Humoral glycolipid is associated with mouse memory impairment caused by lipopolysaccharide

Mouse memory impairment induced by repeated daily dosing of lipopolysaccharide from Escherichia coli 044 was investigated using a passive avoidance method. One dose of 25 mg/kg or 8 repeated daily doses of 2.5 mg/kg of the lipopolysaccharide impaired the memory of 6-week-old male ddY mice. The chemical structure of the lipopolysaccharide was polymannoses Galβ1-3GalNAc-lipid A. Humoral polymannose-lipid reactivity was not found in lipopolysaccharide or in control mice receiving repeated daily doses of physiological saline. Humoral glycolipid with Galβ1-3GalNAc reactivity was found in the mice repeatedly treated with the lipopolysaccharide but not in the control mice repeatedly treated with physiological saline. Intraperitoneal injection of the humoral glycolipid did not impair memory in the normal mice, but mice treated beforehand with the glycolipid showed memory impairment after a subsequent single injection of 2.5 mg/kg of the lipopolysaccharide. These findings suggest that the polymannose component of the lipopolysaccharide is closely associated with the memory impairment effect and that the humoral glycolipid is a subsidiary metabolite of the lipopolysaccharide.