Endotoxin inhibition of drinking behaviour in the rat.

Intravenous (i.v. 320 and 640 micrograms/kg) and intracerebroventricular (i.c.v.; 1 microgram/rat) injection of Escherichia coli lipopolysaccharide (LPS) powerfully inhibited drinking induced by 24 h water deprivation. Pretreatment with acetylsalicylic acid (ASA) into the preoptic area (POA) completely abolished the effect induced by i.v. LPS, but did not modify that elicited by i.c.v. LPS. Intraperitoneal ASA injections significantly reduced the antidipsogenic effect of i.c.v. LPS. Electrolytic ablation of the subfornical organ (SFO) did not modify the effect induced by either i.v. or i.c.v. LPS. Present findings indicate that: (1) the antidipsogenic effect of i.v. LPS is mediated by prostaglandin synthesis into the POA, (2) the SFO is not involved in this effect, and (3) prostaglandins in other brain areas, besides POA, modulate the effect of i.c.v. LPS. It is suggested that at least two different brain sites, inside the blood-brain barrier, might be involved in the antidipsogenic effect of LPS.