Fine structure of cells in the young regenerating spinal cord of the lizard Anolis carolinensis after H3-thymidine administration.

H3-thymidine was injected in a single dose into adult lizards Anolis carolinensis during early stages of tail regeneration when the new tail measured in length 2-5 mm (about 3 weeks). Electron microscopic autoradiography revealed that in the regenerating spinal cord three different cell types were recognizable four hours post-injection. By far the most common type was the ependymal cell. Ependymal or roundish cells with clear electron-density or storing bundles of intermediate filaments were occasionally found. A second rarer, cell type devoid of intermediate filaments was a pale round cell, often highly labelled. This cell showed a very poor ultrastructural differentiation and probably represents the precursor of the few neurons and glial cells observed in older stages of regeneration. The third type was a neuroblast at different degrees of differentiation and did not uptake H3-thymidine revealing it was a post-mitotic cell. Despite the relatively advanced ultrastructural differentiation of these neurons, synapses were rarely seen after three weeks of SC regeneration in Anolis.