DEVELOPMENT OF RADIAL GLIA AND ASTROCYTES IN THE SPINAL-CORD OF THE NORTH-AMERICAN OPOSSUM (DIDELPHIS-VIRGINIANA) - AN IMMUNOHISTOCHEMICAL STUDY USING ANTIVIMENTIN AND ANTI-GLIAL FIBRILLARY ACIDIC PROTEIN

We have shown previously that rubrospinal axons grow around a lesion o f their pathway in developing opossums and that a critical period exis ts for that plasticity. As a first step toward addressing the possibil ity that glial maturation and/or the development of an astrocytic resp onse to lesioning contribute to loss of rubrospinal plasticity, we hav e studied the normal development of radial glia and astrocytes in the spinal cord of the opossum by immunostaining for vimentin (Vim) and gl ial fibrillary acidic protein (GFAP). Vim-like immunoreactivity (Vim-L I) was present in radial glia throughout the spinal cord at birth (12 days after conception), whereas GFAP-like immunoreactivity (GFAP-LI) w as limited to cells of comparable morphology in the ventral part of th e cervical cord. The subsequent appearance of GFAP-LI followed ventral to dorsal and rostral to caudal gradients and by postnatal day (PD) 1 5, it was found in radial glia throughout the cord. At the same age, p rocesses immunostained by either antibody had lost their radial orient ation in the ventral horn of the cervical cord. The subsequent transfo rmation from radial glia to astrocytes also followed ventral to dorsal and rostral to caudal gradients. By PD30, mature appearing astrocytes were immunostained by both antibodies at thoracic levels of the spina l cord, the levels lesioned in the plasticity experiments referred to above, and by PD41, they were found at all levels of the cord. Since r ubral axons are able to grow around a lesion of the thoracic cord unti l PD26-30, there is a rough temporal correlation between the transitio n from radial glia to mature appearing astrocytes and the end of the c ritical period for plasticity. (C) 1993 Wiley-Liss, Inc.