scholarly journals Tectal pathways of regenerating goldfish optic axons after nasal or temporal half retinal removal

Development ◽  
1988 ◽  
Vol 102 (3) ◽  
pp. 479-488
Author(s):  
M.F. Humphrey ◽  
C.A.O. Stuermer
Keyword(s):  
Optic Nerve ◽  
Relative Density ◽  
Relative Proportion ◽  
Axonal Growth ◽  
Nerve Section ◽  
Optic Axons

The tectal pathways of regenerating goldfish optic axons are abnormal but not random. The relative proportion of temporal axons is highest in rostral tectum (65%) drops in midtectum (31%) and is very low in caudal tectum (4%). By contrast, nasal axons proceed into caudal tectum and are therefore relatively evenly distributed throughout the tectum. In this study, we have tested whether temporal axons are confined to rostral tectum by the presence of nasal axons in caudal tectum or whether they have a preference for rostral tectum regardless of other axons. We similarly tested whether nasal axons would grow preferentially into caudal tectum in the absence of temporal axons. At the time of optic nerve section either the nasal or temporal half retina was removed. Either 35 or 70 days after nerve section, the regenerating optic axons were labelled with HRP and both their pathways and distribution determined in DAB-reacted tectal wholemounts. In the absence of nasal axons, the relative density of temporal axons in rostral, mid and caudal tectum was 70%, 28% and 2%, respectively. The corresponding values for nasal axons, in the absence of temporal axons, were 30%, 40% and 30%, respectively. Thus, the overall distribution of nasal and temporal axons in the half retinal regenerates was similar to that of whole retinal regenerates, demonstrating that the retinotopic preferences of the axons were not dependent upon interaxonal interactions. Thus, nasal and temporal axons obviously discriminate between rostral and caudal tectum despite pathway disorganization and the absence of axons from the opposite hemiretina. This is consistent with axonal growth being under the influence of positional markers in tectum.

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.

scholarly journals Effect of NGF on the survival of rat retinal ganglion cells following optic nerve section

1989 ◽  
Vol 9 (4) ◽  
pp. 1263-1272 ◽  
Author(s):  
G Carmignoto ◽  
L Maffei ◽  
P Candeo ◽  
R Canella ◽  
C Comelli
Keyword(s):  
Optic Nerve ◽  
Retinal Ganglion Cells ◽  
Ganglion Cells ◽  
Retinal Ganglion ◽  
Nerve Section

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.

NGF effects on the survival of rat retinal ganglion cells following optic nerve section

1988 ◽  
Vol 20 ◽  
pp. 65
Author(s):  
P. Candeo ◽  
G. Carmignoto ◽  
L. Maffei ◽  
R. Canella ◽  
C. Comelli
Keyword(s):  
Optic Nerve ◽  
Retinal Ganglion Cells ◽  
Ganglion Cells ◽  
Retinal Ganglion ◽  
Nerve Section

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.

Electron microscopy of optic nerves and optic lobes of Octopus and Eledone

1963 ◽  
Vol 158 (973) ◽  
pp. 446-456 ◽  
Keyword(s):  
Electron Microscopy ◽  
Endoplasmic Reticulum ◽  
Optic Nerve ◽  
Schwann Cells ◽  
Synaptic Vesicles ◽  
Optic Lobe ◽  
Granule Cells ◽  
Proximal Region ◽  
Optic Lobes ◽  
Optic Axons

Each optic nerve contains several bundles of axons. The axons have their surface membranes directly apposed and the bundles lie in troughs of the elongated Schwann cells. The axons have pronounced varicosities along their length. The axons enter the optic lobe and run between the granule cells to synapse in the plexiform zone. The granule cells are small neurons. Their cytoplasmic organelles include endoplasmic reticulum, ribosomes, agranular reticulum and of special interest, oval or spherical bodies with a lamellated cortex and granular medulla. The elongated varicose presynaptic bags of the optic axons contain mitochondria in the proximal region, numerous synaptic vesicles and, sometimes, neurofilaments. Below the mitochondrial zone, synaptic contacts are made with small spines invaginated into the bags. The spines probably originate from the trunks of the granule cells. Tunnel fibres that are probably trunks of the outer granule cells, run through channels in the synaptic bags.

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