SLC17A9 and peripheral nerve injury: From studies in human and rodent spinal cord microglia, it has been well established that activation of P2X4 receptors by ATP, such as that released from the vesicular nucleotide transporter (VNUT) following peripheral nerve injury in mice [122], stimulates p38 mitogen-activated protein kinase (MAPK) to induce the release of BDNF from microglia [4,24,27].