Distinct activation of tumor necrosis factor-α and interleukin-6 in the spinal cord after surgical incision in rats.

In a previous study, we showed that a deep thoracic incision induces the segmental upregulation of interleukin-1β (IL-1β) in the spinal cord. However, whether the cytokines tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6) are also activated in response to surgical incision remains to be determined. The present study aimed to investigate the expression pattern of TNF-α and IL-6 in the spinal cord following a deep thoracic incision. After surgical incision, the mRNA levels of TNF-α and IL-6 in the thoracic spinal cord were transiently upregulated as determined by real-time polymerase chain reaction (PCR) assay. However, the activation of IL-6 was detected at 1 h postoperatively, which was earlier compared to that of TNF-α, observed at 6 h postoperatively. The activated TNF-α was mainly localized in the neurons, but not in microglia or astrocytes as determined by immunohistochemistry and confocal microscopy. However, the increased IL-6-immunoreactivity was mainly expressed in blood vessels. The differential upregulation of TNF-α and IL-6 induced by incision suggests that the proinflammatory cytokines may play different roles in the development of surgical pain.