Exposure to an acute stressor causes significant splenic atrophy.

<p>This increase is not impacted by either antibiotics (<b>A</b>) or endotoxin inhibitor (<b>B</b>). Splenic atrophy is typical of acute activation of the sympathetic nervous system such as that which occurs as part of activation of the stress response. (*p<0.05).</p

Stress evokes a significant increase in circulating IL-1β, IL-6, IL-10, IL-18, and MCP-1.

<p>Administration of antibiotics significantly attenuated the impact of stress on IL-1β and IL-18. Antibiotics, however, did not attenuate IL-10 or MCP-1, and actually increased levels of circulating IL-6. (*p<0.05 vs. control, water; Ф p<0.05 vs. stress, water).</p

Exposure to an acute stressor significantly increases circulating corticosterone.

<p>The increase in circulating corticosterone is typical of acute activation of the hypothalamic-pituitary-adrenal axis such as that which occurs as part of activation of the stress response. Neither antibiotics (<b>A</b>) nor endotoxin inhibitor (<b>B</b>) impacted the corticosterone response to tail shock. (*p<0.05).</p

Exposure to a stressor activates the hypothalamic-pituitary-adrenal axis and sympathetic nervous system resulting in changes to the commensal flora (including a decrease in prevotella) and the release of microbe associated molecular patterns (MAMPs) as well as the the release of danger associated molecular patterns (DAMPs) either actively or via cell death.

<p>DAMP and MAMP signals then converge upon the inflammasome to yield IL-1β and IL-18 production. DAMPs may also act to drive responses from inflammasome independent inflammatory proteins including IL-6, IL-10, and MCP-1.</p

The efficacy of antibiotic administration is shown by successful reduction of colony forming units of bacteria in the absence of gross physiological changes such as a reduction in body weight gain.

<p><a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0050636#pone-0050636-g003" target="_blank"><b>Figure 3A</b></a> shows colony forming units of bacteria cultured on nutrient agar were significantly reduced in rats receiving antibiotic treatment. Although many species of commensal bacteria cannot be cultured on nutrient agar, the reduction produced by antibiotics is indicative of successful depletion of commensal bacteria by antibiotics, as neither the agar or the antibiotic regimen are specific for any particular group of bacteria. (*p<0.05). <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0050636#pone-0050636-g003" target="_blank"><b>Figure 3B</b></a><b>:</b> depicts body weight changes across antibiotic treatment regimen. Body weights increased in all groups across time and were unaffected by antibiotic treatment. (*p<0.05).</p