Distribution and characteristics of the different astroglial cell types in the adult lizard (Lacerta lepida) spinal cord.

The astroglial cells have been studied in the lizard spinal cord by means of metallic impregnations, immunohistochemical (glial fibrillary acidic protein) and ultrastructural methods. Three astroglial cell types have been immunohistochemically identified: ependymocytes, radial astrocytes and astrocytes. Transitional forms have also been observed. Scarce immunopositive ependymocytes were located in the dorsal and ventral regions of the ependyma. The radial astrocytic somata were located around the ependymal layer and their processes reached the subpial glia limitans. Typical astrocytes were the most abundant astroglial cell type; astrocytes located in the ventral horn showed a greater development than those of the dorsal horn. In the white matter, the astrocytes were large and their processes formed part of the subpial glia limitans; on some occasions, astrocytic cell bodies also formed part of this subpial limitans. Transitional elements between astrocytes and radial astrocytes were observed in both grey and white matter. The perivascular and subpial glia limitans were continuous and showed a strong immunoreactivity. The comparative analysis of our results in the lizard spinal cord with those in other vertebrate groups leads us to conclude that reptiles could represent the key group in the phylogenetic evolution of the astroglial cells in vertebrates.