Splenic norepinephrine and serum corticosterone level fluctuations associated with bacteria-induced stress

Corticosterone (CORT) and norepinephrine (NE), two effector molecules of the hypothalamic-pituitary-adrenal (HPA) and the sympathetic-lymphoid (SL) axes, respectively, differentially influence murine host resistance to Listeria monocytogenes (LM). Serum CORT and splenic NE levels early (< or =24 h) after infection correlated positively with host resistance, as long as the LM burden did not exceed approximately 10(6) cfu LM per spleen. As previously reported, mice with right-circling preference (R-mice) have significantly greater host resistance to LM than those with left-circling preference (L-mice) and early after infection, R-mice had significantly higher serum CORT levels than L-mice. However, rapid pathogenesis with a high bacterial burden induced high activation of the HPA and SL axes, which prevented observable differences in the defense against LM, especially later in infection. With the high bacterial inoculum (10(5) LM), the splenic NE levels significantly increased, but no differences among R- and L-mice were discernible. We suggest that endogenous asymmetry of neuroimmune circuits contributes to differential host resistance, but the level of stress (bacterial inoculum) is critical. With regard to the neuroendocrine factors assessed, CORT, but not NE, levels significantly correlated with the enhanced defenses of R-mice in comparison to L-mice. The differential host resistance based on brain laterality seems to be more a function of the HPA axis and possibly other CNS effects on peripheral immunity than neurotransmitter release by the sympathetic innervation of the spleen.