Stimulation of the vagus nerve has modulating, anti-inflammatory effects on the cellular immune response in the blood and the spleen, stabilizing brain function. Here, we aimed to investigate its potential effects on immune-to-brain communication focusing on neurophysiological readouts and leukocyte migration to the brain during severe sepsis-like endotoxemia. Systemic inflammation was induced by intravenous administration of lipopolysaccharide (LPS; 5 mg/kg). Animals received either no manipulation of the vagus nerve, vagotomy, or vagotomy plus vagus nerve stimulation of the distal trunk. Somatosensory evoked potentials and evoked flow velocity response were measured for 4.5 h as indicators of brain function and neurovascular coupling, respectively. In addition, brain areas with (cortex) and without (hypothalamus) tight blood-brain barrier were studied separately using immunohistochemistry and RT-PCR. Moreover, plasma cytokine and leptin levels were analyzed by ELISA. LPS induced a decline of both neurophysiological parameters, which was prevented by vagus nerve stimulation. As for peripheral organs, LPS-stimulated neutrophil counts increased in the brain and colocalized in the brain with endothelial intercellular adhesion molecule (ICAM)-1. Interestingly, vagal stimulation reduced this colocalization and decreased nuclear translocation of the brain cell activation marker nuclear factor interleukin 6 (NF-IL6). Furthermore, it reduced the gene expression of inflammatory markers and extravasation signals (IL-6, CXCL-1, ICAM-1) in the hypothalamus but not the cortex linked to a moderate decrease in circulating cytokine levels (interleukin 6, tumor necrosis factor alpha) as well as lower plasma leptin concentration. Our data suggest beneficial effects of anti-inflammatory vagus nerve stimulation on brain function by reducing the interaction of neurotrophil granulocytes with the brain endothelium as well as attenuating inflammatory responses in brain areas lacking a blood-brain barrier.

Background: The transcription factor nuclear factor interleukin 6 (NF-IL6) is known to be activated by various inflammatory stimuli in the brain. Interestingly, we recently detected NF-IL6-activation within the hypothalamus-pituitary-adrenal (HPA)-axis of rats after systemic lipopolysaccharide (LPS)-injection. Thus, the aim of the present study was to investigate whether NF-IL6 is activated during either, inflammatory, or psychological stress in the rat brain. Methods: Rats were challenged with either the inflammatory stimulus LPS (100 μg/kg, i.p.) or exposed to a novel environment. Core body temperature (Tb) and motor activity were monitored using telemetry, animals were killed at different time points, brains and blood removed, and primary cell cultures of the anterior pituitary lobe (AL) were investigated. Analyses were performed using immunohistochemistry, RT-PCR, and cytokine-specific bioassays. Results: Stress stimulation by a novel environment increased NF-IL6-immunoreactivity (IR) in the pituitary’s perivascular macrophages and hypothalamic paraventricular cells and a rise in Tb lasting approximately 2 h. LPS stimulation lead to NF-IL6-IR in several additional cell types including ACTH-IR-positive corticotrope cells in vivo and in vitro. Two other proinflammatory transcription factors, namely signal transducer and activator of transcription (STAT)3 and NFκB, were significantly activated and partially colocalized with NF-IL6-IR in cells of the AL only after LPS-stimulation, but not following psychological stress. In vitro NF-IL6-activation was associated with induction and secretion of TNFα in folliculostellate cells, which could be antagonized by the JAK-STAT-inhibitor AG490. Conclusions: We revealed, for the first time, that NF-IL6 activation occurs not only during inflammatory LPS stimulation, but also during psychological stress, that is, a novel environment. Both stressors were associated with time-dependent activation of NF-IL6 in different cell types of the brain and the pituitary. Moreover, while NF-IL6-IR was partially linked to STAT3 and NFκB activation, TNFα production, and ACTH-IR after LPS stimulation; this was not the case after exposure to a novel environment, suggesting distinct underlying signaling pathways. Overall, NF-IL6 can be used as a broad activation marker in the brain and might be of interest for therapeutic approaches not only during inflammatory but also psychological stress.