Apart from neutralising COX activity, it has been described that indomethacin and ibuprofen are potent inhibitors of thromboxanes (Higgs et al., 1986), while paracetamol or dexamethasone are not (Swierkosz et al., 2002). Furthermore, indomethacin
and ibuprofen can directly bind and activate PPAR-γ that leads to an anti-inflammatory response that is independent of COX (Lehmann et al., 1997). The use of thromboxane inhibitors and a potent PPAR-γ agonist, however, ruled out that the LPS-induced behavioural changes in our model are mediated by these pathways and suggest a pivotal role for COX and subsequent PGE2 production as key players in the communication between periphery and brain. Indomethacin and ibuprofen have a much higher potency for the inhibition of COX-1
than COX-2, as demonstrated EPZ015666 price by their IC50 value, with indomethacin being more potent than ibuprofen (Botting, 2006 and Gierse et al., 1999). We observed that indomethacin is a more potent inhibitor of LPS-induced behavioural changes and PGE2 production in the brain, suggesting a more important role for COX-1. In addition, nimesulide which selectively inhibits COX-2, and the steroid dexamethasone, which is known to repress transcription of NFκB-regulated genes such as cytokines and COX-2 (Adcock et al., 1999) had no effect on LPS-induced behavioural changes despite efficient blockade of peripheral IL-6, IL-1β and TNF-α production. COX catalyses the check details conversion of the lipid metabolites arachidonic acid to PGs, and plays a key role in several physiological and pathological processes. The different isoforms of COX have been described as each having a distinct function in homeostasis and inflammation (Chandrasekharan et al., 2002 and DeWitt and Smith, 1988). COX-1 is constitutively expressed in many cell types (Funk et al., 1991), and responsible for the production of PGs that are necessary for the regulation of physiological functions
(Crofford, Buspirone HCl 1997). COX-2 is induced by diverse inflammatory stimuli (DuBois et al., 1997, Mitchell et al., 1994 and O’Sullivan et al., 1992) and is responsible for the production of PGs in inflammation (Vane, 1994). It is generally believed that LPS, or cytokines produced by LPS, induce COX-2 and mPGES-1 expression in cerebral endothelial cells, with subsequent PGE2 production in the CNS leading to both fever and behavioural changes. (DuBois et al., 1997, Ek et al., 2001, Engblom et al., 2002, Mitchell et al., 1994, O’Sullivan et al., 1992 and Yamagata et al., 2001). In this study, we show that changes in burrowing and open-field activity induced by a systemic LPS challenge are largely dependent on COX-1 activity and correlate with systemic production of PGE2, not cytokines.