Several mechanisms have been proposed for neuroimmune communication supporting the sickness syndrome (fever, anorexia, inactivity, and cachexia) following infection. We examined the role of glutamate as a neurochemical intermediary of sickness behavior induced by intraperitoneal lipopolysaccharide (LPS). Mice implanted with biotelemetry devices capable of detecting body temperature (Tb) were administered LPS (50 or 500 microg/kg i.p., serotype 0111:B4) with or without i.p. pretreatment with vehicle or broad-spectrum antagonists selective for N-methyl-d-aspartate (NMDA), alpha-amino-3-hydroxy-5-methyl-4-isoxazoleproprionic (AMPA)/kainite, or metabotropic glutamate (mGlu) receptors. While NMDA and AMPA/kainate receptor antagonism failed to attenuate LPS-induced sickness behavior, antagonism of metabotropic receptors with l(+)-AP3 reduced the febrile (0-11h: control: 37.32+/-0.16 degrees C, l(+)-AP3: 36.66+/-0.27), anorexic (control: -87+/-5%, l(+)-AP3: 48+/-12% scotophase food intake), and cachexic (control: -8.9+/-0.4%, l(+)-AP3: -6.1+/-1.3% body weight) effects of 500 microg/kg LPS, and produced a biphasic Tb effect in response to 50 microg/kg LPS (1h: -0.90+/-0.26; 6h: 1.78+/-0.35 degrees C relative to baseline). At this dose the Tb of l(+)-AP3-treated mice was 1.18 degrees C lower than controls 2h post-injection, and 0.68 degrees C greater that controls 8h post-injection. These results suggest a role for mGlu receptors in mediating fever, anorexia, and cachexia possibly via activation of extra-vagal pathways, since the attenuating effect of l(+)-AP3 increased with increasing dosages of LPS. Given the critical role ascribed to mGlu receptors in neurotransmitter release and astrocytic processes, it is possible that these observations reflect an l(+)-AP3-induced attenuation of these systems.