The Cytoskeletal Ultrastructure of Guinea Pig Optic Nerve at the Lamina Cribrosa

Abstract

The three-dimensional ultrastructure of guinea pig optic nerve fibers passing through the lamina cribrosa was studied using the quick-freeze, deep-etch, rotary-shadow technique. Elements of cytoskeleton of the optic nerve fibers including neurofilaments (NFs), microtubules (MTs), membranous organelles (MOs), and numerous cross-linker types were readily identified. The length of the cross-linkers between adjoining NFs, between NFs and MTs, and adjacent MTs was 33.9 ± 9.9 nm (n = 109), 34.9 ± 11.2 nm (n = 80), and 20.6 ± 8.9 nm (n = 86), respectively. Cross-linkers also were identified between NFs and MOs and between MTs and MOs; the length of these linkers was relatively short [26.2 ± 7.2 nm (n = 22) and 20.7 ± 8.8 nm (n = 70), respectively] and MOs always were attached or closely apposed to MTs. Quantitative analysis revealed no difference in the dimensions or density of cytoplasmic structures within axons of the pre- and postlamina regions. These results demonstrate that the quick-freeze, deep-etch, rotary-shadow technique is useful for studying optic nerve fiber ultrastructure including the elaborate cross-linker components.