Cyclooxygenase 1 is not essential for hypophagic responses to interleukin-1 and endotoxin in mice

Numerous studies have shown that the effects of interleukin-1 (IL-1) and en dotoxin (LPS) on behavior are sensitive to cyclooxygenase (COX) inhibitors. However, neither the location of the COX involved nor the specific isoform , COX I or COX2, is known. A previous study using selective COX1 and COX2 i nhibitors did not provide an unequivocal answer. Therefore, we tested the r esponse of sweetened milk ingestion to IL-1 and LPS in mice in which the CO X1 or the COX2 gene was deleted (COX1ko and COX2ko). When IL-1 beta was adm inistered 90 min before the milk, COX1ko mice showed responses similar to t hose of normal mice. In contrast, COX2ko mice exhibited responses considera bly less than normal, with some mice showing no response. Indomethacin pret reatment almost prevented the feeding responses to IL-I in normal and COX1k o mice. The milk intake response to LPS in COX1ko mice was like that of nor mal mice. The results from COX1ko mice suggest that COX1 is not necessary f or the decreased milk intake following TL-I and LPS. The results from COX2k o mice are consistent with the involvement of COX2 in the IL-1-induced depr ession of milk intake, but other mechanisms may effect decreases in sweeten ed milk intake. (C) 2001 Elsevier Science Inc. All rights reserved.