Interleukin-10 levels in rat models of nerve damage and neuropathic pain.

Interleukin-10 (IL-10) is an anti-inflammatory cytokine that has been shown to play a role in inflammatory and autoimmune disorders as well as in neuropathic pain conditions. The objective of the present study was to assess the levels of IL-10 in rat's dorsal root ganglion (DRG) and the sciatic nerve following four different forms of sciatic nerve injury. The models used to induce the injury included two models of partial nerve injury: partial sciatic ligation (PSL) and chronic constriction injury (CCI), a model of complete sciatic transection (CST) and a model of perineural inflammation with minimal nerve damage (neuritis). Withdrawal responses for mechanical stimulus and withdrawal latency for thermal stimulation were used to measure mechanical and thermal hyperalgesia, respectively, and duration of the nociceptive withdrawal reflex to mechanical stimulus was used to measure mechanical hyperalgesia. The affected and contra-lateral nerves and the affected side DRG IL-10 levels were assessed by the means of enzyme-linked immunosorbent assay (ELISA), 3 and 8 days following the procedure and were compared to naïve rats' IL-10 levels. The rats exposed to CCI and neuritis developed significant mechanical and thermal hyperalgesia as well as mechanical hyperalgesia 3 and 8 days following the surgical procedure. Rats exposed to CST did not respond to mechanical stimulation and developed thermal hypoalgesia 3 and 8 days after the surgery. The DRG IL-10 levels were significantly reduced 3 and 8 days following CCI and PSL, significantly increased 3 and 8 days following CST, and remained unchanged following neuritis. The sciatic nerve IL-10 levels reduced significantly in both injured and contra-lateral nerves 3 and 8 days following CCI and PSL, elevated significantly in the injured but not in the contra-lateral nerve 3 and 8 days following CST and remained unchanged following neuritis. The results of this study suggest that IL-10's role in the neuropathic pain etiology may be specific to nerve injury type. Complete nerve transection increases while partial nerve injury reduces IL-10 levels in the involved nerve, and DRG. Perineural inflammation with minimal nerve damage has no effect on IL-10 levels.