Schwann cell and DRG cocultures in the presence of GDNF. A, Sudan black staining shows clear myelination, with the formation of nodes of Ranvier (arrowheads).B, The myelinated nerve fibers express MAG in the paranodal (N) and Schmidt–Lanterman (SL) incisure. C, With the addition of a fluorescent ceramide analog to the culture medium, numerous myelinated fibers could be observed by incorporation of the fluorescent ceramide into the myelin. D, When neutralizing anti-NGF antibody was added to the coculture, myelination appeared to proceed at the normal rate compared with the control culture as assessed by the incorporation of fluorescent ceramide analog.