Early and late behavioral changes in sciatic nerve injury may be modulated by nerve growth factor and substance P in...

Chronic constriction injury (CCI) simulates the symptoms of chronic nerve compression, which is characterized by allodynia and hyperalgesia. Nerve growth factor (NGF) is released after nerve injury by immune and Schwann cells and transported in retrograde fashion to the dorsal root ganglion (DRG), resulting in increased synthesis of Substance P (SP) and the triggering of neuropathic pain. Here we performed long-term evaluation of allodynia and hyperalgesia in a CCI model, and evaluated the effects of NGF and SP on the peripheral and central nervous systems. Most previous studies have shown deficits and molecular changes 14 days after surgery, however, the long-term effects have not been evaluated. We performed Randall-Selitto, Von Frey, Hargreaves and acetone tests for the entire 56 days post-surgery. Several of these deficits increased 14 to 56 days after CCI and we measured a constant increase in NGF levels in the DRG and spinal cord over the course of the experiment. In contrast, SP optical density maintained enhanced expression in DRG tissue from 14 to 56 days after CCI, whereas it was significantly increased only 56 days post-surgery in spinal cord. We perform long-term evaluation of symptoms associated with CCI and measure associated molecular changes. Moreover, by characterizing the behavioral signatures of this model, our work supports future studies.