Cell Size-specific Appearance of Neuropeptide Y in the Trigeminal Ganglion Following Peripheral Axotomy of Different Branches of the Mandibular Nerve of the Rat

The effect of peripheral axotomy of the mental nerve (MN) and the cutaneous branch of the mylohyoid nerve (MhN) on the appearance of neuropeptide Y-like immunoreactivity (NPY-IR) in cells in the trigeminal ganglion of the rat was examined with combined retrograde-tracing and immunohistochemistry. Retrograde-tracing with True Blue (TB) revealed that the cell-size spectrum of the trigeminal cells sending peripheral processes to the MN (TB MN cells) ranged from 75.9 to 1560.5 microns2 (or from 9.8 to 44.6 microns in diameter); approximately 53% of TB MN cells were 300-600 microns2. TB MhN cells ranged from 47.7 to 1261.5 microns2 (or from 7.8 to 40.1 microns in diameter); 56% of TB MhN cells were < 300 microns2. In the normal trigeminal ganglion, there were no NPY-IR cells. 14 days after MN transection, approximately 35% of TB MN cells displayed NPY-IR. The distribution of the cross-sectional areas of NPY-IR cells after MN transection was very similar to that of TB MN cells. Transection of MhN also induced the appearance of NPY-IR in the trigeminal ganglion but to a lesser extent (approximately 17% of TB MhN cells). The distribution of the cross-sectional areas of NPY-IR cells after MhN transection was similar to that of NPY-IR cells after MN transection. These results indicate that injury-evoked NPY-IR is specific for the medium- and large-sized ganglion cells.