Stimulating the central nervous system to prevent intestinal dysfunction after traumatic brain injury

Abstract

Background: Traumatic brain injury (TBI) causes gastrointestinal dysfunction and increased intestinal permeability. Regulation of the gut barrier may involve the central nervous system. We hypothesize that vagal nerve stimulation prevents an increase in intestinal permeability after TBI.

Methods: Balb/c mice underwent a weight drop TBI. Selected mice had electrical stimulation of the cervical vagus nerve before TBI. Intestinal permeability to 4.4 kDa FITC-Dextran was measured 6 hours after injury. Ileum was harvested and intestinal tumor necrosis factor-alpha and glial fibrillary acidic protein (GFAP), a marker of glial activity, were measured.

Results: TBI increased intestinal permeability compared with sham, 6 hours after injury (98.5 microg/mL +/- 12.5 vs. 29.5 microg/mL +/- 5.9 microg/mL; p < 0.01). Vagal stimulation prevented TBI-induced intestinal permeability (55.8 +/- 4.8 microg/mL vs. 98.49 microg/mL +/- 12.5; p < 0.02). TBI animals had an increase in intestinal tumor necrosis factor-alpha 6 hours after injury compared with vagal stimulation + TBI (45.6 +/- 8.6 pg/mL vs. 24.1 +/- 1.4 pg/mL; p < 0.001). TBI increased intestinal GFAP 6.2-fold higher than sham at 2 hours and 11.5-fold higher at 4 hours after injury (p < 0.05). Intestinal GFAP in vagal stimulation + TBI animals was also 6.7-fold higher than sham at 2 hours, however, intestinal GFAP was 18.0-fold higher at 4 hours compared with sham and 1.6-fold higher than TBI alone (p < 0.05).

Conclusion: In a mouse model of TBI, vagal stimulation prevented TBI-induced intestinal permeability. Furthermore, vagal stimulation increased enteric glial activity and may represent the pathway for central nervous system regulation of intestinal permeability.

Figure 1

Intestinal permeability (25 mg 4.4 kDa FITC-Dextran in 200 μL phosphate-buffered saline) injected into the terminal ileum 6 hours after procedure. TBI increased intestinal permeability (98.5 μg/mL ± 12.5) compared with sham (29.5 μg/mL ± 5.9); (*p < 0.001). Vagus stimulation + TBI significantly reduced intestinal permeability when compared with TBI alone (55.8 μg/mL ± 4.8 vs. 98.49 μg/mL ± 12.5; **p < 0.02).

Figure 2

Representative H & E staining and microscopy (60×) from terminal ileum was harvested 6 hours after sham, TBI, or vagal stimulation + TBI. Sham animals had normal appearing villi with consistent villous height. TBI caused blunting of intestinal villi and necrosis. Vagal stimulation prevented intestinal injury with histology showing intestinal architecture unchanged from sham.

Figure 3

TNF-α as measured by ELISA in intestinal extracts at 2, 4, and 6 hour intervals after injury. TBI animals increased in intestinal TNF-αat each hourly interval (2 hour: 36.9 ± 5.3 pg/mL; 4 hour: 40.5 ± 1.8 pg/mL; 6 hour: 45.6 ± 8.6 pg/mL). Vagal stimulation prevented an increase in TNF-αafter TBI at each time-point (2 hour: 24.7 ± 4.8 pg/mL; 4 hour: 23.9 ± 3.4 pg/mL; 6 hour: 24.1 ± 1.4 pg/ mL; *p < 0.01; **p < 0.001).

Figure 4

Quantitative PCR was performed on intestinal extracts obtained at several time points after procedure. Relative expression of intestinal GFAP mRNA is shown as fold increase over sham animals. TBI increased intestinal GFAP 6.2-fold higher than sham at 2 hours and 11.5-fold higher at 4 hours after injury. In vagal stimulation + TBI animals, intestinal GFAP was 6.7-fold higher than sham at 2 hours and was 18.0-fold at 4 hours after injury compared with sham. At 6 hours after injury, TBI and vagal stimulation + TBI equalized and were 2.9 and 3.1-fold higher than sham alone.