The expression of neuropeptides and their mRNAs in the trigeminal mesencephalic nucleus following masseteric nerve transection.

By in situ hybridization and immunohistochemistry, we examined the expression of neuropeptides such as neuropeptide Y (NPY), galanin (Gal), substance P (SP), vasoactive intestinal polypeptide (VIP) and their mRNAs in the rat mesencephalic trigeminal nucleus (Mes5) following masseteric nerve transection. On the side contralateral to the nerve transection, none of the peptides examined were labeled in Mes5 cell bodies. However, on the side ipsilateral to the lesion, NPY, Gal and preprotachykinin (PPT) mRNAs appeared in Mes5 cell bodies. Double labeling for mRNAs by in situ hybridization and retrograde tracer fluoro-gold (FG) revealed that almost all (96-97%) the FG-labeled neurons which were cut expressed NPY and Gal mRNAs, whereas less neurons (87%) expressed PPT mRNA. NPY and Gal-like immunoreactivities were detected in Mes5 cell bodies ipsilateral to the axotomy. The results suggested that these neuropeptides play roles in adaptive processes after peripheral nerve injury in Mes5 neurons as they are thought to do so in dorsal root ganglion neurons.