A microglia-driven pathway whereby de novo P2X4 receptor expression and activation leads to release of Brain-Derived Neurotrophic Factor (BDNF; Ulmann et al., 2008; Trang et al., 2009) is critical during the initiation phase of neuropathic pain (shortly after nerve injury) (Tsuda et al., 2003). This evidence concerns the gene BDNF and injury.