Figure 1.

Netrin-1 expression in vivo. a–i, In situ hybridization was performed on rat spinal cord sections using rat netrin-1 antisense (Net-1 anti; a, c, d, e, f, g, h, i) or sense (b) α-³⁵S-UTP labeled probes. a, b, Darkfield images of coronal sections through the adult intact cervical spinal cord. Note the netrin-1 signal in the central canal and throughout gray and white matter, with highest white matter expression levels in the dorsolateral fasciculus (white arrows). c, Autoradiography of sagittal section of adult spinal cord. Netrin-1 is expressed by meninges (m) surrounding the spinal cord and central canal (cc; arrowhead). d, Brightfield image of horizontal section of adult intact cervical spinal cord (Nissl counterstained). Netrin-1 is expressed by cells constituting the central canal. Inset, Coronal section of central canal. e, Coronal section of rat E15 spinal cord (darkfield). Netrin-1 is expressed in floor plate (FP) and by cells constituting the central canal as expected. f, Horizontal section through dorsolateral white matter of adult rat spinal cord. Combination of netrin-1 in situ hybridization with APC (mature oligodendrocyte marker) immunocytochemistry demonstrates netrin-1 expression by mature oligodendrocytes. Inset, Coronal section through dorsolateral white matter. g, h, Netrin-1 does not colocalize with GFAP (g, circled cells) or the neuronal marker NeuN (h). i, Detection of netrin-1 expression by in situ hybridization in the thoracic (T6) spinal cord adjacent to a T7 transection site, 2 weeks after lesion. k, RT-PCR of netrin-1 from spinal cord 1, 2, and 4 weeks after T7 transection, normalized to the housekeeping gene Rplp1. l, Immunolabeling for netrin-1 identifies its presence and enrichment in perinodal segments of adult white matter (black reaction product), using a counterstain for the perinodal marker Caspr (brown). m, n, Netrin-1 labeling in intact white matter of the dorsolateral funiculus (m), and persistent presence 3 months after spinal cord injury in the dorsolateral funiculus (n) located 500 μm rostral to injury site.