Increased neuropeptide Y (NPY)-like immunoreactivity in rat sensory neurons following peripheral axotomy

The effects of peripheral axotomy (sciatic nerve transection) on the presence and distribution of neuropeptide Y (NPY) in rat dorsal root ganglion (DRG) and spinal grey matter were examined using immunocytochemistry. In normal rats and on the sham-operated side of experimental rats, NPY-like immunoreactivity (NPYir) was observed in all laminae of the lumbar spinal cord, with an especially dense concentration of immunostained axons and axonal varicosities in laminae I-II of the dorsal horn. There was no detectable NPYir in L4-L5 DRG cells from normal rats or from the sham-operated side of experimental rats. At 14 days after axotomy, there was a large ipsilateral increase in the density of NPYir axons and varicosities in the lumbar spinal cord on the side of the nerve injury; this was especially apparent in laminae III-V. In the same rats, NPYir was observed in many small, medium, and large neurons in the L4-L5 DRGs on the side of the severed nerve.