, 2011). Both ligands are produced during the synthesis or degradation of peptidoglycan, with MDP being found in Gram-negative and Gram-positive bacteria, while iE-DAP is predominantly found on Gram-negative bacteria (Chamaillard et al., 2003, Grimes et al., 2012 and Mo et al., 2012). NOD1 can also be activated by the synthetic agonist FK565 (Watanabe et al., 1985). Similar to the Selleck Palbociclib activation of TLR4, NOD1 and NOD2 activation results in NF-κB- and MAP kinase-dependent inflammatory responses (Elinav et al., 2011).

Although NOD agonists are less potent in releasing cytokines than LPS, they are able to potentiate cytokine release induced by LPS challenge in innate immune cells (Le Contel et al., 1993, Netea et al., 2005, Wang et al., 2001 and Wolfert et al., 2002). The synergistic induction of cytokine production can also be observed in vivo extending to endotoxin shock, with profound hypothermia as one of its hallmarks ( Krakauer et al., 2010 and Takada and Galanos, 1987). selleck While there are some reports that MDP induces sleep and anorexia (Fosset et al., 2003, Johannsen et al., 1990 and Von Meyenburg et al., 2004), the impact of NOD1 and NOD2 activation on behavior and related brain function has been little studied. Likewise, it is largely

unknown whether the interaction of NOD1 and NOD2 stimulation with the TLR4 agonist LPS at the immune level has a bearing on behavior and cerebral activity (Mccusker and Kelley, 2013). Since in infection both NLRs and TLRs may be activated in parallel, it was the primary aim of the present study

to examine the effects of NOD1 and NOD2 activation, alone and in combination with the TLR4 agonist LPS, on sickness, behavior and cerebral c-Fos expression in order to visualize some of the brain nuclei relevant to sickness. The secondary objective was to analyze potential mechanisms behind the synergistic effects of NOD1, NOD2 and TLR4 activation on sickness and behavior. To this end, the effects of NOD1, NOD2 and TLR4 Calpain activation on inflammatory indices such as peripheral and central cytokine production and plasma kynurenine/tryptophan ratio were characterized. In addition, HPA axis activation was assessed by measuring circulating corticosterone levels. The study was carried out with male C57BL/6N mice from Charles River Laboratories (Sulzfeld, Germany) at the age of 10 weeks. The animals were either kept in groups of 2 or singly housed in the institutional animal house. Light conditions (lights on at 6:00 h, lights off at 18:00 h), temperature (set point 22 °C) and relative air humidity (set point 50%) were tightly controlled. Standard laboratory chow and tap water were provided ad libitum throughout the study. The experimental procedures and number of animals used were approved by an ethical committee at the Federal Ministry of Science and Research of the Republic of Austria (BMWF-66.