crossed axons. However, it has recently been shown that in a marsupial, the quokka wallaby, axons destined to stay on the same side of the brain remain in the lateral part of the optic nerve and chiasm and never approach the midline. The structure of the chiasm reflects this partitioning of axons with different routes by having a tripartite structure. The two lateral regions contain only uncrossed axons in rostral chiasmatic regions and the central region contains only crossed axons. Therefore, axons passing through the chiasm of this species must use guidance cues that differ from those of eutherian mammals. Here I show that the chiasms of species of both diprotodont and polyprotodont Australian marsupials have a similar tripartite structure and that uncrossed axons are confined to lateral regions. It seems likely, therefore, that the chiasm of marsupials has fundamental differences in structure and optic axon trajectory compared with that of eutherian mammals studied to date.

The Pax protein Noi is required for commissural axon pathway formation in the rostral forebrain

Development ◽  
1997 ◽  
Vol 124 (12) ◽  
pp. 2397-2408 ◽  
Author(s):  
R. Macdonald ◽  
J. Scholes ◽  
U. Strahle ◽  
C. Brennan ◽  
N. Holder ◽  
...  
Keyword(s):  
Optic Nerve ◽  
Glial Cells ◽  
Anterior Commissure ◽  
Optic Tract ◽  
Optic Chiasm ◽  
Commissural Axons ◽  
Optic Axons ◽  
Pathway Formation ◽  
Pax Family ◽  
Choroid Fissure

No-isthmus (Noi) is a member of the zebrafish Pax family of transcriptional regulators that is expressed in restricted domains of the developing CNS. In the developing eye and optic nerve, the Noi+ cells are primitive glial cells that line the choroid fissure and optic stalk/nerve to its junction with the optic tract. This pattern of Noi expression is retained in the adult, defining the optic nerve astroglia, which wrap the left and right nerves separately at the midline, thus forming the bodily crossed optic chiasm found in fish. In embryos carrying mutations in the noi gene, the choroid fissure fails to close, glial cells of the optic nerve fail to differentiate and optic axons exhibit abnormal trajectories exiting the eye and at the midline of the diencephalon. Optic axons select inappropriate pathways into the contralateral optic nerve, rostrally towards the anterior commissure and along the ipsilateral optic tract. Noi+ cells also border the pathway of axons in the postoptic commissure, which is located adjacent to the optic chiasm. These postoptic commissural axons are defasciculated and also exhibit pathfinding defects in noi- embryos. These results indicate that Noi is required in cells that line the pathways taken by optic and non-optic commissural axons for guidance across the midline of the diencephalon. We find that expression of two members of the Netrin family of axon guidance molecules and the signalling protein Sonic hedgehog is disturbed in noi- embryos, whereas several members of the Eph family of receptors and ligands show no obvious alterations in expression at the diencephalic midline.

Centrifugal fibres in the avian visual system

1963 ◽  
Vol 158 (971) ◽  
pp. 232-252 ◽  
Keyword(s):  
Optic Nerve ◽  
Bipolar Cell ◽  
Ganglion Cell Layer ◽  
Cell Layer ◽  
Optic Tract ◽  
Amacrine Cells ◽  
Visual Pathway ◽  
Avian Visual System ◽  
Nauta Method ◽  
Number Of Cells

A study has been made of the origin and course of the centrifugal fibres in the visual pathway of the pigeon using the Nauta method. Lesions in the mid-brain involving the isthmo-optic nucleus result in fibre degeneration which can be traced through the isthmo-optic tract to the chiasma and thence into the contralateral optic nerve and retina. In the retin a severe degeneration is found throughout the optic nerve layer, and occasional degenerating fibres can be traced through the ganglion cell layer to the inner aspect of the bipolar cell layer. Here they terminate in endings similar to those described by Cajal (1889) and Dogiel (1895) in relation to amacrine cells. The projection to the retina is completely crossed. Counts of the number of cells in the isthmo-optic nucleus indicate that the number of centrifugal fibres is approximately 10000; they form 1 % of the total number of fibres in the optic nerve. The isthmo-optic nucleus receives afferents from the tectum, and in this projection there would appear to be a well-defined organization.

scholarly journals When is a control not a control? Reactive microglia occur throughout the control contralateral visual pathway in experimental glaucoma

2019 ◽  
Author(s):  
James R Tribble ◽  
Eirini Kokkali ◽  
Amin Otmani ◽  
Flavia Plastino ◽  
Emma Lardner ◽  
...  
Keyword(s):  
Optic Nerve ◽  
Animal Models ◽  
Ganglion Cell ◽  
Retinal Ganglion Cell ◽  
Internal Control ◽  
Visual Pathway ◽  
Optic Chiasm ◽  
Retinal Ganglion ◽  
Reactive Microglia ◽  
Contralateral Eye

AbstractPurposeAnimal models show retinal ganglion cell injuries that replicate features of glaucoma and the contralateral eye is commonly used as an internal control. There is significant cross-over of retinal ganglion cell axons from the ipsilateral to the contralateral side at the level of the optic chiasm which may confound findings when damage is restricted to one eye. The effect of unilateral glaucoma on neuroinflammatory damage to the contralateral visual pathway has largely been unexplored.MethodsOcular hypertensive glaucoma was induced unilaterally or bilaterally in the rat and retinal ganglion cell neurodegenerative events were assessed. Neuroinflammation was quantified in the retina, optic nerve head, optic nerve, lateral geniculate nucleus, and superior colliculus by high resolution imaging, and in the retina by flow cytometry and protein arrays.ResultsFollowing ocular hypertensive stress, peripheral monocytes enter the retina, and microglia become reactive. This effect is more marked in animals with bilateral ocular hypertensive glaucoma. In rats where glaucoma was induced unilaterally there was significant microglia activation in the contralateral (control) eye. Microglial activation extended into the optic nerve and terminal visual thalami, where it was similar across hemispheres irrespective of whether ocular hypertension was unilateral or bilateral.ConclusionsThese data suggest that caution is warranted when using the contralateral eye as control in unilateral models of glaucoma.Translational RelevanceUse of a contralateral eye as a control may confound discovery of human relevant mechanism and treatments in animal models. We also identify neuroinflammatory protein responses that warrant further investigation as potential disease modifiable targets.

Anatomic Basis and Differential Diagnosis of Field Defects

Visual Fields ◽  
2010 ◽  
Author(s):  
Jonathan D. Wirtschafter ◽  
Thomas J. Walsh
Keyword(s):  
Differential Diagnosis ◽  
Optic Nerve ◽  
Visual Field ◽  
Vision System ◽  
Optic Tract ◽  
Optic Chiasm ◽  
Visual Field Defects ◽  
Medical Test ◽  
Ct Angiogram ◽  
Field Defects

The purpose of any medical test is to confirm or rule out a diagnosis based on the clinical facts. In performing perimetry, the printout of the defect is not the end of the test. For even the most experienced reader, the test results at best tell the location of the defect. The next step is to consider the causes of such a defect in that part of the vision system. The experienced perimetrist will look at the results and suggest a differential list of causes. The primary diagnostic list is frequently aided by adding to the perimetry the medical history and other physical signs. The results of both then lead to the next step: ordering tests to confirm the cause of the field defect. It may require the ordering of a magnetic resonance (MR) image, but that may not be the proper test if the original differential diagnosis is faulty. Sedimentation rate and C-reactive protein may be more appropriate tests if the clinical facts suggest cranial arteritis. If carotid disease is suspected, a computed tomography (CT) angiogram may be more appropriate. In the following discussion of these defects, there has been a melding of a discussion explaining anatomically why these defects occur in certain areas. Because the course and relations of the primary visual sensory pathway have been frequently and well described (including in other chapters of this monograph), this chapter concentrates on the multiple anatomic substrates that may explain each particular pattern of visual field abnormality. Visual field abnormalities are represented by three categories: monocular, binocular, and junctional. Monocular field defects include those that can be caused by lesions of one eye or optic nerve. Binocular field defects include those that may result from single or multiple lesions at one or more points along the visual pathway. Junctional field defects include three types of visual field defects resulting from a lesion at the junction of the optic nerve and optic chiasm or of the optic tract and optic chiasm.

A glial palisade delineates the ipsilateral optic projection in Monodelphis

1998 ◽  
Vol 15 (2) ◽  
pp. 397-400 ◽  
Author(s):  
ROBERT E. MacLAREN
Keyword(s):  
Optic Nerve ◽  
Axon Guidance ◽  
Turning Point ◽  
Linear Array ◽  
Ganglion Cells ◽  
Optic Tract ◽  
Optic Chiasm ◽  
Retinal Ganglion ◽  
Discrete Population ◽  
Distinct Morphology

In developing marsupials, the path taken through the optic chiasm by ipsilaterally projecting retinal ganglion cells is complicated. Just prior to entry into the chiasm, ganglion cells destined for the ipsilateral optic tract separate from the remainder of axons by turning abruptly downwards to take a position in the ventral part of the optic nerve. In this report, it is shown that a discrete population of about 10–15 large glial cells transiently form a linear array across the prechiasmatic part of the optic nerve, precisely at this axon turning point. The distinct morphology of these cells and their novel location may reflect a specialized role in axon guidance.

Fibre organization and reorganization in the retinotectal projection of Xenopus

Development ◽  
1987 ◽  
Vol 99 (3) ◽  
pp. 393-410
Author(s):  
J.S. Taylor
Keyword(s):  
Optic Nerve ◽  
Ganglion Cell ◽  
Rana Pipiens ◽  
Optic Tract ◽  
Retinal Position ◽  
Dual Representation ◽  
Optic Chiasma ◽  
Age Related ◽  
Pass Through ◽  
Radial Organization

This study concerns the retinotopic organization of the ganglion cell fibres in the visual system of the frog Xenopus laevis. HRP was used to trace the pathways taken by fibres from discrete retinal positions as they pass from the retina, along the optic nerve and into the chiasma. The ganglion cell fibres in the retina are arranged in fascicles which correspond with their circumferential positions of origin. Within the fascicles the fibres show little age-related layering and do not have a strict radial organization. As the fascicles of fibres pass into the optic nerve head there is some exchange of position resulting in some loss of the retinal circumferential organization. The poor radial organization of the fibres in the retinal fascicles persists as the fibres pass through the intraocular part of the nerve. At a position just behind the eye there is a major fibre reorganization in which fibres arising from cells of increasingly peripheral retinal locations are found to have passed into increasingly peripheral positions in the nerve. Thus, fibres from peripheral-most retina are located at the nerve perimeter, whilst fibres from central retina are located in the nerve core. It is at this point that the radial, chronotopic, ordering of the ganglion cell axons, found throughout the rest of the optic pathway, is established. This annular organization persists along the length of the nerve until a position just before the nerve enters the brain. Here, fibres from each annulus move to form layers as they pass into the optic chiasma. This change in the radial organization appears to be related to the pathway followed by all newly growing fibres, in the most superficial part of the optic tract, adjacent to the pia. Just behind the eye, where fibres become radially ordered, the circumferential organization of the projection is largely lost. Fibres from every circumferential retinal position, which are of similar radial position, are distributed within the same annulus of the nerve. At the nerve-chiasma junction where each annulus forms a single layer as it enters the optic tract, there is a further mixing of fibres from all circumferential positions. However, as the fibres pass through the chiasma some active pathway selection occurs, generating the circumferential organization of the fibres in the optic tract. Additional observations of the organization of fibres in the optic nerve of Rana pipiens confirm previous reports of a dual representation of fibres within the nerve. The difference in the organization of fibres in the optic nerve of Xenopus and Rana pipiens is discussed.

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