Postnatal MNs can be grown in slice cultures of mouse spinal cord. Photomicrographs are shown of 12 μm sections of a single slice, taken from the lumbar enlargement of a P1 mouse, after 6 d of culture in the presence of GDNF. A, Staining for Nissl substance with cresyl violet allows the identification of MNs in the LMC and MMC in the ventral horn of the gray matter.B, Immunohistochemistry for Ret, the signaling component of the GDNF receptor complex, in an adjacent section demonstrates staining confined to MNs (red). C, A high-power view of the Nissl-stained section shows characteristic MN morphology in the LMC. D, A Hoechst 33342 (bisbenzimide) counterstain demonstrates that the nuclei (blue) of the surviving MNs appear healthy. Scale bar, 40 μm.