Fig. 4.

Netrin-1 is not expressed by astrocytes. Double immunolabeling for netrin and the astrocytic marker GFAP indicates that netrin is not expressed by astrocytes. A, The distribution of netrin protein (red) in the ventral spinal cord of an adult rat. The dashed line delineates the border between the gray matter of the ventral horn (above) and the spinal white matter. B, The distribution of astrocytes indicated by GFAP immunoreactivity (green). C, The absence of colabeling between netrin-immunoreactive cells in spinal white matter and GFAP-positive astrocytes. D, A magnification of the central portion of C, illustrating that although the GFAP-positive and netrin-1-positive processes are often intertwined, they are distinctly separate. Confocal microscopy, with Cy3- and FITC-coupled secondary antibodies, is shown. Objective magnification, 20×. Scale bar, 100 μm.