Expression changes of glial cell line-derived neurotrophic factor in a rat model of neuropathic pain.

To reveal roles of neurotrophic factors in plastic changes of the primary afferent neurons following nerve injury, we investigated expression of glial cell line-derived neurotrophic factor (GDNF) as well as nerve growth factor (NGF) in a neuropathic pain model of the rat. The rats exhibited hyperalgesia and allodynia on the injured left side for at least 2 weeks after chronic constrictive injury to the sciatic nerve. Accompanied by the behavioral changes, expression of GDNF decreased in the dorsal root ganglia (DRGs) and the sciatic nerve on the injured side on the fourteenth day after the surgery. In contrast, the amount of NGF in DRGs was unchanged in spite of disturbance of NGF transport in the nerve. The present results suggest that decreased expression of GDNF takes some part in development and/or maintenance of neuropathic pain.