Interleukin-6 Facilitates Lipopolysaccharide-Induced Disruption in Working Memory and Expression of Other Proinflammatory Cytokines in Hippocampal Neuronal Cell Layers

• Published in: The Journal of neuroscience 2006-10, Vol.26 (42), p.10709-10716
• Main Authors: Sparkman, Nathan L, Buchanan, Jessica B, Heyen, Jonathan R. R, Chen, Jing, Beverly, James L, Johnson, Rodney W
• Format: Article
• Language: English
• Subjects: Animals; Cytokines - biosynthesis; Cytokines - genetics; Gene Expression Regulation - immunology; Hippocampus - metabolism; Inflammation Mediators - metabolism; Inflammation Mediators - physiology; Interleukin-6 - genetics; Interleukin-6 - physiology; Lipopolysaccharides - toxicity; Male; Memory - physiology; Mice; Mice, Inbred C57BL; Mice, Knockout; Neurons - immunology; Neurons - metabolism
• ISSN: 0270-6474; 1529-2401
• DOI: 10.1523/JNEUROSCI.3376-06.2006

Proinflammatory cytokines inhibit learning and memory but the significance of interleukin-6 (IL-6) in acute cognitive deficits induced by the peripheral innate immune system is not known. To examine the functional role of IL-6 in hippocampus-mediated cognitive impairments associated with peripheral infections, C57BL6/J (IL-6(+/+)) and IL-6 knock-out (IL-6(-/-)) mice were trained in a matching-to-place version of the water maze. After an acquisition phase, IL-6(+/+) mice injected intraperitoneally with lipopolysaccharide (LPS) exhibited deficits in working memory. However, IL-6(-/-) mice were refractory to the LPS-induced impairment in working memory. To determine the mechanism by which IL-6 deficiency conferred protection from disruption in working memory, plasma IL-1beta and tumor necrosis factor alpha (TNFalpha), c-Fos immunoreactivity in the nucleus of the solitary tract (NTS), and steady-state levels of IL-1beta and TNFalpha mRNA in neuronal layers of the hippocampus were determined in IL-6(+/+) and IL-6(-/-) mice after injection of LPS. Plasma IL-1beta and TNFalpha and c-Fos immunoreactivity in the NTS were increased similarly in IL-6(+/+) and IL-6(-/-) mice after LPS, indicating high circulating levels of IL-1beta and TNFalpha and activation of vagal afferent pathways were not sufficient to disrupt working memory in the absence of IL-6. However, the LPS-induced upregulation of IL-1beta and TNFalpha mRNA that was evident in hippocampal tissue of IL-6(+/+) mice was greatly attenuated or entirely absent in IL-6(-/-) mice. Collectively, these data suggest that humoral and neural immune-to-brain communication pathways are intact in IL-6-deficient mice but that, in the absence of IL-6, the central cytokine compartment is hyporesponsive.