The role of the vagus nerve: modulation of the inflammatory reaction in murine polymicrobial sepsis

Abstract

The particular importance of the vagus nerve for the pathophysiology of peritonitis becomes more and more apparent. In this work we provide evidence for the vagal modulation of inflammation in the murine model of colon ascendens stent peritonitis (CASP). Vagotomy significantly increases mortality in polymicrobial sepsis. This effect is not accounted for by the dilatation of gastric volume following vagotomy. As the stimulation of cholinergic receptors by nicotine has no therapeutic effect, the lack of nicotine is also not the reason for the reduced survival rate. In fact, increased septic mortality is a consequence of the absent modulating influence of the vagus nerve on the immune system: we detected significantly elevated serum corticosterone levels in vagotomised mice 24 h following CASP and a decreased ex vivo TNF-alpha secretion of Kupffer cells upon stimulation with LPS. In conclusion, the vagus nerve has a modulating influence in polymicrobial sepsis by attenuating the immune dysregulation.

Figure 1

Surgical dissection of the vagus nerve using a microscope (40-fold magnification): the abdominal wall was opened through a transverse incision. Esophagus (#) and diaphragm (∗) were exposed and the ventral branch of the vagal nerve (arrows) was dissected. The dorsal branch of the vagus nerve was excised in the same way.

Figure 2

The mortality in polymicrobial sepsis (CASP) is significantly increased compared to sham-operation (laparotomy without CASP or vagotomy) by 63.6% versus 100% (*P = 0.025, n = 10 and 33, resp.). The survival of the vagotomised CASP group (VGX + CASP, n = 33) is significantly decreased further to 35.3% (CASP versus VGX + CASP: ^# P = 0.048). Vagotomy itself (n = 10) does not affect the survival rate (100%).

Figure 3

Images of MRI of the upper abdomen of mice. The asterisk identifies the stomach. Panel a shows the sectional image of an untreated mouse with normal gastric volume (a). Panel b displays the representative scan of a mouse with increased gastric volume after CASP and vagotomy (b). Values of gastric volume are shown in panel c. CASP alone led to a slight but significant increase of gastric volume. In both vagotomy groups, a strong dilatation of the stomach was measured that was independent from the presence of sepsis (c). (n = 6 per group, *P < 0.05, **P < 0.01, and ***P < 0.0001).

Figure 4

(a) To verify the therapeutic dose of nicotine in the murine serum, we analysed the serum cotinine level as this correlates with the amount of nicotine dose applicated by osmotic pumps. Application of nicotine in a dose of 1.5 mg/kgBW/h results in a serum cotinine level of 9.24 μg/l (n = 4). 4.5 mg/kgBW/h nicotine leads to a cotinine serum concentration of 45 μg/l (n = 1) and 40 mg/kgBW/h nicotine induces a cotinine serum concentration of 106 μg/l (n = 1). Serum samples were analysed 18 hours following CASP. (b) The survival in CASP is not altered by continuous nicotine administration through subcutaneously implanted osmotic pumps. A nicotine exposition of 1 mg/kg bw per hour correlates with a survival rate of 20% (n = 10), 1.5 mg/kgBW/h (n = 32) nicotine leads to a survival rate of 21.85% and 3 mg/kgBW/h nicotine correlates with a survival rate of 12,5% (n = 8). In the control group, NaCl was applied where the survival rate was detected with 9.76% (n = 31).

Figure 5

The serum levels of corticosterone in sepsis are modulated by the vagus nerve. Vagotomy in the nonseptic organism does not influence the corticosterone level (205.9 ± 56.75 ng/mL). In polymicrobial sepsis, serum corticosterone is detected with 159.4 ± 53.24 ng/mL. In contrast, 24 h following CASP in vagotomised mice the corticosterone level is significantly increased up to 975.4 ± 261.9 ng/mL (*P = 0.031, Mann-Whitney, n = 5).

Figure 6

The vagus nerve has a stimulating effect on kupffer cells. Kupffer cells were isolated from control mice (column “control”) and from vagotomised mice without sepsis (column “VGX”). The basal TNF release of kupffer cells ex vivo is significantly decreased if mice were vagotomised 7 days before cell isolation (164.7 ± 40.9 pg/mL versus 61.1 ± 4.4 pg/mL, *P = 0.04). In addition, we stimulated the cells ex vivo with 1 μg/mL lipopolysaccharide from E.coli (LPS). In the septic organism, there is a significantly decreased TNF-α release by stimulated kupffer cells from vagotomised mice (2960 ± 513.1 pg/mL) when compared to mice with an intact nervus vagus (5746 ± 292.5 pg/mL, ***P = 0.0002, n = 10 per group).