Effects of peripheral nerve injuries and tissue inflammation on the levels of neuropeptide Y-like immunoreactivity in rat primary afferent neurons

Abstract

Changes in neuropeptide Y-like immunoreactivity (NPYir) in the rat L 4 and L 5 spinal cord and dorsal root ganglia (DRG) were examined after different sciatic nerve injuries (transection, loose ligation, and crush) and a localized, painful inflammation of the hind paw. Inflammation had no effect on NPYir. All the nerve injuries produced comparable increases in NPYir in ipsilateral laminae III–V axons and varicosities, and induction of NPYir in many DRG cells. Most NPYir DRG cells were medium to large (mean diameters: 40–45 μm); less than 2% of the cells had diameters of 25 μm or less. We conclude that the nerve injury-evoked increase in NPYir occurs mostly in the somata and intraspinal arbors of low-threshold mechanoreceptors; very few, if any, C-fiber afferents are involved. Nerve injury, rather than a painful condition, appears to be the stimulus for the induction of NPYir synthesis.