Neuropeptide Y expression in Schwann cell precursors.

Some years ago we showed that in the adult rat and mouse neuropeptide Y (NPY) is expressed by olfactory ensheathing cells, a special type of glial cell involved in guiding of the continuously renewing olfactory axons. In the present study, using immunohistochemistry combined with confocal laser scanning microscopy, and mRNA in situ hybridization, we have analyzed whether NPY is also expressed in other axon-related glial cell systems during prenatal development. NPY was found to be expressed in the dorsal and ventral rootlets along the spinal cord from E13 and onward and in the rootlets of the cranial nerves and in the sensory ganglia from E14 and onward. In some cases, NPY-immunoreactivity (IR) was also found along peripheral nerves. NPY-IR was expressed in a dot-like fashion, similar to the NPY expression observed in olfactory ensheathing cells. At E18 the NPY-immunoreactive dots had disappeared from almost all ganglia and rootlets, and only in the most central part of the rootlets some weak dot-like NPY-IR was observed. At E20 it had disappeared completely from all rootlets and nerves, except the olfactory nerve. Most of the dot-like NPY-IR did not co-localize with the neuronal marker PGP 9.5. Based on its spatiotemporal expression, it is concluded that NPY is expressed by Schwann cell precursors. NPY expressed by Schwann cell precursors might have a role in axonal growth or axonal guidance, or both.