Basal lamina formation by astrocytes in organotypic cultures of mouse spinal cord tissue.

The relationship between astrocytes, basal lamina and mesenchymal tissue was analyzed ultrastructurally in myelinated organotypic cultures of mouse spinal cord tissue grown in combination with its pia-arachnoid membrane. A discontinuous, well-developed basal lamina covered flat astrocytic processes which formed the basal layer of the explant opposing the pia-arachnoid membrane. Some astrocytic processes on the surface facing the pia-arachnoid membrane lacked basal lamina, had an irregular surface with microvillus-like protrusions but within the explant they formed intercellular chambers which were surrounded by basal lamina. Even in the presence of mesenchymal tissue which appeared to facilitate the formation of basal lamina in this system, the absence of basal lamina on some areas of the astrocytic plasma membrane suggests regional differences of the astrocytic processes and might reflect the epithelial nature of the astrocyte.