Astrocytes in the nonmyelinated lamina cribrosa of the rat are less polarized than in the optic nerve proper: a freeze-fracture study.

Astrocytes in the lamina cribrosa of the adult rat optic nerve which is devoid of myelination were investigated by means of quantitative freeze-fracturing. The orthogonal arrays of particles (OAPs) were found to be less concentrated in the membranes of subpial endfeet when compared to the OAP concentration in endfeet of the optic nerve proper. This result corresponds to that found previously in the myelin deficient rat (Rohlmann et al: Glia 5:259, 1992) suggesting that lack of myelination generally correlates with altered astrocytes.