The morphological differentiation of commissural and associational neurons in the rat embryo spinal cord will be studied. Single and double labeling using the lipid soluble dyes, DiI and DiA, will be applied to classify neurons according to origin, migration and dendritic arborization, as well as to determine which classes are innervated by dorsal root afferents. In addition to standard fluorescent methods at the light microscopic level, confocal microscopy and electron microscopy following photoconversion of the fluorescent dyes to electron dense products also will be used. In addition, the role of nerve growth factor (NGF) on the differentiation of specific types of neurons will be assessed following treatment of embryos in utero with antiserum against NGF. These studies are fundamental to understanding how synaptic specificity develops in the mammalian spinal cord.
