Connective tissue structure of the tree shrew optic nerve and associated ageing changes.
OBJECTIVE
To identify the structure and composition of the tree shrew optic nerve to determine its potential as a model for glaucoma.


METHODS
Tree shrew optic nerves, aged 4 weeks to 5 years, were wax or cryoembedded for analysis of overall morphology and cellular (glial fibrillary acidic protein [GFAP]) and extracellular matrix (collagen types I, III, IV, V, VI; fibronectin; and elastin) immunolocalization studies. In addition, transmission and scanning electron microscopy were performed. In vivo optic disc imaging was performed by HRT2 and fundus camera photography.


RESULTS
The optic nerve of the tree shrew comprised regions comparable to the human prelaminar and lamina cribrosa (LC) in the optic nerve head and the retrolaminar region, immediately posterior. The multilayered connective tissue plates of tree shrew LC stretched across the optic nerve canal at the level of the sclera and consisted of collagen types I, III, IV, V, and VI; elastin; and fibronectin. Significant age-related alterations in connective tissue components were indicated. Connective tissue was present in the central retinal vessel sheaths and was identified as longitudinally oriented collagen fibrils in the retrolaminar optic nerve. GFAP immunofluorescence indicated a high concentration of astrocytic processes in the LC. Myelination of axons was evident in the retrolaminar optic nerve. Ultrastructural studies supported the structural organization and spatial distribution of connective tissue.


CONCLUSIONS
In contrast to many rodent models of glaucoma, since the tree shrew optic nerve resembles that in humans, especially at the LC, the tree shrew offers an ideal opportunity to investigate glaucoma pathophysiology in a subprimate model.
Albon
Julie
J
Cell and Molecular Biology Unit, School of Optometry and Vision Sciences, Cardiff Institute of Tissue Engineering and Repair, Cardiff University, Cardiff, Wales, United Kingdom. albonj@cardiff.ac.uk
Farrant
Sarah
S
Akhtar
Saeed
S
Young
Rob
R
Boulton
Mike E
ME
Smith
Gillian
G
Taylor
Martin
M
Guggenheim
Jez
J
Morgan
James E
JE
D000375:Aging / Q000502:physiology*; D000818:Animals; D003094:Collagen / Q000378:metabolism; D003238:Connective Tissue / Q000033:anatomy & histology* / Q000378:metabolism; D003239:Connective Tissue Cells / Q000166:cytology* / Q000378:metabolism; D004549:Elastin / Q000378:metabolism; D005353:Fibronectins / Q000378:metabolism; D019084:Fluorescent Antibody Technique, Indirect; D005904:Glial Fibrillary Acidic Protein / Q000378:metabolism; D008855:Microscopy, Electron, Scanning; D046529:Microscopy, Electron, Transmission; D009898:Optic Disk / Q000378:metabolism / Q000648:ultrastructure; D009900:Optic Nerve / Q000378:metabolism / Q000648:ultrastructure*; D012171:Retinal Vessels / Q000166:cytology; D014418:Tupaiidae
D005353:Fibronectins; D005904:Glial Fibrillary Acidic Protein; D003094:Collagen; D004549:Elastin