Background: We have previously shown that vagal nerve stimulation protects the intestinal epithelial barrier by maintaining the integrity of tight junction proteins following a thermal insult. We have also shown that acute lung injury is prevented when protective strategies to the gut mucosa are employed. The link between prevention of acute lung injury by maintaining the gut barrier has yet to be investigated. We hypothesize that maintenance of the gut epithelial barrier via vagal nerve stimulation and its action on the enteric nervous system prevents the subsequent systemic inflammation and attenuates acute lung injury.

Methods: Balb/c mice were subjected to 30% TBSA burn with and without electrical stimulation directly to the cervical right vagus nerve. Histology, myeloperoxidase (MPO), NFkB, and ICAM-1 immune staining, MPO enzymatic assay, Lung IL-8 levels (ELISA) were performed. Additionally, Lung NF-kB and IkB? immunoblots as well as NF-kB activation measured by photon emission analysis (Ivis Lumina Xenogen) using NF-kB luc transgenic mice were performed. Lung Histology (H&E) was performed at 6 and 24 hours post burn.

Results: At 6 hours post burn, an increase in phosphorylation of both NF-kB p65 and IkB? were observed. These findings coincide with increased photon emission signal in the lungs of the NF-kB luc transgenic animals. Vagal nerve stimulation blunted NF-kB activation to levels similar to sham animals. MPO positive cells were increased in the lung at 24 hours post burn. Similarly, ICAM-1 expression was up regulated in the lung endothelium at 24 hours. Lung histology demonstrated significant pulmonary edema, intra-alveolar hemorrhage and intra alveolar hyaline membrane formation at 24 hours. Vagal nerve stimulation markedly decreased neutrophil infiltration in the lung demonstrated by MPO immune staining and enzyme activity. More importantly, vagal nerve stimulation markedly attenuated acute lung injury at 24 hours (lung injury score similar to sham animals).

This picture demonstrates increased photon emission from transgenic NFkB-luciferase mice as a result of burn injury at 6 hours (picture sequence: Sham, 6 hour burn, 6 hour burn with vagal stimulation). Vagal nerve stimulation reduces the NFkB activity thereby decreasing the expression of the luciferase gene and decreasing the signal.

Conclusion: Vagal nerve stimulation affects the enteric-pulmonary axis by maintaining the integrity of the epithelial gut barrier. Vagal nerve stimulation markedly attenuates lung injury by down regulating NF-kB activation and neutrophil recruitment in the lung.