Neuromodulation of experimental Shigella infection reduces damage to the gut mucosa

Bacillary dysentery arises when Shigella invades the colonic and rectal mucosae of the human gut and elicits a strong inflammatory response, which may lead to life-threatening complications. Hence, downregulation of the host inflammatory response is an appealing therapeutical alternative. The gastrointestinal tract is densely innervated, and nerve endings are often found in the vicinity of leukocytes. We have assessed the impact of experimental Shigella infection on levels of neuropeptides in the intestinal mucosa of rabbits. Ligated small intestinal loops were created in rabbits, and either live, pathogenic Shigella flexneri, a nonpathogenic mutant of Shigella, or NaCl was injected into the loops. Infection was allowed to proceed for 8 or 16 h, after which the rabbits were sacrificed and intestinal biopsies collected. Tissue destruction, fluid secretion and degree of bacterial invasion were monitored. Intestinal biopsies were homogenized, and levels of the neuropeptides calcitonin gene-related peptide, substance P, peptide YY (PYY), vasoactive intestinal peptide, somatostatin, galanin, motilin and neurotensin were measured by radioimmunoassay. Loops exposed to invasive Shigella had 5.7 times lower levels of PYY (P = 0.0095) than loops exposed to NaCl, after 16 h of infection. The levels of the other neuropeptides tested were unchanged. Inhibition of nicotinic cholinergic neurotransmission partly protected the intestinal mucosa from destruction elicited by invasive Shigella. These findings indicate that a tissue-invasive bacterium such as Shigella, which is strictly localized to the intestinal mucosa, activates intramural nerve reflexes that presumably involve a nicotinic synapse as well as the neuropeptide PYY.