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Axons of retinal ganglion cells are insulted in the optic nerve early in DBA/2J glaucoma.

Howell GR, Libby RT, Jakobs TC, Smith RS, Phalan FC, Barter JW, Barbay JM, Marchant JK, Mahesh N, Porciatti V, Whitmore AV, Masland RH, John SW - J. Cell Biol. (2007)

Bottom Line: We show that proximal axon segments attached to their cell bodies survive to the proximity of the lamina.In contrast, axon segments in the lamina and behind the eye degenerate.These experiments provide strong evidence for a local insult to axons in the optic nerve.

View Article: PubMed Central - PubMed

Affiliation: The Jackson Laboratory, Bar Harbor, ME 04609, USA.

ABSTRACT
Here, we use a mouse model (DBA/2J) to readdress the location of insult(s) to retinal ganglion cells (RGCs) in glaucoma. We localize an early sign of axon damage to an astrocyte-rich region of the optic nerve just posterior to the retina, analogous to the lamina cribrosa. In this region, a network of astrocytes associates intimately with RGC axons. Using BAX-deficient DBA/2J mice, which retain all of their RGCs, we provide experimental evidence for an insult within or very close to the lamina in the optic nerve. We show that proximal axon segments attached to their cell bodies survive to the proximity of the lamina. In contrast, axon segments in the lamina and behind the eye degenerate. Finally, the Wld(s) allele, which is known to protect against insults to axons, strongly protects against DBA/2J glaucoma and preserves RGC activity as measured by pattern electroretinography. These experiments provide strong evidence for a local insult to axons in the optic nerve.

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Early focal axon damage occurs in the glial lamina. To allow sensitive detection of axon damage along the entire axon from the soma to the lamina we analyzed D2.Thy1-CFP eyes (Materials and methods). For consistency with previous images, CFP-positive axons are pseudo-colored green. (A) Schematic demonstrating the location in the optic nerve head of the presented prelamina and lamina images (single focal plane) that are from the same eye for each damage level. In the prelamina region, vessels are apparent as a dark region in the center of the nerve. In the lamina, the vessels extend from the center to the edge of the nerve. (B) In an 11-mo-old eye with no or early glaucoma (Fig. 3), axon damage was detected as highly focal swelling of individual axons in the lamina. As previously reported for axonal contents, CFP accumulated in the swellings making them brightly fluorescent (arrowheads). The swellings were not present in other regions of the intraocular axon. (C–K) Representative examples of the prelamina and lamina regions in eyes with different degrees of glaucoma are shown. (C, F, and I) No glaucomatous damage was detected at any level in preglaucomatous young eyes (n = 4). (D, G, and J) Obvious axonal swellings were evident specifically in the lamina of eyes that were at early stages of glaucoma. These eyes were initially classified as having no or early glaucoma based on analysis of optic nerve from behind the eye (Fig. 3), but 5/8 were found to have early damage in the lamina. (E, H, and K) At moderate stages of glaucoma, the axonal damage had spread to portions of the axon in both the prelamina region and nerve fiber layer, and some axons had a highly abnormal morphology. The compressed lamina images represent a compressed Z stack of the entire lamina region that could be imaged in the mounted specimens (it was not possible to image the most posterior lamina). All images were collected using identical conditions. Bars, 20 μm.
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fig5: Early focal axon damage occurs in the glial lamina. To allow sensitive detection of axon damage along the entire axon from the soma to the lamina we analyzed D2.Thy1-CFP eyes (Materials and methods). For consistency with previous images, CFP-positive axons are pseudo-colored green. (A) Schematic demonstrating the location in the optic nerve head of the presented prelamina and lamina images (single focal plane) that are from the same eye for each damage level. In the prelamina region, vessels are apparent as a dark region in the center of the nerve. In the lamina, the vessels extend from the center to the edge of the nerve. (B) In an 11-mo-old eye with no or early glaucoma (Fig. 3), axon damage was detected as highly focal swelling of individual axons in the lamina. As previously reported for axonal contents, CFP accumulated in the swellings making them brightly fluorescent (arrowheads). The swellings were not present in other regions of the intraocular axon. (C–K) Representative examples of the prelamina and lamina regions in eyes with different degrees of glaucoma are shown. (C, F, and I) No glaucomatous damage was detected at any level in preglaucomatous young eyes (n = 4). (D, G, and J) Obvious axonal swellings were evident specifically in the lamina of eyes that were at early stages of glaucoma. These eyes were initially classified as having no or early glaucoma based on analysis of optic nerve from behind the eye (Fig. 3), but 5/8 were found to have early damage in the lamina. (E, H, and K) At moderate stages of glaucoma, the axonal damage had spread to portions of the axon in both the prelamina region and nerve fiber layer, and some axons had a highly abnormal morphology. The compressed lamina images represent a compressed Z stack of the entire lamina region that could be imaged in the mounted specimens (it was not possible to image the most posterior lamina). All images were collected using identical conditions. Bars, 20 μm.

Mentions: The integrity of the axons was assessed from RGC somata to the lamina by confocal microscopy (Fig. 5). In eyes that had no or early glaucoma (Fig. 3), the somata were readily detected and had no obvious abnormalities. In the same eyes, however, discrete and focal swellings were present on individual axons in the glial lamina (Fig. 5). These swellings were characterized by very intense CFP signal. Some of these axons had severe swellings that were similar in diameter to dystrophic neurites (>2 μm, much larger than the majority of unmyelinated axons in this region of a healthy nerve). However, the great majority of damaged axons were less severely altered with mild swellings only slightly larger than normal axons (Fig. 5 B). In the eyes with early glaucoma, axon damage was localized to the glial lamina and was rarely seen in the prelamina or nerve fiber layer (Fig. 5). This damage was not present in young DBA/2J mice and increased in severity as glaucoma progressed. These results confirm that the first morphological damage to the ocular portion of the RGC axon occurs at the glial lamina.


Axons of retinal ganglion cells are insulted in the optic nerve early in DBA/2J glaucoma.

Howell GR, Libby RT, Jakobs TC, Smith RS, Phalan FC, Barter JW, Barbay JM, Marchant JK, Mahesh N, Porciatti V, Whitmore AV, Masland RH, John SW - J. Cell Biol. (2007)

Early focal axon damage occurs in the glial lamina. To allow sensitive detection of axon damage along the entire axon from the soma to the lamina we analyzed D2.Thy1-CFP eyes (Materials and methods). For consistency with previous images, CFP-positive axons are pseudo-colored green. (A) Schematic demonstrating the location in the optic nerve head of the presented prelamina and lamina images (single focal plane) that are from the same eye for each damage level. In the prelamina region, vessels are apparent as a dark region in the center of the nerve. In the lamina, the vessels extend from the center to the edge of the nerve. (B) In an 11-mo-old eye with no or early glaucoma (Fig. 3), axon damage was detected as highly focal swelling of individual axons in the lamina. As previously reported for axonal contents, CFP accumulated in the swellings making them brightly fluorescent (arrowheads). The swellings were not present in other regions of the intraocular axon. (C–K) Representative examples of the prelamina and lamina regions in eyes with different degrees of glaucoma are shown. (C, F, and I) No glaucomatous damage was detected at any level in preglaucomatous young eyes (n = 4). (D, G, and J) Obvious axonal swellings were evident specifically in the lamina of eyes that were at early stages of glaucoma. These eyes were initially classified as having no or early glaucoma based on analysis of optic nerve from behind the eye (Fig. 3), but 5/8 were found to have early damage in the lamina. (E, H, and K) At moderate stages of glaucoma, the axonal damage had spread to portions of the axon in both the prelamina region and nerve fiber layer, and some axons had a highly abnormal morphology. The compressed lamina images represent a compressed Z stack of the entire lamina region that could be imaged in the mounted specimens (it was not possible to image the most posterior lamina). All images were collected using identical conditions. Bars, 20 μm.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2373494&req=5

fig5: Early focal axon damage occurs in the glial lamina. To allow sensitive detection of axon damage along the entire axon from the soma to the lamina we analyzed D2.Thy1-CFP eyes (Materials and methods). For consistency with previous images, CFP-positive axons are pseudo-colored green. (A) Schematic demonstrating the location in the optic nerve head of the presented prelamina and lamina images (single focal plane) that are from the same eye for each damage level. In the prelamina region, vessels are apparent as a dark region in the center of the nerve. In the lamina, the vessels extend from the center to the edge of the nerve. (B) In an 11-mo-old eye with no or early glaucoma (Fig. 3), axon damage was detected as highly focal swelling of individual axons in the lamina. As previously reported for axonal contents, CFP accumulated in the swellings making them brightly fluorescent (arrowheads). The swellings were not present in other regions of the intraocular axon. (C–K) Representative examples of the prelamina and lamina regions in eyes with different degrees of glaucoma are shown. (C, F, and I) No glaucomatous damage was detected at any level in preglaucomatous young eyes (n = 4). (D, G, and J) Obvious axonal swellings were evident specifically in the lamina of eyes that were at early stages of glaucoma. These eyes were initially classified as having no or early glaucoma based on analysis of optic nerve from behind the eye (Fig. 3), but 5/8 were found to have early damage in the lamina. (E, H, and K) At moderate stages of glaucoma, the axonal damage had spread to portions of the axon in both the prelamina region and nerve fiber layer, and some axons had a highly abnormal morphology. The compressed lamina images represent a compressed Z stack of the entire lamina region that could be imaged in the mounted specimens (it was not possible to image the most posterior lamina). All images were collected using identical conditions. Bars, 20 μm.
Mentions: The integrity of the axons was assessed from RGC somata to the lamina by confocal microscopy (Fig. 5). In eyes that had no or early glaucoma (Fig. 3), the somata were readily detected and had no obvious abnormalities. In the same eyes, however, discrete and focal swellings were present on individual axons in the glial lamina (Fig. 5). These swellings were characterized by very intense CFP signal. Some of these axons had severe swellings that were similar in diameter to dystrophic neurites (>2 μm, much larger than the majority of unmyelinated axons in this region of a healthy nerve). However, the great majority of damaged axons were less severely altered with mild swellings only slightly larger than normal axons (Fig. 5 B). In the eyes with early glaucoma, axon damage was localized to the glial lamina and was rarely seen in the prelamina or nerve fiber layer (Fig. 5). This damage was not present in young DBA/2J mice and increased in severity as glaucoma progressed. These results confirm that the first morphological damage to the ocular portion of the RGC axon occurs at the glial lamina.

Bottom Line: We show that proximal axon segments attached to their cell bodies survive to the proximity of the lamina.In contrast, axon segments in the lamina and behind the eye degenerate.These experiments provide strong evidence for a local insult to axons in the optic nerve.

View Article: PubMed Central - PubMed

Affiliation: The Jackson Laboratory, Bar Harbor, ME 04609, USA.

ABSTRACT
Here, we use a mouse model (DBA/2J) to readdress the location of insult(s) to retinal ganglion cells (RGCs) in glaucoma. We localize an early sign of axon damage to an astrocyte-rich region of the optic nerve just posterior to the retina, analogous to the lamina cribrosa. In this region, a network of astrocytes associates intimately with RGC axons. Using BAX-deficient DBA/2J mice, which retain all of their RGCs, we provide experimental evidence for an insult within or very close to the lamina in the optic nerve. We show that proximal axon segments attached to their cell bodies survive to the proximity of the lamina. In contrast, axon segments in the lamina and behind the eye degenerate. Finally, the Wld(s) allele, which is known to protect against insults to axons, strongly protects against DBA/2J glaucoma and preserves RGC activity as measured by pattern electroretinography. These experiments provide strong evidence for a local insult to axons in the optic nerve.

Show MeSH
Related in: MedlinePlus