Neuropeptide Y m-RNA and peptide are transiently expressed in the developing rat spinal cord

The distribution of neuropeptide Y (NPY) m-RNA and peptide were studied during the ontogeny of the rat spinal cord, by means of in situ hybridization and immunohis-tochemistry. NPY expressing neurons were visualized by both techniques, although by in situ hybridization they appeared slightly more abundant than by immunohisto-chemistry. In the ventral horn, a few neurons transiently expressed NPY from the embryonic day 15 to birth, but not in the adult animals. In the embryonic dorsal horn, NPY expressing neurons were numerous and seen as early as embryonic day 15 (E15). In contrast, in the postnatal and the adult dorsal horn, the number of neurons expressing the NPY phenotype was dramatically lower.