Interleukin-6 and nerve growth factor levels in peripheral nerve and brainstem after trigeminal nerve injury in the rat

Earlier studies have demonstrated that inflammation plays a role in the development of evoked pain following partial nerve injury. In this report, we demonstrate bilateral changes in interleukin-6 (IL-6) and nerve growth factor (nerve growth factor) levels following unilateral infraorbital nerve (infraorbital nerve) constriction. infraorbital nerve constriction resulted in an initial period of decreased mechanical sensitivity (1 and 3 days), followed by recovery (7 days) and then a marked bilateral mechanical hypersensitivity (10 and 28 days). nerve growth factor levels in the injured infraorbital nerve were elevated on all days, but peak concentrations of nerve growth factor were observed on day 3. A smaller increase was also observed on days 1, 3, and 7 in the uninjured nerve. A bilateral elevation of IL-6 was also seen on days 3 and 10 in the infraorbital nerve, and in the brainstem on days 3, 7 and 10 after constriction. No changes in mechanical sensitivity were found after a sham-injury, but there was a small increase in brainstem IL-6 ipsilaterally at 7 days. We conclude from these data that increases in IL-6 and nerve growth factor may contribute to the development of mechanical allodynia after trigeminal nerve injury, but they are not specifically correlated with the onset or duration of pain behaviors.