Heterogeneity of astrocytic membranes in the optic nerve and spinal cord of the lizard,Anolis carolinensis

Summary The architecture of astrocytic membranes in the optic nerve and the spinal cord of the lizard, Anolis carolinensis, was investigated by use of the freeze-fracturing technique. Whereas astrocytes in mammals reveal so-called orthogonal arrays of particles (OAPs) in their membranes, astrocytes in lower vertebrates lack these structures. This study demonstrates for the first time OAPs in astrocytes from a submammalian species. They were found commonly in the optic nerve and less frequently in the spinal cord. However, the OAPs in astrocytes of spinal cord were confined to midtrunk levels; the astrocytes in the caudal spinal cord failed to reveal OAPs.Additionally, the ependymal cells around the central canal did not show any OAPs, either in the thoracic or in the caudal spinal cord. They were interconnected by gap and tight junctions, which were not intercalated with each other.The findings support our current working hypothesis according to which the presence and absence of OAPs in astrocytes may be correlated with regenerative incapability or capability of CNS-structures; i.e., whereas the thoracic spinal cord in Anolis carolinensis is known to be incapable of regeneration after injury, the caudal spinal cord is regenerative.