Microglia in the spinal cord increase and become activated in the spinal dorsal horn following peripheral nerve injury [32] and activated microglia are known to produce several neurotrophic factors and proinflammatory cytokines, such as brain-derived neurotrophic factor (BDNF), IL-1ß, IL-6 and TNF-alpha, and are involved in the pain hypersensitivity [33-36]. Here, TNF is linked to peripheral nerve injury.