M1 cholinergic signaling in the brain modulates cytokine levels and splenic cell sub-phenotypes following cecal ligation and puncture.

BACKGROUND: The contribution of the central nervous system to sepsis pathobiology is incompletely understood. In previous studies, administration of endotoxin to mice decreased activity of the vagus anti-inflammatory reflex. Treatment with the centrally-acting M1 muscarinic acetylcholine (ACh) receptor (M1AChR) attenuated this endotoxin-mediated change. We hypothesize that decreased M1AChR-mediated activity contributes to inflammation following cecal ligation and puncture (CLP), a mouse model of sepsis. METHODS: In male C57Bl/6 mice, we quantified basal forebrain cholinergic activity (immunostaining), hippocampal neuronal activity, serum cytokine/chemokine levels (ELISA) and splenic cell subtypes (flow cytometry) at baseline, following CLP and following CLP in mice also treated with the M1AChR agonist xanomeline. RESULTS: At 48 h. post-CLP, activity in basal forebrain cells expressing choline acetyltransferase (ChAT) was half of that observed at baseline. Lower activity was also noted in the hippocampus, which contains projections from ChAT-expressing basal forebrain neurons. Serum levels of TNFα, IL-1ß, MIP-1α, IL-6, KC and G-CSF were higher post-CLP than at baseline. Post-CLP numbers of splenic macrophages and inflammatory monocytes, TNFα+ and ILß+ neutrophils and ILß+ monocytes were higher than baseline while numbers of central Dendritic Cells (cDCs), CD4+ and CD8+ T cells were lower. When, following CLP, mice were treated with xanomeline activity in basal forebrain ChAT-expressing neurons and in the hippocampus was significantly higher than in untreated animals. Post-CLP serum concentrations of TNFα, IL-1ß, and MIP-1α, but not of IL-6, KC and G-CSF, were significantly lower in xanomeline-treated mice than in untreated mice. Post-CLP numbers of splenic neutrophils, macrophages, inflammatory monocytes and TNFα+ neutrophils also were lower in xanomeline-treated mice than in untreated animals. Percentages of IL-1ß+ neutrophils, IL-1ß+ monocytes, cDCs, CD4+ T cells and CD8+ T cells were similar in xanomeline-treated and untreated post-CLP mice. CONCLUSION: Our findings indicate that M1AChR-mediated responses modulate CLP-induced alterations in serum levels of some, but not all, cytokines/chemokines and affected splenic immune response phenotypes.

Determinants of the lung microbiome in intubated premature infants at risk for bronchopulmonary dysplasia.

BACKGROUND: Airway dysbiosis in premature infants may be associated with bronchopulmonary dysplasia (BPD). Early oropharyngeal colostrum (OPC) administration alters the oral microbiome, which may impact the lung microbiome. We aim to compare the oral and tracheal microbiota during the first week of life, and to determine whether early OPC administration affects microbial diversity or leukocyte inflammatory activity in the lung. METHODS: Intubated premature infants (n = 42) were evaluated. The oral microbiome was characterized on day of life (DOL) 3, and the tracheal microbiome on DOL 3 and DOL 7, using 16S ribosomal DNA sequencing. Gene expression for inflammatory markers was quantified in airway leukocytes by real-time q-PCR. RESULTS: The oral and tracheal microbiota were significantly different on DOL 3, but the tracheal microbiome on DOL 7 was more similar to the oral from DOL 3. Tracheal bacterial diversity decreased from DOL 3 to DOL 7. Longer time to first OPC administration tended to be associated with lower bacterial diversity in the airways. CONCLUSIONS: The tracheal microbiome in intubated premature infants in the first week is likely determined, in part, by the composition of the oral microbiome. Bacterial diversity in intubated babies decreases during the first week of life, a pattern that could be consistent with risk for BPD. Decreased bacterial diversity and increased inflammatory activity in the lung may also be associated with delayed administration of OPC.