Effects of peripheral axotomy of the inferior alveolar nerve on the levels of neuropeptide Y in rat trigeminal primary afferent neurons.

The effects of peripheral axotomy of the inferior alveolar nerve (IAN) on the presence and distribution of neuropeptide Y (NPY)-like immunoreactivity (IR) in the trigeminal sensory nuclear complex (TSNC) and trigeminal ganglion were investigated in the rat by immunohistochemistry. In the normal trigeminal ganglion, there were no NPY-IR cells, and some perivascular nerve fibres exhibited NPY-IR. In normal TSNC, many NPY-IR axons and nerve terminals were observed in the superficial layers of the subnucleus caudalis (SpVc) and paratrigeminal nucleus (paraV), but were sparse in the other subnuclei of the TSNC. Fourteen days following peripheral axotomy of the IAN, many large- and medium-sized cells in the trigeminal ganglion displayed NPY-IR, and marked increases in the numbers and staining densities of NPY-IR were observed in deeper laminae (laminae III-V) of the dorso-medial region of the SpVc and other nuclei, in addition to the dorso-medial region of the spinal trigeminal tract. Degrees of alterations of the levels of NPY were most marked in the SpVc. The present results indicate that peripheral axotomy of the IAN evokes the appearance of NPY-IR in the trigeminal ganglion and alterations of NPY-IR in the entire IAN projection areas of the TSNC.