Expression of neurotrophins by MBP-positive OLGs in the P7 BF. Nonradioactive in situ hybridization reveals that NGF, BDNF, and NT-3 mRNA are coexpressed with MBP in vivo. Coronal sections were prepared from P7 rats and examined by in situ hybridization in combination with an immunocytochemical staining technique. A subset of MBP-positive cells, visualized by brown DAB precipitation, is colocalized with NGF (A), BDNF (B), or NT-3 (C) mRNA, visualized by purple precipitation. Scale bar, 50 μm. Arrows indicate small cells. Arrowheads indicate large cells.