Attenuation of neuroinflammation by dexmedetomidine is associated with activation of a cholinergic anti-inflammatory pathway in a rat tibial fracture model

Sustained neuroinflammation contributes to the pathogenesis of postoperative cognitive dysfunction. Dexmedetomidine, a selective alpha-2 adrenergic receptor agonist, exhibits a protective role in the brain. This study investigated whether dexmedetomidine pretreatment attenuates neuroinflammation induced by tibial fracture in rats, as well as the mechanism by which dexmedetomidine provides its neuroprotection. In our study, we observed that tibial fracture significantly increased the levels of tumor necrosis factor-alpha (TNF-alpha) and interleukin-1 beta (IL-1 beta) and the expression of nuclear factor-kappa B (NF-kappa B) in the hippocampus. Overexpression of microglial (CD11b) and astrocytic (GFAP) responses to injury were observed in the hippocampus. Dexmedetomidine pretreatment significantly suppressed the inflammatory responses, as evidenced by lower TNF-alpha and IL-1 beta levels, significantly inhibited NF-kappa B activity, and alleviated overexpression of microglia and astrocytes in the hippocampus. However, pretreatment with dexmedetomidine failed to attenuate cytokine responses and activity of NF-kappa B, CD11b and GFAP after vagotomy or treatment with methyllycaconitine, an alpha-7 nicotinic acetylcholine receptor (alpha 7nAChR) antagonist. These results suggest that pretreatment with dexmedetomidine may attenuate neuroinflammation caused by tibial fracture in rats through vagal-dependent and alpha 7nAChR-dependent mechanisms. (C) 2016 Elsevier B.V. All rights reserved.