3 μg (i.c.v.) did not significantly change this response (Fig. 2B). No changes in body temperature were seen in animals which received the higher dose of SR140333B or vehicle alone (Fig. 2C). In our attempts to induce a febrile response through the i.c.v. injection of SP we tested different doses ranging from 15 to 1000 ng of SP. The responses, however, were Trichostatin A not consistent since only a few animals showed an increase in body temperature when injected with SP (from 200 ng up to 1000 ng, data not shown). We then treated the animals with captopril 5 μg, i.c.v. 30 min before any injection. The injection of 250 ng of SP did not modify the body temperature of animals; however, the injection of SP

(500 or 750 ng, i.c.v., 2 μl) in captopril-treated animals induced a febrile response which started around 2 h after injection and persisted until the end of the experiment (Fig. 3A). The treatment of the animals with SR140333B, at the same dose that reduced the febrile response to LPS (3 μg, i.c.v.), also completely blocked the febrile response

to SP (500 ng, i.c.v., Fig. 3B). Since no difference was found between the 500 ng SP-treated group and the vehicle plus 500 ng SP-treated group, these data were combined BMS-354825 nmr in Fig. 3C. Intracerebroventricular injection of IL-1β (3.12 ng, i.c.v.) clearly induced a significant febrile response that started around 1 h after injection and persisted until 6 h. Surprisingly, the treatment of the animals with SR140333B (3 μg) did not change this response (Fig. 4A and B). CCL3/MIP-1α (500 pg) also induced a febrile response that started around 3 h and lasted up to 6 h. Similarly, SR140333B was not able to reduce the febrile response induced by this cytokine (Fig. 4C and D). The data reported here show that the febrile response

induced by LPS in rats is dependent on the activation of central, but not peripheral, NK1R. On the other hand, NK1R antagonist treatment (i.p. or i.c.v.) did not affect basal body temperature, suggesting that this peptide is not involved in thermoregulatory mechanisms under normal conditions. Meanwhile, CYTH4 our other findings show that substance P is not involved in the febrile response induced by IL-1β or CCL3/MIP-1α. The NK1R antagonist used here was particularly interesting for the investigation of the peripheral action of SP since there is evidence that this antagonist does not cross the blood–brain barrier (Jung et al., 1994). We found that the intraperitoneal administration of SR140333B at a dose of 1.0 mg/kg was not able to reduce LPS-induced fever. To be sure that this dose was sufficient to reduce SP peripheral effects, we tested the effect of this treatment on plasma extravasation induced by SP. This event is caused by SP directly activating NK1R on endothelial cells (Bowden et al., 1994) or through the release of other mediators (Harrison and Geppetti, 2001 and Maggi, 1997).