Temporal analysis of neuropeptide Y expression in the rat trigeminal ganglion following peripheral axotomy of the inferior alveolar nerve.

Temporal changes in the appearance and the cell-size spectrum of neuropeptide Y (NPY)-like immunoreactive (IR) cells in the rat trigeminal ganglion (TG) following peripheral axotomy of the inferior alveolar nerve (IAN) were studied by retrograde neuronal tracing with True Blue (TB) and immunohistochemistry for NPY. The number of labeled cells following application of TB to the cut-end of the IAN increased rapidly up to 3 days, and was maintained at a constant level thereafter. The size distribution of cross-sectional areas of TB-labeled cells was similar at 3 days and afterwards. NPY-IR cells, which were not detected in the normal TG, appeared on the first day following axotomy, and increased gradually in number reaching a maximum at 14 days. The frequency histogram of the cross-sectional areas of NPY-IR cells was similar at 3 days and afterwards. The present results indicate that the effect of nerve injury on the levels of NPY expression in the sensory neurons began soon after nerve injury, reaching a maximum around 14 days, and that induction of NPY in the sensory neurons occurred in the same cell size-specific manner for a long period.