The morphology and spatial arrangement of astrocytes in the optic nerve head of the mouse

Abstract

We evaluated the shapes, numbers, and spatial distribution of astrocytes within the glial lamina, an astrocyte-rich region at the junction of the retina and optic nerve. A primary aim was to determine how the population of astrocytes, collectively, partitions the axonal space in this region. Astrocyte processes labeled with glial fibrillary acidic protein (GFAP) compartmentalize ganglion cell axons into bundles, forming "glial tubes", and giving the glial architecture of the optic nerve head in transverse section a honeycomb appearance. The shapes of individual astrocytes were studied using transgenic mice that express enhanced green fluorescent protein in isolated astrocytes (hGFAPpr-EGFP). Within the glial lamina the astrocytes were transverse in orientation, with thick, smooth primary processes emanating from a cytoplasmic expansion of the soma. Spaces between the processes of neighboring astrocytes were spatially aligned, to form the apertures through which the bundles of optic axons pass. The processes of individual astrocytes were farreaching -they could span most of the width of the nerve -and overlapped the anatomical domains of other near and distant astrocytes. Thus, astrocytes in the glial lamina do not tile: each astrocyte participates in ensheathing approximately one quarter of all of the axon bundles in the nerve, and each glial tube contains the processes of ~ 9 astrocytes. This raises the mechanistic question how, in glaucoma or other cases of nerve damage, the glial response can be confined to a circumscribed region where damage to axons has occurred.

Myelination transition zone astrocytes are constitutively phagocytic and have synuclein dependent reactivity in glaucoma

“…3B) and the MTZ (Fig. 3C), axons were enwrapped by astrocytes with transverse orientation, as previously reported (10). Surprisingly, even in this strain, which does develop RGC loss with age (8), axons at the glial lamina ( Fig.…”

Targeting neuronal gap junctions in mouse retina offers neuroprotection in glaucoma

“…In optic nerves of control CxWT mice, GFAP was expressed in thick processes of astrocytes that formed the glial tubes, which ensheathed bundles of SMI32-positive axons creating a characteristic honeycomb mosaic (ref. 35 and Figure 6A). We found significant changes in the structure of the optic nerve at 8 weeks after the initial microbead injection.…”

Differential Gene Expression in Glaucoma

“…Rodents are susceptible to the disease, yet mice do not show staining for any collagen other than collagen 4 associated with blood vessels, and the ONH of rats contains only sparse collagenous septa (Morrison et al 1995;May and LutjenDrecoll 2002;Sun et al 2009). A commonality between ONH of humans and all other species, including rodents, is that this region contains an abundance of astrocytes that line the pores of the lamina cribrosa and ensheath the axons, or, in rodents, form glial tubes around axon bundles that visually resemble a lamina cribrosa so much that they are referred to as the "glial lamina" (Morcos and Chan-Ling 2000;Howell et al 2007;Sun et al 2009). In addition to astrocytes, the human laminar region contains lamina cribrosa cells (Hernandez et al 1988).…”