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.

A developmental and ultrastructural study of the optic chiasma in Xenopus

Development ◽  
1988 ◽  
Vol 102 (3) ◽  
pp. 537-553
Author(s):  
M.A. Wilson ◽  
J.S. Taylor ◽  
R.M. Gaze
Keyword(s):  
Optic Nerve ◽  
Cell Mass ◽  
Light And Electron Microscopy ◽  
Optic Tract ◽  
Retinal Ganglion ◽  
Intercellular Spaces ◽  
Optic Chiasma ◽  
Cell Processes ◽  
Optic Axons ◽  
The Brain

The structure of the optic chiasma in Xenopus tadpoles has been investigated by light and electron microscopy. Where the optic nerve approaches the chiasma, a tongue of cells protrudes from the periventricular cell mass into the dorsal part of the nerve. Glial processes from this tongue of cells ensheath fascicles of optic axons as they enter the brain. Coincident with this partitioning, the annular arrangement of axons in the optic nerve changes to the laminar organization of the optic tract. Beyond the site of this rearrangement, all newly growing axons accumulate in the ventral-most part of the nerve and pass into the region between the periventricular cells and pia which we have called the ‘bridge’. This region is characterized by a loose meshwork of glial cell processes, intercellular spaces and the presence of both optic and nonoptic axons. In the bridge, putative growth cones of retinal ganglion cell axons are found in the intercellular spaces in contact with both the glia and with other axons. The newly growing axons from each eye cross in the bridge at the midline and pass into the superficial layers of the contralateral optic tracts. As the system continues to grow, previous generations of axon, which initially crossed in the existing bridge, are displaced dorsally and caudally, forming the deeper layers of the chiasma. At their point of crossing in the deeper layers, these fascicles of axons from each eye interweave in an intimate fashion. There is no glial segregation of the older axons as they interweave within the chiasma.

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.

Distribution of uncrossed and crossed retinofugal axons in the cat optic nerve and their relationship to patterns of fasciculation

1990 ◽  
Vol 5 (1) ◽  
pp. 99-104 ◽  
Author(s):  
Glen Jeffery
Keyword(s):  
Optic Nerve ◽  
Optic Tract ◽  
Relative Increase ◽  
Lateral Aspect ◽  
Optic Nerves ◽  
Caudal Region ◽  
Lateral Extent ◽  
Optic Axons ◽  
Horseradish Peroxide ◽  
Caudal Segment

AbstractThe course of optic axons that take different routes at the chiasm have been traced through horizontally sectioned optic nerves in the cat, after unilateral injections of horseradish peroxide into the optic tract. Behind the eye and for most of the course of the nerve, nearly all of the axons that remain uncrossed at the chiasm are located in a retinotopically appropriate position, in the lateral aspect of the nerve. However, in the most caudal segment of the nerve an increasing proportion of these axons are located in regions that are retinotopically inappropriate. Just before the nerve joins the chiasm, uncrossed axons can be found across the full medio-lateral extent of the nerve, although there is still a relative increase in their density laterally.Labeled axons that cross at the chiasm course in a relatively parallel manner along the greater proportion of the nerve. However, in the caudal segment of the nerve their relative positions change and they appear to course in an irregular manner. This occurs where the uncrossed projection becomes increasingly more widespread.Axons in the optic nerve are grouped into fascicules. This pattern of organization also changes in the caudal region of the nerve. Although clear fascicular patterns are present along the greater part of the nerve, they become progressively less distinct caudally. The change in the pattern of fasciculation occurs over the same region of the nerve as the relative changes in axon trajectory and distribution.These results demonstrate that irrespective of chiasmatic route, optic axons in the cat are reorganized in the caudal segment of the nerve. This reorganization is not confined to changes in relative axon position, but is reflected in the structure of the nerve by the change of axon grouping from a fascicular to a non-fascicular arrangement.

scholarly journals Axon guidance modalities in CNS regeneration revealed by quantitative proteomic analysis

2021 ◽  
Author(s):  
Noemie Vilallongue ◽  
Julia Schaeffer ◽  
Anne-Marie Hesse ◽  
Celine Delpech ◽  
Antoine Paccard ◽  
...  
Keyword(s):  
Nervous System ◽  
Axon Guidance ◽  
Optic Chiasm ◽  
Axonal Guidance ◽  
Dorsal Lateral Geniculate Nucleus ◽  
Long Distance ◽  
Nerve Crush ◽  
Guidance Molecules ◽  
Visual Targets ◽  
The Brain

Long-distance regeneration of the central nervous system (CNS) has been achieved from the eye to the brain through activation of neuronal molecular pathways or pharmacological approaches. Unexpectedly, most of the regenerative fibers display guidance defects, which prevents reinnervation and further functional recovery. Therefore, characterizing the mature neuronal environment is essential to understand the adult axonal guidance in order to complete the circuit reconstruction. To this end, we used mass spectrometry to characterize the proteomes of major nuclei of the adult visual system: suprachiasmatic nucleus (SCN), ventral and dorsal lateral geniculate nucleus (vLGN, dLGN) and superior colliculus (SC)), as well as the optic chiasm. These analyses revealed the presence of guidance molecules and guidance-associated factors in the adult visual targets. Moreover, by performing bilateral optic nerve crush, we showed that the expression of some proteins was significantly modulated by the injury in the visual targets, even in the ones most distal to the lesion site. On another hand, we found that the expression of guidance molecules was not modified upon injury. This implies that these molecules may possibly interfere with the reinnervation of the brain targets. Together, our results provides an extensive characterization of the molecular environment in intact and injured conditions. These findings open new ways to correct regenerating axon guidance notably by manipulating the expression of the corresponding guidance receptors in the nervous system.

scholarly journals Multiple Sclerosis

2020 ◽  
Author(s):  
Amirhossein Azari Jafari ◽  
Seyyedmohammadsadeq Mirmoeeni
Keyword(s):  
Multiple Sclerosis ◽  
Spinal Cord ◽  
Central Nervous System ◽  
Nervous System ◽  
Optic Nerve ◽  
Autoimmune Disease ◽  
The Central Nervous System ◽  
Genetic And Environmental Factors ◽  
Chronic Autoimmune Disease ◽  
The Brain

Multiple sclerosis (MS) is a chronic autoimmune disease affecting the central nervous system (CNS), caused by genetic and environmental factors. It is characterized by intermittent and recurrent episodes of inflammation that result in the demyelination and subsequent damage of the underlying axons present in the brain, optic nerve and spinal cord [1][2][3].

The directed growth of retinal axons towards surgically transposed tecta in Xenopus; an examination of homing behaviour by retinal ganglion cell axons

Development ◽  
1990 ◽  
Vol 108 (1) ◽  
pp. 147-158
Author(s):  
J.S. Taylor
Keyword(s):  
Ganglion Cell ◽  
Axon Guidance ◽  
Retinal Ganglion Cell ◽  
Optic Tract ◽  
Retinal Ganglion ◽  
Retinal Axons ◽  
Dorsal Neural Tube ◽  
Abnormal Structure ◽  
Optic Axons ◽  
The Brain

The growth of optic axons towards experimentally rotated tecta has been studied. In stage 24/25 embryos, a piece of the dorsal neural tube, containing the dorsal midbrain rudiment, was rotated through 180 degrees. At later stages of development, the pathways of growing optic axons were investigated by labelling with either horseradish peroxidase or fluorescent dye. It is shown that retinal ganglion cell axons followed well-defined pathways, in spite of the abnormal structure of the brain, and were able to locate displaced tecta. This directed outgrowth of retinal axons in the optic tracts appears to be related either to the tectum or to some other component included in the graft operations. In tadpoles in which the midbrain rudiment was removed, optic axons still followed the normal course of the optic tract. This observation argues against long-range target attraction as being essential in guiding growing retinal axons towards the tectum. An alternative axon guidance mechanism, selective fasciculation, is discussed as a possible alternative to explain the directed axon outgrowth which occurs in both the normal and in these experimentally manipulated tadpoles.

Central origin of the efferent neurons projecting to the eyes of Limulus polyphemus

1991 ◽  
Vol 6 (5) ◽  
pp. 481-495 ◽  
Author(s):  
B. G. Calman ◽  
B.- A. Battelle
Keyword(s):  
Central Nervous System ◽  
Nervous System ◽  
Optic Nerve ◽  
Optic Tract ◽  
Limulus Polyphemus ◽  
Cell Of Origin ◽  
Optic Nerves ◽  
Visual Cells ◽  
Efferent Neurons ◽  
The Central Nervous System

AbstractCircadian rhythms affect the anatomy, physiology, and biochemistry of the visual cells in the eyes of the horseshoe crab (Limulus polyphemus). These rhythms are mediated by the activity of efferent neurons that project from the central nervous system to all of the eyes. In this study, the optic nerves of Limulus were backfilled with Neurobiotin revealing the location of efferent cell bodies and their projections through the central nervous system. We propose that this efferent system mediates the circadian changes in visual functions in Limulus. Whether these cells are the circadian pacemaker neurons is unknown.The cell bodies of the efferent neurons are ovoid and have a diameter of 40−80 μm. They lie within the cheliceral ganglion of the tritocerebrum, just posterior to the protocerebrum. This ganglion is on the lateral edge of the circumesophageal ring, near the middle of the dorsal-ventral axis of the ring. Each optic nerve contains axons from both ipsilateral and contralateral efferent cells, and some, possibly all, of them project bilaterally and to more than one type of optic nerve.The efferent axons form a tract that projects anteriorly from the cell bodies to the protocerebrum, and bifurcates just lateral to the protocerebral bridge. One branch crosses the midline and projects anteriorly to the optic tract and medulla on the side contralateral to the cell of origin; the other branch follows a symmetric pathway on the ipsilateral side. Small branches arising from the major efferent axons in the optic tract project through the ocellar ganglia to the median optic nerves. The efferent axons branch again in the medulla, and some of these branches innervate the ventral optic nerves. The major branches of the efferent axons continue through the lamina and enter the lateral optic nerve.

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

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